Processes of Sediment Transport and Tidal Delta Development in a Stratified Tidal Inlet.

摘要

Flood-tidal and ebb-tidal deltas in East pass, on the northwestern Florida coast, contrast sharply in form and absolute size. The flood-tidal delta, the more extensive, is characterized by a broad middle-ground shoal separating 2 diverging flood channels, whereas the ebb-tidal delta consists of a single seaward-narrowing channel flanked by subaqueous levees and has a symmetrical, crescentic, subaqueous bar at the outlet. Form differences result partially from variations in the intensities of different effluent expansion and deceleration mechanisms arising from vertical density stratification. Over the flood-tidal delta, bayward flood flow is concentrated near the bottom beneath lighter bay water. This inflow expands as a hyperpycnal effluent under the influence of bottom friction to produce the observed configuration of the flood-tidal delta. Because flood currents attain their velocity and duration maxima in the layer near the bottom, bed-load transport in the channels of the flood-tidal delta is flood-dominated. During ebb, outflow over the ebb-tidal delta is initially buoyant and restricted to the upper layer as dense sea water intrudes into the inlet near the bottom. With increasing ebb velocities, the salt wedge is forced seaward to a stationary position over the bar front, and outflow between the outlet and the bar crest becomes turbulent. This sequence is similar to stratified mouths of the Mississippi between low and high river stages.