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    ASSESSMENT OF STORMWATER DRAINAGE SYSTEM IN HAWELA TULA SUBCITY, HAWASSA CITY
    (Hawassa University, 2023-10-28) SINTAYEHU BETISO BERASA
    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
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    PERFORMANCE ASSESSMENT OF URBAN DRAINAGE SYSTEMS OF YIRBA TOWN SIDAMA REGIONAL STATE, ETHIOPIA
    (Hawassa University, 2023-10-22) SITOTA MATHEWOS RIKBA
    Developing countries experience accelerated urbanization without adequate investment in infrastructure. Yirba town, like other towns of Ethiopia, have a lot of problems including inadequacy and poor-quality drainage infrastructure. The objective of this study is to assess the hydraulic performance of stormwater drainage systems of the study area, to identify stormwater management issues and existing urban drainage system problems, and to identify the best management practices for drainage problem mitigation measures and to achieve these specific objective SWMM5.2 model and LID structural measures were used in the study. Rainfall, infiltration, and physical characteristics of the catchment area were organized as three main inputs for the model. Rainfall depths of thirty one years (1992-2022) of Yirba station were obtained from National Meteorological Agency. According to chi-square test of the best fit probability is Log Pearson type III distribution and that is used to developed IDF curve. Infiltration of the model area is represented by Curve number method. Physical characteristics of the sub catchments including topography of the model area was analyzed using Goggle Earth and ArcGIS software. The calibration and validation of the SWMM5.2 model were done and its performance was tested by the goodness of fit using the coefficient of determination (R2) =0.97 and Nash Sutcliffe Efficiency Coefficient (NSE) =0.90. The total simulation area of sub catchment is 80 ha; the model area is divided in to 45 sub catchments with a drainage network of 38 conduits, 38 junctions and 2 outfalls. From model result 50% of conduits and 55% of junctions are flooded; at the outfall total sub-catchment runoff is 4.35m 3 /s average flow rate, 10.84m 3 /s maximum flow rate and 91.10*103 m3 total volumes of both outfalls. Among the various low impact development (LID) structural measures, infiltration trench and vegetative swale are incorporated and simulated in the model. Based on the simulation of LID's 10-year return period, improvements in terms of reduced peak discharges and increased peak discharge times were observed in sites where LID was used. In terms of a 10-year period, the peak runoff from particular sub catchments of drains is reduced by a minimum of 1.82% and a maximum of 19.91%. In general, the Yirba town urban drainage system performance infrastructure overflow was assessed and managed for the problem occurring using the possible mitigation techniques by improved LID control for all study areas.