1.   Purpose and objectives

     The program PEAKFQ performs flood-frequency analysis of annual peak flows using Guidelines For Determining Flood Flow Frequency developed by the Interagency Advisory Committee on Water Data (IACWD, 1982). 

2.   Description

     Flood-frequency analysis using IACWD Bulletin 17B guidelines includes the calculation of a Pearson Type III frequency curve based on the mean, standard deviation, and skew of the logarithms of the instantaneous annual peak flows. The computer program PEAKFQ detects and adjusts for low 
outliers as well as adjusting for zero peak flows and peak flows which do not reach the bottom of the gauge base. If certain peak flows are known to be the highest in an extended (historical) period of time, then the program will make a historical adjustment to the mean, standard deviation, and skew. The station skew is weighted with a regional estimate of skew (if available) to get the final skew used in the frequency analysis.

3.   Input

     The program utilizes annual peak flow records in a card-image format, Watershed Data Management (WDM) format, or data input via the keyboard. Information on the source of the input data, plotting options, historical data and other program-control data are input through a menu-driven user 
interface.

4.   Output

     a. The mean, standard deviation and skew for the systematic record and the final Bulletin 17B          frequency curves. 

     b. A listing of peak flows for selected annual exceedance probabilities ranging from 0.995 to 0.002          both with and without the expected-probability adjustment. Also the 5 and 95 per cent one-sided          confidence limits are provided for each selected exceedance probability flow.

     c. A ranked listing of annual peak flows and their probability plotting positions.

     d. A plot of several flood-frequency curves including the observed, the historically-adjusted, and the          final Bulletin 17B flood-frequency curves.

5.   Operational requirements and restrictions 

     The program PEAKFQ is written in Fortran and has been used on personal computers, workstations, minicomputers and mainframe computers. The Graphical Kernel System (GKS) is used for plotting the frequency curves. A GKS library is required to recompile the program on a DOS-based computer and the library is needed to simply run the program on a Unix workstation. DOS-based computers should have a math coprocessor and 4 megabytes of memory. 

6.   Form of presentation

     Program is distributed on a 3 1/2" floppy diskette or via the Internet. The users manual, written in English, briefly describes the Bulletin 17B analysis technique and provides guidance on the use of the 
program (Kirby and others, 1994). 

7.   Operational experience

     There have been hundreds of applications of the program throughout the United States.

8.   Originator and technical support

     U.S. Geological Survey, Office of Surface Water, Reston, Virginia,  USA. 

9.   Availability

     From the HOMS National Reference Centre for USA for 3 1/2" floppy or  printed documentation; or electronically on the Internet at: http://water.usgs.gov/software/peakfq.html or http://www.geogr.uni-jena.de/software/

10.  Conditions on use

     Program and documentation are available free of charge.

References:

Interagency Advisory Committee on Water Data, 1982, Guidelines for determining flood flow frequency: Bulletin 17B of the Hydrology Subcommittee, Office of Water Data Coordination, U.S. Geological 
Survey, Reston, Virginia, 183 p.

Kirby, W.H., Lumb, A.M., Flynn, K.M., and Thomas, W.O., Jr., 1994, Users manual for program PEAKFQ, Annual Flood Frequency Analysis Using Bulletin 17B Guidelines: U.S. Geological Survey Water-Resources Investigations Report.