scholarly journals Using an airborne electromagnetic method to map saltwater intrusion in the northern Salinas Valley, California

Geophysics ◽  
2020 ◽  
Vol 85 (4) ◽  
pp. B119-B131
Author(s):  
Ian Gottschalk ◽  
Rosemary Knight ◽  
Theodore Asch ◽  
Jared Abraham ◽  
James Cannia
Keyword(s):  
Electrical Resistivity ◽  
Saltwater Intrusion ◽  
Groundwater Resources ◽  
Mitigation Strategies ◽  
Electromagnetic Signal ◽  
Confined Aquifer ◽  
Coastal Regions ◽  
Low Resistivity ◽  
Salinas Valley ◽  
Airborne Electromagnetic

Saltwater intrusion can pose a serious threat to groundwater quality in coastal regions. Estimating the extent of saltwater intrusion is vital for groundwater managers to plan appropriate mitigation strategies. The airborne electromagnetic (AEM) method is commonly used to evaluate groundwater resources, but it is challenging to apply in coastal environments because the low resistivity of saltwater-saturated aquifers attenuates the electromagnetic signal quickly and the relationship between electrical resistivity and pore water salinity is complex. However, if successful, the AEM method can supply information to address questions of critical importance in coastal regions. We investigated the extent of, and controls on, saltwater intrusion using the AEM method in the northern Salinas Valley, CA, USA. We collected 635 line-km of AEM data in the study area, the inversion results of which produced estimates of the electrical resistivity of the subsurface, reaching depths of between 50 and approximately 200 m below the ground surface. We have developed a relationship between the AEM electrical resistivity model and groundwater salinity, calibrated from borehole geophysical and water quality measurements, which allowed us to generate images revealing the distribution of saltwater and fresher groundwater in the study area. This fresher groundwater (defined as “a source of drinking water”) was successfully mapped out in the unconfined aquifer (the Dune Sand Aquifer) and the uppermost confined aquifer (the 180-Foot Aquifer) in the study area, illustrating a groundwater recharge process that helps mitigate saltwater intrusion in the 180-Foot Aquifer. Deep, low-resistivity bodies also were mapped, indicating regions where saltwater likely is migrating vertically from the 180-Foot Aquifer into the lower confined aquifer (the 400-Foot Aquifer). The findings from this case study demonstrate the value of acquiring AEM data for investigating the distribution of salinity in coastal aquifers impacted by saltwater intrusion.

scholarly journals Mapping Saltwater Intrusion using Transient ElectroMagnetic Data in Maopa, Central Province, Papua New Guinea

2021 ◽  
Author(s):  
◽  
Ronald Verave
Keyword(s):  
Papua New Guinea ◽  
Saltwater Intrusion ◽  
Groundwater Resources ◽  
Cost Effective ◽  
New Guinea ◽  
Small Island ◽  
Mixing Zone ◽  
Low Resistivity ◽  
Transient Electromagnetic ◽  
Tem Method

<p>Saltwater intrusion studies in coastal Papua New Guinea (PNG) are a rarity despite recognized vulnerabilities to salination of coastal groundwater resources. For many seaside communities such as Maopa the threat of salination is exacerbated by high extraction rates by a growing population and the likelihood of the effects of climate change. Saltwater intrusion can be addressed using various methods, including direct water sampling from wells and electrical resistivity measurements. This study advances knowledge of a previous assessment of saltwater intrusion and groundwater in this region that used DC Schlumberger resistivity soundings, through an extensive and cost-effective Transient ElectroMagnetic (TEM) survey. The study aims to map the lateral and vertical extent of salination and the characterization of groundwater in the landward direction over seven lines of TEM soundings along Keakalo Bay. The TEM method proved successful in identifying four main geoelectric layers. The top layer has a highly variable resistivity (range of 5 to 355 Ωm) inferred as the vadose zone. Beneath this layer is a layer of intermediate resistivity (100 Ωm > p ≥ 20 Ωm) characterizing a perched freshwater aquifer with a thickness range of 3.2 to 15 m. An intermediate layer of low resistivity (20 Ωm > p ≥ 3 Ωm) was detected at the boundary separating the freshwater aquifer from the inferred saltwater intrusion. This layer is typically thicker than the freshwater aquifer and is referred to as the mixing zone. The deepest layer constituting the salination zone has a very low resistivity (3 Ωm > p ≥ 0.4 Ωm), occurring at depths of up to 42 m. The depth to the salination zone varied from deep in the middle of the survey area to shallow in the fringes of the survey. This pattern is reflective of surface seawater infiltration marked by mangrove forest in the interior and subsurface infiltration from the coast. Similar depth trends but at shallower depths were also observed for the mixing zone, and the freshwater region. In some cases the mixing area overwhelms the freshwater regions. Layering confirmed groundwater resource and salination patterns as those of basic models reflective of small island hydrology, except that salination and the freshwater boundary were less distinctive due to the relatively high thickness of the dispersion zone. The use of different sounding parameters in line 7 provided useful information about the nature of the deep basement unit and thickness of the overlying unconsolidated quaternary sediment.</p>

scholarly journals Mapping Saltwater Intrusion using Transient ElectroMagnetic Data in Maopa, Central Province, Papua New Guinea

2021 ◽  
Author(s):  
◽  
Ronald Verave
Keyword(s):  
Papua New Guinea ◽  
Saltwater Intrusion ◽  
Groundwater Resources ◽  
Cost Effective ◽  
New Guinea ◽  
Small Island ◽  
Mixing Zone ◽  
Low Resistivity ◽  
Transient Electromagnetic ◽  
Tem Method

<p>Saltwater intrusion studies in coastal Papua New Guinea (PNG) are a rarity despite recognized vulnerabilities to salination of coastal groundwater resources. For many seaside communities such as Maopa the threat of salination is exacerbated by high extraction rates by a growing population and the likelihood of the effects of climate change. Saltwater intrusion can be addressed using various methods, including direct water sampling from wells and electrical resistivity measurements. This study advances knowledge of a previous assessment of saltwater intrusion and groundwater in this region that used DC Schlumberger resistivity soundings, through an extensive and cost-effective Transient ElectroMagnetic (TEM) survey. The study aims to map the lateral and vertical extent of salination and the characterization of groundwater in the landward direction over seven lines of TEM soundings along Keakalo Bay. The TEM method proved successful in identifying four main geoelectric layers. The top layer has a highly variable resistivity (range of 5 to 355 Ωm) inferred as the vadose zone. Beneath this layer is a layer of intermediate resistivity (100 Ωm > p ≥ 20 Ωm) characterizing a perched freshwater aquifer with a thickness range of 3.2 to 15 m. An intermediate layer of low resistivity (20 Ωm > p ≥ 3 Ωm) was detected at the boundary separating the freshwater aquifer from the inferred saltwater intrusion. This layer is typically thicker than the freshwater aquifer and is referred to as the mixing zone. The deepest layer constituting the salination zone has a very low resistivity (3 Ωm > p ≥ 0.4 Ωm), occurring at depths of up to 42 m. The depth to the salination zone varied from deep in the middle of the survey area to shallow in the fringes of the survey. This pattern is reflective of surface seawater infiltration marked by mangrove forest in the interior and subsurface infiltration from the coast. Similar depth trends but at shallower depths were also observed for the mixing zone, and the freshwater region. In some cases the mixing area overwhelms the freshwater regions. Layering confirmed groundwater resource and salination patterns as those of basic models reflective of small island hydrology, except that salination and the freshwater boundary were less distinctive due to the relatively high thickness of the dispersion zone. The use of different sounding parameters in line 7 provided useful information about the nature of the deep basement unit and thickness of the overlying unconsolidated quaternary sediment.</p>

scholarly journals Imaging the extent of saltwater intrusion in the Luy river coastal aquifer (Binh Thuan) using electrical resistivity tomography (ERT)

2021 ◽  
Author(s):  
Cong-Thi Diep
Keyword(s):  
Electrical Resistivity ◽  
Coastal Aquifer ◽  
Saltwater Intrusion ◽  
Electrical Resistivity Tomography ◽  
Salt Water ◽  
Groundwater Resources ◽  
Left Bank ◽  
Resistivity Tomography ◽  
South Central ◽  
Recharge Sources

&lt;p&gt;&lt;strong&gt;Imaging the extent of salt water intrusion in the Luy river coastal aquifer (Binh Thuan) using electrical resistivity tomography (ERT)&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Diep Cong-Thi&lt;sup&gt;1,3&lt;/sup&gt;, Linh Pham Dieu&lt;sup&gt;1,3&lt;/sup&gt;, Robin Thibaut&lt;sup&gt;1&lt;/sup&gt;, Marieke Paepen&lt;sup&gt;1&lt;/sup&gt;, Hieu Huu Ho&lt;sup&gt;3&lt;/sup&gt;,&lt;/p&gt;&lt;p&gt;Fr&amp;#233;d&amp;#233;ric Nguyen&lt;sup&gt;2&lt;/sup&gt;, Thomas Hermans&lt;sup&gt;1&lt;/sup&gt;&lt;/p&gt;&lt;p&gt;&lt;sup&gt;&amp;#160;&lt;/sup&gt;&lt;/p&gt;&lt;p&gt;&lt;sup&gt;1&lt;/sup&gt;Department of Geology,&lt;sup&gt;&lt;/sup&gt;Ghent University, 9000-Gent, Belgium&lt;/p&gt;&lt;p&gt;&lt;sup&gt;2 &lt;/sup&gt;Department of Urban and Environmental Engineering,&lt;sup&gt;&lt;/sup&gt;Liege University and Department of Civil Engineering, KU Leuven, B- 4000 Li&amp;#232;ge and 3000 Leuven, Belgium&lt;/p&gt;&lt;p&gt;&lt;sup&gt;3 &lt;/sup&gt;Department of Marine Geology, Vietnam Institute of Geosciences and Mineral Resources (VIGMR), 100000 Hanoi, Vietnam&lt;/p&gt;&lt;p&gt;&amp;#160; ABSTRACT&lt;/p&gt;&lt;p&gt;Seawater intrusion has been one of the most concerning issues of the Vietnam South Central provinces in recent years, especially in the Binh Thuan province which is characterized by a hyper-arid climate. During the dry season extending from November to April, seawater intrudes through estuaries and threatens groundwater resources. The latter are under increasing pressure due to water extraction for agri- and aquaculture. To evaluate the current state of salinity in the shallow coastal aquifer, 21 electrical resistivity tomography (ERT) measurements were collected along the downstream part of the Luy river based on the previous saltwater intrusion boundary which was estimated from water samples collected from shallow boreholes. The data were inverted to get the resistivity distribution of the subsurface and interpreted in terms of salinity. Comparison with well data shows that resistivity values below 6.5 Ohm.m correspond to the presence of saltwater in the aquifers. On the right bank of the river, a higher elevation dune area contains a freshwater aquifer which limits the intrusion of saltwater. On the left bank dominated by lowland areas, saline water fills almost the entire thickness of the aquifer, except locally for small thin freshwater lenses. At larger distances from the sea, the aquifer displays a complex distribution of fresh and saline lenses. Those variations seem to be correlated with the presence of clay lenses, recharge sources and irrigation practices. ERT data also reveals the depth of the rock basement. The geophysical observations show that the extension of saltwater intrusion is much larger and more complex than expected from existing borehole data and is not limited to interaction with the river.&lt;/p&gt;&lt;p&gt;KEYWORDS: saltwater intrusion, groundwater, electrical resistivity tomography, Luy river. &lt;sup&gt;&amp;#160;&lt;/sup&gt;&lt;/p&gt;&lt;p&gt;*Corresponding Authors. Email: [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; [email protected]&lt;/p&gt;

scholarly journals Potential management practices of saltwater intrusion impacts on soil health and water quality: a review

2020 ◽  
Author(s):  
Haimanote K. Bayabil ◽  
Yuncong Li ◽  
Zhaohui Tong ◽  
Bin Gao
Keyword(s):  
Climate Change ◽  
Water Quality ◽  
Environmental Sustainability ◽  
Saltwater Intrusion ◽  
Management Practices ◽  
Groundwater Resources ◽  
Soil Health ◽  
South Florida ◽  
Mitigation Strategies ◽  
Climate Change And Variability

Abstract Several studies have documented the multifaceted impacts of climate change and variability on agricultural and environmental sustainability, and social and economic development. Climate change and variability contribute to increased warmer conditions, increased frequency of heavy rain that accounts for an increasing proportion of total rainfall, extreme weather characterized by spatially variable cycles of drought and wetness, increased frequency of tropical storms/hurricanes, increased frequency of storm surges, and accelerated rate of sea-level rise (SLR). As SLR continues, it is expected that salinity due to saltwater intrusion (SWI) will impact soil health and agricultural production. As such, the significant threats of salinity necessitate more work to be done to better understand its impact on soil health and associated functional ecosystem processes. This is of even greater importance in areas such as South Florida where the surface and groundwater resources are hydrologically connected due to the shallow and highly permeable limestone soils. A better understanding of the impacts of salinity due to SWI on soil health is critical to design effective mitigation strategies. Healthy soil has multifaceted benefits to enhance agricultural productivity, i.e. regulates the flow of water; serves as a source and sink of nutrients; minimizes greenhouse gas emissions and provides optimal biological and chemical conditions for the transformation of nutrients into plant-available forms. Improved understanding of the processes and impacts of SWI on soil health will assist in guiding management decisions and policies to mitigate the impacts of SWI and salinity on agricultural soils. This review paper provides a comprehensive overview of the impacts of SWI and soil salinity on agricultural soil health and water quality.

scholarly journals Crustal architecture of a metallogenic belt and ophiolite belt: implications for mineral genesis and emplacement from 3-D electrical resistivity models (Bayankhongor area, Mongolia)

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Matthew J. Comeau ◽  
Michael Becken ◽  
Alexey V. Kuvshinov ◽  
Sodnomsambuu Demberel
Keyword(s):  
Electrical Resistivity ◽  
Crustal Structure ◽  
Three Dimensional ◽  
Suture Zone ◽  
Fault System ◽  
Magnetotelluric Data ◽  
Low Resistivity ◽  
Ophiolite Belt ◽  
Geological Processes ◽  
Metallogenic Belt

AbstractCrustal architecture strongly influences the development and emplacement of mineral zones. In this study, we image the crustal structure beneath a metallogenic belt and its surroundings in the Bayankhongor area of central Mongolia. In this region, an ophiolite belt marks the location of an ancient suture zone, which is presently associated with a reactivated fault system. Nearby, metamorphic and volcanic belts host important mineralization zones and constitute a significant metallogenic belt that includes sources of copper and gold. However, the crustal structure of these features, and their relationships, are poorly studied. We analyze magnetotelluric data acquired across this region and generate three-dimensional electrical resistivity models of the crustal structure, which is found to be locally highly heterogeneous. Because the upper crust (< 25 km) is found to be generally highly resistive (> 1000 Ωm), low-resistivity (< 50 Ωm) features are conspicuous. Anomalous low-resistivity zones are congruent with the suture zone, and ophiolite belt, which is revealed to be a major crustal-scale feature. Furthermore, broadening low-resistivity zones located down-dip from the suture zone suggest that the narrow deformation zone observed at the surface transforms to a wide area in the deeper crust. Other low-resistivity anomalies are spatially associated with the surface expressions of known mineralization zones; thus, their links to deeper crustal structures are imaged. Considering the available evidence, we determine that, in both cases, the low resistivity can be explained by hydrothermal alteration along fossil fluid pathways. This illustrates the pivotal role that crustal fluids play in diverse geological processes, and highlights their inherent link in a unified system, which has implications for models of mineral genesis and emplacement. The results demonstrate that the crustal architecture—including the major crustal boundary—acts as a first‐order control on the location of the metallogenic belt.

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