Modelling potential urban floods caused by extreme rainfall events at a local scale using SWMM and developing mitigation strategies

The increase in sudden and intense rainfall due to the effects of climate change has made stormwater drainage systems in urban areas critical in terms of flood risk. Under conditions of dense urbanization and high surface imperviousness, aging infrastructure systems designed based on historical climate conditions are unable to provide an adequate hydraulic response to short-duration rainfall events, making flooding inevitable. In this thesis, the flood risk caused by the increase in sudden and intense rainfall in urban areas due to climate change was examined through a case study of an urban catchment located in the Selçuklu district of Konya Province, and the performance of the existing stormwater drainage system under these conditions was evaluated. Within the scope of the study, physical and infrastructural characteristics affecting flood formation were identified through Geographic Information Systems (GIS)-based spatial analyses, and the hydraulic response of the drainage system to different rainfall scenarios was analyzed using SWMM-based numerical modeling. Accordingly, design storms with 2-year and 5-year return periods generated using the Chicago method, along with observational rainfall data, were evaluated as Scenarios 1, 2, and 3, respectively. Model results indicated that the drainage capacity was exceeded at critical junctions prior to the implementation of the storage structure. Following the application of the storage structure, total flood volumes were reduced by 53.8% for Scenario 1, 46.4% for Scenario 2, and 54.5% for Scenario 3. Although flooding was completely prevented in the upstream and downstream sections near the storage structures, low-gradient conditions and insufficient infrastructure capacity caused low-level flooding to persist in more distant areas. In addition, the fact that the utilized storage volume ratios remained within the range of 6.9%–19.2% demonstrated that the storage structures effectively attenuated flood peaks and provided safe hydraulic control of the system without reaching excessive filling levels. In conclusion, this study demonstrates that storage-based solutions offer an effective and feasible flood mitigation approach at the local scale against the increasing urban flood risk under climate change conditions.