41-Suspended Sediment Transfer in a Himalayan Headwater Stream - Glacier vs Monsoon.

Abstract

Sediment load in the Himalayan rivers are many fold than the world average. Being the youngest and tectonically active mountains, increased erosion during the monsoon is sited as one the reasons for the higher erosion rate. Even though the glaciers are widely accepted as a powerful erosion agent, role of glaciers, occupying the higher altitude of Himalayan headwater river catchments received little attention due to lack of data generated from these areas. Hence our present understanding on the sources and processes responsible for the high sediment flux in the Himalayan Rivers is mainly in the realm of hypothesis. Dominant role of monsoon in transporting high sediment load in the Himalayan rivers is assumed because of the high quantum of sediment transported during the active monsoon months of July and August. Present study carried out in the Din Gad catchment, a micro scale Himalayan catchment, has designed for a better understanding of the role of glaciers and monsoon in controlling the suspended sediment transfer in a Himalayan glacier fed stream. Discharge and sediment concentrations were measured at three altitudes, including at the Dokriani glacier snout during the entire ablation period for three consecutive years since 1998. Overwhelming glacier contribution in the stream suspended sediment flux has been demonstrated in the present study. Average contribution of sediment flux from the glacier covering 13% of the Din Gad catchment was around 60% and 75% at 2360 m and 3400 m a.s.l. respectively. Suspended sediment yield of the glacier catchment ranged between 9611-2038 tonnes/km2 and the area under the monsoon influence range between 179 to 1005 tonnes/km2.This study demonstrates the dominant role of glaciers in determining the sediment transfer characteristics of Himalayan headwater rivers.