In the LEED

For “case 1: impervious surface less than or equal to 50% of total site area
pre-development peak discharge rate and quantity equal to or less than post-development” should not pre- and post- be switched with each other?

Thanks, Good luck, I ike your blog, Jerry-testing March 24.

By Jerry on Feb 24, 2008

I know it’s not necessary to know this to be able to get the questions about this credit right, but can anyone tell me what exactly does
1-yr and 2-yr 24 design storm stands for? To my knowledge the reference guide doesn’t explain.

Is it the worst storm in a 24hr period within 1 year? Then that would make the 2-year one a “bigger” storm than the 1-year… or maybe the same one if a …. ok, ok… whatever with the assumptions… anyone care to illuminate me?

Thanxs!

By Sofia on Apr 26, 2008

A 1-yr 24hr design storm refers to the the worst storm that you can expect to happen every year. For example, a L3 hurricane for the Miami area.

A 2-yr 24hr design storm is the worst storm you can expect to happen every other year. For example, a L4 hurricane in the same Miami area.

The concept continues. Therefore, the longer the period the worst the storm. For example, a tsunami that devastates and entire city should have a return period of (let’s say - I’m assuming these values) 100 years. Meaning that every hundred years a tsunami, strong enough to devastate a city, should happen. That would be a 24hr 100-yr design storm.

In these credit you should evaluate both design storm, both histograms (since the two are different), and assure that the post-development peak would not be higher than the pre-development peak.

By AA on May 13, 2008

nice…

thank you!

and I suppose then…

this 24hr 100yr storm should not be confused with the FEMA 100-yr storm since they say it’s not necessarily the worst storm in a hundred years but the storm that has a 1% probability of happening each year…

right?

By Sofia on May 14, 2008

Right. However, FEMA does not define a 100yr “storm”, but rather the 100yr “flood line”. According to FEMA:

“The term “100-year flood” is misleading. It is not the flood that will occur once every 100 years. Rather, it is the flood elevation that has a 1- percent chance of being equaled or exceeded each year.”

So, in that sense, you are right.

However, if you find another standard that defines a 100yr storm, you should check both histograms, because they might not we exactly the same (therefore the peak might be different).

By AA on May 14, 2008

Thanxs AA!

I’m taking the test next Tuesday May 20.

Have you taken it already?

By sofia on May 15, 2008

No problem Sofia, you’re welcome.

Yes, I took it last Friday and passed it.

It’s not that difficult, but very tricky. They just try their best to confuse you, but if you know the credit’s concepts well you should not have any problem. Good luck

By AA on May 15, 2008

Hi,

Here is a question regarding runoff coefficient hopefully any of you here can help me out.

Which has lower runoff coefficient, 6″ green roof or landscaped area(assuming they have same plants and slope)?

Many thanks!

Rachel

By Rachel on May 17, 2008

hi,
I’ve gotten some sample test questions that are doing a good job of confusing me with impelementation switch and bait.. I am needing to clarify that 6.1 and 6.2 use same technologies and measure them differently..
I cannot find in 6.1 any mention of ’structural’ impelementation…right? they lump it all into ‘alternative’
smaller bldg footprint, PERVIOUS PAVING, storm water reuse, green roofs, BIOSWALES, retention ponds,… of these only the Bioswales were mentioned in 6.2 as ‘non structural’ along with ‘disconnection of impervious areas, and pervious pavement(!)

6.1 only interested in how much h20 - submittal is in cubic ft per second

6.2 interested in the particles in the water and where they go, so the the same technologies are listed in terms of structural and nonstructural in terms of their infiltration capacity

It is not intuitive to me..so must memorize..is this the final list? (why are pervious paving area non structural and ponds structural…and the green roofs?)

By valeria on Jul 6, 2008

Rachel, that is a tricky question, especially without knowing the soil type of the landscape area. With all things being equal, I am going to have to go with the landscape area, because there will likely be a greater volume of infiltration.

By mikedee on Jul 8, 2008

valeria…can you rephrase your question just a bit. I think i know what you are getting at, just want to make sure.

FWIW…I’m a PE, and do stormwater management daily. The LEED Ref guide does a horrible job of trying to get their points across.

I’ll give your question a shot…6.1 reduce stormwater QUANTITY and discharge RATE. Typically as engineers, we do this via detention basins. As impervious surface increases, so does the runoff rate and runoff volume. We route this into a basin, and let it come out slowly, thus reducing the peak rate and volume.

6.2 deals with removing TSS from stormwater. You can do this several ways, the most common ways I do this are by using infiltration basins, which store the entire volume of the water quality storm (what they call 90% average annual rainfall) then slowly let it perc back into the ground. We also use structural means, stormtech, vortechnics, etc…structures designed to do just this, remove 80% TSS.

By mikedee on Jul 8, 2008

ok, thanks for the “how it is written” comment.. I fell this whole green building thing is coming down so fast and furious, they have no time to proof read anything..

In your expertise, what is the criteria for a non structural technology?(inLEED land) I get bioswales, form land and put vegetation on it. no structure there, but they list in 6.2 also pervious pavement- pervious says structure to me..and disconnection of impervious areas- i imagined drains or some STRUCTURE to make the water go somewhere on purpose, instead of randomly eroding or gushing into a creek…

By valeria on Jul 9, 2008

In the construction industry “structures” is a term that is synonymous with mahnoles, inlets, etc. not parking lots.

I think that is what they are getting at here.

By mikedee on Jul 10, 2008

ahaaa! thanks!!!!

By valeria on Jul 10, 2008

Can anyone tell me if Option 1 and Opiton 2 both refer to rate AND quantity?

I assume that they do, but I have found a contradiction in the book:
Summary page (77 in my 3rd Ed) says rate and quant for Option 1, and quant “volume” for Option 2.
Over on page 80, calculations, it says rate and quant for both???

By Kim on Aug 31, 2008