U.S. Geological Survey

Cover image from FS 2005-3135 (click for enlargement, 71 KB) The U.S. Geological Survey Hydrologic Benchmark Network

by Peter S. Murdoch, Michael R. McHale, M. Alisa Mast, and David W. Clow

Fact Sheet 2005-3135


In 1962, Luna B. Leopold, then Chief Hydrologist of the U.S. Geological Survey (USGS), proposed the establishment of a network of 'hydrologic benchmarks' on the nationís rivers. The main purpose of the Hydrologic Benchmark Network (HBN) is to provide a long-term database to track changes in the flow and water quality of undisturbed streams and rivers (rivers draining undeveloped lands), and to serve as a reference for discerning natural from human-induced changes in river ecosystems. In the ever-changing landscape of the North American continent, there are few medium- to large-scale watersheds that remain largely undisturbed. The HBN is the only nationwide network of environmental monitoring stations that tracks the health of rivers draining medium sized, undisturbed basins in the United States. HBN watersheds range in size from 2 mi2 to 254 mi2 though one watershed has an area close to 2,000 mi2. HBN watersheds are larger than typical research watersheds in which most ecosystem research is conducted, but are small enough to be responsive to anthropogenic atmospheric inputs and climate change. The HBN thus provides a frame of reference to evaluate changes in river chemistry and flow patterns in large or developed watersheds, such as those commonly sampled as part of State and Federal monitoring programs (for example, USGS National Water-Quality Assessment Program [NAWQA]; U.S. Environmental Protection Agency 305-B program).  

The HBN of 2005 has fewer stations than the original network of Dr. Leopold, but modern sampling strategies and equipment allow a far more detailed understanding of how the Nationís streams and rivers are changing than was feasible in the 1960s when the HBN began. In 2003, 15 of the original HBN stations were equipped with refrigerated, automated samplers and telemetry systems that allow program coordinators to monitor stream conditions and adjust sampling frequency and capture unique stream conditions or special sampling needs. The automated sampling system is designed to collect samples through a wide range of flow conditions and to transmit data by satellite. About 25 water samples are collected annually at each HBN water-quality station and refrigerated on site until retrieved by field personnel who visit the sites regularly. Flow-based automatic sampling assures that samples are collected through the range of flow conditions at each site during each season of the year. Samples are analyzed for major anions and cations, pH, dissolved organic carbon (DOC), dissolved organic nitrogen (DON), acid neutralizing capacity (ANC), silica, and aluminum. HBN basins are often used for investigations of local concern that supplement HBN data collection, provide additional water-quality data such as pathogens, pesticides, stable isotopes, and phosphorus for periods of months to years, and offers the opportunity to collaborate with other local, State, and Federal agencies as well as academia and the private sector. This flexible monitoring capability allows a baseline of long-term data to be maintained while supporting regional and national investigations of emerging environmental issues.  

Citation: Murdoch, P.S., McHale, M.R., Mast, M.A., and Clow, D.W., 2005, The U.S. Geological Survey Hydrologic Benchmark Network: U.S. Geological Survey Fact Sheet 2005-3135, 6 p., 4 figs.

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