1.   Purpose and objectives

     Design of hydraulic structures, optimal operation of reservoirs, and flood forecasting are just some of the areas in which knowledge of the statistical properties of extreme floods or droughts are required. HFA is a technical tool for fitting statistical distributions to series of annual floods, and for estimating flood flows with a given return period and the corresponding confidence intervals.

2.   Description

     HFA contains all the distributions belonging to the Gamma family.For each distribution several estimation methods are available:

Distribution                 Methods

Log-Gamma               Moments, maximum likelihood, moments applied to the logarithms of the                                  observations.

Gamma                     Moments, maximum likelihood.

Pearson Type 3          Moments with three different bias corrections for skewness, maximum                                  likelihood.

Log Pearson Type 3    As for Pearson type 3 plus direct and indirect methods of moments, sundry                                  averages method (SAM), mixed moments.

Generalised Gamma   Moments, maximum likelihood, sundry averages method (SAM), mixed                                  moments.

     HFA offers the possibility to compare graphically several fittings and the confidence intervals associated with the estimation of quantiles.

     To verify the basic assumptions of annual flood series analysis, several tests are available in HFA:

     * test of homogeneity (Mann-Whitney);
     * test of independence and stationarity (Wald-Wolfowitz);
     * presence of outliers (Grubbs-Beck).

     HFA was conceived for the analysis of annual maximum flood series, but the software can be used with any kind of data series that satisfy the basic assumptions of independence and stationarity.

3.   Input

     Annual flood series, or other data to be analysed.

4.   Output

     The results of frequency analyses are printed on the screen or on hard copy. Output includes:

     * results of tests;  
     * estimated parameter values;
     * fitted distribution (table of xT versus T and the confidence
       interval with given significance level);
     * graphics.

5.   Operational requirements and restrictions

     HFA must be used on an IBM (or 100% compatible) personal computer, with an EGA graphic card (or better), and a hard disk with a minimum of 1 megabyte free. It is designed for use with MS-DOS 3.x, or later.

6.   Form of presentation

     The HFA program is provided on 10 diskettes (5.25", 360K). The user guide is written in English and is also available on the installation diskette. The modules of HFA are written in FORTRAN.

7.   Operational experience

     HFA is used by universities, companies, and governmental organizations in Canada (particularly in Quebec) and elsewhere in the world.

8.   Originator and technical support

     HFA was developed at INRS-Eau (National Institute of Scientific Research - Water, Quebec, Canada). Theoretical and technical information can be obtained from the following persons: Dr B. Bobée (Tel: 418 654 2539) or Mr H. Perron (Tel: 418 654 3751, Fax: 418 654 2600).   

9.   Availability

     Through the HOMS National Reference Centre for Canada or directly from Water Resources Publications, LLC via the Internet: http://www.wrpllc.com or by phone (303)-741-9071 

10.  Conditions on use

     The software goes hand in hand with the book (written in English) "The Gamma Family and Derived Distributions Applied in Hydrology" (Bobée and Askhar, 1991), 203 pages. The package (software and book) can be obtained at the price of US$ 88.00 from the publisher (Water Resources Publications). The software and the book are also available separately at the price of US$ 60.00 and US$ 38.00, respectively.