Stormwater quality control for sustainable urban drainage systems

The paper deals with the performance assessment of stormwater facilities in mitigating the negative effects of urban runoff pollutants carried both to the receiving environment and to the urban drainage system. Experimental campaigns and numerical simulations have been carried out on a residential catchment of Pavia, Lombardia, Italy. The rainfall-runoff process and the pollutant dynamics in the catchment and combined sewer network were simulated using a conceptual model based on an instantaneous unit hydrograph of a single linear reservoir system for individual events as well as for a continuous run of events and inter-event periods over one year. Several design configurations and operating conditions of flow regulators and stormwater detention tanks have been evaluated by defining performance indicators that simultaneously account for a large number of technical, environmental, and socio-economic constraints. On many occasions, wet-weather pollutant concentrations substantially exceeded what might normally be expected of raw wastewater, which thus required stormwater treatment facilities for the environmental and ecological protection of the receiving water. Flow regulator was unable to control the acute pollution impact on the river, thereby causing severe ecological deterioration. Stormwater detention tank was very appropriate to safeguard both the quantity and the quality of the entire chain, consisting of the sewer system, the treatment plant, and the receiving water. The results of this research provide information about a key issue related to the implementation of environmental policies in large urban areas for the recovery of impacted receiving water bodies.