Scott Valley groundwater

There has been growing pressure to better understand the Scott River’s groundwater table and how it is recharged. A few weeks ago, Mark Horney and Bill Waggoner of the Natural Resource Conservation Service (NRCS) Watershed Team presented a modest proposal for a voluntary groundwater monitoring program. The strategy protects individual privacy, but would produce information of use to landowners as their management tool. It is estimated that such a study could be accomplished without public funds for a minimal amount of money.
 
In his presentation, Horney indicated that there the aquifer exists below soil deposits that can range from a few feet to several hundred feet in depth. Horney said that it is simplistic to think of the aquifer as a ridge to ridge bathtub holding sediment and water. The depth of bedrock – the rock layer through which water cannot pass, can vary from a few feet in Callahan to several hundred feet in the lower valley. There are also various densities of soil type. For instance, water can pass through gravelly soil quickly, while clay layers are hard to pass through. There may even be underground rock ridges that serve as a barrier to water movement.
 
In the 1940s and 50s, Seymour Mack surveyed the characteristics of the aquifer by monitoring 105 wells. He determined that there were 8-9 different geologic formations in Scott Valley that have contributed to the sedimentary mix in different areas and the rate of recharge. There are nine different drainages. To add more complexity, there are also ancient riverbeds beneath the surface that have filled with sediment.
 
Horney stated that several factors influence how fast groundwater will move: (1) The type of soil material through which it passes; (2) The gradient or slope; (3) The porosity of the material (amount of space between particles); and (4) The permeability (connection of those spaces.)
 
According to Bill Waggoner, groundwater is particularly important to Scott Valley. Nationally, about 50% of domestic water supplies are from groundwater. In the Scott, it is closer to 90%. Summer accretion of groundwater is also important to summer river flows. Monitoring a grid of about 30 wells on a purely voluntary basis on the Scott Valley floor could produce useful baseline data to answer questions for each local area such as: (1) The relationship of groundwater storage to discharge and recharge; (2) The evidence of multiple aquifer strata or layers; (3) Seasonal variation in groundwater levels; and (4) Long-term trends in groundwater levels. The wells could be existing irrigation wells that are not currently in production (not-pumping for at least three days.) Waggoner stated that it will take at least a decade or two to capture a true picture of groundwater for each area.
 
For more information, please contact the Scott River Watershed Council at 468-2487.