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Haïfa University (2012)

Numerical simulation of submarine groundwater flow in the coastal aquifer at the Palmahim area, the Mediterranean coast of Israel

Amir Nadav

Titre : Numerical simulation of submarine groundwater flow in the coastal aquifer at the Palmahim area, the Mediterranean coast of Israel

Auteur : Amir Nadav

Etablissement de soutenance : Haïfa University

Grade : Master 2012

Résumé
The coastal aquifer of Israel is an important water resource being one of the main natural water reservoirs. The aquifer is known to be intruded by seawater mostly in its upper sub-aquifers. At some parts of the aquifer, between Ashdod and Bat Yam, fresh water bodies were detected in the lower sub-aquifers by the geo-electric TDEM method and by direct chemical measurements. Following the existence of these fresh water bodies along with their ages and water geochemistry, differing from the water in the upper sub-aquifers, it was hypothesized that at some places the lower subaquifers might be blocked to the sea and thus to intrusion of seawater. Due to lack of offshore geological information, the connection of these sub-aquifers whether open or closed to the sea remains uncertain. This study examine the groundwater flow system at the Palmahim area using a two -dimensional numerical model - FeFlow. Simulations were conducted to reveal which setting enables the existence of these fresh water bodies in the lower sub-aquifers close to the shoreline and to assess onland possible pumping rates that will prevent salinization of these sub-aquifers. Steady state simulations, which examine the hydrogeological settings, were verified by sea level rise scenarios aiming to test whether the system was fully flushed prior the sea level rise after the last glacial maxima and thus assigning a more realistic initial. The simulations imply that the presence of fresh water in the lower sub-aquifer, whether blocked or connected to the sea, requires offshore separation between the upper and lower sub-aquifers. Such a separation prevents the intrusion of seawater into the lower sub-aquifers. The fresh water can be discharged upward to the upper sub-aquifers through semi impermeable "separating" layers or directly to the sea when the lower sub-aquifers are open to the sea and are overlain by a low permeability separation. On-land pumping simulations show a threshold pumping rate of 250 m3/m strip width/year, hereafter m2/year, to prevent the salinization of the lower sub-aquifers. Alternatively, there is at least a 100 year time leg before on-land salinization begins when pumping at a rate of 1000 m2/year is applied. Differences in pumping scenarios between impermeable and semi permeable separating layers are expressed in the salinity curves, showing sharp and moderate rates, respectively. Extreme pumping scenarios emphasize these differences and allow assessing the amount of separation between the sub-aquifers by comparing the trends of salinization to future field tests, obtained from a pumping well and adjoined observation wells.

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