Permeable Parking Surface

EFMonaco EFMonaco at compuserve.com
Wed Sep 1 17:57:16 EDT 1999


>I've not heard anyone suggest swales under the  cars.  While it would be 
impractical to grow much in them and they would have to be shallow enough
for 
the stray idiot who drives into them to drive back out, but they could
work.  
Actually they could be grated against idiots--expensive both financially
and 
ecologically, unfortunately. <

The problem, as I'm understanding it, is that the swale either winds up
relatively impervious, in which case it doesn't hold much water once it
fills up, then doesn't drain; or, if it does drain, the water runs under
the rest of the pavement in the gravel layer.  In well drained soils (which
are rare under parking lots around here) there can be some significant
infiltration; otherwise however, the outflow from the edge of the gravel
area still becomes runoff.  The benefit is that oil-eating microorganisms
can live in that gravel, cleaning up the water, ref: 
        http://www.sepa.org.uk/guidance/scontrol/oil.htm

The downside is that the travelling water washes away and dissolves the
fines, creating large voids that lead to potholes.

>In many places there are strips between some of the parking rows. 
Typically, 
these strips can be swales with trees such as willow, the tree forms of
alder 
and elder, etc., growing in them for some shade and wind abatement.  Most
any 
tree that handles periodic flooding can be used.
Here in Florida, where every parking lot or other "immprovement" must
absorb 
all rainfall in any circumstance, large parking areas sucha s big malls 
require constructed wetlands.  These quickly become populated with
wildlife.  
 Making the tree strips also serve as swales would actually REDUCE the
total 
area required.   Presumably trees such as sweetgums, water oaks, etc.,
would 
grow better in such swales providing increased cooling by increased shade
and 
transpiration while reducing the windiness of such open spaces.<

In Tennessee, the requirements are different in that their goals are merely
to slow the water's escape from the site, unfortunately.  The outflow from
the site "after" can't be greater than the outflow from the site "before." 
 So they have us build these detention ponds where the outflow pipe is of a
smaller capacity than the inflow pipes.   During storms the pond level will
rise temporarily, then flow out at the same rate as it was "before" the
site "improvement" was made.  One might think that this would allow some
infiltration, but it is IMO negligable in the soils and rock we have around
here.  I've even seen them specify clay liners in the bottom of the ponds
so they don't leak which would weaken the dam crossection.  The whole
situation kind of sucks as far as recharging aquifers goes.

> Whiile it is clearly useful to apply design to parking areas, we need to 
remember that making these spaces more humane and less ecologically 
disasterous is a stopgap measure.  People need to be able to get what they 
need mostly on foot or bicycle, while we attempt to decrease the number of 
cars in the world and the numbers of hours the average car is driven in,
say, 
 a month.  This means producing more at home or nearby of those things we 
need regularly and redesigning the access routes to favor foot travel with 
designated bicycle routes.  Designing better parking surfaces is easy by 
comparison....<

You're preaching to the chior Dan, but I guess we'll have a sing along.  As
you implied, we're in a transitional time.  We all have to do what we must
to survive, trying to make a difference where we can, and in the process
raising our consciousness and that of those around us.  Amen!

>    We need to keep in mind that fixing up parking lots for automobiles is
so 
far back from addressing basic problems of sustainability posed by Western 
(and Westernized) society (meaning economic systems),, that one has to let
go 
of all thought one to work on the other.   I supposed that in this context
it 
is fortunate that our species is basically duplistic (or multiplistic) and 
can embrace all sorts of contradictory states as a normal sort of thing to
do.<

All true.

Gene Monaco
in Knoxville, TN



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