Sea water Intrusion with a focus on the geological heterogeneity

Abstract

Sea water intrusion (SWI) is a natural process describing the salt water encroachment on the fresh groundwater volumes located in the coastal aquifers. Climate change and specifically the sea level rise (SLR) are expected to play a key role on the SWI process in the future. SLR enhances the SWI progression and transforms the natural phenomenon into a significant threat against the qualitative fresh groundwater maintenance of the coastal zone. A growing body of evidence has already demonstrated the importance of this problem and the interrelation of the two phenomena (SWI and SLR). However, researchers in that field have not treated the impact of the geological heterogeneity of coastal aquifers in much detail so as to underline its role on the toe distance evolution during that process. This thesis aims to portray the role of the geological heterogeneity during the SWI process with and without the implementation of SLR. A conceptual, numerical model was used to investigate the toe distance formulation and the fresh salt interface development for three different geological scenarios. This investigation contextualizes the geological heterogeneity into the implementation of clay aquitards into the coastal aquifer’s volume. Each scenario describes a different geological setting. The first scenario demonstrates a homogeneous occasion, the second one focuses on the periodic transposition of a clay aquitard within the aquifer and the last one demonstrates a random distribution of ten clay aquitards. The diverse geological scenarios are examined for different inland boundary conditions (5m, 10m, 15m) with and without the implementation of SLR. The research demonstrated the SLR influence on the SWI process by displaying a value of 400m more for the toe distance based on SLR. It also displayed the important role of the inland boundary conditions which affect the toe distance and the fresh salt wedge shape. Scenario 2 showed that the position of one single clay aquitard within the aquifer does not affect the period that the model reaches its steady state as it is the same with the homogeneous case. However, the upper and seaward positions of the aquitards within the aquifer lead to a bigger toe distance declination from the scenario 1 for the inland boundary 10m. This behaviour is reversed, on the other hand, for the inland boundary 15m as the more inland positions lead to a bigger declination. Scenario 3 is closer to the reality showing a complex salt water wedge shape. The period that the model reaches its steady state is shorter and independent from the inland boundary in contrast to the previous scenarios.