Development and Regionalization of Intensity- Duration­ Frequency (IDF) Relationships for Amhara and Tigray Regions

Abstract

Rainfall of a place can be completely defined if the intensities, durations and frequencies of the various storms occurring at that place are known. Intensity­ Duration-Frequency (IDF) relationship is one of the most commonly used tools which provide essential information for planning, designing and operation of water resource projects. Therefore, the main purpose of this research work was to develop operational IDF relationships for Amhara and Tigray regional states based on thirty three first class stations. Rainfall charts of different years were used to collect annual maximum rainfall depths of varying durations. The best fitted probability distributions are selected for all the principal stations and based on these distributions quantiles are estimated. With the help of the general mathematical forms of IDF, IDF-Curves and IDF-Maps intensities of each station were determined. Amhara and Tigray regional states have been regionalized and five different regions were established based on pooled quantiles of the 24-hour durations. And the regionalization is used for the determination of intensity of rainfall for areas farthest from the principal stations. IDF relationship being an important hydrologic tool it helps to fill the gap between the design need and the unavailability of design information. Therefore,