Permeable Paving

EFMonaco EFMonaco at compuserve.com
Sun Aug 29 16:21:42 EDT 1999


>Then they pave the lot with concentional asphalt, leaving
about 25% of the parking area unpaved. The unpaved areas are laid out as
short, shallow swales between parking spaces, and planted with appropriate
vegetation<

We looked at this in a few areas, and I'm all for it; however, the drawback
as pointed out by the engineers is that it takes a larger parking lot area
because the space between cars increases.  Altogether though, it is
definitely more aesthetic.

>The swales serve as infiltration areas for runoff as well as cleaning up
oil-polluted
rainwater. This design eliminates the need for storm drains in the parking
lot, saving money (though Ben told me that the engineer on one wouldn't
believe it, and put a drain in anyway...<

I'm running into the same thought processes (stinkin' thinking), where they
don't think the swales will absorb any water.  The reason they think this,
I think, is that in doing calculations, they assign a coefficient of
representing absorbtion to each area.  Since the swale area is generally
small, and the soils underneath relatively impermeable (clay and rock), it
tends to have a negligable impact on their calculations.  The fallacy in
the thinking is that they are designing for peak storm events, not everyday
rains.  Their calculations may be correct for peak storms, but they're
missing the boat for everyday rains.  This is a case of permaculture
thinking needing to be institutionalized.  If the engineers read this stuff
in their text books, and it was on the PE exam, they'd think differently. 
Trying to shift their thinking from the fringe is difficult.

On another note, I found some products on the web
(http://www.prestogeo.com/solutions/) that deal with my question; however,
they seem to be designed for infrequent use, like a fire lane that might
only be used during emergencies.  How well they hold up for everyday use
vs. cost is something I'm still evaluating.

Gene Monaco

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