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U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 02-4040

Hydrologic Trends Associated with Urban Development for Selected Streams in the Puget Sound Basin, Western Washington

Prepared in cooperation with the
WASHINGTON DEPARTMENT OF ECOLOGY

By Christopher P. Konrad, U.S. Geological Survey, Tacoma, WA
and Derek B. Booth, University of Washington, Seattle, WA

ABSTRACT

Annual streamflow statistics from 10 selected streams in the Puget Sound Basin in western Washington were analyzed to identify possible hydrologic trends associated with urban development and to evaluate the effect of record length on errors in trend analysis. The analysis used three common streamflow statistics (annual mean discharge, annual maximum discharge, and 7-day low flow) and introduced an alternative statistic (fraction of year annual mean discharge was exceeded) for assessing the hydrologic effects of urban development. Although trends were identified in each of the four statistics analyzed, trends were not consistent in any of the four statistics for all selected streams. Instead, trends in two statistics – (1) fraction of year annual mean discharge was exceeded, and (2) annual (instantaneous) maximum discharge – were evident in streams with the highest levels of urban development over the period of record but not in streams with the lowest levels of urban development. Trends were not consistent for either annual mean discharge or 7-day low flow in urban streams. Trends were sensitive to the period of analysis for all four statistics, but particularly for the 7-day low flow, which showed increasing and decreasing trends for 10 subsets of the period of record in some streams.

CONTENTS

Abstract
Introduction
Description of Study Area
Previous Investigations
Methods for Identifying Hydrologic Trends Associated with Urban Development
Hydrologic Trends
Implications of Trend Analysis for Hydrologic Monitoring
Summary
References Cited

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Send questions or comments about this report to the author, Christopher Konrad (cpkonrad@usgs.gov) 253.428.3600 ext. 2634.

For more information about USGS activities in Washington, visit the USGS Washington District home page.

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