Box Culvert to Steel Pipe (Drainage Structure along road)

[DPBD]

Good day everyone!

I'm currently reviewing a plan that involves the above-mentioned subject. It's a drainage/interceptor connected to a creek upstream and a detention pond downstream. The structure involved originally was a 400m (sta. 0+000 to Sta. 0+400) double barrel box culvert below the alignment of a road with man hole structures every 20m. Due to construction problems, the design was proposed for revision wherein along sta. 0+200 to sta. 0+260, the box culvert will be replaced with a circular steel pipe.

Is there a manual or guidelines in determining equivalent size or diameter of pipes using the design discharge calculated from the previous design? What other critical analysis are required for such changes? Thank you in advance.

 

[cvg]

you will need to run the hydraulics to size the pipe and junction structures. even if you select "equivalent size pipes", there will be significant headloss at each transition structure.

Los Angeles County has a good manual for this analysis:

https://dpw.lacounty.gov/wrd/publication/engineering/design_manual.pdf

 

[Kozzybear]

How are you connecting the concrete box culvert to the steel pipe? Also, why is it necessary to have a manhole every 20m? On a cursory glance that seems excessive without any additional info.

To answer the question about equivalency, I would use Manning's to see how the steel pipe will convey the desired flow at the designed slope. What are the sizes of the double box and steel pipes?

 

[DPBD]

It will serve as an interceptor conveying water from a creek upstream to a detention pond downstream with flood gates at both sides.