Hydrodynamic behaviour of the seawater-freshwater mixing zone induced by cutoff wall installation in sloping coastal aquifers

Sustainable groundwater management depends on understanding the dynamic behaviour of seawater intrusion (SWI), a slow and persistent phenomenon that might go on for decades in coastal aquifers. A crucial element in regulating groundwater flow and solute transport in coastal aquifers is the freshwater-saltwater mixing zone. The hydrodynamic behaviour of the mixing zone under various coastal aquifer geometries with physical barriers like cutoff walls has not received much attention, despite its significance. The dynamics of the mixing zone are examined in this study by employing numerical simulations, with particular attention paid to the various bottom opening widths (S) beneath cutoff walls and the inclination angles of the sloping beach coastal aquifers (0°, 15°, 30°, and 45°). Regardless of the aquifer slope, findings demonstrate that smaller bottom opening widths result in greater mixing zones and faster inland SWI. The dynamics of the mixing zone were shown to be significantly impacted by the aquifer slope, with steeper slopes (30° and 45°) allowing for more rapid and extensive SWI than flatter slopes (0° and 15°). The largest and fastest-expanding mixing zones, especially over time, were created by a steep slope and a modest bottom opening size.