Wilson Creek
Driving east on Highway 36 Wilson Creek is located between Yager Creek and Cummings
Creek monitoring sites but is actually just down the road from Yager Creek. Wilson Creek is a
tributary of Yager Creek, which drains into the Van Duzen River in the lower alluvial plain,
where numerous gravel mining operations are visible. The Wilson Creek site is located adjacent
Highway 36 and is in the town of Carlotta. The site is situated 40o 32.200’ North and 124o
03.494’ West, and its catchment area encompasses approximately 5.11 miles of stream network.
Elevations in Wilson Creek range from 98 feet at its mouth to over 1,735 feet in the upper
reaches, and the monitoring site is approximately 118 feet in elevation. The watershed is
completely in private ownership with virtually all timber holdings and timber harvests conducted
by Green Diamond (formerly Simpson Timber Company). Most of these harvest plans were for
clear cuts conducted on very steep southern facing slopes of the watershed that were,
unfortunately, clearly visible from Highway 36. Vegetation is predominantly mixed and
evergreen (Redwood) forest on the hillsides, with abundant pasture and agricultural land in the
lower elevations. 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 rainfall 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sediment are channeled into the stream down to the point where water is withdrawn for turbidity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. Wilson Creek is relatively small
compared to other streams within the project area, and the stream drains an area of
approximately 4.574 square kilometers which is equivalent to 1.766 square miles. During the
first year of sampling (HY07) volunteers recorded a maximum discharge of 97 cubic feet per
second (CFS) and an average discharge of 20 CFS, a maximum turbidity of 709 Nephlometric
Units (NTU) and an average turbidity of 87 NTU. In HY08, there was a maximum discharge of
180 CFS and an average discharge of 27 CFS, a maximum turbidity of 734 NTU and an average
turbidity of 116 NTU over the winter sampling season. Over the two seasons combined (HY07HY08), the maximum discharge was in HY08 at 180 CFS with an average of 24 CFS, maximum
turbidity was also in HY08 at 734 NTU with an average of 94.
Wilson Creek does not run year round and is therefore referred to as an ephemeral stream (as
opposed to a perennial, year round stream). As the stream runs dry in the summer, temperatures
during this time of the year were not measured. Wilson Creek has the highest road density of
any of the catchment areas within the Lower VDR Basin at 10.4 miles of road per square mile of
watershed. 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 42.8%,
with clear cutting accounting for 34.5% of the total watershed area.
Captions to Photos
Wilson1: Approach to Wilson Creek. Photo by P. Trichilo.
Wilson2: Wilson Creek after a mild Spring storm event. Photo by P. Trichilo.
Wilson3: Looking downstream at Wilson Creek. Photo by P. Trichilo.
Wilson4: Wilson Creek monitoring site during the dry season. Photo by P. Trichilo.