HEC-RAS- culvert modeling- huge jump upstream of culvert

[PT60056]

Hello Everyone

I am running a Hec-Ras model for existing culvert. I am experiencing a huge jump at upstream end of culvert. There are no errors. I know that water surface elevations should be very much same as downstream (as per FIS study flood profiles). I tried adding multiple cross-sections downstream and upstream but i am not seeing any difference. Is anyone experience this kind of issue? and what is the cause and how to resolve the issue? Any insight is appreciated.

Thanks in advance.

 

[pointsman]

Why is the bottom of the culvert above the channel bed? Not only do you have an entrace loss, you also have a vertical expansion followed by contraction.

HEC RAS documentation states that the cross sections upstream and downstream of culvert openings needs to be far enough away from the end of the culvert for the flow profile to develop. It looks like your cross sections might be on the close side?

What is your flow rate, and what is the diameter of your culvert?

Please post the profile output table and the cross section output table for the culvert.

 

[PT60056]

Existing culvert is higher than channel flow line. Culvert size is 10x7 box culvert. Here are the photos that may help see the additional information. I had cross-sections far enough away for expansion and contraction but then it gave me warning that the conveyance ratio is less than 0.7 or greater than 1.4 and may require additional cross-sections.

 

[TerryScan]

As a simple check- I put a rough model of your culvert in HY-8 and got similar water surface elevations.

 

[PT60056]

As a simple check- I put a rough model of your culvert in HY-8 and got similar water surface elevations.

you mean, similar as to Hec-Ras model or similar to downstream of culvert?

 

[pointsman]

Your velocity in the culvert is quite high, so you should expect a high headloss.

If we take the minor loss coefficient of the entrance as 0.5, then the headloss will be v^2 / 2g = 12.92^2 / (2 x 32) = 1.3 ft

Which exactly agress with what HEC RAS found. If this disagrees with observations then check your inputs (geometry, boundary conditions).

 

[pointsman]

What is your upstream boundary condition?

 

[TerryScan]

you mean, similar as to Hec-Ras model or similar to downstream of culvert?

Similar to the the HEC-RAS model.