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Grant Maclaren


Porous Paving

Over-taxed storm sewer systems due to population growth and environmental regulations can cause significant concerns and issues that many communities must soon address.

Porous paving systems, with topsoil/grass infill, offer solutions to many stormwater problems with low environmental impact and high environmental benefit. These permeable systems address areas of storm water retention/control, environmental and aesthetic issues and structural support.

Properly designed and installed system can provide load support requirements for cars and trucks while allowing for maximum groundwater replenishment and minimizing runoff.

Vegetated porous pavement systems can maintain an aesthetic appeal while preventing potential pollutants from entering the storm water system.

When it rains -- sstreams and streets floods -- basements gets wet . . . and someone calls City Hall to ask what's being done. Summer brings more calls -- wells or streams are drying up. What can be done?

Increased runoff comes from impervious surfaces -- roofs and pavement -- which also prevent rainfall from soaking into the ground. Increased runoff means more flooding. Decreased infiltration means less groundwater for wells and streams. The problems are all connected!

The solutions are connected too, and they involve looking at stormwater as a resource.

When we were building our house in Byrnes Mill, I thought it would be a good idea to reduce water runoff by reducing the width of our driveway, so I determined the width needed by measuring my car parked in a neighbor's drive and used the results to specify our new drive.

Our driveway is only 10 ft. wide, not the 16 ft. that would have been installed if we had not requested the change.

I thought about installing a porous driveway and garage apron. But we were building toward a deadline imposed by the "closing" of our previous residense, so did not follow through because of potential delays. I should have, even though our indentures require poured concrete. I did, however, buy a sample "porous paver" from Kirkwood Building Supply. Here is a photo:

Years earlier, when serving as a Parks Commissioner in Des Peres, the City -- in an effort to save some big old "Charter Oak" trees -- required, and gave special permission to a developer to build a parking lot using porous paving. The porous paving worked, as you can see by visiting it today, and in this picture:

The red arrow points to the portion of the parking lot mentioned. (It's on the north side of Manchester Road, acroos the street from McDonald's. Go park on the roots of some healthy trees!)

But then the owner violated his contract with the city and paved over the permiable parking. I took these two photos on Sunday, Aug. 31, 2008:

What a cruel joke -- the shopping mall retains the name "Charter Oaks." On Sept 3, I phoned the Des Peres Director of Public Works Denis Knock (314-835-6133) to ask why the city let the property owner break his contract with the city. He said, "Well, I suppose the city could go after him, but ladies were complaining about walking in high heels, oak tress don't get along withe parking lots anyway, and it was cheaper for the owner to just black top the area." He also mentioned that these old oaks are dying. No kiddong?

On Sept. 3, I also took these photos of some permiable paving In Kirkwood's city park.

Public Works Director Knocks also said "There's a lot of mention of permiable paving but it doesn't work." Maybe he should visit the parking lot in the front of the St. Louis Botanical Gardern:

In the summer of 2007 we visited Scotland and saw beautiful poruus paving of parking lots. Maybe hot summers in Missouri would not permit Scotland's lush grass, but the pavers don't have to support vegitation. I have seen a beautiful porous drive built entirely of brick and stone in Olivette.

Concrete filler serves as parking space marker.

Porous paving allows you to park, drive, walk, ride, or lounge on a beautiful grass surface. It performs the functions of asphalt or concrete pavement, but with the aesthetics of a lawn - all while enhancing the environment.

Porous paving provides incredible load bearing strength while protecting vegetation root systems from deadly compaction.

High void spaces within the entire cross-section enable excellent root development, and storage capacity for rainfall from storm events. For example, a 13 inch cross-section (one inch think pavers with sand and a 12 inch base course) can store 2.6 inches of water - 13 inches x approx. 20% void space).

Stormwater is slowed in movement through and across porous paved surfaces, which deposits suspended sediment and increases time to discharge. Suspended pollutants and moderate amounts of engine oils are consumed by active soil bacteria, which are aided by the system's excellent oxygen exchange capacity.

Some benefits of porous paving system:

  • Provides Load Bearing Surface
  • Provides Stormwater Pollution Filtration and Treatment
  • Provides Airborne Dust Capture and Retention
  • Reflects Heat Energy, Provides "Cool" Surface
  • Permits Tree Growth within Parking Areas
  • No "cracks" as in solid pavement.

    Here are three photos of porous paving in the "old town" of Cancun, Mexico; photos taken in early January of 2009:

    Of course, there is no frost in Cancun, but the paving scheme shown here would work in more severe weather with proper grading and fill under the pavers.

    See more examples here.