WRIA 62 WMP 032305 - Washington State Department of Ecology

March, 2005 -51- 023-1289-003.3040
The concern with flooding in the Box Canyon project area is primarily in the low lying areas of the
Calispell, Trimble and Cusick Creek valleys and includes the town of Cusick. In this area the creeks
usually experience high spring flows in March through April associated with snow melt within WRIA
62. During these high spring creek flows it is important to pump the water from these creeks over the
dikes into the Pend Oreille River as well as to allow the creeks to free flow through the dikes. The
high flows in the Pend Oreille River mainstem usually occur in May and June and are associated with
higher elevation snow melt in the Clark Fork watershed. If the lower lying spring melt in WRIA 62
coincides with high spring flows in the Pend Oreille mainstem (when the creeks are unable to free
flow into the Pend Oreille River mainstem through the dikes), flooding is more likely to occur in the
Calispell, Trimble and Cusick valleys since water discharge from these creeks over the dikes is
limited by the capacity of the pumps. Coordination between Diking Districts, the PUD and the
ACOE at this time is necessary to help limit flooding as much as possible (ACOE, 2002).
This flooding potential in WRIA 62 is exacerbated during those years when the elevation of Pend
Oreille Lake is held high (above 2053 ft amsl) in the winter resulting in a reduction of storage
capacity in the lake. Additional inflow to the lake must be passed on by Albeni Falls Dam to avoid
flooding in the towns along the lakeshore, in particular Sandpoint. When Pend Oreille Lake is held
lower during the winter (i.e. at elevations of 2051 to 2053 ft amsl), there is some storage capacity
available in the lake and there is the potential that the Army Corps of Engineers (ACOE) can assist
the PUD by releasing less than 43,000 cfs from Albeni Falls Dam for enough time to allow the creeks
to free flow into the Pend Oreille mainstem along with pumping of water over the dikes. In addition,
increasing the capacity of the pumps inside the dikes, may in some situations alleviate or reduce the
impacts of flooding within the Calispell, Trimble and Cusick Valleys.
4.1.4.1.2.2 Boundary Dam
Boundary Dam (FERC project 2144) is located on river mile (RM) 17 within the northern portion of
WRIA 62, about one mile south of the U.S. - Canadian border and is the last dam on the Pend Oreille
River in WRIA 62. Boundary Dam is owned by the City of Seattle and is operated by Seattle City
Light under an original FERC license that was issued in 1961. This original license expires at the end
of September 2011.
Boundary Dam provides approximately 40% of Seattle's annual energy and is operated for optimum
energy production and system reliability in the northwest, primarily considering power generation
economics, peak load-following and providing operating reserves.
Seattle's FERC license allows Boundary Dam to operate with a maximum drawdown of forty feet,
from a normal full pool of 1990 ft amsl. Typically, the dam operates within a twenty-foot drawdown
from a full pool of 1990 ft amsl. The Boundary Dam reservoir extends to Box Canyon Dam (located
17.5 river miles upstream of Boundary Dam).
Boundary Dam discharges approximately 52,000 cfs at full generation capability at full pool. At
flows between 52,000 cfs and 160,000 cfs the incremental water is discharged via two radial-gated
spillways located on each abutment. Incremental flow from 160,000 cfs to 395,000 cfs is passed via
seven gated sluiceways.
Due to natural river constrictions and the 17.5 mile distance between Boundary Dam and Box Canyon
Dam, operations at Boundary Dam have limited, if any, impact on operations at Box Canyon Dam
during times when flooding upstream of Box Canyon Dam is a concern. Boundary Dam is required
to notify dams downstream of high flows, including Teck Cominco's Waneta Dam (when flows at
WRIA 62 WMP 032305