Let it snow, let it snow, let it snow

Adam Stoker

Consultant, Sustainability

University of Calgary

LEEDuser Basic Member

2 thumbs up

July 14, 2014

The reference guide and the Rainfall Events Calculator provided by the USGBC alternatingly use the terms 'rainfall' and 'precipitation; while this is fine for temperate climates, it leaves us northerners scratching our heads a bit. For the purpose of identifying the 95th percentile rainfall event, how should projects consider precipitation falling as snow? Exclude those events from the calculation? While the fact that most of the credit language has been tweaked to focus on rainwater (as opposed to stormwater or precipitation) indicates they're likely focusing only on rain events, it would be great if the Reference Guide cleared this up with a few specific comments on how to handle snow (other than just bundling up).

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Lyle Axelarris

Building Enclosure Consultant

BPL Enclosure

LEEDuser Basic Member

58 thumbs up

Tue, 07/15/2014 - 16:34

I agree, Adam. I have reported only rain events for stormwater compliance requirements, but there is a great need for addressing snowmelt runoff which is, by far, the greatest threat to water quality in my region. A long winter's worth of contaminants (leaky vehicles, dog feces, etc.) gets released during a very short, intense thaw season. To make matters worse, the snow cover (and frozen ground beneath) increases runoff rates and prevents biofiltration, infiltration and evapotranspiration from reducing pollutant loads. I think addressing snowmelt with "oversized" detention ponds, wetlands or hydrodynamic separators should earn an EP for this credit.

Theresa Backhus

Sites Technical Specialist, LEED

USGBC

LEEDuser Premium Member

47 thumbs up

Tue, 04/21/2015 - 19:39

Adam, For the purposes of the v4 credit, “rainfall,” “precipitation,” “stormwater,” "storm event," etc are all basically used interchangeably. We did modify terminology from v2009, but for data gathering and calculations we are not excluding any kind of precipitation (like snow). In the US, NOAA's "rainfall" data is typically used, which actually includes all precipitation. The 95th, 98th, etc percentile events are precipitation events that need to be modeled. You can gather the precipitation data from the local NOAA equivalent for Canada and design BMPs accordingly.

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