Instream flow predictions and management options for biota affected by peaking-power hydroelectric operations

Recent studies on the impact of peaking hydropower have indicated that impacts directly associated with peaking releases can be categorized as those which result from the hydraulic surge during start-up of generation and the chronic effects of frequent flow fluctuations to biota occupying the fluctuation zones. The instream flow incremental methodology (IFIM) was not designed for application to dynamic flows. In order to determine if such an application was appropriate, we chose to conduct exacting habitat descriptions at the unique zones associated with peaking hydropower (degradation, aggradation, and recovery) and combine this information with suitability criteria for the banded sculpin (Cottus carolinae) and stage/discharge records to obtain weighted usable habitat estimates under typical peaking releases. The results demonstrate that habitat declines as the peaking surge passes an area and rises during low flow periods. However, the difficulties in interpretation of the results remain. That is, the biological response (lateral or longitudinal movement or entrainment) as well as the refuge value of certain hydraulic conditions remain to be investigated. This suggests that the present management value of IFIM applied to peaking hydropower is in examining minimum habitat values that occur during the generation cycle and a comparison of gains or losses in the minimum (greatest amount of hydraulic refuge available) WUA estimates under various proposed release scenarios.