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Initial Assessment of EIA for Don Sahong Hydropower Project. Environment Programme Mekong River Commission Secretariat. Water quality and aquatic ecosystem health. Technical Consultation for Don Sahong Hydropower Project 07 March 2014, Vientiane. Impacts on environmental flows?

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initial assessment of eia for don sahong hydropower project

Initial Assessment ofEIA for Don Sahong Hydropower Project

Environment Programme

Mekong River Commission Secretariat

Water quality

and aquatic ecosystem health

Technical Consultation for Don Sahong Hydropower Project

07 March 2014, Vientiane

relevant environmental issues
Impacts on environmental flows?

Water quality during construction?

Water quality in the head pond/impoundment?

Water quality during flushing?

Water quality during decommission?

Impacts on sediment balance? (IKMP)

Impacts on nutrient balance?

Impacts on fish migration, both upstream and downstream passage? (FP)

Impacts on habitat continuity (fragmentation)?

Impacts on wildlife?

Impacts on tourism?

Impacts on health and livelihoods? (BDP)

This assessment is based on:

Environmental Impact Assessment Report, Final, January 2013 (EIA)

Engineering Status Report, Volume 1, 27 Sept. 2011 (ESR)

Relevant environmental issues

Environmental flows (EF):Conventional use of term ‘EF’ is different from EIA/ESR. EF over Khone Falls is set at 800 m3/s – the lowest recorded in the extremely dry 2010 season. With DSHPP this will be the flow in 40% of the time. The measured/estimated minimum flow during 1982-2009 was 1,224 m3/s. It would have been appropriate with analysis of the visual impact (tourism) of flows of this magnitude. It would also have been relevant to see impacts of climate change on the flow over Khone Falls.

#1: Assess the impacts of and on the project from selecting a minimum flow over KhonePhapheng of 800-1,224 m3/s and assess the impact of climate change on the flow over KhonePhapheng.

  • Water quality during construction:Some WQ impacts are addressed and mitigation plans anticipated. However, impacts from loss of sediment during excavation and deposition of 1 mio m3 sediment/rock have not been considered.

#2: Assess impacts on water quality from loss of sediments during excavation and deposition.


Water quality in headpond/impoundment:WQ impacts during operation are not addressed. Given the short water residence time (max 4 h), it seems reasonable to expect no significant WQ impacts. Sedimentation of coarse material may occur in a 1 km zone upstream of the dam. The impact on WQ has not been addressed (but is expected to be minimal).

#3: It seems justified not to anticipate any water quality deterioration in the head pond.

  • Water quality during flushing:The EIA briefly mentions flushing and in line with MRC PDG suggests flushing during high flows periods. The amount of flushed sediment will correspond to approx. 2% of the annual mainstream transport. Without further documentation the EIA claims that the sediment plume will bypass the dolphin habitat in the deep pool immediately downstream of the DSHPP. Potential impact on other aquatic organisms by short-term high sediment concentrations has not been addressed.

#4: Investigate potential impacts from sediment flushing on the dolphin deep pool immediately downstream of the dam using 2-D or 3-D hydraulic models.


Water quality during decommission:EIA says there is no other reason to ever decommission the power station than to restore river conditions. To the extent blasting of concrete structures will take place, it may affect dolphins and other aquatic animals. The details of blasting (if and how) are not given in the EIA report. Potential consequences – although perhaps small – from short term blasts and increases in sediment concentrations have not been addressed.

#5: Assess short-term consequences of increased sediment concentrations if blasting of structures during decommission take place.

  • Impact on nutrient balance:This issue has not been addressed. Since the issue is not a local but a regional one (nutrient transport from upstream reaches to downstream Tonle Sap and delta areas), and given the fact that no regional-scale flow or sediment changes occur with the DSHPP it is to be expected that no impacts on the nutrient balance will occur from the project.

#6: It is unlikely that impacts on the nutrient balance (although not addressed by the EIA) will occur.


Impact on habitat continuity:This is not addressed in the EIA. Because the DSHPP is a project that spans only one channel and not the entire Mekong mainstream, the risk of destroying habitat continuity is less than for other mainstream dams. Except, maybe, for fish the dam does not create any insurmountable barrier for movement of species between habitats.

#9: Due to the physical characteristics of the project it is not expected that discontinuity of habitats will be an issue (other than fish migration)


Impact on wildlife:The EIA refers to suggestions of Si Phan Done (including DSHPP site) as Ramsar site but concludes that GoL appears unlikely to nominate it.The EIA has no information on wildlife species of regional importance, except the Irrawaddy dolphins, but seems not to have used the data suggested by MRCS in the 2007 review.The EIA mentions that in order to protect the dolphins living immediately downstream of the dam, underwater blasting will not be permitted as excavation method. The EIA report lacks documentation that flushing of sediment will not affect the dolphin pool.

  • #10: Assess the data suggested by the 2007 MRC Review regarding status of wildlife. Use 2D/3D- models to analyse sediment impact on dolphin pool.

Impact on tourism:The EIA dismisses potential impacts on tourism based on a superficial assessment. Visual impacts and impacts on tourism of flows over Khone Falls of 800 m3/s have not been assessed. Neither has the scenario where dolphins are no longer present. Information on tourist arrivals is generally outdated.

#11: Assess impacts on visual appearance and tourism of flow over KhonePhapheng of 800 m3/s. Up-to-date data on tourist arrivals should be used.

alternative options
The EIA briefly compares some alternative projects of which the most developed option is the Thakho project but the assessment of this project seems to be based on a report from 2004, instead of more recent information such as IEE of 2009. International practice suggests that alternative projects be analysed in more detail.

#13: Compare the DSHPP with the Thakho project alternative, using up-to-date information for the Thakho project.

Alternative options