WMS:NSS

WMS includes an interface to the National Streamflow Statistics Program (NSS). The NSS program is a compilation of all the current statewide and metropolitan area regression equations. The NSS interface in WMS version 8.1 and later uses the same database as the Windows version of the NSS program (released in 2006) which supersedes all previous versions of the NFF program such as the windows version of NFF (released in 2003) and the 1993 derivative used in previous versions of WMS.

Users may need to install the latest version of the NSS program from the following web site to get the program to work:

http://water.usgs.gov/software/NSS/

The regression equations are a result of years of effort by the United States Geological Survey (USGS) to develop regional regression equations for estimating flood magnitude and frequency of ungaged watersheds. The USGS, in cooperation with the Federal Highway Administration and the Federal Emergency Management Agency compiled all the regression equations into a single database file. This database file is the basis of the NFF program, which can be used to guide the user through the input required to compute peak flows for different frequencies using the database of state by state regression equations.

The NSS interface in WMS provides a windows based, graphical user interface to the same database of regression equations. The entire program is run from a single dialog. Further, if a digital terrain model is available for the study area, all of the geometric parameters required for the regression equations are automatically supplied as the individual equations are specified. These parameters include area, slope, elevation, distances, and others. The GIS overlay command can be used to compute other variables such as forest cover, lake cover, etc.

The NSS equations are useful for estimating a peak flood discharge and typical flood hydrograph for a given recurrence interval of an unregulated rural or urban watershed. These techniques should be useful to engineers and hydrologists for planning and design purposes.

WMS uses the DLL's that are part of the USGS Windows based version of the NSS program. The USGS program does not include any kind of GIS component, but if wanting to run the NSS outside of WMS a user can still use WMS to determine the necessary input. Complete documentation on the USGS NSS program, including specific information for each state can be found on line at the following USGS website:

http://water.usgs.gov/software/NSS/

The descriptions for each state are found at the bottom of the above web page.

Saving and Restoring a Simulation

The Save Simulation command in the NSS menu can be used to save topologic tree structures with any state, regions and parameters which have been defined. The Read Simulation command will restore the tree and parameters so that the user may continue with a particular model at a later time.

Model Troubleshooting

If unable to get NSS to run from within WMS, try one of the following:

1. The user may not have write access to the C:\Program Files directory on the computer. To bypass this, perform the following steps:
   1. Navigate to the C:\Program Files\WMS82 directory
   2. Copy the "wmsnss.exe" file and the "NSSv4.mdb" file from this directory and place them in a directory to which the user has write access, such as My Documents
   3. Launch WMS and Select Edit | Preferences
   4. Scroll down to the NSS heading and click the Browse... button.
   5. Navigate to the wmsnss.exe file in the directory to which you have write privileges and click Open
      

    You should now be able to run NSS.

Related Topics

• NSS Region Coverage
• Defining an NSS Simulation