Forum discussion
CS-2009 SSc6.1: Stormwater Design—Quantity Control
Good Morning,
I’m starting with calculations in SS credit 6.1. But I have a question:
Can I use the runoff data of the watershed where is located the project?
Because in my understanding I must use Rational Method just for calculate the runoff in a watershed but not in a square site. The lot area is 47.762 m2 and the watershed where is located the project is in Bogotá city.
Thank you very much.
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Michael DeVuono
Regional Stormwater LeaderArcadis North America
LEEDuser Expert
187 thumbs up
July 7, 2014 - 1:38 pm
You need to develop site specific hydrologic models for your site. The geometric shape of your site has nothing to do with your calculations, and unless your site boundary matches the boundary of the entire watershed, using runoff data from the entire watershed is not a valid approach. But then again, I am not sure I am clear on your question?
Be advised, the rational method does not compute volume.
MKK LEED
MKK Consulting Engineers1 thumbs up
July 7, 2014 - 3:10 pm
Thank you for the answer. So, my conclusion is: I can use the rational method to calculate the runoff of the project. But, I have another question,if the equation of Rational Method is the next:
Q=C*I*A
Where:
C: Is a runoff coefficient
I: Average maximum intensity of rainfall
A: Area of the watershed
Do I have to define an area around the nearest river of the project (a sub watershed) or can I put the value of the project area, in this case 47.762 m2?
Thanks
Michael DeVuono
Regional Stormwater LeaderArcadis North America
LEEDuser Expert
187 thumbs up
July 7, 2014 - 4:14 pm
If your project area all drains to the same point of interest then this is fine. Any stormwater BMP, however, will need to account for all runoff that drains to the BMP, which may be off site. This work is typically handled by a civil engineer.
MKK LEED
MKK Consulting Engineers1 thumbs up
July 9, 2014 - 9:48 am
Hi Michael, I’m sorry but I’m a little confused, and I have more doubts,
1. In my view the Equation 1 of the SS credit 6.1 is the same equation of Rational Method, Am I right?
2. In the example 2 of the SS credit 6.1, LEED says in that example that the design was for treat the 90% of the average rainfall event for humid watersheds. So if I look SSc6.2 I understand that is a classification for watersheds in United States. But, for our project that is in Bogotá (Colombia) There are not this kind of classification, so I was wondering if I can use the average rainfall event of the specific watershed where is located the project (Bogotá River Watershed ? and in that way I can make all calculation that has to do with IDF curves and hydrological model.
Thanks