Condit Dam Removal Condit Dam Removal - Access Washington

Condit Dam Hydroelectric Project
Final Supplemental EIS
spans and are relatively slow growing and would take more time to recolonize new
substrates.
As part of the Settlement Agreement, sediment deposited at the in lieu site could be removed
by the Tribes with mitigation money for maintenance in order to ensure boat access. Any
such actions would be undertaken at the discretion of the Tribes and would be the subject of
separate permits and review. Channel dredging and deepening at the in lieu site might reduce
the total area of spawning gravel created at the mouth of the White Salmon River after dam
breaching and might therefore have a long-term impact on available spawning habitat for
Chinook and chum salmon.
Dam and Appurtenance Removal
Impacts associated with dam and appurtenance removal are primarily associated with the use
of haul roads, staging area, and disposal sites. These impacts have been described above.
When the surge tank tailrace is filled in for safety reasons, BMPs would be used to avoid the
release of fine sediments or concrete particles into the river channel. Impacts to fish from
spills and leaks of fuel and hazardous chemicals would be similar to those described above.
As described above under sediment transport, the cofferdam could create a barrier to the
passage of winter-run steelhead to usable spawning gravel above RM 5.0 during the first year
following dam breaching. Blasting during cofferdam removal would create short-term
effects by killing any fish in the vicinity of the blast through hydrostatic shock. If the
cofferdam is removed soon after the reservoir is drained and while the sediment levels
exclude winter-run steelhead, then blasting would have little or no effect. If the cofferdam
cannot be removed until later, when both winter-run and summer-run fish may be stopped
just below it, then blasting would have major mortalities unless the fish were trapped and
removed or the cofferdam was removed mechanically without blasting.
Tributary Deltas
After dam breaching, Little Buck Creek and Mill Creek would not be able to down-cut
through the cobble and large gravel deposited in the deltas created where the streams enter
Northwestern Lake until major storm events transport the material to the White Salmon River
or the material is removed during post dam removal sediment management. The likely result
would be a fish barrier at Mill Creek that would probably prevent upstream migration of fish
from the river. Until Mill Creek down-cuts to its original channel and access to migratory
salmonids is restored, a short- or long-term adverse impact would occur to fluvial and
anadromous salmonids. The channel could be modified mechanically to remove the barrier,
and PacifiCorp has agreed to do that once at the time equipment is in the vicinity for
sediment management work, after the reservoir is drained.
At Mill Creek, the residual delta sediments, if left to wait for storm removal, might provide a
relatively large slug of sediment that could produce safety or habitat concerns later. The
sediments at tributary deltas will be evaluated as part of the evaluation of unstable sediments
following draining of the reservoir.
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