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Ridin' Point, by Marcia Armstrong, Siskiyou County Supervisor District 5, 11/2/07

Siskiyou County Groundwater Study

Siskiyou County has jurisdiction over groundwater use within the county. In its water quality action plan for temperature pollution, the North Coast Regional Water Quality Control Board (NCRWQCB) requested that Siskiyou County create a plan to “study the connection between groundwater use on surface flow and beneficial uses, and the impacts of groundwater levels on the health of riparian vegetation in the watershed.” In cooperation with the Scott River Watershed Council water committee and the NCRWQCB, a grant was received to contract with Thomas Harter, Ph.D. of University of California Extension Dept. of Land and Water Management. Harter was given the study goals and series of “hypothesis,” (suggested explanations for an observed state that can be scientifically tested to see if they are true.) He has designed a plan for a study using a series of scientific methods to test the hypothesis and better understand the relationship of groundwater use to surface water in Scott Valley.

Participation in the implementation of the study will be voluntary for the landowner. I have publicly stated that “the train will not leave the station until the landowners are on board.” That means that the study will not get off the ground unless it has the participation necessary to get the data needed. This will involve outreach and education so that landowners understand the study and its implications. If the study is unsuccessful, NCRWQCB has stated that the State Water Resources Control Board may decide to conduct a study. Without voluntary landowner cooperation, it is unknown what form this will take.  

At a recent community meeting, Dr. Harter talked about groundwater. He used the example of a plugged flower pot, first filled with dirt, then with water. The water fills the pores between the dirt. The moist top of the dirt is the “vadose zone.” The saturated area at the bottom of the pot is the “aquifer.” The top of the aquifer is the “water table.” If the soil is clay or silt, there are fewer pores to fill.

The direction water drains depends on water pressure. High pressure or water elevation level generally drains to low. The rate it drains depends upon how porous the soil is. Drainage is fast through sand and slow through clay. A stream gains water is the stream water level is lower than the aquifer. It loses water if the stream is higher than the aquifer. Scott River seems to be a gaining stream.

River flows can be influenced by storm events. Depending on how long the precipitation takes to get to the river, storm events can cause the flow to increase to high stage and then decrease. “Base flow” is the flow established from the steady discharge of groundwater into the stream. The stream is connected with the groundwater immediately beneath the stream in what is called the “hyporheic zone.” The coarse streambed material allows the intermixing of the waters. There is flow in the rivers in summer only if the groundwater levels are higher than the river levels are.

The Scott River groundwater study plan will try to identify the areas where groundwater is upwelling into the stream. It hopes also to determine if changes in water management practices, can change the temperature in the streams. According to Dr. Harter, the average annual discharge in the Scott Valley watershed is 615,000 acre feet of water. This is more than the groundwater basin can hold (400,000 acre ft. – U.S. Geological Survey.) It is interesting to note that the Department of Water Resources has estimated that agriculture uses only 70-90,000 acre ft.

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