Performance Assessment of Storm Water Drainage System by Stormwater Management Model

Abstract As urban population numbers increase, it is evident that urbanization areas continue to expand. This expansion of urban areas mainly changes the natural land surface to the artificial landscape. The urban landscape is partly impervious, and it will decrease infiltration and in reverse increase the volume of surface runoff which causes several destructions in the town. Thus, the study was to assess the performance of the stormwater drainage system of Ambo town. The data have been used for this study were both spatial and temporal data. Rainfall data for 1987 to 2018 years and digital elevation models, land use, and soil data were used. Additionally, canal dimensions and sub-catchment data were also used. For this study, SWMM for simulating rainfall-runoff, the water level in the junctions, and flow depth in the canal were used. ARC-GIS was used to obtain spatial information and delineate the catchment of the study area. Intensity duration frequency curves of Ambo were developed using Gumbel distribution methods to analyze peak runoff for different return periods. The total runoff from the whole catchment using the rational method is 60.32m 3 /s, whereas the stormwater management model (SWMM) is 60.87m 3 /s. The model performance was evaluated using performance measuring techniques including Nash Sutcliff Efficiency (NSE) and Coefficient of Determination (R2), and the values were RNS = 0.997 and R2 = 0.997 respectively for a ten-year return period which shows the model gives good results. From simulation results, 22% of junctions are insufficient to accommodate maximum flooding, and 21% of canals are surcharged. So, from the simulation results, most of the junction and canal dimensions are insufficient to drain the generated runoff from the sub-catchments. To alleviate these problems, clearing, on-time maintenance, redesign, and constructing the adequate canal are recommended for Ambo town.