Case study: Targeting species and applying swimming performance data to fish lift design for the Huangdeng Dam on the upper Mekong River

A dam will be built in the upper reaches of the Mekong River, obstructing fish migration and gene exchange, and a fish lift will be constructed to mitigate these impacts. Target species for the lift were selected based on five criteria: (1) passage demand, (2) passage utility, (3, 4) protection worthiness (protection class and economic value) and (5) fish resource status. Swimming performance of target fish species were assessed and the results were used to recommend velocity criteria for the lift. Swimming performance was assessed by measuring induced flow velocity (Uind, the lowest water velocity that induces continuous fish motion against the flow), critical swimming speed (Ucrit) and burst speed (Uburst). The relationship of swimming performance to body length was also investigated. The research led to three primary findings: (1) The absolute Uind and Ucrit (m/s) were positively correlated with body length, whereas the relationship between the absolute Uburst (m/s) and body length were inconsistent. (2) The flow that was 90% effective in reaching the desired endpoint (EF90) was used to set fish lift design criteria for flow velocity. The EF90 value for Uind (90% induction rate) was 0.17 m/s and the values for Ucrit and Uburst (90% success rates), were 0.62 m/s and 0.87 m/s. (3) Recommended velocity criteria for the fish lift are as follows: entrance velocity, 0.37-0.87 m/s (0.6 Ucrit-EF90-Uburst-EF90), with mean velocity 0.50 m/s (0.8 Ucrit-EF90); passageway velocity, 0.17-0.50 m/s (Uind-EF90-0.8 Ucrit-EF90), with mean velocity 0.37 m/s (0.6 Ucrit-EF90); holding chamber velocity, 0.17-0.37 m/s (Uind-EF90-0.6 Ucrit-EF90), with mean velocity 0.27 m/s [(Uind-EF90 + 0.6 Ucrit-EF90)/2]. The approach developed in this case study has good potential as a general method for selecting target fish species and setting site-specific flow velocity criteria for fish passage design.