Flood Impact Analysis for the Saluda Hydroelectric Project
The Federal Energy Regulatory Commission (FERC) requested Dominion Energy to quantify potential effects of a proposed change in reservoir operational procedures on flood levels upstream and downstream from the Saluda Hydroelectric Project located on the Saluda River at Columbia, South Carolina. FERC’s request was addressed by acquiring the necessary data, conducting flow-frequency analyses, and selecting six of the most extreme reservoir inflow events from the historical record for model simulations with a focus on comparing effects between existing (EX) and proposed (PR) reservoir operations.
Reservoir PR antecedent conditions were based on simulations performed using a HEC-ResSim model, while flood event (gate operations) simulations were conducted using a custom R-model developed by cbec. cbec also developed and utilized a HEC‐RAS hybrid 1- and 2‐dimensional model to quantify downstream flood impacts.
Model results indicated that 14 of the 18 simulations produced downstream flooding. For four of the six events, peak discharges differed less than 6% between EX and PR. However, for two of the six events, PR produced peak flows that were significantly higher than for EX. Simulated downstream flooding for five of the six selected events was more extensive when antecedent reservoir elevations were based on PR rather than EX. Differences in flooded areas under the two protocols ranged from +3 acres to +1,367 acres. However, only 0.2 to 117 acres of the additional flooded area comprised developed areas that were not open space.
Many factors control the relationship between operation of the Saluda Project and downstream flooding. The proposed guide curve is generally higher than reservoir levels observed over the last decade because PR includes storage to supply a wide range of flow release requirements. However, the approach taken in this study did not allow for depletion of reservoir storage below the PR by such releases.