Oral Presentation International Conference on River Connectivity (Fish Passage 2018)

Fish passage at the Don Sahong dam site, Khone Falls, Mekong River, southern Laos (#102)

Kent G Hortle 1 , Somphone Phommanivong 2
  1. Independent Consultant, Heathmont, VIC, Australia
  2. Environment Dept, Don Sahong Hydropower Company, Vientiane, Laos

The 260 MW Don Sahong Hydropower project is being constructed from 2015 to 2019 on one of seven Mekong anabranches (Sahong Channel) which cross Khone Falls in southern Laos. The other six channels carry most of the annual flow of the river and provide for variable degrees of upstream fish passage, depending upon discharge, the degree of obstruction by natural barriers (waterfalls, cascades and rapids) and the extent of blockage by large fishing gears. About 200 species of fish are commonly caught; all migrate for feeding, refuge or spawning, with many being long-distance migrators. Fishing, particularly of migrations, is very important for local people, so mitigating the impacts of the project is a high priority for the developer, the Don Sahong Power Company. Upstream fish passage is being enhanced by in-stream modifications to increase dry-season flow of water down channels, to reduce the height of natural barriers, or to create bypass channels, and by removal of illegal gears which block fish migrations. Downstream passage is less problematic than at typical cross-river projects, as flow will be regulated by the operation of the hydropower plant, with excess water flowing down natural channels through which migrating fish can pass safely, so there is no risk from spillway passage. The plant will utilise four 65 MW GE (formerly Alstom) bulb turbines, considered relatively fish-friendly, with an operating head of 16-18 m. The overall probability of mortality of fish from strike, barotrauma and shear stress is likely to be relatively low, and it is planned to adaptively manage any unacceptable impacts through physical or behavioural measures to divert fish upstream of the plant. This presentation will give an overview of the project and the evolution of fisheries mitigation measures.