Flow Assessment Downstream of a Hydroelectric Project in an Ungauged Area

Hydropower dams can induce flash floods, leading to a severe cataclysm in flood-prone areas at downstream regions. On the catchment scale, flooding is not contributed solely by the reservoir releases, and there can be significant flow contributions from tributaries downstream of the dam. The major challenge in estimating the lateral flow contribution is that most tributaries are ungauged and situated in inaccessible areas. To overcome this inconsistency and to increase the precision of downstream flood warnings, a modeling framework was developed to quantify the flow contribution by ungauged tributaries to the mainstream using the drainage area ratio (DAR) method. The model parameters were estimated using optimization algorithms, and the best parameters were selected based on the error metrics. The modeling framework constitutes a reservoir operation model and hydrodynamic model developed in MATLAB version 2020b environment with the ease of coupling the two models. The estimated flow from the lateral tributaries based on the optimal model parameters of DAR and hourly inflow hydrographs were incorporated into the model. Two scenarios were analysed with and without lateral flow from ungauged tributaries. Results impart that the flood peaks have increased by more than 75% with the incorporation of the lateral flow. The model was validated with downstream stage and discharge data. The results indicated that the magnitude of the model generated and actual flow data were in the same range.