[Greenbuilding] quick tools for calculating rainwater run-off?

[Frank Tettemer]

With a buried fiberglass septic tank, one with two man-hole clean-outs 
on it, we gather about 1/3 of our roof area, (approx.700sq.ft. of 
collection area).
This tank was buried on the south side, next to the house footings.  It 
was then covered with 2" styro., and 4" of A-gravel. On top of that was 
built a 6' x 14' lean-to green house, for three-season use.

The over-flow pipe from the septic tank runs a few feet away, 
discharging into a 1200 gallon goldfish/frog pond, dug four to five feet 
deep, and lined with EPDM rubber sheet.  The edge was planted years ago 
with iris, cattails, etc. and surrounded by our extensive vegetable 
garden.  We use this fish-enriched water for the plants in the garden, 
dipping it out with watering cans.

Occasionally, (twice in 12 years), our well has gone dry mid winter.  
I've used a small RV pressure pump, (Shurflo WhisperKing), and run the 
entire household from this buried tank, (except for drinking). By being 
frugal, we managed with that amount of storaged water, to last through 
the remaining winter, until spring thaw re-filled the well.  This 
implies that less than 1200 gallons of water is needed to function for 
three months, being careful of use.  Here's a few photos and short 
description:

http://www.livingsol.com/index.php/home-energy-systems/rain-water-harvest-greywater-systems

Hope this data is helpful.

Cheers,
Frank

-- 
Frank Tettemer
Living Sol ~ Building and Design
www.livingsol.com
613 756 3884