News Release
| Release Number: | 02-080 |
| Dated: | 5/7/2002 |
| Contact: | Heidi Y. Helwig, 503-808-4510 |
Portland, Ore.-Though unsightly, increased turbidity in the McKenzie River below Cougar Dam does not constitute a health risk and is not projected to harm fish, according to the U.S. Army Corps of Engineers. The Corps recognizes, however, that the current turbidity levels exceed state water quality standards and can affect the quality of fishing and other water-based recreation on the McKenzie River. Regrettably, there also may be negative economic effects on river users.
On May 2, George Miller, project manager for the Willamette Temperature Control (WTC) project, and other Corps personnel met with a multi-agency Environmental Coordination Committee established to monitor the environmental impacts of the WTC construction and drawdown. The committee recommended some actions to reduce turbidity, including reconfiguring the current drawdown schedule for Cougar Reservoir. After a Corps technical team reviewed the recommendations, however, it determined that altering the drawdown schedule would only delay the turbidity, possibly creating higher levels of turbidity later in the summer.
In addition, though earlier water sample results did not show any trace of heavy metals or pesticides, the Corps, with input from the public, agreed additional water samples should be taken to test again for the substances.
Normal water clarity levels below Cougar Dam prior to beginning the WTC project construction ranged from 0.6 to 2.9 Nephelometric Turbidity Units (NTUs), Miller said. In the Biological Assessment prepared in 1999, those levels were expected to increase 10-fold to between 6 NTUs and 30 NTUs. At Eugene Water and Electric Board's Hayden Island plant, turbidity levels have been running about 8 NTUs to 12 NTUs and are being filtered accordingly. This week, the NTU levels in the reservoir, however, have been around 80 NTUs, an increase over the projected levels. On occasion, the readings have spiked to nearly 400 NTUs for periods of an hour or less. Miller said the turbidity levels would continue to fluctuate as the reservoir is drawn down. Still, these readings fall well below the environmentally harmful levels of 700 NTUs to 1,000 NTUs, which must be sustained for up to a week before they begin to threaten the health of fish, said fishery biologist Chuck Willis.
"DEQ appreciates the long term benefits of the project and we look forward to working with the Corps and other agencies to help monitor, identify and implement feasible control measures if the short term turbidity levels continue beyond what's projected," said Kerri Nelson, Western Region Division Administrator, Oregon Department of Environmental Quality.
The turbidity is a result of drawing down Cougar Reservoir to allow for construction of a multi-level intake tower. The tower will allow the Corps to draw water from differing depths in the reservoir, mixing it to the optimum water temperature for release below the dam. The changes will improve river conditions for salmon and resident fish in the South Fork McKenzie and McKenzie rivers over a 50-year project life, matching natural conditions needed by the fish.
Because of the drawdown stream sediments that have accumulated during the 39 years since the reservoir was constructed are being exposed and eroding into the pool, resulting in the turbid water, Miller said. The good news is that the turbidity--or lack of water clarity--is temporary. No long-term impacts on fish or the aquatic ecosystem are expected.
The challenges now are to determine the expected duration of turbidity so people can adjust their recreation plans and to review technical data to determine if there are any feasible means of reducing either the levels or duration of the turbidity. Initial thoughts were that the turbidity would last about a month or more. Increased turbidity also is expected following heavy rains.
In conjunction with the planning and environmental compliance process for the Willamette River Temperature Control Project (WTC), the Corps forecasted that the reservoir drawdown would stir up sediments, producing turbidity levels that could exceed state water quality standards. The impacts were documented in the 1995 Environmental Impact Statement and the 1999 Environmental Assessment Supplement. It is fair to say, however, that the Corps did not project that turbidity would extend as far downstream as it has or that it would reach the sustained levels that it has, Miller said. The Corps will continue drawing down the reservoir at a rate of 3 feet per day until it reaches an elevation of 1,375 feet, 100 feet below the current elevation of 1,475 feet. It will take four to six weeks to reach this level. This elevation is needed to allow work to continue on the tower.
The Corps expects to complete work on the Cougar tower in 2004.