SEDIMENT YIELD ESTIMATION AND RISK MAPPING OF NUTRIENT EMISSION IN A SUBTROPICAL WATERSHED

Abstract

Soil erosion in catchment areas and subsequent deposition in rivers, lakes and reservoirs is of great concern for two reasons, firstly, rich fertile soil is eroded from the catchment area, and secondly, there is a reduction in reservoir capacity. On the other hand, nutrients are having strong bonding with sediment, thus they can be transported into the water bodies, which induce the eutrophication phenomenon in receiving water and loss of biodiversity in the aquatic ecosystem. A proper soil conservation planning often requires estimation of soil erosion and identification of nutrient and sediment emission sources. The catchment of Ramganga at Naula gauging site has been used for the present study. The watershed is geographically located between 29°44'N and 30°620"N latitude and 79°615E and 79°3115"E longitude in the Ranikhet forest sub-division of Ramganga river catchment. The study area is located in the Himalayan range and due to complex topography; it is highly vulnerable to soil erosion and nutrient transport. In the present study sediment yield has been estimated using combination of USLE and sediment delivery ratio in a distributed manner in a GIS. The GIS technology has been used to divide the catchment in small grids for application of USLE. The overland flow travel time based distributed sediment delivery ratio has been used for representing sediment delivery characteristics of catchment instead of lumped SDR. For computation of cumulative travel time from an erosion source cell to drainage channel a programme has been developed in C++ language.