Regional flood frequency of Gongola basin (Nigeria) based on L-moment Technique

Abstract

Gongola basin, which has a catchment area of 23,880 square kilometres at Dadinkowa, has only three gauges established in the 1980s. A dam constructed in the 1990s on one of the ungaged rivers failed due to inadequate spillway capacity, which was based on short length of hydrological data. Regional flood frequency of the basin has been developed using L-moment technique to estimate peak flood for the ungaged sub-basin (Cham sub-basin). Daily streamflow data from the three gauged stations (Dadinkowa, Balanga and Tallum) were utilized for the study. L-moment heterogeneity test showed that the three sites constitute a homogenous region. The annual maximum series was fitted to five distributions, namely: extreme value type 1 (EV1), general normal (GNO), Pearson type III (P3), generalized Logistic (GL) and generalized Pareto distributions (GPA). The GPA was adjudged as the best-fit distribution. The mean annual peak floods for various return periods were estimated for the ungauged sub-basin (River Cham basin). The estimated l00 - year flood is 54.88m3/s, which is higher than the value used to construct a dam across River Cham in 1990.