Flow-Frequency Characteristics of Vermont Streams

U.S. Geological Survey Water-Resources Investigations Report 02-4238

By Scott A. Olson

The full report is available in pdf.


The safe and economical design of infrastructure in and near waterways and the effective management of flood-hazard areas require information on streamflow that may not be readily available. This report provides estimates of flow-frequency characteristics for gaged streams in Vermont and describes methods for estimating flow-frequency characteristics for ungaged streams. The flow-frequency characteristics investigated are the magnitude of peak discharges at recurrence intervals of 2, 5, 10, 25, 50, 100, and 500 years, and the magnitude of daily-mean discharges exceeded 25, 50, and 75 percent of the time.

Peak-flow frequency characteristics for gaged streams were computed following the guidelines in Bulletin 17B of the U.S. Interagency Advisory Committee on Water Data. To determine the peak-flow exceedance probabilities at stream-gaging stations in Vermont, a new generalized skew coefficient map for the State was developed. This new map has greater resolution and more current data than the existing National map. The standard error of the new map is 0.269.

Two methods of extending streamflow record were applied to improve estimates of peak-flow frequency for streams with short flow records (10 to 15 years) in small drainage areas (sites less than 15 square miles). In the first method, a two-station comparison, data from a long-record site was used to adjust the frequency characteristics at the short-record site. This method was applied to 31 crest-stage gages--stations at which only instantaneous peak discharges are determined--in Vermont. The second method used rainfall-runoff modeling. Precipitation and evapotranspiration data from 1948 to 1999 for numerous climate data-collection sites were used as input to a model to simulate flows at 10 stream-gaging stations in Vermont.

Also, methods are described to estimate flow-frequency characteristics for ungaged and unregulated rural streams in Vermont. The peak-flow estimating methods were developed by generalized-least-squares regression procedures with data from 138 U.S. Geological Survey stream-gaging stations in Vermont and in adjacent areas of New York, New Hampshire, Massachusetts, and Quebec. The flow-duration (daily flow exceeded a given percentage of the time) estimating methods were developed by ordinary-least-squares regression procedures with data from 81 stream-gaging stations in Vermont and adjacent states.




Streamflow Data Used in This Study

Record Extension

Record Extension Using Two-Station Comparison

Record Extension Using Rainfall-Runoff Modeling

Observed Data Used for Model Calibrations

Rainfall-Runoff Model and Input Parameters

Simulation of Streamflow Record

Flow-Frequency Characteristics at Stream-Gaging Stations

Drainage-Basin Characteristics

Flow-Frequency Characteristics at Ungaged Streams

Regression Analyses

Accuracy and Limitations

Summary and Conclusions

Selected References

Appendix 1. Use of Regression Equations With Metric Units

Appendix 1. References Cited

Appendix 2. Areas of Vermont Above 1,200 Feet in Altitude

Appendix 3. Northing of the Vermont State Plane Coordinate System

Appendix 4. Mean-Annual Precipitation in Vermont

The text and graphics are presented here in pdf format (print quality):

The full report is 3.5 MB

As part of the Vermont Flow-frequency Characteristics for Vermont Streams project, a GIS tool was developed to automatically delineate drainage basins and determine characteristics using the regression equations described in WRIR 02-4238.

For a copy of the Open-File Report describing how to use the GIS Tool, the software application, and data sets needed to run the Tool, click on URL

Document Accessibility: Adobe Systems Incorporated has information about PDFs and the visually impaired. This information provides tools to help make PDF files accessible. These tools convert Adobe PDF documents into HTML or ASCII text, which then can be read by a number of common screen-reading programs that synthesize text as audible speech. In addition, an accessible version of Acrobat Reader 5.0 for Windows (English only), which contains support for screen readers, is available. These tools and the accessible reader may be obtained free from Adobe at Adobe Access.

Send questions or comments about this report to the author, Scott A. Olson ( 603-226-7815.

For additional information write to:

District Chief

U.S. Geological Survey

New Hampshire/Vermont District

361 Commerce Way

Pembroke, NH 03275-3718


or through our Web site at


Copies of this report can be purchased from:


U.S. Geological Survey

Branch of Information Services

Box 25286 Federal Center

Denver, CO 80225

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