1.   Purpose and objectives

     The program computes annual peak discharge frequency curves that can be used to analyse flood damage potential.

2.   Description

     Computational procedures are based on the "Guidelines for Determining Flood Flow Frequency", Bulletin 17B, United States Water Resources Council, June 1982. Frequency curves are computed for Weibull, median, or Hazen plotting positions and using the log-Pearson Type III distribution. 
Generalized skew coefficients can be provided as input. Broken record, incomplete record, zero flood years, high outliers, low outliers and historic events can be taken into account in the calculation of frequency curves. Confidence limits and the expected probability adjustment can also be determined.

3.   Input

     Card image input. Annual peak discharges are the only required data. The following data are optional: historic annual peak discharges, the number of high outliers, the corresponding historic period, and the generalised skew coefficient.

4.   Output

     Tabular results are provided for the annual peak discharges which correspond to both the plotting positions and to selected exceedance frequency ordinates calculated using the log-Pearson Type III distribution. The calculated mean, standard deviation, skew coefficient, and number of events used in the analysis are printed. A printer plot of the frequency curve can also be generated.

5.   Operational requirements and restrictions

     a. Persons with knowledge and experienced in frequency analysis and a 
         basic understanding of computers can run the program.
     b. One week of training is required.
     c. The program was originally written for a CDC 7600 computer in 
         FORTRAN IV. It is now available for PC and UNIX systems.
     d. The annual peak discharge arrays can be reduced.

6.   Form of presentation

     Diskettes or download from www.hec.usace.army.mil. Support documentation consists of a Users' Manual and an addendum. Instructional videotapes are also available.

7.   Operational experience

     Extensive, worldwide.

8.   Originator and technical support

     The program is a modification of the computer program FREQFLO written by Leo R. Beard and David Ford (Center of Research in Water Resources, The University of Texas at Austin) under contract to the Water Resources Council (WRC). 
     Technical support from the Hydrologic Engineering Center, HEC, U.S. Army Corps of Engineers.

9.   Availability

     Download directly from www.hec.usace.army.mil or request from the HOMS National Reference Centre for USA. 

10.  Conditions on use

     Internet download is free. A standard handling fee is charged for supplying the diskettes and documentation.