Technical Bulletins & Special Reports

Technical Bulletin No. 1093: Data Quality Report for the Alsea Watershed Study Revisited Water Quality Measurements

April 14, 2025 Attachment: NCASI_TB1093_Data Quality Alsea Watershed Study_04.2025

Authored by:

Terry Bousquet, NCASI (retired)

Abstract

The original Alsea Watershed study (1959 to 1965) measured the effects of historical forest management practices on aquatic systems, and the results of this study led to the establishment of rules to protect water quality in the Oregon Forest Practices Act in 1971. The original Alsea Watershed Study was one of the first paired watershed studies to simultaneously examine the effects of forest management practices on discharge, water quality, aquatic ecosystem characteristics, and fish. The Alsea Watershed Study Revisited project (began in October 2005) was designed to compare the effects of current forest practices with those historical practices and included many of the same parameters quantified in the original study. All three small watersheds (Needle Branch (clearcut), 175 acres; Deer Creek (patch cut), 750 acres; and Flynn Creek (reference), 500 acres) included in the original study were also monitored in the revisit with only Needle Branch harvested, Flynn Creek remaining a reference. The upper watershed of Needle Branch was harvested using forest practices that were current in 2009, which followed 3 years of pretreatment and then 4 years of posttreatment study. Phase 2 harvest of the lower watershed began in September 2014 with 3 years of postharvest data collection planned as of 2016. We completed a systematic and comprehensive evaluation of data quality prior to releasing any data to collaborators or other data users, and the results of this analysis are described in detail in this report. Here, we provide an overview of the data quality for water quality parameters collected in this study: stage to determine discharge, suspended sediment, turbidity, stream temperature, dissolved oxygen, and nutrients (nitrogen and phosphorus species). This report also describes herbicide data assessment following a silvicultural herbicide application in Needle Branch in 2010.