Project Effectiveness Monitoring
Kenusky Cr
Tributary of the East Fk Nehalem
Summary of results
April 2013
Introduction
Project effectiveness monitoring in the form of summer / winter comparisons of
coho production have been conducted for Kenusky Cr, a tributary of the East Fk
Nehalem, for 4 consecutive years (2009 / 2010, 2010 / 2011, 2011 / 2012, 2012 / 2013).
A 20 percent snorkel survey of pool habitats was conducted during summer flow regimes
and then repeated at the end of winter just prior to smolt migrations to determine the over
winter retention rates of summer coho parr to the smolt stage within a treated stream
segment.
The intent was to compare over winter retention rates in unique stream segments
before and after log placement projects that were designed to increase aquatic habitat
complexity and expand floodplain interaction. The hypothesis being that the additional
low velocity habitats provided by increased floodplain connectivity would boost the
abundance of viable winter habitat and retain more coho through winter flows to the
smolt stage. To test the hypothesis, the abundance of coho was compared between
summer and winter, with the expectation that the addition of full spanning log structures
would result in higher over winter retention rates post treatment when compared to pre
treatment inventories. The treatments were implemented in two separate phases.
1) RM 0 to RM 1.6 was treated in the summer of 2010 just after the summer snorkel
inventory.
2) RM 1.6 to RM 3.8 was treated in the summer of 2009 just after the summer snorkel
inventory.
Treatment 1 (above) included 1 year of pre project inventory. Treatment 2 did not
include a pre project inventory.
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. Although there was still an increase in abundance (33%) during the
second post treatment year when compared to the pre treatment, the increase was
distinctly less significant.
Table 1
EF Nehalem Tributaries Pre - Post Project Effectiveness Monitoring
This analysis examines the differences in the over winter retention rates of coho between pre and post log structure placements in unique stream segments.
The following 3 reaches will be monitored separately over time because they either differ in morphology or treatment.
These estimates of over winter retention of juvenile coho should be utilized to specifically evaluate reach scale project effectiveness and quantify the increase
in smolt production directly associated with LWD placement
Year
2009 (Summer)
2010 (Winter)
Over Winter
Kenusky Cr to RM 1.6 Retention
Pop.estimate
*8,506
1,224
Pre 14.4%
Kenusky Cr above RM
Over Winter
1.6 (Treatment Reach)
Retention
Pop.estimate
*4,716
1,378
Post 29.2%
Trib B EF Nehalem
(Untreated Reach)
Pop.estimate
*5,940
492
Over Winter
Retention
Pre 8.3%
2010 (Summer)
2011 (Winter)
*3,618
1,427
Post 39.4%
*4,320
652
Post 15.1%
*2,184
621
Pre 28.4%
2011 (Summer)
2012 (Winter)
*7462
1,428
Post 19.1%
*5388
1,292
Post 24 %
*7032
1,335
Pre 19 %
2012 (Summer)
2013 (Winter)
*3,882
1,056
Post 27.2%
*5,958
973
Post 16.3%
Not Surveyed
Not Surveyed
* These values include the contributions of Tribs A, B, C and D on Kenusky Cr and Trib B1 and B2 of Trib B on EF Nehalem with the assumption
that summer juveniles drop out of these steep tributaries during winter flow regimes and attempt to winter rear in mainstem habitats.
All population estimates have been expanded utilizing the following electrofish calibration factors developed by ODFW:
N x 1.20 for summer estimates of all habitat complexities
N x 1.23 for winter nocturnal estimates in low and medium complexity habitats (complexity 1-3)
N x 1.89 for winter nocturnal estimates in high complexity habitats (complexity 4-5)
A broad range of over winter retention rates was observed for the 4 years
inventoried in Treatment reach #2 (29.2%, 15.1%, 24 % and 16.3%). There was no pre
project inventory conducted for this reach and therefore we are unable to compare pre
and post log placement values. The most revealing conclusion from this reach is the high
degree of variability in over winter retention rates between years and its implications.
Functioning as somewhat of a local control reach, Trib B of the EF Nehalem
(Gunners Lake Fk) also exhibited broad variability (8.3%, 28.4% and 19% retention)
even without a log structure treatment.
Discussion
Kenusky Cr
These results are confusing and suggest that complex variables exist within the
parameters of this study that have influenced the differential responses observed between
years. The most significant uncontrolled variable is the radical differences in winter flow
patterns that exist between winters. 2011 exhibited very high peak flows with extended
duration. This flow pattern was not observed for the winter of 2010 or 2013 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 it received non volitional migrants out of the higher
gradients in segment 2. This indicates that the placement of full spanning log structures
over an extensive lineal distribution of stream corridor to encompass variable gradients
and floodplain characteristics is 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.
Although winter habitats exist in varied forms and locations, it is uncommon for
any individual site to be capable of providing a continuum of low velocity habitat
throughout the complete range of flow levels that will be encountered through the course
of a full winter (the most common exception to this statement would be for beaver
ponds). Therefore, what we know is that juveniles pulse through a stream system with
each flow event. Fewer flow events result in higher retention. We also have observed
that extremely high flow events occurring early in the winter result in lower retention
rates (Cruiser Cr Final Report). This type of flow pattern was present in 2013 where the
largest event of the winter occurred early in the season. The radical differential between
low summer flows and a peak winter event occurring early winter does not facilitate the
gradual dispersal of parr to nearby low velocity habitat. Instead large percentages of the
rearing population are whisked out of headwater tributaries into mainstem corridors
virtually overnight.
The abundance of high quality winter habitat in an upstream reach can also affect
the abundance of juveniles in lower stream reaches. The capacity of low velocity refugia
existing within a complex stream reach slows the progression of juveniles through the
reach during multiple flow events. This issue was likely a contributing factor to the
extensive variability observed between the over winter retention rates of juvenile
salmonids between 2010 and 2013. During the winter of 2012 at approximately RM 3.0
there was a winter stable beaver pond that had not been present during the 2011 summer
survey. This pond exhibited a massive area of high quality, low velocity winter habitat.
The pond was approximately the size of a football field at 300 ft long and 150 ft wide.
There were hundreds if not thousands of coho in this one habitat unit that functioned as a
habitat sink that continually accumulated migrants pulsing out of upper Kenusky Cr all
winter long. The beaver pond had inundated a vast salmonberry flat and fish were
abundant but unconsolidated by flow, making it impossible to quantify with the nocturnal
snorkeling methodology. In addition, this was the only winter stable beaver pond in the
system but obviously winter rearing a disproportionately high number of coho. The
presence of this high quality habitat unit in year 3 only suggests that over winter retention
rates for Kenusky Cr were likely much higher in 2012 than documented in this report.
The juveniles retained in this high quality habitat unit would have been available to seed
other structure complexes downstream if they had not found a final winter resting place
within this beaver pond. During the winter of 2013, this beaver dam was not present and
there were no other dams within the scope of the survey.
If we combine the separate reaches and simply observe the over winter retention
rates for all of Kenusky Cr for each of the 4 surveyed years (Table 2) the values suggest
that no discernable differences in over winter retention rates exist between the first pre
treatment year and the 3 post treatment years.
Table 2
Year
2009 / 2010
2010 / 2011
2011 / 2012
2012 / 2013
Summer Population
13,222
7,938
12,850
9,840
Winter Population
2,602
2,079
2,720
2,029
Over Winter Retention
19.7% Pre
26.2% Post
21.2% Post
20.6% Post
We would suggest however that the 21.2% over winter retention rate observed in
2011 / 2012 would likely be significantly higher due to the unquantified abundance of
juvenile coho observed in the beaver pond referred to above during that winter alone.
If we look at the individual reach breakdown contained in Table 1, it does appear
that higher over winter retention rates were achieved on the reach scale for the section
from the mouth to RM 1.6. This is the only reach where a pre treatment value was
available for comparing post treatment survival rates. Given that pre treatment retention
to smolt was only 14.4% and the mean over winter retention rate for the 3 post project
years was 28.6% a significant 99% increase in abundance was observed on the reach
scale for the duration of the project.
It appears what we are observing is that the winter rearing capacity of Kenusky Cr
was historically highly variable (similar to what was observed in the Gunners Lake
control, table 1) and dependant on the severity of winter flows when measured in height,
duration, frequency and timing (early or late). With the placement of LWD structures, the
winter carrying capacity of the system has been stabilized to a mean over winter retention
rate of somewhere near 22.7% of the summer population. It is likely that a lower mean
over winter retention rate would have been observed (similar to the 18.6 mean value
observed in the untreated Gunners Lake Fork) if a large wood treatment had not been
implemented in the Kenusky Cr subbasin. It is also likely that the existing LWD
structures will continue to mature in terms of complexity and their capacity to provide
low velocity winter habitat will simultaneously increase to boost over winter retention
rates.
Based on snorkel observations of fish abundance, sites which provide the highest
quality winter habitat occur where continuous low velocity habitat exists through all
winter flow levels (beaver ponds or large dam pool habitats created by well seated log
jam complexes). This occurs when site specific channel and floodplain interactions
complement each other to provide low velocity shelter at different flow levels. This is the
primary feature that distinguishes highly functional winter habitat units from most other
potential winter habitats. These sites are rare within a stream reach and tend to hold
juvenile salmonids at a disproportionately higher density.