|M.Sc Student||Shiri Solomon|
|Subject||The Salinization Mechanism of Inclined Aquifers; the Case|
of the Israeli Coastal Aquifer
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Shavit Uri|
|Full Thesis text - in Hebrew|
The increasing salinity of the Israeli Coastal Aquifer is of special concern as it serves as Israel’s largest storage volume. Apart from a number of salinity plumes, saline regions have been developed along the eastern boundary of the central and southern sections of the aquifer.
The explanation of the salinization mechanisms of the aquifer is under a dispute, whether the salinization source lies under the bottom of the aquifer, at the Eocene formations at the eastern boundary of the aquifer, or at the vadose zone. The hypothesis of the current study was that high salinity might accumulate along the east boundary of the aquifer due to uniform penetration of salt from the vadose zone with no penetration from the Eocene, given a sloping aquifer bottom. We developed a reference model that assumes a steady and uniform influx of water and uniform influx of salt through the vadose zone, a sealed boundary on the east and a homogenous (1%) bottom slope. An analytical solution of the steady state one-dimensional flow equation was developed. The salt distribution throughout the aquifer was obtained by a numerical solution of the transport equation. In addition, vertical two-dimensional numerical solutions of both flow and transport equations were obtained and compared with the one-dimensional solutions.
A steady solution of a horizontal phreatic aquifer shows that the aquifer vertical geometry is thinner downstream. The unsteady solution of the transport equation shows that the concentration rises faster in that part. Solutions for sloping aquifers show that the salt concentration rises faster in the upstream part. This result can be explained by the influence of the aquifer thickness, which changes due to the bottom slope, and the mixing ratio between the salt sources and the water volume inside the aquifer.
An overall mass balance provides reasonable estimate of the total water and salt inputs, however the ratio between the fluxes from the Eocene formations and through the vadose zone is unknown. We used water level and salt concentration data from the 1930s that represent stable aquifer conditions, to assess those fluxes using this model. Finally, the model was used to examine the response of the aquifer to possible changes in management policies that were proposed to slow down the salinization rate. A favorable policy is to reduce the vadose zone salinity and to pump high salinity water a few kilometers from the east boundary.