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Flood of July 2023 in Vermont

Scientific Investigations Report 2025-5016
Prepared in cooperation with the Federal Emergency Management Agency
By: , , , , and 
https://doi.org/10.3133/sir20255016

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Abstract

A major storm caused catastrophic flooding in many parts of Vermont on July 9–12, 2023, resulting in millions of dollars in damages. The high amount of rainfall caused several rivers to peak at record levels, in some cases exceeding records set during Tropical Storm Irene in 2011. The U.S. Geological Survey, in cooperation with the Federal Emergency Management Agency, collected and analyzed data that characterized the flood in Vermont. The data collected included peak water-surface elevations, taken from high-water marks at bridges, dams, and roads, and peak streamflow and annual exceedance probabilities (AEPs) at streamgages, lake gages, and selected ungaged locations. At 11 of the 80 streamgages with 12 to 94 years of record, the July 2023 peak streamflow was the peak of record. Ten streamgages recorded a peak streamflow with an AEP of less than or equal to 1 percent (greater than or equal to a 100-year recurrence interval).

The July 2023 flood affected many of the same communities as the historical flood caused by Tropical Storm Irene in 2011. Twenty of the 45 continuous-recording streamgages running during both events recorded greater peak streamflows during the July 2023 flood than during Tropical Storm Irene in 2011. Four of the 11 U.S. Geological Survey streamgages with period-of-record maximum peak streamflows observed during the July 2023 flood had previously recorded their maximum period-of-record peak streamflows during Tropical Storm Irene. There were 17 rivers in Vermont that were surveyed for high-water marks during both Tropical Storm Irene and the July 2023 flood. On those 17 rivers, a total of 103 sites contained surveyed high-water marks for both events. Thirty-two of these sites had higher surveyed elevations for the July 2023 flood than Tropical Storm Irene, including Black River in Newport, Black River in Springfield, Jewell Brook, Middlebury River, Missisquoi River, Ottauquechee River, Otter Creek, Wells River, Whetstone Brook, and Winooski River. Peak water-surface elevations were not collected on the Lamoille River in 2011.

Federal Emergency Management Agency flood insurance studies were evaluated in the context of the July 2023 flood. Peak streamflows at streamgages and nearby locations were assessed to determine the influence of the July 2023 flood on the AEPs used in past studies. Overall, 21 of 26 streamflow-computation locations in the flood insurance studies had more than a 10 percent difference in the 1-percent AEP streamflow. A hydraulic evaluation of surveyed water-surface elevations following the July 2023 flood was compared with the AEP profiles from past studies. Four of the 10 streamgages analyzed had poor alignment between the AEPs of the observed streamflows and the AEPs of the observed peak water-surface elevations as computed from flood insurance studies.

Plain Language Summary

A major storm caused catastrophic flooding in many parts of Vermont on July 9–12, 2023, resulting in millions of dollars in damages. The high amount of rainfall caused several rivers to peak at record levels, in some cases surpassing records set during Tropical Storm Irene in 2011. The U.S. Geological Survey, in cooperation with the Federal Emergency Management Agency, collected and analyzed data on peak water-surface elevations, peak streamflow, and annual exceedance probabilities at streamgages, lake gages, and selected ungaged locations. Of the 80 streamgages with records ranging from 12 to 94 years, 11 streamgages recorded peak streamflows during the July 2023 flood that were the highest on record, whereas 10 streamgages had peak streamflows with a recurrence interval of 100 years or more. The July 2023 flood affected many of the same communities as Tropical Storm Irene in 2011, but 20 of the 45 monitored streamgages recorded higher peak flows in the July 2023 flood. Seventeen rivers were surveyed for high-water marks during both Tropical Storm Irene and the July 2023 flood, and 32 of the 103 sites had higher water levels during the July 2023 flood compared with Tropical Storm Irene. Flood insurance studies by the Federal Emergency Management Agency were evaluated against the July 2023 flood data. Twenty-one of the 26 locations analyzed had more than a 10 percent difference in the 1-percent annual exceedance probability streamflow.

Suggested Citation

Smith, T.L., Olson, S.A., LeNoir, J.M., Kalmon, R.D., and Ahearn, E.A., 2025, Flood of July 2023 in Vermont (ver. 1.1, May 22, 2025): U.S. Geological Survey Scientific Investigations Report 2025–5016, 21 p., https://doi.org/10.3133/sir20255016.

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Acknowledgments
  • Abstract
  • Introduction
  • Antecedent Conditions
  • Storm Characteristics
  • Description of the Flood
  • Comparison of the July 2023 Flood with August 2011 Tropical Storm Irene
  • Evaluation of Flood Insurance Studies Using Flood Data From July 2023
  • Summary
  • Selected References
Publication type Report
Publication Subtype USGS Numbered Series
Title Flood of July 2023 in Vermont
Series title Scientific Investigations Report
Series number 2025-5016
DOI 10.3133/sir20255016
Edition Version 1.0: May 19, 2025; Version 1.1: May 22, 2025
Publication Date May 19, 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, 21 p.; 2 Data Releases: Application Site
Country United States
State Vermont
Online Only (Y/N) Y
Additional Online Files (Y/N) Y
Additional publication details