When building an EFDC model, we need a bottom elevation (or bathymetric data file) assigned to the model grid. However, we just have cross-section files in the model domain. So, how do we create a bottom elevation file for the model grid by using this cross-section?

This page will provide steps to do this.

Grid+ allows us to create a data point file from grid cells that already have the grid's elevation. As a model setting step, we use that file to assign the initial condition to the model grid cells.

The grid used for generating the bottom elevation file does not have to be the same as your model grid. The density of points in the bottom elevation file will be based on the grid's resolution.


  1. Load the cross-sections file, and after that, generate a grid to cover the cross-section, as shown in Generate Grid's Elevation from Cross-section#Figure 1. To show the color ramp of the cross-section, press Alt+C, then set Min. and Max. values.
  2. Draw a polyline to cover grid cells with cross-section by selecting Add a new polyline button from the toolbar, as shown in Generate Grid's Elevation from Cross-section#Figure 2.
  3. Press the S key from the keyboard (selection mode), select the overlay layer in Layer Control panel, then click on the polyline, then it will be highlighted, as shown in Generate Grid's Elevation from Cross-section#Figure 3. Right-mouse click and select Interpolate Grid Elevations as shown in Generate Grid's Elevation from Cross-section#Figure 3.
  4. Next, select the grid layer in the control panel, Right-mouse click on that layer, then select Show Properties/Bottom Elevation, as shown in Generate Grid's Elevation from Cross-section#Figure 4.
  5. Apply step 3 for grid cells in other cross-sections. We will have cells in two heads of the grid, which have elevation as shown in Generate Grid's Elevation from Cross-section#Figure 5.
  6. Select entire of the grid by selecting the grid block option, then select Interpolation Elevation in I-Direction as shown in Generate Grid's Elevation from Cross-section#Figure 6. Generate Grid's Elevation from Cross-section#Figure 7 shows the entire grid' elevation color ramp after interpolation.
  7. Select the Grid layer and Right-mouse click, then choose Create Scatter Data from Elevation as shown in Generate Grid's Elevation from Cross-section#Figure 8. As a result, a new layer, "XYZ from Grid" will be created in the layer control. We can turn off the grid layer and see the data points as shown in Generate Grid's Elevation from Cross-section#Figure 9
  8. Now we can export the grid's elevation to a data point by selecting "XYZ from Grid" layer and right-mouse click to select Export Data Points as shown in Generate Grid's Elevation from Cross-section#Figure 10. As a default setting, Grid+ will export to a data file with three columns: the first column is longitude, the second column is latitude, and the last column is elevation value. Note that the unit of the elevation value is the same as the unit of the values in the cross-sections. In case we want to export to a data file in the UTM zone coordinates, we can use the feature Convert in Grid+ before exporting.


Figure 1. Load cross-sections with a generated grid.


Figure 2. Draw polyline to select grid cells with cross-section.



Figure 3. Select the interpolate grid elevation option.


Figure 4. A Show bottom elevation of cells.


Figure 5. Bottom elevation of grid cells overlay cross-sections.


Figure 6. Modify Selection form.


Figure 7. Grid's elevation after interpolating in I-direction.


Figure 8. Grid's elevation after interpolating in I-direction.


Figure 9. Grid's elevation data points.


Figure 10. Export Grid's elevation to data file.