ASSESSMENT OF STORMWATER DRAINAGE SYSTEM IN HAWELA TULA SUBCITY, HAWASSA CITY

Abstract

The major goal of this study was to evaluate Tula Town's current storm water drainage system and to provide ideas or engineering solutions that would be able to resolve the current issues. Storm Water Management Model (SWMM), which is a dynamic rainfall runoff simulation model widely applied for urban drainage, was chosen for assessing the triggering factors as well. Due to insufficient drainage network infrastructure and a rise in urban pavement on most urban sub-catchments, this problem developed. The Rainfall depths of sixteen years (2006-2021) of Tula meteorology station were obtained from National Metrological Agency. An intensity duration frequency curve for different return periods (2, 5, 10, 25, 50, 100yrs) formulated by Log person type III distribution method was used as an input for the model due to its slightly better coefficient of determination than other method. The study made use of the SWMM5.2 model and the low impact development control. The calibration and validation of the SWMM5.2 model well-done and its performance was tested by the goodness of fit using the coefficient of determination (R2 ) =0.98, the Nash –Sutcliffe coefficient (NSE) =0.91, and Relative error (RE) =24.13%. The simulated area of the study subdivide to two outlets of the total area of sub-catchment is 70.55ha joint to drainage system infrastructure of 37 nodes, 48 channels, by SWMM 5.2 model. According to the model's results, more than 50% of drainage infrastructure is flooded. At the outfall, total sub catchment runoff has an average flow of 6.0785m3 /s, a maximum flow of 11.39m3 /s, and an overall volume of 222.228*103 m 3 as predicted by the SWMM5.2 model. The town's ongoing drainage issue is helped by the varied implementation of low impact development techniques. In general, the Tula Town urban drainage system evaluation infrastructure overflow studied and regulated for the problem occurred using the best alternative mitigation measures by enhanced low impact development management for all study sites