This command draws 3D polylines starting at user picked points downhill until they reach a local minimum or the end of the grid or TIN. In effect it simulates the path of a rain drop. The surface is modeled by a grid file as created by Make 3D Grid File or a triangulation file created by Triangulate & Contour. The program also reports the horizontal and slope distances, average slope, maximum slope, and vertical drop. These values can be used for time of concentration calculations. Runoff tracking is a convenient way to identify distinct watershed areas and is an alternative to the automated Watershed Analysis command.
Enter the run off path layer <RUNOFF>: press
Enter
Select Surface Model
dialog box
Choose the grid file or triangulation file that models the surface.
If a grid is selected, it will prompt:
Extrapolate grid to full grid size (Yes/<No>)?
Yes If the limits of the surface data doesn't cover the
entire grid area, then the values for the grid cells beyond the
data limit must be extrapolated in order to compute slopes in that
area. This prompt only appears if there are grid cells without
values.
Local pond spillover depth <4.80>: press
Enter This allows the runoff line to continue past flat or low
points in the grid or TIN, by allowing these area to fill up with
water, in essence, up to the specified depth, thus letting the
runoff polyline continue on.
Draw tracking for all grid cells or pick individuals
[All/<Pick>]: press Enter Pressing Enter
leads to individual picking of runoff tracking lines, while A for
All would fill draw runoff polylines starting from each grid cell
or each triangulation triangle.
Pick origin of rain drop: pick a point at the top of the
run off polyline
Pick origin of rain drop (Enter to end): press
Enter
Pulldown Menu Location: Watershed
Keyboard Command: runoff
Prerequisite: A .grd file created by Make 3D Grid File or a
.flt (TIN) file created by Triangulate & Contour.