Analysis of baseflow trends related to upland groundwater pumping for Las Garzas, San Clemente, Potrero, and San Jose Creeks
Thesis (M.S.) Division of Science and Environmental Policy
As Carmel River water supplies have become over-appropriated, new development projects have increasingly utilized groundwater from fractured rock aquifers found in the uplands of the Carmel River watershed. The Santa Lucia Preserve (SLP) is an example of a recent residential development project that has developed its water supply solely from upland fractured rock aquifers. The intensive use of groundwater by the SLP project has generated a great deal of concern because of the potential negative effects this may have by reducing dry season baseflows in Carmel River tributaries and San Jose Creek. Stream baseflows are critical in maintaining quality instream habitat for juvenile steelhead trout during the dry season (a listed species under the Endangered Species Act). This research aims to fill a demand for additional groundwater -- surface water information by analyzing stream baseflows for declining trends associated with groundwater pumping by the SLP. This study used two complimentary multiple-regression model comparison techniques to test for trend at study streams (Las Garzas, San Clemente, Potrero, and San Jose Creek, originating on SLP land) and undeveloped reference streams. A sensitivity analysis was also conducted to test the ability of the analysis methods to detect a simulated reduction in baseflow for records of different lengths (6, 7, 9, and 16 years, representing lengths of available records used in this research). Analysis results provided no substantial evidence to support the hypothesis that declining baseflow trends are occurring in any of the study streams. However, results of the sensitivity analysis revealed that records greater than 9 years are needed to unambiguously detect a trend in baseflow. The sensitivity analysis also revealed that even if a declining baseflow trend is occurring, it cannot be detected using records of 9 years or less. Given that most study streams had records of 9 years or less, declining trends in baseflows cannot presently be ruled out. The methods used in this research will likely be able to produce more useful and unequivocal results on baseflow trends in Carmel River tributaries and San Jose Creek as more streamflow data becomes available in the near future.