Land subsidence dynamics in the Mekong Delta: Insights from local high-resolution geomechanical parameterization,...

Land subsidence poses major threats to human and environmental systems in river deltas worldwide, increasing risks of flooding and damage to civil infrastructure. In deltaic settings, land subsidence can be induced by multiple superimposing processes, including autocompaction, groundwater depletion and infrastructural surface loading. The quantification of each individual process is often uncertain, yet crucial for effective adaptation and mitigation. The Vietnamese Mekong Delta (VMD) is a prominent example of such a subsiding delta, with satellite-derived subsidence rates of up to 30 mm a^-1 and surface elevations largely below 1 m above mean sea level. By presenting a fully coupled flow-deformation model with geomechanical parameterization at high vertical resolution, this study, supported by local geodetic leveling observations, provides an unprecedentedly detailed local-scale assessment of land subsidence dynamics for the VMD. The simulation results indicate subsidence rates of 5-6 mm a^-1 due to groundwater depletion and local infrastructure loading. Additionally integrating one or multiple well-casing failures as localized subsurface disturbances in the model yields spatially heterogeneous subsidence patterns and increases local subsidence rates by an additional 1-20 mm a^-1, depending on the number of implemented failures. While well-casing failures are known consequences of land subsidence, the hypothesis-driven exploratory simulations employed here indicate that such damage may in turn accelerate subsidence by facilitating subsurface drainage pathways and local head equilibration between aquitards and tapped aquifers. This suggests that well-casing failures could contribute to heterogeneous and locally extreme subsidence dynamics. The results reveal significant delays in subsidence due to past groundwater depletion at the investigated site, underscoring the need for proactive water management strategies in the VMD, supported by comprehensive land subsidence modelling. The insights derived from this localized high-resolution analysis suggest that effective management will require preventing shallow aquifer depletion to avoid triggering the Holocene's pronounced, yet largely inactivated subsidence potential.