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A comparison of results from mapping using a swath bathymetric sonar system in the Tay Estuary, Scotland, and remote sensing data on the position of frontal systems, indicates that the frontal systems are controlling the distribution of sedimentary features in the estuary. The boundaries between zones, defined by the advancing flood fronts and exiting fresh water, are sharply defined both by the front and the bottom bedforms. Static fronts, usually axial fronts, exist at well-defined bathymetric changes and result in relatively stable bedforms. However, measurements of current velocities at migrating fronts suggest that the vertical component of velocity accelerated at the front boundary will cause erosion at the bed and migrating bed features. Predictions of sediment movement and sediment feature migration rates across areas where these fronts migrate are confirmed by the bathymetric sidescan sonar results that show asymmetry of the sedimentary dune features. The use of new high-resolution sonar, together with its repeatable precision in locating sedimentary bedforms, has significant implications for long-term modelling of sediment transport in estuaries and other similar areas. [ABSTRACT FROM AUTHOR]

Barrier islands commonly occur in coastal plain and deltaic settings, and a variety of behavioral and stratigraphic models exist. In this paper, a 90 km long barrier island system in the Outer Hebrides of Scotland is identified for the first time. Uniquely among barrier islands, the system rests directly on a planar bedrock (gneiss) surface (a strandflat). This bedrock surface has a profound influence on the morphology of the barrier island chain, and exerts the dominant influence on barrier island form and evolution during transgression. Topographical irregularities on the bedrock surface control both plan and profile morphology of the barrier islands. Under sea-level rise, by barrier migration, sediment is redistributed onshore and alongshore in a strongly three-dimensional manner, determined by topographic variability in the bedrock. The barrier islands represent an endpoint in transgressive barrier island geomorphology that is controlled by the bedrock surface: they are at the upper end of the recognized tidal amplitude for barrier islands; the offshore wave regime is very high-energy; they lack a shoreface; and neither ravinement surface nor transgressive sand sheet are developed. Sediment supply is dominated by offshore-derived skeletal carbonate. [ABSTRACT FROM AUTHOR]