Water-Resources Investigations Report 03-4225
By Pamela J. Lombard, Gary D. Tasker, and Martha G. Nielsen
In cooperation with the AROOSTOOK WATER AND SOIL MANAGEMENT BOARD
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Methods for estimating August median streamflow were developed for ungaged, unregulated streams in the eastern part of Aroostook County, Maine, with drainage areas from 0.38 to 43 square miles and mean basin elevations from 437 to 1,024 feet. Few long-term, continuous-record streamflow-gaging stations with small drainage areas were available from which to develop the equations; therefore, 24 partial-record gaging stations were established in this investigation. A mathematical technique for estimating a standard low-flow statistic, August median streamflow, at partial-record stations was applied by relating base-flow measurements at these stations to concurrent daily flows at nearby long-term, continuous-record streamflow- gaging stations (index stations). Generalized least-squares regression analysis (GLS) was used to relate estimates of August median streamflow at gaging stations to basin characteristics at these same stations to develop equations that can be applied to estimate August median streamflow on ungaged streams. GLS accounts for varying periods of record at the gaging stations and the cross correlation of concurrent streamflows among gaging stations. Twenty-three partial-record stations and one continuous-record station were used for the final regression equations.
The basin characteristics of drainage area and mean basin elevation are used in the calculated regression equation for ungaged streams to estimate August median flow. The equation has an average standard error of prediction from -38 to 62 percent. A one-variable equation uses only drainage area to estimate August median streamflow when less accuracy is acceptable. This equation has an average standard error of prediction from -40 to 67 percent. Model error is larger than sampling error for both equations, indicating that additional basin characteristics could be important to improved estimates of low-flow statistics.
Weighted estimates of August median streamflow, which can be used when making estimates at partial-record or continuous-record gaging stations, range from 0.03 to 11.7 cubic feet per second or from 0.1 to 0.4 cubic feet per second per square mile. Estimates of August median streamflow on ungaged streams in the eastern part of Aroostook County, within the range of acceptable explanatory variables, range from 0.03 to 30 cubic feet per second or 0.1 to 0.7 cubic feet per second per square mile. Estimates of August median streamflow per square mile of drainage area generally increase as mean elevation and drainage area increase.
Abstract
Introduction
Purpose and Scope
Previous Studies
Location of Study Area
Acknowledgments
Data Collection and Analysis
Station Selection and Streamflow Measurements
Basin Characteristics
Estimating August Median Streamflow at Partial-Record Streamflow-Gaging Stations
Computing August Median Streamflow at Index Stations
Estimating August Median Streamflow at Partial-Record Stations
Estimating August Median Streamflow on Ungaged Streams
Statistical Methods
Ordinary Least-Squares Regression
Generalized Least-Squares Regression
Regional Regression of Expected August Median Discharge Using Generalized Least-Squares Regression
Estimating August Median Streamflow of Continuous-Record and Partial-Record Streamflow- Gaging Stations
Estimating August Median Streamflow on Ungaged Streams
Equations for Estimating August Median Streamflow on Ungaged Streams
Two-Variable Model
One-Variable Model
Weighted Estimates of August Median Streamflow at Partial- and Continuous-Record Streamflow-Gaging Stations
Summary and Conclusions
References Cited
For additional information write to:
District Chief
U.S. Geological Survey
Maine District
196 Whitten Road
Augusta, Maine 04330
Copies of this report can be purchased from:
U.S. Geological Survey
Branch of Information Services
Box 25286, MS 517
Federal Center
Denver, CO 80225
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