ABSTRACTThe paper describes a study of the changes in grain-size parameters associated with erosion and deposition on a microtidal flat. Preliminary results suggested that over 11 years the sediment became finer in areas of erosion and coarser in areas of deposition. Closer study revealed that these results primarily reflected the time of sampling: seasonal variations were found to be greater than the long-term changes. An exception was found in an area with rapidly spreading vegetation and consequent high rates of sedimentation. Here long term changes exceeded seasonal changes. Bed load samples, sampled in traps, changed much more than samples taken on the surface. This was particularly the case during a period, in which spill from sand dredging in the navigation channel caused high rates of sediment transport on the micro-tidal flat. Hyperbolic grain-size parameters were found to give much better environmental discrimination than traditional percentile based parameters.