CS(AR)-1/2011 : Modelling non-point source pollution: rainfall-runoff modelling of Dikrong basin using AVSWAT

Abstract

Rainfall-runoff relationship is an extremely complex and difficult problem involving many variables, which are interconnected in a very complicated way. Most of the models work best when data on the physical characteristics of the watershed are available at the model grid scale. This kind of data is rarely available, even in heavily instrumented research watersheds. However, Remote Sensing (RS) and Geographic Information System (GIS) has made it easier to extract land surface properties at spatial and temporal scales. One of the most widely used techniques for estimating direct runoff depths from storm rainfall is the United States Department of Agriculture (USDA) Soil Conservation Service's (SCS) curve number (CN) method. Its use, however, requires a detailed knowledge of several important properties of the watershed which may not be readily available. Many researchers used information derived from satellite data and integrated them with GIS to estimate SCS CNs and runoff. Routing of runoff in river network may be undertaken using a variety of modelling procedures. In this study, variable storage method has been used. In the present report, various model components related to hydrological processes, flow routines, erosion processes, sediment and NPS pollutants yields involved in the SWAT model are discussed with their mathematical relationships used to simulate the processes and their interactions. An attempt has also been made to apply the distributed hydrologic model along with GIS and remote sensing techniques for estimating surface runoff from Dikrong River Basin in Arunachal Pradesh. For the digitization of contours, formation of DEM, and other GIS related tasks, GIS software ArcGIS Desktop 9.3 (ArcInfo License) was used and the modelling part was carried out in distributed parameter model AvSWATX 2005 (Arc View Soil and Water Assessment Tool), which provides a user-friendly graphical user interface over GIS platform ArcView 3.1 for input and output to SWAT2005 model and runs SWAT executables in the backend. The model was calibrated and validated for periods June 2005 to July 2007 and September 2007 to September 2008, respectively. Model was calibrated using the Manning' s n parameter for overland and channel flows. Calibration and validation results revealed that model was predicting daily surface runoff in terms of inflow to proposed Pare reservoir of PHEP (Pare Hydro-Electric Project) at Hoz satisfactorily.