低影响开发报告.ppt

* IN the cross section at the bottom you can see the bottom of the trench is lined with filter fabric or pea gravel; and the top of the cell is designed so it is a foot or so below the level of the adjacent parking area. At the top, you can see that runoff comes from the parking area, onto a level spreader, and then over a grass filter strip that provides some pretreatment. Bioretention cells work because as the water flows through the cell, pollutants attach to the soil or are taken up by plants and microbes. * Bioretention cells can be used in both residential and commercial settings. At the top right, rooftop and driveway runoff is directed to this “rain garden.” It functions as part of the stormwater system, but a smart developer would call this a landscaping extra and charge extra for it. On the bottom you see some commercial applications. On the lower right, this parking lot bioretention cell includes trees that will provide shade in the parking lot once they mature. All of these nonresidential applications also help to fulfill open space and site landscaping requirements. * Here are two typical applications: a roadside swale in a residential subdivision, and a swale that replaces the storm sewer system in a parking lot on the right. * At the bottom you can see a roadside application; this is a 50-foot wide filter strip that treats runoff from a major roadway. At the top, runoff from a parking lot flows onto a concrete level spreader at the right, then onto a filter strip, and into an infiltration trench. In this case, the filter strip provides pretreatment, which is critical for infiltration trenches, our next technique. * Infiltration trenches and dry wells are very utilitarian methods for getting stormwater back into the ground. They don’t have the pollutant removal capability or the landscaping benefits of bioretention areas, but they can be used in some areas where bioretention areas are not applicable, and they are cost-effective me