Intensity duration frequency curve analysis for selected meteorological stations in North Shoa, Amhara Region, Ethiopia

Abstract

The estimation of rainfall intensity is required for the design of hydraulic and water resources engineering control structures. Rainfall data of 11 – 23 years long from four stations was used to generate Intensity-Duration-Frequency (IDF) curves and parameters for selected stations in the study area. The daily rainfall data set obtained was then subjected to frequency analysis to determine the distribution which best characterizes the data set. The result showed that Log Person Type III was the best fit probability distribution function. The annual extreme values of rainfall depth were computed for different rainfall durations and return periods. Ranked rainfall depths for each return period were converted to rainfall intensities. The corresponding rainfall intensities were computed for different rainfall durations and return periods. IDF curves were developed using MIDUSS 2.25 software for return periods of 2, 5, 10, 25, 50, and 100 years and for durations of 1, 2, 3, 6, 12, and 24 h, and determined IDF parameters. The results shown that for shorter durations (1 hour and 2 hours), the IDF curves gave higher intensities for the same return period while for longer durations (3 h, 6 h, 12 h and 24 h), they gave low intensities for the same return period. The IDF relationship developed can be used as valuable tool for the designing of hydraulic structures in the region. This study could serve as a spring board for other studies that imply the calculation of a peak flow and designing of hydraulic structures as an input to help improve flood resilience in the region.