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Acoustic Doppler current profiler surveys along the Yangtze River Zhongyuan Chen a, , Dechao Chen b , Kaiqin Xu c , Yiwen Zhao d , Taoyuan Wei e , Jing Chen e , Luqian Li f , Masataka Watanabe c a State Key Laboratory for Estuarine and Coastal Research, East China Normal University, Shanghai 200062, China b Department of Urban and Environment, College of Suzhou Science and Technology, Suzhou 215011, China c National Institute for Environmental Studies, Tsukuba, 305-8506, Japan d School of Geography, University of Leeds, Woodhouse Lane, Leeds, UK e Department of Geography, East China Normal University, Shanghai 200062, China f Department of Geography, National University of Singapore, Singapore 119260, Singapore Received 2 December 2004; received in revised form 21 February 2005; accepted 29 March 2006 Available online 14 September 2006 Abstract An acoustic Doppler current profiler is used to characterize the river velocity against the morphology of the Yangtze River from Chonqing to the sea. High flow velocities occur in the Three Gorges section and lower velocities in the middle and lower reaches of the river. This is largely due to the change in river pattern from a high gradient deeply-cut valley to a flat fluvial plain. Flow velocities fluctuate in the middle Yangtze due to the presence of meander bends of different length. There are numerous smaller velocity fluctuations in the lower Yangtze channel that reflect multichannel pattern with numerous sand bars and a river morphology affected by bedrock outcrops. Water depths of 40100 m occur in the Three Gorges valley but decrease to 1540 m in the middle and lower Yangtze. At the Gezhou Reservoir, 30 km downstream of the Three Gorges damsite velocity drops to low (b 1.0 m s - 1 ) 20 km reach. A second low velocity (b 0.5 m s - 1 ) zone, about 20 km in length, is located in the lower Yangtze near the coast probably due to the tidal influence. The results from this research will serve as a datum for evaluating changes to the river once the Three Gorges dam is completed in 2009. © 2006 Elsevier B.V. All rights reserved. Keywords: Acoustic Doppler profiler; Yangtze River; Flow velocity; Channel morphology; Three Gorges Dam 1. Introduction River flow, as reflected by discharge and flow velocity, is sensitive to channel morphology, sediment transport, and fluvial variables at the basin-scale and to climate change (Arnell and Reynard, 1996; Millier and Gupta, 1999; Wyżga, 1999; O'Connor and Grant, 2003; Kale and Hire, 2004). For instance, Bart (2001) related river morphology classification, origin and sedimentary pro- ducts to flow patterns; Sidorchuk et al. (2000) demons- trated the evolutionary kinship between channel morphology and river flow in the northern Russian Plain during the Late Glacial and Holocene, and Rimbu et al. (2004) associated decadal variability of the Danube river flow to the North Atlantic Oscillation. The data on river flow can also assist in reservoir management (Baratti et al., 2003). Therefore, river flow characteristics can shed light both on the natural and anthropogenic fluvial environmental changes, particularly with regard to geoengineering practices (Pinter and Heine, 2005). Geomorphology 85 (2007) 155 165 www.elsevier.com/locate/geomorph Corresponding author. E-mail address: [email protected] (Z. Chen). 0169-555X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2006.03.018

Transcript of Acoustic Doppler current profiler surveys along the ...joexu/paper/geomorph.pdf · Acoustic Doppler...

2007) 155–165www.elsevier.com/locate/geomorph

Geomorphology 85 (

Acoustic Doppler current profiler surveys along the Yangtze River

Zhongyuan Chen a,⁎, Dechao Chen b, Kaiqin Xu c, Yiwen Zhao d, Taoyuan Wei e,Jing Chen e, Luqian Li f, Masataka Watanabe c

a State Key Laboratory for Estuarine and Coastal Research, East China Normal University, Shanghai 200062, Chinab Department of Urban and Environment, College of Suzhou Science and Technology, Suzhou 215011, China

c National Institute for Environmental Studies, Tsukuba, 305-8506, Japand School of Geography, University of Leeds, Woodhouse Lane, Leeds, UK

e Department of Geography, East China Normal University, Shanghai 200062, Chinaf Department of Geography, National University of Singapore, Singapore 119260, Singapore

Received 2 December 2004; received in revised form 21 February 2005; accepted 29 March 2006Available online 14 September 2006

Abstract

An acoustic Doppler current profiler is used to characterize the river velocity against the morphology of the Yangtze River fromChonqing to the sea. High flow velocities occur in the Three Gorges section and lower velocities in the middle and lower reaches ofthe river. This is largely due to the change in river pattern from a high gradient deeply-cut valley to a flat fluvial plain. Flowvelocities fluctuate in the middle Yangtze due to the presence of meander bends of different length. There are numerous smallervelocity fluctuations in the lower Yangtze channel that reflect multichannel pattern with numerous sand bars and a rivermorphology affected by bedrock outcrops. Water depths of 40–100 m occur in the Three Gorges valley but decrease to 15–40 m inthe middle and lower Yangtze. At the Gezhou Reservoir, 30 km downstream of the Three Gorges damsite velocity drops to low(b1.0 m s−1) 20 km reach. A second low velocity (b0.5 m s−1) zone, about 20 km in length, is located in the lower Yangtze nearthe coast probably due to the tidal influence. The results from this research will serve as a datum for evaluating changes to the riveronce the Three Gorges dam is completed in 2009.© 2006 Elsevier B.V. All rights reserved.

Keywords: Acoustic Doppler profiler; Yangtze River; Flow velocity; Channel morphology; Three Gorges Dam

1. Introduction

River flow, as reflected by discharge and flow velocity,is sensitive to channel morphology, sediment transport,and fluvial variables at the basin-scale and to climatechange (Arnell and Reynard, 1996; Millier and Gupta,1999;Wyżga, 1999; O'Connor andGrant, 2003; Kale andHire, 2004). For instance, Bart (2001) related river

⁎ Corresponding author.E-mail address: [email protected] (Z. Chen).

0169-555X/$ - see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.geomorph.2006.03.018

morphology classification, origin and sedimentary pro-ducts to flow patterns; Sidorchuk et al. (2000) demons-trated the evolutionary kinship between channelmorphology and river flow in the northern RussianPlain during the Late Glacial and Holocene, and Rimbu etal. (2004) associated decadal variability of theDanube river flow to the North Atlantic Oscillation. Thedata on river flow can also assist in reservoir management(Baratti et al., 2003). Therefore, river flow characteristicscan shed light both on the natural and anthropogenicfluvial environmental changes, particularly with regard togeoengineering practices (Pinter and Heine, 2005).

156 Z. Chen et al. / Geomorphology 85 (2007) 155–165

The physical background of the Yangtze drainagebasin can be found in Yang et al. (2007-this issue). Dueto extensive damming upstream and siltation in riversand lakes in the middle Yangtze reaches in the pastcentury (Yin et al., 2007-this issue), the annual sedimentload delivered to the East China Sea has decreaseddramatically from 4.70×108 t to 3.50×108 t (Yanget al., 2002). Furthermore, rainfall in the middle andlower Yangtze basins has increased in the past 10 years,resulting in a higher risk of flooding (Jiang et al., 2003).The Three Gorges Dam will be closed in 2009, causinglarge changes in river channel erosion and siltationthroughout the middle and lower Yangtze. The changingriver flow will inevitably alter the downstream channelmorphology. Unfortunately, our knowledge about thecurrent Yangtze River flow regime is poor, and it wouldbe difficult to understand and predict such changes in-channel morphology and relate it to fluvial manage-ment. The objective of the present study is to establish ahydromorphological database before and during theconstruction of the Three Gorges Dam. An acousticDoppler profiler, widely tested in rivers and estuaries(Yorke and Oberg, 2002; Filizola and Guyot, 2004;Kostaschuk et al., 2005), has been used for this purpose.This will help to facilitate future studies of the Yangtzedrainage basin by providing a research data base.

Fig. 1. The Yangtze River trunk channel from Chongqing to the river mouth (with the three reaches on the river mentioned in the text.

2. Data and methodology

The Yangtze trunk channel, from the river mouth nearShanghai to Chongqing and back was surveyed duringthe non-flood season, from 7 May to 8 June 8, 2002,using a Sontek 500 Hz acoustic Doppler current profiler(ADP). A differential global positioning system (DGPS)accurate to 1.0 m was used along the middle and lowerYangtze. A global positioning system (GPS), accurate toabout 10 m, was used in the Three Gorges reach of theriver, as the distance was too vast from the beacon stationon the east China coast. The ADP used for the presentstudy can sample at 1.0 m interval to water depths of100 m (see Kostaschuk et al., 2005, for detailedmethodology). The ADP was positioned 1.0–1.5 mbelow the water surface for all surveys. Velocity profileswere averaged over one minute interval and the averagedepth determined. During surveying, maintenance forthe ADP was carried out daily. An echo Sounderpositioned at the bottom of the boat provided higherresolution information on the water depth and riverbedmorphology, which was used to corroborate the ADPdepth estimates.

The boat was navigated along the thalweg of themain channel. A traverse cross-section of the riverchannel was also made upstream of the Gezhou Dam,

about 2100 km). Three-Gorges Dam and Gezhou Dam are shown along

Fig. 2. ADP-flow velocity regimes of the upper (A), middle (B) and lower (C) Yangtze reaches. Marked are the river-water surface gradient, riverwidth and average flow velocity (data sources: The Navigation Survey Department of Chinese Navy Headquarters, Navy Watercourse Plot of P.R.C.1954; 1997; 2002). Numbers from 1–39 and – (A); 40–53 and – (B), and 54–66 and – (C) denote measured river cross-sectionalareas discussed in the text. Numbers without frame indicate the area with high-flow regime, and ones with frame low-flow regime.

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Fig. 3. A) selected river cross-sections from the upper Yangtze Three-Gorges valley with sites of the high and low velocity zones. Numbers (2, 8, 10, 13, 22, 26, 32, 37, – ) of the cross-sections are

shown on Fig. 2A, B) selected river cross-sections from the middle Yangtze River valley with sites of the high and low velocity zones. Numbers (42, 45, 47, 49, 51, 52, , , , , , ) of

the cross-sections are shown on Fig. 2B; C. selected river cross-sections from the lower Yangtze River reaches with sites of the high and low velocity zones. Numbers (54, 57, 60, 61, 64, 66, , ,, , , ) of the cross-sections are shown on Fig. 2C.

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about 30 km downstream of the Three Gorges Damsite(Fig. 1). The river mouth to Chongqing and Chongqingto river mouth datasets were very similar, so only theChongqing to river mouth set of measurements was usedfor the present study. River surface water levels, widths,and the cross-section morphology were determined froma series of maps collected. The morphology of the riverbasin and the channel topography were obtained fromthe ‘Atlas of Changjiang River Basin’, issued by theChangjiang River Water Resources Commission (1999).

3. River-flow velocity in relation to fluvial variables

3.1. The Three Gorges of the upper Yangtze(Chongqing–Yichang)

Since there was little rainfall during the survey periodand there are few large tributaries in the Three Gorges, adischarge of about 15,000 m3 s−1 was estimated on thebasis of the ADP cross-section measurement in the

Fig. 4. A) Correlation between selected cross-sectional areas and flow velocityto the sites indicated Fig. 2A; B) Correlation among cross-sectional area, riv

Gezhou Reservoir, a value similar to that forecastedfrom the local hydrological gauging station. The flowprofile clearly differentiates between upper, middle andbottom layers (Fig. 2A). The average flow velocity ofabout 3.0 m s−1 occurs in the upper and middle layersand 1.0–2.0 m s−1 appears at the bottom (Fig. 2A).

Given the width, water depth and flow velocity of theYangtze, this section of the river through the mountainscan be divided into two units: Chongqing–Wanxianupstream of the gorges and Wanxian–Yichang that in-cludes the three gorges. The average flow velocity fromChongqing to Wanxian (about 300 km long; Fig. 1)fluctuates in-phase withmeasured river width. Higher andlower flow velocity regimes alternate throughout thissection (Fig. 2A). Fig. 2A indicates 20 sites (Nos. 1–20,Fig. 2A) with flow velocity ranging from 3.0 to 4.0 m s−1

where the river channel is wider (N1000 m) and the waterdepth is shallower (b20 m). Large (commonly N500 mlong and N200 m wide) gravel shoals prevail in theselocations (cross-sections 2, 8, 10, 13; Figs. 2A, 3A). In

of the upper Yangtze Three-Gorges valley. Measured sites corresponder width and water depth measured at the same sites as above.

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addition, six sites (Nos. – , Fig. 2A) with low-flowvelocities (b1.5 m s−1) were recorded in the river sectionfrom Chongqing to Wanxian, where the water is deeper(N40 m, cross-sections – on Fig. 3A) in a U-shapedchannel morphology. Between Chongqing and Wanxianthe flow velocity is inversely correlated with channelcross sectional area and river width and positivelycorrelated with water depth (Fig. 4).

Flow velocity from Wanxian to Zigui downstream(about 230 km long; Fig. 2A) is usually greater than thatof the Chongqing–Wanxian section. The average flowvelocity in the middle and upper water layers is between3.0–3.5 m s− 1, with the maximum at 6.0 m s−1 at theWu Gorge, the middle of the three gorges (Figs. 1, 2A).Locations of high velocities are associated with deeperchannels, as evidenced at 19 sites with deeper water(N50 m) and a narrower (b600 m) channel (Fig. 2A;measurement sites 21–39). This river section is dom-inated by a V-shaped morphology (Figs. 2a and 3A,

Fig. 5. A) Correlation between cross-sectional area and flow velocity of the mFig. 2B. B) Correlation among cross-sectional area, river width and water d

cross-sections 22, 26, 32), and one with two paralleltroughs ear Zigui (Figs. 2a and 3A, cross-section 37).There are 3 sites in this section with low-flow velocity ofb2.0 m s−1 (Fig. 2A, sections – ).

The flow velocity of the 22 sites from Wanxian–Zigui is inversely correlated with cross-sectional areaand depth as in the upstream section (Fig. 4A; Wanxianto Zigui), indicating high velocity in deeper riverchannels with a V-shaped valley (Fig. 3A, sites 22, 26,32). A low velocity zone (b1.0 m s−1) occurs belowZigui, about 100 km upstream of the Gezhou Dam(Fig. 2A).

3.2. The middle Yangtze (Yichang–Hukou)

The average discharge during the survey of the mid-dle Yangtze reach was about 40,000 m3 s−1 (Chang-jiang Water Conservancy Commission, 2002). Theaverage flow velocity below the gorges was much

iddle Yangtze River. Measured sites correspond to the sites indicated inepth measured at the same sites as above.

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lower, ranging from 1.3 to 1.8 m s−1, but the maximumreached 2.0–2.5 m s−1 at several sites (Fig. 2B). Theoccurrence of several high and low velocity zonesindicates a pattern that reflects high velocity in deepwater and low velocity in the shallows. There are also atleast 6–8 shorter fluctuations of flow velocity in the400 km reach from Yichang to Loushan (Fig. 2B) andtwo longer fluctuations between Loushan and Hukou(about 420 km). High velocity locations are in straighterchannels and low velocity ones in more sinuous reaches(Figs. 1, 2).

These measurements show that the deep riverchannels with high-flow velocity are narrower (900 to1400 m) and have U-shaped cross-sections (Figs. 2B and3B, cross sections 42, 45, 47, 49, 51, 52). Shallow riverchannels with low velocity are wider (1600–4800 m)and have irregular cross-sectional shape (Fig. 3B, ,

, , , ). There is thus a negative correlation

Fig. 6. A) Correlation between cross-sectional area and flow velocity of the loFig. 2C. B) Correlation among cross-section area, river width and water dep

between flow velocity and river cross-sectional area(Fig. 5A). High flow velocities were also recorded atseveral confluences in the middle Yangtze reaches, suchas the Chenglingji outlet for Dongting Lake and theconfluence with the Hanjiang near Wuhan (Figs. 1, 2B,5A). Of particular interest is the zone of extreme lowflow velocity at Wuxue, the very deep (N90 m) andnarrow (about 1200 m) section of the reach (Figs. 1, 2B,3B, section ).

3.3. The lower Yangtze (Hukou–Jiangyin)

The lower Yangtze was carrying about 45,000 m3 s−1

during the survey (ChangjiangWater Conservancy Com-mission, 2002). No major tributaries join the Yangtze inthis section, except the junction with the drainage fromBoyang Lake (Fig. 1). The average flow velocity of thelower Yangtze ranged from 1.4 to 1.8 m s−1, with a

wer Yangtze River. Measured sites correspond to the sites indicated inth measured at the same sites as above.

Fig. 7. Scatter plot of the correlation between cross-sectional area andflow velocity in the upper, middle and lower Yangtze River channels.Uh and Ul represent the upper Yangtze high and low velocity zones; Mrefers to the middle Yangtze unidentified flow zone; Lh and Llrepresent the lower Yangtze high and low velocity zones.

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maximum above 2.0 m s−1. High- and low-velocityzones alternated throughout the section (Fig. 2C). Highflow velocity occurred in deep, straight reaches and thelow flow velocity in shallower water depths (Fig. 2C). Alocal high-velocity zone occurs at the confluence withBoyang Lake due to additional discharge at this point(Fig. 6A). The cross-sectional area of the lower Yangtzecorrelates better with water depth than with river width(Fig. 6B). Amajor low-velocity zone (about 20 km long)exists in the lower reach, about 350 km from the coast(Fig. 2C), where the average flow velocity is only about0.5 m s−1.

4. Riverbed topography

4.1. The Three-Gorges of the upper Yangtze(Chongqing–Yichang)

The 660 km of the river is bedrock-controlled, withelevation differences about 2000 m between the moun-tain tops and valley bottoms. Our survey data indicatedthat the deeply incised river into the valley can bedivided into two sections as discussed earlier. Conside-rable relief and changes occur in the riverbed and thewater depth ranged from 20 m to 50 m (Fig. 1) alongthe 300 km Chongqing–Wanxian section. The 350 kmlower section from Wanxian to Yichang shows evengreater variation in bed morphology and water depthsranged from 40 m to 80 m with a maximum near100 m at Shibei in the Xiling Gorge upstream of theGezhou Dam (Figs. 1, 2A) The riverbed topography

from Wanxian to Yichang is commonly 10–70 mbelow the present mean sea level (msl). The watersurface slope gradient in the reach is 0.000147 duringthe survey.

4.2. The middle and lower river (Yichang–Jiangyin)

The Yangtze below Yichang changes suddenly to alow gradient channel with water depths (during thesurvey) of 10–15 m between Yichang and Luoshan and30–35 m between Luoshan and Hukou. The maximumwater depth at several river sites reached 60–90 m,especially at Chibishan andWuxue, where local bedrockoutcrops occur (Figs. 1, 2B). The riverbed elevationfrom Yichang to Wuhan (Hankou) is mostly above msl,and gradually drops below msl from Wuhan to Hukou.There is a deep trough in the riverbed (20–30 m) im-mediately below the Gezhou Dam (Fig. 1). The overallwater surface slope gradient of the middle Yangtze Riverduring the survey was 0.000033.

The riverbed of the lower Yangtze River channel,starting from Hukou to the river mouth area, has morerelief than the middle Yangtze. The water depthdeepens to 20–40 m and can be up to 70–90 m insome places, e.g., Madang, Digang, Wufengshan, andJiangyin (Figs. 1, 2C). The riverbed drops 10–40 belowmsl. The water depth near the river mouth tends to beshallower (10–20 m) and the water surface slope of thelower river channel decreased during the survey to0.000008.

5. Interpretation

5.1. Hydromorphology

River discharge (Q) is related to cross-sectional flowvelocity (V) and cross-sectional area (A). as Q=A×V.Since there was little change in discharge during sur-veying, it is expected that the flow velocity measured atThree Gorges section should vary inversely with cross-sectional area (Figs. 2–4A,B). The high velocity zonesbetween Chongqing andWanxian occur in the wider andshallow reaches with many large-scale gravel shoals,summing to smaller cross-sectional areas (Figs. 2A, 3Aand 4A). From Wanxian downstream to Zigui, a rock-cut channel with narrow and V-shaped cross-sections setin a deep valley indicated a smaller cross-sectional areaand high velocity zones (Fig. 7).

In comparison, the velocity regime in the middleand lower Yangtze channel had weaker correlationswith morphology than the upstream valley, especiallyin the middle Yangtze River. This could result from a

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flatter channel topography where discharge, gradient,river cross section and flow velocity are poorlycorrelated (Thorne et al., 1997). In addition, severallarge tributaries enter the middle and lower YangtzeRiver reaches, increasing the discharge and loweringthe correlation between river channel cross section andflow velocity.

Numerous alternating, short-reaches of high and lowvelocities from Yichang to Luoshan downstream (Fig. 1,Jingjiang Reach) are associated with the meanders thatdominate the middle Yangtze. In the early 20th century,many meander cut-offs occurred in the region due tosiltation, leading to river engineering works designed toprevent breaches of the banks, a major cause of flooding(Yang and Tang, 1998; Yin et al., 2007-this issue). TheADP measurement, in combination with on-site fieldinvestigation of the present study verified that the highvelocity is related to straighter reaches and low velocityto meandering courses. The two long sections of highervelocity from Luoshan to Wuhan (Hankou) and fromWuhan to Hukou are probably due to the reaches beingstraighter (Figs. 1, 2B).

Velocity regimes slow down in the lower Yangtze dueto the presence of longitudinal sand bars and bedrockoutcrops (Chen et al., 2001; Shi et al., 2006-this issue).Recent engineering works to prevent bank avalanchinghave also resulted in a narrower river channel increasingthe velocity of the river (Institute of Geography, ChineseAcademy of Sciences, China, 1985).

The low velocity zone 50 km above Jiangyin near theriver mouth reflects the interaction between the riverflow and estuarine tides (Fig. 2C). The average tidalrange along the Yangtze coast is about 2.7 m, but it canreach N5.0 m during the astronomical season (Chenet al., 1988). Previous studies showed that the tidalinfluence (salt-wedge intrusion) can extend to Nanjing,about 400 km from the coast, 150 km above Jiangyin.Presumably, the position and extent of this low velocityzone would vary with tides and river discharge.

5.2. Controls on the riverbed

The Three Gorges of the upper Yangtze has a chan-nel 60–100 m deep and 10–70 m below msl. Thisreflects the intense tectonic uplift that has resulted indowncutting of the river system, mostly during the earlyto middle Pleistocene (Li et al., 2001). This is par-ticularly well illustrated by the deeply incised riverchannel (80–100 m) at Quantang, Wu, and XilingGorges between Wanxian and Yichang. The high topo-graphic relief is represented by the steep water surfacegradient (0.000147).

The shallower river channel of the middle Yangtzewas associated with the rapid sediment accumulationin the subsiding Jianghan and Dongting Lake basinsduring the Quaternary (Huang et al., 1965; Yang andTang, 1998). The thickness of the Quaternarysediment reaches about 200–350 m in the basin.The sudden change of slope from the upper ThreeGorges section to 0.000033 in the middle Yangtzeresults in a rapid deposition of sediment supplied fromupstream. More than 100 Mt of sediment haveaccumulated annually in the middle Yangtze basin inhistorical times, causing channel aggradation andassociated large floods and channel breaches (Instituteof Geography, Chinese Academy of Sciences, China,1985; Changjiang Water Conservancy Commission,2001; Chen et al., 2001; Du et al., 2001; Yin et al.,2007-this issue).

The lower Yangtze is characterized by more variablebed relief than the middle river, such as deeper riversections (70–90 m) and the occurrence below msl.Eastward-tilting tectonic subsidence during the Pleisto-cene (Geological Institute, China Academy of Sciences,China, 1958; Huang et al., 1965) seems responsible tothe presence of the bed relief. Deeper channels are oftencombined with local bedrock outcrops and terraces ofQuaternary age which intensify channel erosion. Alter-nating sections of deeper channels are also associatedwith sandy bars in what has been termed a goose-headanabranching river pattern (Institute of Geography,China Academy of Sciences, 1985). The shallow river-bed near the river mouth area (Chen et al., 1988) is dueto estuarine siltation related to the low-flow velocityzone (Fig. 2C).

5.3. Effect of the Gezhou Dam

The Gezhou dam near Yichang was completed bythe end of 1970s, causing an upstream rise of 27 m inwater level and a backwater effect of 150 m (Fig. 1).Accordingly, heavy siltation has occurred behind thedam on the former riverbed, extending about 20 kmupstream from the dam site. Also, riverbed erosion of20–30 m immediately below the dam site has beenobserved (Fig. 1). The low-flow velocity of b1.0 m s−1

on average, as revealed by the ADP survey in theGezhou Reservoir (Fig. 1) is due to the post-dam effect,which highlights the possible future problems of theThree Gorges Reservoir regarding transport of fine-grained suspended sediment (mainly silty clay) to thecoast. This reduction in supply of fines to the coast islikely to lead to reducing deposition on the delta andcoastal erosion.

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6. Closing remarks

The ADP survey revealed important hydromorpho-logical features of the Yangtze River channel and em-phasized the potential for similar surveys in other largerivers of the world. Water levels in the Three GorgesDam will be regulated between 145 and 175 m after2009, leading to a range of impacts on fluvial envi-ronment change and related management. This studyprovides a pre-dam database that can be used both topredict changes due to the dam and to serve as a basis forcomparison with similar surveys that could be con-ducted well after the dam's completion.

Acknowledgements

The authors greatly appreciate the help from forProfessor R.A. Kostaschuk and Dr. G.F., Yang, whokindly reviewed the manuscript critically. Thanks shouldbe also extended to senior engineer Y.Z. Xue, assistantengineer J.H. Gu, for their generous assistance in fieldsurvey. F.L. Yu and Y.H. Li helped with data processing.The China National Natural Science Foundation (GrantNo. 40341009), APN/START (Grant No. 2004-06-CMY),and theGlobal EnvironmentResearch Fund of theMinistryof the Environment of Japan supported this project.

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