FLOW DYNAMICS NEAR AN IRREGULAR SEDIMENT-WATER INTERFACE UNDER AMBIENT GROUNDWATER DISCHARGE

We investigated the interactions between laminar flow in a water column, current-induced flow in underlying permeable sediments, and discharge of deep groundwater to the water column via numerical simulations. Groundwater discharge reduces the spatial extent of current-induced exchange zones within the sediments and may completely prevent their development when flow in the water column cannot provide sufficient energy to overpower groundwater discharge. Although exchange zone size is reduced by groundwater discharge, the exchange flux does not substantially change, suggesting reduced residence times of materials cycled through these smaller zones. Fluid exchange zones tend to be centered around the reattachment points of water column eddies that also mark the location of flow divides within the sediments; deep groundwater is discharged preferentially along troughs. Exchange zone depth and the water column Reynolds number are functionally related through a Morgan-Mercer-Flodin model. A power law describes the relationship between the current-induced flux through the sediments and the Reynolds number. This study is currently being extended to cases where water column flow is turbulent.