Abstract:
Probable maximum precipitation is a basic and fundamental data for determining the
probable maximum flood in the design of hydraulic structures. It is defined as
theoretically greatest depth of precipitation for a given duration that is physically
possible over a given size storm area at a particular geographical location at a certain
time of the year. Developing Isohyetal map was to overcome the problem of inadequate
information and to facilitate quick estimation of PMP values for ungauged catchments
in the basin. The General objective of this study was to estimate probable maximum
precipitation and development of Isohyetal map for bilate sub river basin. It was
provided to overcome the problem of inadequate information and to facilitate quick
estimation of PMP values for ungauged catchments in the basin. Statistical package
for social science20, Global mapper18, Digital Elevation model and MATLAB R2018a
were the material used to progress the work. L-moment was a parameter for selection
of distribution as candidate distribution. normal, log normal, Gamma, Extreme value
type one and General extreme value was used, and values were subjected to goodness
of fit tests of chi-square and Kolmogorov-smirnov tests to assess how the data has been
the best fits. Diagnostic D-index was used to separate best distribution to predict
different year return period rainfall depth from fitted distribution. Accordingly, the
minimum D-index value was for General extreme value and parameter of Probability
weighting method to station of Angecha with value of 0.024. Isohyetal map over bilate
have been generated by means of Arc Map 10.4.1. Estimated value of Probable
maximum precipitation was found that from 71.581mm to 128.571mm of stations
Durame and Humbo respectively for 1-day duration and the statistical Hershfield Km
was estimated as 1.717 to 3.231, belongs to stations of Durame and Hossana with an
average value of 2.418 for 1-day duration. the overall monitoring data series at stations
are taken into account the Probable maximum precipitation value calculated by
statistical method is more suitable.
