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Parameter Sensitivity in Hydrologic Modeling - page 70 / 163

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Using the rough boundary and stream network defined in the conceptual model, WMS can create a triangulated irregular network (TIN) using the adaptive tessellation algorithm. The adaptive tessellation algorithm generates a mesh of triangular elements. The mesh lies within the model domain, and honors the conceptual model set up of point elevations and channel and watershed boundaries. The boundary defines the TIN extents, and the stream and ridge arcs are forced into the TIN as breaklines to ensure that the triangle edges will be enforced along all streams and ridges. A stream is created from the triangle edges. Following the development of the TIN based on background contour information, a DEM may be used as a background elevation source (Nelson et al., 1999b).

After the TIN has been created, the final step before the TIN can be delineated is to condition the TIN. Conditioning is necessary because there are usually flat triangles and pits in the TIN. WMS comes with tools to condition the

TIN. These elevations, and

tools include elevation smoothing, edge swapping, adding or deleting vertices (Nelson et al., 1999b).

adjusting

3.5.2

TIN Parameter Extraction

Once the basins have been defined, geometric attributes such as stream lengths, stream slopes, basin areas, basin slopes, and maximum drainage distance within a basin, are automatically computed from the TIN model. These attributes may be combined with runoff curve numbers to generate a runoff model.

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