Sediment flux and bed level measurements from a macro tidal mudflat

A detailed analysis is presented of the variations in suspended sediment fl ux and bed level, measured for one year in the Spurn Eight, Humber Estuary (U.K.). Suspended sediment concentrations were correlated to flow speed, an d wave activity dominated the erosion processes and governed the residual t idal flux. An onshore flux and gradual accretion of a few millimetres of se diment were typical of calm hydrodynamic conditions. In contrast, large wav es caused the erosion of several centimetres of sediment and prevented depo sition over slack water, producing significant seaward transport. This erod ed material could be replenished in just a few days under calm conditions. The mudflat level was continually changing in order to reach some equilibri um in balance with the wave climate, tidal cycle, river runoff and seasonal effects. Large differences in the mudflat morphology rapidly occurred when there were significant deviations from the modal forcing conditions. These relatively short term events tended to cancel out with time, and the net s easonal changes in bed level variations were about a few millimetres. Multi ple regression analysis was used to produce empirical expressions predictin g the residual sediment flux and bed level from readily observable environm ental parameters. The results quantified the dominant physical processes af fecting the residual tidal flux and established some site-specific relation ships that provide a basis for more general flux predictions. (C) 1999 Acad emic Press.