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This study employs a multimethod approach to investigate the sediment distribution in two pocket beaches, Ramla Beach and Mellieha S Beach, in Malta. Both study sites were digitally reconstructed using unmanned aerial vehicle (UAV) photogrammetry. For each case, an ERT and a dense network of ambient seismic noise measurements processed through a horizontal-to-vertical spectral ratio (HVSR) technique were acquired. Electrical resistivity tomography (ERT) analysis enables the estimation of sediment thickness in each beach. HVSR analysis revealed peaks related to beach sediments overlying limestone rocks in both sites and also indicated a deeper stratigraphic contact in Mellieha S Beach. Based on ERT measurements, sediment thickness is calculated for each HVSR measurement. Interpolation of results allows for bedrock surface modelling in each case study, and when combined with digital terrain models (DTMs) derived from photogrammetric models, sediment volumes are estimated for each site. The geometry of this surface is analyzed from a geological perspective, showing structural control of sediment distribution due to a normal fault in Mellieha S Beach and stratigraphic control facilitated by a highly erodible surface in Ramla Beach. The results emphasize the importance of adopting a three-dimensional perspective in coastal studies for precise sediment volume characterization and a deeper understanding of pocket beach dynamics. This practical multimethod approach presented here offers valuable tools for future coastal research and effective coastal management, facilitating informed decision making amidst the growing vulnerability of coastal zones to climate change impacts. [ABSTRACT FROM AUTHOR]

The aquifers of the Spanish Mediterranean coast are generally subjected to intense exploitation to meet the growing water supply demands. The result of the exploitation is salinization due to the marine saltwater intrusion, causing a deterioration in the quality of the water pumped, limiting its use for community needs, and not always being well delimited. To prevent deterioration, a groundwater control network usually allows precise knowledge of the areas affected by saltwater intrusion but not the extent of the saline plumes. Moreover, the characterization of aquifer systems requires a model that defines the geometry of aquifer formations. For this objective, we integrated hydrogeological, hydrogeochemical, and electrical resistivity subsoil data to establish a hydrogeological model of the coastal aquifer of Torredembarra (Tarragona, NE Spain). In this research, we have carried out a regional and local-scale study of the aquifer system to define the areas prone to being affected by saline intrusion (electrical resistivity values below 10 Ω·m). The obtained results could be used as a support tool for the assessment of the most favorable areas for groundwater withdrawal, as well as enabling the control and protection of the most susceptible areas to be affected by saltwater intrusion. [ABSTRACT FROM AUTHOR]

Managed aquifer recharge using surface or regenerated water plays an important role in the Barcelona Metropolitan Area in increasing storage volume to help operators cope with the runoff variability and unexpected changes in surface water quality that are aggravated by climate change. The specific aim of the research was to develop a non-invasive methodology to improve the planning and design of surface-type artificial recharge infrastructures. To this end, we propose an approach combining direct and indirect exploration techniques such as electrical resistivity tomography (ERT), frequency domain electromagnetics and data from double-ring infiltration tests, trial pits, research boreholes and piezometers. The ERT method has provided much more complete and representative information in a zone where the recharge project works below design infiltration rates. The geometry of the hydrogeological units and the aquifer-aquiclude contact are accurately defined through the models derived from the interpretation of ERT cross-sections in the alluvial aquifer setting. Consequently, prior to the construction of recharge basins, it is highly recommended to conduct the proposed approach in order to identify the highest permeability areas, which are, therefore, the most suitable for aquifer artificial recharge. [ABSTRACT FROM AUTHOR]

Glauberite (Na2Ca[SO4]2) is an evaporitic mineral which is used in the industries of detergents, paper, glass, pharmacy, etc. Glauberite rocks are seldom found cropping out because they are very sensitive to weathering processes; for this reason their prospection is conducted by means of boreholes. Nowadays, geophysical techniques are not used to support the characterization of glauberite deposits due to the lack of knowledge of their physical properties. In this study geoelectrical methods are proposed as alternative techniques in the early stages of glauberite prospecting. Several glauberite units have been studied in different parts of the Ebro basin (Spain) by means of electrical resistivity tomography sections. The electrical resistivity range showed by glauberite deposits has been found to be low (10–100Ω·m) when the matrix component (clay and microcrystalline carbonates) is above 45% of the bulk composition of the rock. This type of rocks has been studied in Montes de Torrero (Zaragoza) and is the most common glauberite deposit case. Besides matrix-rich glauberite rocks, an exceptional case of a pure glauberite layer has been studied in Alcanadre (La Rioja). From this site, it has been estimated that deposits with glauberite crystal fraction close to 100% show a resistivity range of at least 3×103 Ω·m. Using this extreme value as reference, the Hashin–Shtrikman bounds have been calculated for glauberite rocks considering that they are constituted of four phases (glauberite, gypsum, anhydrite and matrix). When the matrix fraction represents 45% or more of the bulk rock, the resistivity range will be that of the lower Hashin–Shtrikman bound, which is similar for any combination of sulfate (glauberite, gypsum and/or anhydrite) composition; hence, it can be considered as a two-phase system (matrix and sulfate). For rocks with less than 30% of matrix fraction, the upper Hashin–Shtrikman bound trend must be considered; however, the resistivity values overlap, making it impossible to establish a classification. Between 30 and 45% of matrix fraction, there is a transitional domain. Additionally, some theoretical models representing the most common structures in sulfate rocks have been elaborated in order to help in the interpretation of the inverted resistivity images obtained from the field data. Some artifacts generated by the complexity of the resistivity distribution of the terrain have been identified in both data sets. [ABSTRACT FROM AUTHOR]