La posición de la interfase agua dulce-agua salada en un ambiente costero es relativamente estable mientras no sea perturbada por extracción de agua dulce, cambios en la morfología de las unidades que la contienen o el incremento del nivel del mar. Se exponen los primeros resultados del comportamiento de los niveles freáticos y la conductividad eléctrica del agua (CE) en sectores de la costanera del Partido de La Costa. El objetivo es establecer la relación entre el agua dulce del acuífero y el agua marina de acuerdo al grado de afectación de la erosión costera. Se realizan mediciones de nivel mensuales y de conductividad eléctrica del agua en freatímetros de la costanera. La CE se mantiene estable salvo en un pozo donde se manifiesta un incremento durante el evento de marea alta. Las precipitaciones acumuladas en el periodo no parecen ser suficientes para generar un incremento de la capa freática. Los registros de mediciones continuas demuestran que las oscilaciones de los niveles freáticos se corresponden a las ondas de marea. La reducción de las curvas isofreáticas en la costanera muestra un desplazamiento de la cuña salina hacia el continente (1987-2021). Hasta el momento no se observa un comportamiento diferencial entre los datos de las zonas afectadas por distintos grados de erosión y las conservadas. Este estudio se encuentra en sus etapas iniciales por lo que se continúa con la recopilación de información. | Freshwater-saltwater interface location in a coastal environment in relatively stable while it is not disturbed by freshwater pumping, changes in the geomorphological units or sea-level rise. The first results of groundwater level and electrical conductivity (EC) behavior in the shoreline of Partido de La Costa are shown in this work. The aim was to establish the relationship between the aquifer freshwater and the marine saltwater according to the level of coastal erosion. Groundwater level and EC monthly measurements are carried out in wells located in the shoreline. The EC remains stable except in a well where an increased was shown during a high-tide event. The amount of accumulated rainfall during the studied period seems not to be enough to produce an increase in groundwater level. Level logger data shown that groundwater oscillation agreed with tide waves. The increase in the isophreatic curves in the shoreline shows a movement towards the continent (1987-2021). A different behavior between data from the areas affected by different level of erosion and the preserved ones is not observed, for the time being. This study is in its initial stages therefore the data collection is a working process. | Centro de Estudios Integrales de la Dinámica Exógena

The long-term monitoring records of hydraulic heads frequently contain fluctuations originating from different cyclic drivers. Fourier analysis applied to these records can reveal connected surface-water/groundwater system characteristics. The various components of the atmospheric tides, the earth tides and the presence of diurnal responses to evapotranspiration are identified and isolated through band-pass filtering of data recorded from both vented and absolute gauge transducers. The signature of the different cyclic drivers is contained in amplitude and phase of the various signal components and can be used to determine the degree of system confinement. A methodology is described for the calculation of barometric efficiency in confined aquifers based upon the amplitude of the M₂and S₂components of the earth and atmospheric tides. It is demonstrated that Fourier analysis of water-level fluctuations is a simple but underused tool that can help to characterise shallow groundwater systems.

Dynamic variation in the saltwater–freshwater transition zone below a seafront beach in South Korea was investigated with long-term monitoring of the groundwater in relation to the precipitation, wave height, and tide. Correlation, spectral analysis, and regression analysis of monitoring data were performed to deduce the relationships between these factors. The general shape of the transition zone was affected by the seasonal groundwater levels, but temporary fluctuations were predominantly affected by local rising-groundwater-level events. The distinct increases in the groundwater level were closely related to the wave height. Different patterns of electrical conductivity (EC) change were detected in the shallow and deep zones, and these differences indicated that the transition zone was highly dynamic. The EC values at shallow depths were temporarily increased by the wave setup and tidal fluctuations during the rising-groundwater events, but the EC at greater depths was reduced by the seaward or downward movement of the relative freshwater. In exceptional cases, during extreme increases in the groundwater level resulting from seawater flooding, the rapid downward flow of the flooding saltwater through the well bore caused synchronous EC fluctuations at all depths.

The exchange rate between seawater and groundwater in a tidal flat was investigated at Laizhou Bay, China, where there are large-scale seepage faces with horizontal extension of several hundred meters developed during low tides. Taking into account the effects of seepage face and density, a simple and efficient method for estimating seawater–groundwater exchange rate is proposed, based on field measurements of groundwater hydraulic head, temperature and salinity. First, the exchange rate at each well was obtained using the generalized Darcy’s law, then the results were interpolated and integrated along the whole transect. The total submarine groundwater discharge (SGD) and inflow were estimated to be 8.8 and 15.3 m³d⁻¹ m⁻¹, respectively. The spatial distributions of SGD and inflow were different from those of sandy or gravel beaches possibly owing to the low-permeability sediment (silty sand with mud), very gentle slope, and the large-scale seepage faces. A freshwater discharge tube was identified near the low-tide line, as evidenced by significant increase in outflow and low salinity of groundwater observed there. The SGD from the seepage faces accounted for ∼21 % of the total SGD. The outflow rate that occurred from the seepage faces, and the ratio of the outflow from the seepage faces to the total outflow, decreased seaward significantly and monotonically.

In lagoonal and marine environments, both historic monuments and recent buildings suffer from severe salt damage caused by sea flooding, sea-level rise and frequent storm events. Salt-water contamination of groundwater systems, a widespread phenomenon typical of coastal areas, can lead to a deterioration not only of the quality of fresh groundwater resources, but also of building materials in urban settlements. A general overview is given of the hydrogeological configuration of the subsoil of Venice (Italy), with particular reference to the shallow groundwater circulation. The relationship between the seawater in the subsoil and salt decay processes, due to salt crystallization, is highlighted. These processes affect civil constructions in Venice’s historic center. Perched aquifers, influenced by tide variations and characterized by salt-water intrusion, favor the transport of salts within masonry walls through the action of rising damp. In fact, foundations, in direct contact with the aquifers, may become a preferential vehicle for the transportation of salt within buildings. Decay patterns of different building materials can be detected through non-destructive techniques, which can identify sea-salt damage and therefore assist in the preservation of cultural heritage in coastal areas.

Submarine groundwater discharge (SGD) is an important pathway for groundwater and associated chemicals to discharge to the sea. Groundwater levels monitored along a transect perpendicular to the shoreline are used to calculate SGD flux from the nearshore aquifer to Tolo Harbor, Hong Kong (China). The calculated SGD flux—recharge/discharge measured with Darcy’s Law methods—agrees well with estimates based on geo-tracer techniques and seepage meter in Tolo Harbor during previous studies. The estimated freshwater SGD is 1.69–2.0 m²/d at the study site and 0.3 ± 0.04 cm/d for the whole of Tolo Harbor, which is comparable to the river discharge (0.25 ± 0.07 cm/d) and precipitation (0.45 ± 0.15 cm/d). The tide-driven SGD in the intertidal zone is 13.98–17.59 m²/d at the study site and 2.42 ± 0.56 cm/d for the whole of Tolo Harbor. The SGD occurring in the subtidal zone and the bottom of Tolo Harbor is 3.12 ± 4.63 cm/d. Fresh SGD accounts for ~5% of the total SGD, while the rest (~95%) is contributed by saline SGD driven by various forces. About 96% of the tide-driven SGD in the intertidal zone occurs in the ebbing tide period because the head difference between the groundwater level and sea level is great during this period. Tide-driven SGD in the spring tide is ~1.2 times that during neap tide. The tidal fluctuation amplitude and tide-driven SGD in the intertidal zone are positively correlated to each other; thus, a spring neap variation of the tide-driven SGD is observed.