Nuisance Flooding of Roadway Intersection 1

[zahid106]

I am working on mitigating the flooding of a roadway intersection. The area is highly urbanized.
Is there any guidance as to what storm event and/or storm duration to use for designing mitigation measures?

 

[gbam]

Our local, regional and state criteria use a 10-Year return period for onsite drainage. I recommend you check with your governing agency. A great resource is the FHWA HEC22 Manual.

 

[FacEngrPE]

Here is one localities criteria.

https://www.nnva.gov/684/Design-Criteria-Manual[/URL]]

. These criteria are based on

https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_cont.html[/URL]]NOAA Atlas 14 Point Precipitation Frequency Estimates

.
Does your urbanized area have some criteria? The criteria may define what constitutes undesirable roadway flooding

 

[zahid106]

Thank you gbam and FacEngr for the valuable information
The project's jurisdiction has very similar storm event design criteria as in FacEngr's post.
I am still trying to figure out the duration part.
here is some more information on the project
The intersection is located at the downstream end of a pipe run with a drainage area of approximately 25 acres. Outflow from the intersection is connected to a tidal water body.
There is a storage and pumping system in place designed many years ago when the watershed was less developed.
The system design criteria was a 10-year storm event with a 2-hour storm.
The storm volume was estimated by the 10-year peak for 25 acres watershed using the rational method and multiplying the peak flow with two hours to get the volume.
This volume was routed through underground storage, with outflow being the pump system.
I am working on upgrading this system and bringing it to the current code. I think 10-year is a suitable storm event, but I'm not sure about the 2-hour duration part.

 

[gbam]

TR55 may provide you with necessary hydrographs, but you need to confirm with governing agency on the appropriate hydrologic method. There is a Modified Rational Method that can be used for runoff volume estimate or if you have a unit hydrograph that can be used.

 

[FacEngrPE]

Outflow from the intersection is connected to a tidal water body

complicates matters.
Does street flooding coincide with high water in the tidal water body? You may be looking at a concurrent event problem.
Consider if one of the criteria for design should be a maximum water level event, or perhaps a specific high water level.

A tool like this can help estimate some real past events.
Coastal Emergency Risks Assessment Storm Surge Tool
or
NOAA Tides and Currents