Grain size characteristics and provenance determination of sediment and dissolved load of Alaknanda River, Garhwal Himalaya, India

Alaknanda River is a major tributary of river Ganga in its upper catchment area. The significant feature of the river is its high rates of sediment erosion and chemical denudation. The Alaknanda River catchment area has many major hydroelectric power projects and is always in the news because of environmental concerns. In the present study, both suspended and bank sediment characteristics of the river were evaluated for grain size and composition. The results show that suspended and bank sediment sizes vary from 8.79 to 56.34 µm and 23.73 to 563.24 µm, respectively. Suspended sediments are mostly finer to symmetrically skewed, whereas the tributaries are found to be negatively skewed. In case of bank sediments, grains are moderately sorted and mesokurtic. The provenance determination using rare earth elements and major oxide composition in suspended and bank sediments shows the Higher Himalayas as the dominant supplier of sediments. Along with the sediments, the source reservoir of dissolved load was determined using the water composition and an often used forward model. The results of forward model show silicate and carbonate weathering processes as a major contributor of dissolved load. Using this multi-approach of dealing with sediment and water, geochemical nature of water and sediments of the Alaknanda River has been better understood from the present study.