Even though the name suggests a cement driveway painted green, a green driveway refers instead to driveways that are pervious, rather than impervious, to the elements. Both builders and homeowners are considering permeable driveways because of the many benefits they offer. Some of the benefits include a reduction of sewer overflow, less local flooding and less stream and river erosion. In addition, storm water can pick up pollutants such as oil and grease from roadways and driveways. Nutrients from lawn fertilizers along with bacteria from animal waste can also be carried into the streams and waterways. Once the polluted water mixes with fresh, the contaminants degrade water Quality as well as damage the habitat of fish and other wildlife.
Currently, most conventional pavement driveways are considered “impervious surfaces” because of the water barrier they provide. They are made to repel water, rather than allow it to permeate them. By acting as funnels, concrete and asphalt pavement lets rainfall bounce off their surfaces, racing down to storm drains or sanitary sewers.
As urban building has increased, so has the amount of concrete covering open land. As open land surface decreases, there is less land available to retain storm water; increasing sewer overflow and flooding. When homeowners choose to reduce the amount of paved area around a home by implementing permeable paving options (also called porous or pervious paving), rain water can soak through the driveways into the soil below. In addition to decreasing flooding, this infiltration of water can help recharge groundwater supplies, filter out pollutants, and help keep drinking water healthy.find more information:gravel driveways.
Permeable paving options all require a layer of rock or gravel to be placed on top of the soil, to retain water until it can soak into the ground. As a result, permeable drives must be excavated at least three inches below the paving surface, and filled in with rock or gravel. An overflow route for storm runoff must also be created, directing water into street drains, landscaped areas or rain gardens.
There are a number of materials available to use in creating a green driveway.
Porous Asphalt and Porous Cement Concrete products are one choice. They are manufactured using less sand. When the materials have been mixed, there are small air cells left in the mixture, where water can seep through to the ground below.
Permeable Pavers may be one of the most practical porous surfaces for residential driveway, sidewalk and patio use. A wide variety of paver blocks, bricks, and flagstones can be purchased at local building supply and hardware stores. When these blocks are set over tamped sand and clean, crushed rock they allow rain water to flow down into the rock base underneath, and then slowly filter into the soil. Pavers should be inspected once a year for deterioration and to determine if the base has degraded. Permeable pavement should also be kept clear of mud, sediment and leaves.
Interlocking permeable pavers have tabs that space them from one-quarter to one-half inch apart to allow water through the joints. The interlocking shapes provide stability for cars as they drive over the pavers.
Open-celled grids with vegetation or gravel fill are a green option that may actually provide that green-colored driveway. These pavers are constructed mainly from recycled plastic. They do not require drains, detention or retention ponds, or any other associated drainage facility. These open-celled grids are filled with a sand and compost mix that will grow grass or other wear-tolerant ground covers, such as thyme. They can also be filled with clean crushed rock and work well on level ground. These grids should be inspected yearly for soil or vegetation loss, and repaired as needed