Hec-Ras 5.0. [key words: only 2D flow, stedy flow]

[Robert]

Hi ,

I was studying the manual (Combined_1D_and_2D_Modeling_with_HEC-RAS), but there aren’t the examples [only 2D flow area or steady flow in the 2D flow area].

Questions:
1. Can I solve computational area only as 2D Flow Area or I have to define also river banks, floodplains, crosssections or storage. Because I want to set for 2D flow area (upper boundary condition- flow hydrographs) and down boundary condition (normal depth). (see link)
https://drive.google.com/file/d/0B6wWUzbPUM0dOExJTjN3RkV4QkE/view?usp=sharing
https://drive.google.com/file/d/0B6wWUzbPUM0dNEhsYWZlVjVKQ0U/view?usp=sharing

2. Can I solve steady flow only in the 2D flow area? – upper boundary condition- steady flow (example 10, 30,… m3/s) and down boundary condition (normal depth). I think, that we can not calculate steady flow int the 2D flow area. [if I err, you correct me, please]

Regards!
Robert

[Anonymous]

1. Yes, you can have 2D only.

2. No, you cannot have 2D steady flow.

[cameron]

You can have a constant flow for a long period of time which can simulate steady flow if the simulation time is long enough. This is commonly done in other 2D models as many do not have a steady flow option. This idea has also been used with HEC-RAS 1D models which have trouble working in steady mode to get a solution, but work in unsteady mode.

To know if the simulation time is long enough, you would need to verify that the elevations and floodplain extent are not changing which involves having multiple model runs with different simulation times.

[Author]

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