DEVELOPMENT OF INTENSITY-DURATION-FREQUENCY ELATIONSHIPS FOR THE SNNPR

Abstract

Intensity-Duration-Frequency (IDF) relationship of rainfall amount is one of the most commonly used tools in water resources engineering for planning designing, and operation of water resources projects. The IDF allow for the estimation of the return period of an observed rainfall event for different time durations conversely, it may be used to estimate rainfall amount corresponding to a given return period for different aggregation times. The objective of this research is therefore, to develop operational IDF relationships for the SNNPR state based on nineteen first class stations. The annual maximum rainfall magnitudes of varying duration were collected from rainfall charts and fitted to the probability distributions after which quantiles estimated for different return periods based on the best fitted distributions. Rainfall Intensities are then calculated and the parameters of the general mathematical form of IDF were generated for each station. Three different methods expressing rainfall intensities have been developed to the study area; methods expressing rainfall intensities have been developed to the study area; the general mathematical form, curves relating Intensity-Duration-Frequency of rainfall and the IDF maps. To extract the intensity of rainfall of any duration and frequency at areas farthest from the principal stations, the SNNPR State has been regionalized and the regional IDF parameters and IDF curves are developed for the established regions. The result of this study can be used to all water professionals and designers on the activities of water resources and other related disciplines with in the region by supplying important information's on rainfall Intensity, Duration and Frequency relationships.