Identification and Prioritisation of Critical Sub-watersheds for Soil Conservation Management using the SWAT Model

Abstract

A few areas of the watershed are critical and responsible for high amount of soil and nutrient losses. Implementation of best management practices is required in those critical erosion prone areas of the watershed for controlling the soil and nutrient losses. Identification of these critical areas is essential for the effective and efficient implementation of watershed management programmes. In this study, a calibrated Soil and Water Assessment Tool (SWAT) model was verified for a small watershed (Nagwan) and used for identification and prioritisation of critical sub-watersheds to develop an effective management plan. Daily rainfall, runoff and sediment yield data of 7 years (1992–1998) were used in this study. Data related to nutrient losses for few storm events of 1997 were also used. Besides these data, the topographical map, soil map, land resources data and satellite imageries of the study watershed were used in this study. A geographical information system was used for generating the watershed and sub-watershed boundaries, drainage networks, slope, soil series and texture maps. Supervised classification method was used for land use/cover classification from satellite imageries. The weighted average values of parameters such as runoff curve number, surface slope, channel length, average slope length, channel width, channel depth, soil erodibility factor and other soil layer data were taken for each sub-watershed to verify the model. The calibrated SWAT model was verified for the monsoon season on daily basis for the year 1997 and monthly basis for the years 1992–1998 for both surface runoff and sediment yield. It was also tested for the available data on nutrient losses. Critical sub-watersheds were identified on the basis of average annual sediment yield and nutrient losses during the period of 3 years 1996–1998. The erosion rates and their classes were used as a criterion for identifying the critical sub-watersheds. Out of the 12 sub-watersheds, one sub-watershed fell under moderate soil loss group and five sub-watersheds fell under high soil loss group of soil erosion classes whereas other sub-watersheds fell under slight erosion classes. The study revealed that the SWAT model could successfully be used for identifying and prioritising critical sub-watersheds for management purposes.