permaculture

["Paul Osmond" <p_osmond@hotmail.com>]

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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