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sur le développement des zones arides et semi-arides

Titre : Flow and transport processes is an extremely saline aquifers, example from the Dead Sea area

Auteur : Magal, Einat

Université de soutenance : Ben-Gurion University of the Negev

Grade : Doctor of Philosophy (PhD) 2010

Résumé partiel
Understanding groundwater flow is essential for proper management of groundwater resources and monitoring its quality and quantity. Tracing the migration of a tracer that has been injected artificially into the aquifer is a powerful tool for achievement of direct estimate of groundwater flow and transport processes. Since most of the experience in the world comes from groundwater of relatively low salinities, the goals of this work were to quantify directly the flow and transport processes in highly saline hydrogeological environments and specifically at the Dead Sea shore. The importance of real time quantification of these processes is due to the continuous drop of the Dead Sea level that has significant impact on the adjacent hydrological systems. The wide range of groundwater salinities at the Dead Sea coast requires the tracers that are conservative in such system. Therefore, the first goal was the assessment of the sorption properties of fluorescent dyes in highly saline groundwater. The suitable tracers were chosen to be used as conservative tracers at the other parts of the work. The flow properties of the groundwater were directly assessed in a field experiment in Fashkha springs and the transport of colloids was evaluated using colloid size tracers in laboratory experiments with solutions with wide range of salinities including that of the Dead Sea brines. The capability of five fluorescent dyes to serve as conservative tracers in highly saline groundwater was evaluated by a series of batch experiments on pure minerals and natural sediments. Dye sorption was tested in four different salinities (from fresh rainwater to Dead Sea water) on the pure minerals : calcilte, dolomite, quartz, bentonite and kaolinite and on four natural sediments taken from boreholes drilled along the Dead Sea shore. It was found that the dyes Sulfo-Rhodamine B and Eosin are strongly adsorbed on pure minerals and sediments and therefore cannot be used as conservative tracers in saline groundwater. Uranine and Pyranine sorption is increased at higher salinities, therefore they can be used as tracers in moderately saline groundwater only. Na Naphthionate was found to be the best tracer for fresh and saline water, with minimal sorption in all cases. Sorption of the dyes on four natural sediments was measured and values were found to be in accord with those of previous sorption on pure minerals. Sorption on natural sediments was also estimated based on the mineral composition of the sediment and the known sorption on the pure minerals. The estimated sorption values were usually 25% lower than those of the sorption directly measured. Nevertheless, sorption on pure minerals can be used as a first approximation for sorption on natural sediments. The impact of sediment to solution ratio was tested for Uranine as a model dye. The distribution coefficient (Kd) of Uranine in highly saline Dead Sea water was found to be dependent on the sediment to solution ratio (mass/volume), where low ratios resulted in higher values of Kd. Also, higher Kd values were calculated for fine grain size due to higher sorption capacity on larger surface areas. The difference in Kd, however, is not directly related to the specific surface size of the grains and should be examined separately.

Mots Clés : Aquifers — Dead Sea (Israel and Jordan). — Groundwater flow — Dead Sea (Israel and Jordan). — Hydrogeology. — Radioactive tracers in hydrogeology — Saline waters

Présentation : BGU

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