Here's the latest on this design.
I e-mailed a prof in the neighboring county who "wrote the book" on porous paving, as follows:
I am in charge of zoning admin/bldg inspection for Comer, a small town NE of Athens.
I've been given a plan for review by a local civil engineer for a small parking lot adjacent to a seriously underparked commercial development.
Less than a third of an acre, with approx three feet of fall in 125 feet, the designer calls for removal of the top four inches and replacement to same depth with #57 crushed stone. Parking spaces delineated by treated crossties at head end and "treated landscape timbers" at edges, all anchored by rebar.
He is calling it a "pervious" surface.
I posted a query on a national planner's forum and received some "sound's OK" replies from Florida and Texas, and some jeers and sneers from places like Wisconsin and New York.
I have lots of doubts about the feasibility of this in addition to doubts about its adherence to anything like sound engineering practice. (not to mention state accessibility)
Comer's current zoning ordinance does require typical hard paving for parking lots, but does contain one section that reads as follows:
5. Where appropriate, the use of porous pavement and/or specially designed brick or block should be considered to increase onsite water retention for plant material and groundwater supplies and to reduce problems associated with runoff.I have downloaded one document of yours called Porous Pavements: The Overview that talks about porous concrete but doesn't appear to address this kind of low budget approach.
Do you have any comments about simple gravel lots passing as porous paving?
I am likely to direct this submittal to go the route of conditional use application, which would require public hearing and the vote of Mayor and Council for approval.
His timely reply:
Loose crushed-stone aggregate is stable under dead-end parking stalls, because in dead-end stalls there are very few vehicles per day and each of them is moving at close to zero miles per hour when it arrives. "Dead-end" parking stalls are those at the lot's perimeter, or terminated by wheel stops such as this engineer's timbers. Loose aggregate is not stable in a parking lot's moving lanes; numerous braking and turning vehicles displace it. Number 57 crushed stone is a very appropriate choice for aggregate parking stalls: it is angular to resist movement, extremely permeable, and comfortable enough for walking. Four inches might be sufficient thickness for aggregate parking stalls; it amounts to four or five particle diameters of No. 57 stone. Successful parking lots have been built with conventional asphalt moving lanes, and aggregate parking stalls. Those with aggregate moving lanes or cross-traffic across aggregate parking stalls have quickly been displaced by traffic.
Bruce K. Ferguson, FASLA
Franklin Professor of Landscape Architecture
School of Environmental Design
University of Georgia