Section 1. Introduction

Here we provide a limited synthesis of stream gauge data to examine trends in freshwater flows with respect to annual and daily flows, timing of flow, low flows and flows relative to instream flow guidelines. This is intended to supplement a review of published information, but we caution that a full analysis of these data and appropriate vetting of methods and interpretations is needed to fully assess the status of freshwater flows. It is our intention that this data compilation and analysis be used to identify data limitations and other key uncertainties with respect to the Puget Sound Partnership Water Quantity Priorities.

Data sources

There are approximately 90 gauging stations overseen by the United States Geological Survey (USGS) in the Puget Sound basin that are located on unregulated reaches of rivers and streams that may be suitable for the analysis of streamflow status and trends (United States Geological Survey 2010b). A complete analysis of all available data was not performed for this report. Instead, data from at least one unregulated gauging station within each Water Resource Inventory Area (WRIA) were included whenever possible. This selection was based on the intent to capture broad regional coverage.

We included all data from available gauging stations on unregulated reaches in the Skagit River basin in order to determine whether there were basin-wide correlations in the hydrologic indicators. Previous reports have combined streamflow data from several rivers to evaluate regional trends (Puget Sound Partnership 2009). A strong correlation between stream and rivers within the same basin could suggest that this is a valid approach. We review evidence for correlation here using simple descriptive statistics, but emphasize that a more rigorous analysis is warranted.