Fish passage principles to be considered for medium and large dams: The case study of a fish passage concept for a hydroelectric power project on the Mekong mainstem in Laos

Fish passage systems may provide a means to mitigate the barrier effect of dams on migrating fish species. Even though design criteria were initially developed for the fish fauna of temperate regions, they are widely used in tropical rivers with relative success. A fish passage concept has been developed for a hydroelectric power project on the Mekong River in the absence of suitable fish passage design criteria. There are several hydropower dams proposed for development on the mainstem of the Mekong River in Cambodia, Laos, Thailand and China and the impact of hydropower on fisheries is fast becoming a big issue. Located in Laos territory, the present project is one of the promising run-of-river hydropower projects identified by the Mekong Secretariat in 1994. The feasibility study began in 2007 and the outline (basic) design is being completed in 2010. The scheme includes a comprehensive fish passage system, which provides facilities for upstream and downstream passage. The proposed fish passage concept is based on twelve principles and gives emphasis on an adaptive project management, which includes planning, implementation and operation of the fish passage system and other structures of the project. It will cater to the large number of species and high biomass and especially to the variable flow regime and the lack of biological knowledge on the behavior of migrating species.