Stormwater retention/reuse

Elfpermacl at Elfpermacl at
Fri Sep 25 10:01:08 EDT 1998

Here in Florida, USA, state law requires zero runoff, period, on new
"development.":  This means constructed wetlands if you want a parking lot for
a mall, for example, so we get more waterfowl, aligators, etc., due to
otherwise unmitigated environmental destruction.  I know of no formula for
this.  I'd guess that after a while, experience rules.  Also, we have maps of
the entire country giving runoff figures for each situation available in a
handy booklet on pond building from USDA (federal agriculture department).
Runoff, known percolation rates (any builder can tell you), known maximum
water table, and you know how big a volume you need for worst case, say three
hurricanes in a row.  
	Like most places, however, conservation measures are not put into effect
until it is too late, and the worst offenders (industrial users such as paper
mills, suffer little restriction at all).  
	When I took my design course with Mollison, people wanted to know how much
diversion drain we needed to fill a pond.  Make it the shortest you think you
will need, he said, and extend it if not enough.  
	If you can get a cistern made that is relatively cheap, cisterns can become
modular and people can install more as they are needed.  The problem with
cisterns here in the USA is that they are too expensive, roughly $1US for each
US gallon of water stored.  Well that is a good incentive for conservation, I
suppose, if you have no choice, but it is a poor incentive to conserve
aquifers.   Judging from published studies from Texas, home-made ferrocement
tanks cost about as much as ready-made plastic.  Living where we have two
operating deep wells (as we consolidated two adjacent properties), it is hard
to justify thousands of dollars in roof retrofit and catchment storage when
the funds are badly needed for other projects too.  Mollison's "earth tanks"
make no sense on what is basically a small island of sand in a big swamp, I
should add.  What is needed is affordable rigid, self-supporting tanks that
will stand just below gutter level to minimize energy needed for water
transfer via a pitcher pump, etc.  (A slow trickle is adequate, too, for
washing machines.)  

For Mother Earth, Dan Hemenway, Yankee Permaculture Publications (since 1982),
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