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Driving east on Highway 36, Hely Creek is located
between Flanigan Creek and Grizzly Creek monitoring sites but
is actually a much closer to Flanigan Creek. Hely Creek is a direct
tributary to the main stem Van Duzen River, merging with the main
stem in the lower basin very near to where Highway 36 crosses
the stream. The monitoring site is located in the redwoods with
a sizable buffer zone of hardwoods like Red Alder as well as conifers
within the riparian zone around the stream. The site is situated
40° 30.000' North and 123° 58.480' West, and above the
site is a catchment area with approximately 9.2 miles of stream
network. Elevations in Hely Creek range from 203 feet at its mouth
to over 2,360 feet in the upper reaches, and the monitoring site
is approximately 236 feet in elevation. The watershed is completely
in private ownership with virtually all of the timber holdings
and timber harvests operated by Humboldt Redwood Company (formerly
owned by PALCO). Vegetation is predominantly mixed and evergreen
(Redwood) forest throughout. The catchment area of a monitoring
site is important when considering upslope factors that affect
water quality in the stream. This area represents the true watershed
that lies above the point where water from the stream is sampled,
and from which all rain and sediment are channeled into the stream
down to the point where water is withdrawn for turbidity and suspended
sediment analysis.
Stream discharge is directly proportional to the
size of the catchment area - the greater the area, the more water
is carried by the stream during storm events. The Hely Creek catchment
area is about average in size compared with the other areas within
the project area, and the stream drains an area of approximately
9.3 square kilometers which is equivalent to 3.6 square miles.
During the first year of sampling (HY07) volunteers recorded a
maximum discharge of 194 cubic feet per second (CFS) and an average
discharge of 49 CFS, a maximum turbidity of 1,000 Nephlometric
Units (NTU) and an average turbidity of 100 NTU. In HY08, there
was a maximum discharge of 231 CFS and an average discharge of
42 CFS, a maximum turbidity of 3,628 NTU and an average turbidity
of 258 NTU over the winter sampling season. Over the two seasons
combined (HY07-HY08), the maximum discharge was in HY08 at 231
CFS with an average of 46 CFS, maximum turbidity was also in HY08
at 3,628 NTU with an average of 167 NTU. This translates to an
average of 1,518 tons of suspended sediment per square mile per
year.
Hely Creek runs year round at the upper monitoring
site, and is therefore considered to be a perennial stream (as
opposed to an ephemeral stream, which runs dry in the summer).
Maximum weekly average temperature (MWAT) in the summer of 2007
was 14.55 C, and in 2008 it was 14.22 C. Overall, temperatures
were relatively cool compared to many of the other streams sampled
within the lower basin project area, as Hely Creek, along with
Cummings Creek, typically registered the coldest temperatures
of all the streams in the lower basin. Hely Creek has a road density
of about 7.9 miles of roads per square mile of watershed. As with
all of the catchment areas within the lower basin, this density
of road networks receives a rating of extremely high. In the 17-year
period from 1991 through 2007, the proportion of the area harvested
for timber equaled 84.7%, with clear cutting accounting for 10.4%
of the total watershed area.
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