Spatial Estimation of Runoff Using SCS-CN Embedded in GIS Environment: A Case Study of Nalgonda District of Telangana, India

The main aim of the study was to calculate runoff using the Soil Conservation Service Curve Number (SCS-CN) approach in the Nalgonda district of Telangana, India. The data required for the study was a soil map and a land use land cover map for the calculation of the curve number. The curve number ranges from 1-100 for different land use and soil condition. CN I = 62.57, CN II = 79.22, and CN III = 89.93 are the hydrological soil groups of the AMC conditions for dry, normal, and wet conditions. Rainfall is the most important factor influencing the runoff. The daily rainfall data from 2011 to 2020 were collected from the NASA POWER data viewer website based on latitude and longitude. The highest rainfall was observed during 2013 and 2020 with 987.05mm and 1136.62mm respectively. The runoff was also observed highest in the years 2013 and 2020 with 89.24mm and 89.60mm respectively. The year 2015 is absorbed as a drought year by the Telangana state government with rainfall of 451.68mm and the runoff was observed the lowest at 0.22mm. The total average annual volume of runoff calculated for the Nalgonda district is 207773154.2 m3 from the study area of 7148077000 m2. From 2011 to 2020, the observed percentage of rainfall converting to runoff in the study area was 24.22%. According to this study, it has been concluded that an increase in rainfall results in an increase in runoff. The information is useful for the water resource Engineers to plan the water harvesting methods to increase groundwater resources.