HEC-RAS modeling flow into a standing body of water

[jagermeister5]

Hello,

Is there a way within HEC-RAS to model flow into a standing body of water? For instance, I have a case where I have culverts terminating in a standing body of water (lake). I have a cross-section of the lake and a known water surface elevation for the lake. The problem is when using the lake for the downstream boundary condition, HEC-RAS wants to put a flow to it, when, in reality, there is no flow in the lake.

In my particular situation, the culverts are flowing in the subcritical regime. When HEC-RAS puts a flow to the downstream lake boundary condition it comes up with a supercritical answer which creates a discontinuity with the upstream subcritical regime. The model then defaults to critical depth for the downstream boundary condition.

In addition, standing water will act like an energy dissipator for the incoming flow.

Is there any way to simulate this in HEC-RAS?

Thanks

 

[cvg]

how about running your model using subcritical flow regime instead of mixed or supercritical? also set your downstream boundary condition to a known water surface elevation

 

[jagermeister5]

Yep, I am running it in the subcritical flow regime.

I know the starting wse elevation but the question is, is there a way to simulate standing water? HEC-RAS takes the starting wse and calculates a flow for it. That's not what I want. I want to model the effects of flow dissipating into standing water.

Thanks.

 

[cvg]

I'm not sure hec-ras can do what you want. It is a 1-dimensional model, but the energy dissipation at the stream / lake boundary is a 2-dimensional phenomena.

 

[francesca]

Put an ineffective flow area for the known WSE on the downstream cross-section.

 

[MAnderson]

Are you culverts discharding @ NWL of the lake? Can you fake a cross-section out 100 or so feet for your Starting Water Surface Elevation with a depth that will simulate slow moving water (0.001 fps) or is the lake a tailwater for your culverts?