Evaluation of the Existing stormwater drainage System, in the Case of Bishoftu City, Ethiopia

Abstract

Urban stormwater management is a key issue in line with Global problems of urbanization and climate change. Effective management of urban stormwater is essential for alleviating the negative effects of urbanization on the natural hydrological cycle and fostering sustainable urban development. The main aim of this study is to evaluate the current stormwater drainage system from both hydraulic and hydrologic points of view. This assessment seeks to investigate the cause of the flood problem in the study area through site investigation and collecting stormwater drainage structures data, land cover data, soil data, and Digital Elevation Model (DEM) to investigate the actual stormwater-related flooding problem in the study area. The methods utilized to accomplish this goal generally, executing literature reviews of existing studies and data, measuring the dimensions of the existing drainage channels, rainfall data analysis, and soil, DEM, and land cover data analysis. Storm Water Management Model (SWMM) 5.2.4 was implemented for the drainage network modelling, with the rational method employed for comparative analysis. The simulated study area consists of 45 sub-catchments with 695 a total area, 69 junctions, 69conduits, 3 outfalls, and 1 rain gauge station. The simulation indicates that the total runoff from the entire area using SWMM is 97.34 m3/sec, while the rational method yields a runoff of 90.87 m 3/sec. and that 46% of the nodes of the study area are flooded, and 46% of the conduits of the drainage system are surcharged. Accordingly, the overall study result shows that under the current rainfall conditions, the system responded with serious problems and was not able to drain the generated runoff. Therefore, it is essential to understand the hydrologic pattern of the area and its impact on the present functionality of the drainage system in order to develop effective mitigation strategies.