WMS:TOPAZ

The Topographic Parameterization Program (TOPAZ) was developed by the USDA-ARS (United States Department of Agriculture: Agricultural Research Service) National Agricultural Water Quality Laboratory under the direction of Dr. Jurgen Garbrecht. TOPAZ is a public domain program that is distributed free of charge to interested persons. A modified version of the program is distributed with WMS for the purpose of computing flow directions and flow accumulations for use in basin delineation with DEMs. However, TOPAZ is capable of further DEM elevation processing, including raster smoothing, basin and stream delineation and ordering, and development of other watershed parameters. If interested in obtaining the latest, complete version of TOPAZ, visit the USDA-ARS website (here]) and click on TOPAZ.

WMS is capable of writing an input file for the primary TOPAZ module DEDNM (Digital Elevation Drainage Network Model). DEDNM requires as input a file containing the elevations (must be named DEDNM.INP) and a control file named DNMCNT.INP. TOPAZ crashes if the file name is 60 characters or longer.

TOPAZ is included with all editions of WMS.

Computing Flow Data with TOPAZ

In the Hydrologic Modeling Wizard, the Compute TOPAZ 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, specify the directory where WMS/TOPAZ perform this interaction. If the specified directory has an unusually long name TOPAZ may have some difficulties. In such cases, 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 having identified 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, it is possible to 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.

Exporting a TOPAZ Input File

The Export TOPAZ File command (in the DEM menu for the Drainage module) is provided for those who wish to use TOPAZ for purposes outside of what WMS needs (the flow direction and accumulation files). This format should be close to the public domain version of TOPAZ, but may be slightly out of date.

Related Topics

• Flow Directions and Accumulations
• Defining Basins
• References