Dam discharge at full capacity
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April 16, 2014 |
In response to increased snowpack in the
Kootenai Basin during the month of March, the
U.S. Army Corps of Engineers is discharging full
powerhouse capacity, about 25,000 cubic feet per
second, at Libby Dam.
Current projections show that there is about a
40 percent chance of being over flood stage at
Bonners Ferry, elevation 1,764 feet. The
potential for being near flood stage is highest
late-May through June.
Corps' water managers plan to maintain releases
at full powerhouse capacity for the remainder of
April, or until the start of refill, projected
for the first or second week of May.
This action is creating more storage in the
Koocanusa Reservoir and will allow the Corps to
retain more Kootenai River flow behind Libby Dam
during the spring freshet.
Current Koocanusa Reservoir elevation is 2,404
feet and the median projection for the end of
month elevation is 2,387 feet, depending upon
actual April inflows. The reservoir will
continue to be drafted at a rate of roughly one
foot per day until the start of reservoir
refill, when the dam shifts from emptying the
reservoir to create storage space to controlling
the refill through the freshet.
The water supply forecast for April through
August into Koocanusa Reservoir is 117 percent
of normal and snowpack is 115-120 percent of
normal in the Kootenai River basin. The water
supply forecast increased from 93 percent of
normal to 117 percent between the months of
March and April.
The increase was mainly driven by 250 percent of
average precipitation for the month of March
that landed mostly as snow in the higher
elevations in the Upper Kootenai Basin.
Generally, upper river runoff is regulated by
Libby Dam, while lower river runoff is mostly
unregulated since it flows into the Kootenai
River below the dam.
The Corps' flood risk management operational
strategy is to retain as much volume as possible
behind Libby Dam while the downstream
unregulated tributaries, which are forecasted to
be near flood stage, pass as much of their
spring snowmelt and rain flows as possible. It
is possible that Kootenai River flows may be at
or above flood stage from unregulated tributary
flows alone.
Residents and businesses in the river basin
should be prepared for potential flooding once
snowpack begins to melt. Should flows approach
flood stage, the National Weather Service and
downstream communities have plans in place to
promptly alert potentially affected people about
the situation and what action to take.
Citizens are encouraged to contact local
emergency managers and work with them to
determine the best path to prepare for potential
flooding.
The Corps is regulating Libby Dam for flood risk
management, closely monitoring weather
conditions, snowpack readings and inflows to
mitigate flood risk downstream.
A public information meeting for Libby Dam
operations is scheduled for May 29 at the
Kootenai River Inn, Bonners Ferry, at 7 p.m.
Public meetings are also being planned for
Eureka and Libby during early June. |
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