How to Make an Unstructured Floodplain Mesh

Flooding can cause significant--and sometimes devastating--damage to infrastructure, crops, and commercial, residential, and industrial buildings. Unstructured floodplain meshes can be used to anticipate the most likely scenarios and plan prevention and mitigation accordingly. These are only some of the reasons why an unstructured floodplain mesh might need to be created. Your project may include multiple low lying areas that historically flood. You may need to see where berms or channels need to be adjusted to better accommodate sudden flow increases and prevent or mitigate flooding.

There are a few steps that should be taken anytime you model and simulate an unstructured floodplain mesh. SMS simplifies this process.

1. Import Background Data

The first step is usually to import elevation data from a scatterpoint dataset, raster objects, lidar data, mesh, grid, or from an existing project that includes the required elevation information for the floodplain. If the elevation data is not from a scatter set, it will need to be converted to a scatter set or interpolated to the mesh after the mesh is generated.

An aerial photo of the area can also be imported to help with visually referencing rivers, roads, and other structures.

2. Create a Mesh Generator Coverage

Once the elevation data has been imported, create a mesh generator coverage by right-clicking in the Project Explorer and selecting the New Coverage command. From the New Coverage dialog, select the Mesh Coverage type and enter a name for the coverage.

3. Create Feature Objects

The unstructured floodplain mesh will be generated from polygons in the mesh generator coverage. On the mesh generator coverage, create the enclosed arcs encompassing the area of the floodplain using the Create Feature Arc tool. Turn the enclosed arcs into a polygons by using the Build Polygons command.

4. Assign Mesh Type and Bathymetry

Use the Select Feature Polygon tool to double-click on each of your polygons. In the dialog that appears, assign the mesh type you want to create. You can use the Preview Mesh button to ensure your mesh will generate correctly.

After selecting the mesh type, select constant value or scatter set to use as the mesh elevation.

Once this is done for all your polygons, you are ready to generate your unstructured floodplain mesh.

5. Generate the Unstructured Floodplain Mesh

The process of generating your mesh is quite simple if the above processes are followed. Simply right-click on the mesh generator coverage and select the Convert to 2D Mesh command. SMS will start the calculations to create the mesh. Older versions of the software will bring up an options dialog where a few changes can be made to how the mesh is generated. For most projects, the default options are acceptable. A dialog will then appear asking you to name your mesh—the final step in creating the mesh.

Now you have an unstructured floodplain mesh. Explore the mesh to see if you like the results and get started on the rest of your project. You can adjust the display options at this point to make sure your mesh is satisfactory.