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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: |
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Terrain Menu › Drainage › Drainage Network
Two different versions are possible depending on
whether 'Subsequent catchment areas' is checked or
not.
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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. |
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Water course pen |
Choose the colour used for drawing the water route
from the indicated point. |
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Water course cad
output |
Check if you want the route drawn as a cad
polyline and choose which layer it will be drawn
on. |
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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. |
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Subsequent
catchment areas |
Check this option to manually indicate outlet
points subsequent to the function first
determining the dominant flow routes. |
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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. |
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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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Last Updated:
July 30, 2008
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