Scott River Water Balance 

May 11, 2007

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. 

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Source:  http://users.sisqtel.net/armstrng/opinion051107.htm