Delineate the centerline of the structure or feature you wish to incorporate.Expand Rivers and start editing (right-click on Rivers, select 'Edit Geometry').Create a new geometry in RAS Mapper (right-click on Geometry, select :Add New Geometry').Here are the basic steps for modifying terrain in HEC-RAS, with RAS Mapper steps shown in red and Geometry Editor/Plan steps shown in blue: This can be done outside of HEC-RAS using GIS or 3D civil design software, or we can do it directly in HEC-RAS by exporting a geotif using a 1D geometry. Because LiDAR data typically misses the actual invert elevation at a culvert inlet or outlet location (due to debris, vegetation, sedimentation, or inadequate resolution), and because HEC-RAS cannot accommodate the negative depths that would result from a below-ground culvert invert in a 2D Flow Area, the terrain around the inlet and outlet must typically be lowered before the plan will run. A dam or levee in a 2D model, for example, cannot be breached unless the erodible or temporary portion of the terrain has first been removed.Īnother common use of the terrain modification process is to lower the digital elevation model around a culvert. This allows the feature to be modeled as a 1D element within a 2D flow area. Rather than creating features, one of the most common uses of terrain modification is to remove features (such as a dam, levee, roadway, or bridge deck) from the terrain associated with a 2D model. The tool may have initially been intended for the interpolation of bathymetric cross sections, but as long as your feature can be represented with cross-sectional data, the answer is yes! This dam, for example, was constructed using a 1D HEC-RAS geometry, which was then exported as a geotif: Can you use the terrain modification process, for example, to construct the following? We do still get a lot of questions about how to apply the technique to incorporate various structures, especially concerning the application of new features available in RAS Mapper. Interchangeably referred to as terrain interpolation, terrain lifting, terrain modification, or terrain manipulation, it is simply an export option in RAS Mapper that can be applied using any 1D geometry in your model.

These have been some of the most popular posts to date, each having generated almost 10,000 views over the years! Two previous blog posts have addressed terrain modification in HEC-RAS (the December 2014 article entitled Including Channel Bathymetry into your Terrain and the June 2015 article entitled Lifting Terrain in HEC-RAS 5.0). Written by Krey Price | Surface Water SolutionsĬopyright © The RAS Solution 2018.

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