Net sediment transport pathways have been determined in many environments by studying grain size trends. This approach is extended here to an inner shelf environment, with improved statistical techniques. Patterns of net surficial sediment transport are proposed, indicating that the area is dominated by up-estuary transport. Exceptions exist in the form of radial mud transport at the river mouths and (clockwise) sand circulation around linear sandbanks. Six different sedimentary environments are defined on the basis of the shape of the ‘transfer function’ and its relationship to the grain size distributions. Erosion takes place along the axis of the estuary. Dynamic equilibrium is reached around the linear sandbanks, whilst accretion occurs at the head of the estuary and where there are riverine inputs. The results are compared with numerical model outputs, representing water movement and sediment transport. Over the seaward part of the study area, there is agreement between the two approaches; contradictions increase, however, towards the upper reaches of the estuary. The discrepancies can be attributed to: (1) inherent differences between patterns of water and sediment movement; (2) difficulties in modelling intertidal boundary conditions; (3) inadequate representation of river influences in the models; and (4) time-scale differences, associated with sediment transport processes.

InJanuary 1991 GeoSea produced its first repon for the Rijksinstituut voor Kust en Zee, Haren, which presented the results ofa Sediment Trend Analysis (STA TM) for the Eems/Dollard Estuary. Ah STA is a technique pioneered by GeoSea which uses the relative changes in the grain-size distributions ofbottom sediments to develop pattems of net sediment transport. In addition, the technique defnes the dynamic behaviour ofbottom sediments with respect to erosion, deposition and dynamic equilibrium. The data base is comprised of the complete grain-size distributions from sediment grab samples that ate collected over a predetermined grid which is typically at a 500 m spacing.Since the completion of the Eems/Dollard study (680 samples), an STA has been undertaken more or less annually in each of the Dutch Waddenzee tidal basins: Vliestroom (1,500 samples) 1992; Marsdiep (2,000 samples) 1994; Friesche Zeegat (850 samples) 1995; Borndiep (1,200 samples) 1996 and the Lauwers/Schild (1,100 samples) completed in 1997. Two smaller projects were also undertaken. One looked in detail at the Dollard (1992) and another at the NOURTEC beach nourishment site on Terschelling as part of the Bomdiep project (1995). The last time a grain-size data set on a regional scale was collected took place during the 1950's and covered only the intertidal areas.The STA for each tidal basin produced broadly similar results. Offshore ti'oro the barrier islands, sediment transport parallels the shoreline in a north-east and east direction. At each tidal inlet this regime is intermpted by the dynamics associated with its corresponding tidal basin. Over the ebb-tidal deltas there are typically complex transport gyres that originate in the deepest portion of the channel separating the barrier islands. Inside the tidal basins transport is generally landward fi'om the deeps and the sediment trends follow the dendritic network ofchannels with net accretion over the extensive intertidal flats. Fine sediments, often showing bimodal distributions, identified the wantijs of tidal null points that separate the tidal basins from each other.The distributions of the sediments and the interpretative findings of the STA's may be used for many coastal management considerations such as: (i) the best locations for dredged material disposal sites; (ii) optimum channel alignment to minimise dredging; (iii) understanding the effects ofcoastal stmctures; and (iv) determining the dispersal ofcontaminants contained in the sediments. In addition, the Rijksinstituut voor Kust en Zee use the textural data for correlation with numerical models and for generating GIS-derived bottom sediment maps.

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