Regional land subsidence accompanying groundwater extraction

Hydrogeology Journal (Springer) | August 26th, 2011

The extraction of groundwater can generate land subsidence by causing the compaction of susceptible aquifer systems, typically unconsolidated alluvial or basin-fill aquif

The extraction of groundwater can generate land subsidence by causing the compaction of susceptible aquifer systems, typically unconsolidated alluvial or basin-fill aquifer systems comprising aquifers and aquitards. Various ground-based and remotely sensed methods are used to measure and map subsidence. Many areas of subsidence caused by groundwater pumping have been identified and monitored, and corrective measures to slow or halt subsidence have been devised. Two principal means are used to mitigate subsidence caused by groundwater withdrawal—reduction of groundwater withdrawal, and artificial recharge. Analysis and simulation of aquifer-system compaction follow from the basic relations between head, stress, compressibility, and groundwater flow and are addressed primarily using two approaches—one based on conventional groundwater flow theory and one based on linear poroelasticity theory. Research and development to improve the assessment and analysis of aquifer-system compaction, the accompanying subsidence and potential ground ruptures are needed in the topic areas of the hydromechanical behavior of aquitards, the role of horizontal deformation, the application of differential synthetic aperture radar interferometry, and the regional-scale simulation of coupled groundwater flow and aquifer-system deformation to support resource management and hazard mitigation measures.

Regional patterns in hydrologic response, a new three-component metric for hydrograph analysis and implications for ecohydrology, Northwest Volcanic Aquifer Study Area, USA

Journal of Hydrology (Elsevier) | June 12th, 2020

Spatial patterns of hydrologic response were examined for the Northwest Volcanic Aquifer Study Area (NVASA). The utility of established hydrograph-separation methods for

Spatial patterns of hydrologic response were examined for the Northwest Volcanic Aquifer Study Area (NVASA). The utility of established hydrograph-separation methods for assessing hydrologic response in permeable volcanic terranes was assessed and a new three-component metric for hydrograph analysis was developed. The new metric, which partitions streamflow into subcomponents defined by the timescales of hydrologic response (e.g., fast-runoff, intermediate-interflow and slow-baseflow), was used to gain a fundamental understanding of the regional hydrology, investigate sub-regional differences, influencing factors, and ecohydrological implications. The combined effects of NVASA’s physiography, climate and geology create a strongly coupled surface-groundwater system that produces copious baseflow and limited quantities of runoff and interflow. Patterns of hydrologic response are influenced by the type and rate of precipitation and permeability of the underlying geology. Under variable precipitation conditions the hydrologic response of volcanic terranes with similar permeability and subsurface-storage capacity can be significantly different. From a water management and ecohydrology perspective, understanding regional patterns of hydrologic response and sub-regional differences is fundamental. Results indicate that minimum-flow methods provide the most conservative estimate of baseflow and may be the most robust for filtering out snowmelt bias in baseflow estimates. Baseflow contributes ∼75% of the perennial streamflow across the NVASA and represents a critical component of the regional water supply that provides critical cold-water habitat.

Regional water table (1998) and ground-water-level changes in the Mojave River and the Morongo ground-water basins, San Bernardino County, California

U.S. Geological Survey (USGS) | July 1st, 2000

Relative risk of groundwater-quality degradation near California (USA) oil fields estimated from 3H, 14C, and 4He

Applied Geochemistry (Elsevier) | June 5th, 2021

 Relative risks of groundwater-quality degradation near selected California oil fields are estimated by examining spatial and temporal patterns in chemical and isotopic

 Relative risks of groundwater-quality degradation near selected California oil fields are estimated by examining spatial and temporal patterns in chemical and isotopic data in the context of groundwater-age categories defined by tritium and carbon-14. In the Coastal basins, western San Joaquin Valley (SJV), and eastern SJV; 82, 76, and 0% of samples are premodern (pre-1953 recharge), respectively; and 3, 0, and 31% are modern (recharged during or after 1953), respectively. Carbon-14 and helium-4 data indicate most premodern samples are 1000 to 10,000 (33%) or >10,000 (50%) years old. Organic chemicals that could be associated with deeper hydrocarbon reservoirs (e.g. thermogenic gases and benzene) occur most frequently in premodern groundwater, suggesting premodern groundwater has a higher risk of degradation from upward migration of hydrocarbons than modern and mixed-age groundwater. Low sulfate concentrations in some premodern groundwater containing high thermogenic-methane concentrations (>28 mg/L) indicate methane attenuation associated with sulfate reduction can be limited in premodern groundwater. The more common occurrence of manufactured compounds, like tetrachloroethene, in modern and mixed-age groundwater than in premodern groundwater indicates modern and mixed-age groundwater has a higher risk of degradation from land-surface sources than premodern groundwater. Time-series data for chloride in groundwater affected by disposal of oil-field water in unlined ponds indicate some modern and mixed-age groundwater are susceptible to chemical migration within 2–3 km of surface sources. Timescales for diluting chloride concentrations in groundwater with fresh recharge once disposal ponds are decommissioned are shorter in mixed-age groundwater with large fractions of modern water (9–14 years in one example) than in mixed-age groundwater with large fractions of premodern water (no evidence of dilution after 12 years of monitoring in one example). The presence of predominantly premodern groundwater in the Coastal basins and western SJV indicates these areas have relatively high risk from upward migration of hydrocarbons, reduced methane attenuation capacity, and long dilution times, whereas predominantly modern-and mixed-age groundwater in the eastern SJV indicates this area has relatively high risk from chemical migration from land-surface sources and subsequent extensive spreading. Age-based characterizations of relative risk could inform the design of groundwater-monitoring programs near oil fields in terms of the spatial distribution of monitoring points relative to source areas and monitoring frequency and duration. 

Replenishing Groundwater in the San Joaquin Valley: 2024 Update

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

Strategies to replenish groundwater basins—long used in some areas of the San Joaquin Valley—have increasingly come into focus as the region seeks to bring its overd

Strategies to replenish groundwater basins—long used in some areas of the San Joaquin Valley—have increasingly come into focus as the region seeks to bring its overdrafted groundwater basins into balance under the Sustainable Groundwater Management Act (SGMA). In late 2023, following a very wet winter and spring, we conducted a repeat survey of local water agencies about their recharge activities and perspectives, building on a similar survey at the end of 2017, a year with similar levels of precipitation. We found signs of progress on recharge since 2017, as well as areas where more work is needed to take full advantage of this important water management tool.

Resistivity imaging reveals complex pattern of saltwater intrusion along Monterey coast

Journal of Hydrology (Elsevier) | February 22nd, 2017

A coastal region represents a dynamic zone where fresh groundwater in the coastal aquifers interacts with saline ocean water. The location of the freshwater-saltwater int

A coastal region represents a dynamic zone where fresh groundwater in the coastal aquifers interacts with saline ocean water. The location of the freshwater-saltwater interface is governed by the density and pressure differences on the two sides of the interface and the subsurface hydrologic properties that control fluid movement. Saltwater intrusion is the process in which this interface moves landward, with saltwater then occupying parts of the aquifer that were once fresh. While this process has been observed and documented throughout the world for over a century (Bear et al., 1999), climate change, growing water demands, and manipulation of natural hydrologic systems have led to saltwater intrusion being considered a significant threat to future freshwater resources globally (Kinzelbach et al., 2003; Barlow and Reichard, 2009; Werner et al., 2013). Saltwater intrusion can have a number of significant economic and environmental impacts, including diminished freshwater storage capacity, contamination of freshwater production wells, soil salinization, and decreased nutrient laden freshwater discharge to marine ecosystems (Johannes, 1980; Taniguchi et al., 2002; Werner et al., 2013). A number of steps can be taken to attempt to slow the rate of saltwater intrusion, including spatial and temporal changes in the extent of groundwater pumping, in landuse, in surface water diversions, and in artificial recharge (Abarca et al., 2006). What is needed however is a way to prioritize these actions, or combinations of actions, so as to optimize the impact on saltwater intrusion. This requires an accurate understanding of the current distribution of freshwater and saltwater, that can be used to predict future locations in response to these, and other, actions (Sanford and Pope, 2009). Saltwater intrusion is traditionally mapped and monitored using measurements made in wells and predictive flow models (Werner et al., 2013). There are a number of limitations with these methods. Measurements made in wells provide point data, which may fail to capture the spatial complexity in subsurface conditions. Improving spatial coverage with additional wells can be cost prohibitive (Ogilvy et al., 2009). Additionally, salinity measurements from wells can be flux-averaged concentrations, and head measurements in wells are affected by the density of the water column so can be misinterpreted in the presence of unknown salt water, and are susceptible to measurement, instrument, and time lag errors (Carrera et al., 2009; Post and Von Asmuth, 2013). Models are generally calibrated by matching historic head values in wells and/or matching salinity values from well samples (Carrera et al., 2009), thus all the limitations of well data are carried over into the model calibration. Given these limitations there is significant opportunity for additional methods of mapping and monitoring the distribution of saltwater in the subsurface for improved management of coastal aquifers.

River-Aquifer Interactions, Geologic Heterogeneity, and Low-Flow Management

U.S. Geological Survey (USGS) | ?

Low river flows are commonly controlled by river-aquifer exchange, the magnitude of which is governed by hydraulic properties of both aquifer and aquitard mater

Low river flows are commonly controlled by river-aquifer exchange, the magnitude of which is governed by hydraulic properties of both aquifer and aquitard materials beneath the river. Low flows are often important ecologically. Numerical simulations were used to assess how textural heterogeneity of an alluvial system influences river seepage and low flows. The Cosumnes River in California was used as a test case. Declining fall flows in the Cosumnes River have threatened Chinook salmon runs. A ground water–surface water model for the lower river basin was developed, which incorporates detailed geostatistical simulations of aquifer heterogeneity. Six different realizations of heterogeneity and a homogenous model were run for a 3-year period. Net annual seepage from the river was found to be similar among the models. However, spatial distribution of seepage along the channel, water table configuration and the level of local connection, and disconnection between the river and aquifer showed strong variations among the different heterogeneous models. Most importantly, the heterogeneous models suggest that river seepage losses can be reduced by local reconnections, even when the regional water table remains well below the riverbed. The percentage of river channel responsible for 50% of total river seepage ranged from 10% to 26% in the heterogeneous models as opposed to 23% in the homogeneous model. Differences in seepage between the models resulted in up to 13 d difference in the number of days the river was open for salmon migration during the critical fall months in one given year.

Rivers that Depend on Aquifers: Drafting SGMA Groundwater Plans with Fisheries in Mind

Golden Gate University (GSU) | April 12th, 2018

In California, surface waters have historically been regulated as if they were unconnected to groundwater. Yet, in reality, surface waters and groundwater are often hydro

In California, surface waters have historically been regulated as if they were unconnected to groundwater. Yet, in reality, surface waters and groundwater are often hydrologically connected. Many of the rivers that support fisheries such as salmon and trout are hydrologically dependent on tributary groundwater to maintain instream flow. This means that when there is intensive pumping of tributary groundwater the result can be reductions in instream flow and damage to fisheries. For this reason, stakeholders concerned about adequate instream flows for fisheries in California’s rivers, streams and creeks need to be effectively engaged in the implementation of California’s Sustainable Groundwater Management Act (SGMA). Consider the Scott River in Northern California, part of the larger Klamath River Basin. Nearby groundwater contributes to the Scott River. When high volumes of groundwater are extracted from nearby wells, it depletes the Scott River’s instream flow with adverse impacts on salmon and steelhead trout. As discussed further in Section VI of this guidebook, this has led to litigation over the application of California public trust law to groundwater extraction affecting Scott River instream flows, and efforts to use SGMA to ensure that groundwater pumping near the Scott River is compatible with the instream flow needs of fisheries. Situations similar to the Scott River surface and groundwater basin are unfolding throughout California. On a statewide basis, how pervasive is the effect of groundwater pumping on surface water flows? Research by Maurice Hall of the Environmental Defense Fund, utilizing the California Department of Water Resources Central Valley Groundwater Surface Flow Model, provides us with some sense of the magnitude of the problem. In a May 2018 presentation, Hall reported: What the model showed us is that early in the 1900s, 1940s and 1950s, the Sacramento River received a net inflow from the groundwater of something like 1 million acre feet a year…Since that time, the groundwater levels have gone down, and the amount of water that has flowed into the Sacramento River from the surrounding groundwater has gone down accordingly to the point that when we were doing this modeling around 2010, it appeared that on average, the Sacramento River lost just about as much as it gained from the surrounding groundwater in the valley floor. This is the Sacramento River and all of its tributaries upstream of the Sacramento…So the net effect over that period is there was roughly on average 900,000 acre-feet per year less water showing up in the  Sacramento River at Sacramento.” (Hall and O’Brien). SGMA was enacted in 2014. Pursuant to SGMA, by June 2017 a groundwater sustainability agency was required to be designated for each groundwater basin in California. Each groundwater sustainability agency in high and medium priority basins must prepare and adopt a Groundwater Sustainability Plan (SGMA Groundwater Plan) by 2020 if the basin is deemed to be in a critical state of overdraft or 2022 for all remaining high and medium priority basins. Each SGMA Groundwater Plan must detail how the groundwater basin will be managed to avoid overdraft conditions and, importantly for fisheries, to avoid adverse impacts on hydrologically connected surface waters. Although groundwater sustainability agencies and fishery stakeholders recognize that the groundwater-surface water connection needs to be addressed in SGMA Groundwater Plans, at present there is limited guidance on how to do this. That is, what are the specific types of information, modeling, monitoring, and pumping provisions that should be included in SGMA Groundwater Plans to ensure that groundwater extraction does not cause significant adverse impacts on fisheries? The purpose of this guidebook is to provide such guidance.

Root Creek Water District Groundwater Sustainability Agency Groundwater Sustainability Plan

Root Creek Water District | November 11th, 2019

Root Creek Water District Groundwater Sustainability Plan

Root Creek Water District | November 11th, 2019

The RCWDGSA covers almost 10,000 acres in southeast Madera County located southwest of the intersection of State Highway 41 and Avenue 12 along the banks of and just nort

The RCWDGSA covers almost 10,000 acres in southeast Madera County located southwest of the intersection of State Highway 41 and Avenue 12 along the banks of and just north of the San Joaquin River. In size, the GSA accounts for less than 3 percent of the land area within the Madera Basin. The District, which lies wholly within the GSA has recently contracted for surface water supplies from the Madera Irrigation District (MID) and the Wonderful Nut Orchards for up to 17,000 acre-feet (af) of surface water in a given year. The District has also recently completed the first phase of an agricultural conveyance and distribution system that has the ability to deliver surface water to approximately 2,500 acres of farmland. Since its completion, the system has delivered approximately 16,382af of surface water to date in the past three years.To accomplish these achievements the district has invested more than 12 million dollars. While large, the purchase and delivery of surface water supplies are crucial to the long-term groundwater sustainability of not only the District and the GSAbut also the region and the subbasin.