Modelling Runoff from Permeable Surfaces in Urban Areas
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Climate change and urbanization increases the pressure on combined sewer systems in urban areas resulting in increased combined sewer overflows, degraded water quality in receiving waters, and changing stream flows. Permeable surfaces are increasingly used to combat the challenges regarding runoff to combined sewer systems. The variation in urban soil characteristics, and the initial conditions before a rainfall event are important factors affecting the infiltration process and consequently runoff characteristics. In this study SWMM and STORM are used to evaluate the Green-Ampt, Horton, and Holtan infiltration method. Three different urban sandy soils were compared based on field measurements. A sensitivity analysis was carried out to get an improved understanding of the consequences of choosing the incorrect parameter values for urban soils. In addition, long-term simulations were conducted to evaluate the methods ability to account for initial soil moisture content. The results showed that Holtan infiltration method s ability to account for both available storage capacity and maximum infiltration rate gives the method more confidence calculating runoff behavior, but more input data is needed as compared to Green-Ampt and Horton infiltration method. The method is also able to account for evapotranspiration in the regeneration process of the soil moisture, which makes it suitable for long-term simulations. The various results from the different urban sandy soils with different infiltration rate at saturation, together with a high sensitivity to this parameter indicates that field measurements of infiltration rate at saturation are needed to model accurate results from compacted urban sandy soils with these methods.