Numerical Simulation of Coastal Dune–Interdune Lake Evolution Under Groundwater-Controlled Moisture Effects

Abstract

Coastal dune fields provide important ecological and geomorphic functions, while their evolution is strongly influenced by groundwater-controlled surface moisture. However, the effects of seasonal groundwater-level fluctuations and moisture-affected sand on long-term dune development remain insufficiently represented in numerical models. In this paper, a time-varying groundwater-level field and moisture-dependent entrainment thresholds are incorporated into a real-space cellular automaton model to investigate the coupled evolution of coastal dunes and interdune lakes. The results show that rising groundwater levels reduce the wind-erodible surface area, inundate interdune depressions, and delay the growth of peak dune height. Periodic water-level fluctuations also produce a sediment storage–release cycle, in which sand is temporarily stored on inundated interdune surfaces during high-water stages and is progressively remobilized during subsequent low-water stages, while newly exposed moisture-affected sand remains subject to an elevated entrainment threshold. In addition, increasing the critical threshold shear stress within the groundwater-controlled moisture-affected layer suppresses dune development and reduces final peak dune height by approximately 8–17%. Comparison with the observed wet-season water-pond area further shows that incorporating the moisture-affected layer brings the simulated relative water-pond area closer to the observed value in the Lençóis Maranhenses dune field. Overall, the results demonstrate that groundwater regulates dune evolution through both direct inundation and an enhanced entrainment resistance of moisture-affected sand above the water table.