Mitigation for the Construction and Operation of Libby Dam

project initiation. We did not monitor fish abundance within the Grave Creek Phase I
Restoration Project area. However, we did monitor the benthic macroinvertebrate
community within the project area, but none of the seven metrics selected a priori
differed significantly approximately 1 year after the project was completed. Although we
expected the macroinvertebrates to respond relatively quickly to the changes in the
physical environment, our monitoring in Grave and Libby creeks either did not change or
shifted in a direction that was more consistent with a disturbed environment. We
attribute these changes to the disturbance activities and abundance of fine sediment
within the project areas that was present from construction in the fall to the spring
freshet. We believe that the first year following the initial construction period is the
period of time that channel stability is most vulnerable. Much of the bed material can
potentially become mobile until the pavement layer establishes following the initial
bankfull discharge in the stream after project construction (D. Rosgen, personal
communication). We will continue to monitor macroinvertebrates at both the Grave and
Libby creek project to determine if these trends reverse as channel disturbances recover
over time. Although we did monitor fish abundance within the Libby Creek project area,
we did not expect to be able to detect a response from the fish community within the first
year after project construction due to the longer lifecycle of fish compared to
macroinvertebrates. We will continue to annually monitor the fish community at this site
in order to assess the long-term response to the restoration activities.
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