Storm-water runoff from roofs, sidewalks, roads, parking lots and other impervious surfaces is a major source of water pollution today. In fact, an estimated 70% of all water pollution is caused by storm-water runoff.
Storm-water runoff occurs when water from rainstorms, snow-melt, or over-watering hits an impervious surface such as an asphalt road. The water pools in depressions or is channeled into storm-water systems, which typically empty into nearby creeks or rivers with no treatment to remove pollutants.
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Because storm-water systems collect large amounts of water, sometimes very quickly, they frequently cause erosion of stream-banks and another nearby land, contributing further to the pollution of waterways.
In contrast, when storm-water hits a pervious surface such as a lawn, meadow, or forest floor, the water sinks into the ground, where plants and soil organisms remove many of the pollutants before they enter groundwater supplies.
Permeable pavements offer the best of both worlds. They provide a level surface for people and cars to travel on, while also allowing water to sink into the ground as it would in nature. Some permeable pavements even incorporate traffic-resistant plants to provide beauty and absorb water more quickly.
In this way, permeable pavements not only reduce storm-water runoff and the pollution and erosion it causes, but they also prevent dangerous melting and refreezing of ice and snow on the pavement in wintertime and reduce the chances of flooding on sidewalks, roads, and nearby basements.