HEC-RAS Culvert with obstruction 2

[TJS2010]

I am interested in using HEC-RAS to calculate the water surface and flows through a 60' long, 7' x 14' arch culvert pipe with a 3' wide 14" high sidewalk obstruction located in a portion of the pipe.

I have routed the stormwater runoff from the 500 acre watershed area through the existing 7' x 14' arch culvert pipe and calculated the pre-existing flows and water surface elevation for 10, 25, 50 and 100 year storm.

My question is how can you place an obstruction inside a culvert? It appears HEC-RAS will not let you do this.

 

[gbam]

You can represent the sidewalk in your cross section.

 

[TJS2010]

I have tried creating the sidewalk in the cross section, but unsuccessful in placing it through the pipe.

 

[froude]

Since you are trying to account for the blockage in conveyance that the sidewalk may cause, you might be able to just come up with an equivalent depth of the sidewalk along the entire culvert width and use that value in the "Depth Blocked" field in the Culvert Data Editor. Just a thought. I don't think this would have a huge effect hydraulically, but I am not certain either.

You may also be able to define your high/low chords to fit your needs or perhaps even use blocked obstruction in the upstream and downstream culvert sections.

Good luck!

 

[francesca]

A culvert that size can easily be modeled as a bridge. You can then control the internal cross-section manually to place the internal obstruction.

 

[TJS2010]

Dear francesca,

The problem I experienced by modeling it as a bridge was that an error occured "Station data is not in increasing order, stationing needs to maintain (vertical walls) or increase. Any ideas how to get around this?

 

[Ryb01]

SWMM would probably be a better software to use for this type of application. You could split the pipe up into three components and model the expansion and contraction losses associated with the sidewalk. If you are looking for flood elevations you could also code in the channel u/s and d/s of your area of focus.

HEC-Ras although a great program isn't really set up to do what you are looking for.

Hope this helps.

 

[SMIAH]

Make sure that your station data is increasing (from -x to 0 to +x) has the elevation data is changing.

 

[TJS2010]

I want to thank you all for your ideas.

The RAS Team had replied back to me and instructed me how to perform this study. They said use the ground line to account for the channel and top of sidewalk. Use the deck to account for the arch.