Central Coast

Groundwater Accounting Platform — Real-World Impact from DWR Investment in Open, Scalable SGMA Tools

Environmental Defense Fund (EDF) | November 3rd, 2025

Groundwater and Remotely Sensed Phenology Reveal Vulnerability of Riparian Trees to Drought

Wiley | October 27th, 2025

The increasing frequency and magnitude of climatic extremes are altering water availability in dryland ecosystems globally. However, riparian vulnerability to hydroclimat

The increasing frequency and magnitude of climatic extremes are altering water availability in dryland ecosystems globally. However, riparian vulnerability to hydroclimate whiplash remains poorly understood. Here, we examined how riparian willow, cottonwood, and valley oak trees respond to groundwater fluctuations and drought through their water use patterns and phenology. To this end, we combined time-series analysis of in situ, high-frequency groundwater monitoring with high-resolution PlanetScope satellite imagery of a drought-prone and relatively pristine watershed in California (Chalone Creek, Pinnacles National Park). We found that flow regime dictates the potential for trees to access groundwater, while the identity of tree species determines the timing and magnitude of their use. Machine-learning models revealed that at intermittent sites groundwater depth predominantly controlled vegetation greenness, represented by the Normalized Difference Vegetation Index (NDVI). In contrast, variation in photoperiod length dominated at the perennial site where water was more reliably available. During the severe 2020–2022 drought, all species experienced reduced greenness, but phenological responses differed by flow regime. While the start of the season was delayed across all sites, trees at intermittent reaches exhibited a substantially earlier end of season during drought, resulting in growing seasons shortened by as much as 37 days. These phenological shifts vastly exceed those documented across aridity classifications in global datasets from satellite observations, ground-based monitoring networks, and experimental precipitation manipulations. Although riparian trees in drylands have been shaped by exposure to drought over evolutionary timescales, our findings show that trees in these intermittent systems may be operating close to critical groundwater thresholds, rendering them particularly vulnerable to increasingly long and severe droughts.

Groundwater Conditions Report Water Year 2021

California Department of Water Resources (DWR) | March 15th, 2022

Groundwater in California

Public Policy Institute of California (PPIC) | June 6th, 2024

Groundwater level observations in 250,000 coastal US wells reveal scope of potential seawater intrusion

Nature Portfolio (Springer Nature) | June 26th, 2020

Seawater intrusion into coastal aquifers can increase groundwater salinity beyond potable levels, endangering access to freshwater for millions of people. Seawater intrus

Seawater intrusion into coastal aquifers can increase groundwater salinity beyond potable levels, endangering access to freshwater for millions of people. Seawater intrusion is particularly likely where water tables lie below sea level, but can also arise from groundwater pumping in some coastal aquifers with water tables above sea level. Nevertheless, no nation-wide, observation-based assessment of the scope of potential seawater intrusion exists. Here we compile and analyze ~250,000 coastal groundwater-level observations made since the year 2000 in the contiguous United States. We show that the majority of observed groundwater levels lie below sea level along more than 15% of the contiguous coastline. We conclude that landward hydraulic gradients characterize a substantial fraction of the East Coast (>18%) and Gulf Coast (>17%), and also parts of the West Coast where groundwater pumping is high. Sea level rise, coastal land subsidence, and increasing water demands will exacerbate the threat of seawater intrusion.

Groundwater Management Plan Goleta Groundwater Basin

Goleta Water District (GWD) | May 11th, 2010

Goleta Water District (“GWD”) and La Cumbre Mutual Water Company (“La Cumbre”), the purveyors of groundwater in the Goleta Groundwater Basin, joined in developing

Goleta Water District (“GWD”) and La Cumbre Mutual Water Company (“La Cumbre”), the purveyors of groundwater in the Goleta Groundwater Basin, joined in developing a Groundwater Management Plan (“Plan”) for the basin. This Plan reiterates current adjudication and voter-passed components of groundwater management, addresses groundwater issues, adopts Basin Management Objectives, outlines management strategies for the basin, and recommends future tasks and timelines associated with these tasks.

Groundwater Management Principles and Strategies to Monitor, Analyze and Minimize Impacts to Drinking Water Wells: A Framework for State Action to Support Drought Resilient Communities

California Department of Water Resources (DWR) | December 15th, 2021

This framework was developed in response to support drinking water access for groundwater-dependent communities.

This framework was developed in response to support drinking water access for groundwater-dependent communities.

Groundwater Quality in the Santa Barbara Coastal Plain, California

U.S. Geological Survey (USGS) | August 1st, 2016

Groundwater provides more than 40 percent of California’s drinking water. To protect this vital resource, the State of California established the Groundwater Ambient Mo

Groundwater provides more than 40 percent of California’s drinking water. To protect this vital resource, the State of California established the Groundwater Ambient Monitoring and Assessment (GAMA) Program. The Priority Basin Project of the GAMA Program provides a comprehensive assessment of the State’s groundwater quality and increases public access to groundwater-quality information. The Santa Barbara Coastal Plain is one of the study units. The Santa Barbara study unit covers more than 48 square miles in the Transverse and Selected Peninsular Ranges hydrogeologic province and includes parts of Santa Barbara and Ventura Counties (Davis and Kulongoski, 2016). The study unit is flanked by the Santa Ynez Mountains on the north and the Pacific Ocean on the south. The study unit consists of five coastal plain groundwater basins (California Department of Water Resources, 2003). These five groundwater basins are Goleta, Foothill, Santa Barbara, Carpinteria, and Montecito, from west to east.

Groundwater Quality in the South Coast Interior Basins, California

U.S. Geological Survey (USGS) | May 14th, 2014

The South Coast Interior Basins (SCI) study unit covers approximately 653 square miles and consists of the Livermore, Gilroy-Hollister, Cuyama Valley, Castac Lake Valley,

The South Coast Interior Basins (SCI) study unit covers approximately 653 square miles and consists of the Livermore, Gilroy-Hollister, Cuyama Valley, Castac Lake Valley, Cuddy Canyon Valley, Cuddy Ranch Area, Cuddy Valley, and Mil Potrero groundwater basins (California Department of Water Resources, 2003). These basins were grouped into three study areas based on geography: Livermore (LIV), Gilroy (GIL), and Cuyama (CUY) (Mathany and others, 2009). Average annual precipitation across the study unit varies among the three study areas—from more than 20 inches (in.) along the northwest margin of the LIV study area to less than 8 in. in the northern parts of the CUY study area. The study areas are drained by the Arroyo de la Laguna canal in LIV, the Pájaro River and the San Benito River in GIL, and the Cuyama River in CUY. The primary aquifer system consists of Plio-Pleistocene sedimentary formations, Tertiary to Holocene-age alluvial sedimentary sequences, and unconfined Holocene- age and Pleistoceneage alluvium. The primary aquifer system is defined as those parts of the aquifers corresponding to the perforated intervals of the public-supply wells listed in the California Department of Public Health (CDPH) database. Public-supply wells in the study unit are typically drilled to depths between 200 and 600 feet, consist of solid casing from the land surface to a depth of about 50 to 350 feet, and are perforated below the solid casing. Water quality in the primary aquifer system may differ from that in the shallower and deeper parts of the aquifer system. Land use within 500-meter buffer areas around the wells in the study unit is approximately 44 percent (%) agricultural, 29% urban, and 27% natural. Agricultural lands are mostly orchards, row crops, vineyards, or pastures. The largest urban areas are the cities of Livermore and Gilroy. Recharge to groundwater basins occurs as infiltration of spring and streamflow, direct infiltration of precipitation and irrigation, subsurface inflow, and engineered recharge (percolation ponds and river regulation). The primary sources of groundwater discharge are water pumped for irrigation and municipal supply, discharge to rivers and streams, and evaporation.

Groundwater quality near an oil field in a stream-dominated recharge setting, California, USA

PLOS | February 12th, 2026

Alluvial valley aquifers are important sources of water supply in many areas but effects of co-located oil and gas development on these resources have not been widely rep

Alluvial valley aquifers are important sources of water supply in many areas but effects of co-located oil and gas development on these resources have not been widely reported, especially in settings where recharge is dominated by stream infiltration. Interpreting the presence of geochemical indicators in the context of hydrology, geology, and other factors provides a more complete understanding of the relations between groundwater and sources of oil-field fluids and aids in identifying risks associated with oil and gas development. Groundwater and Salinas River water samples were collected in an alluvial valley near the San Ardo Oil Field in Monterey County, California and analyzed for a wide range of dissolved chemical, gas, and isotopic constituents to determine if oil-field fluids (water and gas from oil-producing and non-producing zones) have mixed with fresh groundwater used for supply. Hydraulic gradients, age-dating tracers, and other geochemical indicators showed that recharge from the Salinas River has the potential to dilute oil-field fluids that might migrate or seep into the aquifer. Groundwater and Salinas River water collected downgradient of the San Ardo Oil Field showed little or no evidence of mixing with oil-field fluids. Some samples within the oil field contained trace amounts of hydrocarbons or elevated temperatures, indicating that any potential effects from oil-field activities are minor or have been diluted by recharge from the Salinas River. The two samples with the most geochemical evidence of potential mixing with oil-field fluids (SP-18 and GW-17) were collected west of or along the Los Lobos fault, where naturally occurring hydrocarbons are near the land surface. Those samples were also collected near active or inactive oil-field wells, and so anthropogenic activities and pathways could not be ruled out as a cause of trace detections of hydrocarbons and elevated temperatures in the aquifer.