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.

Groundwater Exchange Pools and Urban Water Supply Sustainability: Modeling Directed and Undirected Networks

American Society of Civil Engineers (ASCE) | August 1st, 2018

Groundwater basins are important sources of water supply and storage for many cities. Groundwater exchange pools offer additional opportunities for utilizing these

Groundwater basins are important sources of water supply and storage for many cities. Groundwater exchange pools offer additional opportunities for utilizing these common pool resources, but their potential role in urban water management is not clear, and modeling such exchanges can be challenging. This paper presents an analysis of the potential for groundwater basin exchange pools to contribute to urban water supply sustainability. Building on an existing model of urban water management in Los Angeles, the analysis assesses the potential for groundwater exchange pools to reduce scarcity and demonstrates a method for modeling two-way (undirected) flows within a directed-network model using linear programming. Results indicate that exchange pools can help alleviate shortages from operational changes (reduced imported water) in Los Angeles, but providing more parties with access to storage improves their effectiveness. Exchange pools could potentially provide 6–12% of total supplies and reduce shortages as much as 86%. Considerations for organizing exchange pools are discussed to explore policy implications for managing common pool resources. The analytical method for embedding undirected network flows within a larger directed-network model has wide applicability for water resource systems analysis applications, including modeling water markets and interbasin transfers. * U.C. Davis hosts a discussion of the content by the authors at California Water Blog. 

Groundwater Flow Model of the East and South Las Posas Sub-Basins – Preliminary Draft Report

Calleguas Municipal Water District (CMWD) | January 17th, 2018

INTERA Incorporated (INTERA) was retained by the Calleguas Municipal Water District (CMWD) to develop a numerical groundwater model of the East Las Posas Management Area

INTERA Incorporated (INTERA) was retained by the Calleguas Municipal Water District (CMWD) to develop a numerical groundwater model of the East Las Posas Management Area (ELPMA), which includes the locally-recognized east and south sub-basins of the Las Posas Valley Basin (LPVB). Groundwater in the ELPMA is found in a multiple-aquifer system characterized by intense faulting and folding, which is known to exert structural controls on groundwater flow and movement. The ELPMA is known to receive recharge from surface water flows in Arroyo Las Posas/Simi that runs east to west along the southern edge of the basin. Flows in the Arroyo have become perennial as a result of discharges from wastewater treatment plants and dewatering wells within and upstream of the ELPMA. Hence, understanding and modeling the surface-water/groundwater interaction along the Arroyo is an important component of the numerical model development. CMWD also owns and operates the Las Posas Basin Aquifer Storage and Recovery (ASR) Project, consisting of eighteen high capacity ASR wells and associated facilities located in the ELPMA that are used to inject and recover potable water purchased from Metropolitan Water District of Southern California (Metropolitan). Basin response to injection/extractions at the ASR well fields and the evaluation of storage capacity of the ASR well field are key considerations for this modeling project. 

Groundwater Management and Safe Drinking Water in the San Joaquin Valley

Water Foundation | June 2nd, 2020

Groundwater Monitoring Protocols for Seawater Intrusion: Example of Challenges and Experiences in a Coastal Groundwater Basin

Groundwater Resources Association of California (GRA) | October 2nd, 2017

“Seawater intrusion refers to the advancement of seawater into a groundwater supply that results in degradation of water quality in the basin, and includes seawater fro

“Seawater intrusion refers to the advancement of seawater into a groundwater supply that results in degradation of water quality in the basin, and includes seawater from any source.” –GSP Emergency Regulations (Preface to a presentation by Kathleen Kuepper of the United Water Conservation District to the 26th annual meeting of the Groundwater Resources Association of California)

Groundwater Pumping Allocations under California’s Sustainable Groundwater Management Act: Considerations for Groundwater Sustainability Agencies

Environmental Defense Fund (EDF) | July 1st, 2018

The Sustainable Groundwater Management Act (SGMA) became law on January 1, 2015, forever changing the manner in which groundwater will be managed in California. It requir

The Sustainable Groundwater Management Act (SGMA) became law on January 1, 2015, forever changing the manner in which groundwater will be managed in California. It requires local Groundwater Sustainability Agencies (GSAs) to be formed and Groundwater Sustainability Plans (GSPs) to be prepared in order to achieve sustainable groundwater management within 20 years of adopting a GSP. SGMA applies to 127 medium and high priority groundwater subbasins around the state. Over 100 of the medium and high priority groundwater subbasins are in conditions of chronic overdraft (DWR, 2018), meaning average annual groundwater extractions exceed average annual water replenishment to many of the subbasins. These conditions have resulted in a variety of undesirable impacts to the subbasin, including, but not limited to, increasing depth to groundwater, reductions of groundwater storage, seawater intrusion, degraded water quality, and land subsidence. In many subbasins, groundwater overdraft conditions will require GSAs to impose reductions in pumping in order to achieve sustainable conditions in the subbasin. To do this, GSAs will need set a limit or “cap” on the overall amount of groundwater that is removed from the subbasin, assigning portions of this capped amount to groundwater pumpers in the form of a pumping allocation. Making pumping allocation decisions will be a difficult task for GSAs, as it will require restricting access to groundwater resources upon which the agricultural community, cities and towns, and others depend. SGMA expressly does not create or adjust groundwater rights and the basic law of groundwater rights remains largely unchanged. Simply put, this means that while GSAs are tasked with managing groundwater with the goal of bringing groundwater conditions into balance and stopping further depletions and other undesirable impacts, they do not have the authority to change or modify groundwater rights. Thus, GSAs should be mindful of the basic law of groundwater as articulated by the common law and a series of adjudicatory court decisions over the last 100 plus years. The subject of this paper is how to address this dilemma, with the reasoning that if GSAs devise groundwater allocation schemes in a manner consistent with the fundamental principles of groundwater law, the schemes are likely to be more durable, and GSAs are more likely to achieve sustainable groundwater management in a legally defensible manner. To do this, we first provide background on the nature of groundwater rights and how the hierarchy of groundwater rights may affect the legal defensibility of pumping allocations imposed by GSAs upon pumpers. We then discuss the role of groundwater allocations and methods for allocating groundwater pumping rights, and then offer a suggested allocation approach with criteria for consideration when using this approach. To help readers work through the allocation process, the paper includes a hypothetical decision tree graphic. We also discuss the importance of measurement, tracking, and enforcement, as well as additional considerations under SGMA before offering some concluding remarks.

Groundwater Quality in the South Coast Interior Basins, California

U.S. Geological Survey (USGS) | May 14th, 2014

The South Coast Interior Basins (SCI) study unit covers approximately 653 square miles and consists of the Livermore, Gilroy-Hollister, Cuyama Valley, Castac Lake Valley,

The South Coast Interior Basins (SCI) study unit covers approximately 653 square miles and consists of the Livermore, Gilroy-Hollister, Cuyama Valley, Castac Lake Valley, Cuddy Canyon Valley, Cuddy Ranch Area, Cuddy Valley, and Mil Potrero groundwater basins (California Department of Water Resources, 2003). These basins were grouped into three study areas based on geography: Livermore (LIV), Gilroy (GIL), and Cuyama (CUY) (Mathany and others, 2009). Average annual precipitation across the study unit varies among the three study areas—from more than 20 inches (in.) along the northwest margin of the LIV study area to less than 8 in. in the northern parts of the CUY study area. The study areas are drained by the Arroyo de la Laguna canal in LIV, the Pájaro River and the San Benito River in GIL, and the Cuyama River in CUY. The primary aquifer system consists of Plio-Pleistocene sedimentary formations, Tertiary to Holocene-age alluvial sedimentary sequences, and unconfined Holocene- age and Pleistoceneage alluvium. The primary aquifer system is defined as those parts of the aquifers corresponding to the perforated intervals of the public-supply wells listed in the California Department of Public Health (CDPH) database. Public-supply wells in the study unit are typically drilled to depths between 200 and 600 feet, consist of solid casing from the land surface to a depth of about 50 to 350 feet, and are perforated below the solid casing. Water quality in the primary aquifer system may differ from that in the shallower and deeper parts of the aquifer system. Land use within 500-meter buffer areas around the wells in the study unit is approximately 44 percent (%) agricultural, 29% urban, and 27% natural. Agricultural lands are mostly orchards, row crops, vineyards, or pastures. The largest urban areas are the cities of Livermore and Gilroy. Recharge to groundwater basins occurs as infiltration of spring and streamflow, direct infiltration of precipitation and irrigation, subsurface inflow, and engineered recharge (percolation ponds and river regulation). The primary sources of groundwater discharge are water pumped for irrigation and municipal supply, discharge to rivers and streams, and evaporation.

Groundwater Resource Management Fundamentals: Groundwater Basin Connectivity

United Water Conservation District (UWCD) | May 14th, 2014

As Ventura County and the rest of the State of California continue to deal with drought conditions there is an increased interest and reliance on groundwater reso

As Ventura County and the rest of the State of California continue to deal with drought conditions there is an increased interest and reliance on groundwater resources. Over the past decade or so the CA Department of Water Resources and others have promoted water supply planning by watershed groups or other local entities, and this approach has generally been accepted by planners and stakeholders. In Ventura County, there is significant groundwater flow between defined groundwater basins both within and between watersheds, and stream flow in the dry seasons is commonly dependent on groundwater discharges to stream channels. Groundwater flow between connected subbasins has long been recognized in southern Ventura County, most notably in the groundwater basins that underlie the watersheds of the Santa Clara River and Calleguas Creek. The intent of this Open-File Report is to document the historical evolution of the concept of the hydrologic connectivity of groundwater basins in the Santa Clara River valley and the Oxnard Plain coastal area, and to summarize the underlying scientific data supporting the hydrologic connectivity principle. The idea of groundwater basin connectivity is not new, and in fact, predates the formation of United Water Conservation District (United), but is a concept that is embraced by United as a key tenet of their groundwater management activities. As a primary groundwater management entity for the Santa Clara River valley and Oxnard Plain area, United has extensive datasets supporting the concept of groundwater flow or movement (i.e., connectivity) between the subbasins in its jurisdiction. The current drought conditions being experienced in Ventura County have reinvigorated a desire by several entities to develop basin-wide or regional water supply management plans. Clearly, the hydrologic relationships between the groundwater basins are important factors for recognition in water supply management plans. The effects of groundwater extraction or wastewater discharge, for example, impact downgradient subbasins and respective stakeholders. Recognition of this important hydrologic relationship is fundamental to creating long-term sustainable groundwater resource management strategies. The current regulatory setting in California includes several attempts to “manage” groundwater resources or water resource, in general, but those attempts are often focused at a local level (e.g., Urban Water Management Plans, Agricultural Water Management Plans) that do not account for the regional nature of this resource. These “entity-specific” plans are not, by themselves, sufficient for water resource sustainability planning purposes as they frequently ignore or minimize the importance of the regional nature of the hydrologic system. This Open-File Report has been prepared to provide Ventura County water resource management agencies (e.g., Fox Canyon Groundwater Management Agency, Ventura County Watershed Protection District, United Water Conservation District) and local municipalities and businesses that may be stakeholders in the development of water resource management and sustainability plans a guiding framework for thinking about how the hydrologic systems in the Santa Clara River valley and the greater Oxnard Plain coastal area function.

Groundwater Sustainability Agency Support and Sustainable Groundwater Management Planning

Freshwater Trust | January 16th, 2018

California’s Sustainable Groundwater Management Act (SGMA) poses significant challenges for the expedited establishment of Groundwater Sustainability Agencies (GSA) and

California’s Sustainable Groundwater Management Act (SGMA) poses significant challenges for the expedited establishment of Groundwater Sustainability Agencies (GSA) and the development of effective Groundwater Sustainability Plans (GSP) or alternative compliance plans. The Freshwater Trust has experience working with eligible agencies, counties, and the California Department of Water Resources to support GSA development. We partner with the respective technical and administrative staff to streamline the governance process and to meet the schedule for implementation.

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.