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

Nick Pyner npyner at tig.com.au
Tue Feb 15 20:47:09 CST 2011


I think you are making a bit of mountain out of a mole-hill here. For the
land run-off, you can calculate and cheat sheet all you like and still get
no better result than an intelligent guess by looking out the window and
making some local inquiry.  You make no mention of terrain, geology, soil
conditions, or the species, size, health and quantity of your trees, if
any - and all these variables are players. You may find that all you need to
do to fix thsi problem, if you actually have one, is to run an absorbtion
pipe across the uphill area that discharges into the existing SWQ dispersal.

For the roof, a more realistic assessment  of your daily rainfall might be
in order but, before you worry about that, the best place to start is the
annual collection. For this, all you need is the plan area of the roof, i.e.
its footprint, and the local annual precipitation.  That gives you a
starting point and it is then up to you to determine your needs, the
desires, and what you are prepared to invest to achieve that.

One thing you can be pretty sure of is that, if you are not harvesting
rainwater now, your water usage when you do is not likely to be what it is
now, thus further adding to the nebulosity of this exercise.



Nick Pyner

Dee Why   NSW

  -----Original Message-----
  From: greenbuilding-bounces at lists.bioenergylists.org
[mailto:greenbuilding-bounces at lists.bioenergylists.org]On Behalf Of Erin
Rasmussen
  Sent: Wednesday, 16 February 2011 11:57 AM
  To: 'Green Building'
  Subject: [Greenbuilding] quick tools for calculating rainwater run-off?






  I live in a low spot, and we've got rainy conditions for 2/3 of the year.
Does anyone have any good cheat sheets for figuring out how much rain water
(in gallons) are coming off my roof, lawn and land? I've got to install some
type of additional drainage system and i'd like to add rainwater catchment -
but I'm not sure what scale I should be looking at.



  Total roof area is about 1000 square feet (including the garage) and it's
about 0.15 acre but I should calculate for 0.25 acre to include run-off from
the neighbors.  Daily rainfall is typically 0.5-1 inch but it's not unusual
to have 3-4 inches in a 2 day period.



  Erin Rasmussen

  TR Miles Techical Consultants Inc.

  and BioEnergy Discussion Lists

  erin at trmiles.com



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