Rainfall-Runoff Analysis using Runoff Coefficient and SCS-CN Methods under GIS Approach

Abstract

Estimation of runoff in a watershed is very important to manage the water resources efficiently. In this regard, surface runoff quantification is an essential study. The main objective of this study is to quantify the surface runoff of the catchment area of a well located in AEC & RI, TNAU, Kumulur, Trichy District of Tamil Nadu State, India. An attempt also made to analyze the surface runoff by SCS-CN event and annual basis as well as by modified runoff-coefficient method. This study identified the variation of runoff volume within different approaches of SCS-CN method and runoff coefficient method. By using GPS and GIS techniques catchment area of a well and slope direction was delineated. With the help of GIS tools and remote sensing technology with ground truth verifications, the land use/ land cover and soil maps were delineated for the study area. Sandy loam and sandy clay loam type of soils are predominating and HSG ‘C’ was identified for the study area. The highest CN value is 92 and the maximum runoff coefficient value is 0.95 for the Built-up land, the lowest CN value is 71 and the lowest runoff coefficient is 0.11 for the area covered with trees. Three AMC conditions were considered while estimating runoff volume by SCS-CN event approach. Among 15 years of rainfall data from 2004 to 2018, the highest runoff 38452.36 m3 was generated in the year 2005 and the lowest runoff 8718.29 m3 was generated in 2018 by SCS-CN event basis method. From this study between two concepts of SCS-CN and runoff coefficient models, the SCS-CN model with an event basis approach is yielding productive results. For quantifying surface runoff and for planning water conservation structures event basis calculations are more effective.