Runoff estimation for the Karjan River basin using NRCS CN method

The Karjan river basin covers the Narmada, Vadodara, and Surat districts of Gujarat state, India, with the majority of the river basin located in the southern part of the Narmada district. The catchment area is about 1538.38 km². The area has the Rajpipla hills, which are merging with the Saputara and Shyadri ranges. The NRCS CN method was adopted for the estimation of runoff for the years 1999–2021. It was found that the highest runoff was observed in the year of 2020 as 842.11 mm, and the lowest runoff was observed in the year of 2016 as 57.85 mm. The highest rainfall contribution to runoff was observed in the year 2020 as 40.29 percent, and the lowest was observed in the year 2016 as 7.25 percent. The value of the RSR was found to be 0.536, which falls under the category of good model performance; similarly, the percent of bias was found to be -0.489, which is under the very good model performance category, and the Nash-Sutcliffe model efficiency (NSE) value was found to be 0.781 under very good model performance. The coefficient of determination (R²) was obtained from the regression analysis of the observed and estimated runoff values and was found to be 0.816, which shows a good correlation for the years 1999 to 2021.