Culvert design - estimating post-construction ordinary high water

[ACtrafficengr]

NYSDOT's scour protection details show stone fill to one ft (0.3 m) over the ordinary high water level. The replacement culvert will be 50% wider than the existing one, which should reduce the OHW elevation.

From Army Corps:


So for design purposes, should I use the existing OHW elevation, knowing I'll be using more stone than absolutely needed? Or pick a reasonably frequent recurrance like the 0.5 or 0.2 storm?

 

[cvg]

that definition from the USACE is the one used for jurisdictional delineation for section 404 permits, does not really pertain to design.

for culvert design I would typically use the design water level for the design storm to set the limits of riprap. That is generally higher than a 2 or 5 year storm. Most culverts are designed for at least 10 year or 25 year, sometimes 50 year.

 

[beej67]

Careful. A wider culvert will only reduce OHW elevations upstream. It will generally increase them downstream.

In Georgia we size rip rap aprons for the 25 year storm. I'm sure this varies by state.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[ACtrafficengr]

Thanks for the advice. Looking again, I realized I was looking at a stream bank protection detail, not a culvert scour protection detail, so it probably doesn't apply.

 

[LincolnPE]

...Careful. A wider culvert will only reduce OHW elevations upstream.

Only if the system is operating under Inlet control.