Management of the Three Gorges Dam

Management of the Three
Gorges Dam
Zhao-Yin Wang
Professor, Tsinghua University
Chairman, Advisory Council of IRTCES
Vice President of IAHR
Chief Editor “International Journal of Sediment
Research”
Outline
1 Construction of the Three Gorges
Dam
2 Sedimentation and Management
strategies
3 Emigration and Resettlement
4 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 Xiling
Gorges).Dam site Sandouping 38 km upstream from the
Gezhouba dam. Project consists of dam, power stations and
navigation structures.
Beautiful three gorges
Comparison Between TGP and World Power
stations
MW
Aswan(EGYPT)
2100
Tucurui(BRAZIL)
Guri(VENUZUELA)
8000
10300
10830
Grand Coulee(USA)
12600
18200
Itaipu(BRAZIL)
TGP(CHINA)
Instalation Capacity MW
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 Chongqing
Shipping 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 1935
Floods in 1998
The floods (dischage at the3
dam site was 67000 m3/s)
caused a direct loss of about
100 billion Yuan （about 12
billion $） in 1998.
The 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
Three Gorges project
Gezhouba
Yichang
Project
Yangtze R.
Qingjiang R.
Zhicheng
Han
jiang
R.
Wuhan
Shashi
Songzikou
n
Ya
Jianli
R.
e
g tz
Shishou
i
Lishu
Chenglingji
Yeyang
Major City
County Town
Tong ting
Lake
0
50km
Levee
Flood-diversion
Area
Lake
River
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 1997
Nov. 1997
The TGP in 1998
The TGP in 1999
The TGP in 2001
Oct. 2002
Closure of
the open
channel
Nov. 2002
The TGP in 2002
TGP in 2003
The TGP in 2004
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 Reservoir
¾ Sedimentation in the reservoir depends on the
operation scheme and pool levels
¾ The main sedimentation control strategies is
Storing 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.
¾ Normal pool level (NPL) is set at 175 m.
¾ Flood season pool level (FCL) is 145 m.
6
Sediment concentration at Yichang
3
S (kg/m )
4
2
0
Jan
April
July
Oct.
Dec.
175
Reservoir pool level
170
E (m)
165
160
155
150
145
Jan
April
July
Oct.
Dec.
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.
Xiangjiaba Dam 1020 km upstream of the TGP dam with a
capacity of 5.06 billion m3 and power instalation capacity of 6000MW
Xiluodu Dam 1180 km from TGP dam with a storage of
11.6 billion m3 and power instalation capacity of 12600 MW
180
Sedimentation volume (10 8m3)
160
140
120
100
80
Scheme 1
60
Scheme 2
40
Scheme 3
20
0
0
10
20
30
40
50
60
Year of operation
70
80
90
100
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 harborChaotianmen harbor, and a freight ship
harbor-Jiulongpo Harbor (602 km).
• Sedimentation in the zoon affect the
navigation channel
Permanently preserved storage
NPL
FCL
Dam
Fluctuating
backwater
region
Sediment deposition
• 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
40
Elevation (m)
35
30
Original bed
After scour
Flood stage wihtout the dam
Stage after scour
25
20
0
20
40
60
80
Distance from Yichang (km)
100
120
Flood stage profiles and bed profiles before and after
scouring of the riverbed
140
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 Areas
Areas 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 Zigui
New County Town of Zigui
Former County Town of Wushan
New County Town of Wushan
Former County Town of Yunyang
New County Town of Yunyang
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 timeschange 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.
Concrete walls installed to stabilize
the sliding body.
A drainage system on a
landslide body in the TGP
to lower the groundwater
table
original surface
anchors
Highwa
Sandstone
y
Limestone
Concrete pier
Schematic of anchors and concrete piers for stabilizing slopes
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 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%
36
46
35
45
34
44
33
43
32
stage at Yichang
Fish spawning
stage at Jianli
Fish spawning
42
41
40
5-10
31
30
29
5-20
5-30
6-9
6-19
6-29
Stage variation at Yichang and Jianli under natural conditions and
the spawning time of fishery species (Cao et al., 1987) ;
stage at JianLi (m)
stage at Yihang (m)
47
2.5
Flux of fries (billion)
2
1.5
1
0.5
0
0
2000
4000
6000
3
△ Q(m /s)
8000
10000
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%.
200
300
Water
160
Sediment
250
9
200
6
3
Water (10 m )
140
Sediment (10 t)
180
120
100
150
80
100
60
40
50
20
0
1956
0
1966
1976
1986
1996
2006
Year
Annual amount of water and sediment diverted
from the Yangtze River into Tongting Lake during the flood
season (data from Sediment Panel, 2009).
Case 3 Restoration of the incised middle Yangtze River due to impoundment of TGP
60
2002
2007
Elevation (m) 1
50
2006
2008
40
30
20
10
0
-10
0
100
200
300
400
500
600
700
800
900
1000
Distance (m)
Measured bed cross sections of the middle
Yangtze River at Baiyanghe, 88 km downstream from
the Three Gorges Dam (data from Sediment Panel, 2009).
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.