2005 Urban Water Management Plan - Sonoma County Water ...

Sonoma County Water Agency
2005 Urban Water Management Plan
Page 4-13
According to the WSA (Luhdorff and Scalmanini Consulting Engineers and Winzler and Kelly
Consulting Engineers, 2005), wells in the shallow aquifer (0 to 200 feet) in the Santa Rosa Plain
Subbasin in the WSA study area near Rohnert Park have generally exhibited stable long-term
groundwater level trends from 1975 to the present. In the depth zone where the City of Rohnert
Park has production wells (200 to 600 feet), groundwater elevations have responded more to
pumping than to hydrologic changes. Groundwater levels were generally stable from 1977 to 1981,
declined from 1982 to 1990 when pumping increased, and gradually rose from 1990 to 1997 when
total pumping in the area (including Rohnert Park, Cotati, Sonoma State University, and private,
commercial, and agricultural users) decreased to an average of 8,700 ac-ft/yr for the WSA study area
because of an increased use of Agency water (Winzler and Kelly Consulting Engineers and Luhdorff
and Scalmanini Consulting Engineers, 2005). From 1997 to 2003, water levels were stable and, by
2003, when total pumping in the WSA study area decreased to 7,100 ac-ft/yr, groundwater levels
recovered significantly. The WSA concludes that although groundwater levels decreased from 1982
to 1990 in the southern Santa Rosa Plain, water levels have subsequently recovered in recent years
(Winzler and Kelly Consulting Engineers and Luhdorff and Scalmanini Consulting Engineers, 2005).
In 2003, the City of Rohnert Park made a shift to obtain water primarily from the Agency. This
shift resulted in an increase in groundwater levels in the vicinity of the City of Rohnert Park’s wells
(Winzler and Kelly Consulting Engineers and Luhdorff and Scalmanini Consulting Engineers, 2005).
A groundwater study for the Canon Manor West Subdivision Assessment District (a residential
neighborhood immediately southeast of Rohnert Park) was prepared for the County of Sonoma in
2004 (Todd Engineers, 2004). The County study generally found water level trends similar to those
described in the WSA. The County study found that groundwater levels had declined over an
extensive portion of the southern Santa Rosa Plain between 1950 and the late 1980s, and that
declines in the 1970s and 1980s correlated with ramping up of municipal groundwater pumpage.
Since 1987, groundwater levels generally stabilized and even increased in some wells, indicating a
new equilibrium between recharge and pumpage. The study further found that although the Canon
Manor potential impact is small relative to existing uses, future development of groundwater in the
Rohnert Park area has a reasonable potential of increasing and thus could induce future groundwater
declines (Todd Engineers, 2004).
P:\27000\127280 - Sonoma County Water Agency\UWMPs\SonomaCWA\Tech Reviewed Chapters\SCWA Master 12-08-06.doc