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Management of the Three Gorges Dam

Zhao-Yin WangProfessor, Tsinghua University

Chairman, Advisory Council of IRTCESVice President of IAHR

Chief Editor “International Journal of Sediment Research”

Outline1 Construction of the Three Gorges

Dam2 Sedimentation and Management

strategies3 Emigration and Resettlement4 Environmental and Ecological

Impacts and management strategies

1. Construction of the Three Gorges Dam

The Yangtz River 6300 km long ,1.8million km2, Total annual runoff (Datong) 1000 billion m3 (37%)The Three Gorges 192 km (Qutan, Wuxia and XilingGorges).Dam site Sandouping 38 km upstream from the Gezhouba dam. Project consists of dam, power stations and navigation structures.

Beautiful three gorges

TGP(CHINA)

Itaipu(BRAZIL)

Grand Coulee(USA)

Guri(VENUZUELA)

Tucurui(BRAZIL)

Aswan(EGYPT)

MW

Comparison Between TGP and World Power Comparison Between TGP and World Power stations stations

Instalation Capacity MW

18200

12600

10830

10300

8000

2100

Main Purposes of the Project • Flood Defense • Power generation 18200 MW - 85 billion

kwh/a=50mton coal; • Shipping - Yichang-Chongqing 660 km with

120 m drop, 130 dangerous shoals and 46 one-way sections

With TGP 10000 tons towboats to ChongqingShipping capacity from 10 mt to 50 mt (2005:

795 mt; 2008 1.2 bt)

Flood disasters

• 214 disastrous floods / 2000 years• 1931 - 3.4 mha, 145000 lives• 1935 -1.5 mha, 142000 lives• 1954 - 3.17 mha, 33000lives, $10 billion• 1998 - 0.33 mha, 2292 lives, $20 billion,

1.6 m were evacuated, 6 m houses damaged,

FLOOD IN WUHAN 1935FLOOD IN WUHAN 1935

Floods in 1998Floods in 1998

The floods (The floods (dischagedischage at the3 at the3

dam site was 67000 m3/s) dam site was 67000 m3/s)

caused a direct loss of about caused a direct loss of about

100 billion Yuan 100 billion Yuan （（about 12 about 12

billion $billion $）） in 1998.in 1998.

The JingJiang Grand LeveeThe JingJiang Grand Levee

Flood defense capacity before TGP

• 3600 km grand levees along the Yangtze River

• 30000 km levees on the tributaries and riparian lakes

• Tongting lake clip peak by 10000 m3/s• Several flood diversion basins• Gezhouba Dam with no flood control

capacity• Capacity- control 20 years flood

Wuhan

ChenglingjiYeyang

Jianli

Shishou

Zhicheng

Songzikou

Shashi

Gezhouba Project

Three Gorges project

Yichang

Major City

County Town

Levee

Flood-diversion Area

Lake

Hanjiang R.

Lishui

Qingjiang R.

Tong ting Lake

Yangtze R.

Yangtze R.

River0 50km

Flood defense system of the middle and lower reaches

Model of the Gezhouba dam

1993-1997

1998-2003

2004-2009

1993

1995

June 1997

The TGP in 1997The TGP in 1997

Nov. 1997




Oct. 2002

Closure of the open channel Nov. 2002


TGP in 2003TGP in 2003


Oct. 2004

2004

Oct. 2004

2000

2002

Power house 2002

2002

Flood control with TGP

• Management of flood: The dam stores flood water if the discharge is exceeds 56,000 cms to guarantee the stage at Shashi can not exceed 45 m

• The food discharge in 2010 was 70000 m3/s, higher than the 1998 flood. The reservoir was operated to store water and released flood discharge was between 40000-45000 m3/s, which successfully controlled the flood and reduced the flood loss to the minimum

2 Sedimentation and Management strategies

The main sedimentation problems are:

1) Reservoir sedimentation and permanent use of the reservoir capacity for flood control;

2) Sedimentation in the navigation channel in the fluctuating backwater zone;

3) Sedimentation in the vicinity of the dam; 4) Degradation in the downstream reaches;

1) Permanent Use of the ReservoirSedimentation in the reservoir depends on the operation scheme and pool levels The main sedimentation control strategies isStoring the clear and releasing the turbid –During the flood season (June-Sept), when the river carries 90% of the annual sediment load and 61% of the annual runoff, the pool level is drawn down to flood season pool level to create a condition in favor of sediment sluicing. After the flood the sediment concentration is low and the reservoir store water for power generation during winter and spring and the pool level rises to the normal pool level.Normal pool level (NPL) is set at 175 m. Flood season pool level (FCL) is 145 m.

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175

Jan April July Oct. Dec.

Jan April July Oct. Dec.

Reservoir pool level

E (m

)0

2

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6

S (k

g/m

3 )

Sediment concentration at Yichang

Storing the clear and releasing the turbid - During the flood season, when the river carries 90% of the annual sediment load and 61% of the annual runoff, the pool level is drawn down to 145 m to create a condition in favor of sediment flushing.

Annual runoff at the dam site = 450 bi m3

Annual sediment load = 532 mi tons (0.8 mi tons gravel bed load). Median diameter = 0.033 mm (24 mm for bed load)

Five operation schemes have been simulated and the accumulated sedimentation volume is a function of the pool levels:

Calculation results with the YVPO model

• 1-D numerical model calculations for 106 years:

• As the recurrence period of the 1954 flood is approximately 40 years, the stream record of 1954 was inserted into the hydrological series in such a manner that it appears three times in 106 years:

• 2 cycles of 1961-1970 plus 1954, 1955; • 2 cycles of 1961-1970 plus 1954, 1955• 4 cycles of 1961-1970 plus 1954, 1955; • 2 cycles of 1961-1970

1-D model: River bed profile after 100 years operation and the original river bed profile.

Sedimentation volume from 2003-2012• In the first 10 years operation of the TGP Dam

the sedimentation volume was only 40% of the modeling results.

• In the upstream the construction of the Xiangjiaba and Xiluodu dams trap sediment and reduce the sediment load into the TGP reservoir.

• It is estimated that about 30 million tons of fine and coarse sand and gravel are mined for building materials per year, which has reduced the sedimentation in the reservoir.

XiangjiabaXiangjiaba Dam Dam 1020 km upstream of the TGP dam with a capacity of 5.06 billion m3 and power instalation capacity of 6000MW

XiluoduXiluodu Dam Dam 1180 km from TGP dam with a storage of 11.6 billion m3 and power instalation capacity of 12600 MW

0

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0 10 20 30 40 50 60 70 80 90 100Year of operation

Sedi

men

tatio

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lum

e (1

08 m3 )

Scheme 1

Scheme 2

Scheme 3

Calculated sedimentation volume in the TGP reservoir for the three scenarios: Scheme 1 = without upstream dams; Scheme 2 = with Xiangjiaba Reservoir; Scheme 3 = with Xiangjiaba and Xiluodu Dams

Gravel mining in the upper Yangtze basin

Sediment mining

2) Sedimentation in the Fluctuating Backwater zoon

• The fluctuating backwater zoon is the river reach with flood stage between 145 and 175m.

• There is a passenger ship harbor-Chaotianmen harbor, and a freight ship harbor-Jiulongpo Harbor (602 km).

• Sedimentation in the zoon affect the navigation channel

Permanently preserved storageNPL

FCL

Dam

Sediment depositionFluctuating backwater

region

• Two major problem are to be addressed :1) whether sedimentation would affect the navigation channel suitable for the navigation of 10000 ton tows, and

2) whether sedimentation would affect the Chaotianmen and Jiulongpo Harbors in Chongqing.

• The problems were studied with physical models.

• The results showed that the sedimentation in the channel and harbors can be minimized by constructing groyins.

Five selected sections of physical model experiments on the influence of sedimentation on the navigation in the fluctuating backwater region of the TGP reservoir.

Sedimentation in the Chongqing reach after 80 years operation of TGP. The shadowed areas indicate the places where cumulative sedimentation would occur (Wang et al. 1986)

3) Sedimentation in the Vicinity of the Dam

• Sedimentation occurs by the right bank in the vicinity of the dam.

• Sedimentation occurs in the upper approaching channel connecting the five step ship locks, which is segregated by a protecting dike.

• Sedimentation in the approaching channel can be controlled with a long dyke separating the approaching channel and the main reservoir water.

Long dykes separating the approaching channel and the main reservoir water.

4) Degradation of the Downstream Reaches• In the downstream reaches, released clear

water scours the riverbed. From January to May the regulated discharge is higher than before TGP but in October and November the regulated discharge is less.

• The sediment load to the downstream reaches is greatly reduced by the trapping of the reservoir. The load reduction causes degradation of the downstream reaches.

• The river bed downstream of the dam has been scoured down by 10-15 m.

Calculated amount of sediment scoured from riverbed of the reach from Yichang to Wuhan in the first 100 years operation of the TGP dam

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0 20 40 60 80 100 120 140Distance from Yichang (km)

Elev

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)

Original bed After scour Flood stage wihtout the dam Stage after scour

Flood stage profiles and bed profiles before and after scouring of the riverbed

Stage-discharge relationship at Yichang before and after the scouring process.

• Although the reservoir is about 1900 km distant from the river mouth, the sediment trap by the reservoir affects the river mouth.

• The sediment load to the estuary has been reduced from 460 mm3 to 130 mm3

• The land creation projects of Shanghai city have been greatly affected. Moreover, the sand bars in the estuary is shrinking due to the sediment reduction.

Land creation planning of Shanghai city in 50 years

3. Emigration and Resettlement

Emigration and Resettlement• A total of 19 counties and cities, 13 county

towns, 140 towns and 4,500 villages are inundated.

• Population dislocated are about 1.2 million, of which 55% urban population and 45% villagers

• Farmland inundated: 23,793 h (paddy field: 7380 hand dry land: 16314 h)

• Highways inundated: 956 km, Factories and mines submerged: 657

Inundated AreasInundated Areas

Areas for Resettlement & RelocationAreas for Resettlement & Relocation

Shibaozhai in Zhongxian county

Relocating new towns

• 13 counties and 114 towns removed• Badong moved to Huangtupo (unstable

and debris flow) and changed to Yuntuo• Wushan moved backward (old landslide

body, after 5 years reconstruction still stable)

Former County Town of ZiguiFormer County Town of Zigui

New County Town of ZiguiNew County Town of Zigui

Former County Town of Former County Town of WushanWushan

New County Town of New County Town of WushanWushan

Former County Town of Former County Town of YunyangYunyang

New County Town of New County Town of YunyangYunyang

Workers are reassembling the sculpture of the corridor of the temple of the river god, which is removed from the reservoir to the new site of the Fenghuang Hill

Resettlement policy

• 60% industries and services (with investment from the central and local governments)

• 40% continue farm production surrounding areas (enhancing productivity 3 times-change the low yield dry farmland into irrigated and paddy fields)

• 67000 ha reservoir surface for aquatic farm

4. Environmental and Ecological Impacts and management strategies

Water quality• About 1 bi tons of waste water and

sewage water are discharging into the reservoir, which caused eutrofication.

• The purification capacity of the river has been reduced and several large events of algal bloom have occurred.

• Pollution control projects have been launched and most of wastewater and sewage water will be treated after the completion of the projects.

Earthquake• In China 5% of reservoirs each with a storage

capacity of more than 100 million m3 have set off tremors.

• Since 1959 China has set up seven seismic monitoring stations in the dam's vicinity. A total of 1,019 shocks of a magnitude of 1 to 4 have been recorded within a 300-km radius of the dam site.

• So far no earthquake has been caused by the dam operation.

• The 2008 Wenchuan earthquake is not caused by the TGP dam. The epicenter is 700 km from the dam.

Landslides • The operation of the reservoir caused

fluctuation in the pool level, which has caused small scale landslides in the Three Gorges reasches.

• The volume of the landslides is limited compare with the reservoir capacity and does not affect the reservoir operation and navigation.

• A new drainage system has been constructed to reduce the ground water table

• Several potential landslide body have been stabilized with piers, anchors and concrete walls

Distribution of potential landslides in the TGP reservoir

Xintan Landslide occurred in 1985 at the left side of the Yangtze River near the Three Gorges Dam: (a) before sliding; (b) after sliding.

A drainage system on a landslide body in the TGP to lower the groundwater table

Concrete walls installed to stabilize the sliding body.

Schematic of anchors and concrete piers for stabilizing slopes

Limestone

Highway

original surface

Concrete pier

anchors

Sandstone

Ecological Impacts• 20 days later for the river water temperature to

rise to the spawning temperature• 8 spawning grounds must be moved upstream,

12 affected• Red list species- Chinese sturgeon (spawning

ground downstream); white-flag dolphin, and Yangtze dolphin are affected by the dam and artificial spawning has successfully applied for Chinese sturgeon.

l

YANGTZE DOLPHINYANGTZE DOLPHIN

Fisheries (Chinese carps)

• Fishery in the Yangtze River is important. The four chinese carps are the main fishery species: Black carp, silver carp, grass carp and big head carp.

• Reservoirs inundate vast spawning-grounds.• The species eggs must be kept floating for

incubation. The dam reduces the flood stage rising that the fish receive no enough signal for spawning.

• The TGP Dam causes scouring and incision of the downstream reaches. Fish can not swim between the rive and the Tongting lake, as a result the flux fry has reduced by 98%

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stage at YichangFish spawning stage at JianliFish spawning

Stage variation at Yichang and Jianli under natural conditions andthe spawning time of fishery species (Cao et al., 1987) ;

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Flux

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Relationship between the discharge increment and flux of fries

• The Tongting Lake regulates the flood flow in the middle reaches of the Yangtze River.

• The ratio of flood water diverted into the Tongting lake through the 3 channels has greatly reduced.

• The river bed has been incised down by more than 10 m and the connection between the river and the Tongting lake has greatly reduced.

• Chinese carps spawn in the river and feed up in the lake. The cut off of the lake and river affect the fish harvest greatly. The flux of fish fry has been reduced by 98%.

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Annual amount of water and sediment diverted from the Yangtze River into Tongting Lake during the flood season (data from Sediment Panel, 2009).

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Measured bed cross sections of the middle Yangtze River at Baiyanghe, 88 km downstream from the Three Gorges Dam (data from Sediment Panel, 2009).

Case 3 Restoration of the incised middle Yangtze River due to impoundment of TGP

Conclusions

• The operation of the TGP dam successfully mitigates flood hazards.

• The sediment management strategy “store the clear and release the turbid” effectively reduces the reservoir sedimentation.

• TGP caused erosion and channel bed incision in the downstream reaches, and partly cut off the connection of the Tongting lake and the river, which greatly impair the ecology and fishery.