[Lonnie A]

Alister, do you have a land classification file associated with the geometry. I’ve not had the error when I’ve ran it.

[Lonnie A]

Alison, You have to select the option to use horizontal 2D n-value for it to apply. There is a check box is in the geometry editor’s 2D editor, lower left corner. It took me a fair amount of time to locate it as the manual doesn’t give any real insight on it….to their defense it’s still called a “beta”. I have yet to be able to back calculate how they are applying it as the cell face resulting n-value isn’t exactly as I’d of expected it to appear. It looks more vertically varied based on how they present the results.

[Lonnie A]

your connection has the same from and to connections….this would be fine if it were a internal connection (inside of a 2D area). You need the from to be the SA and the to to be the 2D area.

[Lonnie A]

the merge terrain in mapper is intended for mostly non overlapping terrain files as there is no control as to the order it merges them.
If you let RAS just build the surface and then export it to a resampled surface be warned that it will likely adjust the background Lidar elevations through its reporcessing.
The best way I’ve found is to bring the individual surfaces into GIS and mosic them there…be sure to set the environment to snap to the background lidar. If you do that it won’t modify the lidar outside of the area of the channel and site survey surfaces.

[Lonnie A]

You need to drag the end of the reach graphically into the SA and then it’ll ask if you want to connect the two. FYI if you have flow assigned to the top xs of a 1D reach and you connect that to a SA at the upper end it won’t warn you that it is not using that flow…just a heads up on that.

[Lonnie A]

Zoran,
Depending on what it is you are trying to do you might be able to export a WSE raster from Mapper and use it to update your base terrain file. You might be able to set known WSE on the sections you want to fill and then just run a model with very minimal flow for a few time steps. Then export the WSE surface and put it on top of the base surface.
Lonnie

[Lonnie A]

yes done automatically but you can preprocess ahead of time using this feature

[Lonnie A]

Derek,
I find the 2D equation to be unstable a lot of times. Particularly if the lateral is cutting across tributaries. If you really want to use the 2D equation I’d suggest breaking the lateral at tributaries and for the short piece across the tributary use the normal weir equation with a weir coefficient of 1 to 2.
Most of my models I use the normal weir equation with a Cd of 0.5 when attached at grade to the floodplain and a 1 to 2 Cd across tributaries. I also bump the stability factor up to 3. You want to try and keep the laterals to a nominal length. I try to keep them to less than 3000′ typically.
I then review the hydrographs across them. If I see some stability issues either tweak the Cd or try the 2D equation. If you start with the weir equation and get it running you can go back and try turning 1 or 2 laterals at a time into a 2D equation and narrow down which ones you have to keep with the weir equation. My models are largely coastal so with the flat terrain the difference between weir equation and 2D equation is usually minimal like 0.2’+/-

[Lonnie A]

The most applicable way is to use laterals like below. The thing it’ll be missing is what flow is trapped in the overbank. What is in the 2D and crosses the lateral will be put in the channel and then spill out into the 1D floodplain. This is usally okay though since you would usually expect the downstream floodplain to have flow if the 2D is carrying flow.

[Lonnie A]

I’ve found that using refinement regions can often provide for reduced cell errors. This is particularly true when the break line needs to close on itself.

[Lonnie A]

If you are in Mapper, have the geometry 2D flow area active, you can right click on a cell or other feature and select plot property tables. From there you have a number of items that you can view including the cell elevations

[Lonnie A]

Check your 1D reach lengths and if you are connecting it to the end of the XS or at the bank. If you look at the HW/TW connection tables in the lateral editor it should help tip you off on what is happening. Sometimes how RAS computes where the 1D intersects the geospatial lateral is off and you have to realign the ends of the XS so that it’ll not compute an incorrect intersection point.

[Lonnie A]

I don’t at which version for sure but HEC removed the point # limit on lateral structures Ras but in V507 put it back in.
What I find in a lot of my model reviews is that folks put in too long of a lateral. It is hard to quantify flow diversions in long laterals when reviewing the hydrographs etc. They are also more prone to stability issues and if its broken up you it is easier to figure out the problem area.
My recomendation is to try and limit lateral lengths to no more than a mile. Typically I’ll add a seperate lateral across a tributary confluence. This gives you flexability in assigning weir coefficients specific to a location when needed (sometimes need to switch from weir equation to 2d equation and viceversa). I also recommend filtering the lateral points down. The lidar I use frequently has 3′ to 5′ pixel resolutions. I use the filter option and typically reduce the number of point to about 10% of what RAS brings in from the surface when I have laterals that are longer than say 500′. The more points and irregular the shape of the lateral the more instability potential you add.

[Lonnie A]

This is how I avoid use of junctions in unsteady. It might be possible to do something similar with 1D but I haven’t tried it.
http://hecrasmodel.blogspot.com/2018/12/using-hec-ras-storage-area-and-lateral.html

[Lonnie A]

monosnap is a free software that allows you to record a window on your desktop. That is what I use.

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