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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".