The Clean Water Act and California’s
Porter-Cologne Water Quality Act required the North Coast Regional Water Quality Control
Board (NCRWQCB) to identify all the “beneficial uses” of the Scott River and its
tributaries. Among uses of the Scott are irrigation, recreation, mining, and cold water
fisheries.
NCRWQCB also looked at the water quality needs of these beneficial
uses to see if they were being met. The Board determined that the needs of cold water
fisheries (salmon and steelhead) were not being met for temperature and sediment.
Accordingly, the Scott River was listed as “impaired” on a national 303(d) list
for these two types of pollution.
The NCRWCB is now in the process of studying the two factors to set
Total Maximum Daily Loads (TMDLs) for allowable human-caused sediment and temperature
change by the close of 2005. A Technical Advisory Group (TAG) is working with Bryan
McFadin, David Leland and Don Coates of the NCRWQCB to
come up with meaningful ways to determine and measure natural background levels of
sediment and water temperature, as well as increases in those levels that could be caused
by both historic and current human management activities. This study portion should be
completed by the fall of 2004.
When it is determined that current human activities are responsible
for boosting levels over “tolerance thresholds” for cold water fish, the NCWQCB
will recommend management practices to reduce sediment and temperature pollutants.
Because the system is “dynamic,” (moving and changing,)
water temperature will be modeled using a computer program called “Heat Source”
- http://www.heatsource.info/
The program uses inputs from all factors important to the temperature
of a stream. At various times last year, data was collected from 21 locations on the
mainstem Scott by the Siskiyou RCD and U.S. Forest Service. Data included factors such as
air temperature, humidity, wind speed, flow, and river channel geometry. Although the data
is still raw, there were some interesting results.
(As a note of reference, lethal temperatures for coho and steelhead
are 25°C. There is 20% reduced growth at 20°C and optimal temperatures around 14.5°C.
On the Mattole River system, surveyors generally did not see coho is areas where
temperature exceeded 16.7°C.)
McFadin determined the hottest or maximum of the weekly average
temperatures occurred around July 22-30, 2003. A thermal infrared (TIR) fly-over was done
on July 25. The Scott is also a “gaining
river” where flows increase from top to bottom. Inflows from springs, subsurface flow
and tributaries seem to cause some localized temperature variability.
Starting with the top of the system, temperatures in the East Fork of
the Scott are relatively warm and the South Fork relatively cool. At the confluence around
river mile 55 from the mouth, temperatures were 20.4° C or
68.7°F. By the end of the dredger tailings, temperature measured 24.9°C, decreasing
slightly around Fay Lane and climbing to 25.2°C by Sweazey’s bridge (river mile 42.)
Temperatures continued to climb to a high of 28.4°C at Kidder Creek, then began to start
declining to 26.0°C at the USGS gage. The Scott River canyon had a slight cooling effect
to 24.1°C at Kelsey Creek, but had climbed again to 26.3 °C at river mile .5 –
Roxbury bridge.
McFadin indicated that other temperature TMDLs had concentrated on
increasing riparian shade in order to moderate water temperatures. UC Davis will be
working on a mapping of vegetation, topography (elevations) and sun path to look at shade
potential. The width of the river and high
summer air temperatures will probably govern potential effects.
Local rancher, Dr. John Menke pointed out that the large gap between
fish needs and river temperatures is probably not correctable by shade. (The tall trees of
the canyon did not have that great an effect.) It would appear that the study will most
probably show that “thermal refugia,,” pockets of cool water from pools with
springs and up the tributaries,) are the few historic areas where coho and steelhead have
been able to over-summer.
U.S. Forest Service maps on sediment have proven unreliable. NCRWQCB
is now working with Fruit Growers Supply and Timber Products on the possibility of using
their road inventory data for the upland slopes. Plans are to also conduct random sampling
of the various types of sedimentary deposits by dominant land uses. Efforts will be made
to screen out natural sources of sediment and historic sources that commenced more than 20
years ago.
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