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Ben22

Reach Boundary in HEC-RAS for floodplain delineation in WMS

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Hey,

I am trying to delineate a floodplain using WMS and HEC-RAS, but I need to ask a question about HEC-RAS. I'm trying to set my reach boundary conditions for steady flow based off a WS elevation according to a certain storm for HEC-RAS, but it only gives me the option of upstream or downstream reach boundary conditions. The problem I'm having is that the specified boundary condition I want to use is between my upstream condition and downstream condition. I have been having to break up the cross sections between the upstream and my specified point, my specified point and downstream cross sections since I can't specify where I want my known WS elevation to be. It only gives me the option of upstream or downstream to specify where I want my known WS elevation to be. It would be so much more helpful being able to delineate the whole project instead of having to break it up into 2 sections based off the known WS elevation.You may not be able to help me since this is more HEC-RAS involved but figured you would be able to help me out.Thanks.

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Hi,

I think what you're doing may be the only way to do what you need for a steady flow model. There's an option to enter a stage hydrograph as a boundary condition at an internal location for an unsteady model if you have that information. Your other alternative is to run the steady state model and calibrate your Manning's roughness or other model parameters until your observed water surface elevation matches the computed value. There is an option to enter an observed water surface elevation in a steady state model to make this comparison easier when viewing the model results. There is also an option to define an observed internal water surface elevation and have RAS skip the computation at that cross section, but this is not a boundary condition and is not what you are looking for.

Hopefully this helps,

Chris

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