Category: Resource Type

DWR’s SGMA Best Management Practices and Guidance Documents

February 2, 2023 No Comments

This link is a one-stop shop for DWR’s SGMA-related Best Management Practices (BMPs) and Guidance Documents to assist Groundwater Sustainability Agencies (GSAs) with developing Groundwater Sustainability Plans (GSPs).

The Sustainable Groundwater Management Act (SGMA), Water Code Section 10729(d), directed DWR to “publish on its internet Web site best management practices for the sustainable management of groundwater,” by January 1, 2017. DWR developed and published 2 categories of information – Best Management Practices (BMPs) and Guidance Documents – to assist Groundwater Sustainability Agencies (GSAs) with developing Groundwater Sustainability Plans (GSPs).

BMPs and Guidance Documents are not substitutes for GSP Regulations or the statutory provisions of SGMA. With the exception of 2 specific BMPs addressed in the GSP Regulations (Section 352.2, Monitoring Protocols and Section 352.4, Data and Reporting Standards), SGMA and the GSP Regulations provide no direction or limitation with respect to what type of BMPs and Guidance Documents should be developed to assist GSAs with making sustainable groundwater management decisions. DWR may develop additional BMPs and Guidance Documents, or make revisions to the existing publications, as needed.

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

February 2, 2023 No Comments

This report was undertaken to provide technical information on the state of streams and groundwater resources in the Central Valley. The findings of this report were used to support the need for what is now known as the Sustainable Groundwater Management Act (SGMA). The intent was to illustrate the physical inter-relationship between the surface and groundwater resources and the potential impacts that groundwater pumping has had and is currently having on our rivers and streams to demonstrate the need for sustainable groundwater management.

Based on the scale of the data used in this study, the findings contained herein should not be used as a definitive source in determining whether a particular stream or river reach should or should not be considered as an interconnected surface water for SGMA purposes. Further study at a finer scale would be necessary for such a determination.

GAMA: Groundwater Ambient Monitoring and Assessment Program

February 2, 2023 No Comments

The State Water Board GAMA Program and the U.S. Geological Survey have created tools to help users understand groundwater quality in California. A range of online tools allow users to access data through web maps and data querying tools.

ICONS: Interconnected Surface Water in California’s Central Valley

February 2, 2023 No Comments

Sustainable groundwater management in California requires an understanding of how groundwater pumping affects surface water features. Groundwater seeps into many river and lake beds in California, providing a steady source of cool clean water. This source of water is crucial for people and nature because it remains steady throughout the year even after the winter rains stop. Under the Sustainable Groundwater Management Act (SGMA),
interconnected surface water (ISW) is defined as “surface water that is hydraulically connected at any point by a continuous saturated zone to the underlying aquifer and the overlying surface water is not completely depleted” (Groundwater Sustainability Plan Emergency Regulations).

SGMA requires special treatment of ISW, but in many parts of the state, ISW is poorly understood. This dataset categories rivers and stream segments on the likelihood that they are ISW, using groundwater depth as a proxy to determine ISW. This data is available to view in an interactive online map at: http://icons.codefornature.org/.

SGMA Data Viewer

February 2, 2023 No Comments

As part of DWR’s technical assistance to Groundwater Sustainability Agencies (GSAs), other water managers, and the public, DWR has developed the SGMA Data Viewer. The SGMA Data Viewer provides access to groundwater-related datasets that are organized by the requirements of SGMA and the Groundwater Sustainability Plan (GSP) regulations for the purposes of supporting GSP development and implementation.

Currently, regional and statewide groundwater information is publicly available, however this information is collected and disseminated through a variety of portals and applications. The SGMA Data Viewer provides centralized data access that will improve coordination across the State and help GSAs meet the requirements of SGMA and the GSP regulations.

This site includes historical and current data on:
Groundwater levels
Groundwater storage
Water quality
Land subsidence
Interconnected surface water
Water budgets
Hydrogeological conceptual models
Reference layers

Management Considerations for Protecting Groundwater Quality Under Agricultural Managed Aquifer Recharge

February 2, 2023 No Comments

Unsustainable groundwater use in California – due in large part to historical over-pumping of aquifer systems, growing reliance on groundwater to meet irrigation and urban water demands, and increasing frequency of drought – affects all water users and threatens agricultural viability into the future, but has disproportionately impacted disadvantaged communities and jeopardizes their access to safe, clean and affordable water. To secure the availability of groundwater for all uses, the state enacted the Sustainable Groundwater Management Act (SGMA) in 2014. Groundwater Sustainability Agencies (GSAs) were charged with developing Groundwater Sustainability Plans (GSPs) to avoid undesirable effects of ongoing groundwater depletion. To meet these goals, many GSPs include managed aquifer recharge (MAR) as one of several key tools to improve groundwater sustainability.

Agricultural Managed Aquifer Recharge (AgMAR) is the act of intentionally flooding fallow, dormant, or active cropland when excess surface water is available. AgMAR has the potential to be a cost-effective and high impact form of MAR due to the large acreage of cropland throughout California. As more farmers adopt AgMAR, there is greater urgency to understand the potential water quality risks and benefits associated with recharge. While pesticides and geogenic contaminants such as arsenic pose additional water quality concerns in MAR projects, this paper focuses specifically on water quality considerations for nitrate and salts related to AgMAR activities.

Nitrate contamination of groundwater is expected to worsen into the future. However, a combination of improved nutrient management and carefully implemented AgMAR projects could improve groundwater quality faster than under business as usual. Improvements in nitrogen management practices should be prioritized to reduce current and future nitrogen (N) loading to groundwater. Furthermore, relatively clean (nitrate free) recharge water (e.g. high magnitude flood flows) should be used during AgMAR events in order to dilute incoming and existing nitrate in groundwater. AgMAR programs should prioritize sites that can recharge in longer-duration single-flooding events, such as sandier sites, to capitalize on the dilution effect and reduce biologically mediated mineralization of organic N (the conversion of organic N to nitrate).

AgMAR alone will not lead to substantive improvement in groundwater quality with respect to nitrate without concomitant improvements in current agronomic nitrogen management and sufficient water for dilution. The development of transparent and easy-to-use tools that estimate the amount of residual nitrate at the end of a growing season, the amount of water needed to dilute nitrate under AgMAR, and time of travel to groundwater will help in the successful implementation of recharge projects to avoid negative water quality externalities. Current nitrogen loading maps and locations of drinking water supply wells can be used by GSAs to get a sense of regional nitrogen loading to groundwater and help in planning and prioritizing efforts on sites to target for AgMAR.

Protecting Groundwater Quality While Replenishing Aquifers

February 2, 2023 No Comments

This document represents a first step towards management guidance for on-farm recharge planners and practitioners to maximize benefits to water quality and to manage risks under AgMAR. This document is also intended to be used as a resource for communities so they can more fully participate in the GSA decision-making process.

The intent of this management brief is to build understanding of how drinking water could be affected by AgMAR and identify management considerations that can be used to design AgMAR projects that are mindful of water quality. These considerations are neither prescriptive nor meant to cover the full scope of considerations needed to implement a successful recharge project or program (i.e., analysis of soil and crop suitability, hydrogeology, water rights and availability, and conveyance infrastructure, among other topics).

Protegiendo la Calidad del Agua Subterranea Mientras se Reponen los Acuiferos

February 2, 2023 No Comments

Este documento representa un primer paso hacia la guía de manejo para los administradores y profesionales de la recarga a nivel parcela para maximizar los beneficios para la calidad del agua y manejar los riesgos bajo Ag-MAR. Este documento también está destinado a ser utilizado como un recurso para que las comunidades puedan participar más plenamente en el proceso de toma de decisiones de la GSA.

La intención de este informe de manejo es desarrollar la comprensión de cómo Ag-MAR podría afectar el agua potable e identificar las consideraciones de manejo que se pueden utilizar para diseñar proyectos Ag-MAR que tengan en cuenta la calidad del agua. Estas consideraciones no son prescriptivas ni pretenden cubrir el alcance completo de las consideraciones necesarias para implementar un proyecto o programa de recarga exitosa (es decir, análisis de cultivos adecuados de suelos y cultivos, hidrogeología, derechos y disponibilidad de agua e infraestructura de flujo, entre otros temas).

Managed aquifer recharge site assessment with electromagnetic imaging: Identification of recharge flow paths

January 31, 2023 No Comments

Surface spreading recharge, the intentional flooding of the ground surface to replenish a groundwater system, is one approach used to mitigate groundwater overdraft in California’s Central Valley (CV). Choosing appropriate sites for surface spreading recharge, in regard to the sites’ ability to convey water from the ground surface to the desired recharge depth, can be challenging because of limited knowledge of the properties of the subsurface. In this study, we present an approach for using a towed time-domain electromagnetic (tTEM) imaging method to develop three-dimensional (3D) models of sediment type, map potential flow paths through the subsurface, and evaluate sites for surface spreading. We began with tTEM data from seven sites in the CV along with an existing resistivity-to-sediment type transform. We leveraged geostatistical methods to generate multiple 3D models of binary (flow and no-flow) sediment type from the tTEM data. We then developed two metrics to assess the quality of sites for recharge: (a) the depth to the shallowest no-flow unit beneath each point at the surface and (b) preferential flow paths lengths measured by finding the shortest distance through connected flow units between surface points and the desired depth. We explored how these metrics can be used to identify optimal areas within a site, then developed a way to compare and assess the relative suitability of each site using the decay in the number of vertical flow paths as a function of depth. Our methods can be used to rapidly identify potential sites for surface spreading recharge.

Airborne geophysical method images fast paths for managed recharge of California’s groundwater

January 25, 2023 No Comments

Given the substantial groundwater level declines in the Central Valley of California, there is an urgent need to supplement the recharge of the groundwater systems by implementing managed aquifer recharge. With approximately 170 km3 (140 million acre-feet) of available groundwater storage space, water deemed to be excess during wet years could be spread on the ground surface at selected locations allowing it to move downward to recharge the underlying aquifer system. Along the eastern edge of the Central Valley there are large paleovalleys that can act as fast paths expediting the downward movement of water. These paleovalleys, incised and then filled with coarse-grained materials—sand, gravel, cobbles—at the end of the last glacial period, are referred to as incised valley fill (IVF) deposits. An IVF deposit has been mapped at one location in the Kings River alluvial fan, with others proposed to exist in the fans of major rivers. If located, these deposits would be optimal sites for managed recharge. In this study, we assessed the use of a helicopter deployed geophysical method to efficiently locate IVF deposits throughout the Central Valley. We acquired 542 line-kilometers of airborne electromagnetic (AEM) data in the Kings River alluvial fan, with dense line-spacing over the Kings River IVF deposit which had been mapped as ∼2 km wide, extending over 20 km into the Central Valley, from the ground surface to a depth of 30 m. The IVF deposit was unambiguously imaged in the AEM data as an extensive linear feature that was more electrically resistive than the surrounding materials due to the high percentage of coarse-grained sediments. This study provides the evidence to support the rapid adoption of the AEM method to locate IVF deposits along the eastern edge of the Central Valley. These deposits provide valuable natural infrastructure for recharging California’s groundwater.