WMS:DEM to Stream Arcs

The DEM->Stream Arcs command is used to create feature arcs from DEM points whose flow accumulation areas are above a defined threshold. An arc vertex is created for each DEM point that has a flow accumulation value greater than the threshold entered. Consecutive stream DEM points are then joined together as arcs with nodes created at junction points where the stream splits.

Outlet points should be created where the watershed outlet of your study area is. These outlet points could be at any DEM point, but should be in a DEM point that has a high enough flow accumulation to pass the threshold (WMS will snap outlet points to the closest threshold cell when you create them in the Drainage module). The Flow Accumulations display option can be very useful for identifying these points and for determining what an appropriate threshold area is.

The DEM Streams->Feature Arcs command can also be very useful for defining stream arcs which are later used for creating a TIN surface.

The resulting stream arcs will be jagged because they are created by inserting a vertex at the center of each DEM cell that make up the stream. In order to make the stream arcs appear smoother and more visually appealing you can redistribute vertices along a cubic spline. If you are using a 30 meter resolution DEM, the average length between vertices will be approximately 30 meters and it is suggested that you redistribute to about 100 meters spacing (be sure to turn on the cubic spline option). In general, redistributing to about 3 times the DEM resolution will produce good results.

Related Topics

• Flow Directions and Accumulations
• TOPAZ
• Creating TINs from Feature Objects