An Estimation of the Probability Distribution of Wadi Bana Flow in the Abyan Delta of Yemen

Wadi Bana is one of the main Wadies in Yemen, where different quantities of water reach the Delta and depends on the amounts of rainfall in the wadi watershed. In order to estimate the spate water flow distribution probability, data on water flow were collected during the period from 1948 to 2008. Seven probability distributions, namely, Gamma, Weibull, Pearson 6, Rayleigh, Beta, Kumaraswamy and Exponential distributions were tested to model the distribution of the Wadi Bana flows and Kolmogorov-Smirnov, Anderson-Darling and Chi- Squared goodness-of-fit tests were used to evaluate the best fit at 5 % level of significance. It suggests that the best frequency distribution obtained for the Wadi Bana flows in the Abyan Delta of Yemen is Gamma followed by weibull distribution for both summer and autumn seasons. The annual maximum runoff was 286.6 million m3 in the 1957 and the minimum runoff was 30.4 million m3 in 1974. The estimated flow during wet, medium and dry years were 103–134, 76–103 and 55–76 million m3 respectively for autumn season and 52–81, 29–52 and 15-29 million m3 respectively for summer season. The flow in autumn season reaches about 70% of total annual flows.