Coastal flow topology

Simulation of density-dependent, variably saturated flow and salt transport incorporating realistic representations of aquifer heterogeneity was conducted within a Monto Carlo framework to investigate intertidal flow topology and salt dynamics. Our results show that heterogeneity coupled with tides creates transient preferential flow paths within the intertidal zone, evolving fingering-type upper saline plumes beneath the beach surface. Compared to homogeneous systems, multiple circulation cells are generated in the intertidal zone with relatively larger spatial extent, creating hotspots of groundwater velocity at depth in the aquifer. Due to the heterogeneity, strain-dominated and vorticity-dominated flow regions coexist at small spatial scales, which alters the flow topology and local-scale mixing. The areal extent of the flow deformation reaches peaks at high tide and low tide, attributed to tidal action for the former and aquifer heterogeneity for the latter. Results suggest aquifer heterogeneity complicates intertidal flow topology, potentially altering pore-scale mixing and nearshore biogeochemical cycles.