FLOOD ESTIMATE USING GIS SPECIFIC TO FLOOD STUDIES FOR UPPER SARADA RIVER BASIN IN VISAKHAPATNAM DISTRICT, ANDHRA PRADESH, INDIA

Abstract

Geographical Information System (GIS) techniques have been effectively used for the study of drainages and estimation of runoff of a catchment. In this paper, the flood estimate of the Upper Sarada River Basin is analyzed using GIS techniques. The Upper Sarada River Basin is analyzed by building a Drainage Elevation Model and thereby extracting the drainage map. The runoff is estimated on this catchment by assuming unit net rainfall (1cm direct runoff) and taking appropriate assumptions. For this purpose, streams in a River Basin are assigned weights with respect to slope of the area and using the same, a travel time contour map represented by isochrones is developed from the equivalent distance map. The flow accumulation map of the drainages is also developed and then this is used to determine discharge at outlet of the catchment. The entire basin area is divided into eleven parts of equal interval of travel time and the yield caused in each part is determined. Further, this is used to determine the discharge at the end of eleven-time steps and the resulting unit hydrograph (UH) is plotted. UH is prepared for the daily average run-off values. An S-hydrograph is also plotted to obtain a UH of selected time duration for the use in flood estimate due to a storm. This hydrograph is validated by taking different selected storm events from the year 1990 to 2019, recorded by Central Water Commission (CWC), Anakapalle station. Eight storm events are observed and these are validated using Thiessen polygon method.