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Methods for peak-flow frequency analysis and reporting for streamgages in or near Montana based on data through water year 2015

Scientific Investigations Report 2018-5046
Prepared in cooperation with the Montana Department of Natural Resources and Conservation
By:  and 
https://doi.org/10.3133/sir20185046

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Abstract

This report documents the methods for peak-flow frequency (hereinafter “frequency”) analysis and reporting for streamgages in and near Montana following implementation of the Bulletin 17C guidelines. The methods are used to provide estimates of peak-flow quantiles for 50-, 42.9-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities for selected streamgages operated by the U.S. Geological Survey Wyoming-Montana Water Science Center (WY–MT WSC). These annual exceedance probabilities correspond to 2-, 2.33-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year recurrence intervals, respectively.

Standard procedures specific to the WY–MT WSC for implementing the Bulletin 17C guidelines include (1) the use of the Expected Moments Algorithm analysis for fitting the log-Pearson Type III distribution, incorporating historical information where applicable; (2) the use of weighted skew coefficients (based on weighting at-site station skew coefficients with generalized skew coefficients from the Bulletin 17B national skew map); and (3) the use of the Multiple Grubbs-Beck Test for identifying potentially influential low flows. For some streamgages, the peak-flow records are not well represented by the standard procedures and require user-specified adjustments informed by hydrologic judgement. The specific characteristics of peak-flow records addressed by the informed-user adjustments include (1) regulated peak-flow records, (2) atypical upper-tail peak-flow records, and (3) atypical lower-tail peak-flow records. In all cases, the informed-user adjustments use the Expected Moments Algorithm fit of the log-Pearson Type III distribution using the at-site station skew coefficient, a manual potentially influential low flow threshold, or both.

Appropriate methods can be applied to at-site frequency estimates to provide improved representation of long-term hydroclimatic conditions. The methods for improving at-site frequency estimates by weighting with regional regression equations and by Maintenance of Variance Extension Type III record extension are described.

Frequency analyses were conducted for 99 example streamgages to indicate various aspects of the frequency-
analysis methods described in this report. The frequency analyses and results for the example streamgages are presented in a separate data release associated with this report consisting of tables and graphical plots that are structured to include information concerning the interpretive decisions involved in the frequency analyses. Further, the separate data release includes the input files to the PeakFQ program, version 7.1, including the peak-flow data file and the analysis specification file that were used in the peak-flow frequency analyses. Peak-flow frequencies are also reported in separate data releases for selected streamgages in the Beaverhead River and Clark Fork Basins and also for selected streamgages in the Ruby, Jefferson, and Madison River Basins.

Suggested Citation

Sando, S.K., and McCarthy, P.M., 2018, Methods for peak-flow frequency analysis and reporting for streamgages in or near Montana based on data through water year 2015: U.S. Geological Survey Scientific Investigations Report 2018–5046, 39 p., https://doi.org/10.3133/sir20185046.

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Acknowledgments
  • Abstract
  • Introduction
  • Overview of Bulletin 17B and Bulletin 17C Guidelines for Peak-Flow Frequency Analysis
  • The Expected Moments Algorithm Procedures in Relation to Montana Peak-Flow Datasets
  • Selected Considerations for Peak-Flow Frequency Analysis
  • Methods for Peak-Flow Frequency Analysis
  • Methods for Peak-Flow Frequency Reporting
  • Summary
  • References Cited
Publication type Report
Publication Subtype USGS Numbered Series
Title Methods for peak-flow frequency analysis and reporting for streamgages in or near Montana based on data through water year 2015
Series title Scientific Investigations Report
Series number 2018-5046
DOI 10.3133/sir20185046
Year Published 2018
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) WY-MT Water Science Center
Description Report: vi, 39 p.; Data Releases
Country United States
State Montana
Online Only (Y/N) Y
Additional Online Files (Y/N) Y
Google Analytic Metrics Metrics page
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