Abstract
Mixing along the salt-freshwater interface is critical for geochemical
reactions,
transport and transformation of nutrients and contaminants in coastal
ecosystems.
However, the mechanisms and controls of mixing are not well
understood.
We develop an analytical model, based on the coupling between flow
deformation and
dispersion, that predicts the mixing dynamics along the interface for
steady state
flow in coastal aquifers. The analytical predictions are compared with
the
results of detailed numerical simulations, which show that
non-uniform flow fields, inherent to seawater intrusion in
coastal aquifer, result in a non-monotonic evolution of mixing width
and
mixing rates along the interface. The analytical model accurately
captures these dynamics over a range of
freshwater flow rates and dispersivities. It predicts the evolution of
the mixing width and
mixing rates along the interface, offering a new framework for
understanding and modeling mixing
and reaction processes in coastal aquifers.