Assessment of design runoff curve number for Maithon watershed

Abstract

Estimation of storm event runoff is one of the major activities in applied hydrology for ungauged small watersheds. There exist a myriad computer models in the field of water resources and irrigation engineering and the most comprehensive and popular ones use the Soil Conservation Service (SCS) curve number methodology to determine the rainfall-excess from rainfall event. The SCS Curve Number (CN) (SCS-CN) technique is one of the most popular and well accepted techniques for it is a simple approach for direct runoff estimation. Its parameter CN is a measure of water retention by a given combination of soil and vegetation and varies from 0 (no runoff) to 100 (all rainfall becomes runoff). In this study, considering each day’s rainfall and corresponding runoff as an event, the SCS-CN method is employed to longterm daily rainfall-runoff data of Maithon watershed located in Jharkhand (India). A simple approach has been suggested for derivation of the design runoff CN for different durations, antecedent moisture conditions (AMC_s), and return periods for use in the SCS-CN methodology.

The derived design CN values are tested for their validity using the design runoff computed from observed data conventionally. The match between the CN-generated design runoff and the conventional one is found to be satisfactory for return periods up to 10-year return period for the studied watershed.