Project Effectiveness Monitoring
Kenusky Cr and Gunners Lake fork (Trib B)
Tributaries of East Fk Nehalem
Summary of results
April 2011
Prepared by Bio-Surveys,LLC.
Contact: Steve Trask
strask@casco.net
Introduction
Project effectiveness monitoring was conducted for Kenusky Cr and the Gunners lake Fk
of the East Fk Nehalem (Trib B of EF Nehalem) in 2009 / 2010 and 2010 / 2011. A 20
percent snorkel survey of pool habitats was conducted during summer flow regimes and
then repeated at the end of winter and just prior to smolt migrations to determine the over
winter retention rates of summer coho parr to the smolt stage. The intent was to compare
over winter retention rates in unique stream segments before and after log placement
projects designed to increase aquatic habitat complexity and expand floodplain
interactions that created low velocity habitats for the provision of winter habitat. The
hypothesis was that the provision of this supplemental habitat complexity (full spanning
log structures) would result in higher over winter retention rates post treatment when
compared to pre treatment inventories.
The treatments in Kenusky Cr were planned in two separate phases:
1) RM 0 to RM 1.6 was treated in the summer of 2010 just after the summer snorkel
inventory (includes 1 year of pre project inventory).
2) RM 1.6 to RM 3.8 was treated in the summer of 2009 just after the summer snorkel
inventory (did not include a pre project inventory).
The treatment in Trib B will be conducted as a separate phase and all inventories in Trib
B to date (2 years) have been to develop pre treatment estimates of over winter retention.
Results
Table 1 exhibits the numerical results of this comparison expressed as a percentage of
summer parr remaining in each stream segment after being exposed to the majority of
winter flows and just prior to smolting. Large increases in over winter retention (174%)
were observed post treatment in segment 1 when compared to its pre treatment inventory.
A large decrease in abundance ( - 93%) was observed in segment 2 when compared to
each other (both post log placement inventories).
Great variability was observed in segment 3 (Gunners Lake Fk) between the two pre
treatment inventories (8.3% and 28.4% retention) where the reach did not receive a log
structure treatment.
Discussion
These results are confusing and suggest that confounding variables exist within the
parameters of this study that have likely influenced the differential responses observed
between the three study segments. These variables include the radical differences in
winter flow patterns that exist between the 2010 and the 2011 winters. 2011 exhibited
very high peak flows with extended temporal duration. This flow pattern was not
observed for the winter of 2010 and may have influence how over wintering juvenile
coho move through a stream in response to the frequency and duration of high flows. The
fact that segment 1 (the lowest in the system with the lowest average gradient) exhibited
exceptional increases in over winter retention when compared to its pre project inventory
suggests that the lower reach may have benefited from emigration out of the higher
gradients in segment 2. This suggests that the placement of full spanning log structures
over a broad lineal distribution that encompasses variable gradients and floodplain
characteristics may be important for achieving the objective of retaining juvenile coho
through an unpredictable range of winter flow regimes. Log structure placement that
succeeds in treating only a small portion of a sub basin may be incapable of providing
winter refugia consistently through all winter flow regimes.
In the case of the radical variation observed in over winter retention rates for the two pre
treatment inventories of Trib B (8.3% and 28.4%), the differences in winter flow
dynamics likely played a significant role (no treatments occurred between inventories). It
is likely that juvenile salmonids utilizing the low velocity habitats that result from the
interaction between LWD and floodplains are in relatively constant horizontal movement
in response to changes in stream elevations driven by run off flows. Flows increase,
juveniles shift horizontally up onto floodplain habitats, flows decrease, and they are
transitioning back into the active channel. Each transition back into the active channel
(flood flow frequency) exposes them to high velocity flows that may cause them to bump
downstream into the next available low velocity niche. Sustained high flows (as observed
in the winter of 2011) may provide much greater potential for retaining winter rearing
populations in low velocity floodplain habitats because of fewer oscillations in stream
elevation that force them back into the active winter channel.
The same pattern observed for Trib B, where over winter retention rates increased in
2011 with no physical change to the habitat was also observed in 2011 for the long term
monitoring project on Green River in the Alsea basin. In this study, the post wood
treatment over winter retention rates for coho remained very constant for 6 consecutive
years (between 50% and 65%). In 2011, these rates jumped radically to 77% of the
summer parr population still present in the system just prior to smolting (March1).