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permaculture - Stormwater retention/reuse

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  • From: "Paul Osmond" <p_osmond@hotmail.com>
  • To: permaculture@listserv.oit.unc.edu
  • Subject: Stormwater retention/reuse
  • Date: Thu, 24 Sep 1998 04:23:43 PDT

We at the City of Port Phillip, Melbourne Australia, are in the midst of
a development boom. We also have an aging stormwater drainage
infrastructure, ill-equipped to cope with the increase in impervious
surfaces (and hence extra runoff) which "urban consolidation" brings.
And of course, we need to think of stormwater as a resource, not as
something to pipe away to the sea, complete with the litter and
pollutants picked up off roads, driveways and roofs.

We are in the process of developing standard conditions to attach to
planning approvals, requiring developers to retain on site the
additional runoff generated as a result of their development (i.e.
additional paved and/or rooftop surfaces). The idea is to get them to
install rainwater tanks, pervious paving, soak pits etc. to use the
stormwater for irrigation, toilet flushing, or groundwater recharge.

One option obviously is to require the use of complex hydraulic
computations for each new development including Manning's Equation,
roughness coefficients and the rest. This has problems, not least of
which being that smaller developers, owner-builders etc. will have
neither the resources nor the expertise to comply. The alternative -
that the City Council staff handle the calculations - is not an option,
given that staff in the development approval area are stretched to the
limit as it is.

The third option is to develop some "rules of thumb" along the lines
that if you are increasing the area of impervious surface by "x" square
metres and you have an irrigable garden area of "y" square metres you
will need a rainwater tank of "z" litres capacity.

OK, it may not be "pure" permaculture as we know it, but it is an honest
attempt by one City Council to move towards a more sustainable system
than currently exists.

Your comments would be very welcome, in particular any ideas on
appropriate rules of thumb or simple but reasonably robust calculations
which we can require developers to work through without the Council
being taken to the planning tribunal for trying to enforce "excessively
onerous" conditions (we have enough problems trying to enforce our
building height restrictions!)

Cheers, Paul Osmond

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