Sediment Flux and Bed Level Measurements from a Macro Tidal Mudflat

Abstract

A detailed analysis is presented of the variations in suspended sediment flux and bed level, measured for one year in the Spurn Bight, Humber Estuary (U.K.). Suspended sediment concentrations were correlated to flow speed, and wave activity dominated the erosion processes and governed the residual tidal flux. An onshore flux and gradual accretion of a few millimetres of sediment were typical of calm hydrodynamic conditions. In contrast, large waves caused the erosion of several centimetres of sediment and prevented deposition over slack water, producing significant seaward transport. This eroded material could be replenished in just a few days under calm conditions. The mudflat level was continually changing in order to reach some equilibrium 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 seasonal changes in bed level variations were about a few millimetres. Multiple regression analysis was used to produce empirical expressions predicting the residual sediment flux and bed level from readily observable environmental parameters. The results quantified the dominant physical processes affecting the residual tidal flux and established some site-specific relationships that provide a basis for more general flux predictions.