ABSTRACT
This project describes a procedure for estimating the design floods from regional frequency curves for ungauged areas drained by rivers Ogun and Oshun of Western Nigeria. Streamflow records at nine gauging stations were used for the study. For estimating purposes, two relations have been derived. The first relates graphically the mean annual flood to basin physiographic factors namely: the size of drainage area and the length of main channel. The second relates the mean annual flood to the physiographic factors empirically. From these, the mean annual floods for a basin is estimated and used to obtain design flood from a regional flood frequency quency curve derived for the basin. The regional flood frequency curve expresses the flood discharge-time relation, showing variation of peak discharge, expressed as a ratio to the mean annual flood, with recurrence interval.