Condit Dam Removal Condit Dam Removal - Access Washington

Condit Dam Hydroelectric Project
Final Supplemental EIS
4.3.5 Significant Unavoidable Adverse Impacts
All fish and aquatic macroinvertebrates within the White Salmon River channel downstream
of the dam would likely be killed or displaced by the load of suspended solids released
during dam breaching. While the actions having the effects will be short-term in duration
and will diminish as the level of suspended sediments is reduced over time, the effect on
populations of macroinvertebrates would likely take several years to fully reestablish.
One potential year-class of chum salmon naturally spawned in the White Salmon River
would be lost because of the high concentrations of suspended and deposited sediment and
their inability to access stream habitat above the dam or cofferdam. Potential chum salmon
spawners that enter the Bonneville pool during the fall and winter immediately following
dam removal would spawn in other tributaries of the Columbia River or in the mainstem of
the Columbia River. Potential chum salmon production is not expected to be lost, but chum
salmon smolts that are imprinted to return to the White Salmon River would not be produced.
This impact would be long term (at least several 3- to 5-year generation cycles for chum
salmon), but slight because chum salmon are in the early stages of recolonizing tributaries of
the Bonneville pool through the process of straying from natal spawning grounds below
Bonneville Dam. Because of their poor jumping ability relative to other species of salmon in
the White Salmon River, adult chum salmon may not be able to pass a fall located at RM 2.6
on the mainstem of the White Salmon River to utilize spawning habitat located upstream of
Condit Dam. In addition, it is likely that the spawning substrate necessary for their
reproduction will be impaired by fine sediment during the second year (and not fully
recovered for 1 to 3 years after that). New gravel recruited from upstream may not reach the
lower 2.6 miles during that time, and what gravel does reach the lower portion of the stream
will likely be heavily embedded with fine sediments. The result would be essentially a
potential loss of several naturally produced year-classes of chum salmon smolts that have
been imprinted to return to the White Salmon River. The number of documented spawning
adult chum salmon in the White Salmon River is very low and likely represents strays from a
population below Bonneville Dam that have the potential of eventually recolonizing the
White Salmon River basin and reestablishing a viable population. The loss of these stray
chum salmon during the removal of Condit Dam and recovery of spawning gravels in the
lower White Salmon River would not be expected to have a measurable effect on the number
of potential chum salmon colonists entering the White Salmon River and other Columbia
River tributaries above Bonneville Dam. The increase in available spawning habitat in the
White Salmon River after natural channel building processes remove deposited fine
sediments should increase the potential for a successful recolonization of the White River
basin by chum salmon. The removal of Condit Dam may also open available chum salmon
spawning habitat above the dam, but chum salmon characteristically spawn in the lower
reaches of high-gradient rivers and may not migrate past the fall at RM 2.6 or upstream
above the Condit Dam site. Large returns of chum salmon can cause competition for
spawning gravel and cause chum salmon to migrate farther upstream than normal. However,
even if none of the falls present in the river below Condit dam or under reservoir sediments is
a barrier to chum salmon migration, this is unlikely to occur at the present levels of chum
salmon occurrence in the White Salmon River.
4.3-29