Development of Intensity Duration Frequency Curves for Wolkite Town

Abstract

One of the major challenges faced by engineer and hydrologist is insufficient or non-availability of hydrological and meteorological data to appropriately design, operate and plan water resources against extreme rainfall event. Such data would be needed for the development of Rainfall _Intensity _Duration-Frequency (IDF) curves for design of culverts, ditches, storm drainage and different hydraulic structures in urban area systems. The main objectives of this paper is to compare and contrast the existed IDF Curve for the study area which is prepared by Ethiopian Road Authority and the one which is calculated and organized specifically for the town by this researchers, and to derive the IDF curve relationship of the rainfall data which is found in Wolkite metrological station of Ethiopia. This study analyzed the daily rainfall data collected from Ethiopian Meteorological Agency (EMA) Addis Ababa, for five (5) stations in the southern nation, nationalities and peoples of Ethiopia. But only one of the stations which founds in Wolkite towns has adequate daily rainfall recorded for about 33 years (1987-2019). The data was processed and analyzed using Microsoft Excel spread sheet to generate series of peak annual rainfall. The rainfall intensity values were calculated for different duration of (10-200) minutes to estimate returns period of (2, 5, 10, 20, 50, and 100 years) using Gumbel Distribution Methods and Log Pearsons III Distribution Methods. The R2 test was used to confirm the appropriateness of the fitted distributions for the locations the two distribution methods. The result shows that Gumbels distribution methods has larger R2 values and the best fit from the two distributions, and the two distribution methods deliver almost all similar results, however the Log Pearsons method has greater results than Gumbles distribution methods. The developed IDF curve delivers larger amount of intensity than that of IDF curve developed by ERA for similar time of duration in minutes. Finally IDF curves were developed for the towns and recommended for the design of storm drainage system.