http://www.mde.state.md.us/assets/document/chapter2.pdf

page no 2.2

Thanks!

Would anyone be able to tell me what is the unit for the 1-yr and 2-yr 24 design storm? Is it a probability value, with no unit? Or is it in mm/inches of rainfall per minute or second?

Thanks,

Maya

Pat this is other way around!

If nothing else exists I would default to the typical annual rainfall file that Wisconsin references. This file shows the rainfall record for what has been designated as a typical year for that part of the state.

However, the LEED Option 2 is tied to the 2 yr rainfall event, and the typical rainfall year files referenced by the Wisconsin regulatory authority do not necessarily include the 2 yr event.

thanks

Thanks

Vid

I’m just trying to fullfill the Pre-Development Site Runoff Quantity in my SSc6.1 Template. I just determined my Pre-Development Site Runoff Rate (cfs), but I can’t figure out how I find the run off quantity (cf). How do I relate this two information.

Thank you

In the v2.2 Reference Guide (under SSc6.2), it says that:
-Alternative Surfaces inlcude vegetated roofs, pervious pavement or grid pavers.
-Nonstructural Techniques include rain gardens, vegetated swales, disconnection of imperviousness and rainwater recycling

“The geometry and health of streams is closely linked to stormwater runoff velocities and volumes. Increases in the frequency and magnitude of stromwater runoff due to development can cause increased bankfull events. As a result, the stream bed and banks are exposed to highly erosive flows and more frequently and for longer peroids.”

It’s not an equasion but it does explain about Velocities, Volume, and Frequency.

~Amy

Can someone clarify why for option 1, we design for both 1 and 2 year 24 hour design storms?

I really need to know the imperviousness of the site but most likely the answer is option 1 because because although the post development runoff rate (CFS) and quantity (CF) must remain the same or less than pre development rate and quantity . . .Option 1 does allow post development rate and quantity to exceed predevelopment rate and quantity given appropriate steps are taken to prevent excessive stream velocities and associated erosion.

Anyways the breakdown is as follows:

Option 1: For sites that have an imperviousness less than or equal to 50%, the post development discharge rate and quantity must remain the same or less than the pre development peak discharge rate and quantity.

OR

You can implement a waterway protection strategy that reduces receiving waterway velocities and associated erosion.

OPtion 2:
For sites with imperviousness greater than 50%, the post development peak discharge rate and quantity must be 25% less than the pre-development peak discharge rate and quantity.

I am a Civil and Environmental Engineer. The right answer is indeed E. With decrease in permeability the volume of the runoff increases. Furthermore these hard surfaces also increase the temperature of the flowing water. Due to lesser resistance to flow the velocity of the flow also increases. More volume also increases the frequency of flows.

I also looked the definition of STORMWATER RUNOFF (ON A SITE) I have the second edition, this definition shows up on page 81, it is the very last paragraph before SSc6.2 starts. This definition DOES NOT say anything either about frequency, velocity or temperature. I continue thinking A) is the right answer. What do you think?

Q – run-on flow (m3 /sec).
C – run-off coefficient for drainage area (%).
i – rainfall intensity (mm/hour).
A – area draining onto the site (km2 ).

I would choose a. since in this formula to calculate the run-on there is nothing regarding frecuency, velocity or temperature!

They do seem to make a distinction between non-structural surfaces and alternative surfaces. I think they also make a distinction between “alternative approaches” and “alternative surfaces.”

The gist of “quantity control” is to either make precipitation sink into the ground or collect it for re-use, cutting down on the amount of water that is flowing off the site. The best way to do this is to reduce the amount of impervious surface (i.e. solid pavement.)

“Alternative approaches” can include rain gardens, vegetated swales, vegetated rooftops, grid paving, pervious paving, and rainwater recycling.

I believe “nonstructural” means vegetated swales and rain gardens – those measures that are plantscaping related, where no one exactly built anything, but just moved a bunch of dirt around and planted things there.

Green roofs, to me, sound structural (although alternative because they’re unusual) because of the weight and hassle of supporting a vegetated roof.

“Alternative surfaces” would be the grid pavers and pervious paving – those measures that are added constructed surfaces different from the typical choices – but are still not part of the building structure – the key word here perhaps being “surfaces,” as in active surfacing or paving.

I hope that helps – maybe someone else can jump in here, but that’s the way I understood it when I took the test.

It’s probably more important to understand the pre- and post-development runoff rules. That if the site was largely undeveloped, there shouldn’t be any more runoff when the project is complete than there was when it started. But if the site was already half paved over or covered, the runoff needs to be 25% less when you’re done than when you started.

Anyone?

However, in the greenexamprep it asks:
What are nonstructural techniques to reduce water pollution from stormwater for LEED certification?
the answer was: rain gardens, vegetated swales (which are listed here as the alternative not the nonstructural).
which is correct?

Thanks alot!

There is no errata issued for this. Which A value should I be using?

I do not understand the Vr calculation lister as:
Vr = (P)(R)(A) / 12′
I am unsure what the P is in the equation. Also, is the 12′ a constant or project specific?

I also do not understand the Rv calculation listed as:
Rv= 0.05 + (0.009)(I) = 0.05 + (0.009)(100) = 0.95
If I= % impervious, are the other numbers constants or were they derived from something project specific?