report

Mainstream dams: An engineer’s dream, a fisher’s curse After several decades, plans to dam the Mekong mainstream are back on the agenda. Gary Lee traces the history of the plans and examines the impacts the dams will have on the Mekong’s fisheries and fishing-based livelihoods.

Mainstream dams: revised, revived, yet again “We’ve had the plan [for the mainstream dams] since 1957: the engineers’ dream we can call it – though now it has been revised and is called the run-of-river scheme.” Khy Taing Lim, Cambodian National Mekong Committee, cited in Watershed Vol. 1 No. 2, p.12.

It was the “engineers’ dream” which led to the formation of the Mekong Committee in 1957, whose mandate was “to promote, coordinate, supervise and control the planning and investigation of water resources development projects in the Lower Mekong Basin.” By

the 1960s, the Mekong Committee had designed plans for a cascade of seven large-scale “multi-purpose” dams on the lower Mekong mainstream to provide hydroelectricity, flood control, irrigation and improve navigation. These plans were outlined in the Mekong Committee’s Indicative Plan of 1970. With a total capacity of 23,300 megawatts (MW), the so-called Mekong Cascade would have transformed much of the lower Mekong River into a series of large reservoirs capable of storing more than one-third of the Mekong’s annual flow. While the plans did not materialise due to geopolitical conflicts in the region and concerns over social and environmental impacts, the Mekong Committee and Secretariat continued to devote significant resources on “revised” plans to dam the Mekong mainstream and its tributaries.

Gary Lee is an Australian-based researcher monitoring developments in the Mekong Region.

Page 4 Watershed Vol. 12 No. 3 November 2008

Then, in 1994, a few months before the signing of mainstream dams, it was the 1997 Asian financial crisis the 1995 Mekong Agreement, the Mekong Secretariat and a subsequent decline in Thailand’s electricity published a study outlining plans for up to eleven demand, which put the plans on hold. “run-of-river” hydropower dams on the Mekong Since that time, however, the economies of the lower mainstream, which were presented as a lower impact Mekong countries have made a staggering recovery and alternative to the cascade of large storage dams growing demand for energy in Thailand and Vietnam in proposed by the Mekong Committee. The “run-of-river” particular have been a significant factor behind the dams proposed by the 1994 study were to be 30 to 60 current hydro boom in the region (see The sleeping metres high, with reservoirs stretching a total of over dragon awakes, this issue). This, coupled with an 600 kilometres of the river, displacing an estimated increase in availability of private capital within the region, 57,000 people. Using information gathered from previous has led to a renewed interest in damming the Mekong dam plans done by the Mekong Secretariat, the 1994 mainstream with feasibility studies now underway for report ranked potential dam sites and short-listed nine up to eleven hydro dams on the main stem of the river dams with a total generating capacity of 13,350 MW. (see Table). With the exception of Lat Sua, all of these Most of this electricity was planned for export to dams were identified in the 1994 study published by the Thailand. Mekong Secretariat. The signing of the Mekong Agreement by the four Fisheries evaluation of Mekong lower Mekong governments in 1995, established the Mekong River Commission (MRC) as an institution mainstream dams through which cooperation was to be achieved for the sustainable development and management of the Lower When the mainstream dams were first proposed as ‘runMekong Basin. Although it was meant to represent a of-river’ schemes, a fisheries evaluation was shift in its mandate towards ensuring sustainability of commissioned by the Mekong Secretariat to assess the the river and related resources, the MRC nevertheless likely impacts on Mekong fish and fisheries. A consistent continued to seek funding to conduct pre-feasibility theme highlighted in the 1994 fisheries evaluation was studies for three mainstream dams proposed in the 1994 the lack of detailed information on fisheries ecology – study – Bank Koum, Don Sahong and Sambor (see fish stocks, migration patterns, location and character of spawning and rearing habitats – in all reaches of the Watershed Vol. 1 No.2). Moves to push forward with plans to dam the Lower Mekong Basin. This led the authors to conclude Mekong mainstream caused widespread concern that “these projects cannot be safely designed or among civil society groups as well as some government officials. As Dr. Mok Mareth, then Vice-Chairman of the Cambodian National Mekong Committee (CNMC) told the Phnom Penh Post in 1996, “It is most dangerous if we still have this idea of building dams across the Mekong River… We would gain electricity and quick economic income…but only for a short time because after that it would change our natural environment.” While there were widespread concerns over environmental and Artist rendition of Ban Koum dam, planned for the Lao-Thai border. social impacts of the proposed

1994

Watershed Vol. 12 No. 3 November 2008 Page 5

Existing and proposed hydropower dams on the Mekong mainstream Gongguoqiao

g an nc La

Xiaowan Manwan

CHINA

Dachaoshan

g on ek /M

adu Nuozh ng Jingho ba Ganlan

r ve Ri

Mengsong

VIETNAM

BURMA

 Pak Beng

HANOI

Luang Prabang

Xayabouri

LAO PDR 

o n

om Ch k Pa

k

Sanakham

e

VIENTIANE

M

Pak Lay

g R iv e r

THAILAND Ban Koum Existing

Lat Sua

Under Construction Planned

Don Sahong



BANGKOK

CAMBODIA

Stung Treng

Sambor

c TERRA 2008

Page 6 Watershed Vol. 12 No. 3 November 2008

Summary of dams planned for the lower Mekong mainstream D am ( C o u n try )

In sta lle d C a p a city*

P ak B eng ( Laos )

1,320 M W

D atang Internati onal ( C hi na ) & G overnm entof Laos ( G oL )

M oU forfeasi bi l i ty study si gned i n A ugust2007.

L u a n g P ra b a n g ( Laos )

1,410 M W

P etrovi etnam P ow er C orporati on ( V i etnam ) & G oL

M oU forfeasi bi l i ty study si gned i n O ctober2007.

X a ya b o u ri ( Laos )

1,260 M W

C H .K arnchang P ubl i c C o. Ltd of( T hai l and ) & G oL

M oU forfeasi bi l i ty study si gned i n M ay 2007.

P ak Lay ( Laos )

X a n a kh a m ( Laos ) P ak C hom ( L a o -T h a ib o rd e r )

P ro je ctS p o n so r ( C o u n try )

S ta tu s

1,320 M W

cs Im port C hi na E l ectroni & E xportC orporati on; Si nohydro C orp.Ltd. ( C hi na) & G oL

M oU forfeasi bi l i ty study si gned i n June 2007.

1,000 M W

D atang Internati onal ( C hi na ) & G oL

M oU forfeasi bi l i ty study si gned i n D ecem ber2007.

1,079 M W

T hai l and' s D E D P reportedl y seeki ng fundi ng to proceed to feasi bi l i ty study stage.

N /A Ital i an-T haiD evel opm ent P ubl i c C o.Ltd.( T hai l and) A si a C orp H ol di ngs Ltd. ( Laos) & G oL

M oU forfeasi bi l i ty study si gned i n M arch 2008.

B an K oum ( L a o -T h a ib o rd e r )

2,330 M W

L a tS u a ( Laos )

800 M W

C haroen E nergy and W ater A si a C o.Ltd.( T hai l and) & GOL

M oU forfeasi bi l i ty study si gned i n A pri l2008.

360 M W

M ega F i rstB erhad C orporati on ( M al aysi a)

P roj ectD evel opm entA greem ent si gned i n F ebruary 2008.

D on S ahong ( Laos )

S tu n g T re n g ( C a m b o d ia )

980 M W

S am bor ( C a m b o d ia )

2,600 M W

A ccordi ng to the C am bodi an country presentati on atthe M R C hydro consul tati on( S ept.2008 ) an M O U forfeasi bi l i ty study has been si gned wi th a R ussi an C om pany.

( R ussi a)

C hi na S outhern P ow erG ri d -C S G P ( C hi na )

F ol l ow i ng si gni ng ofM oU i n O ctober 2006,G uangxiG ri d C om pany,a subsi di ary ofC S G P has been conducti ng studi es.

* Installed capacity figures vary according to source. Those listed in the table (except Pak Chom) are from the Lao and Cambodian country presentations at the Regional Multi-Stakeholder Consultation of the MRC Hydropower Programme, 25-27 September 2008 in Vientiane, Lao PDR. http://www.mrcmekong.org/programmes/Hydropower/stakeholder-consultppt.htm

mitigated without first establishing a sound and reliable database.” While pointing to the lack of fisheries baseline data as a “central problem,” the consultants drew on available knowledge at the time to highlight some key concerns about the dams’ likely impacts on the Mekong’s fisheries and fishing-based livelihoods (see Box: Key findings from 1994 fisheries evaluation). The adverse impacts large dams have on fish and fisheries has become painfully clear to various communities living in the Mekong basin in the fourteen years since the 1994 fisheries evaluation. From local accounts it is clear that large hydro dams built on the

Mekong’s tributaries, such as the Yali Falls on Sesan River in Vietnam, the Theun-Hinboun on the Theun River in central Laos, and the Pak Mun on the Mun River in northeast Thailand, have modified the natural flow regime, damaged or destroyed critical aquatic habitats, and obstructed the movement of fish between seasonal habitats. The result has been a decline in fish stocks and a consequent loss of food and income security for communities upstream and downstream of the dams. Many affected communities are still seeking reparation and compensation for the loss of their means of livelihood.

Watershed Vol. 12 No. 3 November 2008 Page 7

Key findings from

1994 fisheries evaluation of mainstream dams

•

With respect to the six projects proposed for northern Laos and the Lao-Thai border area (i.e. Pak Beng, Luang Prabang, Pak Lay, Xayabouri, Chiang Khan/Xanakham, Pa Mong/Pak Chom), the authors note that if all six dams were built, “they will remove almost all of this reach as a free-flowing stream and convert it into a cascade system that will inundate spawning areas, remove wetland and littoral habitat, increase downstream incubation drift time, block upstream migration, cause turbine mortality, flood the confluences of tributaries, and induce species changes and reduce biodiversity.” (p. 53).

•

The study underlines the exceptional ecological importance of Khone Falls, noting that it is “an ecologically unique area that is essentially a microcosm of the entire lower Mekong River… Such a site is so rare in nature that every effort should be made to preserve all of Khone Falls from any development.” (p. 90).

•

With respect to the proposed Sambor project in Cambodia the study states, “The Sambor project [will] impact upstream and downstream [fish] migration. Target species will be separated from spawning areas between Sambor and Stung Treng. Not only will spawning migrations be eliminated but increased water level behind the dam will affect the migration of young fish into (wet season) and out of (dry season) floodplain habitat… The effect of isolating fish stocks from historical spawning and rearing areas will have effects far upstream to perhaps Pakse and beyond, and on the Great Lake fishery.” (p. 79-80). Noting that the proposed Sambor dam site would be located in a “highly complex migration and rearing corridor and floodplain,” the study states, “The Sambor project will require an effective passage system for all migratory fish species to avoid or minimize significant impacts. Effective fish passage may be a remote possibility, requiring substantial research and development that may not prove fruitful.” (p. vi).

• The study highlights the potential consequences of the barrier effects of the mainstream dams to fish migrations, noting that, “This one impact alone may cause a wholesale decline in the fishery throughout the lower Mekong River. Blocking migration cuts out a critical link in the biological chain of migrating species.” (p.88-89). Excerpted from: Mekong Brief Series 9. What do MRC studies tell us about Mekong fisheries? November 2008 http://www.mekong.es.usyd.edu.au/AMRC%20fisheries%20Brief%209%20%20Final%2031Oct08.pdf Source: Hill, Mark T. and Susan A. Hill, Don Chapman Consultants. 1994. Fisheries Ecology and Hydropower in the Mekong River: An Evaluation of Run-of-the-River Projects. Mekong Secretariat, Bangkok, Thailand.

These impacts and the importance of maintaining the ecological integrity of the river system in sustaining productive fisheries have been well documented by scientists, hydro consultants, many community organisations, and Watershed (see Box: Communities Voices). While there is still insufficient understanding of the complex relationship between the Mekong’s various ecosystems, fish and livelihoods, it is undeniably clear that the future viability and sustainability of the Mekong’s wild capture fisheries is dependent on maintaining the overall health of the river system.

Page 8 Watershed Vol. 12 No. 3 November 2008

There is no substitute for fish With an estimated annual harvest of 2.64 million tonnes, the Mekong’s wild capture fishery is one of the most productive in the world. The bulk of this catch comes from small-scale subsistence or artisanal fishers, who depend on the Mekong’s fishery for food, income and livelihood. Fish and aquatic products are the major source of animal protein for the majority of the basin’s population, contributing 47 to 80 per cent of daily dietary intake, and providing

Community Voices:

“The fish give us strength” “We had a means of livelihood on the Mun

“The river was so plentiful. There were

River, collecting vegetables from the

many sources of food – fishes, birds, rats

forest, catching crabs and fish. Now the

and vegetables. The riverside gardens

reservoir floods the area, the water is

were very fertile. The people along the

deep, and we cannot catch fish. The dam is

Se San River lived off the river – growing

an obstacle to the route of the fish, and

rice and other crops and catching

fish cannot enter the Mun River.

fish…Over the past few years, after the

Communities are disintegrating.”

construction of the [Yali Falls] dam, the

Ms Sompong Wiengchan, Mun River, northeast Thailand, Watershed Vol. 1 No. 1

fish have disappeared. There have been no vegetables on the riverbanks to collect.” Mrs. Nuan Moum,

“People here adapt their lives according to the cycles of the Mekong and the fish. Everything depends on fishing. If we don’t

Pong village, Sesan River, northeast Cambodia, Watershed Vol. 10 No. 2

eat fish for a day, it seems like a month, because the fish give us strength… If the fish were blocked from coming up the

“Without fish, neither Thai, nor Laotian,

Mekong, we would not have enough food

nor Cambodian village people can exist.

and would become poor.”

We were brought up and live on fish from

Say Singsouvan, Khone Falls area, Mekong River,

the Mekong River. We have to collaborate in protecting the fisheries.”

southern Laos,

Mr. Moon Phod,

Watershed Vol. 1 No. 3

Don Phad village, Mekong River, northeast Cambodia, Watershed Vol. 10 No. 2

“We catch fish all year round. Our fishing gears have been developed over a long period of time and are used in different situations. However, during the past two to three years, local fishers have been facing difficulties since the river’s flow has become unpredictable and the fish catch has decreased. The seasonal flow of the river and the fish migrations have changed.” Mr. Somboon Ponsawat, Huay Leuk village, Mekong River, northern Thailand, Watershed Vol. 8 No. 1

Watershed Vol. 12 No. 3 November 2008 Page 9

Fishers, Luang Prabang dam site

an essential source of vitamins and nutrients. Fisheries provide easy access to income generating activities with low investment costs, supporting the poorest households. There is no readily available substitute that can replace the nutritional contribution that fish and aquatic products make to people’s diets. A serious decline in wild capture fisheries would have serious consequences for the food and livelihood security of thousands of communities in the basin. Fisheries is not only important for local fishers, but also a countless number of people who derive an income through the processing and trade of fish and fish-related products, making and repairing of boats, fishing gears and so forth. The cost of replacing fisheries as a source of income, food and nutrition would be prohibitive. Yet, the importance of Mekong’s capture fisheries is often ignored or downplayed by the governments and institutions promoting “development” in the region – favouring more readily measurable economic benefits such as dams that often pose a direct threat to fisheries and the communities dependent on them.

Page 10 Watershed Vol. 12 No. 3 November 2008

Mainstream dams threaten fisheries and fishing-based livelihoods While detailed social and environmental evaluations of the mainstream dams have either yet to be undertaken or publicly released, there is enough evidence pointing to the widespread impacts the dams will have on the Mekong’s fisheries. Mainstream dams block fish migrations All of the proposed mainstream dams will block or significantly impair the movement of fish between habitats critical to the completion of their life-cycles. Many of the 1,300 Mekong fish species undertake seasonal migrations, often travelling long distances across national borders to reach feeding, spawning and refuge habitats at different times and stages of their lifecycle. Generally, fish migrate between downstream feeding habitats and upstream breeding habitats, moving between tributaries and the mainstream. As

the water levels rise, the river breaks its banks and spills over to submerge vast floodplains, bringing rich nutrients and sediments. Many fish species move into these seasonally inundated habitats to feed and spawn, taking advantage of the abundant food and shelter. As the water levels recede, fish migrate back to deeper sections of the river, where they congregate until the next wet season. The reliance of fish on seasonal habitats that are geographically separated is considered a driving force behind fish migrations, which are intimately linked to the Mekong’s hydrological regime. While there is insufficient detailed knowledge of what factors “trigger” migration, mass movements of fish are seen every year, at certain times during the annual flood- drought cycle. In the Tonle Sap River, for example, during peak migration times between November and February, up to 50,000 fish per minute pass through any given point. From subsistencebased to large commercial operations, Mekong fisheries are largely based on and have adapted to the capture of migratory fish, which constitute the bulk of the annual catch in basin. Recently, it has been estimated that 70 per cent of the total fish catch in the Lower Mekong Basin – equivalent to 1.3 million tonnes worth US$2.5 billion – is dependent on long distance migratory fish. According to the preliminary designs presented in the 1994 Mekong Secretariat study, all the mainstream dams, except for Don Sahong, would be cross-channel dams. By obstructing the movement between critical habitats, the mainstream dams would have major impacts on the Mekong’s fish and

fisheries. Given the importance of migratory fish for Mekong fisheries of all sizes and types, this would have significant economic, social and health implications basin-wide. A 2007 report published by the CNMC and WorldFish Center estimates that even a small percentage decline in the Mekong’s fishery will translate to a loss of tens of thousands of tonnes and millions of dollars worth of fish. While Don Sahong would not cross the whole Mekong River, the dam would block the only channel that fish can easily pass through year round on their upriver migration from Cambodia to Laos. In May 2007, more than 30 scientists sent a letter to the governments of the four lower Mekong countries and the MRC expressing concern about the widespread impacts the proposed Don Sahong dam would have on fisheries. While stating that dam construction anywhere in the Khone Falls area is undesirable, the letter stresses that the site of the proposed Don Sahong dam is “the worst possible place [to build the dam] since it is the point of maximum concentration of fish migration in the river that supports the world’s largest freshwater fishery.” Mainstream dams threaten critical habitats The impacts of the mainstream dams will not be confined to the blocking of migration routes. Of equal concern are changes in flow and the degradation or destruction of critical aquatic habitats. Deep pools provide important dry-season refuge for migratory and non-migratory species, including the critically endangered Mekong giant catfish.

WatershedVol. Vol.12 12No. No.33November November2008 2008 Page Page11 11 Watershed

Framing threats and opportunities: MRC and the Lancang Cascade

C

hina is halfway through completing a cascade of eight large dams on the Lancang (Mekong) River. The third dam, Jinghong, began operating in June 2008 and, according to Three Gorges Probe, the two largest dams of the cascade – Xiaowan and Nuozhadu – are currently under construction and expected to be completed by 2010 and 2015 respectively. Once completed, the Lancang Cascade will significantly alter the flow and sediment regime of the Lower Mekong. Dashaosan dam According to the preliminary results of hydrological modelling presented at the recent regional ‘consultation’ on MRC’s Hydropower Programme, the Lancang Cascade will increase average dry season flows by 30 to 50 per cent in northern Laos and Thailand. A number of cumulative impact assessments that have included the impacts of the Lancang Cascade on the Mekong’s flow regime in their assessments, indicate that the Lancang Cascade plus other planned developments will increase the dry-season water level around the Tonle Sap Lake by 0.15 to 0.60 metres. While these figures may appear small, an article published in Ambio in 2008 points out that even “Relatively small rises in the dry-season lake water level would permanently inundate disproportionately large areas of floodplain... and erod[e] the productivity basis of the ecosystem. It is highly important to maintain the natural hydrological pattern of the Mekong River, particularly the dryseason water levels, to preserve Tonle Sap Lake’s ecosystem productivity.” The threat that flow alterations pose for the continuing productivity of the Mekong’s ecosystems and fisheries has been well-documented, not least by the MRC Fisheries Programme. Their research has emphasised the importance of the natural flow regime in maintaining the ecological integrity of the river that sustains the Mekong fisheries. But in spite of its own research pointing to the potential threats the dams on the Lancang pose for fisheries and the livelihoods of people in the Lower Mekong Basin, there is little indication that the MRC and its member states have taken steps to try to minimise the risks and threats posed by dams in China. Under Articles 3 and 7 of the 1995 Mekong Agreement, the MRC has a responsibility “to protect the environment, natural resources, aquatic life and conditions and ecological balance of the Mekong River Basin,” including “making every effort to avoid, minimize and mitigate harmful effects that might occur” from the development and use of the river. The increased risk for downstream communities upon the completion of Xiaowan and Nuozhadu was recognised in MRC’s 2003 State of the Basin report, which noted that the dams “should be planned and operated in consultation with all countries in a river basin. Ideally such a scheme for consultation and rules for dam operation will be established by 2008-2009 – before the commencement of ponding in the Xiaowan reservoir.” While China and MRC have recently renewed an agreement to share hydrological data, China is not a member of the MRC, and so is not under any obligation to notify or consult with downstream countries regarding its plans or operations of exiting and future dams. Instead of pursuing negotiations aimed at minimising the risks people in the basin, the MRC has been quick to point out the ‘opportunities’ that an increase in dry season flow presents in terms of further irrigation and hydropower development. This is hardly surprising, given that MRC member states are keen to capitalise on the economic ‘opportunities’ of increased dry season flows. The Thai government, for example, has renewed its push for transboundary water diversions to irrigate the country’s northeast. While acknowledging potential negative impacts downstream, Jeremy Bird, the CEO of the MRC Secretariat said in an interview with ABC Radio, “[I]n the medium term, we’re going to see a situation where as a result of construction of dams upstream in China, there will be some significant increases in dry season flows in the Mekong which actually then might facilitate Thailand taking water from the river because then there’ll be more water available during the dry season.” Similarly, the Lao government has dusted off old master plans as part of its push to become the “battery of Southeast Asia,” granting hydro developers from neighbouring countries permission to

Page 12 Watershed Vol. 12 No. 3 November 2008

undertake feasibility studies of dams on the mainstream. With average dry season flows predicted to increase significantly in northern Laos, the ‘run-of-river’ schemes proposed in the 1994 study have become a more economically attractive proposition for investors. In this matter, it seems the MRC is more than happy to lend a hand to maximise the benefits for the Lao government, by undertaking a power optimisation study of the five mainstream dams planned for northern Laos. As the governments and investors capitalise on ‘opportunities’, the people of the basin who are threatened with the loss of their livelihood base have been largely left out of the discussion. The impacts from the dams built on the Lancang are already evident from the reports of local fishers in northern Thailand and Laos, indicating that fish catch has declined by as much as 50 per cent since the construction and operation of Manwan and Dachaoshan dams. Unless steps are taken to address the threats posed by further dam construction upstream, the opportunities for local people to derive benefits from the river will continue to decline. Source: ABC Radio Australia 2008. Thai plan threatens Mekong. 7 August 2008. http://www.radioaustralia.net.au/programguide/ stories/200808/s2327081.htm Ms. Hang Pham Thi Thanh 2008. Modelling of Flow Changes in the Mekong Mainstream for a Range of Water Resources Development Scenarios: Preliminary Results presented at Regional Multi-Stakeholder Consultation of the MRC Hydropower Programme, 25-27 September 2008 in Vientiane, Lao PDR. http://www.mrcmekong.org/download/programmes/ hydropower/presentations/Hydropower%20forum%2025-26%20Sept%20final%20version%2025%2009%2008.pdf Kummu, M. and Juha Sarkkula. 2008. Impact of the Mekong River Flow Alteration on the Tonle Sap Flood Pulse Ambio 37(3): 185-192 MRC 2003. State of the Basin Report: 2003. Mekong River Commission, Phnom Penh, Cambodia. Three Gorges Probe The Hydrolancang cascade: Fact box. http://www.probeinternational.org/three-gorges-probe/ news-and-opinion/hydrolancang-cascade-fact-box

The importance of deep pools in sustaining fish and fisheries has been increasingly acknowledged by researchers. Their understanding of the locations and importance of these habitats have been informed by local fisher folk, who have long recognised the importance of deep pools and undertaken initiatives to conserve these critical habitats. The proposed Sambor, Stung Treng and Don Sahong dams would be built in the stretch of the Mekong that has been identified as the most important in terms of deep pool habitats. Based on surveys with local fishers, a paper presented at a technical symposium on fisheries, identified 97 deep pools in the stretch of the river between Kratie and the Lao-Cambodia border, which are used by at least 162 native Mekong fish species. The other proposed mainstream dams would also be located in stretches of the Mekong River containing numerous deep pool habitats, including the stretch from Khone Falls up to Khammouane (which includes Ban Koum and Lat Sua dam sites); and the stretch from the confluence of the Loei and Mekong up to Luang Prabang (Pak Chom, Xanakham, Pak Lay, Xayabouri, and Luang Prabang dams). While all the mainstream dams are being promoted as “run-of-river”, which proponents claim produce less

impacts, all the dams will create reservoirs, albeit smaller than large-storage dams, and modify flows upstream and downstream of the dam site. Given that the proposed mainstream dams would be located in stretches of the river containing numerous deep pools, which are susceptible to changes in flow and sediment regime, the construction and operation of dams on the mainstream could eventually lead to the pools filling up with sediment and disappearing. This is already evident in some of the Mekong’s tributaries such as in the Sesan and Theun rivers, where the Yali Falls and Theun-Hinboun dams are located respectively. As a 2002 MRC Technical Paper notes, “deep pool habitats, and the fishes they sustain, have virtually disappeared” along parts of these two rivers. A 2005 MRC Technical Advisory Body for fisheries management reports that if “any of the pools in the Mekong [were] to silt up, particularly in the stretch between Kratie and Stung Treng, the damage inflicted on fish populations throughout the basin would be serious. Degradation of deep pool habitats may have equal, or more serious, consequences than the often cited blockage of migration routes caused by dams.”

Watershed Vol. 12 No. 3 November 2008 Page 13

Mainstream dams and flows The extent to which the proposed mainstream dams will modify flows, is contingent their operational regime, but presumably they are being built to supply peak power and this will affect downstream flows. Because many commercially important species are sensitive to changes in water levels and discharge as a “trigger” for undertaking migration, changes in flows will have significant implications for fisheries. The impacts of unseasonal and rapid fluctuations in water level are already evident in northern Thailand and Laos, where riparian communities have experienced the destruction of their fisheries, erosion of their river bank gardens, and loss of fishing gear and boats, as a result of Manwan and Dachaosahn dams in China. Like the proposed Mekong mainstream dams, both these dams have been categorised as ‘run-of-river’ dams by the MRC (see Box: MRC and the Lancang Cascade).

Mitigation? Proponents of large hydropower schemes often claim that, if properly managed, negative impacts of dams can be mitigated. Commonly proposed measures to mitigate the negative impacts on fisheries in the Mekong and elsewhere include the establishment of reservoir fisheries and the construction of fish passes to facilitate fish migration past the dams. A report published by the

CNMC and WorldFish Center in 2007 affirms that there are “no examples of positive long-term impacts of dams on fisheries, nor any effective mitigation measures in the Mekong Basin.” The report also states that a reservoir fishery “usually does not compensate for the loss of downstream fisheries,” and that “there are no examples of fish passes that work in the Mekong Basin.” An earlier research published under the MRC Fisheries Programme in 2002, also noted that due to the intensity and diversity of fish migration in the Mekong, “there is no existing fishway technology able to overcome the obstacle created by a dam or weir on the Mekong mainstream or on the lower reaches of its major tributaries. On the mainstream, the choice therefore remains: fish or dams.”

Conclusion The benefits of power generation are being heavily promoted, and much emphasis to date has been on how to share the benefits, and mitigate the impacts of the mainstream dams. Yet it is clear that the impacts of mainstream dams on fish and fisheries cannot be mitigated. Given the central importance of fisheries to the lives and livelihoods of the basin’s population, it is difficult to see how the proposed dams constitute “sustainable hydropower,” which has become the new catch cry of the MRC, its member governments and dam developers.

Selected References Baran E and B. Ratner 2007. The Don Sahong Dam and Mekong Fisheries. A science brief from the WorldFish Center, Phnom Penh, Cambodia. Baran, E., Jantunen T., and Chong C.K. 2007 Values of inland fisheries in the Mekong River Basin. WorldFish Center, Phnom Penh, Cambodia. Baran E., P. Starr, and Y. Kura 2007. Influence of built structures on Tonle Sap fisheries: Synthesis Report. Cambodia National Mekong Committee and the WorldFish Center, Phnom Penh, Cambodia. Chan, S., S. Putrea, K. Sean and K.G. Hortle 2003. Using local knowledge to inventory deep pools, important fish habitats in Cambodia.” In: Proceedings of the 6th Technical Symposium on Mekong Fisheries, Lao PDR 26-28 November, pp. 5776. Hill, Mark T. and Susan A. Hill, Don Chapman Consultants 1994. Fisheries Ecology and Hydropower in the Mekong River: An Evaluation of Run-of-the-River Projects. Mekong Secretariat, Bangkok, Thailand. Mekong Secretariat 1994. Mekong Mainstream Run-of-River Hydropower: Main Report. A study conducted by Compagnie National du Rhone, Lyon, France in cooperation with Acres International Ltd and Mekong Secretariat Study Team. Mekong Secretariat, Bangkok, Thailand. MRC Technical Advisory Body for Fisheries Management (TAB) 2005. Deep pools as dry season habitats in the Mekong River Basin. Mekong Fisheries Management Recommendation No3, August 2005. MRC 2003. State of the Basin Report: 2003. Mekong River Commission, Phnom Penh, Cambodia. Poulsen, A., Ouch Poeu, Sintavong Viravong, Ubolratana Suntornratana & Nguyen Thanh Tung. 2002. Deep pools as dry season fish habitats in the Mekong Basin. MRC Technical Paper No. 4. Mekong River Commission, Phnom Penh, Cambodia. Poulsen, A. F., Ouch Poeu, Sintavong Viravong, Ubolratana Suntornratana and Nguyen Thanh Tung. 2002. Fish migrations of the Lower Mekong River Basin: implications for development, planning and environmental management. MRC Technical Paper No. 8. Mekong River Commission, Phnom Penh, Cambodia. Sverdrup-Jensen, S. 2002. Fisheries in the Lower Mekong Basin: Status and Perspectives. MRC Technical Paper No. 6. Mekong River Commission, Phnom Penh, Cambodia.

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