In many homes, the paved areas around the structure (driveways, walkways, patios) have a surface area that is impervious to water. As a result, rain washing over those areas picks up contaminants, pollutants and pols that dripped from the underside of the family car and carries them to the storm drain where they flow to the local water supply. An increasing number of homes have started to minimize this problem by choosing permeable paving. With permeable paving, water drains naturally through the voids into the ground, where it helps recharge the groundwater.
Porous paving materials are, for the most part, difficult to distinguish from the nonporous materials. Permeable paving can be made from asphalt, paving stones, bricks or concrete. Still, even though the pavement may seem to be the same as traditional pavement, it is manufactured without the “fine” materials used in traditional pavement. Instead, it incorporates void spaces that allow drainage.
The soil particles filter rainwater percolating through soil on its way to surface waters and to groundwater aquifers, very similar to the way drinking water can be filtered to remove impurities. This is a very important step in the natural process of water purification, and is bypassed when rainwater falls on impermeable pavement surfaces on roofs and is carried directly into waterways through storm drainage systems. Engineered curb and gutter storm drainage systems are rather costly to design and build, so use of permeable pavement systems can also result in a considerable reduction of construction costs for developers and municipalities. Pervious pavements are commonly referred to as porous or open-graded pavement.
Another concern, especially in urban areas, is pollution carried in rainwater runoff. Storm water flowing across streets and sidewalks pick up contaminants associated with air pollution particles, detergents, spilled oil, solvents, deicing salts during freezing conditions, dead leaves, fertilizer, pesticides and bacteria from pet waste. Natural filtration of water through soil is the simplest means to control all these pollutants, and is a direct advantage of permeable pavement.
Popular Options for Paved Areas Around the Structure
- porous asphalt
One of the greatest advantages of this material is that the same mixing and application equipment is used as for impervious asphalt. Only the formula for the paving material changes with porous bituminous pavement.
- bituminous permeable paving
This material is appropriate for pedestrian-only areas, as well as foe very low-volume, low-speed areas such as overflow parking areas, residential driveways, parking stalls and alleys. Permeable paving is a great technique for dense urban areas because it does not require any additional land.
- porous concrete
Just as with porous asphalt, the same equipment may be used as for standard concrete. Larger pea gravel and a lower water-to-cement ratio is used to achieve a pebbled, open surface that is roller compacted.
- plastic grid systems
High strength plastic grids, often made from recycled materials, are placed in roadway areas. Some of them are designed to be filled with gravel on top of an engineered aggregate material, others are filled with a sand-soil mixture on top of an aggregate/topsoil mix that allow grass to be planted on the surface. Such grids provide a support structure for heavy vehicles, prevent erosion and after heavy rains, they act as mini holding-ponds, allowing water to gradually absorb into the soil below.
- block pavers
Block pavers can be used to create a porous surface with the aesthetic appeal of brick, stone or other interlocking paving materials. They are typically used for driveways, entryways, walkways or terraces, in order to achieve a more traditional, formal appearance.