Abstract :
The transport of suspended sediment over intertidal mudflats is the principal agent by which sediment is exchanged between the high shore marsh region and the sub-tidal zone. A 16-day time-series of near-bed current velocity and water turbidity, collected during the LOIS LISP (Littoral Investigation of Sediment Properties) experiment on the upper shore of Spurn Bight, Humber estuary, is used to evaluate the mechanisms through which sediments are both deposited and recycled in this zone over a spring–neap tidal cycle. Data analysis indicates that a large proportion of the sediment is delivered to the high shore region during intermediate and spring tides in the form of a shallow, high velocity sheet of water. Neap tides are incapable of resuspending bottom sediments, and simply advect a washload of very small (<50 μm diameter), low settling rate flocs back and forth across the mudflat. A central belt in the mid-shore region of the mudflat is the dominant source of eroded sediments to the high shore; however, comparison of the magnitude of the ambient tidally-induced bed stress to in situ measures of sediment cohesive strength reveals that some local erosion may occur in the high shore during maximum spring tides. Computation of the net suspended flux per tide reveals a temporally variable, predominantly onshore transport of sediments during the observation period. Modulation of this flux by surface gravity waves is discussed.
