HEC-RAS Flood Result Raster Grids

While GeoHECRAS constructs a flood map representing the area of inundation, it can simultaneously generate an elevation raster grid (or elevation grid) file representing the water surface elevation for the mapped area. This raster grid file allows the flood map to be utilized in other software programs, such as ESRI ArcMap and ArcGIS. Each grid cell within the elevation raster contains a single value representing the computed water surface elevation. Areas that are not flooding are marked as “NODATA” in their grid cells.

HEC-RAS Flood Map Types

In addition to creating a flood map elevation raster grid, the software can generate raster grid files for any of the available flood maps that GeoHECRAS can produce, including:

  • Maximum Water Surface Elevation
  • Maximum Water Depth
  • Maximum Velocity
  • Shear Stress
  • Arrival Time
  • Flood Duration
  • And, many other flood map types

It is a simple process to have the software generate a corresponding raster grid file while generating a flood map. The following section details how this is done.

Creating a Water Surface Elevation Raster Grid

This section describes the process used to generate a water surface elevation raster while generating the flood map. However, this same process can be used to generate raster grids for other flood results, such as maximum velocity flood maps.

For the flood map and corresponding water surface elevation raster grid to be generated, the HEC-RAS model analysis results must be available. If not, first perform a HEC-RAS flow analysis for the defined model.

Follow these steps to create the water surface elevation raster grid:

  1. From the Results ribbon menu, click the Flood Map menu item.
    Flood Map menu item
  1. The Flood Map dialog box will be displayed.
    Flood Map dialog box
  1. From the General Specifications section, click on the Flood map type dropdown combo box, and then select the Water Surface Elevation option.
    Selecting Water Surface Elevation option
  1. From the General Specifications section, click on the Flood map computation dropdown combo box, and then select either the Detailed Intersection or Time Series Animation option.
  1. Click the [Options…] button adjacent to the Flood map computation dropdown box. This will display the Flood Map Computation Options dialog box.
    Flood Map Computation Options dialog box
  1. From the Additional Map Layers section, turn on the Create maximum water surface elevation grid checkbox. Enabling this checkbox will cause the software to create an additional layer in the Map Data Layers panel containing a water surface elevation grid corresponding to the flood results.
    Create Maximum Water Surface Elevation Grid
  1. Click the [OK] button.

The software will then generate a water surface elevation grid that corresponds to the flood results from HEC-RAS.

Displaying the Water Surface Elevation Raster Grid

Once the elevation raster grid has been created, it will be automatically added to the Map Data Layers panel. If desired, the user can change the way the computed water surface elevation raster grid is displayed on the Map View.

  1. From the Map Data Layers panel, click on the […] Properties button adjacent to the raster grid layer.
    Elevation Grid Properties
  1. The Elevation Grid Properties dialog box will be displayed.
    Elevation Grid Properties dialog box
  1. Turn on the Elevation Color Fill checkbox to enable it.
  2. Select the desired elevation color fill option.
    Elevation Color Fill Option
  1. Then, click the [OK] button.

If the elevation raster is not displayed, turn off the display of other raster layers or online map layers that lie above the elevation raster in the Map Data Layers panel. The order of the layers listed in the Map Data Layers panel determines the display order of each layer, and there might be another layer that overlays the elevation raster layer. Alternatively, drag the elevation raster above the other layers listed in the Map Data Layers panel so that the elevation raster can be seen on the Map View.

Displaying Water Surface Elevation Grid on Map

About the Author Chris Maeder

Chris Maeder

Chris is an experienced civil engineering and software technology leader, with over 30 years industry experience. With proven expertise in global software development, he has built engineering teams that adapt quickly, focus on what’s important and, most importantly, deliver. He is a licensed professional civil engineer with extensive experience in water resource engineering. He has performed and supervised engineering projects in urban stormwater drainage, transportation and roadway drainage, storm sewer design, detention pond design, stormwater quality, green infrastructure, watershed management planning, wastewater sewers, water distribution networks, pump stations, FEMA flood studies, bridge and culvert design, bridge scour and armoring, dam failure analysis, seepage and groundwater modeling, and environmental permits.

Related Articles