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non-symmetrical cross sections

Fri, 12/14/2007 - 9:42am — Mohammad
I am confused about the cell width in the bathymetry file. I am not sure how a non-symmetrical cross section can be represented in the bathymetry file. The way widths are done in the bathymetry file suggests to me that the second entry is the width of the top most layer and that is why is it is usually the widest and the widths goes down as we move down with layers until the minimum with is reached at the lowest active layer. If this is the case, how does the model know if one side of the cross section is much steeper than the other side? Also, why are those called cell width in the bathymetry file description rather than layer width? Thanks Mohammad
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Hydrodynamics
Fri, 12/14/2007 - 11:57am — Rob

The bathymetry file includes the layer widths for each model segment regardless of the symmetry of the cross section. it is important to make sure to capture the appropriate river cross section in the grid. The model bathymetry does not account for non symmetrical grids because the model is laterally averaged. The model does include the segment orientation angles which ensure that curvature in the river channel is maintained. The difference in description between the bathymetry file description and other description in the User’s manual is an oversight, they are referring to the same thing. The layer widths changed from segment to segment and from layer to layer, only the layer height is consistent for each water body so the layer width is consistent with saying “cell” width as long as you understand the cell width refers to one segment in one water body at one layer.
Fri, 12/14/2007 - 1:30pm — Mohammad

For a given branch or a set of branches in modeling sloping river, does the width of the highest layer in all segments have to be based on equal cross section elevations? or does the model understand that as you go downstream, elevation gets lower and to maintain the same elevation for a given layer, you may need to make the width unreasonably wide. Mohammad
Sun, 12/16/2007 - 2:05pm — Rob

No, All cross section should be based on data in the field. The model control file allows you to put in the river slope. Given the model EBOT, and slope of each branch and then the layer heights the model calculates the the elevation for every layer in every segment. You can see this in the GUI under the bathymetry features. You should not adjust the widths to be unreasonably wide. The model simuates the water surface elevation based on flow rate, geometry, slope, maanning's friction or chezy friction and if you have any structures in the river which may slow down the water, ie.e spillways. I hope this helps. Cheers, Rob