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

Abstract

With global warming and sea level rise, many coastal systems will experience increased levels of inundation and storm flooding, especially along sandy lowland coastal areas, such as the Northern Adriatic coast (Italy). Understanding how extreme events may directly affect groundwater hydrology in shallow unconfined coastal aquifers is important to assess coastal vulnerability and quantify freshwater resources. This study investigates shallow coastal aquifer response to storm events. The transitory and permanent effects of storm waves are evaluated through the real time monitoring of groundwater and soil parameters, in order to characterize both the saturated and unsaturated portions of the coastal aquifer of Ravenna and Ferrara (southern Po Delta, Italy). Results highlight a general increase in hydraulic head and soil moisture, along with a decrease in groundwater salinity and pore water salinity due to rainfall infiltration during the 2 days storm event. The only exceptions are represented by the observation wells in proximity to the coastline (within 100 m), which recorded a temporary increase in soil and water salinity caused by the exceptional high waves, which persist on top of the dune crest during the storm event. This generates a saline plume that infiltrates through the vadose zone down to the saturated portion of the aquifer causing a temporary disappearance of the freshwater lens generally present, although limited in size, below the coastal dunes. Despite the high hydraulic conductivity, the aquifer system does not quickly recover the pre‐storm equilibrium and the storm effects are evident in groundwater and soil parameters after 10 days past the storm overwash recess.

High-Resolution Electrical Resistivity Tomography (ERT) to Characterize the Spatial Extension of Freshwater Lenses in a Salinized Coastal Aquifer

“…The WTD and its landward gradient observed in this study are in agreement with the results of previous studies performed in the same area [13,32,33]. The WTD is controlled by the drainage channel, which crosses the pine forest parallel to the coastline.…”

“…In the 1950s the Ravenna coastline was characterized by continuous and well-preserved dune belts, which were gradually flattened and fragmented to make room for tourism facilities [30], thus increasing coastal vulnerability to storms and erosion [31]. More details about general description, hydrogeological setting, and the natural and anthropogenic factors affecting the entire Regional coastal zone and freshwater lens presence are further described in Cozzolino et al [13] and Giambastiani et al [32,33].…”

“…Between July and December 2014, eight two-dimensional (2D) electrical resistivity tomography (ERT) surveys were carried out across the beach-dune system ( Figure 2), perpendicular to the coastline, as shown in Figure 1. description, hydrogeological setting, and the natural and anthropogenic factors affecting the entire Regional coastal zone and freshwater lens presence are further described in Cozzolino et al [13] and Giambastiani et al [32,33].…”

“…Groundwater salinity was classified based on EC values into: freshwater (EC < 3 mS/cm), and brackish-saline groundwater (EC > 3 mS/cm); as already defined for the same area by Cozzolino et al [13] and Giambastiani et al [32,33]. Groundwater monitoring data (WTD and EC) and local lithological information [13,32,33] were used to constraint the resistivity inversion and calibrate/validate the ERT surveys. The calibration was performed on the ERT profile 5 by simultaneously comparing groundwater data and resistivity values in proximity of the monitoring point (MLS3 in Figure 1).…”

Modelling Actual and Future Seawater Intrusion in the Variconi Coastal Wetland (Italy) Due to Climate and Landscape Changes

“…Under natural conditions, these coastal aquifers are mainly recharged by meteoric water, and this water flowing towards the ocean would prevent saltwater from heading into the freshwater region. However, overexploitation and climate changes effects like sea level rise [24], storm events [25], and tides [26] can be causes of SWI. Moreover, in coastal wetlands salts accretion may induce an alteration from species-rich freshwater biota to species-poor salt tolerant biota [27].…”