Downstream Environmental Impacts

by Joseph S. Larson, Ph.D.

The
impacts which may occur downstream do not affect the overall
environmental feasibility and may indeed enhance the environment.¹

This chapter criticizes the
adequacy of the CYJV feasibility study with respect to its assessment
of downstream environmental impacts. The impact of dams on river
systems has all too often been poorly understood, which has led to
costly and irreversible changes which have had a dramatic impact on
local and regional economies, resources and people.

Downstream of the Three Gorges, there are six
areas which would be subject to impacts: the middle reach of the
Yangtze River between the existing Gezhouba Dam at Yichang down to
Wuhan; Dongting Lake; the Yangtze mainstem between Wuhan and Datong;
Poyang Lake; the estuary; and the coastal/marine area.

• The middle and lower reach extends 1170 kilometres from
  Yichang to Datong. An estimated 75 million people live in this region
  of the Yangtze River basin, which encompasses roughly 60,000 square
  kilometres. Based on its environmental characteristics, the middle
  and lower reach area is further subdivided as follows:
• The middle reach meanders 700 kilometres from Yichang
  to Wuhan, cutting through a wide and low-lying fertile floodplain
  known as the Jingbei Plain. With an average depth of 10 metres, the
  river channel is completely dyked in to protect the surrounding area
  from flooding. Roughly 30,000 kilometres of dykes form part of an
  extensive flood protection system throughout this region.
• Dongting Lake in Hunan province acts as a natural flood
  storage reservoir for the Yangtze River and is strongly influenced
  by flows and water levels in the Yangtze River as well as other tributaries
  flowing into it.
• The Yangtze mainstem, extending 500 kilometres from Wuhan
  to Datong, is flanked by a large, fertile alluvial plain. Broader
  and shallower than the middle reach, varying from three to seven metres
  in depth, the river divides into several channels and islands. Wuhan
  is the final inland port accessible to ocean-going vessels.
• Poyang Lake in Jiangxi province is influenced by the
  seasonal high-water levels in the Yangtze River as well as in the
  rivers in Jiangxi province which flow into it. When water levels are
  high in the Yangtze, Poyang Lake is unable to drain into the Yangtze,
  and the lake spreads out over the surrounding plains.

Yangtze River Hydrology

To
understand the impact the Three Gorges Project would have on downstream
areas, the hydrological characteristics governing the river system must
first be understood. The volume, timing, periodicity, and duration of
water flows, and the dissolved and suspended soil sediment carried,
dictate the fate of downstream fisheries, farming, water quality,
wildlife and estuarine life.

The extent to which the Yangtze River influences
water levels downstream of Three Gorges depends on a number of factors:
flood flows from the upper reaches, timing of regional monsoon
precipitation, and tributary flood patterns in the downstream lake
region. During the rainy season, the two floodplain lakes, Dongting and
Poyang, accept back flow from the Yangtze. But when local flooding
coincides with the Yangtze’s peak flood flows, water is diverted to the
vast Jinjiang Flood Diversion Area and a huge flood spreads over the
land.

CYJV bases its assessment mainly on the 1985
Chinese environmental impact statement which is seriously flawed
because it considered hydrology only as it related to flood control,
power generation and navigation; downstream environmental hydrologic
characteristics are not documented.*

CYJV reports that the occurrence of major floods
cannot be predicted, pointing out that many decades may pass without
serious floods and then several may occur within a few years. It notes
that reservoir operations at the dam would change water levels in the
middle and lower reaches of the Yangtze, which would, in turn, modify
water levels in the mainstem, and in Dongting and Poyang Lakes. In the
flood season, daily flood flows would be significantly reduced, and in
the dry season, water levels would fluctuate widely on an hourly and
daily basis. However, CYJV lacks the data required to determine the
actual impact of changes in river levels.²

Yangtze River Sediment

The
transport and deposition of the river’s nutrient-rich sediment is
second only to hydrology in determining the basic character of the
aquatic environment immediately downstream of the dam to the estuary
1850 kilometres away. In the Chinese environmental impact statement,
sediment was discussed only in terms of sediment management in the
reservoir. Initially, the reservoir is expected to trap 60 to 70
percent of the incoming sediment in the reservoir; then after roughly
100 years the reservoir is expected to reach a state of equilibrium
where sediment is neither accumulating nor being flushed out of the
reservoir. However, the lack of a comprehensive analysis of sediment
processes means that the impact of a reduced sediment load remains
poorly understood.

Without documentation of the relationship between
Yangtze hydrology and sediment processes, and downstream ecosystems,
CYJV’s impact assessment is inadequate, particularly with regard to the
following impacts:

• Channel degradation

Once
the river loses its sediment to the reservoir, it would gain more power
to erode its channel and banks downstream. CYJV expects the increased
erosion downstream could cause the river to shift its course,
threatening all flood protection dykes and low-lying river banks,
thereby increasing the risk of a disastrous flood along the middle and
lower reaches.

An additional problem, which CYJV suggests could
increase channel degradation, would be the mining of sand and gravel
immediately downstream of the Gezhouba Dam. The river would lose a
source of sediment which it normally scours and carries away during
flood flows, thereby causing more of an erosion problem further
downstream.

Yet despite the potential dangers, the available
hydrologic data are not sufficient to make a confident prediction with
respect to this threat, and it is unclear whether the cost of
mitigating channel degradation, either in the short term or long term,
has been included in the cost-benefit calculations.

• Hazardous pollutants

Operation
of the reservoir could induce chemical changes near the reservoir
bottom which would release hazardous pollutants such as heavy metals,
chemical pesticides, and fertilizers. Suspended sediment particles in
the water could distribute the hazardous pollutants downstream. CYJV
notes that the adsorptive capacity of the sediment particles must be
known in order to determine whether pollutants would accumulate in the
reservoir or be dispersed downstream, and to predict the impact this
would have on downstream water quality and fisheries. Despite the
importance of this issue, CYJV merely states that the Chinese
government has evaluated the adsorptive capacity of the three main
types of sediment which would be found in the reservoir. It does not
discuss the results or their impact on downstream water quality and
fisheries.

• Gas bubble disease

The
spillways which would be installed at the Three Gorges Dam are known to
cause gas supersaturation (water supersaturated with air), which
produces a fatal condition in fish and other gilled animals, which is
known as gas bubble disease and is similar to diver’s bends. CYJV
reports that the Chinese government is aware of the potential danger,
but has dismissed it because their investigations at the Gezhouba Dam
indicate little problem among downstream fish fry. The Chinese
government did not provide CYJV with the details of these studies nor
their methodology for verification; and, furthermore, the proposed
spillways are a different design from the Gezhouba spillways.

In Volume 8 on environment, CYJV states that it
is unwilling to dismiss gas bubble disease as a major impact
downstream; and yet, in the study summary (Volume 1), it suggests that
losses in natural fisheries and aquaculture could be compensated for
monetarily or by “enhancement measures” (presumably this means
stocking). No financial, biological, or engineering data is provided to
support this.

Rare and Endangered Aquatic Life

• The Chinese sturgeon, cut off from its traditional
  spawning grounds upstream of the Three Gorges, now spawns in the
  rapidly flowing water 10 kilometres downstream of Gezhouba. CYJV
  acknowledges that sand and gravel mining planned for this area could
  adversely affect the sturgeon, but that the necessary studies to
  examine project effects on this species have not been done. It suggests
  that sturgeon hatcheries could be useful to replace lost spawning
  grounds and to minimize the impact of gas bubble disease, but it is not
  clear whether this cost has been included in the cost-benefit
  calculations.
• The Chinese river dolphin, the rarest
  freshwater dolphin in the world, is found only in the Yangtze’s middle
  and lower reaches and at the confluence of Dongting Lake. According to
  CYJV, there are only 200 to 300 of these dolphins remaining and the
  expected increase in erosion downstream of the dam could adversely
  affect them and the semi-natural dolphin reserves established by the
  Chinese authorities along the Yangtze.* The Chinese environmental
  impact statement did not address the impact of the Three Gorges Project
  on the river dolphins. CYJV recommends more studies and that all means
  available to conserve and protect this species be considered
  appropriate.
• The finless porpoise is commonly found
  along harbours and bays in the coastal area and up the Yangtze into
  Dongting Lake. CYJV predicts that the Three Gorges Project would have
  little impact on the porpoises – a judgment apparently based on the
  assumption that the porpoises have sufficiently adapted to a wide range
  of environments, and would therefore adjust to the environmental change
  caused by the dam.
• The Chinese alligator is found only in the
  lower reaches of the Yangtze. Only 300 to 500 of these alligators
  remain, inhabiting irrigation and storage ponds, rice fields and
  shallow depressions in low-lying plains. CYJV optimistically concludes
  that the impacts of the Three Gorges Project on this species would be
  minimal, and that the real threat to this species is ongoing harvesting
  at a rate that will soon cause extinction.

Dongting and Poyang Lakes

These
shallow low-lying lakes are the largest freshwater lakes in China,
known to support significant and productive fisheries, as well as
aquaculture facilities. Despite this, the Chinese government failed to
provide any substantive information concerning their aquatic
environments and ecology.

• Dongting Lake is China’s second-largest freshwater
  lake and can fluctuate from 600 square kilometres in the dry season to
  2800 square kilometres in the flood season. A nature reserve, adjacent
  to Dongting Lake, provides excellent habitat for birds. Dongting Lake
  acts as a natural flood retention area and a depository for 20 percent
  of the Yangtze’s sediment load carried down through the Three Gorges
  from the upper reaches. Over the past thirty years, the lake’s surface
  area has been reduced by half, losing much of its storage capacity to
  land reclamation and sedimentation. CYJV reports that little is known
  about the dynamics of sediment transport and deposition through the
  lake system.
• Poyang Lake is the largest freshwater lake
  in China and fluctuates from under 1000 square kilometres in the dry
  season to 4000 square kilometres in the flood season. Water, laden with
  nutrient-rich sediment from the Yangtze River and five other rivers,
  provides large areas of rich shallow water (water 10 to 20 centimetres
  deep appears to be critical for cranes) and mud flats* with abundant
  aquatic vegetation. The Poyang Lake Nature Reserve (22,400 hectares),
  adjacent to the lake, provides excellent bird habitat. In 1986, the
  reserve wintered over 95 percent of the world’s population of the rare
  and endangered Siberian crane, plus several other unique or rare crane
  species.**

CYJV notes that the Three Gorges Dam
would change the water levels and the circulation and deposition of
sediment at Poyang Lake, but the study’s lack of quantitative
information makes it very difficult to assess the effect of the dam
operation on crane habitat. Certainly, water level changes in the
growing season would affect the vegetation of the habitat. In Volume 8,
CYJV was unable to estimate what the effects would be and concluded
that a significant potential impact could occur; in Volume 1, CYJV
downplays this concern.

Downstream Agriculture, Fishing, and Aquaculture

Editor’s Note: The author’s observations in this
section are derived in part from a 1986 visit to Poyang Lake and travel
by boat on the Yangtze between Juijang, near the confluence of the lake
and river, and north to Wuhan. The author also draws on data from the
1990 Discussion Draft Management Plan Jiangxi Poyang Lake National
Nature Reserve prepared by D.S. Melville, Director of Conservation,
World Wide Fund for Nature-Hong Kong, Jiangxi Provincial Government.

According
to CYJV, natural fish harvests have declined in the Yangtze River by
roughly 50 percent since the 1950s. And since the Gezhouba Dam was
built in 1981, egg production in several downstream reaches of the
Yangtze has dropped by at least 50 percent. If the Three Gorges Project
is built, CYJV states that changes to Yangtze flows during the months
of April, May and June, when most fish are spawning, could adversely
affect fisheries downstream of the Three Gorges. It further states that
this issue cannot be resolved, since information is inadequate. In any
case, it suggests that other impacts such as overfishing, pollution and
the blocking of spawning migrations into dammed Yangtze tributaries
would mask any changes caused by the Three Gorges Project.

Although CYJV acknowledges that the Three Gorges
Project would affect “the human environment of some 2500 kilometres of
the Yangtze River valley,” it makes only passing reference to the 75
million people living along the middle and lower reaches and the effect
on traditional local agriculture, fishing and aquaculture downstream of
the dam. For the sake of national hydropower development, both the
Chinese government and CYJV have effectively ignored the subsistence
economies along the Yangtze and around the lakes. These economies could
be seriously disrupted and there are few, if any, funds available in
China to compensate people for their loss of livelihood or means of
subsistence.

Between Poyang Lake and the city of Wuhan, the
Yangtze River and its banks and dykes are used extensively by local
fishermen and by farmers grazing livestock. Still common to the area is
the age-old technique of cormorant fishing.* Villagers use the Poyang
Lake Reserve, even though it is flooded to a depth of several metres
for several months of the year, for a wide variety of economically
important activities. For example, they cut grass for fertilizer, grow
subsistence crops, plant trees, fish, plant and cut reeds for paper
making, and collect medicinal herbs to sell.** Around the reserve,
villagers tend about 2500 water buffalo in large herds of up to 400
animals. During the dry months these water buffalo graze on parts of
the reserve. An adequate assessment of the Three Gorges Project would
not ignore local economies in the downstream impact assessment.

Yangtze Estuary, Wetland, and Coastal/Marine Area

It is not possible to totally dismiss the possibility of
significant impacts occurring within the estuary on the basis of
information received to date.³

From Datong, the Yangtze River
branches out into a sprawling delta (or estuary) which stretches 655
kilometres out to sea, and forms one of the largest continental shelves
in the world. Over half of the Yangtze’s annual sediment load is
deposited in the estuary and the remainder is carried by the ocean
currents out to the coastline and continental shelf. Depending on tidal
influence and the seasonal flows of the Yangtze, the river and estuary
waters can be fresh, brackish or salt water.

The Yangtze River estuary is rich in biological
production due to the ongoing deposition of sediment and nutrients from
the Yangtze, and the presence of aquatic species with an affinity for
brackish water. The estuary provides a rich food source for birds and
fish and is also the spawning and nursery grounds for most commercial
fish. CYJV reports that anchovies, herring, eel, crab and shrimp
constitute over 50 percent of the total estuary harvest. But they also
report that, according to the Shanghai Environmental Protection Bureau,
fish stocks in the estuary are declining due to severe pollution,
overfishing, and disruption of fish migration into the dammed
tributaries.

The Three Gorges Project would alter existing
flow patterns and reduce sediment deposition in the estuary. In Volume
8, CYJV suggests that sediment processes may be disrupted for roughly
two hundred years after the dam is in operation, but in Volume 1
concludes that the impact of the Three Gorges Project on the sediment
processes at the estuary would be relatively small. An environmental
impact statement on downstream impacts should have addressed the
relationship between river discharge and marine dynamics, but CYJV
merely states that it found no information on this.

While several Chinese studies are currently
examining the estuary and its potential uses for port and navigation
development, fisheries development, land reclamation and water resource
management, no study of the specific effects of the Three Gorges
Project has been completed. CYJV predicts little impact on aquatic life
in the estuary, but does not provide any supporting evidence.

The Chinese environmental impact statement did
not consider impacts on wetlands adjacent to the river’s middle or
lower reaches or at the estuary. CYJV states that since there is no
information on the wetland environment of the estuary, its assessment
was based on field trips. However, D.S. Melville of WWF-Hong Kong,
reports that the East Shanghai University has studied shorebirds,
intertidal flats,* marsh vegetation and aquatic life in the region.
According to Melville, the mouth of the Yangtze River and nearby
Hangzhou Bay are important wintering grounds for migrant shorebirds,
such as the Great Knot Sandpiper, which probably flies direct to
Shanghai from northwest Australia. Any ecological changes in the
Yangtze estuary could have a devastating impact on the sandpipers.

Salt Water Intrusion

From
December to April, when the flows from the Yangtze into the East China
Sea are low (less than 20,000 cubic metres per second) and ocean
currents are strong, salt water can intrude into the estuary and
tributaries, rendering the water unfit for most purposes such as
drinking and irrigation. In recent years, salt water intrusion has been
occurring more frequently, with disastrous consequences for
agricultural, municipal, and industrial water intakes from the Yangtze
for the city of Shanghai and along the coast.**

The flow of the Yangtze River influences the
pattern and extent of sea water intrusion into the estuary, and
therefore there is considerable concern that the predicted reduced
flows in the Yangtze would increase the risk of salt water intrusion.
The Chinese environmental impact statement dismisses the potential
impacts at the estuary due to salt water intrusion because it assumes
the dam would have a minor impact on average hydrologic conditions in
the estuary, and because of the long distance between the dam site and
the estuary. Although CYJV does not expect that salt water intrusion
would be a problem, it admits that more information is needed.

The coastal/marine area includes the East China
Sea, the Yellow Sea, and the Bo Hui Sea, and is influenced by oceanic
currents, climatic variations, weather patterns (especially typhoons),
and water-sediment discharges especially from the Yangtze River.
Reduced flows from the Yangtze, as a result of the Three Gorges
Project, could affect pollution dispersion and dilution in this area
and potentially exacerbate conditions in the coastal area where
hundreds of kilometres of the coastal shoreline are already severely
polluted.

Although CYJV states that more information is
required to establish a relationship between river discharges and the
characteristics of the estuary and open sea, it says that, in general,
the project would not have any significant impact in this area.

Key Criticisms

• Because CYJV was not provided with sufficient data
  and/or failed to acquire the necessary data, the CYJV study is fatally
  flawed and is not an adequate assessment of downstream impacts.
• CYJV’s Volume 8, Environment, and Volume 8A
  to G, Appendices, demonstrate that, with respect to downstream impacts,
  the feasibility of the project is poorly understood. Therefore, major
  adverse and costly problems cannot be ruled out, and, in many
  instances, there are no grounds for assuming that technological
  remedies exist.
• Volume 8 of the CYJV study and its
  appendices provide strong evidence of these inadequacies; but Volume 1,
  which is intended to stand alone as a summary document, is inconsistent
  with Volume 8 and is misleading with respect to downstream impacts.
• CYJV’s credibility is in question due to
  its conclusion in Summary Volume 1 that engineering solutions and/or
  money can somehow make up for the lack of understanding of critical
  downstream environmental impacts.
• CYJV has identified serious omissions in
  the information required to evaluate and quantify environmental impacts
  downstream of the Three Gorges Project, which render the assessment
  incomplete. Despite this, CYJV glosses over serious concerns raised in
  Volume 8 and recommends the project as “environmentally feasible.”
  Therefore, regardless of which agency is at fault for those omissions,
  CYJV’s conclusion is misleading and irresponsible.

Sources and Further Commentary

*CYJV
states that its assessment is based on the Chinese environmental impact
statement, as well as on data from the YVPO preliminary Design Report
and information from international sources. However, the author was
unable to verify the documentation used by CYJV because prior to the
release of the CYJV study, CYJV deleted various sections of volume 8
pursuant to Section 19(1) of the Access to Information Act.

*Editors’ Note: The World Wide Fund for Nature
(WWF) International designates the Yangtze River dolphin, or baji, as
one of the most endangered species on earth. In 1992, the International
Association for Aquatic Animals’ Medicine named the baji – with a
population of between 150 and 200 animals – the most endangered dolphin
in the world.

*Mud flats are those areas along a watercourse or
surrounding a body of water which become exposed during periods of low
flow. They provide a rich food source and critical habitat for many
aquatic birds.

**CYJV estimates the total number of bird species
in the reserve at 90 but does not indicate when its count was taken. As
of 1986, WWF – Hong Kong put the figure at 236 species. Examples of
some of the larger species which depend on the lake habitat are the
white-naped crane, hooded crane, white stork, white spoonbill, swan
goose, and grey heron.

*The fisherman fits the cormorant, a fish-eating
bird, with a ring around the throat to prevent the bird from swallowing
the fish whole; the bird is then tethered to a long line and the
fisherman allows the bird to dive and capture fish; when the bird
returns to the boat it is rewarded with small pieces of fish.

**Grass-cutting rights are allocated among local
families who live for several months in temporary shelters on the
meadows and cut grass for green fertilizer on vegetable fields. Of 39
medicinal herbs harvested in the Poyang Lake Reserve, 18 species have
commercial value.

*Intertidal flats – mud flats exposed daily due to
tidal fluctuations in estuaries – provide critical feeding areas for
shorebirds during low tide and for fish during high tide.

**When the salt content of water becomes too high
as a result of salt water mixing with surface freshwater and seeping
into the ground-water table, irrigation has to be interrupted for a few
days or even several months. In 1978-79, 1,333 hectares of rice crops
were destroyed due to the very high salt content of the irrigation
water supply. Due to the salinized water supply, Shanghai experienced
an economic loss of $4,963,000.

Continue to Chapter 7

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Chapter 5