Numerical simulation of thermal effects on seawater intrusion management by coastal cutoff walls

Abstract

Seawater intrusion into coastal aquifers poses significant challenges for groundwater management, particularly under fluctuating thermal conditions. This study employs a two-dimensional numerical model to explore the combined effects of temperature gradients and geological stratification on seawater intrusion and the performance of coastal cutoff walls. The results show that temperature gradients between seawater and groundwater substantially affect intrusion patterns, with the wedge extension under variable temperature gradients is 54 times greater compared to the scenario with a constant temperature gradient. Colder seawater exacerbates intrusion, increasing the wedge by 18.7 %, while warmer seawater mitigates it, reducing the wedge by 14.5 %. The performance of cutoff walls is temperature-dependent, with efficiency decreasing as temperature differences widen. In heterogeneous aquifers, cutoff walls can reduce the saltwater wedge by up to 66.73 % under the influence of colder seawater intrusion. In such aquifers, the extent of the saltwater wedge is not solely determined by the thickness of the highly permeable layer, but rather by the proportion of its thickness at the base of the cutoff walls. This study highlights the importance of incorporating thermal and stratigraphic factors in the design of mitigation measures, emphasizing the need for site-specific strategies to address the challenges posed by changing thermal conditions and aquifer heterogeneity.