INVESTIGATIONS--State Flood-Frequency Studies

In Reply Refer To:                               September 2, 1988
WGS-Mail Stop 415


Subject:  INVESTIGATIONS--State Flood-Frequency Studies

As of l987, all Water Resources Division (WRD) Districts have
completed one or more statewide flood-frequency studies using
multiple-regression methods.  Recently it was decided to make
available, in a single format, the results of about two decades
of U.S. Geological Survey (USGS) project work in flood-frequency

The Office of Surface Water (OSW) has developed a microcomputer
program for estimating flood magnitude and frequency at any un-
gaged location in the United States.  This estimation technique is
based on the statewide flood-frequency reports completed by each
District.  The computer program is called National Flood Frequency
(NFF) and includes regression constants and coefficients for all
States and regions.

Reading from a STATE.DAT file, NFF prompts the user for informa-
tion to make either rural or urban flood-frequency computations.
The urban computations utilize the equations in USGS Water-Supply
Paper 2207.  A procedure for weighting computed and observed T-
year peaks is included and comparative flood-frequency plots are
made.  The program also computes a design hydrograph using a
stored dimensionless hydrograph (USGS Water-Supply Paper 2317) and
a basin lagtime relation.  Hydrographs may be plotted and saved.
Finally, the user may route a post-development (urbanized hydro-
graph) through detention storage using the Multiple Stage Routing
Model (MSRM) developed at Pennsylvania State University.

It is expected that the program, with its user manual, will be
widely used within and outside the USGS.  Because of probable wide
use, the STATE.DAT file of NFF needs to be thoroughly tested.
STATE.DAT was compiled using copies of selected pages from 50 or
more flood-frequency reports supplied by the Regional Surface
Water Specialists.

Please have an individual in your District who is familiar with
flood-frequency investigations retrieve the following files.


The files will be located in directory SWB on RVARES.

The following should be done no later than September 30, 1988.
Remember to delete "OSW" from each file name before using it.

1.  Read the DATA.DOC file and verify State/region equations.
Check units carefully and supply equivalent years if available.

2.  Run program on PR1ME to check for accuracy of computations.
Please offer suggestions or comments for improvement of NFF.  A
PC version is available which contains MSRM and improved plots.

3.  Refer to the attachment to determine if the most recent flood-
frequency report(s) is listed for your State.  If not, please
provide a copy to Will Thomas, Office of Surface Water.  All
tables, graphs, figures, and other information needed to apply
the regression equations should be on file with the OSW.

It should take about an hour to perform the checks listed above.
Please provide an EDOC message to MEJENNINGS indicating that the
checks were performed and providing information on any changes
that need to be made.

                                       Ernest F. Hubbard, Jr.
                                       Acting Chief, Office of Surface


WRD Distribution:  B, FO