Assessing the Sensitivity of SWMM to Variations in Hydrological and Hydraulic Parameters: A Case Study for the city of Istanbul

Overland flow is highly affected by increasing urbanization, and variations in land use and climatic variables, especially in the last few decades. This necessitates the development of modeling approaches for planning and management of catchments that play a significant role on water supply. The main objective of this study is to determine the effects of major hydrological and hydraulic parameters on runoff production in the Alibeyköy Reservoir catchment area in Istanbul. Storm Water Management Model (SWMM) is chosen to develop the catchment hydrological model and the model’s sensitivity is assessed based on the variations in eight major parameters of the model affecting runoff production. 55 years of time series precipitation data are used for model simulations. GIS-based maps including land use and land cover information are used to determine the imperviousness values required for SWMM. A one-at-a-time parametric sensitivity analysis is carried out to determine the most significant parameters affecting the model outcomes. Analysis results reveal that area of subcatchments, precipitation and conduit depth are the most significant parameters in SWMM affecting runoff production. Percent imperviousness and percent slope are the least significant parameters amongst other parameters influencing the output.