Suspended sediment dynamics and bed erosion in the high shore mudflat region of the Humber estuary, UK

The transport of suspended sediment over intertidal mudflats is the princip al 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 Eight, Humb er estuary, is used to evaluate the mechanisms through which sediments are both deposited and recycled in this zone over a spring-neap tidal cycle, Da ta analysis indicates that a large proportion of the sediment is delivered to the high shore region during intermediate and spring tides in the form o f a shallow, high velocity sheet of water. Neap tides are incapable of resu spending bottom sediments, and simply advect a washload of very small (<50 mu m 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 sourc e of eroded sediments to the high shore; however, comparison of the magnitu de of the ambient tidally-induced bed stress to in situ measures of sedimen t cohesive strength reveals that some local erosion may occur in the high s hore during maximum spring tides, Computation of the net suspended flux per tide reveals a temporally variable, predominantly onshore transport of sed iments during the observation period. Modulation of this flux by surface gr avity waves is discussed. (C) 1999 Elsevier Science Ltd. All rights reserve d.