Over the next 45 years, new development and climate change will likely alter stormwater runoff quantity and water quality in the Waubesa Wetlands watershed. To forecast these changes, the models HydroCAD (stormwater runoff quantity) and STEPL (water quality) were used. Currently, land use in the 8,434-acre watershed is 41% agriculture, 37% natural, and 22% urban. The model forecast assumed that by 2054, watershed land use will transition to 25% agriculture, 30% natural, and 45% urban. Furthermore, rainfall intensity was assumed to increase by 14% from current conditions by 2062.
In light of these changes, the HydroCAD models predicted, on average, a 20% increase in storm event runoff volume and peak flow rate from land use change, and a 39% increase in storm event runoff volume and peak flow rate from climate change by 2062. Our STEPL models predicted a reduction in nutrient loads resulting from the conversion of agricultural land to urban land; however, natural land converted to urban land will increase nutrient runoff. To help mitigate these effects, restoring wetlands along Swan and Murphy’s creeks is recommended to moderate and store stormwater runoff. It is also recommended to revisit stormwater management design standards to account for a more intense hydrologic climate.