Scott River
Temperature Pollution: Several years ago, the Scott River was listed as polluted for
not meeting minimum temperature standards for cold water fisheries (salmon and steelhead.)
Assessments by the North Coast Regional Water Quality Control Board (NCRWQCB) determined
that additional shade would cool the water. They also determined that it was likely that
cold water from groundwater interaction with river surface water cooled the river. NCRWQCB
issued a five year “waiver” of individual permit requirements and issued a TMDL
(Total maximum Daily Load) “action plan” allowing for a voluntary effort to go
forward to address sources of pollution. A recent NCRWQCB meeting discussed how actions
have proceeded during the past five years.
For decades, the Siskiyou Resource Conservation District (RCD) has
worked with landowners to fence 90% of the mainstem Scott River where livestock are
present, (80% of tributaries and mainstem together.) 92 of 110 active water diversions
have fish screens, (100% of diversions where coho salmon are present.) In addition, many
landowners signed up for the Conservation Reserve Program (CRP.) This provided a rental
payment for land taken out of production, fenced and livestock excluded from grazing
vegetation. It has been a very successful program which encouraged riparian conservation.
(However, the state Natural Resource Conservation Service/NRCS has recently decided that
local landowners are ineligible for the program and they are cancelling all the lease
contracts.)
In the early twentieth century, Yuba type dredges ran in the Scott River
system. In 1930s, the Army Corps of Engineers channelized and rip rapped sections of the
Scott and in 1955 and 1964, large floods removed streamside vegetation. There has been a
significant attempt to re-establish riparian vegetation in areas along the Scott where it
had been removed. More than 300 acres of planting was subsequently done by the Soil
Conservation Service and RCD. An analysis on the success and failure of plantings was done
and an additional 35 acres were recently planted along the Scott in areas where it was
thought there would be a likelihood of success. Another 20 acres is planned.
The RCD has also worked on what is called a “water balance.”
This is basically a spread sheet model of water inputs and outputs. It includes annual
precipitation, snow pack, runoff and streamflow data.
A year or so before the Scott River TMDL action plan, local water
users had started a community static well study. Dr. Thomas Harter from U.C. Davis had
been selected to collect and compile the data. During the years, an average of 36 wells
have participated. The TMDL directed the RCD, Siskiyou
County and other partners to work with Dr. Harter on a study plan, which was completed. A
computerized groundwater model was also funded and the first phase has been completed.
The model is made up of 150 foot square cells. Each cell is
individually characterized by factors that will affect the flow of groundwater. This
includes the depth to bedrock; the type of soil (water moves quickly in porous soil); and
the slope of the land. It was assumed that broad hydrological areas had the same soil
type. Rough assumptions were made that everyone was growing the same alfalfa crop so the
evapo-transpiration factors would all be the same. Records are not kept on groundwater
use, so that was estimated by using gross irrigation allotments under the Scott River
adjudication and spreading them evenly over a river section.
The model has produced contour lines that indicate the direction that
water flows down the hills to the river. It is able to roughly approximate trends in
recharge that compare with actual experience. It shows that certain drought conditions can
create losing sections of the river where water can spread out away from the river
creating dry or pooled river bottom. Other areas are gaining, where groundwater flows into
the stream
The newly appointed Scott River Groundwater Advisory Committee will
be looking at the model to see if they can improve it with local knowledge. It could be used to identify potential pilot
projects such as recharging an upland area with winter flow to extend flow further into
the summer season or thinning upland vegetation to see if that reduces evaporation of snow
from heavy tree canopy in the winter and produces additional summer flows.
A Phase 2 model is expected to be completed this winter and released
next spring. Dr. Harter indicated that in his opinion the Scott Valley is not in an
overdraft situation. The system produces a little over 600,000 acre ft./year. Actual water
consumption from crop evapo-transpiration (plant use and evaporation) is only 120,000
– 140,000 AF. |
