San Joaquin River

Grassland Groundwater Sustainability Agency Revised Groundwater Sustainability Plan

Grassland Groundwater Sustainability Agency (GGSA) | July 8th, 2022

This GSP, including the Common Chapter, has been revised (changes are shown in Appendix G) to address items of concern raised by DWR in its initial “Incomplete” Deter

This GSP, including the Common Chapter, has been revised (changes are shown in Appendix G) to address items of concern raised by DWR in its initial “Incomplete” Determination Letter dated January 21, 2022. Every effort was made to ensure that this revised GSP and the revised Common Chapter are consistent. In the event of an inconsistency, the revised Common Chapter controls. The Grassland Plan Area will continue to be sustainable by maintaining the historically balanced groundwater system in order to avoid causing significant and unreasonable undesirable impacts to beneficial users of groundwater as they relate to the six sustainability indicators. The Plan Area participants are committed to continued coordination with neighboring GSP areas and neighboring subbasins in order to aid in the localized and statewide groundwater sustainability goals as defined by each GSP and Subbasin. Due to size, this file has been divided. Part 1, Part 2, Part 3, Part 4, Part 5, Part 6, Part 7

Gravelley Ford Water District Groundwater Sustainability Plan

Gravelly Ford Water District (GFWD) | August 12th, 2019

Gravelly Ford Water District Groundwater Sustainability Plan

Gravelly Ford Water District (GFWD) | March 19th, 2023

In 2022, the Technical representatives for the four GSPs representing the seven GSAs in the Madera Basin started meeting to revise the four GSP Plans to resolve deficienc

In 2022, the Technical representatives for the four GSPs representing the seven GSAs in the Madera Basin started meeting to revise the four GSP Plans to resolve deficiencies identified by the DWR in their review of the four GSP plans as stated in the September 2022 Incomplete determination letter. During the period from September 2022 through March 2023 the group also had meetings with DWR staff to establish direction on the recommendations in the DWR Incomplete letter. This Incomplete letter established a 180-day period to provide a revised GSP to address the deficiencies. The Technical group developed a corrective action plan to address the items identified by DWR staff in the Incomplete letter to address the noted deficiencies. During the last quarter of 2022 and the first quarter of 2023 the four GSPs revised their individual plans to coordinate approaches and methodologies that would provide similar language and approach across the Madera Subbasin, those items being: • Resolve the potential deficiencies identified by DWR in their September 2022 incomplete determination letter, and discussed during five DWR consultation meetings between November 2022 and January 2023; • Summarize the progressive implementation actions taken by the GSAs since submission of the GSP in January 2020; • Recognize the Madera Subbasin GSAs’ clear and formal commitment to fund and implement a Domestic Well Mitigation Program beginning no later than January 1, 2024, including the execution of a memorandum of understanding (MOU); and • Reaffirm their commitment to implementing the GSP and achieving sustainable groundwater conditions by 2040.

Gravelly Ford Water District Groundwater Sustainability Plan

Gravelly Ford Water District (GFWD) | June 28th, 2022

This Plan is for the Gravelly Ford Groundwater Sustainability Area, one of seven components of the Madera Subbasin. It encompasses approximately 8,500 acres; its boundari

This Plan is for the Gravelly Ford Groundwater Sustainability Area, one of seven components of the Madera Subbasin. It encompasses approximately 8,500 acres; its boundaries are coterminous with those of the Gravelly Ford Water District (District). Grape vineyards, nut tree groves, and on-farm rural residences are the only land uses in the Area. The District has from the beginning bee’n a conjunctive use operation with the import of surface water for both recharge and irrigation. The management of this operation has been to utilize the maximum amount of available surface waters prior to using groundwater for the production of crops.

Ground Water in the Central Valley, California - A Summary Report

U.S. Geological Survey (USGS) | June 1st, 1991

The agricultural productivity of the Central Valley depends on irrigation. Half of the 22 million acre-feet of irrigation water applied annually is ground water. The va

The agricultural productivity of the Central Valley depends on irrigation. Half of the 22 million acre-feet of irrigation water applied annually is ground water. The valley is a long, narrow structural trough filled with about 32,000 feet of sediment in the south and as much as 50,000 feet in the north. Nearly all the fresh ground water is contained in the continental rocks and deposits younger than Eocene age. Streamflow, an important factor in recharging the aquifer system, is influenced by precipitation in the mountains surrounding the valley. The majority of recharge from infiltration of streamflow occurs on the east side of the valley. Ground-water pumpage, which greatly exceeds the natural recharge rate, has dramatically altered the ground-water flow in the Central Valley. During the 1960's and 1970's, the recharge rate was more than five times that of the predevelopment period and was largely derived from percolation of imported surface water or recirculated pumped ground water rather than precipitation and recharge from streams. Prior to development, most ground water was discharged as evapotranspiration; however, in recent years, most discharge has been well pumpage. Computer simulation of the Central Valley aquifer system suggests that the total flow through the system has increased from about 2 million acre-feet per year to nearly 12 million acre-feet per year. The vertical movement of ground water has been artificially enhanced by many of the 100,000 irrigation wells that contain long intervals of perforated casing. When unpumped, these wells permit vertical flow between permeable layers within the aquifer system. The total fresh ground water presently (1986) in storage in the upper 1,000 feet of the aquifer system is about 800 million acre-feet. During the 1960's and 1970's, ground water in storage was depleted at an average rate of 800,000 acre-feet annually. In the San Joaquin Valley from the 1940's to the late 1960's, substantial withdrawals of ground water were accompanied by hundreds of feet of head decline. This head decline caused inelastic compaction of fine-grained beds, resulting in land subsidence that is unequaled anywhere else in the world. More than one-half of the San Joaquin Valley (or about 5,200 square miles) underwent subsidence of more than 1 foot. In one location, subsidence exceeded 29 feet. Within the areas of heavy withdrawals, subsidence is greatest where the aquifer system contains thick sections of montmorillonite clay. Land subsidence created engineering and economic problems, including damage to canals and drainage systems, and loss of irrigation wells caused by casing failure. More recently (since the drought of 1976-77), surface-water imports have increased, ground-water pumpage has decreased, and in places, ground-water levels have recovered. Land subsidence has virtually ceased; however, it could resume with increased pumpage, if water levels decline below previous lows. Ground-water quality in the Central Valley is generally influenced by the water from streams that are a major source of recharge. In general, water on the east side of the valley and from east-side streams contains low concentrations of dissolved solids compared to water on the west side and from west-side streams. Concentrations of dissolved solids in ground water generally are lower in the northern part of the valley than in the southern part. There are, however, localized exceptions in many places through the valley. Local concentrations of boron, chloride, and nitrate in the ground water of the Central Valley are large enough to be a problem either to crops or humans. Human activities have some influence on the concentration and location of water-quality problems in the valley. Significant increases in concentrations of dissolved solids and, specifically, dissolved nitrate indicate that ground-water quality is degrading as a result of increasing application of fertilizer in agricultural areas and the growth of urban population. Pesticides such as dibromochloropropane (DBCP) as well as selenium and other trace elements in agricultural drainage water cause ecological and health problems in the San Joaquin Valley.

Ground-Water Flow in the Central Valley, California

U.S. Geological Survey (USGS) | June 15th, 1989

The agricultural productivity of the Central Valley is dependent on the availability of water from irrigation. About 7.3 million acres of cropland in the Central Valley

The agricultural productivity of the Central Valley is dependent on the availability of water from irrigation. About 7.3 million acres of cropland in the Central Valley receives about 22 million acre-feet of irrigation water annually. One half of this irrigation water is supplied by ground-water, which amounts to about 20 percent of the Nation's ground-water pumpage. Ground water is important as a stable supply of irrigation water because of the high variability of surface-water supplies in the Central Valley. This large ground-water development during the past 100 years has had major impacts on the aquifer system, such as decline in water levels, land subsidence, depletion of the aquifer storage, and increase in recharge. The flow conditions before and during development were simulated on a regional scale using a three-dimensional finite-difference flow model. The Central Valley is a large (20,000-square-mile) structural trough filled with poorly permeable marine sediments that are overlain by coarser continental sediments. In general, previous investigators have conceptualized the northern one-third of the valley the Sacramento Valley as a water-table aquifer and the southern two-thirds the San Joaquin Valley as a two-aquifer system separated by a regional confining clay layer. A somewhat different concept of the aquifer system was suggested during this study by analyses of water-level measurements, texture of sediments interpreted from electric logs, and flow model simulations. Vertical hydraulic head differences are found through out much of the Central Valley. Early in development, flowing wells and marshes were found throughout most of the central part of the valley. More than 50 percent of the thickness of the continental sediments is composed of fine-grained lenticular deposits that are discontinuous but are distributed throughout the stratigraphic section in the entire Central Valley. The concept presented in this report considers the entire thickness of the continental deposits as one aquifer system which has varying vertical leakance that depends on several factors, including amount of fine-grained sediments. The average horizontal hydraulic conductivity is about 6 feet per day, and the average thickness of the continental deposits is about 2,400 feet. Irrigation use, which averaged 22 million acre-feet of water per year during 1961-77, increased evapotranspiration about 9 million acre-feet per year over its predevelopment value. This is a large figure compared with the average annual surface-water inflow to the Central Valley of 31.7 million acre-feet per year. Precipitation on the valley floor is mostly lost to evapotranspiration. The overall post-development recharge and discharge of the aquifer system was about 6 times greater than the predevelopment estimated values. The increases of pumpage associated with development mostly in the San Joaquin Valley have caused water-level declines that exceed 400 feet in places and have resulted in the largest known volume of land subsidence due to fluid withdrawal in the world. Water in aquifer storage declined about 60 million acre-feet from predevelopment to 1977; 40 million acre-feet were derived from the water-table zone, 17 million acre-feet from compaction of sediments, and 3 million acre-feet from elastic storage. During 1961-77, ground water withdrawn from aquifer storage averaged about 800,000 acre-feet per year. The flow model constructed during this study was calibrated principally in accordance with the hydrologic data observed during 1961-75 because little predevelopment data were available for analysis. An explicit algorithm to simulate land subsidence was developed and calibrated. The simulated land subsidence was within 6 percent of the estimated observed volume; however, the time lag associated with this type of subsidence was not adequately simulated. Simulated water level changes averaged 2.6 and 12 feet higher than observed water level changes for the water table and the lower pumped zones, respectively, and the standard deviation of the simulated changes minus the observed change was 22 and 27 feet, respectively. The flow model was tested for the period of 1976-77 drought with good results. The simulations indicated that vertical leakance greatly increased from the predevelopment values as a result of water flowing through some of the more than 100,000 irrigation well casings that are open to different aquifer layers.  

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

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

Groundwater and Stream Interaction in California's Central Valley: Insights for Sustainable Groundwater Management

Nature Conservancy | June 16th, 2016

Sustainable water management requires ensuring ecosystem water needs are met in balance with water needs for people. The Nature Conservancy (TNC) is working across Califo

Sustainable water management requires ensuring ecosystem water needs are met in balance with water needs for people. The Nature Conservancy (TNC) is working across California to demonstrate how to achieve this balance in the context of integrated water management programs. Sustainable water management must also recognize that surface water and groundwater resources are interconnected and that proper management of these resources includes understanding this interaction and managing the resources accordingly. Management of groundwater and surface water systems in an integrated manner is impeded by California water law and policy, which has separate rules and regulations for managing groundwater and surface water resources. The Central Valley of California is the hub of the state’s water supply system. An extensive network of dams and canals supplies surface water to users within the Central Valley as well as to the San Francisco Bay Area, the Central Coast, and Southern California. Analysis of information collected in this study reveals that just within the Central Valley, agricultural and urban sectors use an average of 13 million acre-feet (MAF) of surface water and over 8 MAF of groundwater per year. Approximately 2 MAF of water is exported annually to areas outside the Central Valley. Because the availability of surface water supplies varies significantly from year to year, groundwater use also varies considerably on annual basis. In an average year, groundwater meets about 40% of the state’s water demand and up to 60% or more during droughts, when groundwater provides a water supply buffer against economic and environmental harm from water scarcity (DWR, 2014). In some areas, groundwater provides 100% of the supply, even in wetter years, and then is heavily pumped during drought. In other locations, where surface water supplies are reasonably abundant, groundwater use may be relatively light during wetter years, but more heavily pumped during drier years when surface water supplies are cut back. Accordingly, the impact of groundwater use is much more evident during dry years, and especially in drought conditions. A case in point is the drought condition of 2013-15. This drought is exerting significant stress on the state’s water supply. The surface water deliveries have been reduced dramatically, to near zero in many regions; therefore, agricultural and municipal water users in the Central Valley and other parts of the state that normally rely on surface water for much of their supplies, are now greatly increasing their use of groundwater to meet their needs. A 2014 UC Davis report indicates that expected increase in Central Valley groundwater pumping would be in the range of 20% to 25%, during the 2014 irrigation season. To the authors’ knowledge, there are no reports of actual estimates of increase in groundwater use for the recent drought conditions. The long-term increase in groundwater pumping and especially recent drought related increases in pumping would translate into significantly more adverse impacts on the surface water and stream systems, as well as groundwater dependent ecosystems. In addition, this increase in groundwater pumping could potentially result in more land subsidence throughout the valley. The drought has also affected the irrigated lands under cultivation. A November 2014 DWR publication “Public Update for Drought Response” 3 reported that based on NASA satellite imagery, approximately 700,000 acres of land were estimated idled between 2011 and 2014. Majority of these acreages idled are reported to be due to the drought conditions, although, some were also due to normal agronomic practices, crop markets, and other reasons. This report provides the results of a number of analyses and evaluations of Central Valley hydrologic conditions using the California Central Valley Groundwater-Surface Water Simulation Model (C2VSim). The study examines important hydrologic and operational characteristics and behaviors of the California’s Central Valley water system during the historical development in the Valley. In addition, the study presents results of model simulations conducted to assess potential impacts of several water management scenarios. The results of this study contribute significantly to the understanding of how management of groundwater and surface water are interrelated and will inform the development of more effective integrated water management in the Central Valley and throughout California. The interaction between groundwater and surface water resources has been evaluated and illustrated by many researchers. As early as 1941, Theis (1941) documented the hydraulic connection between stream and aquifer systems and quantitatively described the general behavior of stream-groundwater systems. Many others, including Glover & Balmer (1954) and Hantush (1965) built on Theis’ work, which demonstrated and confirmed the basic principles of hydraulic connection between stream and aquifer systems. In recent years, significant work has been conducted regarding regional impacts of groundwater pumping and operation on regional surface water systems. For example, the recent USGS study (Barlow & Leake, 2012) presents original findings of the stream-aquifer interaction in the context of sustainable groundwater management. In an effort to quantify the interaction between the groundwater and the surface water system, DWR’s C2VSim model was employed in this study. The C2VSim model was originally developed in 1990 for DWR, U. S. Bureau of Reclamation (USBR), and California State Water Resources Control Board (SWRCB) as the Central Valley Groundwater and Surface water Model (CVGSM) (James M. Montgomery Consulting Engineers, 1990a). Subsequently, the model was enhanced through numerous key applications, including the Central Valley Project Improvement Act – Programmatic Environmental Impact Statement (CVPIA-PEIS). In 2005, the CVGSM model was upgraded to the newly developed Integrated Water Flow Model (IWFM) platform, and was renamed the C2VSim model. The detailed features of the model are described and presented in Section 2 of this report. The C2VSim model is a leading Central Valley-wide integrated hydrologic model adopted by DWR and many other regional and state-wide agencies, as well as non-governmental organizations (NGOs) to evaluate various water management scenarios throughout the Valley. This report is organized in six sections: Section 1: Provides the background information and lays out the goals and objectives of this study. Section 2: Provides information on the status of C2VSim model, refinements made during this study, and assumptions on the modeling analysis. Section 3: Discusses simulation of the historical hydrologic conditions in the Central Valley. Section 4: Provides the assumptions and results of the existing baseline conditions, assuming that no changes to the facilities and their operations, as well as water management actions, take place over the course of a predetermined hydrologic condition. Section 5: Provides a description of three water management scenarios that may have major impacts on the future of surface water and groundwater interaction in Central Valley. Results of simulation of these management scenarios are presented and discussed in detail. Section 6: Provides conclusions from this study and a list of recommendations for future work.

Groundwater and Urban Growth in the San Joaquin Valley

Public Policy Institute of California (PPIC) | September 20th, 2021

The San Joaquin Valley is ground zero for the Sustainable Groundwater Management Act (SGMA). It has the largest groundwater deficit in California and faces some of the

The San Joaquin Valley is ground zero for the Sustainable Groundwater Management Act (SGMA). It has the largest groundwater deficit in California and faces some of the worst impacts from overdraft, including land subsidence and drying wells. SGMA will help the region address these issues—while also building its climate resilience. But this will require hard work, not only by farmers—the largest groundwater users—but also by the valley’s urban water utilities, which serve a growing population while relying mostly on groundwater. As the valley confronts limits on groundwater pumping, urban utilities, local land use authorities, other water users, and state agencies must all engage to ensure a smooth transition for the region’s residents.

Groundwater Availability of the Central Valley Aquifer

U.S. Geological Survey (USGS) | July 15th, 2009

California’s Central Valley covers about 20,000 square miles and is one of the most productive agricultural regions in the world. More than 250 different crops are grow

California’s Central Valley covers about 20,000 square miles and is one of the most productive agricultural regions in the world. More than 250 different crops are grown in the Central Valley with an estimated value of $17 billion per year. This irrigated agriculture relies heavily on surface-water diversions and groundwater pumpage. Approximately one-sixth of the Nation’s irrigated land is in the Central Valley, and about one-fifth of the Nation’s groundwater demand is supplied from its aquifers. The Central Valley also is rapidly becoming an important area for California’s expanding urban population. Since 1980, the population of the Central Valley has nearly doubled from 2 million to 3.8 million people. The Census Bureau projects that the Central Valley’s population will increase to 6 million people by 2020. This surge in population has increased the competition for water resources within the Central Valley and statewide, which likely will be exacerbated by anticipated reductions in deliveries of Colorado River water to southern California. In response to this competition for water, a number of water-related issues have gained prominence: conservation of agricultural land, conjunctive use, artificial recharge, hydrologic implications of land-use change, and effects of climate variability. To provide information to stakeholders addressing these issues, the USGS Groundwater Resources Program made a detailed assessment of groundwater availability of the Central Valley aquifer system, that includes: (1) the present status of groundwater resources; (2) how these resources have changed over time; and (3) tools to assess system responses to stresses from future human uses and climate variability and change. This effort builds on previous investigations, such as the USGS Central Valley Regional Aquifer System and Analysis (CV-RASA) project and several other groundwater studies in the Valley completed by Federal, State and local agencies at differing scales. The principal product of this new assessment is a tool referred to as the Central Valley Hydrologic Model (CVHM) that accounts for integrated, variable water supply and demand, and simulates surface-water and groundwater-flow across the entire Central Valley system. The development of the CVHM comprised four major elements: (1) a comprehensive Geographic Information System (GIS) to compile, analyze and visualize data; (2) a texture model to characterize the aquifer system;(3) estimates of water-budget components by numerically modeling the hydrologic system with the Farm Process (FMP); and (4) simulations to assess and quantify hydrologic conditions. Chapter A: Introduction, Overview of Hydrogeology, and Textural Model of California’s Central Valley Chapter B: Groundwater Availability in California’s Central Valley Chapter C:  Numerical Model of the Hydrologic Landscape and Groundwater Flow in California’s Central Valley Appendix 1: Supplemental Information—Modifications to Modflow-2000 Packages and Processes