Box Culvert to Steel Pipes (Equivalent diameter)

[DPBD]

Good day everyone!

I'm currently involved in a drainage project which was originally a double barrel box culvert along a road (which serves as an interceptor) but due to construction problems, the client has decided to use two parallel steel pipes instead. Is there a manual or guidelines in determining equivalent size or diameter of pipes using the design discharge calculated from the previous design? Thank you in advance.

 

[ACtrafficengr]

You can download HY-8 software from FHWA for free and analyze the culverts. It's a simplified analysis compared to say, HECRAS, but it would be better than any rule of thumb. [URL unfurl="true"]https://www.fhwa.dot.gov/engineering/hydraulics/software/hy8/[/url]

I don't know what jurisdiction you're in, but we have to bury the new structure invert 20% for aquatic organism passage. That may limit your structure options.

Also, if you get debris in the stream, a single span would be desirable.

My glass has a v/c ratio of 0.5

Maybe the tyranny of Murphy is the penalty for hubris. -

http://xkcd.com/319/

 

[cvg]

suggest that you send this back to the engineer of record and ask for a re-design with pipes. simply substituting two pipes may result in impacts to the floodplain not to mention require redesign of headwalls, etc. a hydraulic analysis done by somebody that is knowledgeable in this is required.

 

[1503-44]

Capacity at low flow will be reduced considerably unless the invert elevations are lowered.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[cvg]

reducing inverts will reduce the head at lower flow rates but would allow sediment to accumulate, reducing the overall capacity. by steel pipes it is assumed they would be corrugated metal pipes. they have a much higher roughness than concrete and very large sizes may be a challenge to install in parallel. a multi-plate arch might be a better choice

 

[1503-44]

I thought that the reduced invert elevation would tend to increase the effective width at the mud line(assuming it would accumulate sediment there) to accommodate equal volumes at low flows, but it would also require a larger pipe diameter to acvomodate higher level flows as well. It would appear that a much larger pipe would be required. Basing pipe size on an equal hydraulic radius would not seem to work at all.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"