Stormwater Characterization and Detention Pond Modeling for Effective Stormwater Management: The Case of Adama Science and Technology University Campus, Ethiopia

Abstract

Urban runoff if not managed properly is a major catastrophic trait of many cities around the world, which is a result of manifold and uncertain factors such as, hydrological factors, urbanization, climate change and infrastructure inadequacy and failures that result in property damage, critical infrastructure distraction and loss of lives. Adama Science and Technology University (ASTU), with approximately 150 ha area, sits on high ground relative to the surrounding flood-prone neighborhoods. Although the university campus is not prone to prolonged flooding, the excess stormwater drains to the downstream catchments without provision of proper stormwater management and stormwater reuse causing erosion and pollutant migration to the downstream areas. The main objective of this research was to assess the stormwater characteristics of ASTU campus and to model its detention ponds for effective stormwater management. To achieve the objective, the ASTU campus catchment was delineated into 18 sub-catchments, and the Sewer Geospatial Engineering Modeling (SewerGEMS) software was used to determine the peak runoff from the campus catchment and to analyze the hydraulics of the drainage system on campus. Additionally, manning equation was used to assess the existing drainage network of ASTU campus. Model simulation for pre- and post development scenarios was also performed to identify the effects of land use land cover (LULC) change on runoff flow. Moreover, using hydrology studio modeling software, storage ponds were routed to attenuate peak runoff flow. Based on the results of the research, for a 100-year return period, the total peak stormwater runoff flow of the entire catchment was estimated to be 14.64 m3/s. The hydraulic analysis revealed that six pipe sizes with diameters ranging from 150 to 1200 mm, covering a total distance of 10.28 km could securely convey 11.25m3/s 25-year return period peak runoff flow from the campus catchment. The existing drainage network assessment result revealed that channels type 1, 2, 4, and 6 and conduit 42-inch diameter in sub-catchment CM-1, CM-7, and CM-15 were over-designed while channels type 1 and conduit 30-inch in sub-catchment CM-13 and CM-16 were found to be under-designed. According to the modeling results for the pre- and post-development scenarios, 38.23% of what was once cropland with open woodland land cover was converted into impervious land covers, causing the study area's peak runoff flow to rise by 47%, from 5.33 m3/s to 11.25 m3/s. It is also found that, two detention ponds with volumes of 6,408 and 9,384m3 can successfully attenuate 50.9% of the study area's average peak runoff flow. It can be concluded that the peak runoff flow has significantly increased as a result of the establishment of the ASTU campus and the proposed ponds could potentially reduce the risk of flooding and its related problems on the society downstream of the campus. Furthermore, the stored water can be used as a supplementary source of water for the campus.