Recent studies and computer modeling indicate groundwater pumping in the Santa Rosa Plain watershed has caused an average annual imbalance between the total amount of water flowing into and out of the basin of approximately minus 4% (-3,300 acre feet) per year between 1976 and 2010. This imbalance can lead to declines in groundwater levels and reduce the water flowing in creeks and streams. Careful monitoring and management of groundwater and surface water is needed to ensure a sustainable, reliable supply of water in our wells, creeks and streams.
Groundwater levels in the Santa Rosa Plain’s shallow aquifer are relatively stable over time. Water levels range from close to ground surface near the Laguna de Santa Rosa to about 15 to 30 feet below ground surface along the eastern basin boundary and 50 feet below the surface near the southern end of the Santa Rosa Plain.
In intermediate and deeper wells in the southern Santa Rosa Plain, groundwater levels declined in the late 1970s and 1980s. The decline peaked in the early 1990s and began to recover in the early 2000s. This recovery coincided with reduced groundwater pumping due to water conservation and increased use of water from the Russian River.
Groundwater quality is generally high in the Santa Rosa Plain subbasin, but naturally occurring elements such as iron, manganese, boron, and arsenic are widely variable in groundwater and can pose problems in some areas. Areas in southern Santa Rosa Plain also exhibit increasing chloride concentrations.
Groundwater sources and usage
The 78,720-acre Santa Rosa Plain Groundwater subbasin is located within the larger 167,680-acre Santa Rosa Plain watershed (generally corresponding to the Laguna de Santa Rosa and Mark West Creek watersheds). It is estimated that 13.7 billion gallons of groundwater were used in the Santa Rosa Plain between 2004 and 2012, representing nearly 50% of the basin’s water supply. On average, about 96% of the water used is replenished annually.