NID: Water quality improves as turbidity is reduced from Combie Reservoir flows

October 17, 2018 – There is marked water quality improvement at Combie Reservoir after water levels dropped significantly last week, causing a turbidity event.

After Nevada Irrigation District (NID) began raising water levels, turbidity has reduced, and water tests indicate oxygen levels are returning to normal in the reservoir. Additional testing also shows mercury levels at non-detectable in the waters flowing through the District’s canals and down the Bear River, according to multiple sampling locations.

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The turbidity situation began last week after NID dropped water levels not seen in years in an effort to accommodate both a sediment removal project and a hydroelectric upgrade project. The low-water levels caused a hydraulic scouring of previously settled silt in the bottom of the reservoir, which increased of turbidity outflowing from the reservoir and into the Bear River. The situation was not caused by the sediment removal or hydroelectric projects. Turbidity in the system is similar to that of heavy rain events during winter months.

NID crews and professional consultants have been monitoring and testing waters in the Bear River and District canals since the onset. In addition, NID has been in close contact with the California Fish and Wildlife Department and the California Regional Water Quality Control Board. The District has been working with professional biologists, regulatory agencies and staff to determine viable solutions to the problem. The turbidity mostly has affected Placer County NID irrigation water customers.

Reservoir levels have returned to near normal levels for this time of year, and the scouring of sediment has stopped. It’s now just a matter of time until the reservoir is completely displaced with clear water, and each day brings substantial improvement. NID and consultants continue to closely monitor the water quality of the Bear River and District Canals during this period.