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.
Abstract
Introduction
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
District Chief
U.S. Geological Survey
New Hampshire/Vermont District
361 Commerce Way
Pembroke, NH 03275-3718
or through our Web site at http://nh.water.usgs.gov
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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