Hydrodynamic time parameters response to meteorological and physical forcings: toward a stagnation risk assessment device in coastal areas

Identifying zones of stagnation and deposition of terrigenous matter or contaminants induced by human activity is a key issue in coastal areas. In this paper, circulation processes and potential contaminant stagnation and deposition zones were assessed using hydrodynamic time parameters forced with meteorology. The study focused on an Eulerian time parameter, the local e-flushing time (eFT). The hydrodynamic modeling of coastal zones was applied to two bays of New Caledonia, located downstream of open mining sites. Numerous simulations were performed to classify the influence of forcing conditions on the eFT variability. The need to consider meteorological forcings rather than average weather conditions for the calculation of eFTs was demonstrated. In coastal zones, high wind velocity was the major forcing influencing eFTs, but below a threshold wind velocity, tidal range and river inputs became significant parameters. Spatial variations of eFT values, depending on meteorological conditions, induced varying risks of stagnation zones. General responses of the bays' hydrodynamics and the exposure of zones to potential contaminants were defined under various forcings. Our findings demonstrate that strong turbulence zones are not always characterized by short eFTs because of antagonistic forcing effects. Diurnal tidal alternations were also proven to have less influence on eFT variations than tidal range changes over a lunar cycle.