Effects of Sea‐Level Rise on Ground Water Flow in a Coastal Aquifer System

National Groundwater Association (NGWA) | January 29th, 2007

The effects of sea‐level rise on the depth to the fresh water/salt water interface were simulated by using a density‐dependent, three‐dimensional numerical ground w

The effects of sea‐level rise on the depth to the fresh water/salt water interface were simulated by using a density‐dependent, three‐dimensional numerical ground water flow model for a simplified hypothetical fresh water lens that is similar to shallow, coastal aquifers found along the Atlantic coast of the United States. Simulations of sea‐level rise of 2.65 mm/year from 1929 to 2050 resulted in an increase in water levels relative to a fixed datum, yet a net decrease in water levels relative to the increased sea‐level position. The net decrease in water levels was much greater near a gaining stream than farther from the stream. The difference in the change in water levels is attributed to the dampening effect of the stream on water level changes in response to sea‐level rise. In response to the decreased water level altitudes relative to local sea level, the depth to the fresh water/salt water interface decreased. This reduction in the thickness of the fresh water lens varied throughout the aquifer and was greatly affected by proximity to a ground water fed stream and whether the stream was tidally influenced. Away from the stream, the thickness of the fresh water lens decreased by about 2% from 1929 to 2050, whereas the fresh water lens thickness decreased by about 22% to 31% for the same period near the stream, depending on whether the stream was tidally influenced. The difference in the change in the fresh water/salt water interface position is controlled by the difference in the net decline in water levels relative to local sea level.

Effects of structure and volcanic stratigraphy on groundwater and surface water flow: Hat Creek basin, California, USA

Hydrogeology Journal (Springer) | January 16th, 2022

Hydrogeologic systems in the southern Cascade Range in California (USA) develop in volcanic rocks where morphology, stratigraphy, extensional structures, and attendant ba

Hydrogeologic systems in the southern Cascade Range in California (USA) develop in volcanic rocks where morphology, stratigraphy, extensional structures, and attendant basin geometry play a central role in groundwater flow paths, groundwater/surface-water interactions, and spring discharge locations. High-volume springs (greater than 3 m3/s) flow from basin-filling (

Effects of Surface-Water Use on Domestic Groundwater Availability and Quality During Drought in the Sierra Nevada Foothills, California

U.S. Geological Survey (USGS) | January 13th, 2020

Approximately 2 million California residents rely on privately owned domestic wells for drinking water. During the California drought of 2012−16 groundwater lev

Approximately 2 million California residents rely on privately owned domestic wells for drinking water. During the California drought of 2012−16 groundwater levels declined in many parts of the state and wells were deepened in response. Most of the wells deepened during this time were domestic wells that were drilled into fractured bedrock throughout the Sierra Nevada foothills region of northern California (California Department of Water Resources, 2014). To understand the impacts of extreme drought on groundwater supply availability and quality in this setting, the United States Geological Survey (USGS) completed a geochemical survey of domestic wells throughout the Yuba and Bear River watersheds during 2015–16 (fig. 1) as part of the State Water Board’s Groundwater Ambient Monitoring and Assessment Program Priority Basin Project (GAMA-PBP). This fact sheet highlights key findings from the GAMA-PBP assessment (Levy and others, 2020).

Electrical Resistivity Imaging of Seawater Intrusion into the Monterey Bay Aquifer System

National Groundwater Association (NGWA) | June 17th, 2015

We use electrical resistivity tomography to obtain a 6.8‐km electrical resistivity image to a depth of approximately 150 m.b.s.l. along the coast of Monterey Bay. The

We use electrical resistivity tomography to obtain a 6.8‐km electrical resistivity image to a depth of approximately 150 m.b.s.l. along the coast of Monterey Bay. The resulting image is used to determine the subsurface distribution of saltwater‐ and freshwater‐saturated sediments and the geologic controls on fluid distributions in the region. Data acquisition took place over two field seasons in 2011 and 2012. To maximize our ability to image both vertical and horizontal variations in the subsurface, a combination of dipole–dipole, Wenner, Wenner‐gamma, and gradient measurements were made, resulting in a large final dataset of approximately 139,000 data points. The resulting resistivity section extends to a depth of 150 m.b.s.l., and is used, in conjunction with the gamma logs from four coastal monitoring wells to identify four dominant lithologic units. From these data, we are able to infer the existence of a contiguous clay layer in the southern portion of our transect, which prevents downward migration of the saltwater observed in the upper 25 m of the subsurface to the underlying freshwater aquifer. The saltwater and brackish water in the northern portion of the transect introduce the potential for seawater intrusion into the hydraulically connected freshwater aquifer to the south, not just from the ocean, but also laterally from north to south.

Electrical Resistivity Investigation of Fluvial Geomorphology to Evaluate Potential Seepage Conduits to Agricultural Lands along the San Joaquin River, Merced County, California, 2012–13

U.S. Geological Survey (USGS) | ?

Increased flows in the San Joaquin River, part of the San Joaquin River Restoration Program, are designed to help restore fish populations. However, increased seepage los

Increased flows in the San Joaquin River, part of the San Joaquin River Restoration Program, are designed to help restore fish populations. However, increased seepage losses could result from these higher restoration flows, which could exacerbate existing drainage problems in neighboring agricultural lands and potentially damage crops. Channel deposits of abandoned river meanders that are hydraulically connected to the river could act as seepage conduits, allowing rapid and widespread water-table rise during restoration flows. There is a need to identify the geometry and properties of these channel deposits to assess their role in potential increased seepage effects and to evaluate management alternatives for reducing seepage. Electrical and electromagnetic surface geophysical methods have provided a reliable proxy for lithology in studies of fluvial and hyporheic systems where a sufficient electrical contrast exists between deposits of differing grain size. In this study, direct-current (DC) resistivity was used to measure subsurface resistivity to identify channel deposits and to map their subsurface geometry. The efficacy of this method was assessed by using DC resistivity surveys collected along a short reach of the San Joaquin River in Merced County, California, during the summers of 2012 and 2013, in conjunction with borings and associated measurements from a hydraulic profiling tool. Modeled DC resistivity data corresponded with data from analyses of core samples, hand-auger samples, a hydraulic profiling tool, and aerial photographs, confirming that DC resistivity was effective for differentiating between silty and sandy deposits in this setting. Modeled DC resistivity data provided detailed two-dimensional cross-sectional resistivity profiles to a depth of about 20 meters. The distribution of high-resistivity units in these profiles was used as a proxy for identifying areas of high hydraulic conductivity. Estimates of the cross-sectional area of channel deposits from DC resistivity pseudosections can provide critical input for groundwater-flow models designed to simulate river seepage and evaluate seepage-management alternatives.

Elsinore Valley Subbasin Groundwater Sustainability Plan

Elsinore Valley Municipal Water District | December 23rd, 2021

The Elsinore Valley Subbasin is located within the service area of Elsinore Valley Municipal Water District (EVMWD or District). No other agencies overlap the boundaries

The Elsinore Valley Subbasin is located within the service area of Elsinore Valley Municipal Water District (EVMWD or District). No other agencies overlap the boundaries of this subbasin therefore no inter-agency coordination was required for the development of this GSP. Two outside technical experts participated as the technical advisory committee for the GSP development. EVMWD conducted public outreach throughout the development of the GSP.

Empirical Models of Shallow Groundwater and Multi-Hazard Flood Forecasts as Sea-Levels Rise

American Geophysical Union (AGU) | February 8th, 2025

Knowledge of coastal hydrogeology and hazards as groundwater responds to sea-level rise (SLR) can be improved through installation of shallow groundwater monitoring piezo

Knowledge of coastal hydrogeology and hazards as groundwater responds to sea-level rise (SLR) can be improved through installation of shallow groundwater monitoring piezometers and continuous observations. Interpolation of site data enables mapping of the present-day state of groundwater elevation, depth to groundwater (DTW), their temporal statistical variation, and differing spatial responses to tides and rainfall. Future DTW and its variability can be projected under increments of SLR, with assumptions and caveats, to show where and when episodic and/or permanent inundation can be expected. This methodology is outlined in a case study of Dunedin, New Zealand, which enabled comparison of rising groundwater's contribution to pluvial flooding and groundwater emergence with coastal inundation. Changes in relative land exposure with SLR shows evolution in flood hazard from current pluvial-dominated events, into “flooding from below” and groundwater emergence, in advance of any overland coastal inundation. Dunedin exemplifies how groundwater transfers effects of SLR surprisingly far inland, but the lowest-lying or shoreline-proximal suburbs are not necessarily the most vulnerable. Unlike coastal inundation, rising groundwater is unconstrained by protective topography and presents as a creeping hazard, or contributor to hazards such as pluvial flooding, which can be widespread, occurring already and difficult to defend against. The empirical models contain assumptions and uncertainties important to the veracity of results and application. While conservative (“risk averse”) and a compromise from computationally expensive numerical solutions, their value is in providing the spatial and temporal precision needed for multi-source hazard assessment and holistic adaptive planning.

Ending groundwater overdraft without affecting food security

Nature Portfolio (Springer Nature) | June 14th, 2024

Engineer’s Report for the North Fork Kings Groundwater Sustainability Agency: Proposition 218 Procedures for Benefit Assessments

North Fork Kings Groundwater Sustainability Agency (NFKGSA) | January 15th, 2018

The North Fork Kings Groundwater Sustainability Agency (NFKGSA or Agency) recently formed with the primary purpose of compliance with the Sustainable Groundwater

The North Fork Kings Groundwater Sustainability Agency (NFKGSA or Agency) recently formed with the primary purpose of compliance with the Sustainable Groundwater Management Act (SGMA). As a Groundwater Sustainability Agency (GSA), the Agency may develop, adopt, and implement a Groundwater Sustainability Plan (GSP) for sustainable management of groundwater for that portion of the Kings Subbasin (Subbasin) underlying the Agency. The newly formed Agency needs to implement an assessment rate structure that is sufficient to fund Agency operations and required activities pursuant to SGMA. The NFKGSA will develop, in coordination with other GSAs in the Kings Subbasin, a GSP that provides for achieving groundwater sustainability in the Kings Subbasin of the San Joaquin Valley Groundwater Basin underlying the Agency by January 2040. SGMA requires that a GSP be submitted to the California Department of Water Resources (DWR) by January 31, 2020 since the Kings Subbasin is considered a high priority, critically overdrafted subbasin. Based on the Agency’s needs, the NFKGSA Board of Directors is requesting landowner approval to levy assessments to generate sufficient revenue to fund both annual Agency operation costs and expenses associated with the development and implementation of a GSP. The annual operational costs have already begun and are used to fund Agency operations and activities required by SGMA, including retaining consulting firms and legal counsel to provide Agency oversight and lead the Agency through the steps for SGMA compliance. Expenses consist of administrative support, GSP development, and GSP implementation, with GSP development occurring over the next several years and GSA administration and GSP implementation anticipated to be on-going expenses. The administrative annual expenses include an assumed annual 3% inflation factor. The assessments are planned to apply equally to all assessable lands within the Agency’s boundaries. The Assessment Roll provided in Attachment D identifies the acreage for each assessable parcel according to the 2017 tax rolls of Fresno County and Attachment E identifies the acreage for each assessable parcel according to the 2017 tax rolls of Kings County. The following table provides an example schedule of the proposed assessments during the next five years that are the subject of this Proposition 218 Engineer’s Report. The actual assessment rate will be set annually by the Board, based on the budget needs, but will not exceed the proposed maximum rate. Assessments will continue beyond Fiscal Year 2022-23, but at this time the assessment rate after this initial five-year period is unknown because the GSP Implementation costs will not be fully determined until the GSP is developed. The projects that will be proposed as part of the GSP implementation to attain sustainability and maintain the threshold levels established in the GSP will likely require supplemental funding and assessments greater than the maximum assessments recommended in this report, and approval by the landowners in a future Proposition 218 election will be required.

Enhancing Water Supply through Invasive Plant Removal: A Literature Review of Evapotranspiration Studies on Arundo Donax

Nature Conservancy | February 11th, 2019

Removal of the invasive, non-native plant Arundo donax (Arundo, giant reed) along riparian corridors is being considered by groundwater sustainability agencies

Removal of the invasive, non-native plant Arundo donax (Arundo, giant reed) along riparian corridors is being considered by groundwater sustainability agencies as a potential water savings strategy that could provide co-benefits for groundwater sustainability as well as native ecosystem restoration. Arundo is a fast growing, densely vegetated reed that has purportedly high-water consumption (i.e., transpiration). This paper is intended to help agencies develop estimates of the water supply benefits that could be realized from Arundo removal.