ANEW OPERATIONAL PLAN THAT would conserve water in the winter months is being proposed for Hungry Horse and Libby dams in northern Montana, US.

The two dams, owned by the US Bureau of Reclamation (USBR) and the US Army Corps of Engineers (USACE), are to be operated using the ‘variable discharge’ formula, also called VAR-Q, intended to improve the annual refill potential of Hungry Horse reservoir and Lake Koocanusa at Libby. It is expected that the plan will better position the reservoirs to provide higher flows for threatened fish species in late spring and late summer.

If approved, the formula will also lead to deeper drafts in Washington’s Lake Roosevelt, above Grand Coulee dam, to create more flood control storage space. VAR-Q would represent a significant departure from the flood control operations formula that had previously been used at the two dams.

USBR and USACE have jointly launched a public review process of the operational plans, that will lead to an environmental impact statement in 2003 to include several operating options for the dams, including the proposed VAR-Q option.

Because of the extreme low water conditions this year, Hungry Horse dam implemented the VAR-Q formula. According to the USBR, the benefit of this is that it helps keep the reservoir higher, as the pool is not drawn down as deep as required for flood control, thereby increasing the probability of refill. At Libby dam, instead of releasing the water in January and February, VAR-Q will enable it to be stored until spring. That is typically when Lake Koocanusa is called on to release 1.2B m3 of water to help white sturgeon spawning upstream from Bonner’s Ferry.

The variable discharge proposal is largely driven by the results of ‘biological opinions’ that assessed the ecological effects of dam operations throughout the Columbia Basin. The federal agencies have said that the variable discharge formula does not increase the risk of flooding because of its flexibility.

During high water years, operations would resemble the flood control operations of the past.