WRIA 62 WMP 032305 - Washington State Department of Ecology

March, 2005 -47- 023-1289-003.3040
1) VARQ results in slightly lower flows in the Pend Oreille River below Albeni Falls Dam during
March and April when flooding at Cusick can be a problem; and, 2) flows in the Pend Oreille River
below Albeni Falls Dam are slightly higher in June under VARQ but the frequency of exceeding the
flood warning threshold of 100,000 is essentially the same for VARQ as the Standard flood control
plan. This study can be viewed on the internet at http://137.77.133.1/pn/programs/VARQ/links.html.
Implementation of VARQ does not generally change Hungry Horse reservoir levels unless water
volume is between 80-100% of a typical water year (otherwise VARQ elevations are consistent with
Standard Flood Control elevations). In terms of flooding in WRIA 62, the biggest concern is that
Hungry Horse reservoir is held high in the winter in order to achieve flood control levels by April 10.
If there is unusually high precipitation in March, it is likely that Hungry Horse would be required to
spill water (to maintain flood control levels) at the same time, therefore exacerbating the impact of the
local spring melt and runoff occurring in WRIA 62. The combination of Hungry Horse spilling and
high local runoff increases the potential for flooding to occur in the Calispell Valley and other low
lying areas along the Pend Oreille River.
4.1.4.1.1.2 Albeni Falls Dam
Albeni Falls Dam is a multiple purpose water resource project owned by the U.S. Government and
regulated under authorization from Congress by the Army Corps of Engineers (ACOE) Northwestern
Division and Seattle District. Any change in operations that cause river flows and elevations outside
authorized limits (see Table 4-3 and the bullets below) would require authorization from Congress.
The project is located in Idaho on the Pend Oreille River at river mile 90.1, about 2.5 miles upstream
and east of the City of Newport and the upstream boundary of WRIA 62. The project is operated to
regulate Lake Pend Oreille considering upstream flood control (primarily for the City of Sandpoint)
and also for recreation, fish and wildlife conservation and power generation. Flood control benefits
are realized upstream of the dam by lowering the elevation of Lake Pend Oreille during peak floods
(between 80,000 and 220,000 cfs). The ACOE is mandated to operate Albeni Falls Dam in a manner
that does not make flooding any worse downstream than it would be under natural conditions.
The inflows to Pend Oreille Lake are largely determined by the outflow of Avista’s Cabinet Gorge
Dam upstream of Albeni Falls. The outflows from Albeni Falls Dam are managed to maintain lake
elevations. Project operating limits (resulting in useable storage of about 1,155,100 AF) range from a
minimum authorized lake elevation of 2,049.7 ft amsl to normal full pool at 2,062.5 ft amsl.
However there is no scheduled or anticipated plan to draft the lake below the minimum normal pool
elevation of 2,051 ft amsl (resulting in actual useable storage of 1,042,700 AF). Typically summer
pool is held at 2062.5 feet amsl to just after Labor Day and winter pool is between 2051 and 2055 feet
depending on fish needs. Spring fill rate is generally determined by inflows and the natural
constriction at Dover.
Table 4-3 summarizes the Lake Pend Oreille Elevation Rule Curves. In addition to the rule curves,
the following elevation change and discharge limits are imposed on operations at Albeni Falls Dam:
WRIA 62 WMP 032305
• Maximum Lake Pend Oreille elevation change of 0.4 ft per day above elevations of
2,058 ft amsl.
• Maximum Lake Pend Oreille elevation change of 0.5 ft per day below elevations of
2,058 ft amsl.
• Minimum instantaneous discharge of 4,000 cfs.