Water Quality Modeling Using Soil And Water Assesment Tool: A Case Study Of Rawal Watershed

Abstract

The water quality of Rawal watershed has been highly deteriorated because of increased concentration of organic nitrogen and phosphorous coming from non­point sources causing eutrophication. The main objective of this study was to use a watershed scale model SWAT(Soil& Water Assessment Tool)as a modeling tool for predicting the impact of the Land Use change on water quality of Rawal Lake. In the pre field study phase the collection and preprocessing of data (DEM & Landsat images was done. Land Use (2001 & 2010) classification was done using Landsat imagery in ArcGIS. For the pollution source inventory mapping the study area was surveyed. In the post field study phase the model was calibrated (2002-2006) by using the observed and simulated surface runoff data and then validated (2007-2010).The model's accuracy was further verified by using R2 and Nash Sutcliffe Efficiency statistics. SWAT simulations resulted in 392.40 % and 391. 72 % increase in the quantity of organic nitrogen and phosphorus with respect to Land Use change (2001 & 2010). By the application of BMP's such as filter strips, the average reduction in the concentration of N could be 75.15% while that of P could be 96.93%, similarly by the application of terracing the average reduction in the concentration of N could be 52.73% while that of P could be 94.18% in the selected sub basins. By the application of contouring the average reduction of 35.64% for N and 92.09% for P could be achieved. This study could provide decision maker a source of information on most feasible and cost effective BMP's XII