Processes Influencing Groundwater Level and the Freshwater-Saltwater Interface in a Coastal Aquifer

Abstract

Few studies have focused on the relationship between the various causes of groundwater level fluctuations and the seawater intrusion process, due to the complexity of this relationship, being the aim of this paper. Piezometric fluctuations in coastal aquifers are determined by a number of processes and their characterization depends on the complexity of the aquifer stratigraphy, as well as many other hydrodynamic factors. The precipitation regime, tides, wave setup and storm surges, as well as atmospheric pressure are the most relevant of these processes. By means of a series of observations made at an experimental site in south-eastern Spain, this study demonstrates the complexity of water table fluctuations in coastal zones. The study employed two piezometers situated very close to the shoreline, excavated in detritic deposits with highly variable hydraulic conductivity (semi-confined aquifer). Continuous measurements were taken of hydraulic head, tide height, electrical conductivity and water temperature. The study concludes that precipitation has the greatest effect on piezometric level, followed by atmospheric pressure and wave action, while the semi-diurnal and fortnightly tidal cycles caused variations of smaller amplitude in the piezometric logs. All these oscillations affect the position of the fresh water-seawater interface. The attenuation of the tidal amplitude observed at the two monitoring points was lower than the value calculated using analytical solutions, and this is due to the semi-confined nature of the aquifer. The calculated tidal efficiency is around 0.4-0.5, giving a t lag of about 3 h, with a 10-15 min delay between monitoring boreholes, P-II and PI. We also identified that the response of water conductivity and temperature to tidal cycles is not synchronized with the variations in the piezometric level influenced by tidal fluctuations.

Coastal aquifer response to extreme storm events in Emilia‐Romagna, Italy

“…Understanding how extreme events may directly affect groundwater hydrology in shallow unconfined coastal aquifers is important when assessing the vulnerability of coastal zones and freshwater resources. Coastal aquifers are complex because of the combined influences of marine oscillations and landward groundwater gradients (Vallejos, Sola, & Pulido‐Bosch, ). Coastal groundwater hydrodynamics are the result of combined forces from tidal motion (Guo, Jiao, & Li, ), wave setup and wave run‐up (Nielsen, ), atmospheric pressure variations (Balugani & Antonellini, ), storm surges (Yang, Graf, Herold, & Ptak, ), and wind setup (Giuliano & Manda, ).…”

“…Coastal aquifers are complex because of the combined influences of marine oscillations and landward groundwater gradients (Vallejos, Sola, & Pulido-Bosch, 2015). Coastal groundwater hydrodynamics are the result of combined forces from tidal motion (Guo, Jiao, & Li, 2010), wave setup and wave run-up (Nielsen, 1999), atmospheric pressure variations (Balugani & Antonellini, 2011), storm surges (Yang, Graf, Herold, & Ptak, 2013), and wind setup (Giuliano & Manda, 2012).…”

A Standardized Index for Assessing Seawater Intrusion in Coastal Aquifers: The SITE Index

“…Because of intensive use of groundwater and pollution from a wide range of sources, these aquifers have been subjected to increasing pressure over the last few decades. As a consequence, a large number of aquifers worldwide are affected by seawater intrusion, which deteriorates groundwater to the point that it cannot be used for any activity (Renau-Pruñonosa et al 2014, Vallejos et al 2015. This situation may be exacerbated in the near future by the effects of climate change and potential sea level rise Pérez-Martín et al 2014).…”

A Methodology to Analyse and Assess Pumping Management Strategies in Coastal Aquifers to Avoid Degradation Due to Seawater Intrusion Problems

“…They depend on aquifer stratigraphy and other hydrodynamic factors (precipitation regime, tides, wave setup and storm surges, etc) (Vallejos et al, 2015). The coastal aquifers have important hydrodynamic and hydrogeochemical peculiarities (Custodio, 2010;Werner et al, 2013).…”