Flood Resources Utilization in the Yangtze River Basin [1st ed.] 9789811581076, 9789811581083

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Shouren Zheng · Zhiyu Zhong · Qiang Zou · Yi Ding · Lin Yang · Xue Luo

Flood Resources Utilization in the Yangtze River Basin

Flood Resources Utilization in the Yangtze River Basin

Shouren Zheng · Zhiyu Zhong · Qiang Zou · Yi Ding · Lin Yang · Xue Luo

Flood Resources Utilization in the Yangtze River Basin

Shouren Zheng Changjiang River Water Conservancy Commission Wuhan, China

Zhiyu Zhong Changjiang River Water Conservancy Commission Wuhan, China

Qiang Zou Changjiang Institute of Survey Planning Design and Research Wuhan, China

Yi Ding Changjiang Institute of Survey Planning Design and Research Wuhan, China

Lin Yang Bureau of International Cooperation Science and Technology Changjiang Water Resources Commission Wuhan, China

Xue Luo Changjiang River Scientific Research Institute Changjiang Water Resources Commission Wuhan, China

ISBN 978-981-15-8107-6 ISBN 978-981-15-8108-3 (eBook) https://doi.org/10.1007/978-981-15-8108-3 Jointly published with Changjiang Press (Wuhan) Co., Ltd. The print edition is not for sale in China (Mainland). Customers from China (Mainland) please order the print book from:Changjiang Press (Wuhan) Co., Ltd. © Changjiang Press (Wuhan) Co., Ltd. 2021 This work is subject to copyright. All rights are reserved by the Publishers, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publishers, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publishers nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publishers remain neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Preface

The Yangtze River originates from the southwest of the Geladandong snow mount, the peak of the Tanggula Mountain Range of the Qinghai-Tibet Plateau, with a total length of more than 6,300 km and a gross head of approximately 5,400 m. On its way across the Southwest, Central and Eastern China, the Yangtze River mainstream traverses 11 provinces (autonomous regions and municipalities) including Qinghai, Sichuan, Tibet, Yunnan, Chongqing, Hebei, Jiangxi, Anhui, Jiangsu and Shanghai, flowing into the East China Sea. While its tributaries flow through 8 provinces (autonomous regions) including Guizhou, Gansu, Shaanxi, Henan, Zhejiang, Guangxi, Guangdong and Fujian. The Yangtze River drains a total area of 1.8 million km2 , representing 18.8% of the territorial area of China. In 2012, the total population of the Basin was 427.27 million, accounting for 32.3% of the nation’s total; the urbanization rate was 42%, the regional GDP was 8.4778 trillion yuan (occupying 34% of the nation’s total) along with the per capita GDP of 19,842 yuan; the farmland area was 30.8 million hm2 , representing 25.3% of the nation’s total; the total grain output was 163 million tons, taking up 32.5% of the nation’s total. The theoretical reserves of hydropower resources in the Yangtze River Basin are 305,000 MW, with an average annual power generation of 2.67 trillion kW h, accounting for about 40% of the country’s total. Particularly, the technical exploitable installed capacity is 281,000 MW and the average annual power generation is 1.3 trillion kW h, accounting for 47% and 48% of the nation’s total, respectively. The Yangtze River is rich in shipping resources with more than 3600 navigable rivers and the corresponding total length of more than 71,000 km, representing 56% of the nation’s total. The Yangtze River Basin serves as the strategic tank for nationwide allocation of water resources, the major base for implementing the energy strategy, the natural treasure house for rare aquatic organism, the “golden waterway” linking the western, central and eastern China and the vital underpinning to improve the ecology and environment in northern China, which possesses an extremely important strategic position in the socio-economic development and Eco-environment conservation of China. Whether the Yangtze River is under good stewardship has special implications on not only the well-being of more than 400 million inhabitants in the Basin, but also in broader sense the overall sustainability of socio-economic development of the whole country. v

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The Yangtze River Basin possesses an average annual precipitation of 1,100 mm and an average annual inflow to the sea of 919 billion m3 (excluding the water from the Huai River). The Basin is relatively rich in water resources with a total volume of 996 billion m3 , accounting for 35% of the nation’s total; otherwise the average per capita share is 2,330 m3 within the Basin, slightly higher than the nation’s average level. Most parts of the Yangtze River Basin belong to typical monsoon climate areas; the intra-yearly distribution of precipitation is quite uneven, with concentrated rainfall from May to October in the flood season in the form of flood, while less precipitation in the other months. The runoff of the mainstream of the Yangtze River from May to October in the flood season accounts for 70% of the year’s total while that in the drought season takes up 30%. The Yangtze River Basin is suffering from severe problems on both flood and drought, along with disasters of continuous, alternating and simultaneous droughts and floods. In recent years, the runoff from the upper Yangtze River is relatively small. The average annual runoff of the Yichang Station from 2003 to 2013 was 396.1 billion m3 , which was 549 m3 (representing 12.2% of 451 m3 ) less than that of 451 billion m3 in the preliminary design (1877–1990); with the gradual construction of the key reservoirs on the mainstream and tributaries of the Upper Yangtze River, the decreased runoff from September and October accounted for 20% of the total runoff in the same period as a result of the water impoundment at the end or after the flood. With population growth and socio-economic development, the quantity of water use and volume of sewage emissions continue to increase. Contradictions exist prominently between the uneven temporal-spatial distribution of the water resources overall the Yangtze River Basin and the demand on domestic and production water use of the riparian inhabitants. The relation between water supply and demand is really tense; furthermore, the shortage of water resources has become one of the main constraints for the sustainable development of the social economy. In terms of the flood incorporating the natural resources, environmental elements and disaster-causing factors, on the one hand, flood may do harm, as the severe flood is likely to cause such disasters as people and land inundation, river erosion and embankment breach; on the other hand, flood serves as a kind of important freshwater resource, the dual nature on both benefit and harm of flood constitutes a contraction that plays a key role in sustainable development for social economy and in eco-environmental restoration. The practice on carrying out the study on flood resources utilization over the Yangtze River Basin aims to make use of flood resources in a moderate way relying on modern flood regulation technology on the premise of flood control safety, which is not only an urgent need to ease the contradiction between water resources supply and demand in the Yangtze River Basin, but also an urgent need to give full play to the hydropower resources and to improve eco-environment in the Yangtze River Basin. Furthermore, the study is of great strategic significance to alleviate the water resources shortage in the north part of China in order to safeguard the national water security. At present, from the point of water works condition and with the full implementation of comprehensive management engineering over the Yangtze River Basin, an integrated flood control engineering system including embankments along mainstream and tributaries, reservoirs, flood storage and detention areas, river regulation

Preface

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works has been basically constructed within the Basin, which not only plays an important role in flood control and disaster mitigation in the Basin, but also provides good engineering conditions for implementing flood resources utilization; in terms of science and technology level and with the technical innovation on hydrology and meteorology, the accuracy and reliability of flood forecasting are constantly improved, and the flood lead-time is prolonged, which serves as necessary technical guarantee for further optimizing flood regulation mode; as for the ideological concept, the wars with thousands of years history that the human beings have ever waged to fight against the natural disasters tell us that we should always guard against extraordinary floods to avoid disastrous consequences, on the premise of flood control security, take the moderate risk, regulate flood control behaviors, make use of flood resources, shift from “flood control” to “flood management” and finally achieve “human and water in harmony”. Facing the new circumstances of socio-economic development and flood control, the Master Plan of the Yangtze River Basin (2012–2030) approved by the State Council in 2012 has clearly pointed out that “based on the overall requirements that clarified in the central government’s First Document of the Year 2011, such systems are expected to be basically set up by the year 2020 as flood control and drought relief system, water resources rational allocation and effective use system, water resources conservation and rivers & lakes health security system, as well as an institutional system conducive to the development of hydraulic science, it is imperative to accelerate the construction of key hydro works (works which are capable to control flood and regulate water resources and play an important role on regulate and control flood and water resources in rivers or some sections) in the river basin, strengthen the scheduling management of key water conservancy and hydropower projects, enhance the capability to cope with disasters like flood, waterlogging and droughts, improve the efficiency of water resources utilization and maintain a sound water environment”, the Master Plan has also called for “strengthening major scientific and technological research on flood risk management and flood resources utilization, technical index system of water allocation and integrated regulation of water resources”. The Report on Flood Resources Utilization proposed by the Flood Resources Utilization Research Group of the Office of State Flood Control and Drought Relief Headquarters (hereinafter referred to as “the Office”) has also noted that “the flood resources utilization possesses new characters keeping pace with the Times, is the product of water management concept renovation, is the objective requirement of social-economic development, is the practice under the guidance of water governance theories in new era, is the outcome by moving with the Times and being pioneered and innovative, which is put forward in view of traditional water conservancy and traditional practices, and is the concrete embodiment of combining benefit promotion and damage mitigation and implementing both flood control and drought relief”. Zheng Shouren, the academician of the Changjiang Water Resources Commission applied for the Research Project on Flood Resources Utilization and risk-optimized countermeasures in the Yangtze River Basin as required in the 2014 Guideline for Consultation and Research Projects of the Chinese Academy of Engineering (hereinafter referred to as “CAE”). Approved by the CAE, the Research Project has been

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listed as the consultation and research project in 2014 of the civil & water conservancy & construction sector. This project aims to analyze the potential utilization of flood resources in the Yangtze River Basin and to explore its effective means, then to put forward the countermeasures against the risks. The research methods and theoretical explorations of this project are of general scientific and important guiding significance, as the suggestions on flood resources utilization could be reference of decision-making for the competent authorities. The main research contents of this project include: (1) the feasibility study on the upstream inflow and sediment variation and the flood resources utilization; (2) the feasibility study on the benefit brought by the Three Gorges Project when utilizing the Yangtze River flood resources; (3) study on the flood resources utilization in the Yangtze River Basin and the countermeasures to reduce flood control risks; (4) study on flood resources utilization in the Three Gorges Project and the countermeasures to reduce its risks, etc. The study objectives of this project include: (1) revealing the characteristics of the inflow and the sediment variation in the upper reaches of the Yangtze River, quantitatively evaluating the potential utilization of the flood resources in the Yangtze River and demonstrating the feasibility of its utilization in the Basin; (2) proposing the necessity and feasibility of utilizing the flood resources by the Three Gorges Project; (3) throwing light on the characteristics of the flood resources, presenting different methods of flood resources utilization in different regions over the Basin, and raising the overall risk-optimized strategies of the flood resources utilization in the Yangtze River; (4) analyzing the risk of flood resources utilization for the Three Gorges Project on flood control, sediment, ecology, etc., and putting forward the risk-optimized countermeasures of flood resources utilization for the Three Gorges Project. This book is mainly based on the research report derived from above-mentioned project, and is enriched and improved with combination of related research report. Wuhan, China

Shouren Zheng Zhiyu Zhong Qiang Zou Yi Ding Lin Yang Xue Luo

Contents

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2

Necessity of Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Discrimination and Analysis of Flood Resources Utilization . . . . 1.2 Development of Flood Resources Utilization Thoughts . . . . . . . . 1.3 Development Process of Flood Resources Utilization . . . . . . . . . . 1.3.1 Practices on Engineering Flood Resources Utilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.2 Practices on Non-engineering Flood Resources Utilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Main Problems of Flood Resources Utilization in the Yangtze River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.1 Grim Situation of Flood Control in the Basin . . . . . . . . . 1.4.2 Frequent Occurrence of Drought and Water Shortage in the Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.3 Adverse Effects on Water Supply and Ecology Induced by Inflow Shortage . . . . . . . . . . . . . . . . . . . . . . . . 1.5 Importance of Flood Resources Utilization in the Yangtze River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5.1 Urgent Need to Alleviate Water Resources Supply and Demand Tension in the Basin . . . . . . . . . . . . . . . . . . . 1.5.2 Urgent Need to Alleviate Water Resources Supply and Demand in Dry Season in the North by Ensuring Adequate Water Supply for South-to-North Water Transfer Project . . . . . . . . . . . . 1.5.3 Urgent Need to Alleviate Water Environment Bearing Pressure in Dry Season and Improve Ecological Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5.4 Urgent Need to Improve Utilization Efficiency of Hydropower Resources in the Basin . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 1 3 6

17 18

Overall Situation of Yangtze River Basin . . . . . . . . . . . . . . . . . . . . . . . . 2.1 General Situation of the Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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6 8 10 10 12 13 14 15

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Planning on River Systems in Mainstream and Tributaries and Key Reservoirs . . . . . . . . . . . . . . . . . . 2.1.2 Characteristic Analysis of Rainstorm Flood . . . . . . . . . . . 2.2 Flood Control Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1 Flood and Flood Disasters . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.2 Flood Control Situation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.3 Principles, Standards and Objectives of Flood Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.4 Flood Control Areas Division . . . . . . . . . . . . . . . . . . . . . . . 2.2.5 Flood Control System and Layout . . . . . . . . . . . . . . . . . . . 2.3 Overview of Yangtze River Basin Management . . . . . . . . . . . . . . . 2.4 Profile of Major Key Reservoirs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.1 Ertan Hydropower Station . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.2 Xiluodu Hydropower Station . . . . . . . . . . . . . . . . . . . . . . . 2.4.3 Xiangjiaba Hydropower Station . . . . . . . . . . . . . . . . . . . . . 2.4.4 Tingzikou Hydraulic Complex . . . . . . . . . . . . . . . . . . . . . . 2.4.5 Three Gorges Hydraulic Complex . . . . . . . . . . . . . . . . . . . 2.5 Major Cities and Towns Along the Mainstream and Tributaries of Upstream Yangtze . . . . . . . . . . . . . . . . . . . . . . . . 2.5.1 Sichuan-Chongqing Reach . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.2 Middle and Lower Reaches of Mainstream Jialing . . . . . 2.5.3 Middle and Lower Reaches of Mainstream Wujiang . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6 Key Reaches and Areas of Midstream and Downstream Yangtze . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.1 Jingjiang Reach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.2 Chenglingji Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.3 Wuhan Reach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.4 Hukou Reach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7 Overview of Flood Detention Basins in Middle and Lower Reaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7.1 Jingjiang Flood Storage and Detention Areas . . . . . . . . . 2.7.2 Flood Storage and Detention Area Around Chenglingji . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7.3 Flood Storage and Detention Area Around Wuhan . . . . . 2.7.4 Flood Storage and Detention Area Around Hukou . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Analysis on Characteristics and Changes of Flow-Sediment in Yangtze River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Characteristics and Changes of Upstream Yangtze Inflow . . . . . . 3.1.1 Analysis on Runoff of Control Stations on Mainstream and Tributaries . . . . . . . . . . . . . . . . . . . . . . 3.1.2 Characteristics of Inflow into Dam Site of Three Gorges Reservoir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

21 34 37 37 38 40 42 43 45 47 47 47 48 49 50 54 54 55 55 56 56 57 58 58 59 59 62 65 67 69 71 71 71 74

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Flood Characteristics of Major Tributaries . . . . . . . . . . . . . . . . . . . 3.2.1 Flood Characteristics of Yalong River . . . . . . . . . . . . . . . . 3.2.2 Flood Characteristics of Jinsha River . . . . . . . . . . . . . . . . 3.2.3 Flood Characteristics of Minjiang River (Dadu River) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.4 Flood Characteristics of Jialing River . . . . . . . . . . . . . . . . 3.2.5 Flood Characteristics of Wujiang River . . . . . . . . . . . . . . 3.3 Analysis of Flood Encounters Among Mainstream and Major Tributaries of Yangtze River Basin . . . . . . . . . . . . . . . . 3.3.1 Analysis of Flood Encounters Between Jinsha River and Minjiang River . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.2 Analysis of Flood Encounters Between Jinsha River and Jiangling River . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.3 Flood Correlation Between Cuntan and Yichang . . . . . . . 3.3.4 Analysis of Flood Encounters Between Jinsha River and Dongting Lake . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.5 Analysis of Flood Encounters Between Jinsha River and Hanjiang River . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.6 Study on Flood Spatial Pattern and Encounter on Middle and Lower Reaches of Yangtze River in Typical Years . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Sediment Characteristics and Changes in Upstream Yangtze . . . . 3.5 Characteristics and Changes of Flow-Sediment in Midstream and Downstream Yangtze . . . . . . . . . . . . . . . . . . . . . 3.5.1 Inflow Characteristics and Changes in Midstream and Downstream Yangtze . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.2 Sediment Characteristics and Changes in Midstream and Downstream Yangtze . . . . . . . . . . . . . . 3.6 Analysis and Prediction of Inflow Change in Yangtze River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6.1 Trend of Future Climate Change in the Yangtze River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6.2 Trend of Future Runoff Change in the Yangtze River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.7 Analysis and Prediction of Sediment Change in Yangtze River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.7.1 Cause Analysis of Sediment Reduction . . . . . . . . . . . . . . 3.7.2 Prediction of Recent Sediment . . . . . . . . . . . . . . . . . . . . . . 3.8 Brief Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

80 81 82 82 82 85 86 87 92

95 103 105 105 106 107 107 109 110 110 110 112 113

Feasibility Study on Flood Resources Utilization in Yangtze River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 4.1 Evaluation System for Flood Resources Utilization in Yangtze River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

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Current Situation Evaluation of Flood Resources Utilization and Potential Calculation Methods . . . . . . . . . . . . . . . . 4.3 Current Situation and Potential Evaluation of Flood Resources Utilization in Yangtze River Basin . . . . . . . . . . . . . . . . . 4.3.1 Analysis on Potential of Flood Resources Utilization in the Yangtze River Basin . . . . . . . . . . . . . . . 4.3.2 Analysis on Potential of Flood Resources Utilization in the Second Level Water Resources District of the Yangtze River Basin . . . . . . . . . . . . . . . . . . 4.4 Analysis on Potential of Flood Resources Utilization of Large and Medium-Sized Reservoirs in the Yangtze River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Brief Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Feasibility Study on Flood Resources Utilization of Three Gorges Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 Comprehensive Demand of Three Gorges Reservoir Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.1 Flood Control Requirements . . . . . . . . . . . . . . . . . . . . . . . . 5.1.2 Power Generation Requirements . . . . . . . . . . . . . . . . . . . . 5.1.3 Navigation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.4 Water Supply Requirements . . . . . . . . . . . . . . . . . . . . . . . . 5.1.5 Eco-Environment Protection Requirements in Middle and Lower Reaches . . . . . . . . . . . . . . . . . . . . . . 5.1.6 Geological Disaster Prevention Requirements in Reservoir Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.7 Comprehensive Requirements . . . . . . . . . . . . . . . . . . . . . . 5.2 Analysis on Utilization Condition of Flood Resources in Three Gorges Reservoir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Analysis on Forecasting Level of Three Gorges Reservoir and Its Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.1 Analysis on Generating Law and Predictability of Typical Major Flood . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.2 Analysis on Level of Short-Term, Medium-Term and Long-Term Hydrometeological Forecast Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.3 Accuracy Analysis on Hydrological Forecasting Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 Flood Resources Utilization Methods of Three Gorges Reservoir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 Brief Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Countermeasures for the Utilization of Flood Resources and Risk Reduction in the Yangtze River Basin . . . . . . . . . . . . . . . . . . 6.1 Risk Analysis of Flood Resources Utilization . . . . . . . . . . . . . . . . . 6.1.1 Definition of Risk Analysis for Flood Resources Utilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1.2 Flood Resource Utilization Risk Analysis Process . . . . . 6.2 Risk Analysis of Flood Resources Utilization in the Yangtze River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.1 Classification of Risk Analysis of Flood Resources Utilization in the Yangtze River Basin . . . . . . . . . . . . . . . 6.2.2 Analysis of Flood Resources Utilization Risk of Main Reservoirs in the Yangtze River Basin . . . . . . . . 6.2.3 Risk Analysis of Flood Resources Utilization in the Two Lakes of the Yangtze River Basin . . . . . . . . . . 6.3 Overall Strategy for Risk Management of Flood Resources in the Yangtze River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4 Countermeasures for Flood Resources Utilization Risks of Major Reservoirs in the Yangtze River Basin . . . . . . . . . . . . . . . 6.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Study on Floating Water Level During Flood Season of the Three Gorges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1 Research Necessity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Analysis of the Effect of Floating Water Level During Flood Season . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.1 Analysis of the Impact on Flood Control in the Middle and Lower Reaches . . . . . . . . . . . . . . . . . . . 7.2.2 Impact on Sediment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.3 Impact on the Power Generation Efficiency . . . . . . . . . . . 7.2.4 Influence Analysis of the Eco-Environment . . . . . . . . . . . 7.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Study on Regulation Mode of Small and Medium Floods in the Three Gorges Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1 Research Necessity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 Selection of Dispatching Plan for Medium and Small Flood in the Three Gorges Reservoir . . . . . . . . . . . . . . . . . . . . . . . . 8.2.1 Study on the Rules of Flood Resources Utilization and Dispatching in the Three Gorges Reservoir . . . . . . . 8.2.2 Start Timing of Flood Resources Utilization and the Forecast Pre-discharging . . . . . . . . . . . . . . . . . . . . 8.2.3 Study on the Dispatching Mode of Flood Resources Utilization in the Three Gorges Reservoir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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8.2.4

8.3

8.4

8.5

8.6

Comparison Plan for Flood Resources Utilization Scheduling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Benefit Analysis of Flood Resources Utilization in the Three Gorges Reservoir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.1 Analysis of Flood Control Impact and Power Generation Benefit of Different Flood Resources Utilization Schemes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.2 Analysis of Flood Control Impacts and Power Generation Benefits of Flood Resources Considering the Forecast Errors . . . . . . . . . . . . . . . . . . . . . 8.3.3 Analysis of Flood Control Impacts and Power Generation Benefits of Flood Resources During the Foreseeable Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Analysis of Small and Medium Flood Dispatching Examples in 2010 and 2012 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.1 Analysis of Flood Control Effects and Power Generation Benefits of Flood Resources Utilization in 2010 and 2012 . . . . . . . . . . . . . . . . . . . . . . . 8.4.2 Flood Resources Utilization and Dispatching Process of the Three Gorges Reservoir in 2010 and 2012 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.3 Utilization of Flood Resources in 2010 and 2012 Considering Forecast Errors . . . . . . . . . . . . . . . . . . . . . . . . 8.4.4 Considering the Upstream and Downstream Storage of Flood Resources in 2010 and 2012 . . . . . . . . . Analysis on Flood Control Risk of Small and Medium Flood Dispatching in Three Gorges Reservoir . . . . . . . . . . . . . . . . 8.5.1 Risk Analysis of Medium and Small Flood Dispatching Considering Floods with Different Design Frequencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.2 Risk Analysis of Medium and Small Flood Dispatching Considering the Flood Control Capacity of the Jingjiang Dike . . . . . . . . . . . . . . . . . . . . . . 8.5.3 Risk Analysis of Medium and Small Flood Dispatching Considering the Improvement of Shipping Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.4 Risk Analysis of Medium and Small Flood Dispatching Considering the Impact of Immigration in the Reservoir Area . . . . . . . . . . . . . . . . 8.5.5 Risk Analysis of Water Resources Utilization of the Three Gorges Reservoir Considering the Storage of Upstream Reservoirs . . . . . . . . . . . . . . . . . Analyzing the Impact of Small and Medium Flood Dispatching on Sediment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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8.6.1

Overview of Sedimentation Calculation in the Three Gorges Reservoir . . . . . . . . . . . . . . . . . . . . . . 8.6.2 Impact of Small and Medium Flood Dispatching on Reservoir Siltation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.6.3 Influence of Upstream Reservoirs Operation on Three-Port Diversions of Dongting Lake . . . . . . . . . . 8.6.4 Impact of Medium and Small Floods Operation on the River Bed Forming in the Lower Reaches of the Reservoir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.7 Analysis of the Impact on the Ecological Environment . . . . . . . . . 8.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Study on Pre-impounding Method of the Three Gorges Project at the End of Flood Season . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1 Research Necessity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2 Analysis of Water Conditions During Water Storage . . . . . . . . . . . 9.3 Analysis of Impact of Pre-impoundingat the End of Flood . . . . . . 9.3.1 Analysis of the Impact on Flood Control . . . . . . . . . . . . . 9.3.2 Analysis of the Impact on Sediment . . . . . . . . . . . . . . . . . 9.3.3 Analysis of the Impact on the Ecological Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10 Study on Countermeasures for Risks of Flood Resources Utilization in the Three Gorges Project . . . . . . . . . . . . . . . . . . . . . . . . . . 10.1 Countermeasures to Reduce Risk of Flood Control . . . . . . . . . . . . 10.1.1 Countermeasures for Reducing Flood Control Risk by up Floating Water Level During Flood Season . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.1.2 Countermeasures for Reducing Flood Control Risk by Small and Medium Flood Dispatching . . . . . . . . 10.1.3 Countermeasures for Reducing Flood Control Risk by Pre-impounding . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.2 Countermeasures for Reducing Sedimentation in Reservoirs . . . . 10.2.1 Optimize Reservoir Dispatching and Improve the Sediment Discharge Effect of Sand Holes (Caves) in Hub Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . 10.2.2 According to the Characteristics of the Three Gorges Reservoir, the Test Yielded a New Model of “Storage and Drainage” . . . . . . . . . . . . . . . . . . . . . . . . . 10.2.3 Implement Engineering Measures to Prevent Siltation at the Tail of the Reservoir to Avoid Shipping Obstruction and to Control the Scouring of the Downstream Channel of the Dam . . . . . . . . . . . . . .

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297 310 310 313 315 315 316 318 319 320 321 322 323 325 325

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10.3 Countermeasures to Reduce Adverse Impacts on Ecological Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.3.1 Implement Ecological Regulation for Reservoir Operation to Improve Water Ecological Environment at Upstream and Downstream of Dam . . . . 10.3.2 Strengthen Experimental Research and Follow-up Monitoring to Explore Measures to Reduce Adverse Impacts on the Ecological Environment . . . . . . . . . . . . . . . . . . . . . 10.3.3 Construction of Ecological Environmental Protection Projects to Mitigate the Adverse Effects on the “Two Lakes” (Dongting Lake, Poyang Lake) in Dry Season . . . . . . . . . . . . . . . . . . . . . . . 10.3.4 Study the Joint Operation and Dispatch of Controlling Reservoirs in the Mainstream and Tributaries of the Yangtze River Basin and Reduce the Adverse Impact on the Ecological Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4 Benefits of Flood Resources Utilization in the Three Gorges Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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11 Conclusion and Prospect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347 11.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347 11.2 Prospect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

Chapter 1

Necessity of Study

1.1 Discrimination and Analysis of Flood Resources Utilization At present, there are some disputes and differences in the basic concept of flood resources utilization within the academic circles. The existing concepts of flood resources utilization are summarized, compared and sorted out in this study and the definitions and connotations generally accepted nowadays are adopted. Generally speaking, flood refers to the phenomenon that rivers and lakes see a sharp increase of flow and a significant rise of water level within a short time. Flood always occurs fiercely and has great natural destructive power. To this end, the main purposes of flood study are to explore the flood characteristics, master the evolution law, and actively take effective measures for flood resources utilization and risk prevention (Zheng 2010). Flood resources refer to the natural river flood runoff formed by local precipitation in a certain area. Flood resources utilization is to further tap the potential of flood resources which is difficult to make use of in the past on the basis of general water resources development, in the case of causing no disasters, to make the most of such water storage projects as reservoirs, sluices and dams, natural depressions, artificial lakes, underground lakes to impound water, to extend the retention time of flood in river channels and in flood storage and detention areas, to restore the eco-environment of rivers, lakes and depressions, and to replenish groundwater as much as possible. Its essence to make use of the water volume beyond the scope of human and environment adaptation or beyond the capacity of current regulation through new technical means and management methods, so as to realize the transformation of flood from disaster water to resource water and environment water. In the actual operation of reservoirs, combined with advanced meteorological and hydrological forecasting means, the purpose of making better use of flood resources can be achieved by adjusting the operation mode of the flood limit water level of reservoirs or by optimizing the regulation mode of reservoirs (Wang et al. 2010). © Changjiang Press (Wuhan) Co., Ltd. 2021 S. Zheng et al., Flood Resources Utilization in the Yangtze River Basin, https://doi.org/10.1007/978-981-15-8108-3_1

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1 Necessity of Study

Flood resources utilization risk refers to the unexpected events and the probability of occurrence and the resulting loss degree in the process of utilizing flood resources to cope with water shortage and maintain river health under specific temporal and spatial environment conditions (Zheng 2004; Wang and Yin 2004). From the above discrimination and analysis of related concepts of flood resources utilization, it is not difficult to see that flood resources possess such multiple features as distinct resource and risk compared with constant water resources utilization. On the one hand, confronting increasingly severe water resources shortage, in the face of the fact that constant water resources cannot meet the requirement of basic life for local resident and of socio-economic development, the large amount of water resources occupied by flood has endowed itself with distinct resources attribute. On the other hand, flood resources have also inevitably brought relatively serious risks while contributing relatively great resource benefits, there are not only inherent flood risks under natural conditions, but also additional risks inducing by adopting flood utilization measures, including uncertainty risks of upstream incurrent flood, reservoir regulation decision-making, and calculation parameters of flood resources utilization benefit, as well as risks of eco-environmental impact. The flood utilization and its risks are both contradictory and interdependent, reducing the loss of flood disasters and improving the level of flood resources utilization are important measures to solve the problem of water shortage and to strengthen the capacity of river basin flood control and disaster mitigation, and also is a new task facing the current river basin water resources management. In conclusion, the risk analysis theory must be introduced into the utilization of flood resources to work out a series of scientific problems such as flood resources volume, conditions and ways to utilize flood resources, countermeasures to reduce risks and so on, and to realize risks pooling and benefits sharing, in order to provide important basis for decision-making and management of flood resource utilization. In general, the flood resources utilization is the object request under the dual-drive of uneven distribution in time and space of precipitation and prominent contradiction of water shortage. According to the research status abroad, the local practices of flood resources utilization have been generally carried out, covering reservoirs, flood storage and detention areas and local areas. However, there are few researches on the flood resources utilization at the river basin level. At present, the researches on flood resources utilization in China mainly focus on the rivers in the norther regions such as the Haihe River and the Yellow River, yet existing lack of such researches for the Yangtze River, only some preliminary studies on the flood resources utilization for a single reservoir. Therefore, it is urgent to take advantage of innovative methods and technologies to guide the flood resources utilization in the Yangtze River Basin in view of the controversies.

1.2 Development of Flood Resources Utilization Thoughts

3

1.2 Development of Flood Resources Utilization Thoughts The utilization of flood resources has existed since ancient times, and its application in economy, society and even military is not uncommon. More than 2200 years ago, Li Bing and his son who lived in Qin State during the Warring States Period built Dujiangyan Project by taking advantage of fluvial process principle and keeping to the Taoist thoughts of “following the natural world” and “harmony between man and nature”, and realized the scientific concept on integration of flood control, sediment diversion and water resources utilization, which made the Dujiangyan Project a typical comprehensive hydro works of benefit promotion and damage mitigation and turned the Central Plain of Sichuan into a land of abundance and wealth. Since the Ming Dynasty, the river governance strategy of utilizing flood water with guidance, clearing sands with converging flow and diverting flood with floodplain has formed, which thought that “it is preferable to implement river governance by using natural low of the river rather than blessing and praying. By taking advantage of the nature of raging river and playing its role, it is possible to deepen the river channel and heighten the floodplain, then man is able to handle river governance.” During the reign of Emperor Kangxi if the Qing Dynasty, after the development and improvement on river governance by Jin Fu and Chen Huang on the basis of Pan Jixun in the Ming Dynasty, a system of river management and flood control was formed for the Yellow River to utilize floodplain deposition and main channel erosion in a controlled way, which made use of front embankment to clear sand with converging flow and remote levee to control flood, with combination of separation dike, overflow dam and dam for releasing floodwater. When it came to the Republic of China, Mr. Li Yishe wrote Irrigation and Water Conservancy and Flood Utilization and Underground Water Storage, and clearly put forward flood utilization and flood resources utilization. Mr. Li believed that the northern region had always been suffering from drought and lack of harvest, however, whenever it rained heavily, the river rose sharply and the water volume would be more than dozens of times larger than usual, it was not worthy letting the water flow down directly into the sea; if the flood broke out of the embankment without restrictions, it would cause greater damage. From a global perspective, the contradiction between supply and demand of water resources is tending to intensify worldwide, the objectivity of the flood risk has been recognized gradually and the understanding of the flood and its effect on the environment and ecology has been deepening. As for flood control and disaster mitigation, while the countries is taking engineering measures, they are also getting down to constantly value such non-engineering measures as floodplain management, flood insurance, flood risk map, flood forecasting and warning system and flood administrative legislation management, transferring form “flood defense” to “flood management”, in order to realize the guiding concept of “people-oriented” and “harmonious coexistence between man and flood”. After the flood occurring in the United States during 1993, there are no reinforcement or reconstruction of embankments damaged by the flood in high-risk areas featuring sparse population and low-density asset and thus the flood water is allowed to be detained and stored within the land once

4

1 Necessity of Study

protected by the embankments, which not only make use of the eco-environmental function of the flood, but also alleviate the flood control pressure in order important areas. Since the 1960s, Japan has been striving to realize the flood control strategy of “safety assurance”, and has established a relatively high-standard flood control engineering system after more than 30 years of practice, otherwise, it has recently realized that it is neither possible nor economical to ensure safety through flood control engineering, as a result, its flood control concept has shifted to a strategy of “risk selection” under certain flood control standards; in terms of flood resources utilization, such measures are taken as in situ digestion of rain and flood, as well as construction of artificial beach and wetland and cultivation of aquatic species on the channelized riverbanks to seek for a “multi-natural river” similar to the natural state. When it comes to China’s attitude to flood, from the founding of the People’s Republic of China, the basic thought usually focused on how to safeguard the security of rivers and dams by discharging the flood water into the sea as soon as possible rather than taking the flood as a resource. Since the late 20th century, facing the aggravating contradiction between supply and demand of water resources and the severe situation of increasing flood loss, China has changed its flood control strategy, and consciously taken some engineering and non-engineering measures to fulfill flood utilization, instead of blindly discharging the flood into the sea. After the serious floods occurred in the Yangtze River Basin and Songhua River Basin in 1998, we have taken profound consideration of flood issue and made strategic adjustment again on flood control work. The major breakthroughs in adjustment for flood control strategy are as follows: in terms of construction, it emphasizes the deployment of flood control construction under the framework of river basin ecosystem reconstruction; in terms of management, the System Theory and Risk Management Method are applied to change from flood control to flood management. The construction of flood control has transferred from such engineering construction as embankments and reservoirs to construction of a comprehensive flood control system, with a view to take moderate risks, formulate reasonable and feasible flood control standards, flood prevention schemes and flood regulation plans, and comprehensively make use of various measures to ensure flood control security within the standards for reducing the loss to the minimum in case of excessive flood, instead of trying to totally eliminate the flood disasters or to discharge the flood into the sea for safety. Flood is not completely harmful; it is also the carrier for transporting river material, as well as an important condition for maintaining ecosystem balance in the river basin. In a country like China which is short of water, flood also serves as a significant component of the available water resources. To this end, flood regulation has shifted from simple flood control and disaster mitigation to the combination with flood resources utilization, which means that our flood control concept has realized the change from “flood is a kind of disaster” to “flood can be taken advantage as a kind of resource”. This change will have a fundamental impact on flood control strategy and play a positive role in propelling the process of realizing the flood resources utilization (Li 2007). Thousands of years of campaigns waged against natural disasters has warned us that it is unrealistic and impossible to completely control and eliminate flood disaster

1.2 Development of Flood Resources Utilization Thoughts

5

and then get flood issues solved once and for ever. For flood control and disaster mitigation, the United States once carried out large-scale construction of flood control projects, however, the investment of substantive bankroll didn’t effectively control the flood, on the contrary, the loss caused by flood was increasing. This was because of socio-economic development and increase of population size, but the land development and economic deployment didn’t take account of flood risks, which led to the increase of vulnerability; moreover, the water conservancy projects for flood control changed the natural hydrological characteristics of rivers and lakes, which aggravated the frequency and scope of flood disasters. Each dynasty of China mainly relied on the construction of water conservancy projects for fighting against flood, but engineering measures could neither fundamentally avoid the occurrence of flood nor completely eliminate flood risks, which would inevitably weaken the utilization of flood resources (Zheng 2009). All these lessons and experiences on water governance prove that we should learn to live with flood when promoting engineering measures for flood control, take moderate flood disaster risks, implement river basin risk management instead of simple flood control and emergence rescue, shift from “flood control” to “flood management”, achieve “harmony between man and water”, leave flood necessary discharge path and room, give full play to such advantages as flood resources utilization, eco-environmental restoration and groundwater resources supplement, as well as minimize the losses caused by flood disasters by engineering and non-engineering measures. Judging from the history of flood control and disaster mitigation at home and abroad, man’s ways and attitudes to deal with flood have changed gradually with the development of history and the progress of society, and roughly experienced three different stages. The first one is the stage of passive adaptation to flood. During this period, the world was generally sparsely populated, the social productivity was low, and the human ability to transform the nature was very low. Therefore, the strategy of adapting to the nature was widely adopted, the flood was regarded as beast of prey and there was nothing to do but to escape. The second one is the stage of control and defense. With the development of society and the improvement of productivity, the settlements gradually expanded, and people’s demand for land was increasing, so they began to March to flood channels and lakes for flood storage, resulting in smaller and smaller flood storage areas for rivers. The third one is the stage of consciously and actively adapt to the flood. Facing the continuous severe flood disasters, people find that despite the continuous increase of the investment in flood control and disaster mitigation, and the continuous reinforcement of embankments, the dream of eradicating flood disasters still cannot be realized. Not only that, but with the continuous development of human society and economy, the economic loss caused by flood disasters is still increasing day by day, thus falling into the vicious circle of mutual competition between economic development and flood disaster. In short, the relation between human beings and flood has experienced the avoidance and defense in agricultural society and the resistance and conquest in industrial society. In today’s knowledge age, the relation between human beings and flood should be harmonious coexistence and flood resources utilization, which is supposed to become a new concept of flood control in the 21st century.

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1 Necessity of Study

1.3 Development Process of Flood Resources Utilization Since the 1950s, the People’s Republic of China has begun to carry out large-scale infrastructure construction of water conservancy projects in three stages. Up to now, a relatively complete system of flood control and disaster mitigation has been formed, which has made great progress in flood control and water resources utilization. Entering into the 1990s, with the rapid development of China’s national economy, the advance of urbanization and large increase of population, the demand for water in all walks of life has been growing, and water shortage has become more and more serious, especially in our northern region. Many places have actively carried out explorations and experimental practices for flood resources utilization (Xu et al. 2008).

1.3.1 Practices on Engineering Flood Resources Utilization 1. Reservoirs to impound flood According to the comprehensive plan of water resources, the annual distribution of river runoff with a volume of 2737.5 billion m3 is mainly concentrated in summer, which is more obvious in the northern region. In the north, the mean annual maximum river runoff of four consecutive months accounts for 60–80% of the total annual runoff, with some stations on the Haihe River and the Yellow River exceeding 80%, and some stations on the northwest rivers up to 90%. In the south, the mean annual maximum river runoff of 4 consecutive months accounts for 50–70% of the total annual runoff. The main way of flood utilization is to build reservoir, so as to effectively control flood and redistribute reasonably natural water. By 2000, China had built more than 80,000 large, medium and small-sized reservoirs, 5.85 million pond and retaining dams, with a total storage capacity of 575.6 billion m3 and benefit storage capacity of 313.4 billion m3 , occupying respectively 22 and 12% of the mean annual runoff. On the whole, the regulation and storage capacity of water conservancy projects in China is lower than that in the United States, Canada, Russia, Mexico and other countries with higher level on water resources development and utilization, so there is still room for development and exists need for development. 2. Flood storage and detention areas to retain flood There are 40 flood storage and detention areas in the middle and lower reaches of the Yangtze River, 6 in the lower reaches of the Yellow River, 27 in the Huaihe River Basin and 26 in the Haihe River Basin, with a total number of 99 and total flood storage and detention volume of 97 billion m3 . Flood storage and detention areas have played an important role in ensuring flood control safety in key areas, large and medium-sized cities and major traffic arteries and in minimizing disaster losses by timely diverting and storing flood as well as reducing flood peak. The application of the flood storage and detention areas in Haihe River Basin shows

1.3 Development Process of Flood Resources Utilization

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that the rational planning, construction and scientific scheduling of the flood storage and detention areas can not only decrease the disaster losses, but also replenish the groundwater and make full use of flood resources. 3. Dams and sluices across river to realize water reallocation between river and channel Building dams and sluices across the river is able to impound rain and flood in the flood season and achieve water reallocation between river and channel, and reduce the surplus water as much as possible, which can not only alleviate the flood control burden of the river channel, but also achieve the effect of using flood and rain, with the aim of making the best of flood resources, improving the surrounding environment, prolonging the contact time between flood and ground, and increasing the recharge of groundwater. For example, Beijing has built nine cascade barrages (rubber dam) on the Chaobai River, with a total storage capacity of 20 million m3 . The completion of these projects has effectively utilized flood resources and greatly improved the urban landscape along the river, which makes this place a famous tourist resort in Beijing and a beautiful scenery line in the river basin. 4. Small-sized hydro projects to collect rain and store water Using the ground and small-sized hydro projects, water conservation works to retain and store rainfall flood. In mountain areas, soil and water conservation engineering should be taken full advantage of to intercept and utilize rainwater, such as forest, grass, vegetation, terraced field, fish-scale pit, horizontal ditch and pool, water cellar, check dam, pond and retaining dam, and strive to achieve “less flood flowing down the mountain, fresh water slowly flowing off the plain”; in the plain areas, farmland works should be made full use of to retain rainwater and reduce flood disasters, such as ridge, weir, forest network and close-end border. For example, the construction of rainwater collection projects focusing on the excavation of ponds and cellars to collect rainwater, the improvement of channel network and the detention of floods in Baoding City has resulted in the excavation of nearly 14,000 water cellars, the construction of 850 reservoirs and more than 400 water diversion and impoundment projects, which has solved the problems of drinking water for 150,000 people in mountainous areas and seeding irrigation for farmland of nearly 6667 ha. 5. Soil and water conservation to impound water and promote benefit By taking measures as reforestation in fenced-up mountains, transforming farmland to forests, conservative grazing and building terraces, it works to intercept rainwater as much as possible, reduce mountain torrents, increase low water runoff, prevent surface soil from erosion, and decrease deposition in the downstream riverbed, which is not only beneficial to flood control, but also can increase irrigation water source in mountainous areas. For example, owing to the slope treatment for erosion control within the Weihe River Basin, a total of 6.38 billion m3 of runoff was intercepted and impounded from 1970 to 1980, with an average annual runoff of 319 million m3 ; giving the credit to Dashugou Ditch in Dantaizi Village, Qingshuihe County of Inner Mongolia autonomous region, which covers an area of 18 km2 and is afforested with an area of 1133 hm2 (inter-row grass

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planting), there was no flood in the ditch when suffering continuous rainfall of 56 mm within 3 h in the summer of 1984, instead, it yielded a bumper crop of wheat. 6. Inter-regulation of river channels to replenish wetlands In the middle and lower reaches of the River Basin, the diversion river channels that flow into the sea and the connections among river systems are utilized to adjust the abundance and shortage of water resources among rivers, rationally arrange the storage and discharge of flood water, and change flood water into resource water. For example, in Heilongjiang Province, the Liugan Canal and Wenghai Aqueduct Bridge in Jiangdong Irrigation Area of Nen River Diversion Project have been transformed into a cross pivotal project, and emergency water replenishment is made to Zhalong Wetland through Liugan Canal and Wenghai Drainage Channel, with a water supplement of 105 million m3 in 2001, effectively alleviating the water shortage for the wetland; In 2003, Jilin Province diverted a total of 1.058 billion m3 of flood water from the Di’er Songhuajiang River and Nenjiang River to replenish water for the five wetlands of Xianghai and Momoge, effectively protecting the wetlands. 7. Urban rainwater management to mitigate damage and promote benefit Urbanization significantly increases the total amount of surface runoff and flood peak discharge, which may lead to flooding in urban basins and downstream areas. Engineering measures are taken by artificial means, such as rainwater collection, infiltration and recharge, rainwater storage, pipe network transportation, water storage and utilization, etc., to make urban rainwater recycle, which can reduce urban runoff, decrease flood peak, delay confluence time, and increase urban water supply. For example, according to the its topography, nearby sewage pipeline, green space location, landscape lake layout and other conditions, Beijing Water Conservancy School collects rainwater from playground, green space, road, building roof, etc. for washing the playground and greening.

1.3.2 Practices on Non-engineering Flood Resources Utilization 1. Reservoir optimal operation Reservoir optimal operation refers to the rational utilization of reservoir storage capacity according to the principle of integrated management of water resources in accordance with the importance of each task undertaken by the reservoir, so as to regulate the natural runoff of the river and give full play to the comprehensive benefits of the reservoir on the premise of ensuring the safety of the multipurpose project. With the rapid development of our national construction of water conservancy projects, the major hydropower bases planned for the Yangtze River Basin, the Yellow River Basin and the Pearl River Basin have been built one after another, which make the reservoir optimal operation attract concern from academic and engineering circles (Feng 2009).

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With the aggravation of the contradiction between water supply and demand, the domestic engineering and academic circles have paid more attention on the research on the utilization of flood resources in recent years, and have made remarkable achievements. At present, the utilization of flood resources in China is mainly based on the existing water conservancy facilities, combined with nonengineering measures as satellite, meteorology, runoff forecasts, to study the options of the comprehensive operation modes of reservoirs, so as to realize the utilization of flood resources. 2. Active use of flood storage and detention area Flood storage and detention area can be used as an important means for flood resource utilization. Through benefit comparison analysis, its scheduling and application plan can be adjusted to actively divert flood with purpose in the case of flood, so as to achieve the purpose of recharging groundwater and raising underground water level with proper inundation of some low-lying lands and wetlands in the area. Haihe River Basin suffered from a big flood in August 1996, although the spring drought was severe in the following year, but it still embraced a wheat harvest thanks to the use of flood storage and detention area in 1996. One year of flood brings three years of harvest; this case urges people to re-understand the role of flood storage and detention area. While strengthening the safety construction of flood diversion project such as flood storage and detention area, the river channel project for flood diversion and detention should be constructed in a planned way, so that flood diversion and water replenishment can be done well and the plain underground water source can be recharged. 3. Policy, regulation and scientific planning Reasonable planning is also a means of flood resources utilization. According to the principle of comprehensive utilization, the relation between flood control and benefit promotion should be well planned so as to exploit water resources as far as possible and meet the requirements of eliminating harm and promoting benefit. Reasonable land use planning can make full use of rainwater resources through natural landform, soil and water conservation planning and water use planning. Relevant laws and regulations shall be established and improved, publicity shall be intensified, national water literacy shall be cultivated, production and living activities shall be regulated, and flood risks shall be actively prevented and adjusted. Public awareness of participation shall be stepped up. 4. Risk management The flood resources utilization lives with the risk, and it should be combined with risk management to achieve risk and benefit sharing. Under the background of water resource shortage and increasing water environment deterioration, the flood resources utilization becomes an essential way to alleviate this contradiction. However, if any local region or department only pursues the maximization of its own interests in water governance, it may endanger others at the expense of ecological environment.

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1.4 Main Problems of Flood Resources Utilization in the Yangtze River Basin The Yangtze River Basin is relatively rich in water resources, while its runoff is mainly formed by rainfall, which is unevenly distributed throughout the year with great inter-annual variation. In the flood season, the main stream accounts for about 70–75% of the annual runoff, and the tributaries between 55 and 80%. The economic and social development of the Yangtze River Basin has put forward new and higher requirements for the water resources utilization, while the traditional utilization of flood resources cannot meet the these needs with uneven spatial and temporal distribution and insufficient water supply projects, which still exists problems as following (Changjiang Water Resources Commission 1990, 2010, 2012).

1.4.1 Grim Situation of Flood Control in the Basin The Yangtze River Basin drains a large area, and the flood usually occurs earlier in the lower reaches than in the upper reaches, and earlier in the south than in the north. According to the regional distribution and moving situation of rainstorm, the floods in the Basin can be divided into such 2 types as regional big flood and river basin big flood, of which the regional big flood is formed by one or two regional rainstorms, occurs in some tributaries or some mainstream section in upper, middle and lower reaches of the Yangtze River featuring high flood peak, large volume and short duration, and causes flood disasters in some tributaries or local sections of mainstream local river floods with high the probability of occurrence; the river basin big flood is formed by continuous rainstorms within a large area, when the upper and lower reaches suffer from floods at the same time, and the mainstream and tributary floods are encountered, resulting in the serious floods or extraordinary floods with high peak, large volume, long duration and serious outcomes in the middle and lower reaches of the Yangtze river, such as the floods occurring in 1931, 1954 and 1998. Since the 20th century, the Yangtze River has been flooded many times, leading to serious flood disasters. In 1931, the river basin flood occurring in the Yangtze River affected an area of 130,000 km2 , inundated 3.39 million ha of farmland, affected 28.5 million people and killed 145,000; in 1954, the river basin flood occurring in the Yangtze River flooded 3.17 million ha of farmland in the middle and lower reaches, affected 18.88 million people and killed more than 30,000, making the Beijing-Guangzhou railway out of service for 100 days; in 1998, another river basin flood occurring in the Yangtze River inundated 239,067 ha of cultivated land, affected 2.316 million people and caused 1,562 deaths, with 1,975 embankments in the middle and lower reaches bursting and 2.125 million houses collapsing. In 1935, the regional flood occurring in the middle reaches of the Yangtze river inundated 1.51 million ha of farmland, affected 11.03 million people and caused 140,000 deaths; in 1981, the

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flood occurring in the upper reaches of the Yangtze River flooded 0.874 million ha of farmland, caused 888 deaths and 13,010 people were injured. With the operation of the Three Gorges Project, the capacity has been greatly upgraded in flood control for the middle and lower reaches of the Yangtze River, especially that the flood control situation of the Jingjiang River has been fundamentally improved. The capacities in flood control for the main reaches of the mainstream and tributaries of the Yangtze River have roughly been up to the following standards: the Jingjiang River Basin can defend floods with return period of 10 years with the help of embankments; after the completion of the Three Gorges Project and with its operation, in case of floods with return period of 100 years or below, the water level of Shashi City can be regulated to be no more than 44.5 m without operation of the Jingjiang flood storage and detention area, the embankment standard along Jingjiang Reaches can be raised to defend the one-in-100-year flood; in case of the one-in-1000-year flood in 1000 years or the severe flood equivalent to that in the year of 1870, the discharge flow of Zhicheng City can be regulated to be no more than 80,000 m3 /s with the operation of the Three Gorges Project, and the water level of Shashi City can be controlled to be lower than 45.0 m in combination with operation of the Jingjiang flood storage and detention area to ensure the flood running through Jingjiang Reach in security level. The Chenglingji Reach can defend floods with return period of 10–20 years with the help of embankments, considering the operation of flood storage and detention area in this region, it is able to defend the flood equivalent to that in the year of 1954; in the event of recurrence of floods equivalent to those in the years of 1931, 1935, 1954, with regulation of the Three Gorges Project, the flood diversion volume and the inundated area would be substantially reduced, and there is no need to carry out flood diversion in general years (except for the estuary of each tributary). The Wuhan Reach can defend floods with return period of 20–30 years with the help of embankments, considering the operation of flood storage and detention area in its upper reach and local region, it is able to defend the flood equivalent to that in the year of 1954 (its maximum 30-day flood volume is approximately equivalent to that of flood with return year of 200 years); as the upstream flood can be controlled by the Three Gorges Project, the flood threatto Wuhan City can be avoided in case of the outburst of the Jingjiang embankments; because of the operation of the Three Gorges Reservoir and the enhancement of flood control ability in the vicinity of Chenglingji, the flood control flexibility of the mainstream Yangtze River has been improved, and the water level of Wuhan City can be prevented from getting out of control when cooperating with the operation of Danjiangkou Reservoir and flood storage and detention area near Wuhan. The Hukou Reach can defend floods with return period of 20 years relying on embankments, in consideration of the operation of flood storage and detention area in its upper reach and local region, and it is able to defend the flood equivalent to that in the year of 1954. Although the flood control ability of the Yangtze River has been greatly improved, its flood control is still faced with the following main problems and challenges: first, the contradiction is still outstanding between the security discharge of river channel in the middle and lower reaches of the Yangtze River and the flood in the Yangtze River

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with high peak and large volume, despite of a flood control capacity of 22.15 billion m3 occupied by the Three Gorges Project, the flood control capacity is still insufficient in view of the huge excess flood in the middle and lower reaches of the Yangtze River. In case of the big flood equivalent to that in the year of 1954, there still exists excess flood of 40 billion m3 to be well arranged. However, most of the flood storage and detention areas are weak in the security construction, once they are come into service, the losses will be huge; second, the flood control capacity of the tributaries and lakes in the upper, middle and lower reaches of the Yangtze River is relatively low, many small and medium-sized rivers has not been managed effectively and systematically, resulting in low capacity of flood control capacity; third, the prevention and control of mountain torrent disasters is in its infancy and its defense is very difficult due to extensive distribution, fast confluence, high impulse and heavy destruction, and the non-engineering measures of flood control lag behind; fourth, the long-term adjustment resulting from scouring and silting in extensive reaches of the middle and downstream Yangtze River has brought great impact on the river regime and river-lake relationship in the middle and downstream Yangtze River, to this end, it still need to strengthen observations and study corresponding countermeasures; fifth, the frequency of extreme hydro-climatic events and the intensity of rainstorms in some parts of the Yangtze River Basin have increased due to the impact of global warming in recent years, leading to severe floods in some areas; sixth, the river basin is experiencing rapid development of economic society and urbanization along with concentration of population and wealth, once the flood occurs, the losses will be increasing.

1.4.2 Frequent Occurrence of Drought and Water Shortage in the Basin Although the Yangtze River Basin is rich in water resources, local drought phenomena also occur from time to time due to uneven distribution in time and space. According to statistics, the frequencies of flood and drought disasters in the Yangtze River Basin are generally equal, and the losses caused by drought are also quite serious. According to historical records, during the period of 825 years from 1163 to 1987, there were 494 droughts and floods in the middle and lower reaches of the Yangtze River during the Mei-yu period, including 62 severe droughts, 63 severe floods, 185 floods, 184 droughts and 321 normal events. Compared with the arid and semi-arid areas in the north, the Yangtze River Basin belongs to humid area. Although the drought in the Basin is less severe, the economic losses caused by the drought are serious and the social impacts are huge (Changjiang Water Resources Commission 2012). With the rapid development of economy and society and the people’s increasing demand for water resources security, water shortage has often appeared in recent years within the Yangtze River Basin, where water resources are relatively abundant.

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The annual and seasonal alternations of flood and drought disasters are more and more prominent. Not only do drought and flood occur in the same frequency, but also have the obvious characteristic of annual and seasonal alternations. Not only do drought and flood disasters appear in the same year, but also the degrees of flood and drought tends to develop towards the poles, that is to say, hydrologic events of extreme disasters increase. In 2006, a severe drought event occurred in Chongqing City in the upper reaches of the Yangtze River, which not only seriously affected the normal production of industry and agriculture, but also made it difficult for residents to use water; moreover, at the beginning of 2007, the Jialing River in Chongqing City in the upper reaches of the Yangtze River saw its lowest dry water level within 50 years, seriously affecting its navigation, while in the fall of 2007, the upstream of the Yangtze River and some regions around the Two Lakes experienced the worst drought with return period of 50 years; Yunnan Province and Guizhou Province suffered from continuous droughts from 2009 to 2011; the middle reaches of the Yangtze River were hit by droughts in the first half of 2011; droughts and process of low water flow have continuously occurred in the Two Lakes region. In the wake of increasing demand for water resources resulting from eco-social development and the impact of climate changes, there exists problems as water resources shortage, regional water shortage, seasonal water shortage and engineering water shortage to varying degrees in some regions, what’s more, the coexistence of drought and flood and the sharp turn between drought and flood are relatively prominent. In conclusion, the tasks of drought relief and water supply in the Yangtze River Basin are arduous.

1.4.3 Adverse Effects on Water Supply and Ecology Induced by Inflow Shortage Water resources protection has made great progress in the Yangtze River Basin, but there is still a long way to go considering the important role of the Yangtze River Basin and the requirement of eco-social development. Especially in dry season, because of increased water withdrawals, decreased flow in the river channels, and pollutant emissions, water pollution is serious in some river sections, which has adverse effects on water use security and water ecosystem. Although the average annual amount of water use in the Yangtze River Basin is less than 20% of its total annual runoff (for example, the total amount of water use was 184.22 billion m3 in the Yangtze River Basin in 2005, occupying about 19% of the total annual runoff), as 70% of the runoff occurring in the flood season, It is calculated that the water use in non-flood season has taken up for more than 30% of the runoff during the same period, while the proportion even above 50% in some tributary sections. Due to the lack of river runoff in the dry season and the large amount of water withdraws, the remaining flow in the river channels cannot meet the ecological base flow required by the dilution of sewage and the habitat of aquatic

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animals and plants, which is also one of the main reasons for the deterioration of the water environment. The water quality of the Yangtze River Basin is good on the whole, but the eutrophication of the water body tends to worsen. Cities along riverside in the Yangtze River Basin have strengthened the pollution management, but there is still a lot of waste water flowing into rivers without processing, making pollution in the water body aggravate. The eutrophication degree of lakes and reservoirs in the Basin surrounding the cities is generally high, “bloom” events occur repeatedly in reservoirs and rivers. Moreover, the phenomenon of ecological environmental degradation due to drought is worrisome, such as the phenomenon of drying up in the Poyang and Dongting lakes during the dry season in 2007, which had serious influence on aquatic organisms and birds living in the lake regions. In addition, with the increasing frequency of extreme drought events in the Yangtze River Basin, the salt water intrusion in the Yangtze estuary during the dry period became increasingly serious. To sum up, the Yangtze River Basin integrated management is faced with contradictions which are difficult to reconcile at present stage and are embodied as floods caused by “dangers from excess water” and droughts caused by “concerns from insufficient water”, as well as the higher new requirements put forward by river basin water security for flood control and drought relief, the urge calls for a sound system of water resources unified scheduling management and for an improved overall strategy of flood resources utilization in the Yangtze River Basin. It is necessary to alleviate the above contradictions, promote the comprehensive harmony between human and water, and strengthen the utilization of flood resources. At present, there have been long-term and important tasks to strengthen the comprehensive utilization of water resources and solve the problems of drought and water shortage for the integrated management of the Yangtze River Basin.

1.5 Importance of Flood Resources Utilization in the Yangtze River Basin The flood resources utilization in the Basin is an important measure to give full play to the characteristics of flood resources, alleviate the shortage of water resources, reduce the losses caused by flood and drought disasters, and realize the optimal allocation of water resources and the sustainable development and utilization. It has important practical significance to evaluate the status quo and potential of flood resources utilization in the Yangtze River Basin, make pointed overall strategy for scientific and effective flood resources utilization, put forward countermeasures for flood resources utilization in the Yangtze River Basin, coordinate the relation among flood resources utilization, flood control security and eco-environment protection within the Yangtze River Basin. Specifically, the importance of flood resources utilization in the Yangtze River Basin is embodied in the following aspects.

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1.5.1 Urgent Need to Alleviate Water Resources Supply and Demand Tension in the Basin The total amount of water resources in the Yangtze River Basin is abundant, but with uneven distribution in space and time and prominent contradiction between supply and demand of water resources in some areas and in periods of dry season. Furthermore, with the rapid development of economy and society, as well as the extensive use of water and low water use efficiency, the discharge of waste sewage is huge and is increasing year by year, the contradiction between the supply and demand of water resources in the Basin is intensifying. The utilization of flood resources is an effective way to alleviate the contradiction between supply and demand of water resources. Through combination of engineering and non-engineering measures, we are able to equalize floods both in time and space to a certain extent, give full play to the reservoirs’ comprehensive benefits on the premise of ensuring flood control security, and make reasonable spacial and temporal redistribution of some water resources without effective utilization. By feat of the above measures, more potentially harmful floods can be converted into water sources that can be safely utilized for drought relief in the downstream of reservoirs and for environmental protection of wetlands, in order to make up for the shortage of water resources in dry season and dry year and to meet the demand of water resources for economic development, serving as effective guarantee to solve the drought and water shortage in dry season.

1.5.2 Urgent Need to Alleviate Water Resources Supply and Demand in Dry Season in the North by Ensuring Adequate Water Supply for South-to-North Water Transfer Project The Yangtze River Basin serves as the strategic tank for nationwide allocation of water resources and the golden waterway linking the western, middle and eastern China, and is also pivoting to improve the ecological environment in North China. The mainstream and tributaries of the Yangtze River also serve as the sources for many inter-basin water transfer projects, such as the Eastern, Middle and Western Routes of the South-to-North Water Transfer Project, Water Diversion to Central Yunnan, Hanjiang-to-Weihe Water Transfer Project, Yangtze-to-Chaohu-Huaihe Water Transfer Project and Yangtze Water Diversion Projects in Jiangsu coastal areas. The strategic position of the Yangtze River Basin is very prominent in China’s economic and social development. Flood is the most potential water resources, especially in the Yangtze river basin where flood resources are much more abundant, not only to ensure that there is sufficient water, but also to strive to provide high-quality water, in order to support the economic and social development in the north. In summer, it is not a problem to

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transfer water from the Yangtze River to the North; but in winter, when the north is most short of water and is also the dry season of the Yangtze River, water diversion will affect the water resources and environment security of the middle and lower reaches of the Yangtze River, especially in the estuary areas. Therefore, it is necessary to impound the Yangtze flood until the dry season to transfer water to the North. It can be seen that strengthening the flood resources utilization is one of the important measures to alleviate the shortage of water resources in China.

1.5.3 Urgent Need to Alleviate Water Environment Bearing Pressure in Dry Season and Improve Ecological Environment The Yangtze River Basin is our national unique and important germplasm resource bank for aquatic organisms, which preserves the main germplasm resources of freshwater fish in China. In recent years, the interference of human activities has led to the change of water habitat, and the diversity of aquatic life has an obvious downward trend, with the problems as shrinkage of fish population and degradation of germplasm resources. The pollution trend has not been curbedin the coastal waters of the Mainstream Yangtze River, some tributaries are seriously polluted, the eutrophication of lakes within the Basin is still developing and the security of water ecology is threatened. Meanwhile, over the past half century, and the wetlands serving as an important habitat for fish, waterfowl and other environmental conditions are gradually losing resulting from the serious degradation of the wetlands in the Yangtze River Basin. The practice of flood resources utilization will keep the flood water in the flood season as the runoff for the dry season, and make use of the flood water in the flood season for water renewing and sewage disposal, regulation between flood season and dry season, mutual supplement between abundance and scarcity and improvement of flood control, irrigation and water supply in the downstream, as well as for the ecological water supplement to the downstream lake wetlands in the dry season to avoid the ecological impact caused by dried-uplakes, which is conducive to conserve the virtuous cycle of river basin ecosystems, guarantee the water use requirements of the ecological environment in the downstream, and satisfy the water demands of sensitive areas like nature reserves, landscapes, wetlands, spawning grounds for fish and so on.

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1.5.4 Urgent Need to Improve Utilization Efficiency of Hydropower Resources in the Basin The total amount of hydropower resources in the Yangtze River Basin is rich, and the development and construction conditions of hydropower resources are superior. Hydropower resources are mainly composed of large scale hydropower stations with large capacity, among which the large hydropower stations are mainly concentrated in the upstream, while the small and medium-sized hydropower stations are distributed in the whole basin, and most hydropower stations have comprehensive utilization benefits. The Hydropower development in the Yangtze River Basin has dual functions of both the primary energy construction and the secondary energy construction, which is an important component of the integrated utilization of water resources and can promote the comprehensive treatment and development of rivers (Changjiang Water Resources Commission 2010). However, the utilization of hydropower resources in the Yangtze river basin is still not in a high level and need to be improved, especially for the rivers possessing ample hydropower resources in the upper reaches like the Jinsha River, Yalong River and DaduRiver where have great development potential. At the same time, the inflow from the mainstream and tributaries in the Yangtze River Basin is mostly concentrated in the flood season, a large amount of flood water in the flood season have to be abandoned for the need of flood control, while the volume of water storage after the flood is very limited. The utilization efficiency of reservoirs hydropower resources can be effectively increased by strengthening the scientific operation of reservoirs, which contributes to increasing the utilization level of flood resources and giving full play to the comprehensive benefits of flood control, power generation, navigation and water supply of reservoirs. Moreover, with the continuous construction and operation of reservoir groups in the Yangtze River Basin, it is also quite necessary to strengthen the optimal and unified operation of reservoir groups and give play to the high efficiency of reservoir groups in the flood resources utilization. In conclusion, the contradiction is increasingly prominent between the uneven temporal and spacial distribution of water resources and the water demand in the Yangtze River Basin. Along with the consecutive construction and operation of the Three Gorges Project and a number of large and medium-sized water conservancy and hydropower projects and on the premise of ensuring the flood control safety of the river basin, measures should be taken to rationally allocate the Yangtze River flood resources in time and space through scientific regulation, in order to deal with water demands of different parts in different seasons and realize the optimal allocation of water resources in the Yangtze River Basin. With the eco-social development, flood resources play an increasingly important role in human life and production, and the concept for guiding flood control and drought relief has also changed in practice. As long as it is used scientifically and rationally, flood can become an advantageous resource for the benefit of mankind.

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References Changjiang Water Resources Commission. (1990). Brief Report on Plan of Integrated Development of the Yangtze River Basin [R]. Changjiang Water Resources Commission. (2010). Yangtze River Rehabilitation, Development and Protection for 60 years [M]. Wuhan: Changjiang Press. Changjiang Water Resources Commission. (2012). Master Plan of the Yangtze River Basin (2012– 2030) [Z]. Feng, F. (2009). Research on identification and quantitative evaluation of river flood resources utilization benefits [R]. Dalian University of Technology Jijun, Xu, Jin, Chen, & Siping, Huang. (2009). Discussion on the approaches of flood resource utilization in the Poyang Lake [J]. Journal of Hydraulic Engineering, 40(4), 474–480. Li, W. (2007). Division of river flood resources structure and research on flood resources utilization [D]. Journal of Dalian University of Technology. Wang, H., & Yin, J. (2004). Review of research on flood resources utilization risk management [J]. Water Resources Development Research, 4(5): 1–5. Wang, Z., Xie, Z., Liao, S., et al. (2010). Development and application on flood resource utilization technology [M]. Beijing: Tsinghua University. Xu, J., Wu, D., & Huo, J. (2008). Preliminary discussion on approaches and measures of flood utilization in the Yangtze River Basin [J]. Yangtze River, 39(15): 1–4, 17. Zheng, S. (2004). Harnessing and development of Yangtze River in the 21st Century and sustainable development in its valley [J]. Journal of China Three Gorges University (Natural Sciences), 26(2), 97–103. Zheng, S. (2009). Some considerations of optimal scheduling and flood resources utilization of Three Gorges Project [J]. Engineering Journal of Wuhan University (Engineering Sciences), 42(5): 545–549, 564.

Chapter 2

Overall Situation of Yangtze River Basin

2.1 General Situation of the Basin The Yangtze River drains a total area of 1.8 million km2 , representing 18.8% of the territorial area of China, with a total mainstream length of 6300 km. The Yangtze River Basin possesses total water resources of 996 billion m3 , and its population, GDP and water resources respectively account for 32.3, 34.0 and 35.1% of each national total, standing a very important position in China’s economic and social development (Changjiang Water Resources Commission 1990). The Yangtze River Basin is located between 24°27 −35°54 N and 90°33 −122°19 E. The basin is shaped long and narrow from east to west and short from north to south. It is bounded by Mankang Mountain, Ningjing Mountain and Lancang River System in the west, Qinling Mountain in the north, Funiu Mountain, Tongbai Mountain, Dabie Mountain, Yellow River and Huaihe River in the northeast, and Nanling Mountain, Central Guizhou Plateau, Dayu Mountain, Wuyi Mountain, Tianmu Mountain, Pearl River and Fujian and Zhenjiang river systems in the south. The Yangtze River Basin stretches across the western, central and eastern parts of China, connects the interior with the coast, covers a vast area and is rich in resources. The upstream of the Yangtze River flows from the river source to the Yichang City of Hubei Province with a length of about 4504 km and a catchment area of about 1,000,000 km2 , of which the section from the Zhimenda Village to the Yibin City is called Jinsha River with a length of about 3481 km and a catchment area of about 473,200 km2 ; the midstream flows from the Yichang City to the Hukou County at the outlet of the Poyang Lake in Jiangxi Province with a length of about 955 km and a catchment area of about 680,000 km2 ; the downstream flows from the Hukou County to the estuary with a length of about 938 km and a catchment area of about 120,000 km2 . The terrain of the Yangtze River Basin is high in the west and lower in the east, with three-stepped distribution characteristics. The first step consists of the Western Sichuan Plateau of South, Transverse Mountain Area and Longnan Chuan-Dian Mountain Lands, generally with elevation of 3500−5000 m. The second step consists © Changjiang Press (Wuhan) Co., Ltd. 2021 S. Zheng et al., Flood Resources Utilization in the Yangtze River Basin, https://doi.org/10.1007/978-981-15-8108-3_2

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2 Overall Situation of Yangtze River Basin

of the Yunnan-Kweichow Plateau, Qin-Ba Mountain Area, Sichuan Basin and E-Qian Mountain Area, generally with elevation of 500−2000 m. The third step consists of the Huaiyang Hills, the plains in the middle and lower reaches of the Yangtze River and the hills in the south of the Yangtze River, generally with elevation of 500 m except for some mountain tops approaching or exceeding 1000 m. There are many types of landform in the Basin, including mountains, hills, basins, plateaus and plains. The mountains, plateaus and hills in the Basin account for approximately 84.7%, of which the high mountains and plateaus are mainly distributed in the western region, while the central region is dominated by the mountains with moderate size and height, the low mountains are mostly found in the mountain areas in Huaiyang District and the hilly areas in the south of the Yangtze River, and the hills are mainly distributed in the Central Sichuan, Southern Shaanxi, Western Hunan, Eastern Hunan, Western Jiangxi, Eastern Jiangxi and Southern Anhui. The plains account for 13.3%, mainly constituted by the plains in the middle and lower reaches of the Yangtze River, the Feidong Plain and the Nanyang Basin, of which the Hanzhong Plain and Chengdu Plain are high plains with elevation above 400 m. Rivers and lakes account for 4%. There are many lakes in the Basin, with a total area of about 22,000 km2 , which are mainly distributed on both sides in the middle and lower reaches of the Mainstream Yangtze. Among them, the Poyang Lake is the largest one with an area of 3,965 km2 , which controls the inflow of five tributaries, namely, Gan River, Fu River, Xin River, Rao River, and Xiu River; the Dongting Lake is the second largest one with an area of 2740 km2 , which accepts the water from four tributaries, namely, Xiang River, Zi River, Yuan River and Li River; the Taihu Lake ranks third with an area of 2460 km2 , while the others cover area less than 1000 km2 . These lakes play an important role in regulating floods in the middle and lower reaches of the Yangtze River. Apart from the Qinghai-Tibet Plateau in the west, most areas of the Yangtze River Basin belong to the subtropical monsoon climate zone, with a mild and humid climate and abundant rainfall. The Basin is extremely rich in water resources. In addition to meeting the water supply needs of the Basin, it is also responsible for optimizing the allocation of water resources in China through the south-to-north water diversion. However, due to the influence of monsoon climate, the rainfall is unevenly distributed both in time and space and does not adapt to the growing season of crops in the Yangtze River Basin. Droughts and floods occur from time to time. Within the Yangtze River Basin, the middle and lower reaches is one of the regions hit most seriously by the flood disasters, and the Sichuan Basin in the upper reaches also suffer from prominent problems on flood disasters. The Yangtze River is the most developed inland water system in China, connecting the eastern, central and western regions, as well as the north and south of the Yangtze River. The navigable mileage on both mainstream and tributaries aggregates to approximately 71,000 km, accounting for 56% of the national inland navigable total mileage, of which the Level III waterway with length of 3,920 km and Level IV waterway with length of 3,130 km respectively occupy 45.4% and 46.8% of the nation’s total.

2.1 General Situation of the Basin

21

In 2007, the Yangtze River System carried 128.2 million passengers with a turnover volume of 3.86 billion passengers km; completed 1.85 billion tons of freight volume with tonnage mileage of 2816.8 billion tons km. In particular, owing to the construction and impoundment of the Three Gorges Reservoir, the waterway from Yichang City to Chongqing City has been completely improved and the transportation capacity has been greatly enhanced. The one-way annual passage capacity of the shiplock of the Three Gorges Project will exceed 50 million tons. The Yangtze River is our national “golden waterway” with huge shipping capacity. If the shipping is fully developed on the Yangtze River main line, its shipping capacity will reach more than 3 billion tons, which is roughly 10 times the transportation capacity of the Beijing-Guangzhou railway.

2.1.1 Planning on River Systems in Mainstream and Tributaries and Key Reservoirs There are many tributaries of the Yangtze River, totaling more than 7,000, among which 437 ones drain an area of more than 1000 km2 ; 49 ones drain an area of more than 10,000 km2 ; 8 ones drain an area of more than 80,000 km2 , namely, the Yalong River, the Minjiang River, the Jialing River, the Hanjiang River, the Wujiang River, the Yuanshui River, the Xiangjiang Rive rand the Ganjiang River while the first four of these rivers have a drainage area of over 100,000 km2 . There are 18 tributaries with a length of more than 500 km, among which 6 ones are with a length of more than 1000 km i.e. the Yalong River, the Dadu River, the Jialing River, the Wujiang River, the Yuanjiang River and the Hanjiang River ranking the longest with a length of 1,577 km. There are 90 tributaries with an average annual flow of more than 100 m3 /s, among which 8 one exceed 1500 m3 /s i.e. the Yalong River, the Minjiang River, the Jialing River, the Wujiang River, the Xiangjiang River, the Yuanshui River, the Ganjiang River and the Hanjiang River. These tributaries distributing densely on both north and south sides of the Yangtze River and Mainstream Yangtze constitute a huge Yangtze River System. The characteristics indicators of the main rivers in the Yangtze River Basin are showed in Table 2.1. The River System of the Yangtze River Basin is demonstrated in Fig. 2.1. Within the Yangtze River Basin, the key reservoirs that have great influences on flood control and water resources management in the middle and lower reaches of the Yangtze River are mainly distributed in the Jinsha River on the mainstream, the section from the Yibin City to the Yichang City on the mainstream, the Yalong River, the Minjiang River, the Dadu River, the Jiangling River, the Wujiang River and the Qingjiang River (Changjiang Water Resources Commission 2012). 1.

Jinsha River The Jinsha River is the mainstream in the upper reaches of the Yangtze River, with management and development tasks of power generation, water supply and irrigation, flood control, navigation, water resources protection, water ecology

Midstream

Tributary

Mainstream

8.79

Wujiang River

Qingjiang River

Jingjiang River

16.00

Jialing River

Zhicheng to Chenglingji

460

2.04

Chishui River

1.67

68

702

Tuojiang River 2.87

Midstream Yangtze

1155

9.08

Dadu River

Yichang to Hukou

735

Minjiang River 13.58

428

360

955

1037

1120

307

1.48

1571

1033

Hengjiang River

50

3481

4504

River length (km)

12.84

Chuanjiang River

Yibin to Yichang

47.32

100

Catchment area of the river (104 km2 )

Yalong River

Jinsha River

Zhimenda to Yibin

Tributary

Upstream Yangtze

River head to Yichang

Upstream

Mainstream

River

Basin

1430

2124

2300

1588

2829

4175

3560

2080

3870

5142

5370

Natural drop (m)

133.0

505.0

663.0

97.4

124.0

495.0

882.0

93.3

596.0

1450.0

4510.0

Mean annual runoff (108 m3 )

Table 2.1 Table of characteristic values of river systems in mainstream and major tributaries of the Yangtze River

421

1600

2100

309

393

1570

2790

296

1890

4600

14100

Mean annual flow (m3 /s)

1450

1150

934

1000

1010

963

1090

1040

848

720

1100

Mean annual rainfall (mm)

675

728

681

708

633

858

796

874

974

(continued)

1000

296

Mean annual evaporation (mm)

22 2 Overall Situation of Yangtze River Basin

Downstream

Basin

Tributary

Mainstream

Table 2.1 (continued)

Hukou to estuary

Poyang Lake System

Dongting Lake System

Catchment area of the river (104 km2 )

1.85

Yuan River Li River

1.03 0.72

Shuiyang River Qingyi Riuver

12

1.47

Xiu River Downstream Yangtze

1.59 1.54

Rao River

309

254

938

419

299

361

340

Xin river

819

1.65

Fu River

388

1022

713

844

1577

River length (km)

Ganjiang River 8.28

16.22

2.81 8.92

Zi River

9.47

Xiangjiang River

26.28

Hanjiang River 15.5

River

305

750

581

937

620

1462

972

756

1962

Natural drop (m)

123.0

153.0

184.0

147.0

687.0

146.0

641.0

230.0

656.0

490.0

Mean annual runoff (108 m3 )

390

485

583

466

2180

463

2030

729

2080

1550

Mean annual flow (m3 /s)

1660

1850

1850

1730

1580

1550

1360

1500

1480

904

Mean annual rainfall (mm)

857

818

891

983

941

657

701

682

783

791

(continued)

Mean annual evaporation (mm)

2.1 General Situation of the Basin 23

Basin

Table 2.1 (continued)

0.14 1.35 0.80

Zhang River Chaohu Lake Chu River

Catchment area of the river (104 km2 )

River

269

54.5

95

River length (km)

Natural drop (m)

Mean annual runoff (108 m3 )

Mean annual flow (m3 /s)

Mean annual rainfall (mm)

Mean annual evaporation (mm)

24 2 Overall Situation of Yangtze River Basin

2.1 General Situation of the Basin

25

Fig. 2.1 Aerial view of Ertan hydropower station

2.

and environment protection, water and soil conservation, mountain torrents prevention and control, tourism, etc., among which power generation, water supply and irrigation and flood control stand as the main tasks. According to the MasterPlan Report of Jinsha River Mainstream, it is preliminarily drawn up that the upper section of the Jinsha River (from the Zhimengda Village to the Shigu Town) shall adopt the 8-cascade development plan, and the middle and lower sections of the Jinsha River (from the Shigu Town to the Yibin City) shall be developed in 13 cascades, including the Hutiaoxia Section Cascade, Liyuan, Ahai, Jin’anqiao, Longkaikou, Ludila, Guanyinyan, Jinsha, Yinjiang, Wudongde, Xiluodu, Xiangjiaba. River Section from Yibin to Yichang on Mainstream Yangtze The river section of the Mainstream Yangtze from the Yibin City to the Yichang City is commonly known as the Chuanjiang River, with main development tasks of flood control, power generation and navigation, in combination with the development of aquaculture and tourism, and creating conditions for the south-to-north water diversion. According to the MasterPlan of the Yangtze River Basin (2012−2030), the Chuanjiang Section is planned in 3-cascades scheme including Xiaonanhai, Three Gorges and Gezhouba. Along with the implementation of the experimental impoundment operation with a water level of 175 m since 2008, the Three Gorges Project has begun to bring into full play the huge comprehensive utilization benefits of flood control, power generation and navigation.

26

3.

4.

5.

6.

2 Overall Situation of Yangtze River Basin

Yalong River The Yalong River is a typical canyon river with abundant water volume, concentrated fall and abundant water resources. It mainly focuses on power generation, and control the flood in this section at the same time in order to share the flood control task of the Mainstream Yangtze. Besides that, its upper river sections also share the water diversion task along the western route of the South-to-North Water Transfer Project, with due consideration to industrial and agricultural water use. On the basis of the hydropower planning on Mainstream Yalong River, the Mainstream Yalong River will be developed in 23 cascades, among which Lianghekou, Jinping Cascade-I and Ertan possess relatively large capability on runoff regulation. After the completion of the these three reservoirs, it is supposed to realize complete annual regulation through cascade reservoirs and increase the firm output and power generation of cascade reservoirs in the downstream of the Jinsha River and in the Mainstream Yangtze, with a significant benefit on power generation. Meanwhile, some flood control capacity can be reserved to share the flood control task of the middle and lower reaches of the Yangtze River. Minjiang River (Including Dadu River) The Mainstream Minjiang is abundant in water and energy resources. The upstream takes its main responsibility for power generation, which tries its utmost to meet the requirements of irrigation, flood control, urban and industrial water use in the middle and lower sections; the midstream focuses on irrigation and implements river channel regulation in combination with flood control and industrial water use; the downstream gives priority to irrigation, in consideration of comprehensive utilization requirements of navigation, power generation and so on. According to the relevant planning, the Mainstream Minjiang shall be developed in 26-cascades, with the Zipingpu Reservoir as its main key reservoir. The Tributary Dadu undertakes its main development task of power generation takes into account of shipping and irrigation and shares the flood control task of the middle and lower reaches of the Yangtze River, while its upper river section also shares the water diversion task of the western route of the Southto-North Water Transfer Project. The Mainstream Dadu adopts the 37-cascades development plan, with the Shuangjiangkou Reservoir and Pubugou Reservoir as its main key reservoirs. Jialing River The Mainstream Jialing takes on such development tasks as irrigation, flood control, navigation, power generation and water and soil conservation and other comprehensive utilization. The Mainstream Jialing is planned in 28-cascades development scheme, with the Tingzikou Reservoir and Caojie Reservoir as its main key reservoirs. Wujiang River The Mainstream Wujiang mainly focuses on power generation, followed by navigation and in consideration of flood control and others. The Mainstream

2.1 General Situation of the Basin

27

Wujiang is planned to develop in 11 cascades, with main key projects including Hongjiadu, Dongfeng, Wujiangdu, Goupitan, Silin, Shatuo, Pengshui and so on. At present, such hydropower stations have been built as Puding, Yinzidu, Hongjiadu, Dongfeng, Wujiangdu and Suofengying, Goupitan, Pengshui, Silin, Shatuo and Yinpan. 7. Qingjiang River The Mainstream Qingjiang assumes its main development responsibilities of power generation, flood control and shipping. The Mainstream Qingjiang is planned to develop in 13-cascades, with completed major key projects as Shuibuya, Geheyan and Gaoba. 8. Dongting Lake River System The River System of the Dongting Lake takes on its main development tasks of flood control and waterlogging treatment, water supply and irrigation, water resources conservation, power generation, navigation, water and soil conservation, schistosomiasis control in water conservancy, etc. 9. Hanjiang River The Hanjiang River undertakes its main tasks of flood control and waterlogging treatment, water supply and irrigation, inter-basin water diversion, water resources and water ecological environment protection, power generation, shipping, water and soil conservation, schistosomiasis control in water conservancy, etc. It has initially formed an embankments-based flood control pattern, retaining and impounding flood by Shiquan, Ankang and Danjiangkou Reservoirs, diverting and storing flood by Dujiatai and midstream polders, in coordination with water diversion by Dongjing River and river regulation. The first phase of the Middle Route of the South-to-North Water Transfer Project officially started operation in December 2014, with a mean annual water transferring volume of 9.5 billion m3 . The Mainstream Hanjiang will be developed in 15-cascades hydropower planning, with continuous constructions such 7 cascades as Huangjinxia, Xunyang, Baihe, Gushan, Xinji, Yakou and Nianpanshan. 10. Poyang Lake River System The River System of the Poyang Lake mainly focus on such development tasks as flood control and waterlogging treatment, water supply and irrigation, power generation, navigation, water and soil conservation and water resources conservation. After the completion of the Three Gorges Reservoir, a flood control system has been preliminarily formedin the middle and lower reaches of the Yangtze River with the Three Gorges Reservoir as its backbone. The basic situation of the key reservoirs on the mainstream and the tributaries is shown in Table 2.2. According to the overall requirements in the MasterPlan of the Yangtze River Basin (2012−2030), in addition to undertaking the flood control task of the river (section) where they are located, the reservoirs on the mainstream and tributaries of the upper reaches should also cooperate with the Three Gorges Reservoir to play a role in the middle and lower reaches of the Yangtze River. It is planned

28

2 Overall Situation of Yangtze River Basin

Table 2.2 Overview of the key reservoirs on the mainstream and tributaries of the Yangtze River Basin River

Midstream Jinsha River

No. Reservoir

Normal Flood water control level level (m) (m)

Dead water level (m)

Regulated storage capacity (108 m3 )

Storage capacity for flood control (108 m3 )

1

Liyuan

1618

1605

0.83

1.73

2

Ahai

1504

1493.3

1492

2.38

2.15

3

Jin’anqiao

1418

1410

1398

3.46

1.58

4

Longkaikou

1298

1289

1290

1.13

1.26

5

Ludila

1223

1212

1216

3.76

5.64

Downstream Jinsha River

6

Xiluodu

600

560

540

64.6

46.5

7

Xiangjiaba

380

370

370

9.03

9.03

Yalong River

8

Jinping Cascade I

1880

1859

1800

49.1

16

Ertan

1200

1190

1155

33.7

9

Minjiang 10 River(including 11 Dadu River)

9

Zipingpu

877

850

817

7.74

1.67

Pubugou

850

841

790

38.82

15

Jialing 12 River(including 13 Bailong River) 14

Baozhusi

588

583

558

13.4

2.8

Tingzikou

458

447

438

17.5

10.6

Caojie

203

200

178

4.87

2

Wujiang River

15

Hongjiadu

1140

1076

33.61

1.55

16

Dongfeng

970

936

4.91

0

17

Wujiangdu

760

720

13.6

0

18

Goupitan

630

628.12

590

29.52

4

19

Silin

440

435

431

3.17

1.84

20

Shatuo

365

357

353.5 2.87

2.09

21

Pengshui

293

287

278

5.18

2.32

22

Three Gorges

175

145

155

165

221.5

Qingjiang River 23

Shuibuya

400

391.8

350

23.83

5

24

Geheyan

200

192.2

160

19.75

5

25

Ankang

330

325

305

16.77

9.8

26

Danjiangkou 170

Yangtze River

Hanjiang River

160−163.5 150

163.6−190.5 110−81.2

to reserve the flood control capacity for the mainstream and tributary reservoirs in the upper reaches of the Yangtze River by stages. The upstream reservoirs cooperate with the Three Gorges to retain the flood by impounding flood water base flow, and come into play by impounding water gradually according to the flood situation. In July, a total of 34−36 billion m3 of flood control capacity is

2.1 General Situation of the Basin

29

reserved for mainstream and tributary reservoirs in the upstream of the Yangtze River, with 22.39 billion m3 for the cascade reservoirs in Shigu-Yibin Section of the Mainstream Jinsha, 5−6 billion m3 for the Yalong River and 3−4 billion m3 for the Minjiang River. In alignment with the flood control plan for the Yangtze River Basin, these flood control reservoirs gradually impound water in a limited way from August, which can not only make the middle and lower reaches of the Yangtze River have large flood control capacity for flood control in the upper reaches of the Yangtze River during the frequent flood disaster season, but also realize a better combination of flood control and water storage, providing enough water source for the dry season. At the same time, the flood control capacity is also reserved for the reservoirs with flood control function in the midstream and downstream of the Yangtze River. In general, the basic situation of important reservoirs in the Yangtze River Basin undertaking flood control task is shown in Table 2.3. Table 2.3 Important reservoirs for flood control in Master Plan of the Yangtze River Basin River system

Reservoir

Local river

Yangtze River

Hutiaoxia River Section

Jinsha River

Controlled drainage area (104 km2 )

Maximum storage capacity for flood control reserved in the plan (108 m3 )

Storage Note capacity for flood control Total amount (108 m3 )

58.6

452.81

Liyuan

22.0

Ahai

23.5

1.73 2.15

Jin’anqiao

23.74

1.58

Longkaikou

23.97

1.26

Ludila

24.73

5.64

Guanyinyan

25.65

5.42

Wudongde

40.61

24.4

Baihetan

43.03

75.0

Xiluodu

45.44

46.5

Xiangjiaba

45.88

9.03

Three Gorges

Mainstream 100

New construction in plan Under construction

New construction in plan Under construction

221.5 (continued)

30

2 Overall Situation of Yangtze River Basin

Table 2.3 (continued) River system

Reservoir

Yalong River

Upstream cascade Lianghekou

Local river

Wujiang River

5.0

50

20

9.67

16

Built-up

11.64 Mainstream 1.35

Zipingpu Xia’erga

Storage Note capacity for flood control Total amount (108 m3 )

Mainstream 5.96

Ertan Shilipu

Maximum storage capacity for flood control reserved in the plan (108 m3 )

New construction in plan

Jinping Cascade I Minjiang River

Controlled drainage area (104 km2 )

Dadu River

9 1.0

Built-up 30

New construction in plan

2.27

1.67

Built-up New construction in plan

1.55

8.7

Shuangjiangkou

3.93

6.63

Pubugou

7.27

11

Under construction, current flood storage capacity of 730 million m3 , planned to be expanded to 1.1 billion m3

1.03

1.0

New construction in plan

Shangzhai

Chuosijia River

Goupitan

Mainstream 4.33

Silin Shatuo Pengshui

4

4.86

1.84

Mainstream 5.45

2.09

6.9

10.25

Built-up Under construction

2.32 (continued)

2.1 General Situation of the Basin

31

Table 2.3 (continued) River system

Reservoir

Local river

Controlled drainage area (104 km2 )

Maximum storage capacity for flood control reserved in the plan (108 m3 )

Storage Note capacity for flood control Total amount (108 m3 )

Jialing River

Baozhusi

Bailong River

2.84

2.8

21.89

Shengzhong

Xihe River

0.18

2.7

Tingzikou

Mainstream 6.26

Built-up

14.4

Under construction, storage capacity for flood control of 1.06 billion m3 below normal water level

15.61

1.99

Under construction

0.19

0.80

Shuibuya

1.09

5

Geheyan

1.44

5

Juzhang River

Zhanghe River

0.22

3.43

3.43

Built-up

Dongting Lake

Dongjiang River Xiangjiang Shuangpai River River

0.47

1.58

58.08

Built-up

1.03

0.58

Centian River

0.25

3.0

Caojie Qingjiang Yaojiaping River

10.8

New construction in plan Built-up

Built-up, current storage capacity for flood control of 41 million m3 , planned to be expanded to 300 million m3 (continued)

32

2 Overall Situation of Yangtze River Basin

Table 2.3 (continued) River system

Reservoir

Local river

Taoshui Zhexi

Maximum storage capacity for flood control reserved in the plan (108 m3 )

0.08

1.0

Under construction

Pre-flood season: 7.0, main flood season: 10.6−3.7, Post-flood season 3.7−1.6

Built-up

1.6

New construction in plan

Zishui River 2.26

Jintangchong

Fengtan

Controlled drainage area (104 km2 )

2.8

Wuqiangxi

Yuanjiang River

Jiangya

Lishui River 0.37

Storage Note capacity for flood control Total amount (108 m3 )

1.75

2.8

Built-up

8.38

17.05

Built-up, current storage capacity for flood control of 1.36 billion m3 , planned to be expanded to 1.705 billion m3

7.4

Built-up

Zaoshi

0.3

7.8

Under construction

Yichongqiao

0.58

2.5

Liangshuikou

0.1

1.32

Xinjie

0.06

0.85

New construction in plan (continued)

2.1 General Situation of the Basin

33

Table 2.3 (continued) River system

Reservoir

Local river

Controlled drainage area (104 km2 )

Maximum storage capacity for flood control reserved in the plan (108 m3 )

Storage Note capacity for flood control Total amount (108 m3 )

Lushui

Lushui

0.34

2.29

2.29

Built-up

Hanjiang

Ankang

3.86

3.6

124.01

Built-up

Danjiangkou

9.52

110

Built-up

Yahekou

Baihe River 0.3

5.21

Built-up

Pankou

Duhe River

0.9

4

Sanliping

Nanhe River

0.2

1.2

Under construction

Fushui

Fushui

0.25

8.53

8.53

Built-up

Poyang Lake

Zhelin

Xiushui River

0.93

15.72

41.17

Built-up, current storage capacity for flood control of 437 million m3 , planned to be expanded to 1.572 billion m3

Liukou

Xinjiang River

1.04

3.2

New construction in plan

Wan’an

Ganjiang River

3.69

10.19

Built-up, current storage capacity for flood control of 533 million m3 , planned to be expanded to 1.019 billion m3

6.29

6

New construction in plan

0.71

3.1

Built-up

Xiajiang River

Liaofang

Fuhe River

(continued)

34

2 Overall Situation of Yangtze River Basin

Table 2.3 (continued) River system

Reservoir

Local river

Wuxikou

Raohe River 0.29

2.96

Wanhe River

Hualiangting

Changhe River

0.19

8.44

8.44

Built-up

Laizi Lake

Xiaxushan

Dasha River 0.04

0.44

0.44

New construction in plan

Qingyi River

Chencun

Qingyi River

0.28

9.55

9.55

Built-up

Shuiyang River

Gangkouwan

Xijin River

0.11

4.11

4.11

Built-up

Chaohu Lake

Longhekou

Hangbu River

0.11

3.03

4.17

Dafangying

Nanfei River

Built-up Built-up Built-up

1.88

Built-up

Dongpu Chuhe River

Controlled drainage area (104 km2 )

Maximum storage capacity for flood control reserved in the plan (108 m3 )

0.02

0.48

0.02

0.66

Huanglishu

Xianghe River

0.03

1.05

Shaheji

Qingliu River

0.03

0.83

Total amount in the whole basin (108 m3 )

Storage Note capacity for flood control Total amount (108 m3 ) New construction in plan

841.85

2.1.2 Characteristic Analysis of Rainstorm Flood 2.1.2.1

Rainstorm Characteristic

The rainy season of the Yangtze River Basin is concentrated from May to October, and rainstorm generally occurs earlier in the middle and lower reaches than in the upper reaches, and earlier in the south than in the north. The general law of rainfall distribution is as follows: the rain belt in May mainly distributed in Hunan and Jiangxi River Systems; from mid-June to mid-July, the rain belt lingers on both sides of the Mainstream Yangtze, the midstream and downstream are in the plum rain season, the upstream rain belt is distributed in east-west direction and the rainfall in the south of the Yangtze River is greater than in the north; from mid-July to early August, the rain belt move to Sichuan and the Hanjiang River Basin, except for a slight decrease in precipitation over the Wujiang River, the precipitation increases in other areas, and

2.1 General Situation of the Basin

35

the rain belt is mainly featured in northeast and southwest zonal distribution in the west of Sichuan; in mid-to-late August, the rain belt move northward to the Yellow River Basin and Huaihe River Basin, and the Yangtze River Basin is sometimes prone to summer drought; in September, the rain belt return southward to the upstream and midstream of the Yangtze River, and the precipitation center in the upstream of the Yangtze River move from the west of Sichuan to the east, resulting in much less rainfall in Western Sichuan (Changjiang Water Resources Commission 1997). Heavy rains begin to occur in the south bank of the middle and lower reaches of the Yangtze River in February and March, while in April in the Hanjiang River, Jialing River, Minjiang River, Tuo River and Wujiang River; in parts of the Yalong River and Dadu River, heavy rains occur only in July and August. The end time of the rainstorm is opposite to the beginning time, which is delayed from northwest to southeast of the Basin. Most of the upper reaches of the Yangtze River and the north bank of the middle reaches of the Yangtze River end in September and October, only the Three Gorges Area and the upper reaches of the Jialing River end in late October, and some years end in early November, for example, the Three Gorges Area and the Wujiang River Basin suffered from heavy rains in early November 1996. The south bank of the middle and lower reaches of the Yangtze River mostly end in November. The inter-annual variation of annual rainstorm days in the Yangtze River Basin is much larger than that of annual precipitation, especially in the upper reaches of the Yangtze River. Except for the areas of about 350,000 km2 in the upstream of Batang on the Jinsha River and in the upper reaches of the Yalong River and Dadu River, where have almost no rainstorms due to high terrain and water vapor conditions, the distribution of rainstorms cover the other vast areas. The distribution trend is as follows: in the upstream, the rainstorm decreases from the northwest margin of the Sichuan Basin to the central basin and western plateau, while decreases from the southeast to northwest in the midstream and downstream. More rainstorms occur in the mountains than in the valleys and plains, and more in the windward slope than in the leeward slope.

2.1.2.2

Flood Characteristic

Floods in the Yangtze River Basin are mainly caused by heavy rains, and there are few floods in the upper reaches above Zhimengda. The Jinsha River stretches from Zhimengda to Yibin, where flood is caused by heavy rains and melting of ice and snow. In the upstream section from Yibin to Yichang, there are rainstorm areas in Western Sichuan and Daba Mountain with frequent rainstorms. The Minjiang River and Jialingj River respectively flow through these two rainstorm areas with large flood peak flow. The trend of rainstorm is mostly consistent with the direction of flood flow, which makes the floods in the Minjiang River, Tuojiang River and Jialing River encounter each other, prone to form flood with high peak and large amount in Cuntan and Yichang stations. The flood of the river section between Yichang andLuoshan River mainly came from the flood in the upper reaches of the Yangtze River. As for the Qingjiang River and the Dongting Lake System, there are rainstorm

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2 Overall Situation of Yangtze River Basin

areas in northwest Hunan and southwest Hubei with occurrence of rainstorms mainly in June−July and May−June, correspondingly, the floods in the Qingjiang River and the Dongting Lake System also occur in June−July. The flood of river section between Luoshan and Hankou mainly come from the upstream of Luoshan, as well as the flood in Hanjiang River serving as an important part. The big flood in Hankou is caused by the multiple rainstorm processes in the middle and upper reaches of the Yangtze River. There are two rainstorm areas in Dabieshan Mountain and Jiangxi Province within the watershed downstream Hankou. In Jiangxi Rainstorm Area with frequent rainstorms, large rainfall and wide range, the occurrence time of rainstorms is early, correspondingly, the occurrence time of flood in the Poyang Lake System is also relatively early. The reach downstream Datong is the tidal reach, which is influenced by both upstream inflow and tide, while the high water level in the lower reaches of Jiangyin is greatly affected by tide, and the sharp change of water level in the Yangtze estuary is mainly affected by the storm surge caused by typhoon. The mean annual maximum flood peak exceeded 10000 m3 /s in the tributaries of the Minjiang River, Jialing River, Wujiang River, Xiangjiang River, Hanjiang River and Ganjiang River. In the composition of the maximum 30-day flood volume at Yichang station, the import water from the Jinsha River accounts for roughly 30%, the two river systems of the Jialing River and Minjiang River accounts for roughly 38%, the Wujiang River accounts for 10%, and the others accounts for 22%. In the composition of the 60-day maximum flood volume at Datong station, the import water from Yichang accounts for 51%, the Dongting Lake System and Poyang Lake System account for 21% and 15% respectively, the Hanjiang River accounts for 5%, and the reach between Yichang and Datong accounts for about 8%. The Yangtze River Basin drains a large area, and the flood of the Yangtze River can be divided into two types i.e. basin-wide flood and regional flood according to the distribution and movement of rainstorm areas. Regional flood occurs in some tributaries or some reach of the mainstream, with high flood peak, large flood volume in short time and short duration of flood process, such as the “81.7” great flood in the Upstream Yangtze, the “35.7” great flood in the Midstream Yangtze, the “69.7” great flood in the Qingjiang River, the “83.10” autumn great flood in the Hanjiang River, the “91.7” great flood in the Chuhe River and the floods in the Midstream and Downstream Yangtze in 1995 and 1996. The basin-wide flood is formed by a series of large-scale rainstorms. The upper and lower reaches of the Yangtze River are deluged at the same time, and the main and tributary floods encounter each other, resulting in big flood or extraordinarily flood with high peak, long duration and disastrous consequence in the middle and lower reaches of the Yangtze River, such as the floods in 1931, 1954, 1998 and so on.

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2.2 Flood Control Planning 2.2.1 Flood and Flood Disasters Flood disasters in the Yangtze River Basin are basically caused by storm floods with a wide distribution. Except for the alpine and rainless regions of the Qinghai-Tibet Plateau above 3000 m (above sea level), floods are likely to occur wherever there are heavy rains and floods. According to the distribution and coverage of rainstorm areas, the Yangtze River floods are usually divided into two types: one is the regional flood, such as the floods in 1860, 1870, 1935, 1981 and 1991; another one is the basin-wide flood, such as the floods in 1931, 1954, 1998, as well as in 1788, 1849. No matter what kind of flood it is, there will pose a great threat to the middle and lower reaches. In addition, sudden floods in mountainous areas caused by torrential rains in short duration and small scale often result in mountain torrents, mudslides, landslides and other disasters, which seriously threaten the safety of people’s lives and property. There are disasters induced by glacial lake outbursts in high altitude areas in the upstream. The Yangtze River estuary delta is most threatened by the storm surge (Changjiang Water Resources Commission 2012). The riparian banks along the middle and lower reaches of the Yangtze River play important role in China’s economic and social development, but the land elevation of the plain areas on both banks is generally several to dozens of meters below the water level in flood season. Considering the frequent and serious flood disasters, once the embankments burst, it will lead to inundation in long time and huge losses. For example, the floods in 1931 and 1935 respectively brought about casualties of 145,000 and 142,000 people in the Midstream and Downstream Yangtze. The flood in 1954 was the most severe one in the Yangtze River Basin over the past century, inundating 3.17 million hm2 of farmlands and causing casualties of more than 30,000 people, making the Beijing-Guangzhou railway out of service for 100 days. The flood in 1998 affected 5271 towns and villages in 334 counties (cities and districts) in the Midstream and Downstream Yangtze, 2,128,500 houses collapsed and 1,562 people killed. In the upper reaches of the Yangtze River and the hilly regions in its tributaries, the flood usually has the characteristics of high peak, rapid arrival, short duration and scattered disaster areas. Local regional big floods sometimes also cause local destructive disasters, and mountain torrent disasters often lead to a large number of casualties. In July 1981, the Minjiang River, Tuojiang River and Jialing River in the hinterlands of Sichuan Province and Chongqing City were hit by extraordinarily serious flood disasters, flooding 874,000 hm2 of farmlands, affecting 15.84 million people and killing 888. On July 17, 2007, the Chongqing City suffered from local torrential rain and floods in a short period of time. Rivers in mountainous areas surged, affecting an area of 233,333 hm2 and killing 56 people. On August 8, 2010, a massive mudslide hit Zhouqu County, Gannan Tibetan Autonomous Prefecture in Gansu Province, killing 1,501 people and leaving 264 missing.

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2 Overall Situation of Yangtze River Basin

2.2.2 Flood Control Situation After decades of flood control construction, an integrated system of flood control has basically been put in place in the middle and lower reaches of the Yangtze River, with the embankments as the basic component, the Three Gorges Reservoir as the backbone project, integration of such engineering measures as reservoirs in mainstream and tributaries, flood retention and detention basins, and river regulation works as complementation, together with non-engineering measures, which has significantly improved the flood control capacity. Up to now, the total length of the Yangtze River embankments have aggregated to 34,000 km, of which more than 3,900 km along the middle and lower mainstream have basically reached the standard-compliance figure as set in the Executive Report on Plan for Comprehensive Utilization of the Yangtze River Basin approved by the State Council in 1990. In order to ensure the flood control safety of key areas, 40 flood storage and detention areas with excess flood capacity of about 59 billion m3 have been arranged for the mainstream of the middle and lower reaches of the Yangtze River, of which 5 ones namely Jingjiang Flood Diversion Area, Dujiatai Flood Storage and Detention Area, Embankment Lake Polder, Linan Dyked Marsh and Xiguan Dyked Marsh have been included in the control by construction of flood-diversion sluices. The major reservoirs as Three Gorges, Danjiangkou, Jiangya and Zaoshi have been built with flood control as the primary task, other reservoirs with relatively large flood control capacity include Zipingpu, Wuqiangxi, Zhelin, Zhexi, Geheyan, Shuibuya, Wan’an, Zhanghe and so on. River regulation has been carried out in an all-round way, and the river regime in the middle and lower reaches is basically stable. More than 7,000 flood forecast stations have been built in the Basin, and a hydrologic data collecting system has been preliminarily established. Other non-engineering measures as communication early warning systems, various management laws and regulations are also being gradually improved. With the operation of the Three Gorges Project, the capacity has been greatly upgraded in flood control for the middle and lower reaches of the Yangtze River, especially that the flood control situation of the Jingjiang River has been fundamentally improved. The capacities in flood control for the main reaches of the mainstream and tributaries of the Yangtze River have roughly been up to the following standards: the Jingjiang River Basin can defend floods with return period of 10 years with the help of embankments; with the operation of the Three Gorges Reservoir, in case of floods with return period of 100 years or below, the water level of Shashi City can be regulated to be no more than 44.5 m without operation of the Jingjiang flood storage and detention area; in case of the one-in-1000-year flood in 1000 years or the severe flood equivalent to that in the year of 1870, the discharge flow of Zhicheng City can be regulated to be no more than 80,000 m3 /s with the operation of the Three Gorges Project, and the water level of Shashi City can be controlled to be lower than 45.0 m in combination with operation of the Jingjiang flood storage and detention area to ensure the flood running through Jingjiang Reach in security level. The Chenglingji Reach can defend floods with return period of 10−20 years with

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the help of embankments, considering the operation of flood storage and detention area in this region, it is able to defend the flood equivalent to that in the year of 1954; in the event of recurrence of floods equivalent to those in the years of 1931, 1935, 1954, with regulation of the Three Gorges Project, the flood diversion volume and the inundated area would be substantially reduced, and there is no need to carry out flood diversion in general years (except for the estuary of each tributary). The Wuhan Reach can defend floods with return period of 20−30 years with the help of embankments, considering the operation of flood storage and detention area in its upper reach and local region, it is able to defend the flood equivalent to that in the year of 1954 (its maximum 30-day flood volume is approximately equivalent to that of flood with return year of 200 years); as the upstream flood can be controlled by the Three Gorges Project, the flood threat to Wuhan City can be avoided in case of the outburst of the Jingjiang embankments; because of the operation of the Three Gorges Reservoir and the enhancement of flood control ability in the vicinity of Chenglingji, the flood control flexibility of the mainstream Yangtze River has been improved, and the water level of Wuhan City can be prevented from getting out of control when cooperating with the operation of Danjiangkou Reservoir and flood storage and detention area near Wuhan. The Hukou Reach can defend floods with return period of 20 years relying on embankments, in consideration of the operation of flood storage and detention area in its upper reach and local region, and it is able to defend the flood equivalent to that in the year of 1954. Although the flood control ability of the Yangtze River has been greatly improved, its flood control is still faced with the following main problems and challenges: first, the contradiction is still outstanding between the security discharge of river channel in the middle and lower reaches of the Yangtze River and the flood in the Yangtze River with high peak and large volume, despite of a flood control capacity of 22.15 billion m3 occupied by the Three Gorges Project, the flood control capacity is still insufficient in view of the huge excess flood in the middle and lower reaches of the Yangtze River. In case of the big flood equivalent to that in the year of 1954, there still exists excess flood of 40 billion m3 to be well arranged. However, most of the flood storage and detention areas are weak in the security construction, once they are come into service, the losses will be huge; second, the flood control capacity of the tributaries and lakes in the upper, middle and lower reaches of the Yangtze River is relatively low, the prevention and control of mountain torrent disasters is in its infancy and the non-engineering measures of flood control lag behind; third, the long-term adjustment resulting from scouring and silting in extensive reaches of the middle and downstream Yangtze River has brought great impact on the river regime and riverlake relationship in the middle and downstream Yangtze River, to this end, it still need to strengthen observations and study corresponding countermeasures; forth, the frequency of extreme hydro-climatic events and the intensity of rainstorms in some parts of the Yangtze River Basin have increased due to the impact of global warming in recent years, leading to severe floods in some areas; fifth, the river basin is experiencing rapid development of economic society and urbanization along with concentration of population and wealth, once the flood occurs, the losses will be increasing.

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2 Overall Situation of Yangtze River Basin

2.2.3 Principles, Standards and Objectives of Flood Control 1. Governance Principles It is supposed to carry out flood risk management, combine engineering measures with non-engineering measures, and deal with the relationship between people and flood. The middle and lower reaches of the Yangtze river basin are the focus of flood control, and we should follow the governance policy of “overall consideration of flood discharge and storage with preference to discharge” and the principle of “win-win for both rivers and lakes, balancing between both banks of the river, and coordinating among upstream, midstream and downstream”. The upstream area should adhere to the combination of dredging and reservoir regulation, river regulation and slope treatment. The combination of engineering and non-engineering measures should be taken to prevent storm surge in Yangtze River estuary. The work on prevention and control of mountain torrent and glacial lake disasters should stick to the policies of mass prediction and disaster prevention, combination of prevention and control with preference to prevention, and combination of non-engineering and engineering measures with preference to the former one. 2. Flood Control Standards The middle and lower reaches of the Yangtze River are important commodity grain bases in China. Along the river, there are large and medium-sized cities such as Wuhan, Nanjing and Shanghai and a number of important industrial enterprises. Beijing-Guangzhou, Beijing-Shanghai, Beijing-Kowloon railways and Beijing-Zhuhai and Shanghai-Chengdu expressways pass through this area, making the Midstream and Downstream Yangtze one of the most developed areas in China. According to the political and economic status of the plain areas in the middle and lower reaches of the Yangtze River, as well as the flood and flood situations in the 20th century and before, the overall flood control standard of the middle and lower reaches of the Yangtze River is capable to prevent the biggest flood since the founding of the People’s Republic of China, namely the 1954 flood, that is to say, in case of the flood equivalent to that of 1954, measures should be taken to ensure the flood control safety for the key protected areas. On the grounds of the importance and the severity of flood disasters of Jingjiang Reach, its flood control standard is set to be capable to defend the flood in recurrence of 100 years, that is to say, with the goal of defensing the peak flow in recurrence of 100 years in Zhicheng Town, reliable measures should be taken to ensure that the embankments on both sides of the Mainstream Jingjiang do not collapse naturally in the event of encountering flood equivalent to that in 1870, so as to prevent devastating disasters. For the embankments along tidal reaches, flood or surge control standard can be determined in accordance to relevant codes considering the influence of tide and typhoon. For the south bank of the Yangtze estuary (including Baoshan District and Pudong New Area), as well as the embankments of Changxing Island and the urbanized area of Chongming Island in the Shanghai City, the construction should reach the standard-compliance feature which is

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capable to defend the high tide level with return period of 200 years in case of hurricane. For the embankments in Hengsha Island, the other areas of Chongming Island and the mainstream of the Yangtze estuary in Jiangsu Province, the construction should reach the standard-compliance feature which is capable to defend the high tide level with return period of 100 years in case of storm. The overall flood control standard for the mainstream and major tributaries of the Upstream Yangtze should be up to defending the flood with return period of 20 years. At the same time, there should be reliable prevention countermeasures for great floods that have occurred and caused serious disasters in the basin, so as to ensure flood control safety in key areas. For the prefecture-level cities in the basin, the flood control standard should be up to defend the flood in recurrence of 50 years, while the county-level towns in recurrence of 20 years. As for the major prefecture-level and county-level cities and important industrial towns, their flood control standards can be raised appropriately. For the 13 riparian cities at or above the prefectural level located at the middle and lower reaches of the Mainstream Yangtze i.e. Yueyang, Wuhan, Huanggang, Ezhou, Huangshi, Jiujiang, Anqing, Chizhou, Tongling, Wuhu, Maanshan, Nanjing, Zhenjiang, the flood control standards should be up to fight against the flood equivalent to that of 1954 on the whole; for Yichang City and Jingzhou City, the flood control standards should be up to defend the flood in recurrence of 100 years; for Nantong City, the embankment construction should reach the standard-compliance feature which is capable to defend the high tide level with return period of 100 years in case of storm; for the Mainstream Huangpu flowing through the urban areas in Shanghai City, the flood control standard should be up to defend the flood with return period of 1000 years. For the main urban areas of Chongqing City (except for Beibei District), the construction of flood control and embankment works should reach the standard-compliance feature which is capable to defend the flood in recurrence of 50 years, and it should achieve the capability to fight against flood in recurrence of 100 years by non-engineering measures; for the main urban areas of Yibin City and Luzhou City, the flood control standards should be up to defend flood in recurrence of 50 years, and their flood control capacity will be gradually improved through the engineering construction of flood control embankments and in combination with the construction of upstream reservoirs. For the main urban areas of 6 provincial capital cities of Chengdu, Kunming, Guiyang, Changsha, Nanchang and Hefei along the tributaries, the flood control standards should be up to defend the flood with return periods of 100−200 years, 50−100 years for the major reaches in the central city beyond the main urban city, and 20−50 years for the common reaches. 3. Flood Control Planning Objectives The integrated flood control system of the Yangtze River should be improved considering the effects of the Three Gorges and other key water conservancy and hydropower projects on flood control of the Yangtze River. By 2020, the flood control capacity of Jingjiang will reach the standard-compliance feature to defend the flood in recurrence of 100 years, and no devastating disasters will occur in the event of flood equivalent to that of 1870. Chenglingji and its lower

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2 Overall Situation of Yangtze River Basin

reaches of the mainstream can defend the flood equivalent of that in 1954, and the important flood storage and detention areas can be taken advantage of in time in accordance to the flood volume. Major cities, key polders in Dongting Lake and Poyang Lake areas, upper reaches of the mainstream, major tributaries basically reach the planned flood control standards. A system is preliminarily put in place for mountain torrent disaster prevention and mitigation, which combines non-engineering measures focusing on monitoring, communication and early warning in key prevention and control areas with engineering measures. By 2030, the flood control capacity will be further improved by further perfecting the integrated flood control system and reducing the operation probability and application range of flood storage and detention areas. In case of frequent flood and big flood, economic development and social security can be guaranteed; in case of basin-wide flood or extraordinary flood, economic and social life will not be greatly disturbed, the ecological environment will not be seriously damaged, and disaster losses will be obviously reduced, which will not have significant impact on the process of sustainable development. A system is basically put in place for mountain torrent disaster prevention and mitigation.

2.2.4 Flood Control Areas Division Flood control areas refer to the areas which are likely to be flooded. The flood control areas within the Yangtze River Basin cover an area of 153,800 km2 , of which 13,400 km2 lie in the upper reaches of the Yangtze River (mainly including Yunnan Province, Sichuan Province, Guizhou Province and Chongqing City) and 144,400 km2 lie in the middle and lower reaches of the Yangtze River (Changjiang Water Resources Commission 2012). Flood control areas in the middle and lower reaches of the Yangtze River can be divided into three categories: flood protection areas, flood storage and detention areas and flood flowing areas. Flood protection areas mean the areas where flood control safety should be guaranteed in case of standard floods, mainly including the embankment protection areas in the mainstream of middle and lower reaches, key polders in Doting Lake and Poyang Lake areas, main tributary towns and estuarial parts. The flood control protection areas in the middle and lower reaches of the Yangtze River totally cover an area of 118,500 km2 , with a population of roughly 97.1 million and a cultivated land area of approximately 4.5 million hm2 , accounting for 84.4%, 90.0% and 84.8% of each one’s total, respectively. Flood storage and detention areas refer to the low-lying areas and lakes that temporarily retain flood water outside the downstream face of river banks including flood diversion mouth. Flood storage and detention areas are mainly distributed in the mainstream of the middle and lower reaches of the Yangtze river and some tributaries, with a total area of 13,500 km2 , with a population of about 7.4 million

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and a cultivated area of about 552,000 hm2 . There are 40 flood storage and detention areas in the mainstream of the middle and lower reaches of the Yangtze River, with a total area of 12,000 km2 , a population of about 6.86 million, cultivated land of about 474,667 hm2 , and an effective flood storage volume of about 59 billion m3 . Flood flowing areas signify the floodplain polders between the embankments on both sides of the Mainstream Yangtze River and its main tributaries, and the common polders within the Dongting Lake and Poyang Lake areas, which are delugedin case of big flood, except the flood control protection areas and flood storage and detention areas. The flood flowing areas in the middle and lower reaches of the Yangtze River cover a total area of 8,400 km2 , with cultivated land of roughly 256,000 hm2 and a population of roughly 3.34 million.

2.2.5 Flood Control System and Layout 1. Mainstream of the Middle and Lower Reaches For the middle and lower reaches of the Yangtze River, efforts are made to reasonably heighten and reinforce the embankments, carry out watercourses regulation, arrange and construct flood storage and detention areas in plains, build the reservoirs on mainstream and tributaries combining with the purpose of benefit promotion, so as to form an integrated flood control system, with the river embankments as the basic component, the Three Gorges Project as the backbone project, integration of such measures as other reservoirs in mainstream and tributaries, flood storage and detention basins, and river regulation works as complementation, together with other non-engineering and engineering measures, such as removing river-encroaching polders to give room back to floods, returning reclaimed lands to lakes, and water and soil conservation. The flood control water levels of the four main control stations in the middle and lower reaches of the Yangtze River are respectively 45.00 m in Shashi District, 34.40 m in Chenglingji, 29.73 m in Wuhan City and 22.50 m in Hukou County. In terms of the flood control water level in Chenglingji, this planning carries out the special topics from the aspects of the influence of changes in river-lake relation on the flood control situation near Chenglingji, the effect of the Three Gorges Project and the reservoir construction on the mainstream and tributaries in the upper reaches on the flood control near Chenglingji. It is believed that after the completion the key reservoirs located in the mainstream and tributaries of the upper reaches, the impact on the erosion and deposition and water level in the river channels of the middle and lower reaches has yet to be tested by the actual flood, and the general trend should be that the water level of areas in the vicinity of Chenglingji will decrease under the same flood conditions. Therefore, the flood control water level should remain 34.40 m for Chenglingji in the near future. From now on, further studies should be conducted on the flood control water level of Chenglingji based on the adjustment of river and

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lake erosion and silt in the middle and lower reaches, changes in the relationship between rivers and lakes, and the actual situation of upstream reservoir construction, so as toverify whether the flood control water level needs to be adjusted. In prior to the completion of the Three Gorges Project, in case of the flood equivalent to that in 1954, there existed excessive flood of 49.2 billion m3 to be properly arranged for the middle and lower reaches of the Yangtze River, of which 5.4 billion m3 for Jingjiang Reach, 32 billion m3 for areas around Chenglingji (flood division of 16 billion m3 for both Honghu Lake and Dongting Lake areas), 6.8 billion m3 for areas in vicinity of Wuhan City, and 5 billion m3 for areas near Hukou County (2.5 billion m3 for both Poyang Lake area and Huayang Lake). After the completion of the Three Gorges Project, according to the flood control regulation method initially designed for the Three Gorges Project, the total flood diversion volume is 336−39.8 billion m3 for the middle and lower reaches of the Yangtze river in the event of flood equivalent to that in 1954. In recent years, the river-lake relation has undergone some changes. According to various conditions under current situation and on the basis of the preliminary design of the Three Gorges Project, research has been made on the flood control scheduling scheme during the test impoundment period for the Three Gorges Project, and it is deemed that considering the flood control scheduling mode by compensation for Chenglingji and in case of flood equivalent to that in 1954, the total flood diversion amount will be of roughly 40 billion m3 in the middle and lower reaches of the Yangtze River, of which 30 billion m3 is contributed by the areas in vicinity of Chenglingji. Giving further consideration of the successive completion of the mainstream and tributary reservoirs in the Upstream Yangtze, such as Xiluodu, Xiangjiaba, Wudongde, Baihetan, Tingzikou, the total amount of flood diversion will be significantly reduced in the middle and lower reaches of the Yangtze River. However, due to the different degree of river scouring, the discharge capacity of the upper and lower reaches of the Yangtze River will increase by different degrees, and the amount of excessive flood may be adjusted by regions. In the future, measures should be taken on the basis of strengthening prototype observation and scientific research. 2. Mainstream of the Upper Reaches and Major Tributaries Key reservoirs with flood control purpose are put in place on the mainstream of the upper reaches and major tributaries in combination with benefit promotion. They are supposed to undertake the flood control task of the middle and lower reaches of the Yangtze River as far as possible while undertaking the flood control task of the region. Measures are taken to reinforce the reservoirs at risk by stages and in groups, regulate watercourses in mainstream and tributaries, build embankments and revetments for important towns and areas that need to be protected, strengthen small and medium-sized rivers regulation and mountain torrents prevention and control, enhance soil and water conservation, and intensify hydrological monitoring and forecasting system and the construction of other non-engineering measures for flood control.

2.3 Overview of Yangtze River Basin Management

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2.3 Overview of Yangtze River Basin Management The Yangtze River development and protection have ushered in a new era since the founding of the People’s Republic of China. There are four stages in the process of river governance over the past more than 60 years: the first one is the stage of gradual recovery from 1949 to 1957; the second one is the stage of proceeding with turns and twists from 1958 to 1977; the third one is the stage of reform and development from 1978 to 1997; the fourth one is the stage of in-depth advance from 1998 to present. The details are as follows (Changjiang Water Resources Commission 1997, 2012). During the first stage from 1949 to 1957, in the beginning period after the founding of the People’s Republic of China, in view of the severe flood control situation at that time and the dilapidated Yangtze River embankments, great efforts were made to block up the historical breached embankments and renovate and reinforce the embankments. At the same time, works were carried out on basic data collection and collation, analysis and research, as well as flood control and drainage planning in the middle and lower reaches of the Yangtze River. Provinces within the river basin vigorously restored and renovated embankments, so that the elevation of embankments in the mainstream of the middle and lower reaches of the Yangtze River reached the local standard of 1 m above the maximum flood level in 1949 or 1931; vigorously build more flood storage and reclamation works, mainly including Datong Lake Flood Storage and Reclamation Project in Dongting Lake, Flood Diversion Project on Jingjiang Reach, Dujiatai Flood Diversion Project on Han River; restored and renovated small-sized water conservancy facilities and constructed small irrigation and drainage projects with particular emphasis, with over 3 million small water conservancy facilities, such as small reservoirs in hilly areas, put in place in Sichuan Province, Hubei Province and Hunan Province; constructed large reservoirs focusing on irrigation, such as Shimen Reservoir in Southern Shaanxi, Hewuwan Reservoir in Hubei, as well as hydroelectric power generation projects, such as Shangyoujiang Hydroelectric Power Station in Jiangxi, Shizitan Hydroelectric Power Station on Longxi River in Sichuan. During the second stage from 1958 to 1977, water conservancy construction on Yangtze River centered in river governance, irrigation and water conservancy construction in consideration of water resources utilization. Influenced by the “great leap forward” boom and “cultural revolution”, water conservancy construction on Yangtze River went through a tortuous journey, but still made important progress, especially the master plans of the Yangtze River Basin and some key engineering construction had advanced significantly. More than 40,000 large, medium and small reservoirs had been built in the Yangtze River Basin, with 106 large reservoirs under construction. Among them, Danjiangkou Multipurpose Hydraulic Project commenced in September 1958, following by successive completions of a number of large reservoir with storage capacity of more than 1 billion m3 , such as Yahekou, Bailianhe, Zhexi, Zhanghe, Fushui, Chencun, Zhelin, Huanglongtan, Hualiangting, etc. Large-scale pivotal hydro works with comprehensive benefits of flood control, irrigation and power generation set about construction during this period, such as

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2 Overall Situation of Yangtze River Basin

Fengtan, Wujiangdu, Dongjiang, Shengzhong, Ankang, Wan’an and so on. During this period, efforts were also made to build flood control and drainage projects and irrigation projects on a large scale, execute intervention to bank collapse and embankment and bank defensive works, and implement the Cut-off Works on the lower Jingjiang Reach. During the third stage from 1978 to 1997, the work of river governance was carried out in an all-round way, the investment was further increased, and the benefits of the existing projects were consolidated and improved. Positive progress was made in the construction of a number of key projects, including the Three Gorges Project, Gezhouba Project, and South-to-North water Transfer Project. At the end of 1988, the Gezhouba Project was completed, and in December 1994, the main part construction of the Three Gorges Project was officially commenced. A series of large hydro works had been completed or started in succession in the Yangtze river basin, including Dongjiang, Wan’an, Geheyan, Wuqiangxi, Ertan; the construction had been strengthened for the embankments and flood control and drainage works on the Yangtze River, along with the reinforcement of the key reservoirs; Dongting Lake and Poyang Lake had seen further treatment, key embankments had been improved, and estuarial floodway had experienced comprehensive rehabilitation; small watershed management of key water and soil loss areas had been strengthened in the upper reaches of the Yangtze River; regulation had been executed for the key reaches of the middle and lower reaches of the Yangtze River. These mark that the Yangtze River management and development and water resources integrated utilization ushered into a new historical period. During the fourth stage from 1998 to present, after the successful fight against the extraordinary flood in the Yangtze River Basin in 1998, measures has been taken to make major strategic arrangements for post-disaster reconstruction, rivers and lakes regulation, and water conservancy projects construction, with great increase of the investment in water conservancy. In alignment with the fact that the main tasks of the flood-control-centered “three stages of river governance” have been basically put into practice, the river governance guidance has been put forward as “maintaining health of the Yangtze River and promoting harmony between human and water”, and in accordance with the principle of “promoting development under protection and implementing protection during development”, it calls for giving overall consideration of protection and development, coordinating ecology and development, accelerating the “Four Systems” construction of flood control and disaster mitigation, comprehensive water resources utilization, water resources and water ecological environment protection, and integrated river basin management, so as to gradually realize the “Four Strategic Goals” of safeguarding flood control security, rational development and utilization, maintaining good ecological activities, stabilizing river regime and riverbed.

2.4 Profile of Major Key Reservoirs

47

2.4 Profile of Major Key Reservoirs 2.4.1 Ertan Hydropower Station Ertan Hydropower Station is a comprehensive hydropower project mainly for power generation. It is located in the downstream of the Yalong River and 33 km from the confluence of the Yalong River and the Jinsha River. In line with the flood control planning, the flood control tasks of Ertan Reservoir are as follows: 1. ensuring its own flood control security; 2. undertaking flood control task of the middle and lower reaches of the Yangtze River in cooperation with the Three Gorges Reservoir and other reservoirs; 3. easing the pressure of flood control in Sichuan-Chongqing Reach in cooperation with Jinsha reservoir group. The operation principle of the reservoir is prepared as follows: from June 1 to July 31, the water level of the reservoir is controlled to be no more than 1,190.0 m, and the operating water level of the reservoir is generally 1,195.0 m in August. When there is a great flood in the middle and lower reaches of the Yangtze River, the reservoir is supposed to impound inflow from the Yalong River, so as to decrease the flood volume flowing into the Three Gorges; if there is a flood occurring in the SichuanChongqing Reach, the reservoir is taken advantage of toretain the flood, cut and stagger peak timely to reduce the flood control pressure in the Sichuan-Chongqing reach; once the water level reaches 1200.0 m, the security operation is implemented to safeguard the pivotal project. In mid-September, the water level of the reservoir can be regulated to the normal water level of 1200 m. In non-flood season, the reservoir is operated according to the demand on benefit promotion.

2.4.2 Xiluodu Hydropower Station Xiluodu Hydropower Station serves as the backbone electricity source of “Westto-East Electricity Transmission Project” in China and an important project in the Yangtze River flood control system. Xiluodu Hydropower Station mainly focuses on power generation, taking into account of flood control, sediment retaining and improving downstream navigation conditions. On the one hand, the project development aims to meet the electricity demand for economic development in east China, central China and south China, so as to realize the sustainable development of national economy; on the other hand, the construction of Xiluodu Reservoir is the main engineering measure to solve the flood control problem in Sichuan and Chongqing, which is able to significantly improve the flood control standard for the riparian cities in Sichuan and Chongqing areas, such as Yibin, Luzhou, Chongqing and so on. Meanwhile, the flood volume flowing directly into the Three Gorges Reservoir can be reduced by making use of Xiluodu Reservoir and its downstream Xiangjiaba Reservoir, which enhances the flood control role of the Three Gorges Reservoir on the

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2 Overall Situation of Yangtze River Basin

Fig. 2.2 Aerial view of Xiluodu hydropower station

middle and lower reaches of the Yangtze River, and relieves the flood control pressure of the middle and lower reaches of the Yangtze River to some extent (Fig. 2.2). The operation principle proposed in the design stage is as follows: during the flood season (June to early September), the water level of the reservoir shall be operated at no higher than the restricted water level in flood season of 560 m; impoundment begins in mid-September, and the daily rise speed of the reservoir water level should be no less than 2 m, and the output of the power station should controlled to be no less than the guaranteed output, the reservoir water level is up to 600 m at the end of September; the water supply period extends from late December to the end of May, with the reservoir water level dropping to the dead water level of 540 m.

2.4.3 Xiangjiaba Hydropower Station Xiangjiaba Hydropower Station is the most downstream cascade power station of the Mainstream Jinsha cascade hydropower stations. The distances between the dam site and the upstream Xiluodu river channel and downstream Yibin City are respectively 156.6 km and 33 km. The development task of Xiangjiaba Hydropower Station is mainly for generating electricity, improving navigation conditions at the same time, combining flood control with sediment retaining, and taking into account of irrigation, as well as playing reverse regulation role on its upstream Xiluodu Hydropower Station (Fig. 2.3).

2.4 Profile of Major Key Reservoirs

49

Fig. 2.3 Aerial view of Xiangjiaba hydropower station

The operation principle proposed in the design stage is: during the flood season from mid-June to early September, the reservoir is operated at the restricted water level in flood season of 370 m, and starts impounding from mid-September to reach the normal water level of 380 m at the end of September; from October to December, the water level is generally maintained at or near the normal water level; the water supply period is from late December to early June, part of the reservoir capacity is restored in April and May when the inflow is relatively abundant, and the water level of the reservoir drops to 370 m by the end of early June.

2.4.4 Tingzikou Hydraulic Complex Tingzikou Hydraulic Complex is located in the area of Cangxi County, Guangyuan City, Sichuan Province, about 15 km away from its downstream Cangxi County. It is the only controlled project in the development of the Mainstream Jialing, which serves as a comprehensive project mainly focusing on flood control, power generation, urban and rural water supply and irrigation, taking shipping into account, and playing an important part in sediment retaining and deposition reduction (Fig. 2.4). The dam site of Tingzikou Hydraulic Complex controls an area of 61,089 km2 in the river basin, accounting for 81.4% of the basin area in the upstream of Nanchong City, 78.5% of the basin area in the upstream of Wusheng Hydrological Station and 39% of the basin area in the upstream of Beibei District, which controls the main source of the flood of the Midstream Jialingj and takes flood control capacity improvement for the Mainstream and Downstream Jialing as one of its engineering

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2 Overall Situation of Yangtze River Basin

Fig. 2.4 Aerial view of Tingzikou hydraulic complex

tasks. The Jialingji River is one of the main sources of flood in the upper reaches of the Yangtze River and is frequently encountered with flood in the main reaches of the Yangtze River. Tingzikou Hydraulic Complex not only undertakes the flood control task of the middle and lower reaches of Jialing River, but also plays an important role in flood control of the middle and lower reaches of Yangtze River by cooperating with the Three Gorges Reservoir.

2.4.5 Three Gorges Hydraulic Complex The Three Gorges Project is the last cascade of the Mainstream Yangtze development and the key control project in the flood control system of the Yangtze River Basin. After the completion of the Three Gorges project, it is capable to effectively regulate the flood in the Upstream Yangtze, improve the flood control capability of the Midstream Yangtze, especially bring fundamental changes to the flood control situation of the Jingjiang Reach: the Jingjiang Reach can be up to defend the flood with return period of 100 years, in case of flood in recurrence of 100−1000 years, including the most serious flood equivalent to that in 1870, the discharge flow of Zhicheng County can be controlled to be no more than 80,000 m3 /s, with the cooperation of Jingjiang Flood Diversion Area and other flood storage and detention areas, devastating disaster of embankment outburst can be prevented in Jingjiang Reach; the flood diversion probability and volume of the flood storage and detention areas

2.4 Profile of Major Key Reservoirs

51

around Chenglingji can also be greatly reduced, which can delay the silting in the Dongting Lake and maintain its flood regulation function for a long time (Fig. 2.5). The following expounds the flood control operation method of the Three Gorges Reservoir. During the demonstration and preliminary design stage of the Three Gorges Project, a lot of researches had been carried out on the flood control regulation mode of the Three Gorges reservoir, which adopted the compensation operation method in the Jingjiang Reach as the designed operation method for the Three Gorges Reservoir, and proposed the idea of implementing compensation operation for the Chenglingji Reach; in the study of the optimal regulation scheme for the Three Gorges Reservoir, in addition to the review of the operation method executed by the Three gorges on the Jingjiang Reach which is drawn up during the preliminary design stage, there is also a combination with the recent River-Lake relation change, so as to make further researches on storage capacity allocation, compensation flow, control water level and other factors for Chenglingji. The scheme was submitted by the Ministry of Water Resources in October 2009, and has been implemented by approval of the State Council. 1. Compensation Operation Method Executed by the Three Gorges Reservoir on Jingjiang Reach According to the flood control plan of the Three Gorges Project, the Three Gorges Project will regulate the flood of the Yangtze River to make the Jingjiang Reach meet standard-compliance feature to defend the flood in recurrence of 100 years, and in case of one-in-1000-year flood or flood equivalent to that in 1870, the discharge flow of Zhicheng County is controlled to be no more than 80,000 m3 /s, the flood is ensured to run through Jingjiang Reach in security level with operation of the flood storage and detention areas, so as to avoid devastating disasters. Based on the flood control target, the Three Gorges Reservoir implements hierarchical compensation operation mode for the Jingjiang Reach.

Fig. 2.5 Aerial view of three Gorges reservoir hydraulic complex

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2 Overall Situation of Yangtze River Basin

1. In case of flood in recurrence of less than 100 years, the compensation operation is executed by controlling the water level of Shashi City at 44.5 m and the compensation flow of Zhicheng County at 56700 m3 /s, correspondingly. 2. In case of flood in recurrence of 100−1000 years, after the reservoir reaching the flood storage level equivalent to that of a one-in-100-year flood, the compensation operation is executed by controlling and compensating the maximum flow of Zhicheng County to be no more than 80000 m3 /s, and controlling the water level of Shashi City at 45 m with combination of adopting flood diversion measures on Jingjiang Reach. 3. In case of flood in recurrence of more than 1000 years or reservoir water level up to 175 m, it should adhere to the principle of ensuring dam security, and the reservoir should discharge in accordance with its discharge capacity without considering the flood control requirements of the downstream, 2. Operation Method Executed by the Three Gorges Reservoir in consideration of Compensating Chenglingji In order to ensure the flood control safety of Jingjiang Reach in case of extraordinary flood, the compensation operation for Chenglingji is executed based on the large amount of water from downstream to improve the flood control effect of the Three Gorges Project on general flood and reduce the flood diversion volume in Chenglingji as far as possible. The optimal operation scheme of the Three Gorges Reservoir carries out in-depth study on compensation operation method for Chenglingji flood control on the basis of the preliminary design of the Three Gorges Project. The flood control reservoir capacity of the Three Gorges Project is divided into three parts from bottom to top through research: the first part reserves a storage capacity of 5.65 billion m3 for flood control compensation for both Chenglingji and Jingjiang Reach; the second part the reserves a storage capacity of 12.58 billion m3 merely for flood control compensation for Jingjiang Reach; the third part reserves a storage capacity of 3.92 billion m3 for extraordinary flood regulation on Jingjiang Reach. The reservoir water level corresponding to the full flood control storage capacity of the first part is called “compensation controlled water level for flood control in Chenglingji” (the corresponding water level is 155 m), and the reservoir water level corresponding to the sum of the flood control storage capacities of the first part and the second part is called “compensation controlled water level for flood control on Jingjiang Reach” (the corresponding water level is 171 m), as shown in Fig. 2.6. Specific flood control operation methods are as follows: (1) When the water level of the Three Gorges Reservoir is lower than the “compensation controlled water level for flood control in Chenglingji”, the daily discharge of the reservoir is: the smaller one of the allowable discharges between compensated Jingjiang Reach on that day and compensated Chenglingji on the third day (generally,

2.4 Profile of Major Key Reservoirs

53

Fig. 2.6 Distribution schematic diagram of storage capacity for flood control of Three Gorges Reservoir

the allowable discharge of compensated Chenglingji is always less than that of compensated Jingjiang Reach) q1 = 56700—interval flow from Yichang to Zhicheng on that day q2 = 60000—interval flow from Yichang to Zhicheng on the third day actual discharge flow q = min(q1, q2) But if q < 25000 m3 /s then q is 25000 m3 /s. (2) When the water level of the Three Gorges Reservoir is higher than the “compensation controlled water level for flood control in Chenglingji”, and lower than the “compensation controlled water level for flood control on Jingjiang Reach”, the daily discharge of the reservoir on that day is equal to the allowable discharge of the compensated Jingjiang Reach on that day, that is: q = 56700—interval flow from Yichang to Zhicheng on that day. (3) When the water level of the Three Gorges Reservoir is higher than the “compensation controlled water level for flood control on Jingjiang Reach”, the daily discharge of the reservoir on that day is q = 80000—interval flow from Yichang to Zhicheng on that day, while not greater than the actual daily inflow on that day (flood storage and diversion measures is taken at this time, and the water level of Shashi is controlled to be no more than 45.0 m) (4) When the water level of the Three Gorges Reservoir exceeds 175 m, the main purpose is to ensure dam security, and measures are taken to properly regulate the discharge of the flood.

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2 Overall Situation of Yangtze River Basin

2.5 Major Cities and Towns Along the Mainstream and Tributaries of Upstream Yangtze According to the Flood control Standards (GB 50201), the overall flood control standards for the mainstream and main tributaries of Upstream Yangtze should be up to defend the flood in recurrence of 20 years, and there should also be reliable countermeasures against great floods that have already occurred in the basin and caused serious disasters to ensure the flood control safety in key areas. As for the tributaries in the upper reaches like Minjiang River, Jialing River, Wujiang River and other rivers, the protection objects are mainly riparian cities and towns. It is planned that the flood control standards for prefecture-level cities should be up to defend once-in-50-year flood, and for county-level towns should be up to defend once-in-20-year flood. As for the Chongqing City located in the mainstream of the upper reaches, its flood control standard should be up to defend the flood with return period of more than 100 years according to the size of non-agricultural population and loss in flooding area and combining with the importance of the city’s position. As for the Yibin City and Luzhou City, the flood control standard should be up to defending once-in-50-year flood.

2.5.1 Sichuan-Chongqing Reach 1. Yibin City In the Yibin City, there have constructed embankments capable to defend oncein-50-year flood in the Central District, and once-in-20-year flood in Boxi District and Caiba District. In the future, with the completion and operation of the upstream cascade reservoirs, such as Xiluodu Reservoir and Xiangjiaba Reservoir on the Jinsha River, the flood control standard will be further improved for the city. 2. Luzhou City In the Luzhou City, there have constructed embankments capable to defend oncein-50-year flood in the Gaoba Industrial Park on the north bank of the Yangtze River and in the Central City on the right bank of the Tuojiang River, and embankments capable to defend once-in-20-year flood on the left bank of the Tuojiang River and on the south bank of the Yangtze River. With the construction of upstream reservoirs, its flood control standard will be further improved. 3. Chongqing City The Chongqing City lies in the upper reaches of the Yangtze River, and the main urban zone is located at the confluence of the Yangtze River and the Jialing River and is divided into three districts by the Two Rivers, namely Nan’an District, Yuzhong District, Jiangbei District. According to the Flood Control Standard and considering the specific terrain of the urban area at the same time, the flood control standard of the main urban zone of Chongqing is formulated to defend

2.5 Major Cities and Towns Along the Mainstream and Tributaries …

55

once-in-100-year flood, the flood control standard of the major reaches in the central city area except for the above main urban zone is formulated to defend once-in-50-year flood, and general reaches to defend once-in-20-year flood.

2.5.2 Middle and Lower Reaches of Mainstream Jialing 1. Nanchong City The Jialing River and its right bank tributary Huanzi River divide the Nanchong City into three sections, namely Shunqing District, Jialing District and Gaoping District. Through comprehensive analysis, the flood control standards of the above three districts are determined to defend flood in recurrence of 50 years. 2. Langzhong City The urban population of status quo and the 2010 development planning of the urban area in the Langzhong City are both less than 200,000 people. However, this city is state-list famous historical and cultural city named by the State Council, with national historical relics and ancient architectural complex of Ming and Qing Dynasties in its urban area, which is prone to be damaged and difficult to recover in case of inundation. Referring to relevant provisions in the Flood Control Standard, the Langzhong City is classified at IV level and its flood control standard is up to preventing the once-in-50-year flood. 3. Five Counties including Cangxi, Nanbu, Yilong, Peng’an and Wusheng According to the Flood Control Standard, the five counties of CangXi, Nanbu Yilong, Peng’an and Wusheng are classified at IV level and the flood control standard is up to prevent the once-in-20-year flood.

2.5.3 Middle and Lower Reaches of Mainstream Wujiang 1. Sinan County The Sinan County lies in the middle and lower reaches of the Wujiang River and the northeast of Guizhou Province. According to Flood Control Standard, Sinan County should reach the standard-compliance feature to defend once-in-20-year flood. 2. Yanhe County The Yanhe County lies in the northeast corner of Guizhou Province, which is a typical mountain county built against the mountains. Due to the influence of topography, the elevation of the foundation plane of buildings along the river is relatively low, which makes the riparian buildings important flood control objects within the downstream of Shatuo Hydropower Station and the reservoir area of Pengshui Hydropower Station. Stipulated in the Flood Control Standard, the flood control standard for the Yanhe County should be up to defending the once-in-20-year flood.

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2 Overall Situation of Yangtze River Basin

3. Pengshui County The Pengshui County is located in the southeast of the Chongqing City with a flood control standard to defend once-in-20-year flood based on the Flood Control Planning for Pengshui County. 4. Wulong County The Wulong County is located on the southeastern edge of the Chongqing City with a flood control standard to defend once-in-20-year flood based on the Flood Control Planning for Wulong County of Chongqing City.

2.6 Key Reaches and Areas of Midstream and Downstream Yangtze 2.6.1 Jingjiang Reach The Jingjiang Reach is faced with the most serious flood control situation of the Yangtze River, and has always been the most important focus on flood control of the Yangtze River and even the whole country. Since the formation of the Jingjiang Embankment in the Ming Dynasty, the regions within the Embankment have gradually become a vast and fertile plain inNorth Jingjiang. The south bank of the Jingjiang River lies in the Dongting Lake Plain, in case of breach of embankment or forced flood diversion, it will also lead to extremely serious flood disaster. The flood control station of Jingjiang Reach is Shashi hydrological station, where the guaranteed water level is 45.0 m. At present, the embankments on both sides of the Jingjiang Section have reached the designed standard. The crest elevation of the Jingjiang embankment on the north bank is 2.0 m above the designed water level (45.0 m for the water level of Shashi District, corresponding to the water surface line of 34.4 m for Chenglingji); the elevation of the Songzi embankment and Mainstream Yangtze embankment on the south bank of Jingjiang Reach is 1.5 m above the designed water level (the lower section of the Mainstream Yangtze embankment on the south bank of Jingjiang Reach belongs to the polder embankment of the Jingjiang flood storage and detention basin, with a flood storage level of 42.0 m, which is 2.0 m above the designed level). According to the current rating curve of Shashi hydrological station, when the water level in Shashi District is 45.0 m and the corresponding water level in Chenglingji is 34.4 m, the discharge in Shashi is roughly 53,000 m3 /s, slightly larger than the 50,000 m3 /s adopted in the Executive Report, and the flow in Zhicheng County is roughly 60,600 m3 /s. When the water level in Shashi County is 44.5 m and the corresponding water level in Chenglingji is 33.95 m, the discharge of Shashi District is about 50,000 m3 /s, and the flow in Zhicheng County is about 57,300 m3 /s, slightly larger than the controlled flow of 56,700 m3 /s in Zhicheng County at the demonstration stage of the Three Gorges Project.

2.6 Key Reaches and Areas of Midstream and Downstream Yangtze

57

If the controlled water level in Shashi District is raised to 45.0 m, the flood diversion volume in vicinity of Chenglingji will be increased, which is not conducive to flood control in Chenglingji Reach. In order to give full play to the flood control function of the Three Gorges Project, the controlled water level of Shashi District is still adopted 44.5 m during the operation of the Three Gorges Project.

2.6.2 Chenglingji Area Chenglingji area is affected by the floods from both the Mainstream Yangtze and the Four Tributaries of the Dongting Lake, which is the most flood-prone area in the middle and lower reaches of the Yangtze River, with a lot of flood storage and detention basins around the area, once they go into operation, it will cause larger losses. Therefore, the goal of flood control in Chenglingji is to minimize the flood diversion volume in this area. The flood control station of Chenglingji Reach is Chenglingji hydrological station, and the guaranteed water level of Chenglingji (Lianhuatang) hydrological station is 34.4 m. Since this station is a stage gauging station, the discharge corresponding to a certain water level is based on the correlation between Chenglingji and Luoshan, and then figured out by the stage-discharge relation of Luoshan. Therefore, the stagedischarge relation of Luoshan actually reflects the discharge capacity of Chenglingji section. The influencing factors of the stage-discharge relation of Luoshan are very complicated. According to the research results of stage-discharge relation of Luoshan and compared with the results adopted in the Executive Report, the current rating curve reflects the following characters: within the range of medium and low water level, the water level corresponding to the same flow condition slightly raises; with the gradual increase of the flow in Luoshan, the elevation value decreases. During the research on the compensation regulation of Chenglingji in the feasibility study phase of the Three Gorges Project, the water level of Chenglingji is controlled to 34.4 m, and the corresponding flow of Luoshan is adopted 60,000 m3 /s. According to the measured water level and flow data of Luoshan during the flood year from 1980 to 2002, the stage-discharge relation can be drawn with points and it can be seen that the points are distributed in strip, and when the flow of Chenglingji is 60,000 m3 /s, the water level is 32.4−34.6 m, with an average value of 33.5 m. The drop between Chenglingji (Lianhuantang) station and Luoshan station is 0.95 m, the corresponding water level of Chenglingji is 34.4 m, and Luoshanshui is 33.45 m, which have a small gap from that of 33.5 m. That is to say, when the water level of Chenglingji is 34.4 m and the corresponding flow of Luoshan is about 60,000 m3 /s, the controlled discharge of Chenglingji in this study stage still adopt the value that has been used in the demonstration stage of the Three Gorges Project. At present, the embankments on both sides of Chenglingji Reach have been up to the designed standard. In order to enhance the flexibility of the flood control in Chenglingji Reach, the crest elevation of embankments in Jianli, Honghu on the north bank(upstream of Longkou) and embankments on Mainstream Yangtze within

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2 Overall Situation of Yangtze River Basin

Yueyang City on both sides shall be increased by another 0.5 m as stipulated in the Executive Report, with an excess height of 2.0 m in crest, so that the security of embankments against flood will be obviously improved.

2.6.3 Wuhan Reach The Wuhan City is located in the east of Jianghan Plain, where the outlets of the Yangtze River and the Han River meet each other. It communicates with nine provinces internally, opens to the sea externally, links the east to west, and connects the north and south, which stands as the transportation hub by integration of water, land and air, always known as “thoroughfare of nine provinces”. Wuhan is divided into three parts of Hankou, Wuchang and Hanyang by the Yangtze River and the Han River, which has formed its own flood control system. The total length of the planned embankments aggregates to 195.77 km in the urban area of Wuhan, which are reinforced by an excess height of 2.0 m according to the corresponding water level of 29.73 m in Hankou. The flood control station of Wuhan Reach is Hankou hydrological station, where the guaranteed water level is 29.73 m. After the implementation of flood control planning, the embankment flood control standard is up to defend flood in recurrence of 20−30 years, to control bigger flood by flood diversion, and to fight against flood equivalent to that in 1954 (the maximum 30-day flood volume in Hankou equivalent to that with return period of 200 years) under the conditions of ideal operation of the planned flood storage and detention basins. Owing to the completion of the Three Gorges Project, the city’s flood control capacity is further improved with less necessity to make use of the flood storage and detention basins. In the Executive Report, considering the importance of Wuhan’s status, the controlled water level of flood diversion at Hankou station was adopted 29.5 m, and the corresponding discharge was adopted 71,600 m3 /s. Based on the analysis of the current rating curve of Hankou station, when the water level at Hankou station is 29.5 m, the corresponding discharge is approximately 73,000 m3 /s, which is slightly larger than the 71,600 m3 /s adopted in the Executive Report.

2.6.4 Hukou Reach The flood control station of Hukou Reach is Hukou hydrological station, with a guaranteed water level of 22.5 m. Up to now, the embankments on both sides of Hukou Reach have made the designed grade. The safety of embankments against flood has been greatly improved by heightening and strengthening the embankments. In the Executive Report, when the water level at Hukou station reached 22.5 m, the corresponding discharge adopted 83,500 m3 /s. According to the analysis of the current rating curve of Hukou station, when the water level at Hukou station is 22.5 m,

2.6 Key Reaches and Areas of Midstream and Downstream Yangtze

59

the corresponding discharge is about 83,000 m3 /s, which is close to the 83,500 m3 /s adopted in the Executive Report.

2.7 Overview of Flood Detention Basins in Middle and Lower Reaches According to the research on flood control plan for Midstream and Downstream Yangtze, in the event of flood equivalent to that in 1954 and before the Three Gorges Project coming into play, an excess flood of 49.2 billion m3 need to be properly arranged in the middle and lower reaches of the Yangtze River, of which 5.4 billion m3 need to be diverted in Jingjiang area, 32 billion m3 in vicinity of Chenglingji (each one of Honghu Lake and Dongting Lake retaining and storing a volume of 16 billion m3 ), 6.8 billion m3 around Wuhan, and 5 billion m3 near Hukou (each one of Poyang Lake and Huayang Lake retaining and storing a volume of 2.5 billion m3 ). To this end, 40 flood storage and detention basins, including Jingjiang area, areas in vicinity of Chenglingji, Wuhan and Hukou, have been arranged, with a total area of 12,200 km2 , a cultivated land area of 474,533 hm2 , a population of roughly 6.325 million and an effective flood storage volume of about 58.965 billion m3 . See Table 2.4 for details.

2.7.1 Jingjiang Flood Storage and Detention Areas Jingjiang flood storage and detention areas including Jingjiang flood diversion area, Yuanshi expanded flood diversion area, Renmin Polder, Huxi alternative flood storage area, with a total flood storage area of 1465.3 km2 , a cultivated land area of 474,533 hm2 , a population of 887,000 and an effective flood storage volume of 7.16 billion m3 . 1. Jingjiang Flood Diversion Area Jingjiang flood diversion area is located between Jingjiang River and Hudu River in the middle reaches of the Yangtze River, within Gong’an County, Hubei Province, with an average width of 13.6 km from east to west, a length of 68 km from north to south and an area of 921 km2 . The designed flood storage water level is 42.0 m, with an effective flood storage capacity of 5.4 billion m3 . The flood diversion area was built with the approval of the Central Government Administration Council in 1952. The main project consists of embankment of 208 km, Taipingkou flood inlet sluice (north sluice) and Hudu control sluice (south sluice). The reinforcement works of Taipingkou flood inlet sluice have been completed, and the flood inlet capacity is 7700 m3 /s corresponding to the Shashi District water level of 45.0 m (frozen Wusong elevation, all of the following are frozen

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2 Overall Situation of Yangtze River Basin

Table 2.4 Overview of flood storage and detention areas in the Yangtze River Basin No.

Flood storage and detention area

Flood storage water level (m)

Flood storage area (km2 )

Cultivated area (103 hm2 )

Population (104 )

Effective volume (108 m3 )

Total value

11894.3

474.53

632.53

589.65

1

Jingjiang Area

1465.3

60.13

88.67

71.60

1.1

Jingjiang Flood Diversion Area

921.34

32.87

58.18

54.00

1.2

Yuanshi Expanded 43.00 Flood Diversion Area

96.00

5.77

6.12

2.00

1.3

Renmin Polder

38.50

362.00

16.50

19.04

11.80

1.4

Huxi Alternative Flood Storage Area

42.00

86.00

5.01

5.34

3.80

2

Area around Chenglingji

5770.51

242.65

295.32

344.75

2.1

Dongting Lake Flood Storage and Detention Area

2973.11

159.73

165.80

163.81

Western Dongting 36.00−44.61 Lake Area

780.49

39.98

45.30

48.38

Southern Dongting Lake Area

34.83−35.41

907.40

53.67

55.20

53.09

Eastern Dongting Lake Area

34.61−36.69

1074.22

56.26

57.37

51.93

Lucheng in the south of the Yangtze

33.50

211.00

9.82

7.92

10.41

2.2

Honghu Lake 32.50 Flood Storage and Detention Area

2797.4

82.91

129.52

180.94

3

Area around Wuhan

2943.88

109.65

175.84

122.10

4

42.00

Xiliang Lake

31.00

1095.00

24.76

48.64

42.30

Dongxi Lake

29.50

444.00

14.76

29.50

20.00

Wuhu Lake

29.10

277.90

12.43

14.59

18.10

Zhangdu Lake

28.30

309.00

26.30

30.37

10.00

Baitai Lake

27.50

204.00

7.87

39.98

8.80

Dujiatai

30.00

613.98

23.53

12.75

22.90

1714.55

62.11

72.69

51.20

Area around Hukou

(continued)

2.7 Overview of Flood Detention Basins in Middle and Lower Reaches

61

Table 2.4 (continued) No.

Flood storage and detention area

4.1

Poyang Lake

4.2

Flood storage water level (m)

Flood storage area (km2 )

Cultivated area (103 hm2 )

Population (104 )

Effective volume (108 m3 )

549.55

20.48

16.68

26.20

Kangshan

22.55

312.37

10.13

6.17

15.70

Zhuhu Lake

22.54

152.49

5.33

9.39

5.60

Huanghu Lake

23.26

49.28

3.09

0.29

2.90

Fangzhouxietang Pond

22.67

35.41

1.93

0.82

2.00

Huayang River

19.20

1165

41.63

56.01

25.00

Note Western Dongting Lake Area includes: Wendihu, Liujiaoshan, Jiuyuan, Xiguan, Anli, Linan, Anchang, Anhua, Nanding, Hekang, and Nanhan; SouthernDongting Lake Area includes: Minzhu, Gongshuangcha, Chengxi, Beihu, Yihe, Quyuan; EasternDongting Lake Area includes: Jicheng’anhe, Qianlianghu, Jianshe, Jianxin, Junshan, Datong Lake Four Polder

Wusong elevation unless otherwise specified). If necessary, embankments can also be opened in Lalinzhou to increase the flood diversion flow. Jingjiang flood diversion area is an important part of Jingjiang Reach flood control system, and its main function is to retain the excess flood from upstream going beyond the security discharge of the Upstream Jingjiang. That is, when inflow from Zhicheng is diverted by Songzi and Hudu, the flood water level in Shashi tend to exceed 45.0 m and the upstream water is predicted to continue increasing, then the Jingjiang flood diversion area is put into effect with the approval of the Central Government to safeguard the flood security in Jingjiang embankment and alleviate the flood threat to Dongting Lake area and Wuhan City. 2. Yuanshi Expanded Flood Diversion Area Yuanshi expanded flood diversion area starts from Taipingkou of Jingzhou District in the east, facing south towards the Jingjiang flood diversion area located across the river (Huduhe River), reaches the Yuanli separation dike in the west, neighbors to the Yangtze River in the north, and ends to Lijiakou Village in the south, with an average width of 5.33 km from east to west, length of 17.2 km from south to north, an area of 96 km2 , designed flood storage water level of 43.0 m and effective flood storage capacity of 200 million m3 , which was reported to the State Council by the Ministry of Water Resources and Electric Power and executed with approval. The main part of the project is composed of separation dyke from Yuanshi to Jialikou, Mainstream Yangtze embankment from Yuanshi to Taipingkou and Huxi embankment from Taipingkou to Lijiakou, with a total embankment length of 52.6 km. The flood inlet gate in the flood diversion area is planned to be located on the river embankment about 500 m downstream of the northern end of the separation dike, with the designed flood diversion flow of 5000 m3 /s.

62

2 Overall Situation of Yangtze River Basin

Expanded flood diversion area is made used of when the inflow from Zhicheng on the Mainstream Yangtze is larger than 75,000−80000 m3 /s. Its main function is to make up for the flood inflow of the Jingjiang flood diversion area and to magnify the flood diversion effect by combining with the Jingjiang flood diversion area. 3. Huxi Alternative Flood Storage Area Huxi alternative flood storage area was built in 1954 as a supplement to the Jingjiang flood diversion area. This area is located in the west of the Huduhe River, from the Dazhigang Village, down to the Huangshantou County, bounded by the hills in the west, with an average width of 3.3 km from east to west, length of 28 km from north to south, an area of 86 km2 , a designed flood storage water level of 42.0 m, and an effective flood storage capacity of 380 million m3 . The main parts of the projects include Huxi embankment from Dazhigang to Huangshantou, Shangang embankment from Dazhigang to Huangshantou. Flood inlet is proposed at Xiaojiazui Village. When the water level of the Jingjiang flood diversion area reaches or approaches the designed water level, and the predicted flood diversion volume may exceed 200−300 million m3 , in the condition of controlling the south sluice discharge no more than 3800 m3 /s, Hudongand Huxi embankments are opened to let flood flow into the alternative flood storage area to supplement the insufficient capacity of the flood diversion area. 4. Renmin Polder Flood Storage and Detention Area Renmin Polder flood storage and detention area is located on the left bank of the middle section of the Jingjiang River, bordering the Jingjiang embankment in the north and the Yangtze River in the south, starting up from the Liukou Village of Jiangling County and ending down to the Yangjiawan of the Jianli County, with a total area of 362 km2 and a total flood storage capacity of 1.18 billion m3 . The flood storage and detention area is divided into upper and lower Renmin Polder, and the flood diversion gate is located in Maolingkou Village on the branch levee of upper Renmin Polder, about 4 km below the Xinchang County, with stake number no. 33 + 800−36 + 500. The designed gate width is 2700 m, and the designed flood diversion flow is 20000 m3 /s. RenMin Polder is part of the Jingjiang flood diversion project. When Yuanshi expanded flood diversion area is put into effect, Wuling’an embankment is opened and the flood is discharged, RenMin Polder should be taken advantage of in principle to divert (storage) the flood discharged into Jingjiang from Wuliang’an in equal amount.

2.7.2 Flood Storage and Detention Area Around Chenglingji The flood storage and detention area around Chenglingji is composed of Honghu Lake flood storage and detention area and 24 flood storage and detention areas in Dongting Lake area, with a flood storage area of 5770.5 km2 , a cultivated land area

2.7 Overview of Flood Detention Basins in Middle and Lower Reaches

63

of 242,600 hm2 , a population of 2.953 million, and an effective flood storage area of 34.475 billion m3 . 1. Dongting Lake Flood Storage and Detention Area At the symposium on flood control in the middle and lower reaches of the Yangtze River in 1980, it was made clear that Dongting Lake area should undertake the task of flood storage of 16 billion m3 . For this reason, Hunan Province identified 24 polders (fields) such as Qianlianghu Lake, Minzhu and Gongshuangcha polders as flood storage areas. It possesses a flood storage area of 2834 km2 , an effective flood storage capacity of 16.381 billion m3 , and a total embankment length of 1214.6 km within the polder. The flood storage embankments and polders in Dongting lake area are relatively independent and have dual functions. One function is to divert flood of the mainstream; the other one is to play a role in regulating and storing local flood of the four tributaries. Generally, the flood storage embankments and polders can be made use of one by one according to flood frequency and excess flood volume of the mainstream and four tributaries. After years of construction, the flood control capacity of embankments and polders for flood storage has been improved to some extent, but none of them has reached the standard. In terms of safety construction: construction of refuge platforms and refuge platforms along the embankments aggregates to 1096,500 m2 ; construction of 4,761 public and civil flood-avoiding buildings with an floodavoiding area of 816,300 m2 ; transferring of roads and bridges respectively 1102.5 km and 3654.3 m; solving the problem of partial mass transfer. 2. Honghu Lake Flood Storage and Detention Area Honghu Lake flood storage and detention area serves as an important engineering measure to deal with the excess flood near Chenglingji and ensure the flood control security of Jingjiang embankment and Wuhan City. The flood storage and detention area is located within Honghu City and Jianli County on the north bank of Jingjiang river section in the Midstream Yangtze, bounded by Honghu Lake embankment in Jianli, Dongjinghe River embankment and Honghu Lake main separation dike, with a flood storage area of 2,797.4 km2 , a designed flood storage water level of 32.50 m, and an flood storage volume of 18.094 billion m3 . In case of flood equivalent to that in 1954 occurring in the middle and lower reaches of the Yangtze River, it is supposed to undertake the task of diverting and storing excess flood of 16 billion m3 . The total length of the embankment in the Honghu Lake flood storage and detention area is 334.51 km, including embankment on Mainstream Yangtze of 226.85 km within Jianli County and Honghu City, Dongjinghe River embankment of 42.84 km, and main separation dike of 64.82 km. The first phase of Honghu main separation dike was started in the winter of 1972 and basically completed in 1980. As a section of the main separation dike with length of 16 km was built on the weak foundation, the dike body had been long unstable, which was collapsed reinforcement after reinforcement.

64

2 Overall Situation of Yangtze River Basin

In 1986, with the approval of the Ministry of Water Resources and Electric Power, the remaining works of the main separation dike has been continued constructing. Dongjinghe River embankment has not been up to the designed standard, while embankment on Mainstream Yangtze within Jianli County and Honghu City has reached the designed standard by completing works of heightening and reinforcing. According to the requirement proposed in the Opinions on improving flood control project construction on the Yangtze River in the near future (No. 12 State council issued [1999]) approved by the State Council, it was made clear that “the prominent problems in flood control of the Yangtze River mainly focus on the areas in vicinity of Chenglingji in 1996 and 1998, concentrated efforts should be made as soon as possible to build flood storage and detention area with a flood storage capacity of about 10 billion m3 , which can not only greatly relieve the tension of flood control here, but also play an important role in flood control of Dongting Lake and security of Wuhan City and Jingjiang embankment. Through research and based on the reciprocity principle for Hubei and Hunan provinces, it should arrange a flood storage and detention area with capacity of about 6 billion m3 for each one, Dongting Lake chooses the flood diversion polders of Qianlianghu Lake, Gongshuangcha Polder and Datonghu East Polder, a part of Honghu Lake flood storage and detention area is marked out for pioneer construction”. It is planned to divide Honghu Lake into east, middle and west blocks from top to bottom, and to construct the east block first on the basis of coordinating the relationship between flood storage in blocks and overall flood storage, so as to meet the flood diversion needs of different flood types, and achieve the goal of flexible application and decreased flood diversion losses. The east block is located in the eastern part of Honghu Lake flood storage and detention area. An east separation dike will be built from the Mainstream Yangtze embankment to the Dongjinghe River embankment to form a closed circle together with the Dongjinghe River embankment and the Mainstream Yangtze embankment. It is proposed to build a sluice gate for flood inlet at Taokou (the original flood diversion gate selected by the design of the second phase of the Honghu Lake flood storage and detention area) and a sluice gate for retreating flood at Buyuan Village, Xintankou Town. The embankment is arranged as: from Yaokou sluice (stake no. 485 + 000) on the Mainstream Yangtze embankment to Jinchuan Bay (stake no. 8 + 000) on the Honghu Lake main separation dike, with a total embankment length of 24.52 km. The total area is 889.74 km2 , with an effective flood storage capacity of 6.186 billion m3 and a flood storage water level of 32.5 m. The middle block mainly takes advantage of the Honghu Lake to store and retain flood, the separation dike on western side is the west separation dike of the west block, with a length of 49.85 km; the separation dike on eastern side is the east separation dike of the east blocks, with a length of 24.52 km; the total length of the upper and lower separation dike lines is 74.37 km. The upper and lower separation dikes,

2.7 Overview of Flood Detention Basins in Middle and Lower Reaches

65

together with the Mainstream Yangtze embankment within Jianli County and Honghu City and Honghu Lake main separation dike, form a closed flood storage circle. The total flood storage area is 1018.99 km2 , of which the lake area is 597.78 km2 (accounting for 58.66% of the total flood storage area), with a flood storage water level of 32.5 m, and an effective flood storage volume of 6.683 billion m3 . The flood inlet sluice is located at the site with stake no. 520 + 000 on Mainstream Yangtze embankment within Jianli County and Honghu City, and two flood retreating lines are considered: one line uses the Xindisluice to retreat the flood into the Yangtze River, with a flow of 800 m3 /s; the other line retreats the flood through Neijing River, with a flow of 500 m3 /s. The west block is a section divided from the western part of Honghu Lake flood storage and detention area, mainly under the administration of the Jianli County, Hubei Province. Flood inlet and retreating make use of the same sluice, which is proposed to build at the site with stake no. 533 + 000 on Mainstream Yangtze embankments within Jianli County and Honghu City. According to the topography and the crossing situation of canal system in the sub-block area, the sub-block separation dike line is arranged as follows: it starts from the Luoshan Town, extends along the west bank of the Luoshan pumping canal to Bayi fish ground, then turns westwards to the Maotaiqiao Village on Huhong Lake main separation dike, with a total dike line length of 49.85 km. The separation dike together with the Huhong Lake main separation dike and river embankment within Jianli County and Honghu City forms a closed flood storage circle. The flood storage water level is 32.5 m, the total flood storage area is 888.63 km2 , and the effective flood storage volume is 5.225 billion m3 .

2.7.3 Flood Storage and Detention Area Around Wuhan The flood storage and detention area in vicinity of Wuhan City is located in the middle reaches of the Yangtze River. It is composed of six flood storage and detention areas including Dujiatai, Xilianghu Lake, Wuhu Lake, Zhangduhu Lake, Baitanhu Lake and Dongxihu Lake, and is administrated by Hubei Province. The total flood storage area of this flood storage and detention area is 2,943.9 km2 , with a cultivated land area of 109,666 hm2 , an effective flood storage capacity of 12.210 billion m3 , and a population of 1.758 million people. 1. Dujiatai Flood Storage and Detention Area Dujiatai flood storage and detention area is located within Caidian District, Hannan District of Wuhan City and Xiantao City on the left bank of the Yangtze River and the right bank of the Downstream Hanjiang River, with a total area of 613.98 km2 , a flood storage water level of 30.0 m and an effective flood storage volume of 2.29 billion m3 . Built in 1956, the flood diversion area consists of the Dujiatai flood diversion sluice, diversion canal, Huanglingji spillway gate and the closing dike on the flood storage and detention area (with a length of 177.37 km).

66

2.

3.

4.

5.

2 Overall Situation of Yangtze River Basin

The designed water level of the Dujiatai flood diversion sluice is 35.12 m (above the sluice, similarly hereinafter), the checked water level is 35.45 m, and the corresponding flow is 4000 m3 /s and 5300 m3 /s, respectively; the designed flow of Huanglingji gate is 2700 m3 /s. Dujiatai flood storage and detention area is an important component of the flood control engineering system of the middle and lower reaches of the Yangtze River. Since its completion in 1956, Doujiatai flood diversion project has been used for 21 times, with a total flood diversion volume of 19.674 billion m3 , playing an significant role in ensuring the flood control security of Downstream Hanjiang and Wuhan City. Xiliang Lake Flood Storage and Detention Area Xiliang Lake storage and detention area is located in Xianning City, Chibi City, Jiayu County and Jiangxia District of Wuhan City on the south bank of the Yangtze River, including Xiliang Lake, Futou Lake, Luhu Lake, with a flood storage area of about 1095 km2 , a water level of 31.0 m, and an effective storage volume of 4.230 billion m3 . Flood diversion gate is located in Xiaojiazhou, Panjiawan Town, Jiayu County, with a designed gate width of 1000 m, a designed flood diversion flow of 10000 m3 /s, and a maximum flood diversion flow of 14350 m3 /s. Dongxi Lake Flood Storage and Detention Area Dongxi flood storage and detention area is located in the northwest of Wuhan City, bordering the Yangtze River in the west and the Fuhuan River in the east, with a flood storage area of 444 km2 , a flood storage water level of 29.50 m, and an effective flood storage volume of 2.0 billion m3 . The flood storage and detention areas is constructed by reclamation in 1958, and the closing dike is composed of Mainstream Hanjiang embankment, Dongxihu closing dike and Zhanggongdi embankment, with a total length of 114.3 km. The flood inlet and retreating are both in pattern of artificial levee breach, and the artificial levee breach position for flood inlet is between Xiongjiatai and Pengjiatia on north dike of Mainstream Hanjiang embankment, with a designed gate width of 560 m, and a designed flood inflow of 5000 m3 /s; the gate for flood retreating is set at the site with stake no. 12 + 000 on Dongxi Lake closing dike, with a designed gate width of 180 m, a designed flood retreating flow of 2500 m3 /s. Wuhu Lake Flood Storage and Detention Area Wuhu flood storage and detention area is located in Huangpi and Xinzhou districts of Wuahn City on the north bank of the Yangtze River, with a flood storage area of 277.9 km2 , and a flood water level is 29.1 m, and an effective flood storage volume of 1.81 billion m3 . The flood storage and detention area is completed by reclamation in 1969, and its closing dike has a total length of 37.24 km. The flood inlet gate is selected at Shakou between Yaotougou Ditch and Xianglushan Mountain, with a gate width of 500 m and a flood inflow of 5000 m3 /s. Zhangdu Lake Flood Storage and Detention Area ZhangduLake flood storage and detention area is located within Xinzhou District of Wuhan City on the north bank of the Yangtze River, and adjacent to Wuhu Lake flood storage and detention area, with a flood storage area of 309 km2 , a flood

2.7 Overview of Flood Detention Basins in Middle and Lower Reaches

67

storage water level of 28.3 m, and an effective flood storage volume of 1.000 billion m3 . The flood storage and detention area is constructed by reclamation in 1954, with a total dike length of 95.6 km. The flood inlet gate is selected near the ditch on Dulingdi embankment, with a gate width of 580 m and a flood inflow of 5000 m3 /s. 6. Baitan Lake Flood Storage and Detention Area Baitan Lake flood storage and detention area is located within Huangzhou City on the north bank of the Yangtze River, adjacent to Zhangdu Lake flood storage and detention area, with a flood storage area of 204 km2 , a flood storage water level of 27.5 m, and an effective flood storage volume of 880,000,000 m3 . The flood storage and detention area is completed by reclamation in 1953, with a total dike length of 71.125 km. The flood inlet gate is selected near Zushi temple on the riverbank, with a gate width of 550 m and a flood inflow of 5000 m3 /s.

2.7.4 Flood Storage and Detention Area Around Hukou The flood storage and detention area near Hukou is composed of four flood storage areas such as Fangzhou Xiatang Pond of Poyang Lake in Jiangxi Province, Huanghu Lake, as well as Huanyanghe River flood storage and detention area in Anhui Province, with a flood storage area of 1,714.55 km2 , a cultivated land area of 62,107 hm2 , a population of 726,900 people, and an effective flood storage volume of 5.120 billion m3 . 1. Kangshan Flood Storage and Detention Area Kangshan flood storage and detention area is located on the southeast bank of Poyang Lake, and the downstream estuary of the confluence of three rivers, namely south branch of Ganjiang River, Fuhe River and Xinjiang River, under the administration of Yugan County, Shangrao City. The closing embankment of the flood storage and detention area consists of Kangshan dike facing the lake in the north, discontinuous separation dikes and narrow mountain passes in the south, with a total length of 39.13 km, a flood storage area of 312.37 km2 , and an effective flood storage volume of 1.57 billion m3 . The flood diversion gate lies between stake no. 17 + 500−18 + 200 of Kangshan embankment, with a gate width of roughly 700 m. 2. Zhuhu Lake Flood Storage and Detention Area Zhuhu Lake flood storage and detention area is located on the east bank of Poyang Lake and near the outlet of Raohe River, under the jurisdiction of Boyang County, Shangrao City. The flood storage and detention area is mainly composed of low hills and lake plains, with wide water surface and numerous hills, which belongs to typical lakeside hill landform. The total rainfall collection area is 256 km2 , with a flood storage water level of 22.54 m, a flood storage area of 152.49 km2 , and an effective flood storage volume of 560 million m3 . The main closing embankment within the flood storage and detention area is Zhuhu embankment in the west, which was built in 1985 with a total length of 19.56 km. Both inside and outside

68

2 Overall Situation of Yangtze River Basin

parts of the embankment are adjacent to water. The flood diversion gate is located between stake no. 14 + 100−14 + 600 (near Baishazhou), with a gate width of 500 m. 3. Huanghu Lake Flood Storage and Detention Area Huanghu flood storage and detention area is located in the northeast of Jiangxiang embankment in Nanchang County, which is under the jurisdiction of Nanchang County. The total rainfall collection area of the whole plave is 49.28 km2 , with a flood storage water level of 23.26 m, a flood storage area of 49.28 km2 , and an effective flood storage volume of 290 million m3 . Built in 1964, the closing embankment of the Huanghu Lake flood storage and detention area is composed of two sections of embankments adjacent relatively to the lake and the river, with a total length of 27.13 km. Flood diversion gate is located between stake no. 59 + 600−59 + 800 on Jiangxiang embankment, with a gate width of 200 m. 4. Fangzhou Xiatang Pond Flood Storage and Detention Area Fangzhou Xietang Pond flood storage and detention area is located in the northwest of Ganxi embankment in Xinjian County, which is under the jurisdiction of Tiehe Town, Xinjian County. The total rainfall collection area of the whole place is 39.05 km2 , with a flood storage water level of 22.67 m, a flood storage area of 35.41 km2 , and an effective flood storage volume of 200 million m3 . Built in 1962, the closing embankment of the flood storage and detention area is composed of two sections of levees, one adjacent to the lake and the other adjacent to the river, with a total length of 14.21 km, of which 7.21 km is adjacent to the river and 7.0 km is adjacent to the lake. Flood diversion gate lies between Tiehe sluice on Ganxi embankment and Fangzhou pumping station, with a gate width of 170 m. 5. Huayang River Flood Storage and Detention Area Huangyang River flood storage and detention areais located in the north bank of Poyang lake estuary at the junction of the middle and lower reaches of the Yangtze River, which spans Anhui and Hubei provinces and is composed of most lakes in the Huayang river basin and reclamation areas along the lake. When the water level of the area goes to 19.20 m, the flood storage area is 1,165 km2 and the effective flood storage volume is 2.5 billion m3 . The closing embankment in the flood storage and detention area consists of Huangguang dike (2.55 km), Tongma dike (83.77 km), East separation dike (8.14 km) and West separation dike (38.94 km), with a total length of 133.40 km. Up to now, except the West separation dike has not been up to the designed standard, the other dikes have reached the designed standard. There are six culverts and sluices on the Tongma dike, such as Huayang sluice and Yangwan sluice, with a drainage flow of 882 m3 /s, while 10 water drainage sluices on the West separation dike with a drainage flow of 1100 m3 /s.

References

69

References Changjiang Water Resources Commission. (1990). Brief Report on Plan of Integrated Development of the Yangtze River Basin[R]. Changjiang Water Resources Commission. (1997). Research on comprehensive utilization and reservoir regulation for Three Gorges Project[M]. Wuhan: Hubei Science and Technology Press. Changjiang Water Resources Commission. (2012). Master Plan of the Yangtze River Basin (2012– 2030)[Z].

Chapter 3

Analysis on Characteristics and Changes of Flow-Sediment in Yangtze River Basin

3.1 Characteristics and Changes of Upstream Yangtze Inflow 3.1.1 Analysis on Runoff of Control Stations on Mainstream and Tributaries The Upstream Yangtze is the reach above Yichang City on the Mainstream Yangtze, draining an area of about 1 million km2 . Most of the Jinsha River above Yibin City on the mainstream belongs to canyon reach, with a length of 3464 km and a drop of about 5,100 m, accounting for about 95% of the total drop of the mainstream. The major tributary feeding into the Jinsha River is the Yalong River on the north bank (Changjiang Water Resources Commission 2012). The comparison between the runoff and sediment volume of the main control stations in the Upstream Yangtze and the annual mean values is shown in Table 3.1 (Changjiang Survey and Design and Research Co., Ltd 2012). The UpstreamYangtze runoff mainly comes from the JinshaRiver on the Mainstream Yangtze and the main tributaries of the Minjiang River, Jialing River, Wujiang River and Tuojiang River, of which the annual mean runoff of the Jinsha River (Pingshan station) is 143.9 billion m3 , the annual mean runoff of the Minjiang River (Gaoyang station) is 85 billion m3 , and those of the Jialing River (Beibei station), Wujiang River (Wulong station) and Tuojiang (Fushun station) are respectively 66 billion m3 , 48.7 billion m3 and 12.5 billion m3 . The analysis on various stages shows that, as seen in Fig. 3.1, since 1990s, the change of Upstream Yangtze runoff has tended to decrease, and compared with the average values prior to 1990, during 1991–2002, although the inflowof the Jinsha River and Wujiang River increased slightly, the inflow of the Tuojiang River, Minjiang River and Jialing River was dwindling, the runoff into the Three Gorges Reservoir (Cuntan plus Wulong) decreased by approximately 4% under comprehensive influences. Since the impoundment of the Three Gorges Project, the inflow of © Changjiang Press (Wuhan) Co., Ltd. 2021 S. Zheng et al., Flood Resources Utilization in the Yangtze River Basin, https://doi.org/10.1007/978-981-15-8108-3_3

71

Sediment concentration (kg/m3 )

Sediment runoff (104t)

Runoff (102 million m3 )

Item

788 −11%

1364

−5%

1439

2003–2013

Change rate

Mean annual value

2860 −46%

12,900

−48%

23,000

Change rate

Mean annual value

−39%

−45%

Change rate

−47%

0.477

−62%

0.947

2003–2013

−29% 0.362

9%

Change rate

0.345

0.907

864

−56%

0.423

1.87

1991–2002

0.596

1.71

Before 1990

4400

518

−68%

2003–2013

372

−34%

14%

Change rate

1170

125

3450

28,100

1991–2002

5260

24,600

Before 1990

850

0%

129

−15%

−8%

5%

Change rate

110

129

Fushun

Tuojiang River

815

1506

882

1440

1991–2002

Gaochang

Gaojiaba

Before 1990

Minjiang River

Jinsha River

−47%

0.635

−8%

1.1

1.19

27,800

−50%

15,900

−7%

29,300

31,600

2631

−6%

2500

0%

2672

2660

Zhutuo

Yangtze River

−75%

0.478

−63%

0.703

1.9

10,000

−76%

3180

−72%

3720

13,400

660

−6%

665

−25%

529

704

Beibei

Jialing River

−58%

0.554

−23%

1.01

1.31

38,500

−61%

18,100

−27%

33,700

46,100

3442

−7%

3264

−5%

3339

3520

Cuntan

Yangtze River

−79%

0.127

−37s%

0.384

0.614

2310

−83%

527

−33%

2040

3040

487

−16%

414

8%

532

495

Wulong

Oujiang River

Table 3.1 Statistical analysis of runoff, sediment runoff and sediment concentration of main control stations in Upstream Yangtze

(continued)

−56%

0.547

−25%

0.939

1.25

40,810

−62%

18,627

−27%

35,740

49,140

3929

−8%

3678

−4%

3871

4015

Cuntan + Wulong

Runoff into TGR

72 3 Analysis on Characteristics and Changes …

Mean annual value

0.522

Gaochang

Gaojiaba

1.62

Minjiang River

Jinsha River

0.729

Fushun

Tuojiang River

1.06

Zhutuo

Yangtze River

1.52

Beibei

Jialing River

1.12

Cuntan

Yangtze River

0.479

Wulong

Oujiang River

1.06

Cuntan + Wulong

Runoff into TGR

Note 1. The change rate was the relative change between the mean value of each period and the mean value before 1990; 2. The mean values before 1990 were the preliminary design values of the Three Gorges Reservoir, except that the mean value of Zhutuo station was derived from the statistical year from 1956 to 1990 (lack of data from 1967 to 1970); 3. Beibei station was moved downwardby 7 km in 2007, Pingshan station was moved downward by 24 km to Xiangjiaba station in 2012, Lijiawan station was moved upward by about 7.5 km to Fushun in 2001;4. Statistical years of mean annual values: Xiangjiaba station (Pingshan station) was from 1956 to 2013, Gaochang station was from 1956 to 2013, Fushun station (Lijiawan station) was from 1957 to 2013, Zhutuo station was from 1954 to 2013 (lack of data from 1967 to 1970), Beibei station was from 1956 to 2013, Cuntan station was from 1950 to 2013, and Wulong station was from 1956 to 2013

Item

Table 3.1 (continued)

3.1 Characteristics and Changes of Upstream Yangtze Inflow 73

74

3 Analysis on Characteristics and Changes …

Fig. 3.1 Comparison chart of runoff at main control stations in Upstream Yangtze

the Jinsha River, Tuojiang River, Minjiang River, Wujiang River and Jialing River had decreased significantly from 2003 to 2013,which decreased by 5%, 0%, 11%, 16% and 6%respectively compared with the average values before 1990, while the inflow of Zhutuo and Beibei stations decreased by 6% respectively. The runoff into the Three Gorges Reservoir had declined by 8% under comprehensive influences ([2]Changjiang Water Resources Commission 2010).

3.1.2 Characteristics of Inflow into Dam Site of Three Gorges Reservoir In the preliminary design of the Three Gorges Project, a statistics was carried out by a total of 114 years’ measured flow at Yichang station from 1877 to 1990, which drawn conclusions that the average annual flow was 14,300 m3 /s and the average annual runoff was 451 billion m3. According to the daily average flow data of the inflow long series (1877–2013) at Yichang station, the annual average flows of different series were calculated and compared with those of the initial series, as shown in Table 3.2. The analysis shows that, compared with the initial series, the series after 1991 all decreased to different degrees, and the decreasing degree was increasing year by year (Bureau of Hydrology, Changjiang Water Resources Commission 2013). From the perspective of hydrological characteristics, the inflow of the Yangtze River is distributed unevenly during the year. According to the statistics of the measured long series data from 1877 to 2013, the annual runoff at Yichang station is mainly concentrated in the main flood season from July to August, and the runoff in the flood season from June to September accounts for more than 60% of the annual

Runoff 1.55%

Difference in percent

0.70%

−30

−70

Compared with initial series

−100 4480

14,200

−200

1877–2002

14,100

Long series 1877–2013

4440

Annual average runoff

4510

14,300

Compared with initial series

Flow

Annual average flow

Initial series 1877–1990

Series

Table 3.2 Analysis on inflow of dam site of Three Gorges Reservoir (Unit of flow: m3 /s)

−380 −8.43%

−4.94%

4130

−1200

13,100

1991–2013

−223

4287

−710

13,590

1991–2002

−12.17%

−549

3961

−1740

12,560

2003–2013

−12.11%

−546

3964

−1730

12,570

2008–2013

3.1 Characteristics and Changes of Upstream Yangtze Inflow 75

76

3 Analysis on Characteristics and Changes …

runoff. The three months with the least runoff were from January to March, occupying 7.7% of the annual runoff. The annual water distribution process is shown in Table 3.3 and Fig. 3.2. In eyes of the distribution of runoff water, the inflow during the main flood season from July to August is the largest, the inflow in September is relatively abundant, and the inflow in October starts to decrease significantly. The frequency statistics of long series runoff were conducted by year, and the extraordinary dry years were shown in Table 3.4. The calculation shows that water inflow was weakened and runoff was decreased in 2006, 2011 and 2013. It can be clearly seen from the figure of the sliding average process of the Three Gorges Reservoir inflow (Fig. 3.3) that after entering the 1990s, the curve showed a downward feature, especially after 2000, the inflow of the Yangtze River has entered a relatively dry period with more dry years. In general, it can be learned from the analysis on the inflow water of the above mainstream and tributary key stations and the Three Gorges Reservoir that since the 1990s, the inflow water of the upper reaches of the Yangtze River has tended to significant decrease. Considering that the annual runoff at Yichang station mainly focuses on the flood season from June to September, it is very important to carry out flood resources utilization during this period (The Ministry of Water Resources of People’s Republic of China 2009).

3.2 Flood Characteristics of Major Tributaries 3.2.1 Flood Characteristics of Yalong River Floods in the Yalong River Basin are mainly caused by heavy rains. The flood season in Yalong River Basin is from May to October, and the biggest flood usually occurs from June to September. The flood process of the Yalong River is usually in bimodal or multi-peak pattern, with a single peak process of 6–10 days and a bimodal process of 12–17 days. In the upper reaches of the Yalong River, the flood peak is not prominent, the fluctuation is slow and the duration is long; in the lower reaches, the flood peak is high, the fluctuation is more dramatic, and the duration is short. The flood composition of the Yalong River can be divided into three types: the first one is basin-wide flood, the main rainfall area first occurs in the upstream and then moves to the downstream, the inflow from the upstream of the Yalong River can account for more than 40% of the flood of Xiaodeshi in the downstream; the second one is mainly the upstream inflow, and the rainfall area is mainly in the plateau area above the Yalong River, characterized by large rainfall area, long duration and low intensity, such as the flood occurring in 1904; the third one is mainly the interval inflow from Yalong River to Xiaodeshi, the rainfall area is mainly in the middle and lower reaches, the inflow above the Yajiang River is small, only accounting for 20% of Xiaodeshi, such as the flood occurring in 1965.

Jan

4400

118

2.6

Month

Average flow (m3 /s)

Water volume (102 million m3 )

Percentage (%)

2.4

97

4000

Feb

2.7

121

4500

Mar

4.0

174

6700

Apr

7.0

313

11,700

May

Table 3.3 Annual water distribution process at Yichang station June

10.9

477

18,400

July

17.8

801

29,900

Aug

16.4

737

27,500

Sept

15.4

672

25,900

Oct

11.2

504

18,800

Nov

6.1

267

10,300

Dec

3.6

161

6000

Annual

100.0

4440

14,100

3.2 Flood Characteristics of Major Tributaries 77

78

3 Analysis on Characteristics and Changes …

Fig. 3.2 Pie chart of annual water distribution process at Yichang station

Table 3.4 Statistics of extraordinary dry years ofThree Gorges Reservoir

Year

Mean annual flow (m3 /s)

Annual runoff (102 million m3 )

Empirical frequency

2006

9500

2996

99.3%

1942

10,600

3343

98.5%

1900

10,700

3374

97.8%

2011

10,800

3406

97.1%

1884

11,000

3469

96.4%

1994

11,000

3469

95.6%

1936

11,200

3532

94.9

1972

11,300

3564

94.2

1997

11,500

3627

93.4

1959

11,600

3658

92.7

1969

11,600

3658

92.0

2013

11,700

3690

91.2

It needs to flood at the same time in three areas of the upstream area, Litang River and Luning to Xioadeshi, if lacking one of the three areas, there can only form local big flood or relative serious flood.

3.2 Flood Characteristics of Major Tributaries

79

Fig. 3.3 Sliding average process of long series annual average flow of Three Gorges Reservoir

3.2.2 Flood Characteristics of Jinsha River Floods in the Jinsha River are mainly formed by heavy rains, and there is supply of ice and snow melt water in the upstream area. The floods of the Jinsha River usually occur from June to November, especially occurring most frequently from July to September. According to the statistics of measured flood data at Shigu and Pingshan stations, the occurrence time of annual maximum flood peak flow in the upper section of the Jinsha River is mainly in July and August, and the frequency of annual maximum flood peak flow appearing in these two months accounts for 85%. The occurrence time of the maximum annual peak flow in the lower section of the Jinsha River is mainly in August and September, and the frequency of the annual maximum peak flow appearing in these two months accounts for 80%. The floods in the Jinsha River mainly come from the Downstream Yalong and Shigu, as well as the interval reach from Xiaodeshi to Pingshan. In the composition of flood at Pingshan station, the inflow above Shigu on the Jinsha River takes up for roughly 25–33%, the inflow above Xiaodeshi on the Yalong tributary accounts for about 27–35%, and the inflow from Shigu and Xiaodeshi to Pingshan occupies for approximately 26–37%, with the percentages of above-mentioned watersheds to total river basin are respectively 46.7%, 25.8% and 27.5%. The total flood amount of the Jinsha River in flood season generally accounts for one third of the total flood amount of the area above Yichang. For the extraordinary flood occurring in the Yangtze River Basin in 1954, the 30-day flood volume of the Jinsha River in August accounted for 50% of the flood volume at Yichang station, and the 60-day flood volume in July and August accounted for 46% of the flood volume at Yichang station.

80

3 Analysis on Characteristics and Changes …

3.2.3 Flood Characteristics of Minjiang River (Dadu River) Floods in the Minjiang River Basin are mainly formed by rainstorms. The occurrence time of floods is corresponding to that of the rainstorms, and the flood area and magnitude are also closely related to those of the rainstorms. The annual maximum flood peak flow in the lower reaches of the Mainstream Minjiang appears in June at the earliest and September at the latest, and the annual maximum flood occurs in July and August at the most. The duration of one single flood is long in the Minjiang River basin, and the flood hydrograph usually has multiple peaks. According to the analysis on flood data of Gaochang hydrological station in 1961, 1975 and 1981, the duration of one single flood is generally 7–21 days and the peak duration is 5–6 h. The flood in the upper reaches of the Minjiang River (river head–Dujiangyan City), the rainfall intensity and amount in the areas above Wenchuan are all small, and the occurrence time is not corresponding to that of the rainstorms in the areas below Wenchuan, so the floods are not likely to encounter with each other, and the impact on the areas below Wenchuan is limited. The areas below Wenchuan basically belong to Lutoushan Mountain rainstorm area. When torrential rain or heavy downpour occurs in this area, there will be relatively heavy rain occurring above Wenchuan at the corresponding time, which tends to form extraordinary flood in the upper reaches of the Mainstream Minjiang. The flood in the middle reaches of the Minjiang River (Dujiangyan City– Leshan City) mainly consists of floods in three parts: the Mainstream Minjiang, the Mainstream DaduRiverand the Qingyi River. In most cases, when the downpour occurs in the plain area, torrential rain or heavy rain will also occurs simultaneously in the small tributaries around and the lower section of the upstream. Combined floods from both mainstream and tributaries often form big flood or extreme flood in the mainstream above Leshan, such as the floods in 1955 and 1961. The magnitude of flood in the lower reaches of the Minjiang River is affected by the heavy rain occurring in Lutoushan Mountain and Qingyi River. If the Nanhe River, Qingyi River and Dadu River within the Qingyi rainstorm area and the Mainstream Minjiangare flooded at the same time, then extraordinary flood will occur in the lower reaches of the Minjiang River, resulting in serious flood disaster in towns and cities along the downstream river. The flood peak in the Downstream Minjianglasts for about half a day. In the Minjiang River Basin, one single rainstorm can often hangs over the nearby river basins. For example, in 1917, when the middle and lower reaches of the Minjiang River suffered from extraordinary flood, the upper and middle reaches of the Qingyi River also experienced severe flood, while the lower reaches saw extraordinary flood. Big floods occurred simultaneously in Minjiang River and Tuojiang River in 1934, 1964 and 198. The main flood season of Dadu River Basin is from June to September, and the flood is caused by precipitation. The annual maximum flow mostly appears in June and July, with the most opportunities in July, accounting for about 50%; the opportunities of appearing the annual maximum flow in August are less, accounting for about 10%; while the opportunities are relatively more in September, accounting

3.2 Flood Characteristics of Major Tributaries

81

for about 20%. The bigger floods occurring in the Mainstream Dadumainly come from the middle and lower reaches, and also from the upper reaches or from the combination of the upper and middle and lower reaches. Due to the influence by elevation, topography and geographical location, most areas of the Upstream Dadu have not seen heavy rains yet. The middle and lower reaches are located within the area influenced by the Qingyi River, Mabian River and Anning River rainstorm areas, as a result, it is likely to appear torrential rain, where stand as the main source of floods. One single rainstorm in the Qingyi River can hang over the whole basin. The rainstorm center usually appears between Ya ‘an and Jiajiang River in the middle and lower reaches, especially in the Zhougong River and Huaxi River at the northwest foot of the Emei Mountain. Qingyi River drains a relatively large area and accepts numerous small tributaries, and the floodsjoin quickly with each other, making it easy to form a big flood.

3.2.4 Flood Characteristics of Jialing River The flood in the Jialing River is mainly formed by the heavy rain, mainly occurs in the flood season from May to October. The annual maximum flood peak always occurs in July to September, the earliest may appear in May, and the latest may appear in October, especially in July at the most. In August, the basin is controlled by the Pacific subtropical high, which is often prone to summer drought, while the probability of annual maximum flood peak is relatively rare. After September, due to the southward rotation of the polar peak and sometimes in quasi-stationary peak, autumn flood occurs in the basin, and the probability of annual maximum flood peak flow is only next to that in July. Although there is less chance of appearing annual maximum flood peak in October, there are also late-term extraordinary floods such as the one occurring on 3 October 1975. Many tributaries flow into the Jialing River Basin, especially after the Hechuan Section of Qujiang River and the Fujiang River feeding into the Jialing River respectively from the left and right banks, there forms a huge fan-shaped river system with a fast confluence speed, coupled with that the Mainstream Jialing as well as the Qujiang River and the Fujiang River are all located within the famous rainstorm area in Sichuan Province, so it is prone to form big flood. The flood process in the lower reaches of the Jialing River is mostly bimodal or in multi-peak, a single flood peak lasts for 3–5 days and multi-peak for 7–12 days, with a peak crest duration of about 4 h.

82

3 Analysis on Characteristics and Changes …

3.2.5 Flood Characteristics of Wujiang River The Wujiang River Basin is featuring river of precipitation replenishment, and the flood is mainly induced by heavy rain. The annual maximum flood peak flow occurs in the flood season from May to October, concentrated in June and July, especially in the mid-to-late June at the most. One single flood in the Downstream Wujiang lasts for about 20 days. Most of the water is concentrated within 7 days. The 7-day flood volume accounts for over 65% of the 15-day flood volume, the 3-day flood volume accounts for 60% of the 7-day flood volume, and the 1-day flood volume accounts for 40% of the 3-day flood volume, while flood volume is more concentrated in the flood years. The spatial pattern of the mean annual flood volume and the 7-day flood volume in the Wujiang River Basin are even. The proportion of the flood volume of each section in the upstream of the Jiangjie River to the flood volume of Wulong station is smaller than their catchment controlled areas ratio, while the proportion of the flood volume of each section in the downstream of the Jiangjie River to the flood volume of Wulong station is larger than their catchment controlled areas ratio. Due to the uneven distribution of rainstorms in flood years in the Wujiang River Basin, the spatial pattern of flood is different from that of the mean annual situation. For example, in 1999, the proportion of the flood volume of Yachi River to Jiangjie River section to the flood volume of Wulong station is larger than their catchment controlled areas ratio. The percentages of the annual maximum 7-day flood volume and 15-day flood volume of the Yichang station to those of the Wulong station on the Wujiang River respectively account for 1.2–24.3% and 1.6–25.5%, with a large variation range and average percentages of 8.5% and 9.5%, which are slightly larger than the catchment area ratio between Wulong station and Yichang station. According to the analysis of data from 1951 to 2000, the encounter times of each one’s annual maximum 7day and 15-day flood volumes in the above-mentioned two stations are 8 and 12 respectively, accounting for 16% and 24% of the total encounter times, with less chances of flood encounters. In 1909 and 1935, big floods occurred in Yichang and Wulong at the same time, but only part of the floods occurred.

3.3 Analysis of Flood Encounters Among Mainstream and Major Tributaries of Yangtze River Basin 3.3.1 Analysis of Flood Encounters Between Jinsha River and Minjiang River Based on the analysis of Pingshan station on the Jinsha River, Gaochang station on the Minjiang River and Lizhuang station on the lower reaches of the confluence, by

3.3 Analysis of Flood Encounters Among Mainstream …

83

Table 3.5 Spatial pattern of flood at Lizhuang station Station

1d Flood volume (102 million m3 )

Percentage to that of Lizhuang (%)

3d Flood volume (102 million m3 )

Percentage to that of Lizhuang %

7d Flood volume (102 million m3 )

Percentage to that of Lizhuang (%)

Area proportion between the station and Lizhuang (%)

Pingzhuang

11.57

44.4

37.38

53.6%

89.3

59.6

75.9

Gaochang

11.4

43.7

25.73

36.9%

48.1

32.1

21.2

Note the statistics is carried out for flood volumes of Pingshan and Gaochang stations in corresponding periods by mainly used the annual maximum flood volume of Lizhuang station

mainly selecting the annual maximum flood volume time of Lizhuang station from 1953 to 2012 and considering the flood propagation time, the statistics is carried out for flood volumes of Pingshan and Gaochang stations in corresponding periods, and thus the mean annual situation of spatial pattern of flood at Lizhuang station is obtained, as shown in Table 3.5. The annual maximum flood volume in period exceeding 3 days of Lizhuang station is dominated by the Jinsha River, and the longer the period is, the greater the proportion of the Jinsha River occupies. The proportion of flood volume in the Minjiang River to the flood volume at Lizhuang station is much larger than the area proportion (Bureau of Hydrology, Changjiang Water Resources Commission 2008). Statistics are carried out for theoccurrence time of annual biggest floodsatPingshan, Gaochang and Lizhuang stations from 1953 to 2012,the appearing number of annual biggest floods at Pingshan and Gaochang stations when Lizhuang station suffering from annual biggest flood, and the annual biggest floods encounter times between Pingshan and Gaochang stations and the results are shown in Table 3.6. It can be seen from Table 3.6 that, the probability of annual biggest flood encounters between Jinsha River and Minjiang River increases with the time period prolongs. In the 60-year measuredseries, the annual maximum 1-day flood volumes of Pingshan and Gaochang stations only encountered in 1966 and 2012; the annual maximum 3-day flood volumes encountered in 4 years, accounting for 6.7%; the maximum 7-day flood volumes encountered in 9 years, accounting for 15.0%. The magnitude situation of flood encounters in typical years between Pingshan station on Jinsha River and Gaochang station on Minjiang River is shown in Table 3.7. It can be seen that except for the flood in 1966, the magnitude of floods in other encounter years is all small, and the magnitude of combined floods is also small. In September 1966, the 3-day flood volumes of Jinsha River and Minjiang River were equivalent to floods with return periods of 33 years and 5 to 10 years respectively, and the combined flood was in recurrence of 50 years, which was a typical example of encounters between two rivers. In July 2012, the annual biggest floods in Jinsha River and Minjiang River encountered with each other, although the magnitude of

84

3 Analysis on Characteristics and Changes …

Table 3.6 Statistical table of flood encounters between Pingshan and Gaochang stations (1953– 2012) Station

Flood volume in 1 day

Flood volume in 3 days

Flood volume in 7 days

Times

%

Times

%

Times

%

Occurrence situation of Pingshan when Lizhuang suffering from flood

7

11.7

23

38.3

41

68.3

Occurrence situation of Gaochang when Lizhuang suffering from flood

25

41.7

23

38.3

17

28.3

Encounters between Pingshan and Gaochang

2

3.3

4

6.7

9

15.0

Table 3.7 Flood encounters situation between Pingshan and Gaochang stations (1953–2012) flood volume: 100 million m3 Item

Year

Pingshan

Gaochang

Flood volume

Start date

Return period (years)

Flood volume

Start date

Return period (years)

1-day flood volume

1966

24.7

Sept.1

33

20.8

Sept.1

5–10

2012

14.3

July 22