|WORLD METEOROLOGICAL ORGANIZATION||
|Explanation of the criteria for classification and numbering of components||
|Explanation of the dates on the component's description|
THE LOW FLOW FREQUENCY ANALYSIS PACKAGE (LFA)
1. Purpose and objectives
To provide a user-friendly interactive computer package to analyse the data with respect to the underlying assumptions of frequency analysis and
to perform low flow frequency analyses using the three-parameter Weibull (Gumbel III) frequency distribution.
The LFA Package allows the user to: easily enter flood data for analysis; modify data sets so as to add, delete, or modify all stored information; save modified data sets for future use; perform nonparametric tests for homogeneity, trend, independence and randomness; graphically display data in various fashions; determine low flow quantiles for the straightforward case and samples with zero flow values.
The three-parameter Weibull distribution forms the basis of this technique. Parameters are estimated by one of three methods. They are maximum likelihood, moments, or smallest observed drought.
The LFA manual provides the technical background of all analytical
procedures incorporated in the package, as well as program documentation and worked examples.
Minimum n-day discharge and the year and (start) month of its
occurrence constitute the data required for analysis.
Output constitutes results of nonparametric tests for homogeneity,
trend, independence and randomness. Graphical displays of the data are also
available as a visual aid in assessment of the data regarding the assumptions of the frequency analysis. Once a sample passes the screening
5. Operational requirements and restrictions
The LFA software was written in Fortran 77 to run under DOS 3.1 on IBM-type microcomputers with a math coprocessor. However, it can also be used on computers running Windows 95 and 98.
LFA was designed to be user friendly and interactive, thus no
knowledge of programming is required to operate the package. Interpretation
of results should be performed by analysts having knowledge of the assumptions and limitations of the approaches, mathematical treatment, and implications regarding the selection of the low flow quantiles.
6. Form of presentation
The user manual and appendices are in English. Diskettes contain the source code, executable module, and a sample data set. Source code is in
7. Operational experience
LFA has been applied to several hundred hydrometric sites in Canada and is currently used by government agencies and private industry.
8. Originator and technical support
Atmospheric Environment Service
10. Conditions on use
The diskettes and user manual are available free of charge.
|(First entered: 24 AUG 90||
Last updated: 14 DEC 1999)