This paper re‐evaluates previous records and adds new data to the relative sea level (RSL; namely the sea level related to the level of the national terrestrial datum) reconstruction in Israel from the last 2400 years based on ancient coastal water wells. Different methods for obtaining the most accurate modern offset between coastal groundwater level and mean sea level are also tested, since this is a crucial component for using wells as reliable sea‐level indicators in the Mediterranean and beyond. Very few, if any, sea‐level studies outside of Israel use coastal wells as RSL indicators; refinements to the methods associated with this indicator type will facilitate their use in other regions. Coastal wells in the study are located within 200 m of the present‐day coastline. The functional age range for the wells is based on site stratigraphy, artifacts, historical records, and the coastal water well typology. These archaeological indicators rely on finding the vertical offset between present‐day coastal groundwater and sea level, and applying it to ancient times. The current study explores two methods to calculate accurate vertical offsets: a) modern averages of the upper aquifer groundwater elevation in the vicinity of ancient wells, which are calculated from 60 years of measurements by the Israeli Hydrological Service; and b) a hydrological model where groundwater elevation is a function of distance from the modern coastline. The model uses a simulation of the coastal aquifer with a two‐dimensional, vertical cross‐section. The modeled approach is found to be preferable. The results show that sea level in Roman times (1st century CE) was similar to present‐day, slightly higher in the Byzantine period (4th to 7th centuries CE), and lower in part of the Early Islamic period (9th to 10th centuries CE). For the later Fatimid/Ayyubid and Crusader periods (11th to 13th centuries CE), RSL reaches its lowest elevations (of about −0.5 m) as previously found. Following these low levels, sea level rose going into the 18th and 19th centuries CE.
This study deals with the reliability of monitoring the transition zone between fresh and saline waters in coastal aquifers, considering the effect of tides in long‐perforated boreholes. Electric conductivity (EC) fluctuations in the coastal aquifer of Israel, as measured in long‐perforated borehole, were found to have the same periodicities as the sea tide, though some orders of magnitude larger than sea‐level or groundwater level fluctuations. Direct measurements in the aquifer through buried EC sensors demonstrate that EC measurements within the long‐perforated boreholes might be distorted due to vertical flow in the boreholes, whereas actual fluctuations of the transition zone within the aquifer are some orders of magnitude smaller. Considering these field data, we suggest that monitoring of the transition zone between fresh and saline water adjacent to the sea through long‐perforated boreholes is unreliable. EC fluctuations in short‐perforated boreholes (1 m perforation at the upper part of the transition zone) were somewhat larger than in the aquifer, but much smaller than those in the long‐perforated borehole. The short‐perforation diminishes the vertical flow and the distortion and therefore is more reliable for monitoring the transition zone in the shoreline vicinity.
The accepted mechanism for the formation of thousands of sinkholes along the coast of the Dead Sea suggests that their primary cause is dissolution of a salt layer by groundwater undersaturated with respect to halite. This is related to the drop in the Dead Sea level, which caused a corresponding drop of the freshwater‐saltwater interface, resulting in fresher groundwater replacing the brines that were in contact with the salt layer. In this study we used physical laboratory experiments to examine the validity of this mechanism by reproducing the full dynamic natural process and to examine the impact of different hydrogeological characteristics on this process. The experimental results show surface subsidence and sinkhole formation. The stratigraphic configurations of the aquifer, together with the mechanical properties of the salt layer, determine the dynamic patterns of the sinkhole formation (instantaneous versus gradual formation). Laboratory experiments were also used to study the potential impact of future stratification in the Dead Sea, if and when the “Red Sea‐Dead Sea Canal” project is carried out, and the Dead Sea level remains stable. The results show that the dissolution rates are slower by 1 order of magnitude in comparison with a nonstratified saltwater body, and therefore, the processes of salt dissolution and sinkhole formation will be relatively restrained under these conditions.
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