Within 21 days after pouring, the road held up to all heavy concrete and lumber trucks as well as general traffic, and it took water as fast as a garden hose could flow, with virtually no water spread. Despite heavy rains, there has been a complete absence of ponding or overflow In fact, not one drop of water left the site during a record seven-week rainfall.
THE UNIQUE CHALLENGES
Yes, pervious is trickier than standard concrete. System design is site-specific, for example, and requires a soils survey and storm water calculations that factor in the percability and characteristics of native soils.
If the pervious is too wet or overworked during placement, the voids between the stone are reduced or eliminated, and it won't drain. If the concrete is too dry, it's impossible to get proper compaction for cross section strength, and if curing precautions aren't tightly maintained pervious concrete can fail. On the other hand, when the site is properly prepared, you can significantly reduce your potential for costly errors.
Care should be taken to keep the surface free from silty or clay-like material, and to avoid clogging it with sand, topsoil, beauty bark and other debris. Chemical cleansers are not recommended; plan to use plain water to flush the pervious pavement voids, and to sweep or vacuum one to two times a year to remove soil and debris.
THE MAJOR ADVANTAGES
Pervious concrete eliminates storm water detention vaults, ponds and piping systems, which are not only the most time-consuming and costly elements in plat development, they can take up a couple of otherwise profitable lots. Getting those lots back can often pay for the entire system.
Environmentally, it just makes good sense to let rainwater directly recharge our groundwater. By eliminating untreated storm water and runoff, the system mitigates "first flush" pollution and protects our streams, watersheds and ecosystems in much the same way as bioswale and natural soil drainage and filtration, rather than concentrating pollutants by channeling storm water.
Pervious doesn't get as hot as standard concrete, which reduces heat island effects, and it provides a higher albedo surface reflectivity index (0.35 or higher).
In addition, pervious concrete has been designated an LID (Low Impact Development) tool for storm water management and a BMP (Best Management Practice) by the EPA.
Concerned about plugging? Don't be. Properly placed pervious takes water at more than 200 inches per hour.
From every viewpoint--dollars, aesthetics, environment and performance--pervious concrete makes good sense. Costs are coming down, acceptance is rising, and my bet is that we're all going to see a lot more of this smart storm water solution.
Craig L. Morrison is the owner and president of both CMI Homebuilders and Pervious Concrete in Snohomish. He thanks the Smokey Point Concrete team and GM Scott Mickels for their dedication and hard work, Bruce Chattin from WACA, and especially the City of Sultan, Planner Rick Cisar, Engineer Jon Stack, Public Works Director Connie Dunn, Building Official Craig Bruner, the mayor and the city council for their support of Stratford Place.