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Disconnected rivers: Human impacts to rivers in the United States

By
Ellen Wohl
Ellen Wohl
Department of Geosciences, Colorado State University, Fort Collins, Colorado 80523, USA
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Published:
January 01, 2005

Abstract

Human activities impact an estimated 98% of rivers in the United States. This chapter summarizes impacts associated with pioneer societies, commercial activities, and public works. In pioneer societies, individuals or small groups undertake activities such as timber harvest, agriculture, or navigation improvements. Nineteenth-century placer mining of gold along rivers of California's Sierra Nevada is used as a case study. Commercial activities are conducted by groups of people seeking profit through industry, commerce, or agriculture. Commercial activities impacted rivers much more extensively than most activities of pioneer societies. Impacts to water quality, and particularly the U.S. Geological Survey National Water Quality Assessment (NAWQA) program, provide a case study. Results from the 1991–1995 NAWQA program indicate that approximately half the sites sampled in urban areas have surface-water contamination exceeding levels at which adverse biological effects can occur in aquatic biota. Public works such as dam and levee construction undertaken by local and federal governmental agencies caused massive alteration of river systems. Channelization is used as a case study of the impacts of public works on rivers; more than 56,000 km of waterways were channelized by the Corps of Engineers and the Soil Conservation Service after 1940.

The net effect of human activities in the United States has been to disconnect rivers from adjacent hillslopes, floodplains, and valley bottoms, underlying hyporheic and groundwater zones, and from headwaters and downstream processes. Because a connected river is a functioning ecosystem, rather than simply a canal for moving water and sediment, disconnection simplifies and impoverishes the ecosystem. This has resulted in widespread loss of biological diversity in rivers of the United States.

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Reviews in Engineering Geology

Humans as Geologic Agents

Judy Ehlen
Judy Ehlen
Department of Geology, Radford University, Radford, Virginia 24142, USA
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William C. Haneberg
William C. Haneberg
Haneberg Geoscience, 10208 39th Avenue SW, Seattle, Washington 98146, USA
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Robert A. Larson
Robert A. Larson
Los Angeles County Department of Public Works, Alhambra, California 91803, USA
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Geological Society of America
Volume
16
ISBN electronic:
9780813758169
Publication date:
January 01, 2005

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