Need help routing through HydroCAD a peak of 1.05 inches in a 15 min period.

[Sean Naylor]

Hello, Have a routing question... The City of Pittsburgh, PA has the following language in their ordinance for green infrastructure...

[ul]
[li]At least 50% of 1.5 inches of rainfall in a 24-hour period, including a peak of
1.05 inches in 15 minutes, or a 95th percentile rain event on-site, whichever is greater, is captured using Green Infrastructure installations; or[/li]

[li]At least 15% of total volume of rainfall in a 24-hour period, including peak of 1.05 inches in 15 minutes, or a 95th percentile rain event on-site, whichever is greater, can be captured and reused on-site;[/li]
[/ul]

I am not sure how to analyze either step. The 50% of 1.5 in in a 24 hour period seems easy, but the rest I do not understand how to analyze. Any help in this matter will be greatly appreciated.

Sincerely,
Sean

 

[psmart]

It's hard to decipher those requirements as you've quoted them. Can you provide the preceding part of the regulations, or a link?

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[Sean Naylor]

Hello Psmart.

That's just it, there really is not much else. I have reached out to the CoP reviewer. I just don't understand how to analyze the... 1.05 inches in 15 minutes, or a 95th percentile rain event on-site... In my 16 years of designing stormwater, I have never been asked to do either, at least not in this way.

 

[psmart]

I still don't understand the context. What's the document you're quoting from? I assume it contains references to these items? (5.a and 5.b) Perhaps there's a rainfall distribution elsewhere in the document matching these characteristics?

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[Sean Naylor]

I am not sure if this will give more clarification. Page 32 has the table I shared above.

https://pghriverfrontzoning.files.wordpress.com/2018/08/sections-905-04-and-915.pdf

Sean

 

[psmart]

So this pertains to green infrastructure credits for Pittsburgh? (Helps to know what we're talking about.)

Looks like this may be referring to a specific rain event. I found "The event condition analyzed was an August 31, 2014 event with a peak rainfall intensity of 1.05-inches in 15 minutes, and a rainfall volume of 2.25-inches in 10 hours." at

https://apps.pittsburghpa.gov/pwsa/PWSA-City-Wide-GI-Assessment-public-summary.pdf

Just speculating, but is there data for this historic rainfall event? Otherwise you may need to define/create a rainfall distribution which meets the stated requirements.

But definitely ask the agency, otherwise we're just guessing.


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[TerryScan]

This appears to be a horribly written city code. They took a historic event with 1.05 inches in 15 minutes and 2.25 inches in 10 hours....then mashed it in with their 1.5 inches in 24 hours 95th percentile storm. It was two different things....

How does one model this Frankenstein?