Exploring the dependence between discharge indices and catchment descriptors for suspended sediment load in Indian Rivers

ABSTRACT In this paper, we have explored the dependence of discharge indices (and their return period) on various catchment descriptors, such as average slope, basin relief, drainage area, maximum elevation, and mean elevation. Discharge indices, viz., effective discharge, functional-equivalent discharge, and fraction-load discharge, are considered in this study. These indices characterize long-term sediment transport through stream networks and are generally adopted as design flows for restoration of streams and in geomorphic, as well as in eco-hydrologic studies. These indices (and their return period) were determined based on a continuous probability distribution (e.g. log-normal and Gamma)-based Magnitude-Frequency Analysis approach. These indices and their return period were found to have a negative correlation with all these catchment descriptors except the drainage area. This is because there is a reduction in the magnitude of discharge indices with the rise in average slope, basin relief, maximum elevation, and mean elevation, which indicates that a lesser magnitude of flows/discharges is effective in carrying a considerable amount of sediments over time as the transport of sediments is assisted by high slopes of upstream catchments, viz., headwater catchments. These correlated descriptors can be useful in the determination of indices (and their return period) for ungauged catchments.