Groundwater Depletion in the United States (1900-2008)

U.S. Geological Survey (USGS) | June 1st, 2013

A natural consequence of groundwater withdrawals is the removal of water from subsurface storage, but the overall rates and magnitude of groundwater depletion in the Unit

A natural consequence of groundwater withdrawals is the removal of water from subsurface storage, but the overall rates and magnitude of groundwater depletion in the United States are not well characterized. This study evaluates long-term cumulative depletion volumes in 40 separate aquifers or areas and one land use category in the United States, bringing together information from the literature and from new analyses. Depletion is directly calculated using calibrated groundwater models, analytical approaches, or volumetric budget analyses for multiple aquifer systems. Estimated groundwater depletion in the United States during 1900–2008 totals approximately 1,000 cubic kilometers (km3). Furthermore, the rate of groundwater depletion has increased markedly since about 1950, with maximum rates occurring during the most recent period (2000–2008) when the depletion rate averaged almost 25 km3 per year (compared to 9.2 km3 per year averaged over the 1900–2008 time-frame). 

Groundwater development leads to decreasing arsenic concentrations in the San Joaquin Valley, California

Science of the Total Environment (Elsevier) | January 18th, 2021

In the San Joaquin Valley (SJV), California, about 10% of drinking water wells since 2010 had arsenic concentrations above the U.S. maximum contaminant level of 10μg/L.

In the San Joaquin Valley (SJV), California, about 10% of drinking water wells since 2010 had arsenic concentrations above the U.S. maximum contaminant level of 10μg/L. High concentrations of arsenic are often associated with high pH (greater than 7.8) or reduced geochemical conditions. Although most wells have low arsenic(<3μg/L) and do not have changing arsenic concentrations, this study found that most wells with concentrations above 10μg/L had arsenic trends. Overall, about 24% of wells had time-series trends since 2010 and 59% had paired-sample trends since 2000. Most wells had decreasing arsenic trends, even in wells with higher arsenic concentrations. These wells often had co-detections of increasing nitrate and sulfate trends that reflect oxic groundwater likely derived from agricultural recharge. Wells with increasing arsenic trends were deeper or located in the valley trough where aquifer materials are more fine-grained and where reducing conditions favor arsenic mobility. Wells with arsenic trends also tend to be clustered near areas of higher well density. Groundwater pumping in these areas has likely increased the contribution of younger, more oxic groundwater in wells with declining arsenic or, less frequently, increased the contribution of higher pH or reduced groundwater in wells with rising arsenic. Projections of arsenic trends indicate that 37 wells with high arsenic presently will be below 10μg/L in ten years. Unfortunately, these improvements will be largely offset by 31 wells that are expected to increase above 10μg/L in addition to expected rises in nitrate in wells where arsenic decreased. This study shows how human-altered flow systems can impact the natural geochemical character of water in both beneficial and deleterious ways.

Groundwater Dynamics in the Colorado River Limitrophe

Pacific Institute | May 23rd, 2013

The Colorado River, diverted and channelized and intensively managed, only rarely has enough water to flow even 20 miles past Morelos Dam, the last dam on the river, near

The Colorado River, diverted and channelized and intensively managed, only rarely has enough water to flow even 20 miles past Morelos Dam, the last dam on the river, near the California/Arizona/Baja California border. The river’s limitrophe reach – the roughly 22.5 mile stretch from Andrade to San Luis that separates Baja California from Arizona – is generally considered the uppermost extent of the remnant Colorado River delta, with some of the most extensive stands of native cottonwoods and willows left on the lower Colorado River and one of the few areas where the river still occasionally has enough water to exceed its banks and reach its floodplain. Because of this, there has been intense restoration interest in the limitrophe reach for more than a decade. In recent years, however, concern has grown that deteriorating groundwater conditions in the lower portion of the limitrophe will limit the success of restoration efforts. Groundwater Dynamics in the Colorado River Limitrophe describes and explains the changing groundwater conditions in and adjacent to the Colorado River’s limitrophe reach, and analyzes the impact of groundwater pumping on these overdraft conditions. The key question underlying this study asks how changing groundwater conditions in the limitrophe could affect the sustainability of planned habitat restoration projects. This study indicates that, even after the exceptionally dry period of 2005-2009, when surface flows failed to reach the gage at the downstream end of the limitrophe on 90 percent of days, more than a third of the channel through the limitrophe still exhibited connectivity with the water table, and roughly two-thirds of the limitrophe still had a water table that remained within the reach of the roots of cottonwoods and willows. The plunging water table at the downstream end of the limitrophe suggests that the final five miles of the river within the limitrophe may not respond to efforts to restore riparian habitat, at least not without a long-term commitment to supplemental irrigation, but areas upstream appear well-insulated from the recent drawdown and would benefit from restoration activity, such as that proposed by the recent Minute 319.

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 and Safe Drinking Water in the San Joaquin Valley

Water Foundation | June 2nd, 2020

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 microbiomes balance resilience and vulnerability to hydroclimatic extremes

Nature Portfolio (Springer Nature) | August 20th, 2025

Groundwater Simulation and Management Models for the Upper Klamath Basin, Oregon and California

U.S. Geological Survey (USGS) | May 5th, 2012

The upper Klamath Basin encompasses about 8,000 square miles, extending from the Cascade Range east to the Basin and Range geologic province in south-central Oregon and n

The upper Klamath Basin encompasses about 8,000 square miles, extending from the Cascade Range east to the Basin and Range geologic province in south-central Oregon and northern California. The geography of the basin is dominated by forested volcanic uplands separated by broad interior basins. Most of the interior basins once held broad shallow lakes and extensive wetlands, but most of these areas have been drained or otherwise modified and are now cultivated. Major parts of the interior basins are managed as wildlife refuges, primarily for migratory waterfowl. The permeable volcanic bedrock of the upper Klamath Basin hosts a substantial regional groundwater system that provides much of the flow to major streams and lakes that, in turn, provide water for wildlife habitat and are the principal source of irrigation water for the basin’s agricultural economy. Increased allocation of surface water for endangered species in the past decade has resulted in increased groundwater pumping and growing interest in the use of groundwater for irrigation. The potential effects of increased groundwater pumping on groundwater levels and discharge to springs and streams has caused concern among groundwater users, wildlife and Tribal interests, and State and Federal resource managers. To provide information on the potential impacts of increased groundwater development, and to aid in the development of a groundwater management strategy, the U.S. Geological Survey, in collaboration with the Oregon Water Resources Department and the Bureau of Reclamation, has developed a groundwater model that can simulate the response of the hydrologic system to these new stresses. The groundwater model was developed using the U.S. Geological Survey MODFLOW finite-difference modeling code and calibrated using inverse methods to transient conditions from 1989 through 2004 with quarterly stress periods. Groundwater recharge and agricultural and municipal pumping are specified for each stress period. All major streams and most major tributaries for which a substantial part of the flow comes from groundwater discharge are included in the model. Groundwater discharge to agricultural drains, evapotranspiration from aquifers in areas of shallow groundwater, and groundwater flow to and from adjacent basins also are simulated in key areas. The model has the capability to calculate the effects of pumping and other external stresses on groundwater levels, discharge to streams, and other boundary fluxes, such as discharge to drains. Historical data indicate that the groundwater system in the upper Klamath Basin fluctuates in response to decadal climate cycles, with groundwater levels and spring flows rising and declining in response to wet and dry periods. Data also show that groundwater levels fluctuate seasonally and interannually in response to groundwater pumping. The most prominent response is to the marked increase in groundwater pumping starting in 2001. The calibrated model is able to simulate observed decadal-scale climate-driven fluctuations in the groundwater system as well as observed shorter-term pumping-related fluctuations. Example model simulations show that the timing and location of the effects of groundwater pumping vary markedly depending on the pumping location. Pumping from wells close (within a few miles) to groundwater discharge features, such as springs, drains, and certain streams, can affect those features within weeks or months of the onset of pumping, and the impacts can be essentially fully manifested in several years. Simulations indicate that seasonal variations in pumping rates are buffered by the groundwater system, and peak impacts are closer to mean annual pumping rates than to instantaneous rates. Thus, pumping effects are, to a large degree, spread out over the entire year. When pumping locations are distant (more than several miles) from discharge features, the effects take many years or decades to fully impact those features, and much of the pumped water comes from groundwater storage over a broad geographic area even after two decades. Moreover, because the effects are spread out over a broad area, the impacts to individual features are much smaller than in the case of nearby pumping. Simulations show that the discharge features most affected by pumping in the area of the Bureau of Reclamation’s Klamath Irrigation Project are agricultural drains, and impacts to other surface-water features are small in comparison. A groundwater management model was developed that uses techniques of constrained optimization along with the groundwater flow model to identify the optimal strategy to meet water user needs while not violating defined constraints on impacts to groundwater levels and streamflows. The coupled groundwater simulation-optimization models were formulated to help identify strategies to meet water demand in the upper Klamath Basin. The models maximize groundwater pumping while simultaneously keeping the detrimental impacts of pumping on groundwater levels and groundwater discharge within prescribed limits. Total groundwater withdrawals were calculated under alternative constraints for 2 Groundwater Simulation and Management Models for the Upper Klamath Basin, Oregon and California drawdown, reductions in groundwater discharge to surface water, and water demand to understand the potential benefits and limitations for groundwater development in the upper Klamath Basin. The simulation-optimization model for the upper Klamath Basin provides an improved understanding of how the groundwater and surface-water system responds to sustained groundwater pumping within the Bureau of Reclamation’s Klamath Project. Optimization model results demonstrate that a certain amount of supplemental groundwater pumping can occur without exceeding defined limits on drawdown and stream capture. The results of the different applications of the model demonstrate the importance of identifying constraint limits in order to better define the amount and distribution of groundwater withdrawal that is sustainable.

Groundwater sustainability and land subsidence in California’s Central Valley

Water (MDPI) | April 22nd, 2024

The Central Valley of California is one of the most prolific agricultural regions in the world. Agriculture is reliant on the conjunctive use of surface-water and groundw

The Central Valley of California is one of the most prolific agricultural regions in the world. Agriculture is reliant on the conjunctive use of surface-water and groundwater. The lack of available surface-water and land-use changes have led to pumping-induced groundwater-level and storage declines, land subsidence, changes to streamflow and the environment, and the degradation of water quality. As a result, in part, the Sustainable Groundwater Management Act (SGMA) was developed. An examination of the components of SGMA and contextualizing regional model applications within the SGMA framework was undertaken to better understand and quantify many of the components of SGMA. Specifically, the U.S. Geological Survey (USGS) updated the Central Valley Hydrologic Model (CVHM) to assess hydrologic system responses to climatic variation, surface-water availability, land-use changes, and groundwater pumping. MODFLOW-OWHM has been enhanced to simulate the timing of land subsidence and attribute its inelastic and elastic portions. In addition to extending CVHM through 2019, the new version, CVHM2, includes several enhancements as follows: managed aquifer recharge (MAR), pumping with multi-aquifer wells, inflows from ungauged watersheds, and more detailed water-balance subregions, streamflow network, diversions, tile drains, land use, aquifer properties, and groundwater level and land subsidence observations. Combined with historical approximations, CVHM2 estimates approximately 158 km3 of storage loss in the Central Valley from pre-development to 2019. About 15% of the total storage loss is permanent loss of storage from subsidence that has caused damage to infrastructure. Climate extremes will likely complicate the efforts of water managers to store more water in the ground. CVHM2 can provide data in the form of aggregated input datasets, simulate climatic variations and changes, land-use changes or water management scenarios, and resulting changes in groundwater levels, storage, and land subsidence to assist decision-makers in the conjunctive management of water supplies.

Groundwater Sustainability Assessments: A Review of the Department of Water Resources’ Determinations on Groundwater Sustainability Plans in Critically Overdrafted Basins

Groundwater Leadership Forum (GLF) | August 31st, 2022

Of the 46 GSPs submitted in January 2020, the Department of Water Resources (DWR) determined eight GSPs to be adequate and 34 GSPs to be incomplete. In this paper we eval

Of the 46 GSPs submitted in January 2020, the Department of Water Resources (DWR) determined eight GSPs to be adequate and 34 GSPs to be incomplete. In this paper we evaluate to what extent DWR’s determinations provide oversight on the key issues of drinking water, disadvantaged communities, the environment, stakeholder involvement,and climate change. We summarize the corrective actions that DWR is recommending or requiring, as well as compare DWR’s determinations to the assessment of 31 GSPs that we conducted in 2020. We also reviewed the 11 comment letters submitted by the State Water Resources Control Board (SWRCB), 25 comment letters submitted by the California Department of Fish and Wildlife (CDFW), and seven comment letters submitted by the National Oceanic and Atmospheric Administration’s National Marine Fisheries Service (NMFS) to compare deficiencies identified in GSPs across agencies.