Use watersheds to analyze how water flows along and off of a surface.
Surface TIN lines are used to calculate the areas that water would flow along the surface. From these areas, the drain targets and watersheds are determined.
Different drain targets are calculated for watersheds. For example, some watersheds include a boundary point as a drain target, which is the point where the channel of water would drain off the surface. Other watersheds have depression areas that the water flows into, while some watersheds are defined as boundary segments where the drain target includes the boundary of a surface.
If AutoCAD Civil 3D determines that water from one surface triangle could flow into more than one watershed, then it splits the TIN triangle to make two triangles. This ensures that each watershed consists of complete triangles, and that the boundary of each watershed consists solely of TIN edges.
Types of Watersheds
Watershed types are based on the type of drain target the watershed has. A drain target is the location where the water flow either stops or leaves the surface. Water that flows along an area or across a surface triangle eventually flows off the surface, or it reaches a point from which there is no downhill direction.
For each drain target in a surface, AutoCAD Civil 3D determines the region of the surface that drains to that target. This region is called the watershed for that drain target.
Tutorial Exercise: Creating a Watershed and Water Drop Analysis