Flood Risk and Management of California's Sacramento-San Joaquin Delta Levee System

University of California, Santa Cruz (UC Santa Cruz) | September 15th, 2020

Friant Water Authority vs. Eastern Tule Groundwater Sustainibilty Agency

Superior Court of California, County of Tulare | February 15th, 2024

Friant-Kern Canal Middle Reach Capacity Correction

U.S. Bureau of Reclamation (USBR) | January 25th, 2022

Geohydrology, Geochemistry, and Numerical Simulation of Groundwater Flow and Land Subsidence in the Bicycle Basin, Fort Irwin National Training Center, California

U.S. Geological Survey (USGS) | July 19th, 2018

Groundwater pumping from Bicycle Groundwater Basin (referred to as Bicycle Basin) in the Fort Irwin National Training Center, California, began in 1967. From 1967 to Dece

Groundwater pumping from Bicycle Groundwater Basin (referred to as Bicycle Basin) in the Fort Irwin National Training Center, California, began in 1967. From 1967 to December 2010, about 46,000 acre-feet of water had been pumped from the basin and transported to the Irwin Basin. During this time, not only did water levels in the basin decline by as much as 100 feet, the quality of the groundwater pumped from the basin also deteriorated in some wells. The U.S. Geological Survey collected geohydrologic data from existing wells, test holes, and 16 additional monitoring wells installed at 6 sites in Bicycle Basin during 1992–2011 to determine the quantity and quality of groundwater available in the basin. Geophysical surveys, including electrical, gravity, and seismic refraction surveys, were completed to help determine the geometry of the structural basin, delineate depths to the interface between Quaternary and Tertiary rocks, map the depth to the water table, and used to develop a geohydrologic framework and groundwater-flow model for Bicycle Basin. Water samples were used to determine the groundwater quality in the basin and to delineate potential sources of poor-quality groundwater. Analysis of stable isotopes of oxygen and hydrogen in groundwater indicated that present-day precipitation is not a major source of recharge to the basin. Tritium and carbon-14 data indicated that most of the groundwater in the basin was recharged prior to 1952 and had an apparent age of 15,625–39,350 years. Natural recharge to the basin was not sufficient to replenish the groundwater pumped from the basin. Interferograms from synthetic aperture radar data (InSAR), analyzed to evaluate land-surface subsidence between 1993 and 2010, showed 0.23 to 1.1 feet of subsidence during this period near one production well north of Bicycle Lake (dry) playa. A groundwater-flow model of Bicycle Basin was developed and calibrated using groundwater levels for 1964–2010, and a subsidence model using land-surface deformation data for 1993–2010. Between January 1967 and December 2010, the simulated total recharge from precipitation runoff and underflow from adjacent basins was about 5,100 acre-feet and pumpage from the Bicycle Basin was about 47,000 acre-feet of water. Total outflows exceeded natural recharge during this period, resulting in a net loss of about 42,100 acre-feet of groundwater storage in the basin. The Fort Irwin National Training Center is considering various groundwater-management options in the Bicycle Basin. The groundwater-flow model was used to (1) evaluate changes in groundwater levels and subsidence with the addition of capture and recharge of simulated runoff in retention basins (scenario 1) for predevelopment through 2010; (2) simulate a base case (scenario 2) for reference; and (3) compare projections of alternative future pumping strategies for 2011–60 (scenarios 3–5). Model results from the runoff-capture simulation (scenario 1) indicated that total recharge, including runoff captured using retention basins, locally increased water levels, which partially offset, but did not mitigate, groundwater depletion associated with pumping. Groundwater-storage depletion in scenario 1 was about 14 percent less than without runoff capture. Simulated-drawdown results in model layer 1 in the eastern part of the basin indicated that, because of the captured runoff, simulated heads were as much as 100 feet higher in December 2010 than prior to the onset of development in 1967. In contrast, simulated drawdown for model without runoff capture indicated that, without captured runoff, simulated heads for December 2010 in this area were 80–90 feet lower than during the predevelopment period. Subsidence was mitigated slightly in scenario 1 compared to without runoff capture; the largest decrease in subsidence at observation sites was about 0.07 feet. Scenario 2 results indicated that simulated drawdown in model layer 6 at the end of 2060 ranged from about 46 to 135 feet. Subsidence at observation sites at the end of 2060 ranged from 0.83 to 2.8 feet. Reducing the base case pumping rate by 25 percent in the existing production well in the subsidence area and redistributing the pumpage to the other two production wells (scenario 3) resulted in a reduction of drawdown in the subsidence area compared with the base case (scenario 2). The difference in subsidence at the end of 2060 between scenario 3 and the base case was small (less than 0.07 feet) for all observation locations. Repeating the simulation scenario 3 but additionally reducing the basin-wide pumpage by 3 percent per year from 2011 through 2020 (scenario 4) resulted in about 60 feet less drawdown in the subsidence area than for the base case. Subsidence at observation sites ranged from 0.12 to 0.43 feet less than for the base case. Reducing the pumpage in the existing production well in the subsidence area to zero, while continuing the base case pumping rate in the other two existing production wells (scenario 5), resulted in more than 100 feet less drawdown in the subsidence area than in the base case. The simulated subsidence at the end of 2060 ranged from about 0.19 to about 1.16 feet less than in the base case, indicating that the discontinuation of pumpage at well 14N/3E-14P1 would result in substantially reduced subsidence. Overall, continued water-table declines dewatered the more productive upper layers of the aquifer, causing more groundwater to be withdrawn from deeper, lower yielding layers and resulting in faster declines in the water table and greater vertical gradients in the future. If the water table declines into the perforated intervals of wells, increased maintenance costs and altered well-water quality could potentially result. Water-management scenario 1 indicated that adding managed recharge resulted in a modest decrease (4–5 percent) in the rate of subsidence compared with historical conditions. The reduction of pumpage in the area of subsidence and redistribution of the amount of reduced pumpage to wells in other parts of the basin (scenario 3) resulted in modest decreases (5–6 percent) in the rate of subsidence compared with continuation of historical pumpage. Including either a basin-wide reduction of pumpage of 3 percent annually (cumulatively, a 24 percent decrease) as well as redistribution of the pumpage (scenario 4) or discontinuing pumping in the area of greatest subsidence (scenario 5), however, demonstrated that subsidence could be reduced substantially (22–26 percent for scenario 4 and 62–68 percent for scenario 5) compared with subsidence for continuing historical pumpage.

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 Conditions in Las Vegas Valley, Clark County, Nevada, Part 2, Hydrogeology and Simulation of Ground-Water Flow

U.S. Geological Survey (USGS) | July 1st, 1996

Click here for part 1

Click here for part 1

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.  

Ground-water Hydrology of the Hollister and San Juan Valleys 1913-68

U.S. Geological Survey (USGS) | August 31st, 1972

The Hollister and San Juan Valleys are within the Gilroy-Hollister ground-water basin. That part of the ground-water basin underlying the valleys consists of thre

The Hollister and San Juan Valleys are within the Gilroy-Hollister ground-water basin. That part of the ground-water basin underlying the valleys consists of three subbasins each of which contains two or more ground-water subunits. The subbasin and subunit boundaries are formed by known or postulated faults, folded sedimentary rocks, and igneous rocks. The principal water-bearing units are lenticular beds of sand and gravel interbedded with clay, silt, sand, and gravel, or their locally consolidated equivalents, which range from Pliocene to Holocene in age. Ground water occurs mainly under artesian or semiartesian conditions but also under unconfined (water-table) conditions in areas adjacent to most surface streams and, locally, under perched or semiperched conditions. In 1968 the depth to water in wells ranged from approximately 20 feet above land surface to more than 200 feet below land surface. Water-level differences in wells across the boundaries of adjacent subunits ranged from about 10 to more than 100 feet. Withdrawals of groundwater for irrigation began in 1878. Since that time water levels in wells have declined more than 180 feet in the Hoilister Valley and more than 100 feet in the San Juan Valley. Serious declines in water levels probably did not begin, however, in most of the area until after 1945. Since 1945 large cones of depression have formed in each of the major subbasins. The centers of the cones are approximately one-half mile northeast of Hoilister in the Hollister subbasin, 1% miles northwest of Hollister in the Gilroy-Bolsa subbasin, and one-half mile east of San Juan Bautista in the San Juan subbasin. Ground-water movement beneath both valleys is now toward and into the cones. Ground water in the eastern part of the Hollister Valley locally contains objectionable concentrations of boron and chloride. However, available data indicate that significant changes in the distribution patterns of these constituents have not occurred since 1939.

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

Groundwater depletion in California’s Central Valley accelerates during megadrought

Nature Portfolio (Springer Nature) | December 19th, 2022

Groundwater provides nearly half of irrigation water supply, and it enables resilience during drought, but in many regions of the world, it remains poorly, if at all mana

Groundwater provides nearly half of irrigation water supply, and it enables resilience during drought, but in many regions of the world, it remains poorly, if at all managed. In heavily agricultural regions like California’s Central Valley, where groundwater management is being slowly implemented over a 27-year period that began in 2015, groundwater provides two–thirds or more of irrigation water during drought, which has led to falling water tables, drying wells, subsiding land, and its long-term disappearance. Here we use nearly two decades of observations from NASA’s GRACE satellite missions and show that the rate of groundwater depletion in the Central Valley has been accelerating since 2003 (1.86 km3/yr, 1961–2021; 2.41 km3/yr, 2003–2021; 8.58 km3/yr, 2019–2021), a period of megadrought in southwestern North America. Results suggest the need for expedited implementation of groundwater management in the Central Valley to ensure its availability during the increasingly intense droughts of the future.