Determination of probability distribution for data on rainfalland flood levels in Bangladesh

Abstract

To evaluate flood (Discharge or water level) as well as rainfall frequency of given returns period, it is essential that one probability distribution function be used as a standard. In many countries one distribution function is used as a standard but in Bangladesh various frequency distribution function are in use. The main objectives of this study are to compare the probability distribution function for the application on flood and rainfall frequency analysis in Bangladesh. To compare it, three widely used distributions have been used namely: (1) Log Normal (Two parameters, LN2 and three parameters, LN3); (2) Extreme value Type-1 (EV1) or Grumbel and (3) Log-person type-3 (LP3) distributions. For this purpose, 5 set data of annual maximum runoff of different main rivers in Bangladesh and 3-days and 5-days rainfall data of Bhola Island (8 sets) have been used. The parameters of the distributions have been estimated by using the method of moments and method of maximum likelihood.