Triangular edge cells in EEMS

A curvilinear orthogonal grid, like that used in EFDC, can effectively represent complex river systems and coastlines. However, sometimes a user would prefer to display the grid domain near the shoreline using triangular rather than quadrilateral cells. EEMS has a feature that allows users to better represent the edges of the model domain using triangular cells. Although this does not change cells internal to the domain, it makes the grid edges look more realistic, as described below.

Many users are unaware of the ability to display cells as triangles in EEMS rather than quadrilateral shapes. EE can represent the grid domain near the shoreline using triangular cells on the staggered boundary of the model grid for an individual cell, several cells, or the entire model grid edge cells. These triangular edge cells have half the volume of the quadrilateral cells. This process blocks the flow from the edge. It should be noted that this feature does not apply to any cells other than edge cells. A typical model grid, in this case, a model of Lake Washington, is shown in Figure 1 below.

To change individual edge cells to a triangular shape, set the Model Grid to the editing mode by clicking on the pen icon. Then RMC on a corner cell and select Change to Triangular Cells. To revert to quadrilateral cells, RMC on the selected cell and select the option Change to Quadrangular Cells. The result is shown in Figure 2 below.

EE also allows you to modify multiple corner cells at the same time. After activating the editing mode of the Grid Layer, you can select cells to be changed by holding the Shift key. Then RMC and apply the feature of Change to Triangular Cells.

To use this feature for all the staggered edge cells of the domain, simply press Alt + T from the keyboard to apply the triangularization. A message form of Triangular cells on the border will pop up, as shown in Figure 3. Select Yes to convert all corner cells to triangular cells.

See our Knowledge Base for more details on these operations. To try this yourself without buying EEMS, activate EEMS in demo mode. Demo mode activation instructions can be found here. The Lake Washington model can be downloaded here and is able to be run and edited EEMS in the demo mode.