Cascade Reservoir Water Quality Study Set

By Brad Carlson, Capital Press

The U.S. Bureau of Reclamation will study the Cascade Reservoir in Idaho to figure out ways to improve its water quality.

Cascade Reservoir, near timberlands and meadows about 80 miles north of Boise, is shallow and subject to algae blooms. The blooms are driven by high water temperatures and nutrient levels.

It also is known as Lake Cascade.

The Snake River Area Office received a $308,200 grant for the pilot project to model the reservoir’s operations.

The goal is to find operations-related ways to improve water quality.

The pilot project will evaluate whether operations at Cascade and nearby Deadwood Reservoir can be coordinated to improve water quality.

Operating alternatives will consider “all requirements and constraints” such as physical capacity, irrigation demands, flow augmentation and flood control, the bureau said.

The study will use hydrologic and water quality models to simulate the upper Payette River Basin from Cascade Reservoir, near the town of Cascade, south to the Horseshoe Bend area.

Public concern about water quality at Cascade Reservoir — which is near recreation and second-home sites as well as farms — dates from the 1970s. It has been addressed in part by a state management plan that includes total maximum daily loads of pollutants and  efforts to increase the number of sewer connections.

“One of the things that really hasn’t been investigated is potential operational change,” Middle Snake Field Office Manager Bryan Horsburgh said. “Reclamation recognizes the tremendous public interest in protecting water quality in Cascade Reservoir, and is using this grant as an opportunity to evaluate potential operational opportunities to do so.”

For example, the study will investigate whether adjusting operations “affects the way the reservoir reacts to factors that could impact algae growth,” he said.

The two-year study and its recommendations will not impact water delivery contracts, flood control obligations, or required annual releases to benefit Columbia Basin salmon and steelhead, Horsburgh said. Public meetings are expected to start by the end of this year.

Cascade is one of six reservoir operation pilot studies Reclamation funded in June through its WaterSmart grant program. Others are in part of the Colorado River Basin and at the Newlands Project, both in Nevada, Folsom Reservoir in California, McKay Reservoir in Oregon and Ruedi Reservoir in Colorado.

Reclamation said the studies will look at approaches and potential operating alternatives to increase flexibility in reservoir operations. Projects seek to address risks from changes in timing and volume of snowpack and runoff — as well as water supply shortfalls due to drought or competing demands — changing water demands and reservoir evaporation.