Nov 16 2007
As we become more aware of how our homes affect the environment surrounding us, it may be time to take a look outside. Your driveway has a bigger impact than you think.
Rainwater that falls onto paved driveways, sidewalks, and roads has no place to go except straight to drainage systems or the nearest pond or stream. Soap from washing the car, pet waste and fertilizer can all contaminate runoff when it doesn’t go through the ground’s natural filter.
When evaluating driveway material, consider a permeable one, which will have a reduced need for drainage systems to redirect water and fewer contaminants washing into our streams. While permeable driveways may not be ideal for high-traffic areas, they are typically sufficient for residential use. We will discuss three common types of permeable driveways, one of which may suit your needs best.
Grass and Gravel
A fairly simple and cost effective way to reduce rainwater run-off is to make your driveway and walkways with grass or gravel. Gravel is inexpensive and requires minimal labor, but it doesn’t always stay in its place. After a long winter you may find yourself collecting gravel that has been displaced by plows, storms or just general wear.
Grass or other types of vegetation can also do the job, but as you can imagine grass does not hold up nearly as well as pavement. To help hold together grassy areas prone to heavy use, special grid systems can be assembled under the topsoil to keep your driveway from washing away.
Plastic Grid System
Plastic grid systems are used where heavier loads are expected. The plastic grid (usually made of recycled material) is filled with a sand and soil mixture or with gravel that lies on top of an aggregate mixture and keeps these materials in place as the driveway is used. Top soil can also be used so grass can be planted to disguise the grid system. Check out a great example at HGTV.com.
Block systems provide a traditional aesthetic and use materials like brick or stone. With block systems, it is the method in which the blocks are laid that makes the surface area permeable. Gaps (which vary in size depending on the specific driveway) are left between the block material and filled with sand or soil. Water slowly seeps into the ground instead of pooling or becoming run-off as the case with a typical brick or concrete driveway. To see some typical block system options, visit TreeHugger.com.
So What Will It Be?
Deciding on a permeable driveway has a lot to do with the look you want, available materials, and usage. And, with improved stormwater handling, a permeable driveway will certainly benefit your surrounding environment and that downstream from you.
Looking Further - Permeable Asphalt
Permeable pavement may not be necessary in your driveway unless you’re planning a huge swath big enough for the entire neighborhood to park in, but the concept is worth looking at.
At first glance, permeable pavement looks like regular pavement; however, fine aggregates are reduced so that rainwater can pass through the asphalt to an underlying stone bed. Water is then absorbed by underlying soil instead of traveling to drainage systems.
The stone bed is typically made from rocks free of dirt and dust so the passing of water is not slowed or clogged. Permeable asphalt parking areas are best where salt and sand are not used, unless the area is swept regularly to avoid clogging the stone bed. Cold climates can pose a problem since stone beds have to take into account the expansion of storm water when temperatures reach freezing.
However, according to Stormwater, the journal for storm water quality professionals, there are also fewer cracks and potholes because the stone bed foundation is a strong base for the overlying pavement. Despite its apparent strength, permeable asphalt is not meant for high-traffic areas because the reduction of fine materials in the asphalt mix somewhat reduces its durability.
With each of these systems, the need for drainage is usually eliminated, there is less contamination of nearby water, and flooding during storms is reduced. So while permeable pavement may not be necessary for your own driveway, it can make a difference in large areas of non-permeable surfaces. For your own home, one of the systems described above should do the trick.