Abstract
This study focuses on the salinization of the coastal aquifer in the Mazandaran Province (Iran) within four different sites. Many factors can lead to declining groundwater quality, but this study focuses on the seawater intrusion area. Therefore, locating the interface between saltwater and freshwater is very important. For this purpose, three characterization methods with different accuracies have been employed: the Verruijt equation, vertical resistivity sounding, and an electromagnetic survey. Vertical resistivity sounding and the electromagnetic survey were performed near existing exploration boreholes and were used to determine the saltwater interface. The results showed that the Verruijt equation provides a reliable localization in two of the sites, but in the other two sites, the determined interface is lower than the observed data. The geoelectrical method showed acceptable results, but often this method cannot distinguish between the saltwater and saline aquitard boundary. The electromagnetic method showed a high accuracy in all the study sites and proved to be the most reliable method compared with the other techniques employed in this study. The results from this study are useful in helping to identify the most suitable technique for locating the freshwater/saltwater interface, especially in those sites where a detailed characterization via multilevel sampling is not feasible for technical or economic reasons.
Highlights
In coastal aquifers, because of the high density of marine saltwater, usually, gravity forces the distribution of saltwater below the freshwater lenses [1]
This study focuses on the salinization of the coastal aquifer in the Mazandaran Province (Iran) within four different sites
In the Mazandaran Province, the freshwater supply for agricultural and domestic needs is mostly covered by groundwater exploitation of the coastal aquifers, either because the water table is accessible, being less than 10 m below ground level (BGL) [28], or because the storage capacity is wide, as this alluvial aquifer can be up to 250 m thick
Summary
Because of the high density of marine saltwater, usually, gravity forces the distribution of saltwater below the freshwater lenses [1]. The boundary between saltwater and freshwater is not sharp because of the diffusion processes and mechanical dispersion, but it is rather a volume [2,3] that is called the transition zone [4]. Determining the depth and the extent of the interface between saltwater and freshwater in coastal aquifers is very important. Badon-Ghyben [8] and Herzberg [9] were the first scientists that studied the interface between saltwater and freshwater with a simple one-dimensional analytical solution. Glover [10] provided a two-dimensional approach, which was subsequently improved [11,12,13]
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