[cameron]

You can not export out the results with the hybrid method that I am aware of.

The description below is from HEC and what the hybrid method does.

“The hybrid rendering method takes the best parts of the sloping method and
attempts to make it more accurate when it detects the potential for failure.
We do this with a couple of tricks to raise and lower the water surface as
needed. When shallow flow is detected, we fall back to the horizontal
rendering mode for that particular 2D cell since the horizontal method renders
low-volumes much more accurately. This will show the water stair-stepping,
but won’t incorrectly show large areas of dry land. We also add extra weight
to the water-surfaces computed at the center of a face, so the downhill ravine
case won’t be so dramatically affected by the high-ground face points. Finally,
we make an adjustment to the computed face-point values to drag them up
or down so their average matches the computed cell water surface. This
allows us to create a sloping water-surface, but ensures that we don’t
dramatically over-estimate or under-estimate the rendered volume.”

[cameron]

What do the breach hydrographs look like?

[cameron]

HMS creates a DSS file with the hydrographs. You just select the DSS file as the inflow.

[cameron]

export out the cell center as a point shapefile, assign a WSE to each cell center, then create a wse raster from the points. You can then subtract your terrain from the WSE to get a sloping surface.

To help, set the depths at which it displays from 0.001 (default) to -9999.

[cameron]

I will have to double check, but I believe it calculates the WSE for each cell and back calculates the depth from that and the terrain.

[cameron]

If you follow 44 CFR 60.3(d)(4) it states you can have an increase, but you need to do a CLOMR

[cameron]

did the velocities go up in the channel? You are basically forcing water to stay in the channel which probably has a lower roughness value.

[cameron]

You can try minimizing the number of points in the weir for the lateral structures to see if that helps, but you definitely need to have the 1D/2D iterations turned on. You may need to go smaller on the weir coefficient than 0.2, 0.05 might be appropriate depending on if it is natural ground or not. Timestep may also help.

As for fixing the model for the 2D equation, you would just need to add breaklines at all splits between lateral structures and it will fix your problem.

I would identify which lateral structures are having the 1D/2D iterations and see if you need to split them up or adjust them.

[cameron]

First off, you should not use 2D equation for a dam (see below).

To answer the breach question, it uses the weir coefficient you specify in the breach input window.

If you do have overtopping of a Dam, the weir equation would be the better option to use than 2D equation anyway as that type of flow fails to meet the shallow water equations assumptions. It is more like a waterfall. This would be similar to any large levee that over tops.

The 2D Users Manual states this specifically on page 3-67.

[cameron]

export out each raster for each computation output and set up the animation in either google earth, QGIS or, ArcMAP. The Raster outputs will look different than Mapper.

[cameron]

I agree with Lonnie on splitting laterals down to about every mile or so and filtering them. It is a little bit of a pain sometimes, but it makes the models a lot more stable. Just remember that if you want to use the 2D equation instead of the weir coefficient, you have to split the lateral structures at cell faces.

[cameron]

Looks like some instabilities. If you sent me the model I could play with it.

[cameron]

Did you try extending the 2D model to the next downstream 1D XS?

[cameron]

do you have the 1D/2D iterations option turned on?

[cameron]

The image you presented from the post is a 1D/2D model so the flow in the overbank is 2D.

There is not an easy way to extend the wse outside of the cross-sections. For your particular model, is appears the main channel does not contain the flow, so either extend your cross-sections, make the overbank 2D, or add a split reach.

As for near the tributary, you would need to add lateral structures so flow can spill from one cross-section to the next.

[Author]

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