When the user selects Run Catchment Delineation from the Terrain Modeling Manager, the button for Catchment Delineation will be placed in the depressed position. At this time, whenever a catch basin is added or moved within the Digital Terrain Model (DTM) the catchment is identified.

The catchment delineation tool works by first performing an upstream trace from a point at the center of the catch basin until the trace reaches a high point. Additional traces are then performed until sufficient traces are available to complete a catchment boundary.

When the user picks Run Catchment Delineation a second time, the catchment delineation tool stops running and the button is no longer in the depressed position.

The catchment delineation tool cannot identify portions of the catchment that lie outside of the DTM. The boundaries of this portion of the catchment is must be identified with some other approach as it is considered a separate catchment. The outflow from this external catchment can be assigned to the same catch basin as that within the DTM. The catch basin can have two catchments associated with it-one from within the DTM and one from outside the DTM.

The catchment delineation tool is intended to be used with final DTM's of the area to be served. These DTM's should be sufficiently precise that features such as gutters and swales can be detected by the tool. Gutter elements in the hydraulic model are not be used in catchment delineation.

There are several parameters that can be adjusted to improve the performance of the automated catchment delineation. These are described in the Catchment Delineation Settings topic.