2D modeling – modifying terrain/DEM

[Matt T]

I’ve gotten pretty good with the 2D modeling inHEC RAS 5, to the point where depending on the project it’s often easier and quicker to go 2D rather than 1D. However, I’m struggling to find a good solution where a project calls for evaluating potential post-project future conditions.

With traditional 1D RAS models it’s easy enough to modify cross sections where the project will change things, re-run the model, etc, etc.

However with 2D, evaluating project effects means actually “building” the project in the DEM/terrain that RAS uses. I’ve had good luck using the “burn-in” technique for adding bathymetry information to a DEM, as well as doing the opposite and adding a raised feature such as a levee.

But what if I want to go beyond simple “burn-ins”? Does anyone have suggestions for good tools to manipulate, modify, edit, etc DEM/terrains? I’m sure it could be accomplished via GIS but going and editing raster cell elevations 1 by 1 doesn’t sound particularly efficient.

Thanks!

[AJ]

It depends on what you are trying to do. GIS will give you the most options. I use ArcMap so the examples I will give apply to that software but I imagine you can do similar things with other software.

I have used the following to add buildings and other solid obstructions (Arc Tool names are in bold):

Create Feature
– create the 2D (XY) surface shape (e.g., polygon)
Add Surface Information
– add shape area and elevation (Zmax)
– area information can be obtained using the Measure tool
Feature to Raster
– Convert the feature to a raster
Mosaic to New Raster
– Combine the raster you created with your terrain raster

Another option that I have used to alter/edit raster terrains is to create a table in excel of lat, long, and elevation data for the shape you want to add. You can then import the data into Arc as a .CSV file. Once in Arc you can manipulate the data further using the Spatial Adjustment toolbar (if you have the license for it). When your satisfied with the data, create a raster of it and combine it with your terrain raster as described above. Although I have not done it, I think there is way to do this directly in RAS by importing geometry data as a .CSV file, creating a terrain from the data and merging it with your model terrain raster.

I figured out how to do the methods above by trial and error (playing with Arc Tools) and by searching forums so there are probably several other ways to manipulate raster data in GIS. If you come up with any others, please post.

[Ski907]

Perhaps more involved, and not as quick as what you’re looking for, but we’ve had success using AutoCAD Civil3D to model site improvements using assemblies and feature lines, then those 3D surfaces are exported to a DEM and merged over the base terrain in RAS. A major benefit of this approach is that the hydraulic model uses the exact same geometry that is on our design drawings.

I’m curious to try AJ’s recommendations using GIS tools in ArcMap, which may be faster for quick preliminary work, or situations where design drawings aren’t being produced.

[Lonnie A]

I use a GIS addin tool from Aris that lets you edit raster cell elevations either one by one or as a group. Usually I can edit the tif made by mapper but sometimes RAS doesn’t acknowledge the edits even though I can see them in the terrain. When that happens I recreate the terrain from the edited surface. Works particularly well when you need to lower cells near culverts.

Here is a link to the tool. I’m not affiliated with them but it’s the simplest tool I’ve found. Interested to hear what others are using.
http://www.aris.nl/index.php?option=com_content&view=article&id=210:aris-grid-editor-for-arcmap&catid=64:arcgis-tools&Itemid=161&lang=en

[Chad Ballard]

I have been using ArcGIS and creating a new raster similar to AJ but it takes some work to get it to reflect what is to be modeled. ARIS looks promising and more control cell by cell.

[Tung]

@AJ and everyone

I know this one a little bit old but what if you have the new design in a Microstation DGN file? What is your go-to method to quickly get it into HEC-RAS?

Thanks!

[Author]

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