Processes controlling import of fine-grained sediment to tidal areas: a simulation model

Salt marsh and mud flat sedimentation in the Wadden Sea and in similar depositional regions is usually dependent on the net import of fine-grained sediments from adjacent marine environments. This net import rakes place as a result of several processes such as settling lag and scour lag. This paper utilizes a database comprising time series of tidal Velocity and turbidity in the Gradyb tidal area of western Denmark as the basis of a simple conceptual model which describes the transport, deposition and resuspension of fine-grained material in the area. The results demonstrate that: (a) grain sizes close to the sand/silt boundary are most sensitive to lag effects; (b) scour lag is much more important than settling lag; (c) raised temperatures enhance the net-lag effect for silt with increasing importance for finer grain sizes; (d) with increased suspended concentrations, the time it takes to resuspended the material deposited at slack water (the resuspension lag) is of increasing importance for the net-lag effect.