RAINFALL-RUNOFF MODELLING IN AN UNGAUGED WATERSHED USING GIS

Abstract

Hydrological models are powerful tools for the investigation of many hydrological phenomenas. The historical approaches of the development of rainfall-runoff models, with regard to the choice of model structure and the calibration of the free parameters, has been to focus on gauged catchments where sufficient data, in particular stream flow data, are available. Applications of models were then extended to the ungauged catchments. In recent years, it has become apparent that these approaches did not lead to satisfactory results in ungauged catchments, and that the main focus should instead be on ungauged catchments for the implementation of new modelling strategies. Geographic Information System (GIS) is a computer based system design to store, process and analyzes spatial data and their corresponding attribute information. GIS generates more valuable information from the existing data (digital map) by overlaying two or more data base. User can apply a mathematical model for analysis of data and can get outputs in digital form. The work presented in this study is "Rainfall - Runoff Modelling in an Ungauged Watershed Using GIS". Determination of runoff using SCS (curve number) method is widely used to assess the runoff generated from small agricultural watershed. In this dissertation emphasis is given on the application of GIS for rainfall-runoff modelling using SCS Method. Some basic principles of GIS have been systematically explained with illustrative figures for general conceptual understanding. Deshgaon (Dist. Khandwa, M.P.) and Ozarkhed watershed of district Nashik, Maharashtra (No. 11/06/05/DC1 a) of Damanganga catchment have been taken for the case study. Available maps and data have been compiled for the purpose of this 111 study. Basic of GIS and SCS runoff methodology have been described in details. ERDAS 8.6 and ARC GIS 8.3 software are used for Image Registration, Digitization and Modelling purposes. The runoff generated from watershed was estimated using SCS method and historical rainfall data. The model parameters, Curve Number (CN) and Surface Retention (S) were evaluated under different Antecedent Moisture Condition (AMC), hydrological soil group (HSG) and land use conditions. Runoff was estimated using both GIS and Conventional method and results are compared. Sensitivity Analysis was also done to determine the most sensitive parameter for the SCS model. Finally the results, along with brief discussion, summary and conclusion are presented.