Effects of layered heterogeneity on mixed physical barrier performance to prevent seawater intrusion in coastal aquifers

Mixed physical barriers (MPB), which combine a cutoff wall and subsurface dam, were applied in heterogeneous coastal aquifer settings, and their ability to prevent seawater intrusion (SWI) was tested. The performance of MPB was examined in a typical stratified aquifer using laboratory experiments and numerical modelling. The performance of the MPB was compared to that of a single cut-off wall by measuring the percentage of reduction of the intrusion length. SEAWAT was used for validation purposes and to further evaluate the effectiveness of MPB in five additional realistic heterogeneous configurations. Experimental results show that the MPB effectively reduced the saltwater wedge length by up to 71%. The MPB outperformed the single cut-off wall by up to 55 %. Also, numerical results show that the MPB proved to be effective, achieving a SWI length reduction of up to 69% in the scenario regardless of the aquifer layering structures. Comparable performance was observed when the high K layer was confined between two low K layers or when the aquifer presented a monotonically increasing/ decreasing K pattern. The findings of this study provide insights into the applicability of the MPB in realistic heterogeneous coastal aquifers.