IMPACT OF LAND USE CHANGES THE CATCHMENT ON THE QUALITY AND QUANT1TY OF WATER IN THE RAJANGANA RESERVOIR

Abstract

The condition of the watershed plays an important role in the quality and quantity of thewater of reservoirs. Among the factors, which affect the health of a watershed, areclimate, geology and land use management. Rajangana watershed drains water to theRajangana reservoir, which irrigates about 5520 ha in the dry zone.

In the present study, total monthly inflows to the reservoir were calculated through awater balance study and water inflows from the catchments were obtained through asensitivity analysis using past records. Land use changes were studied by using existingland use maps (1: 50,000) using GIS software. Some water quality parameters in thereservoir waters were analysed. These parameters were compared with the ones takenduring the past 10 years from past records of the MASL in order to identify any trendswith the changes of rainfall, temperature, land use etc.

The results showed that the annual total water inflow and also the inflow during the dryseason decreased with time. These trends correlated with the increase in built up areas,reduction of forest cover. Further, there was a marked increase of the pH and alkalinity inthe waters with time