Control of water pollution deriving from the outflow of waters in urban environments

The phenomenon of outflow of waters in urban areas is one of the main reasons for the decay of watercourses and lake basins. While, in fact, in natural environments such as woods, prairies and wetlands, meteoric waters are slowly washed out and filtered from and through the soil and therefore are naturally purified, in urban environments, the non-filtering surfaces of buildings andpaved roads allows for a rapid washing out towards receptor bodies or mixed and separated drainage systems. Waters mostly full of more or less polluting sediments and solid materials therefore reach drainage systems. Finally, the waterproofing of soil in urban areas brings damage to the environment with chemical-physical consequences but also hydrological. The inflow of great volumes of water that happens at the same time as prolonged or intense meteoric events causes significative morphological and hydrological consequences on receptive bodies, connected to the sudden increase in rate and velocity of the flow and to erosive phenomena causing damages to the fish fauna and other aquatic life forms or even make the watercourse useless for its purpose (drinking water or bathing waters). Given the current pace of urbanization, it is clear that an intervention in order to limit and manage the outflow of waters from urbanized areas, also subject to a rapid increase,  is needed. In order to protect the quality of surface waters and groundwaters it is clearly necessary to limit the outflow and decrease the pollution load deriving from urban runoff. Particularly, it is necessary to focus on the first 5 mm of water from each rainfall event that wash out the urban surface bringing with them a higher concentration of polluting agents and sediments.

The pollution of body of surface water is another phenomenon connected to intense rain events, deriving from the overflowing floodways and flood water spillways in purification plants.