Observations of some sedimentary processes acting on a tidal flat

In order to examine sedimentary processes acting on tidal flats, eighteen foot valves were “plumbed” into a small tidal cove in southern New Hampshire. Transport of suspended sediment was determined by comparing concentrations (determined by filtering) at 15 and 30 cm above the tidal flats throughout a tidal cycle. In general, sediment resuspension occurs more readily on the flood tide than the ebb. The concentration of suspended sediment follows the water mass distribution and is affected to a lesser degree by tidal currents and small amplitude waves. Deposition occurs during slack water shortly after high tide primarily in the bottom regime (15 cm); it is probably related to coarser particle sedimentation. The water mass distribution was not a simple rise and fall perpendicular to the bottom contours, but rather followed a slow clockwise gyre. The net effect on the suspended sediments was to impart a “longshore” component of drift to the suspended load during the tidal cycle.