Cycle of vertical and horizontal mixing in a shallow tidal creek

Abstract

An experimental study of vertical mixing and along‐channel dispersion parameterized in terms of horizontal mixing near the mouth of the Duplin River (a tidal creek bordered by extensive intertidal salt marshes on Sapelo Island, Georgia) was carried out over several spring/neap cycles in the fall of 2005. Vertical mixing is modulated on both M4 and fortnightly frequencies with maximum turbulent stresses being generated near the bed on periods of maximum flood and ebb and propagating into the water column showing a linear dependence with depth. Values are significantly greater on spring tide than on neap. Horizontal mixing evaluated by salt fluxes is driven and dominated by tidal dispersion, which is also modulated by the fortnightly spring/neap cycle. Net export of salt from the lower Duplin is shown to be due to residual advection modified by upstream tidal pumping. The tidal dispersion coefficient exhibits a pulsating character with greater values on spring tide followed by smaller values on neap tide.