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HEC-RAS modeling excessively long culverts

HEC-RAS modeling excessively long culverts

HEC-RAS modeling excessively long culverts

Has anyone had any experience with modeling a structure on the order of a triple 7' x 7' box culvert in HEC-RAS? I seem to have run across an issue with the program when trying to model a proposed 2,400'+ long version of the aforementioned structure for a project. We were tasked with needing to show the backwater effects for blocking one of the three, as crazy as that seems, and HEC-RAS was giving very unstable results, including a lower WSEL for the 100-yr than the 25-yr. It was defaulting to the Critical WSEL since it wasn't able to calculate a WSEL for the given circumstances; however, some troubleshooting revealed that upon shortening the culvert to approximately 1500' it gave reasonably accurate results. Anyone ever seen this issue previously?


RE: HEC-RAS modeling excessively long culverts

is the model under steady state or unsteady?

RE: HEC-RAS modeling excessively long culverts

Steady State. Originally we didn't have the time to develop an unsteady flow model, but if someone believes this might alleviate the issue I'm willing to develop it.

RE: HEC-RAS modeling excessively long culverts

Quick question is the long box sealed or free surface during the blockage and regular condition? if unsealed you used to be able to model a lidded structure in HECRAS, I haven't done that in years, however. Can you perform a calculation externally using a storm cad type model to develop a rating curve at the inlet to compare your results?

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