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Permeable pavers keep stormwater runoff off streets

Come the end of July, there is nothing better than relaxing on the patio after a hot summer’s day. The steak was done to perfection and there are still a few cold ones in the cooler.

As beautiful and useful as impervious paved surfaces are, they do contribute to stormwater runoff issues, especially when you add the effect of all of the paved roads and parking lots in a community. Local governments have to shell out big bucks to capture and treat stormwater runoff so it doesn’t create flooding or pollution problems. These are dollars that governments aren’t going to have available any time soon. The most cost-effective and environmentally sound way to manage water runoff is to capture it onsite and return it to the earth.

Unlike impervious, conventional paving, permeable paving systems are engineered to allow excess water to drain into spaces between the stones and soak into the ground below. No more rivers of water going down the street after a car wash or rainstorm. When they are combined with onsite bioswales and rain gardens, they are even more effective.

Permeable paving comes in a number of styles but are very similar to conventional paver systems. They are available from most hardscape suppliers in the region. The difference is there are engineered spaces between the blocks that allow water to drain away. One common one is the honey comb concrete grids found in parking lots and other places where there is light vehicle traffic. The spaces between the grids are filled with gravel or soil planted with a ground cover. For patios, walks and driveways, permeable paver stones come in a wide range of block shapes, sizes and colors very similar to their conventional cousins.

Installing permeable pavers is a little trickier than conventional paving systems. Because the water is draining through them, the base layers of gravel must be installed carefully to assure proper drainage. Areas around the project need to be prepared to accept more groundwater and grades adjusted to keep the extra water out of basements and other undesirable low spots.

The area needs to be dug down to stable mineral soil. This base soil needs to be loosened to enhance drainage. Several progressively smaller layers of gravel are placed on top of the soil. If a lot of water is expected, a permeable drain tile may need to be laid at the base of the gravel. The soil and gravel layers usually aren’t tamped very much to maintain the drainage. Once the pavers are installed, gravel is swept into the spaces between the stones.

While laying permeable pavers can be a do-it-yourself project, it is probably a good idea to consult a professional on the design and types of materials you will need. Professional installers will also come with the right equipment and experienced crews to do the heavy lifting so your project comes out the way it is suppose to.

Pat Munts is a Master Gardener who has gardened the same acre in Spokane Valley for 30 years. She can be reached by e-mail at pat@inlandnwgardening.com


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