[Lonnie A]

The calculation’s assume a level WSE within each cell. The distance between cell centers provide the HGL for driving flow across cell faces. So the cell centers get assigned the cell WSE which is based on the underlying cell data (storage, cell face hydraulics etc).
I’m not understanding your question I guess.

[Lonnie A]

I think it is actually coming from the highest adjacent minimum cell elevation. I checked a recent model and the mapper WSE elevations match the results hydrograph stages for the two highest adjacent cells. The two cells located at the left end of the structure had the WSE that matched what was reported in the hydrograph output.

RAS mapper result

[Lonnie A]

I think you are confusing how RAS performs its calculations. In simplest terms it treats every cell as a storage area with interconnection to adjacent cells. So there is a stage storage curve for each cell. The center point is just a location for the most part and isn’t reading a elevation from the underlying terrain to create a TIN.

Read item #6 in the 2D user manual introduction for a better description.

[Lonnie A]

I’m assuming you are asking about 2D capability?
V5.0.4 will have ability to set the xy coordinate of pipe ends which hopefully will be out in the next few months.
In v5.0.3 the work around is explained in this series of post

[Lonnie A]

Every cell along the connector can have a different HW and TW. I believe what is reported in the hydrograph is the HW and TW from the lowest connected cell. If you want to know what the HW and TW is at a certain location you need to look at the results in Mapper. If you are just reading the max WSE and not plotting a hydrograph of the target cell within mapper be sure you set the render mode to horizontal so you get the elevation that the calculations are based on.

[Lonnie A]

Not in Version 5.0.3. The next release will have this capability. Last I heard they were hoping to have v5.0.4 out around the end of 2017.

[Lonnie A]

The easiest way to fix the slivers is usually to extend the XS to where it has a small overlap with the 2D. This is easier than pulling the 2D area to overlap with the XS and causing the mesh to change forcing edits to the lateral etc. Usually the slivers are small enough that I know there is no impact on results and is just a graphical thing so I let them slide sometimes.

[Lonnie A]

No idea if this is the issue but I’ve seen this type of error report when I had deleted a boundary condition line in the geometry but the flow editor still had the BC listed.

[Lonnie A]

A simpler work around if you have the areas as shapefiles is to select GIS tools in the geometry editor, then land cover region table. Once that is open select import lines and select your file. From there you can select the xy coordinates and then just draw a random storage area and paste the coordinates in to georeference the area and then delete the regions after you’ve copied the xy points.

[Lonnie A]

Not sure if this will work but you could try to take the created static depth map and build a terrain file in mapper from that. Then rt click on it and export to a geo tiff. IYou would then be able to specify the raster cell size there.

[Lonnie A]

No flow is being transferred between bounding XS of structures.

What I do with long culverts in cases like this is model the area over the culvert in 2D…I stich the left and right 2D areas together with a storage area connector along the culvert. You have to set the culvert deck in 1D artificially high so it doesn’t count the weir flow which is already being accounted for in the 2D.

[Lonnie A]

Are the two stream watersheds similar in size? Meaning do you expect to have the peak flows occurring near the same time at the confluence? If so then you might consider using the BFE in the receiving stream as the starting WSE on your stream. If they aren’t going to likely be coincidental then normal depth should work. This is how FEMA typically maps things. You run the trib as normal depth and then project the backwater elevation of the receiving stream back up the trib until it intersects with the profile of the normal depth SWSE run.

With the distance away from the receiving stream does either choice impact the elevation at the crossing? In coastal areas it probably would but in areas with steeper channel gradients your backwater assumption typically only impacts WSE over a short distance.

[Lonnie A]

Andy,
Here are a few things I would try.
-Why are the ineffective elevations set so high at this crossing? Is there something downstream that would make the effective flow area this narrow and stack the water that high? With out seeing the downstream topo I would put the ineffective as single points using the elevation and stage of the ones set at the culvert face. And then expand the effective flow width going away from the crossing.

-suggest editing the internal cross-section in the bridge editor so the section flowline matches the culvert opening. What you have typically works for steady state but I know in unsteady I have to often do the internal XS edit for stability.

-there are a lot of changes happening at the outfall, you have large change in flow area and added flow at XS 2. If the first two suggested edit doesn’t help you might add a XS between 1 and 2 to insert the flow a little further downstream.

The lateral structure location isn’t a issue. Another thing to consider is the weir coefficient you are using on the lateral. Is there a true weir flow condition or is it just sheet flowing away? If it isn’t a weir flow condition I’d lower the coefficient to values like are recommended in the 2D manual. Maybe something in the 0.5 to 1.0 range. With a high coefficient it could suck off a lot of flow in one iteration which then drops the WSE significantly so it can’t iterate to a solution.

[Lonnie A]

You might try ramping up to your steady flow instead of throwing all at the mesh at once.

[Lonnie A]

Are you modeling this as a steady state or a unsteady state model?
If unsteady a trick I use often is to use a storage area as the junction. You can then drag and drop the ends of the reaches into the area and use it to split the flows.

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