Developing Rainfall Intensity Duration Curve for Selected Towns in Western Part of Ethiopia

Abstract

Rainfall and Its Intensity is needed for planning and designing of various water resource projects including infrastructure such as the design of urban drainage works, Storm Sewers, Culverts and etc. The main aim of this research was to develop Rainfall intensity duration curve for the selected towns in western part of Ethiopia. Gumbel and the Log Pearson Type III Probability distribution (LPT III) were used to develop rainfall intensity duration curves for the selected towns in western part of Ethiopia. The IDF curves developed by Gumbel’s Extreme value distribution shows, the pattern similarity for all return period, duration and all considered stations but the rainfall intensity shows an increasing with increase in the return period and decrease with rainfall duration increase in all return periods and also show high Rainfall intensity (mm/hr.) so that it was used to derive Empirical equation using Logarithmic transformation method to determine the constants (C, m, a) considered to derive the equation. Then the comparison was made between rainfall developed by using Gamble’s Probability distribution and computed by Empirical equation. In all return period and duration of time it shows good relation which approximately equal to unity (R2) but for 1000 return period differs which is still acceptable without any uncertainty for further application. So, the developed Rainfall intensity duration curves and derived empirical equations can be used for the planning and design of any Water Resources projects and infrastructure in the towns related to water resources.