Drainage Network

This function is used to show the dominant water routes over a grid surface. A water route is considered to be dominant if at least a user defined set number (threshold) of upstream grid cells flow into it.

The drainage network calculation uses a DTM grid, so before running this function a DTM grid has to be created using the DTM Grid Volumes function. It needs to be of type Single Surface and not a Ground / Design type grid file.

If no grid has been generated the following error will appear:


Terrain Menu › Drainage › Drainage Network

Two different versions are possible depending on whether 'Subsequent catchment areas' is checked or not.

 


Threshold value This is the number of upstream cells that you consider sufficient to be considered a dominant water route. It is a site-specific value. A trial-and-error approach will quickly lead to the value giving the best result. Too low a value will give too many dominant routes, while too great a value will not give all the dominant routes.
Water course pen Choose the colour used for drawing the water route from the indicated point.
Water course cad output Check if you want the route drawn as a cad polyline and choose which layer it will be drawn on.
Shade grid with flow directions Check this option to have each cell (grid point) temporarily drawn in a colour reflecting the 8-point compass direction flow direction.
Subsequent catchment areas Check this option to manually indicate outlet points subsequent to the function first determining the dominant flow routes.
Catchment area pen Visible only if 'Subsequent catchment areas' is checked. Choose the colour used for drawing the area that will contribute to the same catchment area as the the indicated point.
Catchment area cad output Visible only if 'Subsequent catchment areas' is checked. Check if you want the catchment area drawn to a cad layer, and choose which layer it will be drawn to.


Press OK to accept any changes or Cancel to close the dialog losing the changes and ending the function.

The dominant water routes are plotted. This works by considering each cell that has more than the threshold number of upstream cells flowing into it as dominant. Then the direction from this cell to the next adjacent cell is plotted. If the threshold value is set too small, the results will be as shown below.


Increasing the threshold value, and switching off Shade grid with flow directions makes it easier to see the water routes.




If you chose Subsequent catchment areas, the program will prompt: Click at outlet point (Esc to quit)


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