2010-04-07 HEX# 10-002 Exhibit KPage 1 of 4
Hylebos Creek Tributary 16A Habitat Assessment
March 30, 2010
Overview
• Tributary 16A originates in the parking lot of the Federal Way Mall and
flows south on the west side of 1-5 through a series of residential
developments, wooded wetlands, and light industrial areas.
• In the Triangle project area, 16A crosses underneath the 1-5/SR18
cloverleaf interchange and then through a culvert underneath 1-5 before
joining the mainstem Hylebos Creek just south of SR161 (Figure 1).
Habitat quality
• The stream is severely altered from original condition.
o It used to flow into the West Fork of Hylebos Creek, but has been
diverted to East Hylebos Creek.
o Hydrology is driven chiefly by runoff and precipitation, and is
extremely flashy, alternating between wet and dry during a very
short time frame. The stream often runs dry even in wintertime and
is usually dry from April to October of most years (Figure 2).
o Habitat upstream of the project area alternates between heavily
urbanized residential areas, light industrial areas (such as
warehouses) and wooded wetlands.
• Trib 16A could provide juvenile rearing and foraging areas if water were
present. However, given the flashy nature of the stream, if fish were able
to access it they would likely be subject to stranding in residual pools
during low or intermittent flows (Figure 3).
Fish use
• Fall Chinook, fall chum, winter steelhead, coho, and cutthroat trout have
all been documented in the East Fork of the Hylebos, but there is no
documented anadromous fish use of Tributary 16A north of SR161, over
3000 feet downstream of the 1-5 culvert and outside the Triangle Project
area.
■ Only one fathead minnow was observed upstream of SR161 (downstream
of the Triangle project area) during a two-year electrofishing investigation
conducted by King County.
• A year -long survey of the tributary by King County Surface Water
Management noted the ephemeral nature of the stream and absence of
salmonids in the upper portion of the creek.
■ No macroinvertebrates were observed during a 2005 stream survey, and
the intermittent nature of the stream likely does not support enough
aquatic invertebrates for fish.
• The stream often runs dry in the vicinity of the SR161 crossing
downstream of 1-5, limiting the ability of salmonids or other species to
access upstream habitat. Stream hydrology essentially serves as a
barrier to fish.
EXHIBIT K
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