A New Technique for Modeling Land Subsidence Facilitates Better Groundwater Management

Stanford University | December 1st, 2019

Land subsidence – the sudden sinking or gradual settling of Earth’s surface – can occur naturally or be triggered by human activity. One of the most comm

Land subsidence – the sudden sinking or gradual settling of Earth’s surface – can occur naturally or be triggered by human activity. One of the most common human-affected factors is groundwater pumping, a practice that has been steadily increasing due to prolonged periods of drought. Groundwater pumping is so prevalent in some areas that it is severely compromising the quantity and quality of the groundwater as well as the physical structure of the land and aquifer capacity beneath it. Large-scale initiatives for putting water back into the ground, or groundwater recharge, are being implemented in some regions. However, groundwater resource managers still need better information to determine where the land is at greatest risk of subsidence as well as where recharge efforts would be the most effective. Integrating two reliable data gathering sources – helicopter-deployed systems (airborne electromagnetic or AEM technology) that measure electromagnetic fields and satellite-deployed systems (interferometric synthetic aperture radar or InSAR) to measure deformations – offers groundwater managers an improved method for more accurately modeling changes in the land surface related to the pumping and recharge of groundwater. Additionally, the ability to more precisely detect subsidence may offer an early warning system for declining groundwater levels.

A simmering revolt against groundwater cutbacks in California

Stanford University | December 14th, 2022

In 2014, California legislators, focused on groundwater’s accelerating decline during a prolonged drought, passed the Sustainable Groundwater Management Act. Its impera

In 2014, California legislators, focused on groundwater’s accelerating decline during a prolonged drought, passed the Sustainable Groundwater Management Act. Its imperatives: keeping groundwater levels sustainable by 2040 and keeping control of groundwater in local hands. Both goals are now in limbo. As the state endures yet another prolonged drought and state water managers have balked at approving plans covering the basins at greatest risk – the vast majority in the San Joaquin Valley – more growers in a few of the new local groundwater agencies are in revolt at the new rules that will curtail access to the water they once took for granted.

A Simulation-Optimization Model for Water-Resources Management, Santa Barbara, California

U.S. Geological Survey (USGS) | September 1st, 1998

A simulation-optimization model has been developed for the optimal management of the city of Santa Barbara's water resources during a drought. The model, which links grou

A simulation-optimization model has been developed for the optimal management of the city of Santa Barbara's water resources during a drought. The model, which links ground-water simulation with linear programming, has a planning horizon of 5 years. The objective is to minimize the cost of water supply subject to: water demand constraints, hydraulic head constraints to control seawater intrusion, and water capacity constraints. The decision variables are monthly water deliveries from surface water and ground water. The state variables are hydraulic heads. The drought of 1947–51 is the city's worst drought on record, and simulated surface-water supplies for this period were used as a basis for testing optimal management of current water resources under drought conditions. The simulation-optimization model was applied using three reservoir operation rules. In addition, the model's sensitivity to demand, carryover [the storage of water in one year for use in a later year(s)], head constraints, and capacity constraints was tested.

A State Role in Supporting Groundwater Trading with Safeguards for Vulnerable Users: Findings and Next Steps

California Department of Water Resources (DWR) | May 18th, 2022

In those parts of California where groundwater pumping has long exceeded replenishment, people are striving to bring groundwater basins into sustainable conditions within

In those parts of California where groundwater pumping has long exceeded replenishment, people are striving to bring groundwater basins into sustainable conditions within 20 years, between 2040 and 2042, as the Sustainable Groundwater Management Act (SGMA) requires. In some areas, groundwater sustainability agencies (GSAs) – the local agencies tasked with sustainable groundwater management – are beginning to work with other entities and stakeholders to discuss and experiment with the idea of giving groundwater pumpers allocations – allowances to remove a certain amount of water from a groundwater basin – and allowing them to either use their allocation individually or trade allocations between specified parties. Ideally, groundwater trading could ease the economic disruption of cutting back the overall amount of water pumped from a groundwater basin; growers who have less need for pumping could sell their allocation to others willing to pay for it, helping buyers keep their operations functional while compensating sellers. But the concept of groundwater trading raises many questions: How would wetlands, streams, and other ecosystems fed by aquifers be treated in a groundwater trading program? Would operators of farms who lack the resources of larger neighbors be able to benefit from trading? How might trading affect people who depend upon a household well or communities that need reliable groundwater supplies for homes and businesses? How can GSAs work with local stakeholders to develop, implement, and oversee trading programs that help with sustainable groundwater management? There is a State interest behind all of these questions – and a clear need for a focused discussion about groundwater trading.

A Water Resources Data Network Evaluation for Monterey County, California; Phase 1; South County

U.S. Geological Survey (USGS) | July 12th, 1986

An evaluation made of rainfall, surface water, groundwater, and water quality monitoring networks in Salinas River basin in southern Monterey County, California, proposed

An evaluation made of rainfall, surface water, groundwater, and water quality monitoring networks in Salinas River basin in southern Monterey County, California, proposed all long-term rain gages be continued for extending short-term records and suggested the installation of two additional recording gages. Eight new storage rain gages were suggested at midaltitudes of east and west sides of Salinas Valley where few data are available. The evaluation revealed some short-term gaging stations could be discontinued because of good regression relations between them and the long-term stations Arroyo Seco near Soledad. Of 16 stations selected for the proposed network, 4 are new recording stations, 6 are new nonrecording streamflow and water quality sampling sites, 5 are existing stations, and the last is a station operated from 1969 to 1976; also included are water quality sampling stations on Lakes Nacimiento and San Antonio. The proposed groundwater network was developed from information on geology, geohydrology, and groundwater quality, high priority objectives for groundwater network, and consideration for providing good areal coverage of levels and water quality. Of 145 sites selected, 86 are existing monitoring wells.

A Water Resources Data Network Evaluation for Monterey County, California; Phase 3, Northern Salinas River Drainage Basin

U.S. Geological Survey (USGS) | December 13th, 1990

Continuing data collection and analysis are vital to efficient development and management of water resources. To insure that water managers have adequate information on c

Continuing data collection and analysis are vital to efficient development and management of water resources. To insure that water managers have adequate information on conditions and trends, data-collection programs must be evaluated and updated periodically. Changes in population, land use, and agricultural practices may increase the demand for water, so that effective water management and supporting data collection become even more critical. Consideration of cost effectiveness, however, means that every site must count, and redundancy must be minimized. Water resources management and monitoring are ever-changing, and periodic reevaluation is a necessary part of this process. This report presents an evaluation of precipitation, surface-water, and ground-water monitoring networks in the northern Salinas River drainage basin of Monterey County, California. This report is third in a series of reports prepared in cooperation with the Monterey County Flood Control and Water Conservation District (MCFCWCD). The phase 1 report (Showalter and Hoffard, 1986) covers the southern Salinas River drainage basin, the phase 2 report covers the north county and coastal areas of Monterey County (W.E. Templin, P.E. Smith, and R.C. Schluter, U.S. Geological Survey, written commun., 1989), and this report (phase 3) covers the northern Salinas River drainage basin.

A Water Resources Data-Network Evaluation for Monterey County, California, Phase 3: Northern Salinas River Drainage Basin

U.S. Geological Survey (USGS) | December 15th, 1990

This report presents an evaluation of water resources data collection networks in the northern Salinas River drainage basin, Monterey County, California. The eval

This report presents an evaluation of water resources data collection networks in the northern Salinas River drainage basin, Monterey County, California. The evaluation, done in cooperation with the Monterey County Flood Control and Water Conservation District, covers both quantity and quality monitoring by precipitation, surface-water, and ground-water networks. The report describes existing networks in the study area and possible additional data collection. The study identified 34 precipitation gages in the study area, of which 20 are active. The stations are concentrated in the northwestern part of the study area. Data are lacking for the eastern and southern parts of the study area, as well as the southwestern slopes of the Gabilan Range. No precipitation-quality networks were identified. Possible data-collection efforts for precipitation quality include monitoring for acid rain and for pesticides in precipitation. The study identified 10 streamflow-gaging stations, of which 6 are active. To meet the objectives for streamflow networks that are outlined in the report, all sites could be reactivated, and two of the inactive sites could be relocated to improve the reliability of the data. Besides these stations, nine possible additional streamflow-gaging sites were identified. The Monterey County Flood Control and Water Conservation District samples one surface-water site for suspended sediment, specific conductance, and chlorides. Several agencies have done water-quality sampling in the past, but only five sites are active. Reactivation of the 45 inactive sites might help to meet the various surface-water-quality objectives described in the report. Development of a stream-reach rating system also could help to identify parts of the study area most in need of sampling. The Monterey County Flood Control and Water Conservation District maintains three networks to measure ground-water levels on a monthly basis, during peak irrigation, and at the end of the irrigation season. The District measures water levels in 318 wells. The only other network identified for this report was operated by the U.S. Geological Survey, and none of its five wells are active. The study identified 128 sections in which no ground-water-level monitoring is presently done. Well coverage is densest in the saltwater-intrusion areas near Castroville, California. Wells in the rest of the study area are more sparsely distributed and are concentrated down the center of the drainage basin in the alluvial ground-water basin. The ideal initial baseline network of ground-water-quality wells would be an evenly spaced grid of index wells within each aquifer, with a density of one per section. Once baseline conditions were established, representative wells could be selected and monitored annually. As of 1985, the Monterey County Flood Control and Water Conservation District monitored 379 study wells in the area for various water-quality conditions. Other networks monitor (or propose the monitoring of) 135 wells. The District collects samples in summer months to monitor saltwater intrusion near Castroville. Annual samples also are analyzed for chloride, specific conductance, and nitrate. Every 5 years, the District does a complete mineral analysis on each study well. Improvements in network coverage are suggested to better approximate ideal network coverage. The adequacy of wells in existing monitoring networks for representing actual conditions in the ground-water basins was not established conclusively. Possible redundancy of information from existing networks was not evaluated statistically. Despite these limitations, this report does provide a basis for assessing the adequacy of ground-water-level networks in the study area. The computerized Geographic Information System (GIS) that is planned for Monterey County could easily use the information in this report for the needed initial analysis of network adequacy. The feasibility of management and analysis of large complicated data bases (such as the ground water networks identified in this report) is substantially improved through the use of state-of-the-art GIS tools now available.

Adapting to Climate Change and Drought in Selected California Groundwater Basins: Local Achievements and Challenges

California Natural Resources Agency (CNRA) | August 27th, 2018

Climate change projections are for higher temperatures and extreme droughts by the end of the 21st century. This will alter the natural recharge of groundwater, including

Climate change projections are for higher temperatures and extreme droughts by the end of the 21st century. This will alter the natural recharge of groundwater, including decreased inflow from runoff, increased evaporative losses, and warmer and shorter winter seasons, impacts that are likely to exacerbate already existing groundwater overdraft in many basins. Additionally, the imported surface water that can be delivered from the Central Valley Project (CVP) and State Water Project (SWP) to areas reliant on this water for groundwater recharge and consumptive use is projected to be less reliable and more expensive. Yet groundwater is a critical water supply source during drought when it compensates for reduced surface water supplies. The need for proactive adaptation strategies to address the extreme droughts projected under climate change are frequently discussed, yet there are limited examples of such groundwater management strategies. This paper therefore explores:  1) How groundwater management agencies are planning for drought  2) What new approaches are currently being used that show promise for addressing the more extreme droughts projected under climate change? 

Addressing Nitrate in California’s Drinking Water Technical Report 1: Project and Technical Report Outline

University of California, Davis (UC Davis) | July 2nd, 2012

Addressing Nitrate in California’s Drinking Water Technical Report 2: Nitrogen Sources and Loading to Groundwater

University of California, Davis (UC Davis) | July 2nd, 2012

Nitrate loading to groundwater in the Tulare Lake Basin and Salinas Valley is widespread and chronic, and is overwhelmingly the result of crop and animal agricultural ac

Nitrate loading to groundwater in the Tulare Lake Basin and Salinas Valley is widespread and chronic, and is overwhelmingly the result of crop and animal agricultural activities. Urban wastewater, septic systems, and other sources may have significant localized impact. Due to long transit times, the impact on groundwater resources is a legacy for years and decades to come.