Assessing the Influence of Upstream Basin and Climatic Characteristics on Post-Dam Downstream Streamflow Changes: Empirical Insights from Peninsular India

Abstract

Size of the reservoir and dam operation are cited as the primary causes of changes in the post-dam downstream hydrograph in scientific literature. This study investigates whether upstream basin and climatological characteristics also contribute to such changes. Drawing upon the case study of 18 sites across Peninsular India, we employed Multiple Linear Regression (MLR) with two dam-related and five geophysical as well as climatological factors of upstream basins as predictors to determine key influencing causes. Pre- and post-dam flow duration curves were used to characterise changes in flow post dam construction. We considered periods with the least rainfall difference pre- and post-dam and eliminated rainfall’s effect on downstream hydrograph changes. Two additional machine learning feature extraction algorithms, such as SelectKBest with f_regression and mutual information score, were also deployed to identify the most influential driver of changes in the post-dam downstream hydrograph. The outcome of three separate methods provided a robust and unbiased result. The three methods agreed that while dams are the primary determinant of changes in the typical peak monsoon flow and overall flow variability, potential evapotranspiration and land use-soil-slope, represented by US Soil Conservation Service Curve Number (CN) of the upstream catchment, could also be key factors affecting changes in the post-dam flood peak. These findings highlight the importance of considering the geophysical and climatological characteristics of upstream catchments when assessing the impact of dam construction on downstream hydrology, and potentially aid in the placement, size, and operation of new and existing reservoirs.