Terrain Manipulation in HEC-RAS

In Workshop #1 of our HEC-RAS 5.0 course, we import terrain from the free ELVIS database hosted by Geoscience Australia. For those who haven’t taken the course, feel free to download Workshop #1 as a pdf file and follow along with the instructions.

At the end of Workshop #1, we should have terrain data loaded into RAS Mapper. Once we’re at that point, we can adjust the terrain to include any number of features and then compare the results with and without the feature in place. These features can include:

  • Levees
  • Roadways
  • Building pads
  • Channels/drains
  • Detention basins
  • Dredging

Are there any other features you’ve added to previous models or would like to add to future models? Let me know and I’ll add some examples. Basically, anything you can draw in a series of cross sections – so long as it doesn’t cross over on itself (sorry, no caverns!) – can be added to your terrain. In our HEC-RAS course, I let participants choose what I should put into the terrain in the demonstration model. One time I was asked if I could make levees in the shape of a client’s logo. Luckily it was a fairly simple shape, so we embedded a 10-kilometre diameter logo into the Bonneville Salt Flats and ran a flood over it. The possibilities are endless!

To see how to modify terrain data with cross sections, see the posts titled “Terrain Lifting” (for building a raised surface such as a roadway, bund, levee, or building pad) or “Bathymetry” (for excavating a drain or removing a water surface of a channel or reservoir to account for bathymetry) on the HEC-RAS Blog. The functionality in HEC-RAS is a bit limited, particularly in terms of projecting cut or fill templates to daylight, but you can still do some pretty cool things with it.

In addition to the techniques described in the blog post, the Channel Improvement tool – which has been part of previous versions of HEC-RAS for quite some time – can now be used in whole new ways when combined with RAS Mapper. The Channel Improvement tool automates the process similar to what can be done with templates/assemblies InRoads, Civil3D, 12D, or other civil design software. Sure it’s a bit less versatile than the other packages, but after all, it’s free!

In our courses, I let everyone choose their own location for workshop exercises. We try to use real projects where possible, but if there is time, we also go online and find free DEM data anywhere on the planet and try to out-engineer each other. We’ve done some pretty interesting (and very much hare-brained) projects in class – for example:

  • Slice New Zealand’s North Island in two and generate tidal power with the out-of-phase tides across the canal – follow along with this exercise here.
  • Take the subsurface bathymetry of Sydney harbour, drop the sea level, put a dam across the inlet, fill in the harbour, and let the dam fail.
  • Dig a Grand Canyon Bypass that connects Lake Powell to Lake Mead with a straight L.A. River-style trapezoidal monstrosity (that unfortunately also wipes out some of my favourite National Parks!).
  • Construct a Dutch-style seawall across the Strait of Gibraltar, turn the Mediterranean Sea into a reservoir, and control its elevation with gates.
  • Create a Niagara Falls Bypass that connects Lake Huron’s Bay to Lake Ontario, bypassing Lake Erie completely (and unfortunately displacing a few thousand homes in the process).
  • Put the 600-metre high ice dam back on the Clark Fork and recreate the Missoula floods through the Columbia Gorge;
  • Rebuild the Red Rock Pass spillway to re-create Lake Bonneville and then drain it back to the Great Salt Lake by excavating another outlet to the Ocean;
  • Construct the fabled Northwest Passage by connecting the Missouri River with the Columbia;
  • Put a canal across the Swiss Alps or the Himalayas
  • Make reservoirs out of craters on the moon, or even put a dam across palaeochannels on Mars!

You may need to use upwards of 1 km grids for some of the larger examples I’ve listed, but you can scale projects up or down to suit your needs. If you’ve got to practice with something, you might as well think big! Why learn the ropes with a boring old bund or drain? It doesn’t take any extra time to use real locations for your example projects now that Google can hook you up with free DEM data anywhere in the solar system, so go crazy with it!


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