Development of Fishway Design Criteria for Floodplain Species of the Lower Mekong and Murray Darling Basins

Irrigation development in Lao P.D.R. has led to construction of numerous water regulation devices (over 10,000) which limit migratory fish movement. Movements of fish (and other aquatic animals) between rivers and floodplains is subsequently restricted, or may be entirely prevented, and this has led to severe declines in fish production in many areas. Previous research in Lao P.D.R. has demonstrated that fish-passage technology has the potential to enable movement of migratory fish past these low-level (less than 6 m) barriers.  Consequently, fisheries agencies are interested in increasing capacity to design manage and operate fish passage facilities on new and existing low-level water control structures in order to ensure the long-term sustainability of fish resources. Preliminary work identified that vertical slot fishways, on conservative slopes, can provide effective passage for many species and individuals of fish in the Lower Mekong Basin. Over 20,000 fish from 78 species were found to ascend an experimental fishway facility over a 40 day period. A 1:15 slope hydraulic slope was most successful but there was no single design that provided passage for all species. This suggests that the Lower Mekong Basin has a highly diverse fish community with many different movement strategies.