Assessment and Modeling of Urban Drainage System Performance (A Case Study of Mojo Town)

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Addis Ababa University


The drainage system is one of the most important factors to be considered in the urban drainage infrastructure plan. Now inadequate urban stormwater drainage problems represent one of the most common sources of compliant numerous towns of Ethiopia. Drainage problem in mojo town the worst issue of over flooding on the surface runoff at high rainfall season. This difficulty occurred due to inadequate drainage network infrastructure and the increase in the urban pavement on most urban sub-catchments. The objective of this study to identify the critical condition and related problem with a drainage system, assess the hydraulic performance of stormwater drainage infrastructures, and to evaluate alternatives for drainage problem mitigation measures are achieving this specific objective SWMM5.1 model and LID control was used in the study. The calibration and validation of the SWMM5.1 model well-done and its performance was tested by the goodness of fit using the coefficient of determination (R 2 ) =0.97, the Nash –Sutcliffe coefficient (NSE) =0.96, and Relative error (RE) =11.16%. The simulated area of the study subdivide to four outlets of the total area of sub-catchment is 745.2ha joint to drainage system infrastructure of 93 nodes, 101 channels, and one divider are simulated by SWMM 5.1 model. From model result greater than 60% of drainage infrastructure is flooded, at the outfall total sub-catchment runoff is 6.88m 3 /s average flow, 22.44m 3 /s maximum flow and 3 583.07*10 3 m total volume of all outfall. The LID control used in this study for reduced the peak runoff overflow and select the best alternative on the outlet one of the project in the same sub-catchment S1, S2, S3, S5, S6, S9, S10, and S12 were the reduced the total outlet one volume by 28.12% using bio-retention Cell scenario, 25.9% infiltration trench scenario, 26.71% using permeable pavement scenario and also on sub-catchment reduced total volume outfall one reduced by 3.02 % using vegetation swale scenario. All scenarios used two of the highest value of runoff decreased by Bio-retention Cell scenario and permeable pavement for total study applied. by using two selected Lid control total volume of all outfall from 583.07*10 3 3 m is reduced to 425.89*10 3 3 m by 36.92% from the total study. Generally, the mojo town urban drainage system performance infrastructures overflow assessed and controlled for the problem occurred using the best alternative mitigation measures by improved LID control for all study areas.



Drainage systems, SWMM5.1, performance, LID, alternative mitigation