By Robert W. Dudley
U.S. Geological Survey Scientific Investigations Reports 2004-5026
In cooperation with the
Maine Department of Transportation
Maine Department of Environmental Protection and
Maine Atlantic Salmon Commission
This report is available as a pdf.
Regression equations to estimate monthly, annual, and low 7-day, 10-year (7Q10) streamflows were derived for rivers in Maine. The derived regression equations for estimating mean monthly, mean annual, median monthly, median annual, and low 7Q10 streamflows for ungaged rivers in Maine presented in this report supersede those derived in previous studies.
Twenty-six U.S. Geological Survey streamflow-gaging stations on unregulated, rural rivers in Maine with 10 years or more of recorded streamflow were used to develop the regression equations. Ordinary least squares (OLS) regression techniques were used to select the explanatory variables (basin and climatic characteristics) that would appear in the final regression equations. OLS regression of all possible subsets was done with 62 explanatory variables for each of 27 response variables. Five explanatory variables were chosen for the final regression equations: drainage basin area, areal fraction of the drainage basin underlain by sand and gravel aquifers, distance from the coast to the drainage basin centroid, mean drainage basin annual precipitation, and mean drainage basin winter precipitation (the sum of mean monthly precipitation for December, January, and February). Generalized least-squares regression techniques were used to derive the final coefficients and measures of uncertainty for the regression equations.
The forms of many of the derived regression equations indicate some physical, mechanistic processes. Drainage basin area is the most statistically important explanatory variable and appears in all derived regression equations. Monthly streamflows are related inversely to the distance from the coast to the drainage basin centroid during December, January, February, and March; that is, the closer a river basin is to the coast, the higher monthly streamflows are per unit drainage basin area during the winter. The relation reverses in May when higher streamflows are attributed to basins farther from the coast. These relations are consistent with colder, inland drainage basins storing more water in snowpack during the winter and releasing it in the spring. The monthly streamflows (and low 7Q10) during July, August, September, and October are related positively to areal fraction of the drainage basin underlain by sand and gravel aquifers. In general, sand and gravel aquifers underlying Maine river basins have excellent water-yielding characteristics and can provide water to streams during low-flow conditions in the summer and early fall.
Abstract
Introduction
Purpose and Scope
Description of the Study Area
Data Used For This Study.
Streamflow
Monthly and Annual Streamflow
Low 7-day, 10-year Streamflow.
Basin and Climatic Characteristics
Regression Analyses
Ordinary Least Squares Regression
Final Explanatory Variables
Drainage Area
Fraction of Drainage Basin Underlain by Sand and Gravel Aquifers
Distance from the Coast to the Drainage Basin Centroid
Mean Annual Precipitation
Mean Winter Precipitation
Generalized Least Squares Regression
Regression Equations for Estimating Monthly, Annual, and Low 7-Day, 10-Year Streamflows for Ungaged Rivers in Maine
Accuracy and Limitations of the Equations
Summary
References Cited
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