Three Gorges Probe

Chapter 6 – 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.

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