Erosion response model for watershed prioritisation in Bajaj sagar sub catchment, Mahi basin

This case study presents a erosion response model for watershed prioritisation in Bajaj sagar sub catchment of Mahi basin. The natural hydrologic processes like erosion of soil, movement of soil and its deposition in various parts of reservoir are very crucial phenomena occurring in any watershed. Erosion of soil is a very complex process which is affected by many factors and the loss caused is irreversible.

Soil erosion starts from the upper reaches of watersheds and then slowly gets transported to the downstream reservoir causing the reduction in useful storage capacity of reservoir. Land and water management on watershed basis has a scientific proven base, which helps in reducing soil erosion, increasing the productivity along with proper and sustainable utilisation of resources. 

For larger watersheds, where the detailed soil maps are not available and preparation is costly and time consuming, a method which uses the layers derived from satellite data is most convenient. Priority of watershed depends upon various parameters. The present paper analyses the response from a watershed using Erosion Response Model (ERM). In this method vegetation density, soil brightness, slope and morphometric parameters are used for watershed prioritisation. ERM utilises drainage and slope characteristics of watershed for prioritisabon. ERM model adds the weights of each affecting parameter and calculates the response of watershed. 

The process of prioritisation requires integration of all the themes and coding the watershed for priority. Higher the sum weight, more is the priority of watershed. As per the coding the watersheds were prioritised as highly critical, critical,, low critical and not critical.

Results of prioritisation of all the seven water-sheds of Bajaj Sagar dam sub-catchment, based on satellite data of October 1994 and March 1993 have been given. The watersheds of the sub-catchment are forested watersheds hence the response from the watersheds will be almost similar for different seasons. Seasons do not have a major influence on the response. One of the three direct draining watersheds is in highly critical category and the other is critical. Direct draining watersheds have very high priority. This is also justified by the fact that these watersheds will give more silt load to the reservoir. Form factor and slope are other prominent factors affecting the priority.

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