PERFORMANCE ASSESSMENT OF URBAN STORM WATER DRAINAGE SYSTEM OF BUTAJIRA TOWN, SNNPR, Ethiopia (USING SWMM MODEL

Abstract

Storm water drainage problem is a major challenge facing most of the Cities and Towns in Ethiopia including Butajira Town. Drainage problem in Butajira Town cause the worst problem of over flooding and over toping drainage system during high rainfall season in a town. The objective of this study isto assess the performance of drainage system of Butajira town. The study employed both primary and secondary data collection. To achieve the specific objective SWMM5 model and LID control used as method. The SWMM was used to simulate the storm drainage flow. The calibration and validation of the SWMM5.1 model was done and its performance was tested by the goodness of fit using the coefficient of determination R2 = 0.98, the Nash –Sutcliffe coefficient NSE =0.87 and Relative error RE =19%. The total simulated sub catchment in this study is 173.83ha joint to drainage system infrastructure of 12 junction, 12 channels, are simulated by SWMM5.1, From model result greater than 25% of drainage infrastructure is flooded, at the outfall total sub-catchment runoff is 1.904m3/s average flow, 2.011 m3/s maximum flow and 33.95*103 m3 total volume of all outfall. Finally, from simulation results, most of junction’s canal dimensions are insufficient to drain the generated runoff from sub-catchments. To alleviate these problems, applying LID and construction of additional drainage structures with proper dimension, design and construction of well-connected structures, adopting the culture of clearing waste materials and periodic maintenance of drainage structures before failure were the remedial measures to be taken to solve the problem of highly flooded study area specially sub catchment S8 and S9.