WMS:Computing Flow Data with TOPAZ

This command will save the current DEM elevations to a TOPAZ formatted input file along with a TOPAZ control file and then start the TOPAZ program. When TOPAZ is finished WMS will automatically read the flow directions (FLOVEC.DAT) and flow accumulations (UPAREA.DAT) computed by TOPAZ.

Because WMS is communicating with TOPAZ through disk files you must specify the directory where WMS/TOPAZ perform this interaction. If your specified directory has an unusually long name TOPAZ may have some difficulties. In such cases you will want to specify a directory with a shorter character string length.

TOPAZ assumes that all depressions are a function of a lack of resolution in the DEM data and therefore it is not possible to delineate the watershed of a closed basin unless you identify the DEM cell of a natural depression to be a Depression Point from the DEM Point Attributes.

TOPAZ also creates a file named RELIEF.DAT that has the elevations of the depressionless or filled DEM. TOPAZ (and most grid-based delineation algorithms) assumes that any depression in the DEM is a result of inadequate resolution and not a natural depression. This is true for most depressions, but means that basins for natural depressions cannot be determined. However, with WMS you can define a low point in a natural depression as such and then WMS will flag it so that TOPAZ does not fill the depression and the drainage computed. This is done using the DEM Point Attributes dialog prior to running TOPAZ.

Related Topics:

• DEM Point Attributes
• TOPAZ
• Flow Directions/Accumulations
• Watershed Delineation with DEMs