Pipe-Arch Culvert Dimensions

Chris,

We have RiverCAD but I am hoping that you can answer a simple HEC-RAS question. I would like to enter a C.M. Pipe-Arch from Chart 34 in HEC-RAS. On my Chart 34 from the Federal Highway Administration, a 58"x36" is available. However HEC-RAS only allows you to enter the rise. When I try to enter 3' (36") it calculates a width of 3.98' instead of the 58" allowed in Chart 34. Why is this? How can I enter a 58"x36" C.M. Pipe-Arch.

Bob Givens

Dear Bob Givens :

HEC-RAS does not allow you to define the culvert span for a pipe-arch culvert, only the rise. It is using the FHWA nomographs, which have a specific rise to span ratio that HEC-RAS honors. So, you are limited to the span that HEC-RAS computes for you.

If you have any additional questions or need any further information, please contact me again.

Sincerely,

Chris E. Maeder, M.S.
Senior Technical Engineer
chris.maeder@bossintl.com