Is Imperviousness = Runoff coefficient ?

Maya Karkour

EcoConsulting

LEEDuser Basic Member

549 thumbs up

November 1, 2010

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Jean Marais

b.i.g. Bechtold DesignBuilder Expert

LEEDuser Basic Member

581 thumbs up

Mon, 11/08/2010 - 09:58

Yes. It is generally the opinion that site "imperviousness" (fraction) = area weighted Run-off coefficient (also fraction) for the site.

J.W. Shin

LEEDuser Premium Member

9 thumbs up

Sun, 02/13/2011 - 07:14

Hi. I have a little doubt of comment from Jean. See the page 95, on BD+C Reference guide. Rv(volumetric Runoff Coef.) = 0.05 + 0.009xI (where, I = percentage of imperviousness) Following the equation above, when "I" is 100, Rv will be 0.95. So, Rv and I are not equal, but propotional.

Petra Hajná

Sustainability Consultant

Skanska Czech Republic

LEEDuser Basic Member

128 thumbs up

Thu, 12/08/2011 - 14:40

I think Jean is right. Taking into acount the equation, you are actually considering the "I" value and doing a weighted average based on surface area. Hope my explanation is clear and correct.