Welcome to the Unofficial
PeakfqSA/EMA-Peak Home Page


hosted by Tim Cohn
20 March 2014
 
USGS Annual Peak Flows at Point of
Rocks         USGS Annual Peak Flows at Point of Rocks

Introduction

PeakfqSA/EMA-Peak is an implementation of the Expected Moments Algorithm (EMA) for flood frequency analysis. It is intended to serve the same purpose as PEAKFQ, the current and official flood frequency program supported by USGS.

Statistical Aspects of PeakfqSA

PeakfqSA uses Cohn et al.'s (1997) Expected Moments Algorithm to estimate flood frequency based on at-site ("Station") systematic and historical annual peak flow data possibly combined with regional ("Generalized") flood frequency information. PeakfqSA/EMA-Peak is documented in a set of papers published in Water Resources Research (see below).

History of PeakfqSA

The underlying idea for the Expected Moments Algorithm (EMA) was first suggested by Bill Lane of the U.S. Bureau of Reclamation, and developed jointly by Tim Cohn and Bill Lane. Subsequent testing and research on confidence intervals, low outliers, skewness, and other features, have been performed by a group of researchers including John England, Veronica Webster Griffis, and Jery Stedinger. The computer software for EMA is called PeakfqSA/EMA-Peak and was developed at the U.S. Geological Survey by Tim Cohn. PeakfqSA/EMA-Peak is expected to be available eventually as part of a future and official USGS software release of PEAKFQ. In the meantime, enjoy this unofficial version of the program.

Version History

Version 0.998 and 0.997 contain improvements in numerical precision and function evaluation. Versions 0.995 and 0.996 incorporates much more accurate confidence interval calculations employing Inverse-Gaussian-Quadrature procedures. These are accurate over a very wide range of skews, employ stable numerical methods that do not rely on numerical derivatives and therefore provide smooth curves in all cases, and are much -- two orders of magnitude -- faster to compute. Version 0.993 also reports the MSE of at-site skew estimates, as well as the corresponding effective record length (ERL).
Version 0.992 incorporates the three-sweep low-outlier detection procedure devised by Stedinger and Lamontagne [2013].
Version 0.974 introduced regional information related to M, S, and G. It also provided the variance of the (log10) of the quantile estimator, which is useful when computing weighted averages (e.g. with regional equations to estimate quantiles).

Downloadable Software

 2014 Version (0.998) of PeakfqSA zip file for Windows (includes test data set)

 2014 Version (0.998) PeakfqSA zip file for MacOS X

Additional Information

 PeakfqSA User Manual

Old Versions of Software

 2013 Version (0.996) of PeakfqSA zip file for Windows (includes test data set)

 2013 Version (0.996) PeakfqSA zip file for MacOS X

 2013 Version (0.995) of PeakfqSA zip file for Windows (includes test data set)

 2013 Version (0.995) PeakfqSA zip file for MacOS X

 2013 Version (0.993) of PeakfqSA zip file for Windows (includes test data set)

 2013 Version (0.993) PeakfqSA zip file for MacOS X

 2013 Version (0.992) of PeakfqSA zip file for Windows (includes test data set)

 2012 Version (0.974) of PeakfqSA zip file for Windows (includes test data set)

 2012 Version (0.974) PeakfqSA zip file for MacOS X

 2011 Version (0.972) of PeakfqSA zip file for Windows (includes test data set)

 2011 Version (0.974) PeakfqSA zip file for MacOS X

 2011 Version (0.971) of PeakfqSA zip file for Windows (includes test data set; note this version does produce correct confidence intervals when the skew is too close to zero (abs(G)<0.0633))

 2011 Version (0.960) of PeakfqSA zip file for Windows (does not currently include test data sets)

 2011 Version (0.950) of PeakfqSA zip file for Windows (includes test data sets)

 2011 Version (0.950) PeakfqSA zip file for MacOS X (includes test data sets)

 2007 Version (0.937) of PeakfqSA zip file for Windows (includes test data sets)

 2007 Version (0.937) PeakfqSA zip file for MacOS X (includes test data sets)

Additional Information

 PeakfqSA/EMA-Peak User Manual

 Frequently Asked Questions (Under Construction):

References

Site last updated 20 March 2014

Comments or suggestions? Email tim@timcohn.com