Evaluation of synthetic unit hydrograph methods for the development of design storm hydrographs for Rivers in South-West, Nigeria. Journal of American Science, July, 5(4):23-32.

Abstract

Abstract: This report presents the establishment of appropriate method of synthetic unit hydrograph to generate ordinates for the development of design storm hydrographs for the catchment of eight selected rivers located in the South West Nigeria. Unit hydrographs were developed based on Snyder, Soil Conservation Service (SCS) and Gray methods; while the SCS curve Number method was used to estimate the cumulative rainfall values for storm depth of different return periods. The peak storm hydrographs corresponding to the excess rainfall values were determined based on the unit hydrograph ordinates established. The peak storm hydrograph flows obtained based on the unit hydrograph ordinate determined by Snyder for 20-yr, 50-yr, 100-yr, 200-yr and 500-yr, return period varies from 112.63m3/s and 13364.30m3/s, while those based on the SCS varies from 304.43m3/s and 6466.84m3/s and those based on Gray varies from 398.06m3/s and 2607.42m3/s for the eight watersheds. The analysis shows that the values of peak flows obtained by Gray and SCS methods for five watershed were relatively close, while the values of peak flows obtained by Gray and Snyder methods for two watershed were relatively close and the values of peak flows obtained by Snyder and SCS methods for only one watershed was relatively close. This inferred that SCS method can be used to estimate ordinate required for the development of peak storm hydrograph of different return periods for the river watersheds considered. [Journal of American Science 2009, 5(4); 23-32] (ISSN: 1545-1003