Nearshore Habitat Use by Juvenile Chinook Salmon in Lentic ...

CHAPTER 6. USE OF NONNATAL TRIBUTARIES
Introduction and Methods
The lower reaches of several nonnatal tributaries were surveyed in 2002. Juvenile
Chinook salmon commonly used the tributary delta areas within the lake but they were
only found in the lotic environments of a few tributaries (Tabor et al. 2004b). Nonnatal
tributaries that had a high abundance of juvenile Chinook salmon were small- to mediumsized
streams, which had a low gradient and were close to the mouth of the natal system.
In 2003 and 2004, we surveyed Johns Creek and Culvert Creek to collect additional
information on the use of nonnatal tributaries. Johns Creek was surveyed to determine if
the tributary is used extensively from year to year and to collect some information on
Chinook salmon habitat use that could be used to design restoration projects of other
nonnatal tributaries. For example, the City of Seattle has proposed to daylight the mouth
and lower 100 m of Mapes Creek (currently in a culvert and enters the lake a few meters
below the lake surface), yet little information is available on what type of habitat
conditions would be best for Chinook salmon. In 2004, we also surveyed Culvert Creek
because it is also a small, low-gradient creek that is close to the mouth of the Cedar
River; however, the creek is located entirely within a culvert. The creek is located
approximately 0.65 km north of Johns Creek.
Johns Creek.—Johns Creek is located in Gene Coulon Park in the southeast
corner of Lake Washington, 1.5 km from the mouth of the Cedar River. Typical winter
streamflow is about 0.8 cfs (Tabor et al. 2004b). Juvenile Chinook salmon use the lower
460 m of the stream (Tabor et al. 2004b). Upstream of this, there are two equal-sized
streams that appear to be completely in culverts.
In 2003 and 2004, we repeatedly surveyed the same 260-m long reach that was
surveyed in 2002 (Tabor et al. 2004b). The downstream end of the study reach was the
lake. There was no developed delta unlike other tributaries to Lake Washington. The
upstream end was a large culvert near the entrance to Gene Coulon Park. The study
reach was delineated into habitat units, which were either classified as a convergence
pool, scour pool, glide, or riffle. The convergence pool was the lower 61 to 136 m of the
index reach that the water level was directly influenced by the lake level (Figure 31). As
the lake rose from February to June, the convergence pool grew progressively larger.
Scour pools were other pools upstream of the convergence pool that had a maximum
depth > 0.35 m. Glides or shallow pools were other slow water habitats that had a
maximum depth < 0.35 m (Figure 31). The maximum pool depth of 0.35 m was adapted
from Timber-Fish-Wildlife (TFW) stream ambient monitoring methodology (Pleus et al.
1999). For a stream the size of Johns Creek (5- to- 10-m bankfull stream width), the
authors recommended pools have a residual pool depth of 0.25 m (residual pool depth =
max. pool depth–outlet pool depth). Because the outlet depth of pools was
approximately 0.1 m deep, we used a maximum pool depth as > 0.35 m. Riffles were
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