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permaculture - Rainfall/cistern calculation - results (fwd)

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  • From: Piedmont Communities Online <piedmont@sunsite.unc.edu>
  • To: london@sunsite.unc.edu
  • Subject: Rainfall/cistern calculation - results (fwd)
  • Date: Wed, 31 Jul 1996 09:57:43 -0400 (EDT)


---------- Forwarded message ----------
Date: Tue, 30 Jul 1996 15:19:53 -0700
From: Loren Davidson <loren@wombat.net>
To: permaculture-mg@amani.ces.ncsu.edu
Subject: Rainfall/cistern calculation - results

First, thanks to the various kind souls who sent me responses on this. I
hope over time I'll be able to "give back" with contributions of my own.

I was asked by one list member to post any response I got. I've received
two versions of this, one in English and one in metric terms, and I think
I'll quote both here. (I haven't tested the metric one.)

>From Jeff Jacobsen in Washington state (US)(English measure):

>Here is what I do for my calculations:
> Roof size has to be the calculated equal to the ground area the roof
>covers. Hence, do your measurements parallel to the ground; if you
>measure at an angle your result will be too high. Determine area, i.e.
>length x width. Add all roofs or roof segments together to get your
>catchment area. If you work in inches you won't have to worry about
>conversion. Include your gutters too, since they catch water too.
>
>Divide by 231, the number of cubic inches in a gallon.
>
>This gives you the number of gallons for one inch of rainfall.
>
>Mulitply by annual rainfall to get annual catchment.

And from Murray Hopkins in Australia (Metric):

> If you want to do the conversions, the metric formula is:
>
> 1 litre of water per 1 mm of rainfall per square metre of roof.
>
>(4.5 litres per gallon, 305 mm per foot, approx 39 inches per metre.)
>
>You then need to subtract a percentage for losses. This depends upon how
>hot the roof is; how much water ends up in the gutters etc etc.
>We work on about 10% here but thats very variable.

I also got some suggestions as to storage media, from stock tanks to 40 gal.
plastic barrels to ferrocement to pre-formed large plastic tanks (we've got
one already -- they're not cheap!). We're leaning toward ferrocement at
this point, but with at least a year before we have the resources (time and
labor) to essay this, anything is still possible.

Again, thanks to those who wrote!

Loren
Loren Davidson
loren@wombat.net
http://www.batnet.com/beauty/
The First Amendment went too far. It should have said, "Congress shall
make no law".



  • Rainfall/cistern calculation - results (fwd), Piedmont Communities Online, 07/31/1996

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