Application of SCS and Snyder Unit Hydrograph Methods for Enhanced Flood Response and Peak Runoff Hydrograph Development in the Foma River Watershed, Ilorin, Kwara State

This study estimated unit hydrograph ordinates and developed runoff hydrographs for the Foma River watershed.  The Snyder’s and SCS synthetic approaches were used to produce the unit hydrograph ordinates, while the SCS type II curve was used to determine the cumulative excess rainfall values for storm depths with 20-yr and 50-yr return periods.  To develop the peak runoff hydrograph, the synthetic unit hydrograph ordinates were convoluted with the cumulative excess rainfall for the 20-yr and 50-yr storm return periods, using the Gumbel Extreme Value Type I (EV-I) probability distribution.  Peak runoff values obtained based on the SCS for the watershed ranged from 68.0 m3/s to 112.0 m3/s for the return periods of 20 and 50 years, while peak runoff values obtained based on the Snyders ordinates for the 20- and 50-year return periods varied between 70.0 m3/s and 90.0 m3/s.  The findings demonstrate that the SCS approach was the most effective for calculating the flow ordinate required to develop the peak runoff hydrograph for various return periods in the research area.