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Water-Quality Sampling at Five Hydrologic Benchmark Stations in the Western United States

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Water-Quality Sampling at Five Hydrologic Benchmark Stations in the Western United States

Study Area: California, Colorado, and Montana
Period of Project: September 2001 - September 2004
Project Number: CO345
Project Chief: David W. Clow and M. Alisa Mast
Cooperator: Office of Water Quality


The Hydrologic Benchmark Network (HBN) was established in 1963 to provide Swiftwater Creek, MT long-term measurements of streamflow and water quality in areas of the United States that are minimally affected by human activities. These data were collected to study temporal trends in streamflow and water quality and to serve as controls for separating natural from artificial changes in other streams. The HBN is the only national-scale network of undisturbed basins in the United States operated for the purpose of detecting long-term trends.

Historically, the HBN has used a fixed-interval sampling strategy, with sampling frequency ranging from monthly to quarterly. Although fixed-interval sampling has advantages, primarily simplicity for field personnel, other more robust sampling strategies are now available. Trend networks can take advantage of recent advances in hydrochemical modelling to devise more powerful approaches for detecting trends. For example, by creating concentration-discharge models that also incorporate seasonality, it is possible to account for variations in stream chemistry due to changes in flow or season. This makes it possible to isolate trends that may be due to environmental changes, such as atmospheric deposition or climate change.


To develop improved sampling strategies for detecting surface-water trends in high-elevation, snowmelt dominated basins in the western United States.The five basins in the study are part of the Hydrologic Benchmark Network and include Merced River and Sagehen Creek in California, Vallecito Creek and Halfmoon Creek in Colorado, and Swiftcurrent Creek in Montana.

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