Recently, the Scott River
Watershed Council (SRWC) gave an update on its progress in developing a water balance for
the Scott River system. A water balance takes into account inputs from precipitation -
rain and snow. It examines how that materializes into surface water flows, groundwater
storage and snowpack storage to be delivered later though snowmelt. It also looks at
outputs - diversions of surface water and pumping of groundwater and how that affects
hydrology/the water system. It creates a model over space and time to help us understand
how the entire system functions.
The water balance will be helpful in improving water management
practices, implementing the water leasing or Water Trust concept, developing a dry year
water plan and in identifying stream reaches with the highest potential for habitat
restoration.
In 1998, the Siskiyou Resource Conservation District (RCD) began to
compile all available water data for the system. This included flow readings from 1941 to
present at the USGS gauge below Fort Jones. In 2002, the California Department of Water
Resources and the U.S. Fish and Wildlife Service installed additional river flow gauges
at: East Fork Scott, South Fork Scott, McConaughy, Sugar Creek, Shackleford , Mill,
Kidder, French and Etna Creeks. In addition to two existing U.S. Forest Service gauges, in
2003 the RCD installed 10 rain gauges.
From 2003-2005, a rough spreadsheet model of the hydrology of the
system or water balance was developed by Mike Deas Ph.D, which continues to be refined as
more detail is known.
In 2005, a draft run-off forecast model was created. This model has
taken into account all snowpack and rainfall data for the past 50 years. (See DWR Bulletin
120.) The run-off forecast considers precipitation and groundwater conditions of the
previous year, variations in precipitation over time and space throughout the system, and
changes in land and water use patterns. The model predicts the volume of water that will
flow through the Fort Jones gauge from April 1-October 1 based on April 1 snowpack and
precipitation conditions. Refinements are underway to forecast at the subwatershed level.
A water year type index has also been created categorizing years as
wet, dry or normal and looking at the combined effects of a two year span. Keeping in mind
that the forecast is limited to conditions as they were prior to April 1 of the current
year, this information can be used to describe the water supply conditions anticipated in
a given year.
DWR has periodically taken measurements from 3 wells over a 50 year
period. In 2006 an additional voluntary groundwater study piece was added. This study
selected 33 wells located in a grid over the central portion of Scott Valley to measure
the static water level of each well throughout the year. It was determined from the first
year’s measurements that all wells do not react similarly. During the year, wells in the main part of the
valley near the river followed the river’s hydrograph – dropping 3-4 feet during
the summer. They began to inch up in October after the first frost, but did not really
begin to recover until December. A few wells in other areas did not see the same recharge.
It is anticipated that at least 10 years or more of readings will need to be taken to
capture most of the water year and runoff variations so that we have a better idea of how
groundwater responds to various water conditions. |
