Science, society, and the coastal groundwater squeeze

American Geophysical Union (AGU) | April 28th, 2017

Coastal zones encompass the complex interface between land and sea. Understanding how water and solutes move within and across this interface is essential for managing r

Coastal zones encompass the complex interface between land and sea. Understanding how water and solutes move within and across this interface is essential for managing resources for society. The increasingly dense human occupation of coastal zones disrupts natural groundwater flow patterns and degrades freshwater resources by both overuse and pollution. This pressure results in a ‘‘coastal groundwater squeeze,’’ where the thin veneers of potable freshwater are threatened by contaminant sources at the land surface and saline groundwater at depth. Scientific advances in the field of coastal hydrogeology have enabled responsible management of water resources and protection of important ecosystems. To address the problems of the future, we must continue to make scientific advances, and groundwater hydrology needs to be firmly embedded in integrated coastal zone management. This will require interdisciplinary scientific collaboration, open communication between scientists and the public, and strong partnerships with policymakers.

Sea-level rise and coastal groundwater inundation and shoaling at select sites in California, USA

Journal of Hydrology: Regional Studies (Elsevier) | January 5th, 2016

Study region: The study region spans coastal California, USA, and focuses on three primary sites: Arcata, Stinson Beach, and Malibu Lagoon. Study focus: 1m and 2m sea-

Study region: The study region spans coastal California, USA, and focuses on three primary sites: Arcata, Stinson Beach, and Malibu Lagoon. Study focus: 1m and 2m sea-level rise (SLR) projections were used to assess vulnerability to SLR-driven groundwater emergence and shoaling at select low-lying, coastal sites in California. Separate and combined inundation scenarios for SLR and groundwater emergence were developed using digital elevation models of study site topography and groundwater surfaces constructed from well data or published groundwater level contours. New hydrological insights for the region: SLR impacts are a serious concern in coastal California which has a long (∼1800km) and populous coastline. Information on the possible importance of SLR-driven groundwater inundation in California is limited. In this study,the potential for SLR-driven groundwater inundation at three sites (Arcata, Stinson Beach,and Malibu Lagoon) was investigated under 1m and 2m SLR scenarios. These sites provide insight into the vulnerability of Northern California coastal plains, coastal developments built on beach sand or sand spits, and developed areas around coastal lagoons associated with seasonal streams and berms. Northern California coastal plains with abundant shallow groundwater likely will see significant and widespread groundwater emergence, while impacts along the much drier central and southern California coast may be less severe due to the absence of shallow groundwater in many areas. Vulnerability analysis is hampered by the lack of data on shallow coastal aquifers, which commonly are not studied because they are not suitable for domestic or agricultural use. Shallow saline aquifers may be present in many areas along coastal California, which would dramatically increase vulnerability to SLR-driven groundwater emergence and shoaling. Improved understanding of the extent and response of California coastal aquifers to SLR will help in preparing for mitigation and adaptation.

Sea-level rise impacts on seawater intrusion in coastal aquifers: Review and integration

Journal of Hydrology (Elsevier) | February 6th, 2016

Sea-level rise (SLR) influences groundwater hydraulics and in particular seawater intrusion (SWI) in many coastal aquifers. The quantification of the combined and relativ

Sea-level rise (SLR) influences groundwater hydraulics and in particular seawater intrusion (SWI) in many coastal aquifers. The quantification of the combined and relative impacts of influential factors on SWI has not previously been considered in coastal aquifers. In the present study, a systematic review of the available literature on this topic is first provided. Then, the potential remaining challenges are scrutinized. Open questions on the effects of more realistic complexities such as gradual SLR, parameter uncertainties, and the associated influences in decision-making models are issues requiring further investigation. We assess and quantify the seawater toe location under the impacts of SLR in combination with recharge rate variations, land-surface inundation (LSI) due to SLR, aquifer bed slope variation, and changing landward boundary conditions (LWBCs). This is the first study to include all of these factors in a single analysis framework. Both analytical and numerical models are used for these sensitivity assessments. It is demonstrated that (1) LSI caused by SLR has a significant incremental impact on the seawater toe location, especially in the flatter coasts and the flux-controlled (FC) LWBCs, however this impact is less than the reported orders of magnitude differences which were estimated using only analytical solutions; (2) LWBCs significantly influence the SLR impacts under almost all conditions considered in this study; (3) The main controlling factors of seawater toe location are the magnitudes of fresh groundwater discharge to sea and recharge rate. Regional freshwater flux entering from the landward boundary and the groundwater hydraulic gradient are the major contributors of fresh groundwater discharge to sea for both FC and head-controlled (HC) systems, respectively; (4) A larger response of the aquifer and larger seawater toe location changes are demonstrable for a larger ratio of the aquifer thickness to the aquifer length particularly in the HC systems; (5) The lowest sensitivity of seawater toe location is found for the density difference ratio of the seawater and freshwater, and also for the aquifer bed slope; (6) The early-time observations show seawater fingers below the inundated lands due to SLR which are diminished and ultimately extinguished; and (7) A less than 2% reversal effect on the seawater toe location after overshoot mechanism is observed in the transient simulations which suggests that this mechanism is an insignificant and impractical factor compared to other more significant factors.

Seawater intrusion processes, investigation and management: Recent advances and future challenges

Advances in Water Resources (Elsevier) | January 17th, 2013

Seawater intrusion (SI) is a global issue, exacerbated by increasing demands for freshwater in coastal zones and predisposed to the influences of rising sea levels and ch

Seawater intrusion (SI) is a global issue, exacerbated by increasing demands for freshwater in coastal zones and predisposed to the influences of rising sea levels and changing climates. This review presents the state of knowledge in SI research, compares classes of methods for assessing and managing SI, and suggests areas for future research. We subdivide SI research into categories relating to processes, measurement, prediction and management. Considerable research effort spanning more than 50 years has provided an extensive array of field, laboratory and computer-based techniques for SI investigation. Despite this, knowledge gaps exist in SI process understanding, in particular associated with transient SI processes and timeframes, and the characterization and prediction of freshwater–saltwater interfaces over regional scales and in highly heterogeneous and dynamic settings. Multidisciplinary research is warranted to evaluate interactions between SI and submarine groundwater discharge, ecosystem health and unsaturated zone processes. Recent advances in numerical simulation, calibration and optimization techniques require rigorous field-scale application to contemporary issues of climate change, sea-level rise, and socioeconomic and ecological factors that are inseparable elements of SI management. The number of well-characterized examples of SI is small, and this has impeded understanding of field-scale processes, such as those controlling mixing zones, saltwater upconing, heterogeneity effects and other factors. Current SI process understanding is based mainly on numerical simulation and laboratory sand-tank experimentation to unravel the combined effects of tides, surface water–groundwater interaction, heterogeneity, pumping and density contrasts. The research effort would benefit from intensive measurement campaigns to delineate accurately interfaces and their movement in response to real-world coastal aquifer stresses, encompassing a range of geological and hydrological settings.

Second Report of Recharge Parties Pursuant to RWQCB Resolution No. R8-2008-0019 Cooperative Agreement to Protect Water Quality and Encourage the Conjunctive Uses of Imported Water in the Santa Ana River Basin, Yucaipa and San Timoteo Management Zones

San Bernardino Valley Municipal Water District | July 18th, 2012

The importation of water (i.e., State Water Project (SWP) water, Colorado River water, and imported groundwater) to groundwater basins within the Santa Ana River Region

The importation of water (i.e., State Water Project (SWP) water, Colorado River water, and imported groundwater) to groundwater basins within the Santa Ana River Region is necessary to meet increasing demand. However, long-term conjunctive use of water within the Region could affect groundwater quality. As such, the California Regional Water Quality Control Board Santa Ana Region (RWQCB) is requiring that groundwater quality be managed to meet the water quality objectives for total dissolved solids (TDS) and nitrogen (i.e., Salinity Objectives) regulated in the 1995 Water Quality Control Plan for the Santa Ana River Basin (Basin Plan). On January 22, 2004, the RWQCB adopted Resolution No. R8-2004-0001, incorporating an updated TDS and nitrogen management plan that includes revised groundwater subbasin boundaries; revised TDS and nitrate-nitrogen water quality objectives for groundwater; revised TDS and nitrogen waste load allocations; and revised reach designations, TDS and nitrogen objectives and beneficial uses for specific surface waters. On May 19, 2006, the RWQCB considered a resolution and order that would have adopted general waste discharge requirements for the recharge of imported water to the Santa Ana River Basin. Based on input from stakeholders, it was decided by the RWQCB that the feasibility of a cooperative program should be investigated that would achieve the objectives of and obviate the adoption of the draft resolution and order under consideration. On January 18, 2008, the RWQCB adopted Resolution No. R8-2008-0019 authorizing a “Cooperative Agreement to Protect Water Quality and Encourage the Conjunctive Use of Imported Water in the Santa Ana River Basin.” The purpose of the cooperative agreement is to allow the participating parties to “…monitor and improve water quality objectives within the Santa Ana River Region in a manner that is consistent with the needs of the inhabitants of the Region for a reliable supply of water.” (Cooperative Agreement, 2008). The following Parties have entered into this cooperative agreement: California Regional Water Quality Control Board, Santa Ana Region, City of Corona, City of Riverside, City of San Bernardino Municipal Water Department, Eastern Municipal Water District, Elsinore Valley Municipal Water District, Orange County Water District, San Bernardino Valley Municipal Water District (Valley District), San Gorgonio Pass Water Agency, and Western Municipal Water District of Riverside County (Western).  

Select Water Quality Parameters During Wet and Dry Conditions in the Colorado River Delta

American Water Resources Association (AWRA) | August 27th, 2022

Simulated Effects of Ground-Water Management Alternatives for the Salinas Valley, California

U.S. Geological Survey (USGS) | December 15th, 1988

A two-dimensional digital ground-water flow model was developed to analyze the geohydrology of the ground-water basin in the Salinas Valley. The ground-water model was ca

A two-dimensional digital ground-water flow model was developed to analyze the geohydrology of the ground-water basin in the Salinas Valley. The ground-water model was calibrated for steady-state and transient simulations by comparing simulated with measured or estimated inflows, outflows, and water levels for 1970-81. Preliminary estimates of hydraulic properties and some inflows and outflows were adjusted during model calibration. The simulated mean annual water budget for the basin was 559,500 acre-feet per year each of outflow and inflow. Inflow components consisted of Salinas River recharge (38.3 percent), percolation of irrigation water (34.0 percent), small stream and Arroyo Seco recharge (20.9 percent), seawater intrusion (3.4 percent), and other sources (3.4 percent). Outflow components consisted of agricultural pumpage (91.5 percent), municipal pumpage (4.0 percent), and riparian phreatophyte evapotranspiration (4.5 percent). For the steady-state calibration, 70 percent of the simulated water levels were within 9 feet of measured water levels for 1970-81. A sensitivity analysis determined the overall stability of the model results. The model input variable that probably contributes most to the uncertainty of the results is the quantity of ground-water recharge contributed by irrigation return flow to the unconfined aquifer. A 15-percent change in the estimate of this variable causes an 11-percent change in the simulated river-seepage rate and a 6-percent change in the simulated seawater-intrusion rate. The calibrated model was used to investigate several water-resources management alternatives. Projected pumpage increase at a rate of 1 percent per year for 20 years caused declines in mean annual water levels of 10 to 20 feet in some areas and an increase in seawater intrusion from 18,900 to 23,600 acre-feet per year. Pumpage decreases in the coastal area decreased seawater intrusion more effectively than pumpage decreases farther inland. When pumpage was decreased near the coast, seawater intrusion decreased oneseventh as much. When pumpage was decreased uniformly throughout the valley, the decrease in seawater intrusion was only one-fourteenth the decrease in pumpage. Simulations indicated that replacement of ground-water pumpage with imported surface water in a 9,000-acre service area near the coast would result in a decrease in seawater intrusion equaling nearly onehalf the quantity of imported water. This further confirmed that the rate of seawater intrusion is most sensitive to pumpage near the coast.

Sources of high-chloride water and managed aquifer recharge in an alluvial aquifer in California, USA

Hydrogeology Journal (Springer) | July 3rd, 2015

Southern California winter precipitation variability reflected in 100-year ocean salinity record

Nature Portfolio (Springer Nature) | April 27th, 2023

Rainfall in southern California is highly variable, with some fluctuations explainable by climate patterns. Resulting runoff and heightened streamflow from rain events in

Rainfall in southern California is highly variable, with some fluctuations explainable by climate patterns. Resulting runoff and heightened streamflow from rain events introduces freshwater plumes into the coastal ocean. Here we use a 105-year daily sea surface salinity record collected at Scripps Pier in La Jolla, California to show that El Niño Southern Oscillation and Pacific Decadal Oscillation both have signatures in coastal sea surface salinity. Averaging the freshest quantile of sea surface salinity over each year’s winter season provides a useful metric for connecting the coastal ocean to interannual winter rainfall variability, through the influence of freshwater plumes originating, at closest, 7.5 km north of Scripps Pier. This salinity metric has a clear relationship with dominant climate phases: negative Pacific Decadal Oscillation and La Niña conditions correspond consistently with lack of salinity anomaly/ dry winters. Fresh salinity anomalies (i.e., wet winters) occur during positive phase Pacific Decadal Oscillation and El Niño winters, although not consistently. This analysis emphasizes the strong influence that precipitation and consequent streamflow has on the coastal ocean, even in a region of overall low freshwater input, and provides an ocean-based metric for assessing decadal rainfall variability.

SSALTS Final Phase 3 Report: Evaluate Potential Salt Disposal Alternatives to Identify Acceptable Alternatives for Implementation

Central Valley Salinity Alternatives for Long-Term Sustainability (CV-SALTS) | October 31st, 2016

The purpose of the Strategic Salt Accumulation Land and Transportation Study (SSALTS) is to identify the range of viable Central Valley alternatives for salt disposal to

The purpose of the Strategic Salt Accumulation Land and Transportation Study (SSALTS) is to identify the range of viable Central Valley alternatives for salt disposal to provide input for consideration during development of the Salt and Nitrate Management Plan (SNMP) for the region under the jurisdiction of the Central Valley Regional Water Quality Control Board (Central Valley Water Board). The findings have been used to guide discussions regarding establishment of regional salt management policies and the need for changes to the existing Central Valley Water Board Water Quality Control Plans (Basin Plans) to facilitate salt disposal in a manner that is most beneficial to the region and consistent with the State Water Resources Control Board’s (State Water Board) Recycled Water Policy. This work is being conducted under the direction of the Central Valley Salinity Alternatives for Long-Term Sustainability (CV-SALTS) initiative, which is developing the SNMP for the Central Valley. The SSALTS project has been conducted in three phases (Figure 1-1): Phase 1: Identify and Characterize Existing Salt Accumulation Study Areas – The selection of representative study areas served as archetype situational examples to facilitate discussions regarding salt accumulation and disposal in the Central Valley. Each of these study areas was characterized to establish baseline information that was subsequently used to support development of salt disposal alternatives in Phases 2 and 3. Phase 2: Develop Potential Salt Management Strategies – Phase 2 of SSALTS developed potential long-term salt disposal alternatives in three parts: (1) in-valley alternatives; (2) out-of-valley alternatives; and (3) hybrid alternatives that combined in-valley and out-of valley salt disposal options. Phase 3: Evaluate Potential Salt Disposal Alternatives to Identify Acceptable Alternatives for Implementation – Alternatives developed under Phase 2 were evaluated in this report using selected feasibility criteria (e.g., regulatory, institutional, economic, technological, etc.). The outcome of this evaluation was the identification and prioritization of acceptable salt disposal alternatives for potential incorporation into Central Valley SNMP as salt management implementation measures. The Phase 1 and Phase 2 SSALTS final reports were submitted to the CV-SALTS Executive Committee in December 2013 and September 2014, respectively (CDM Smith 2013; CDM Smith 2014). The Phase 3 SSALTS draft report was submitted to the CV-SALTS Executive Committee in March 2015. Comments were received and incorporated into the Phase 3 SSALTS draft report. The Executive Committee recommended postponing the finalization of the Phase 3 SSALTS report until a draft of the Nitrate Implementation Measures Study (NIMS) report was completed, so that salt and nitrate implementation measures and mitigation strategies could be coordinated. While based on the March 2015 Phase 3 SSALTS draft report – and thus including the changes based on the March 2015 Phase 3 SSALTS draft report – and thus including the changes based on the original comments, the September 2016 Phase 3 SSALTS draft report had major changes in terms of content and structure. The September 2016 Phase 3 SSALTS draft report was sent to the Project Committee on September 20, 2016 and comments were received on October 5, 2016. The second set of comments were addressed and incorporated into this October 2016 Phase 3 SSALTS final report. Appendix E. provides the comments and responses on the September 2016 Phase 3 SSALTS draft report. The Phase 3 SSALTS report provides a path forward, based on the foundation of Phases 1 and 2 and CV-SALTS Executive Committee discussions.