Irrigation & Drainage Systems Engineering

Study of Design Rainfall for the case of Beles Sugar Development Project Irrigation Command Area

Abstract

Fikadu Kinfe*, Getachew Gedefaw and Moges Ademe

Drainage problem in Beles Sugar Project is becoming severe during rainfall season that the effective rainfall was greater than the sugarcane water requirement and higher area coverage of vertisols. To remove this excess rainfall through installations of surface drainage system, this study was conducted to estimate design rainfall in magnitude and recurrence interval based on the recorded maximum rainfall. The independent, homogeneity, and outliers of the recorded data were tested accordingly. Probability of exceedence and return periods for daily maximum rainfall was determined using Kimball’s method. Gumbels method was used to compute design rainfall of different desired return period. The relation between observed and computed data was undertaken using regression function. Thus, recorded rainfall data was independent and homogenous at 5% signifance level. Also there was no value greater than the high outliers (151.3 mm) and no value less than the low outliers (41.0 mm).The lowest maximum rainfall (48.6 mm) had a probability of 96 .9% which likely to occur every one year. The highest maximum rainfall (150.1 mm) had a probability of 3 .1% which likely to occur three times in every 100 years period. Within the same 10 years return period, the computed design rainfall (114.7 mm) was deviate by 0.04 with the observed rainfall (110.3 mm).The average deviation of observed and computed rainfall data from its trend line function were 0.004 and 0.002 respectively. The correlation between observed and computed rainfall of trend line function was 0.98, thus it was highly correlated and the perfect reality. Design rainfall for 10 years return period (110.3 mm) was suggested for estimation of Beles Sugarcane open earth drainage channels. Thus, the Project Engineers and Hydrologists has to considered this study pre-requisite for planning, design and management of hydrological, hydraulic, drainage structures, barrages, dams, spillways, bridges, culverts and so on that have been executed in the Project.