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Use natural infiltration
Many project teams are reluctant to attempt this credit because conventionally engineered solutions don’t always meet LEED requirements. Don’t be deterred. The best and easiest way to improve the quality of stormwater is to let water permeate the ground through increased landscaping and reduced impervious areas. As long as your soil type has a good infiltration rate, letting stormwater seep into the ground will treat 100% of the pollutants associated with the stormwater runoff. Let natural infiltration do as much of the work possible before using more expensive mechanical methods. In urban sites, infiltration options can be very limited and a rainwater cistern or green roof might be the best approach for credit compliance.
Pollution Prevention
This credit deals with...
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4 Comments
Estimating credit acheivement
1) Does anyone know of any local/regional programs with the 80% standard in the Vancouver, BC area? Our project is located in Surrey, BC.
My civil engineer tells me that he knows of no local/regional stormwater programs that have adopted the 80% TSSTotal suspended solids (TSS) are particles that are too small or light to be removed from stormwater via gravity settling. Suspended solid concentrations are typically removed via filtration. removal standard. Therefore, we need to provide field measurements after the installation.
2) Does anyone know of any good tools to estimate stormwater TSS removal? We have mostly non-structural measures (a lot of green roofs). It would be very helpful to know if we're getting close to this point.
Thanks!
-Amanda
How to determine the 90% of the average annual rainfall
Hello
I'm very confused by the methods determining the 90% of the average annual rainfall in SSS Credit 6.2 LEED guide.
In p103 of LEED guide, they said "For this credit, managing 90% of the average annual rainfall is equivalent to treating the runoff from the amounts listed in Table:
Watershed Rainfall per 24 Hours(ins)
Humid 1
Semiarid 0.75
Arid 0.5
I wondered Why the 90% of average rainfall is equivalent to treating the runoff of 1,0.75 and 0.5 (this is the quantity of 24 hours? not entire year?).
Thanks
1) Intensity-Duration-Frequency (IDF) Charts. These charts show the relationship between the rainfall intensity (rate) and the corrisponding rainfall duration (minutes). This data is required for 1 and 2 year statistical return periods.
2) Depth-Duration-Frequency (DDF) Charts. These charts show the relationship between the rainfall depth (volume) and the corrisponding rainfall duration (minutes). This data is required for 1 and 2 year statistical return periods.
3) Volume of the 90% rainfall event, i.e. only 10% of rainfall events have a cummilative depth of more than this amount.
4) 90% Shortest Time between rainfall events, i.e. only 10% of rainfall events have between them a dry time less than this time.
5) Volume of yearly rainfall for "water shed" classification as per LEED.
in plain english this means that it is the volume of rain coming down for an entire rainfall 24 hour equivalent event AND the event is the one that statistically happens most of the time.
I think the reason the userguide wording is comfusing is because the statistical concepts are confusing and these calculations are usually done by an expert civil engineer. I also am not 100% certain of this area.
Links:
http://www.hydrocad.net/pdf/TR-55%20Chapter%203.pdf
http://www.bossintl.com/download/SoilCharacteristics.html
http://www.bossintl.com/download/RunoffCurveNumbers.html
also google
RUN-OFF VOLUME CALCULATION - TR-55 Method
Stromwater Retention Volume - Schueler's Simple Method
RUN-OFF RATE CALCULATION - Rational MethodA formula that can be used for calculating stormwater flow rates. Q = CIA, where C represents a coefficient for physical drainage area, I is the rainfall intensity, and A is area. The method is suitable for watersheds smaller than 300 acres in size.
Hello Jean,
Thanks very much for your detailed explanation. I think what you said is right.
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