Abstract

This study applied Log-Pearson Type III probability distribution to model time series annual peak flow records of River Niger recorded at Lokoja gauging station. This was necessitated by the need to provide reliable data for safe and economic hydrologic design for security of lives and property at downstream of river Niger basin. Though several methods have been adopted in the study area for flood mitigation, however, it has become apparent that these measures are inadequate and no attempt has been made to apply statistical approach for provision of sustainable solution. Though flood cannot be prevented but the impact can be reduced by applying adequate counter measures. Therefore, this study shows the result of flood frequency analysis based on annual peak  flow measurement covering a period of 18 years (1995-2012) carried by National Inland Water Ways (NIWA) at Lokoja gauge station. The probability distribution function was applied to return periods (T) of 2, 5, 10, 25, 50, 100 and 200 years. The predicted discharges corresponding to these return periods are 18886.065, 22425.127, 24889.683, 28145.456, 30670.104, 33281.363 and 35997.757 m3/s, respectively. This study also revealed that the return period of 2012 flood is over 50 years. The predictive model which relates the expected discharge to return period is given by X = 3679.7 In(R) + 16381 where X is the expected discharge and R is the return period.

Key words: Flood, return periods, discharge, prediction, hydrologic design.