Permeable pavers offer a solution for rainy Northwest climates
by Pat Munts
Here in the Northwest, rain is a fact of life. In fact, it's the reason we enjoy green forests and gardens nearly year-round. Unfortunately, the runoff from all that "liquid sunshine" takes a heavy toll on the environment and creates major infrastructure maintenance and budget issues for communities. As development spreads, the challenges of dealing with rain only become greater.
Capturing rain and extra water at its source is one of the most cost effective ways to deal with runoff. If most of the water from an average rainstorm or a car washing could just sink back into the earth where it landed, no one would have to deal with the environmental and infrastructure issues created by the traditional impervious concrete, asphalt and paver surfaces.
Permeable paving is engineered to allow water to flow into the earth where it comes down through spaces in the stone open to the ground below. The most popular types are either a honeycombed grid of concrete that is filled with gravel, sod or ground cover, or paving stones engineered with half-inch spaces between the stones that are filled with fast draining soil or crushed rock.
"Using permeable pavers is much more sustainable than traditional surfaces," says Tristan Heberlein of highly rated Solstice Landscape Design in Seattle. "When combined with bio-swales and rain gardens, a homeowner can keep all but the worst storm runoff on their property."
Permeable pavers come in a wide range of styles and colors and can be used for patios, pathways and driveways, anywhere conventional paving is used. Most hardscape supply companies will carry a variety of styles. However, these paving systems must be engineered properly to perform effectively.
"Existing grades, the permeability of base soil types and the potential for erosion must be planned and built for," says David Dang of highly rated Structure Landscapes in Portland, Ore.
Both Dang and Heberlein emphasize that technically trained professionals will be able to engineer a site so that the proper slopes and gradients are established to maximize absorption and drainage. A competent designer and contractor will be able to engineer the necessary base layers of crushed rock and sand underneath the pavers to account for the differing absorption capabilities of the soils on your site.
Lastly, a good contractor will have the necessary equipment and manpower to move the large quantities of heavy materials needed for excavation and installation of the pavers so the project can be completed in a timely manner.
Both Dang and Heberlein have been called in to deal with improperly designed and installed systems and the unanticipated problems that it created. "Do it right the first time," Dang says.
Maintaining a permeable paving system is relatively easy and basically the same as impervious materials. Surfaces need to be swept or washed regularly and have leaves and needles removed to keep the drain passages open and ready to accept water.
"The larger spaces in the honeycomb grids may need to be replenished with gravel or soil periodically," Heberlein says. "The little bit of maintenance needed far outweighs the positive impact they have on the environment."
Pat Munts grew up in western Washington but has spent the last 30 years gardening on the dry east side of the state near Spokane. She freelances for the Spokesman-Review and has served as eastern Washington editor for Master Gardener Magazine. She's the small farms coordinator for both WSU Spokane County Extension and the Spokane County Conservation District.