USGS

August Median Streamflow on Ungaged Streams in Eastern Coastal Maine

Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2004-5157

 

By Pamela J. Lombard

 

Prepared in cooperation with

Maine Geological Survey,

Department of Environmental Protection,

Maine State Planning Office,

Maine Department of Agriculture,

Maine Department of Transportation

 

This report is also available as a pdf.

Abstract

Methods for estimating August median streamflow were developed for ungaged, unregulated streams in eastern coastal Maine. The methods apply to streams with drainage areas ranging in size from 0.04 to 73.2 square miles and fraction of basin underlain by a sand and gravel aquifer ranging from 0 to 71 percent. The equations were developed with data from three long-term (greater than or equal to 10 years of record) continuous-record streamflow-gaging stations, 23 partial-record streamflow- gaging stations, and 5 short-term (less than 10 years of record) continuous-record streamflow-gaging stations. A mathematical technique for estimating a standard low-flow statistic, August median streamflow, at partial-record streamflow-gaging stations and short-term continuous-record streamflow-gaging stations was applied by relating base-flow measurements at these stations to concurrent daily streamflows 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 streamflow-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 different periods of record at the gaging stations and the cross correlation of concurrent streamflows among gaging stations. Thirty-one stations were used for the final regression equations.

Two basin characteristics—drainage area and fraction of basin underlain by a sand and gravel aquifer—are used in the calculated regression equation to estimate August median streamflow for ungaged streams. The equation has an average standard error of prediction from -27 to 38 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 -30 to 43 percent. Model error is larger than sampling error for both equations, indicating that additional or improved estimates of basin characteristics could be important to improved estimates of low-flow statistics.

Weighted estimates of August median streamflow at partial- record or continuous-record gaging stations range from 0.003 to 31.0 cubic feet per second or from 0.1 to 0.6 cubic feet per second per square mile. Estimates of August median streamflow on ungaged streams in eastern coastal Maine, within the range of acceptable explanatory variables, range from 0.003 to 45 cubic feet per second or 0.1 to 0.6 cubic feet per second per square mile. Estimates of August median streamflow per square mile of drainage area generally increase as drainage area and fraction of basin underlain by a sand and gravel aquifer increase.

Contents

Abstract

Introduction

Purpose and Scope

Previous Studies

Description of Study Area

Data Collection and Analysis

Station Selection and Streamflow Measurements

Basin Characteristics

August Median Streamflows at Streamflow-Gaging Stations

Computation of August Median Steamflow at Long-Term Continuous-Record Stations including Index Stations

Estimation of August Median Streamflows at Partial-Record Stations and Short-Term Continuous-Record Stations

Estimation of August Median Streamflow on Ungaged Streams

Statistical Methods

Ordinary Least-Squares Regression

Generalized Least-Squares Regression

Equations for Estimating August Median Streamflow on Ungaged Streams

Two-Variable Model

One-Variable Model

Weighted Estimates of August Median Streamflow at Partial- and Short-Term Continuous-Record Streamflow-Gaging Stations

Summary and Conclusions

Acknowledgments

References Cited.


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