Hydrologic and Environmental Impacts of Imperviousness in an Industrial Catchment of Northern Italy

The increase of imperviousness due to urbanization creates adverse effects on the hydrological and environmental processes in a catchment. The increase in impervious areas leads to a higher runoff peak flow and stormwater pollution, even for a short duration of low-intensity rainfall. The present study focuses on the Bivio Vela catchment, an urban catchment of Pavia in northern Italy. This paper emphasizes both experimental and modeling approaches to the rainfall-runoff process and pollutant dynamics on the catchment surface and in the combined sewer system, considering significant increases in impervious area. Recent and future catchment developments caused the conversion of approximately 33% of the total area from nonurban pervious area to impervious area. The study also deals with the performance assessment of the wet-weather control system of the catchment, introducing simple indicators that account for the requirements of the urban drainage system and treatment plant. Imperviousness associated with urbanization in the catchment is invariably reflected in the receiving river flow regime and water quality. The simulation results indicate that the annual number and duration of sewer overflows and volume, peak flow, and pollutant mass discharged into the river have increased to different degrees due to urban expansion during the recent period and will continue to increase as urban areas increase in the future. The impact of urbanization on rainfall runoff and water quality should therefore be considered for effective urban and water infrastructure planning. The methodological approach and the proposed performance indicators, which take advantage of experimental data and are suitable for complex urban drainage systems, are original and promising for their help in formulating policy guidelines and intervention strategies that minimize the negative effects of urbanization on both the water environment and the treatment plant.