Short‐lived pause in Central California subsidence after heavy winter precipitation of 2017

American Association for the Advancement of Science (AAAS) | August 29th, 2018

The Tulare Basin in Central California is a site of intensive agricultural activity and extraction of groundwater, with pronounced ground subsidence and degrada

The Tulare Basin in Central California is a site of intensive agricultural activity and extraction of groundwater, with pronounced ground subsidence and degradation of water resources over the past century. Spatially extensive observations of ground displacements from satellite-based remote sensing allow us to infer the response of the aquifer system to changes in usage and to marked recharge events such as the heavy winter rainfall in 2017. Radar imagery from the Sentinel-1a/b satellites (November 2014 to October 2017) illuminates secular and seasonal trends modulated by changes in withdrawal rates and the magnitude of winter precipitation. Despite the increased precipitation in early 2017 that led to a marked decrease, or in some areas, reversal, of subsidence rates, subsidence returned to rates observed during the drought within a matter of months.

Simulation of ground-water/surface-water fow in the Santa Clara-Calleguas ground-water basin, Ventura County, California

U.S. Geological Survey (USGS) | July 17th, 2003

Groundwater is the main source of water in the Santa Clara–Calleguas ground-water basin that covers about 310 square miles in Ventura County, California. A steady incre

Groundwater is the main source of water in the Santa Clara–Calleguas ground-water basin that covers about 310 square miles in Ventura County, California. A steady increase in the demand for surface- and ground-water resources since the late 1800s has resulted in streamflow depletion and ground-water overdraft. This steady increase in water use has resulted in seawater intrusion, inter-aquifer flow, land subsidence, and ground-water contamination. The Santa Clara–Calleguas Basin consists of multiple aquifers that are grouped into upper- and lower-aquifer systems. The upper-aquifer system includes the Shallow, Oxnard, and Mugu aquifers. The lower-aquifer system includes the upper and lower Hueneme, Fox Canyon, and Grimes Canyon aquifers. The layered aquifer systems are each bounded below by regional unconformities that are overlain by extensive basal coarse-grained layers that are the major pathways for ground-water production from wells and related seawater intrusion. The aquifer systems are bounded below and along mountain fronts by consolidated bedrock that forms a relatively impermeable boundary to ground-water flow. Numerous faults act as additional exterior and interior boundaries to ground-water flow. The aquifer systems extend offshore where they crop out along the edge of the submarine shelf and within the coastal submarine canyons. Submarine canyons have dissected these regional aquifers, providing a hydraulic connection to the ocean through the submarine outcrops of the aquifer systems. Coastal landward flow (seawater intrusion) occurs within both the upper- and lower-aquifer systems. A numerical ground-water flow model of the Santa Clara–Calleguas Basin was developed by the U.S. Geological Survey to better define the geohydrologic framework of the regional ground-water flow system and to help analyze the major problems affecting water-resources management of a typical coastal aquifer system. Construction of the Santa Clara–Calleguas Basin model required the compilation of geographic, geologic, and hydrologic data and estimation of hydraulic properties and flows. The model was calibrated to historical surface-water and ground-water flow for the period 1891–1993. Sources of water to the regional ground-water flow system are natural and artificial recharge, coastal landward flow from the ocean (seawater intrusion), storage in the coarse-grained beds, and water from compaction of fine-grained beds (aquitards). Inflows used in the regional flow model simulation include streamflows routed through the major rivers and tributaries; infiltration of mountain-front runoff and infiltration of precipitation on bedrock outcrops and on valley floors; and artificial ground-water recharge of diverted streamflow, irrigation return flow, and treated sewage effluent. Most natural recharge occurs through infiltration (losses) of streamflow within the major rivers and tributaries and the numerous arroyos that drain the mountain fronts of the basin. Total simulated natural recharge was about 114,100 acre-feet per year (acre-ft/yr) for 1984–93: 27,800 acre-ft/yr of mountain-front and bedrock recharge, 24,100 acre-ft/yr of valley-floor recharge, and 62,200 acre-ft/yr of net streamflow recharge. Artificial recharge (spreading of diverted streamflow, irrigation return, and sewage effluent) is a major source of ground-water replenishment. During the 1984–93 simulation period, the average rate of artificial recharge at the spreading grounds was about 54,400 acre-ft/yr, 13 percent less than the simulated natural recharge rate for streamflow infiltration within the major rivers and tributaries. Estimated recharge from infiltration of irrigation return flow on the valley floors averaged about 51,000 acre-ft/yr, and treated sewage effluent averaged about 9,000 acre-ft/yr. Artificial recharge as streamflow diversion to the spreading grounds has occurred since 1929, and treated-sewage effluent has been discharged to stream channels since 1930. Under predevelopment conditions, the largest discharge from the ground-water system was outflow as coastal seaward flow and evapotranspiration. Pumpage of ground water from thousands of water-supply wells has diminished these outflows and is now the largest outflow from the ground-water flow system. The distribution of pumpage for 1984–93 indicates that most of the pumpage occurs in the Oxnard Plain subareas (37 percent) and in the upper Santa Clara River Valley subareas (37 percent). The total average simulated pumpage was about 247,000 acre-ft/yr (59 percent); of which about 146,000 acre-ft/yr was from the Fox Canyon Groundwater Management Agency (FGMA) subareas and 101,000 acre-ft/yr (41 percent) from the non-FGMA subareas. Of the total 1984–93 pumpage, 46 percent was contributed by natural recharge, 22 percent was contributed by artificial recharge from diverted streamflow, 20 percent was contributed by irrigation return flow, 4 percent was contributed from sewage-effluent infiltration, 6 percent was contributed from storage depletion, and 2 percent was contributed from coastal landward flow (seawater intrusion). Seawater intrusion was first suspected in 1931 when water levels were below sea level in a large part of the Oxnard Plain. The simulation of regional ground-water flow indicated that coastal landward flow (seawater intrusion) began in 1927 and continued to the end of the period of simulation (1993). During wet periods or periods of reduced demand for ground water, the direction of coastal flow in the upper-aquifer system reverses from landward to seaward. During the 1984–93 period, the simulated total net seaward flow was 9,500 acre-feet in the upper-aquifer system, which is considerably less than that simulated for predevelopment conditions. During the same period, total simulated landward flow in the lower-aquifer system was 64,200 acre-feet. Water-level declines in the basin have induced land subsidence that was first measured in 1939 and have resulted in as much as 2.7 feet land subsidence in the southern part of the Oxnard Plain. The model simulated a total of 3 feet of land subsidence in the southern part of the Oxnard Plain and as much as 5 feet in the Las Posas Valley subbasins. Model simulations indicate that most of the land subsidence occurred after the drought of the late 1920s and during the agricultural expansion of the 1950s and 1960s. The results also indicate that subsidence occurred primarily in the upper-aquifer system prior to 1959, but in the lower-aquifer system between 1959–93 owing to an increase in pumpage from the lower-aquifer system. The calibrated ground-water flow model was used to assess future ground-water conditions based on proposed water-supply projects in the existing management plan for the Santa Clara–Calleguas ground-water basin. All the projections of the proposed water-supply projects in the existing management plan have reduced pumpage in the FGMA areas which resulted in a reduction but not an elimination of storage depletion and related coastal landward flow (seawater intrusion) and subsidence, a reduction in streamflow recharge, and an increase in coastal seaward flow and underflow to adjacent subareas from the Oxnard Plain. A comparison of management simulations based on historical inflows and a spectral estimate of inflows shows increased coastal landward flow (seawater intrusion), storage depletion, and increased land subsidence due to a drought projected earlier in the spectral estimate of inflows than in the historical inflows. The spectral estimate probably provides a smoother and more realistic transition between historical and future climatic conditions. The model also was used to simulate potential alternative water-supply projects in the Santa Clara–Calleguas ground-water basin. These seven alternative water-supply projects were proposed to help manage the effects of increasing demand and variable supply on seawater intrusion, subsidence, increased withdrawal from storage, and vertical and lateral flow between subareas and aquifers systems. Stopping pumpage primarily in the lower-aquifer system in the South Oxnard Plain subarea had the largest effect on reducing coastal landward flow (seawater intrusion) of all the potential cases evaluated. Shifting pumpage from the lower- to the upper-aquifer system in the South Oxnard Plain subarea yielded the largest combined effect on coastal flow with a reduction of coastal landward flow in the lower-aquifer system and coastal seaward flow from the upper-aquifer system. A seawater-barrier injection project stopped coastal landward flow (seawater intrusion) in the upper-aquifer system but also resulted in large quantities of coastal seaward flow. The recharge of water in Happy Camp Canyon resulted in water-level rises that were above land surface (not feasible) in the East Las Posas Valley subarea but in no significant changes in hydrologic conditions in other parts of the basin.

State of the Estuary 2019 Update

San Francisco Estuary Partnership (SFEP) | October 22nd, 2019

The San Francisco Estuary is a large and diverse system. Hundreds of miles of coastline stretch from the wide valleys of the Sacramento and San Joaquin Rivers to the stee

The San Francisco Estuary is a large and diverse system. Hundreds of miles of coastline stretch from the wide valleys of the Sacramento and San Joaquin Rivers to the steep headlands of the Golden Gate, with vast agricultural fields in the Delta and urbanized shorelines in Silicon Valley and many of the region’s cities. The complexity and scale of this system means it can take years to detect and assess changes. This interim State of the Estuary Report checks in on a few indicators of health and explores where the assessment should head over time. In the four years since the 2015 State of the Estuary Report, two issues have emerged as critical to how we assess the health of the estuarine ecosystem at the heart of the Bay Area and the Delta. First, the health of the Estuary and of the people who live near it and depend on it are inextricably linked. We need a healthy Bay and Delta to protect our shorelines from sea level rise, help keep our waters clean, provide food and habitat for fish and wildlife, and give people a place to enjoy nature. We also need to think more about human communities as we assess the health of natural communities. This focus means addressing environmental injustices that are deeply embedded in our culture and patterns of development. The second critical issue to emerge is the need for a greater focus on landscape resilience—how well the Bay and the Delta are equipped to respond to change—so that people and wildlife can thrive as climate change progresses. Taking these two ideas together, this report focuses on the nexus of social and ecological resilience as we look toward the future. The first section of the Report updates indicators of ecological health that span the entire extent of the San Francisco Estuary (Bay and Delta). Recent data show continued progress along the trajectories of the past decade. Tidal marsh restoration is proceeding at a brisk pace in the Bay and gaining traction in the Delta, while urban water conservation continues to meet mandated benchmarks, even during the drought. On the other hand, flows through the Estuary and across its floodplains continue to be well below levels that could increase and restore ecosystem health. Freshwater flows are a lynchpin of ecosystem processes that sustain physical habitats, fuel the food web, and regulate water quality. Creative approaches to using and re-using fresh water for environmental purposes are needed. Long-term trend analysis shows that fish communities in the Bay are declining. This analysis scores an index of 10 attributes of a healthy fish community. The index focuses on fish in offshore areas, and may not capture benefits to fish from near-shore wetland restoration projects. Despite this slow decline, fish communities in the saltier parts of the Estuary remain in good condition, while those in the brackish and freshwater areas are in poor condition. The next section of the report discusses three emerging indicators of Estuary health, offering options for how to assess resilience in future reports. Here, for the first time, the resilience of the Estuary’s shores is evaluated through the lens of subsidence and nature-based features. Elevation relative to sea level is a basic currency that must be tracked as the Pacific Ocean rises into the Estuary. The potential for the Estuary shore to be resilient to climate change and continue to provide benefits to people is related to how much of the shore zone is nature-based. The final emerging indicator, urban green space, is a first attempt to assess how access to nature is distributed across more and less advantaged communities. More work is needed to finalize all these emerging indicators before they can be included in any future quantitative assessment of the State of the Estuary. These emerging and updated indicators will help focus efforts to restore the Estuary’s health. In addition to continuing the successful aspects of restoration and conservation that this report describes, we need more investment in creative ways to use and restore flows for environmental health, to expand and build resilient shorelines and to weave considerations of social equity more strongly into efforts to improve environmental health. - J. Letitia Grenier, Lead Scientist

Subsidence (2004-2009) in and near lakebeds of the Mojave River and Morongo groundwater basins, southwest Mojave Desert, California

U.S. Geological Survey (USGS) | July 1st, 2014

Subsidence: A critical challenge to Friant-Kern canal water deliveries

Friant Water Authority | January 17th, 2018

The Friant Water Authority is facing a critical challenge right now - one that has reduced our ability to deliver water to many Friant Division Contractor’s

The Friant Water Authority is facing a critical challenge right now - one that has reduced our ability to deliver water to many Friant Division Contractor’s by nearly 60%. It is a challenge that must be met today if we are to ensure our long-term commitment to delivering high-quality, dependable water, in the amounts needed by farmers and cities in the San Joaquin Valley.

Sustained groundwater loss in California's Central Valley exacerbated by intense drought periods

American Geophysical Union (AGU) | July 4th, 2018

The accelerated rate of decline in groundwater levels across California’s Central Valley resultsfrom overdrafting and low rates of natural recharge and is exacerbated b

The accelerated rate of decline in groundwater levels across California’s Central Valley resultsfrom overdrafting and low rates of natural recharge and is exacerbated by droughts. The lack of observations with an adequate spatiotemporal resolution to constrain the evolution of groundwater resources poses severe challenges to water management efforts. Here we present SAR interferometric measurements of high-resolution vertical land motion across the valley, revealing multiscale patterns of aquifer hydrogeological properties and groundwater storage change. Investigating the depletion and degradation of the aquifer-system during 2007–2010, when the entire valley experienced a severe drought, we find that ~2% of total aquifer-system storage was permanently lost, owing to irreversible compaction of the system. Over this period, the seasonal groundwater storage change amplitude of10.11 ± 2.5 km3modulates a long-term groundwater storage decline of 21.32 ± 7.2 km3. Estimates for subbasins show more complex patterns, most likely associated with local hydrogeology, recharge, demand, and underground flow. Presented measurements of aquifer-system compaction provide a more complete understanding of groundwater dynamics and can potentially be used to improve water security.

Tectonic evolution of the Salton Sea inferred from seismic reflection data

Nature Portfolio (Springer Nature) | July 26th, 2009

Oblique extension across strike-slip faults causes subsidence and leads to the formation of pull-apart basins such as the Salton Sea in southern California. The f

Oblique extension across strike-slip faults causes subsidence and leads to the formation of pull-apart basins such as the Salton Sea in southern California. The formation of these basins has generally been studied using laboratory experiments or numerical models. Here we combine seismic reflection data and geological observations from the Salton Sea to understand the evolution of this nascent pull-apart basin. Our data reveal the presence of a northeast-trending hinge zone that separates the sea into northern and southern sub-basins. Differential subsidence (>10 mm yr−1) in the southern sub-basin suggests the existence of northwest-dipping basin-bounding faults near the southern shoreline, which may control the spatial distribution of young volcanism. Rotated and truncated strata north of the hinge zone suggest that the onset of extension associated with this pull-apart basin began after ∼0.5 million years ago. We suggest that slip is partitioned spatially and temporally into vertical and horizontal domains in the Salton Sea. In contrast to previous models based on historical seismicity patterns, the rapid subsidence and fault architecture that we document in the southern part of the sea are consistent with experimental models for pull-apart basins.

Tentative Ruling, Friant Water Authority vs. Eastern Tule Groundwater Sustainability Agency

Superior Court of California, County of Tulare | June 25th, 2024

Time-varying land subsidence detected by radar altimetry: California, Taiwan and north China

Nature Portfolio (Springer Nature) | June 21st, 2016

Contemporary applications of radar altimetry include sea-level rise, ocean circulation, marine gravity, and icesheet elevation change. Unlike InSAR and GNSS, which are wi

Contemporary applications of radar altimetry include sea-level rise, ocean circulation, marine gravity, and icesheet elevation change. Unlike InSAR and GNSS, which are widely used to map surface deformation, altimetry is neither reliant on highly temporally-correlated ground features nor as limited by the available spatial coverage, and can provide long-term temporal subsidence monitoring capability. Here we use multi-mission radar altimetry with an approximately 23 year data-span to quantify land subsidence in cropland areas. Subsidence rates from TOPEX/POSEIDON, JASON-1, ENVISAT, and JASON-2 during 1992–2015 show time-varying trends with respect to displacement over time in California’s San Joaquin Valley and central Taiwan, possibly related to changes in land use, climatic conditions (drought) and regulatory measures affecting groundwater use. Near Hanford, California, subsidence rates reach 18 cm yr with a cumulative subsidence of 206 cm, which potentially could adversely affect operations of the planned California High-Speed Rail. The maximum subsidence rate in central Taiwan is 8 cm yr. Radar altimetry also reveals time-varying subsidence in the North China Plain consistent with the declines of groundwater storage and existing water infrastructure detected by the Gravity Recovery and Climate Experiment (GRACE) satellites, with rates reaching 20 cm yr and cumulative subsidence as much as 155 cm.

Tracking California’s sinking coast from space: Implications for relative sea-level rise

American Association for the Advancement of Science (AAAS) | July 31st, 2020

Coastal vertical land motion affects projections of sea-level rise, and subsidence exacerbates flooding hazards. Along the ~1350-km California coastline, record

Coastal vertical land motion affects projections of sea-level rise, and subsidence exacerbates flooding hazards. Along the ~1350-km California coastline, records of high-resolution vertical land motion rates are scarce due to sparse instrumentation, and hazards to coastal communities are underestimated. Here, we considered a ~100-km-wide swath of land along California’s coast and performed a multitemporal interferometric synthetic aperture radar (InSAR) analysis of large datasets, obtaining estimates of vertical land motion rates for California’s entire coast at ~100-m dimensions—a ~1000-fold resolution improvement to the previous record. We estimate between 4.3 million and 8.7 million people in California’s coastal communities, including 460,000 to 805,000 in San Francisco, 8000 to 2,300,00 in Los Angeles, and 2,000,000 to 2,300,000 in San Diego, are exposed to subsidence. The unprecedented detail and submillimeter accuracy resolved in our vertical land motion dataset can transform the analysis of natural and anthropogenic changes in relative sea-level and associated hazards.