WMS:Watershed Delineation with TINs

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A TIN terrain model can be used in WMS to delineate stream networks and drainage basin boundaries. Since the terrain model is an accurate geometric description of the watershed, parameters such as areas, slopes, and flow distances can automatically be computed by WMS. This terrain model then serves as a map to guide entry of all data necessary to run HEC-1, TR-20, or other hydrologic analysis programs.

It should be emphasized that it is highly recommended to prepare the TIN for drainage analysis by using feature objects with a background elevation source. The elevation source could be TIN or DEM, but retriangulate using feature objects as guides in order to insure that stream edges are honored by triangle edges.

Detailed steps for delineating watersheds using TINs can be found on this page. The first process in performing drainage analysis is to edit the TIN where necessary. Flat triangles, flat channel edges, and flat ridge edges must all be eliminated before trying to delineate stream networks and basin boundaries. Automatic editing procedures, such as TIN filtering and removal of flat objects, should be used. In addition, manual insertion of breaklines, the addition of new points, and edge swapping can aid in removing anomalies which are introduced into the TIN as a byproduct of the triangulation process. With the TIN properly edited, stream networks and drainage basins can be defined as preparation for defining a complete hydrologic analysis.

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