A procedure for determination of design runoff curve number for Bamhani Watershed

Probalistic estimation of one day maximum runoff is essential for safe and cost effective planning and design of surface runoff storage system. In Present study, One-day maximum and consecutive 2 and 3 day maximum runoff were computed for the Bamhani Watershed. The curve numbers are treated as random variables with the curve numbers associated with antecedent runoff condition II (Normal) representing 50% CN. Those associated with dry and wet are shown to be representative of 10% and 90 % CN value respectively. The design runoff (CN) was estimated for 10-year period by using SCS-CN model. Furthermore, 1, 2, and 3 day maximum runoff was fitted with three probability distribution (Log-normal, Gumble and Log Pearson-III. Of the Three probability distributions employed, Log Pearson type 3 distribution exhibited the best fit for the data. Finally 1, 2, and 3 day maximum runoff was estimated at return periods of 2, 5, 10, 25, 50, 100 and 200 years. The match between the design CN (for dry condition)-generated runoff and the conventional design runoff is found to be satisfactory for all return periods and rain durations for the studied watersheds, indicating the versatility of the proposed approach.