Morphometric diversity of supply-limited and transport-limited river systems in the Himalayan foreland

Abstract

The Indo-Gangetic basin exhibits highly diverse hydro-geomorphic settings that influence the hydrology, sediment production, and transport rates of the rivers draining this region, and this, in turn, is manifested in morphometric diversity of river systems. The rivers draining the western Gangetic plains (WGP) show incised channels attributable to high stream power and low sediment yield. In contrast, the rivers draining the Eastern Gangetic Plains (EGP) have formed aggradational landforms such as megafans due to low stream power and high sediment yield. For a better process understanding of the causal factors of such spatial inhomogeneities in a river basin, a morphometric characterization of its hinterland is necessary. In this work, a set of morphometric parameters such as stream network, longitudinal profile, and hypsometric curve have been integrated with data on sediment connectivity and stream power index to establish the form-process relationships in two contrasting basins, the upper Ganga basin (UGB) and the upper Kosi basin (UKB). The results of this study suggest that high sediment flux in the UKB is attributed to high rainfall, steep topography, unstable channel longitudinal profiles, and high sediment connectivity. A large part of these sediments gets deposited within the channel belt in the alluvial reaches and is remobilized during high flow events. However, the UGB produces fewer sediments due to low rainfall, mild topography, stable channel longitudinal profile, and low sediment connectivity. Also, the presence of a major dam at Tehri further reduces the functional sediment connectivity in the Upper Ganga Basin.