Impact of Urban Development on Local Water Balance

Urbanization affects the local hydrologic cycle. Accurate methods for quantifying and analyzing the hydrologic effects of urbanization are vital for sustainability research. In this study, continuous annual water balances are constructed for the Mill Creek Watershed, a highly developed catchment in the Cincinnati, Ohio metropolitan area. Annual urban water fluxes are generated for a period of 41 consecutive years (1970-2010) and compared against predevelopment hydrologic conditions. Findings show that urbanization has increased the annual average volume of water entering and leaving the Mill Creek Watershed by nearly 30 percent; concurrently annual average evapotranspiration has decreased about 20 percent. The computer program Aquacycle is used to simulate the evolution of the local water balance in the Mill Creek catchment from predevelopment to postdevelopment conditions. Looking to the future, green infrastructure projects (i.e., rain barrels, green roofs, porous pavement, etc.) are incorporated into Aquacycle to assess the potential for alternative stormwater management strategies to mitigate and reverse the hydrologic effects of urbanization. Results show that widespread implementation of rain barrels has relatively little impact on the overall catchment water balance; in contrast, conversion to green roofs has promise for reducing streamflow (6 percent) and wastewater (5 percent) and increasing annual evapotranspiration (8 percent) in the Mill Creek Watershed.