Pacific Northwest Research Station

Title: Clarifying muddy water: probing the linkages to municipal water quality.

Author: Duncan, Sally.

Date: 2003

Source: Science Findings 59. Portland, OR. U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 5 p

Description: In the Pacific Northwest, several recent and dramatic "muddy waters" events have created major problems for water utilities. Resulting from floods and measures to retrofit dams to reduce impacts on temperature, these events also have focused public and scientific attention on interactions among dams, forest-land use, and municipal water supplies. Far from being a simple cause and effect, the key agent is tradeoffs.

The large Cascade watersheds that provide drinking water for OregonÂ’s biggest cities (Portland, Salem, Eugene) include actively managed forest lands, large flood-control dams and reservoirs, and urban and agricultural areas. Historically, the impacts of these various land use practices on rivers, aquatic systems, and water supplies have been evaluated individually. But the connections can no longer be ignored.

Recent research at the Pacific Northwest (PNW) Research Station has explored these linkages and their implications for river and watershed management. The Salem water supply was closed down during the 1996 flood because of excess turbidity. And when the Cougar Reservoir east of Eugene, Oregon, was drawn down to be retrofitted with a temperature control structure in spring 2002, sediments in the reservoir were remobilized. The unanticipated result was a sustained release of turbid water.

Building on the lessons from 1996, PNW researchers investigated the rate of movement of the Cougar Reservoir sediment downstream and whether the sediment that intruded into the river created potentially negative consequences for spawning fish and other aquatic biota.

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Citation

Duncan, Sally.  2003.  Clarifying muddy water: probing the linkages to municipal water quality..   Science Findings 59. Portland, OR. U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 5 p