Abstract:
Hydrological studies are useful in planning, designing and managing water resources,
infrastructures. Probable maximum precipitation is ideally the maximum precipitation
depth for a given duration at a definite geographical location at a specific time in a year
or season. PMP value should be estimated by more than one method for critical
hydrologic regulations, and preferably by both statistical and moisture maximization
methods. The aim of this study is to estimate and compare the reliable probable maximum
precipitation values and computing Various return period Rainfall Depth for estimated
PMP values for Abelti watershed, Omo Gibe River basin, in South Western Ethiopia.
Daily Rain fall, maximum temperature and relative humidity and Micro soft excel-2016,
R-package, digital elevation model and Arc Map 10.4.1 were data and software used to
analysis the study respectively. In this research, annual maximum one day duration
rainfall data of 31 years from 8 stations based on statistical and three station based on
moisture maximization methods in the Abelti catchment were analyzed to estimate PMP
respectively. Probability distribution such as normal, lognormal, gamma and Weibull
values were subjected to GoF test and Chi-square, Anderson-Darling and Kolmogorov Smirnov tests to assess how best the fits had been. Results showed that the lognormal
distribution performed best for study area. The statistical Hershfield’s Km varied from a
minimum of 2.16 at Sekoru station to a maximum of 5.0 at Gedo for a 1-day rainfall
duration. So, the maximum frequency factor (Km) obtained from statistical method on the
study area was 5.0. The maximum PMP values estimated from statistical method for 1-
day durations were 173mm observed at Limu Genet station. The PMP values Estimated
by statistical method was 1.63 times higher than the maximum rainfall record. The PMP
estimated from the Moisture Maximization method is average of 1.94 times higher than
the PMP founded from statistical approach. The PMP values were also derived for
different return period values and found to vary between 45.5 mm at 2 years return
period for Gedo station and 194.5 mm at 10,000 years return period at Wolkite station.
