Professor John F. K e n n e d y * SEDIMENT, FLOOD-CONTROL AND NAVIGATION ASPECTS OF THE THREE GORGES PROJECT, YANGTZE RIVER, CHINA Sediment-, Hochwasserregulierungs- und Schiffahrtsaspekte des Drei-Schluchten-Projektes am Yangtze Fluß in China John F. Kennedy Hunter-Reuse-Professor of Hydraul1cs und Direktor, Iowa Institute of Hydraul1c Research, The Un1vers1ty of Iowa Geboren 1933, Studium des Bauingenieurwesens an den Uni­ versitäten Notre Dame und Cal1forn1a Institute of Tech­ nology (Cal Tech); 1956 - 1960 Assistent am Cal Tech; 1960 Promotion, 1961 - 1966 Assoc1ate Professor am Mas­ sachusetts Institute of Technology, Cambr1dge; seit 1967 Direktor und Professor des Iowa Institute of Hydraul1c Research; 1980 - 1984 Präsident der IAHR. Veröffent 11 chungen a 1s Autor, Co-Autor und Herausgeber (über 170 Beiträge) auf den Gebieten Sed1menttransport, Hydromechanik, Wasserwirtschaft, Umwelt- und Eisfor­ schung sowie Ausbildung und Forschung 1m Ingen1eurwesen. Abstract The Three Gorges Project on China's Yangtze River has been under 1nvest1gat1on s1nce 1t was first proposed, by Dr. Sun-Yat San, in 1922. The rapid econom1c development of China, and the steadily increasing population and investment that are at r1sk from flooding of the Yangtze R1ver, have given new impetus to 1nvestigation of the project. The Chinese go­ vernments' continuing investigation of the project, and design of 1ts var1ous components, recently has been complemented by an extensive feas1b1lity study sponsored by World Bank. Several aspects of the project are reviewed in this paper. The proposed project would pro­ duce the world's largest hydroelectric plant. It appears to be technically feas1ble, and economically very attractive. The princ1pal problems surrounding it relate to the popula­ tion relocation it would require, its possible environmental impacts, and the tremendous drain it would place on China's resources at a time when these resources are needed also for other types of development. This paper reviews principally the sediment, flood-control and navigation aspects of the project. Inhalt Das Drei-Schluchten-Prejekt an Chinas Yangtze Fluß wird untersucht, seit es von Dr. Sun­ Yat San im Jahr 1922 erstmals vorgeschlagen wurde. Die schnelle wirtschaftliche Entwick­ lung Chinas, die weiterhin zunehmende ·Bevölkerung und Investitionen, die durch Hochwasser des Yangtze Flusses gefährdet sind, haben einen neuen Anstoß zur Untersuchung dieses Pro­ jektes gegeben. Die fortgesetzten Untersuchungen des Projektes durch die chinesische Re­ gierung und die Planung der verschiedenen Bereiche wurden kürzlich durch eine umfassende Durchführbarkeitsstudie der Weltbank abgeschlossen. Verschiedene Aspekte dieses Projektes werden in diesem Beitrag besprochen. Das vorgeschlagene Projekt würde zur größten Wasser­ kraftanlage der Welt führen. Es erscheint technisch durchführbar und wirtschaftlich äu• ßerst vorteilhaft. Die Hauptprobleme beinhalten die erforderliche Umsiedlung der Bevölke• rung, mögliche Umweltaspekte und die gewaltige Bindung von Ressourcen Chinas zu einer Zeit, da diese ebenfalls für andere Entwicklungsprojekte benötigt werden . Dieser Beitrag geht vorwiegend auf Aspekte der Sedimente, der Hochwasserregulierung und der Sch1ffahrt ein. * Director, Iowa Institute of Hydraulic Research- The University of Iowa, Iowa City, Iowa (USA) Mitt.bl. BAW {1989) Nr. 64 169 Kennedy: Sediment, Flood-Control and Navigation Aspects INHALT Seite 1 Introduction 171 2 Rivers: flows of water and sediment 171 3 Flooding and flood protection of the valley of the 173 middle reach of the Yangtze River 4 Sediment and Three Gorges Project 177 5 Navigation Aspects 178 6 Summary and Conclusions 181 7 References 182 170 Mitt:bl. BAW (1989) Nr. 64 Kennedy: Sediment, Flood-Control and Navigation Aspects 1 Introduct1on Many benefits accrue to large-scale dam-reservoir systems (hydroprojects), including flood control, improved navigation, power generation, and recrea­ t i on and touri sm. However, 1arge hydroprojects i nvari ably carry with them some associated, not wholly quantifiable costs, including environmental im­ pacts, submergence of archeologically and anthropologically significant sites, and population displacement. In view of the tremendous benefits they produce and the sensitivity of the problems which accompany them, it is not surprising, therefore, that planning for major hydroprojects is attended by often shrill controversy, some of which frequently tends to mask the issues which should be key to the decision-making processes involved in project planning. There are some almost purely technical aspects of large hydroprojects about which there can be little sensible disagreement. First, there is no equally effective alternative available, at any reasonable price, for protection of downstream areas against the ravages of large floods, or for water conser­ vation. Second, they are practically unequalled as sources of renewable, low-cost electric power. Third, many ancillary often unanticipated, bene­ fits arise after the projects are placed in operation. Fourth, suitably de­ signed hydroprojects are an invaluable aid to navigation, because of the enlarged, low-velocity waterways they produce upstream of the dam, and of the control they exert on the downstream discharges. Finally, at many dam sites the sediment-management strategy is one of the most challenging eng1- neering aspects of the project. This paper is concerned principally with the first and last of these questions. 2 R1vers: Flows of Water and Sediment To the casual observer, rivers appear tobe flows of water, but in fact they are flows of water and of sediment. One of the fundamental laws of geomorphology is that the mountains are moving into the oceans. It is the things that happen along the way that form the basis for Sedimentation engineering. Table 1 presents a summary, compiled from data presented by Jansen, et al. (1), of certain characteristics of 17 of the world's rivers that are signi­ ficant in one sense or another. A river may pose major problems because of its large water discharge, its large sediment discharge, or its high sedi­ ment concentration. Noteworthy in the last category are the Waipapa and the Murray-Darling Rivers (in New Zealand and Australia, respectively), which have very small water di scharges but sediment concentrations that are so high as to make them difficult to manage. The Yangtze River, on which the Three Gorges Project (TGP) will be instal­ led, is one of the world's major rivers both in terms of water discharge (number 4) and sediment discharge (number 5). With a length of 6,300 kilo­ meters, the Yangtze River is the langest river in Asia, and the third lan­ gest in the world (after the Nile and Amazon). Table 2 (2) shows that of the total of about 13.5 bi 11 ion tonnes (annual average) of sediment rea­ ching the world's oceans, approximately three-fourths comes from Asia and the large Pacific Ocean islands. It is especially noteworthy that more than 25 percent of the sediment reaching the world's oceans is delivered by Chi­ na alone. Mitt.bl. BAW (1989) Nr. 64 171 Kennedy: Sediment, Flood-Control and Navigation Aspects Table 1 Rankings of the World 1 S Major Rivers (1) (Data correspond to river mouths) River Catchment Water Sediment Sediment Area Discharge Discharge Concentration 2 3 (106 km ) (m /s) po6re/Yr) (mg/1) Amazon 7.0 100 ,000 (1) 900 (3) 290 (South America) Conga 3.7 44,000 (2) 70 50 (Africa) Orinoco 0.95 25.000 (3) 90 110 (South America) Yangtze 1.8 22 ,000 (4) 500 (5) 1,400 (China) Brahmaputra 0.64 19,000 ( 5) 730 (4) 1,200 Yellow 0. 77 4,000 1,900 ( 1) 15,000 ( 1) (China) Waipapa 0.0016 46 11 7,500 (2) (New Zealand) Ganges 1.0 14,000 1,500 ( 2) 3,600 ( 3) (India) Mi ssouri 1.4 2,000 200 3,200 (4) (USA) Murray-Darling 1.1 400 30 2,500 (5) (Australia) Mississippi 3.9 18,000 300 530 (USA) Rhine 0.36 2,200 o. 72 10 (Europe) Danube 0.82 6,400 67 330 (Europe) Nile 2.9 3,000 80 630 (Africa) Indus 0.96 6,400 400 2,000 (Pakistan) Yenisey 2.6 17,000 (6) 11 20 (USSR) 0,41 13,000 (12) 300 750 172 Mitt.bl. BAW (1989) Nr. 64 Kennedy: Sediment, Flood-Control and Navigation Aspects The fact that China's proportional contribution to the world's sediment budget is roughly the same as its fraction of the world's population is by no means a spurious correlation; intensive land use increases overland erosion, the sediment loads imposed on rivers, and consequently the rate of sediment delivery to the oceans. Even though it is one of China's major ri vers, the sediment di scharge of the Yangtze Ri ver i s quite modest in relation to its water discharge, and the sediment concentration is surpris­ ingly low when compared to that of other major rivers of China and other parts of Asia. Table 2 World Sediment Budget by Geographical Region (2) Drainage area Sediment Yield Sediment Discharge 2 po6 km ) {t km-2 ~r-1) po6t ~r-1) N. & C. America 17.50 84 1462 S. America 17.90 97 1788 Europe 4.61 50 230 Eurasian Arctic 11.17 8 84 Asia 16.88 380 6349 Africa 15.34 35 530 Australia 2.20 28 62 Large Pacific 3.00 1000 3000 Islands Totals 88.60 150 13,505 Note: Northern Africa, Saudi Arabian peninsula and western Austral ia are primari ly desert, and assumed to have 1i tt 1e annua 1 di scharge of ri ver sediment. Total land area is 11.40 km 2 x 106. At the site of the TGP dam, Sanduoping, the annual-average water flow in the Yangtze River is about 453 billion cubic meters, and the average water discharge at the proposed site of the dam is 14,300 m3 /s. The dry season discharges about 3,000 m3 /s at Sanduoping (3). The average annual sediment discharge at the dam site is about 523 million tonnes, and the correspond­ ing concentration amounts to only 1.19 kilogram per cubic meter (4).