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Estimating Flood Discharges at Selected Annual Exceedance Probabilities for Unregulated, Rural Streams in Vermont, 2023

Scientific Investigations Report 2025-5088
Federal Emergency Management Agency
By:
https://doi.org/10.3133/sir20255088

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Abstract

This report provides estimates of flood discharge at selected annual exceedance probabilities (AEPs) for streamgages in and adjacent to Vermont and equations for estimating flood discharges at AEPs of 50-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent (recurrence intervals of 2-, 5-, 10-, 25-, 50-, 100-, and 500-years, respectively) for ungaged, unregulated, rural streams in Vermont with drainage areas between 0.47 and 851 square miles. The equations were developed using generalized least-squares regression and flood-frequency and drainage-basin characteristics from 156 streamgages. Flood-frequency analyses were completed using data through the 2023 water year. The drainage-basin characteristics used as explanatory variables in the regression equations are drainage area, percentage of wetland area, and basin-wide mean of the average annual precipitation. The average standard errors of prediction used to estimate flood discharges at the 50-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent AEP with these equations are 34.9, 37.1, 38.2, 41.6, 43.8, 46.0, 49.1, and 53.2 percent, respectively.

Flood discharges at selected AEPs for streamgages were computed using the Expected Moments Algorithm. Techniques used to adjust an AEP discharge computed from a streamgage record with results from the regression equations and to estimate flood discharge at a selected AEP for an ungaged site upstream or downstream from a streamgage using a drainage-area adjustment are both described. The final regression equations and the flood-discharge frequency data used in this study will be available in StreamStats. StreamStats is an internet-based application that provides automated regression-equation solutions for user-selected sites on streams.

Suggested Citation

Olson, S.A., 2025, Estimating flood discharges at selected annual exceedance probabilities for unregulated, rural streams in Vermont, 2023: U.S. Geological Survey Scientific Investigations Report 2025–5088, 22 p., 7 app., https://doi.org/10.3133/sir20255088.

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Acknowledgments
  • Abstract
  • Introduction
  • Estimating Flood Discharges at Selected Annual Exceedance Probabilities for Streamgages
  • Characteristics of Streamgage Drainage Basins
  • Regression Equations Used to Estimate Flood Discharges at Selected Annual Exceedance Probabilities for Ungaged Stream Sites
  • Vermont StreamStats
  • Summary
  • References Cited
  • Appendix 1. Streamgages with Data Used in this Investigation and the Maximum Annual Peak Discharge Recorded at the Streamgages in Vermont and Vicinity
  • Appendix 2. Summary of Peak Discharge Data Used in the Flood-Frequency Analyses at Streamgages in Vermont and Vicinity
  • Appendix 3. Flood Discharges for Selected Annual Exceedance Probabilities for Selected Streamgages in Vermont and Vicinity
  • Appendix 4. Variance of Estimate at Selected Annual Exceedance Probabilities for Streamgages in Vermont and Vicinity
  • Appendix 5. Basin Characteristics Tested for Use in the Regression Equations
  • Appendix 6. Basin Characteristics Used to Develop the Regression Equations
  • Appendix 7. Example Application
Publication type Report
Publication Subtype USGS Numbered Series
Title Estimating flood discharges at selected annual exceedance probabilities for unregulated, rural streams in Vermont, 2023
Series title Scientific Investigations Report
Series number 2025-5088
DOI 10.3133/sir20255088
Publication Date November 24, 2025
Year Published 2025
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) New England Water Science Center
Description Report: vii, 22 p.; Data Release; Appendix
Country United States
State Vermont
Online Only (Y/N) Y
Additional Online Files (Y/N) Y
Additional publication details