WMS:Texas Department of Transportation

WMS Modeling Tips for Texas Department of Transportation

Coordinate Systems

The state of Texas is divided into several State Plane zones. Within each zone, there is an additional surface adjustment factor for each county within the zone. The surface adjustment factors for each county are shown in this pdf file

NSS

The TXDOT Regression Equation for watersheds in rural areas is listed in the NSS program as "Peak Rural Statewide 2009 5087". The equation requires the following parameters:

1. Drainage Area: Computed by WMS
2. Main Channel Slope: Computed by WMS. The parameter computed by WMS that corresponds to the Main Channel Slope required by the regression equation is called "Maximum Flow Slope (MFS)"
3. Mean Annual Precipitation: Derived from a map located at the TNRIS website. It is also possible to download the shapefiles directly from here. The shapefiles were developed from a PRISM rainfall grid of mean annual rainfall in the United States. Read the mean annual rainfall shapefile for the period of interest and use the mean annual rainfall value for the watershed area.
4. OmegaEM residual from 2009 5087: Derived from a map located in this report. A link to the report is also contained on the USGS Documentation Site for NSS. The map in this report has been saved as an image file and georeferenced so it can be opened directly in WMS. A link to the map is located here (OmegaEM.zip).
   • NOTE: The zip archives contain an image file (.png) and a world file and can be opened in WMS using File | Open and opening the PNG file

TR-55

The TR-55 method uses a Curve Number to determine watershed losses. A sample curve number table for use with WMS is located at the Compute GIS Curve Number page in the "NRCS Curve Numbers (CN)" section. The sample curve number table for vector land use data can also be downloaded here. The sample curve number table for gridded 2006 NLCD land use data can be downloaded here.

Exporting Data to Microstation

1. Finish building the watershed.
2. Turn on the display of any coverages, DEM contours, etc. to export to Microstation. If desired, trim the DEM to the watershed boundary.
3. In the map module, select File | Save As....
4. Select "*.dwg" from the Save as type drop-down box.
5. Enter a file name and save the file as a DWG file. Remember the location of the file.
6. Go to the location of the file in Windows Explorer and double-click on the file to open the file in Microstation.

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