SCS-CN-BASED LONG-TERM HYDROLOGIC SIMULATION

Abstract

Runoff estimation is essential for planning and management of water resources projects. A number of models varying from the simplest empirical relations to the most complex physically based models have been suggested in literature to mimic the complex phenomenon of rainfall-runoff. The Soil Conservation Service Curve Number (SCS-CN) method is one of the simplest and most popular methods available and widely used world over for predicting direct surface runoff from given storm rainfall amount. Of late, the method has also been employed in long term hydrologic simulation. In this study, an SCS-CN-based long-term simulation model is proposed and tested on the 10-year daily data of three watersheds namely Betwa catchment (area = 4122 sq. km), Ret catchment (area = 262sq. km), and Siul catchment (area = 360 sq. km). The available 10 years of data of each watershed was split into two parts. The first part of data was used for calibration, and the other for validation. Simulation was carried out using yearly data and the whole data. Besides, a yearly volumetric analysis, a sensitivity analysis of the three parameters of the • proposed model was also carried out. It was seen that the model performance degraded with the increase in length of data. In both yearly simulations and in calibration as well as validation, the proposed model showed a satisfactory performance, i.e. with significantly low relative errors. The least sensitive and most significant parameter CNo of the SCS-CN model indicated its • amenability to field applications employing the NEH-4 CN values or the CN values derived using remote sensing data. Over and above all, the model is simple, has three parameters, and is dependable for field applications.