WRECK MARKS - INDICATORS OF NET SAND TRANSPORT

Sonographs have revealed the presence of many obstacle marks that have been generated by scour and deposition near wrecks which interrupt tidal current flow. These features have been named wreck marks. In an area of known direction of net sand transport, longitudinal wreck marks have been shown to extend for up to 1 km in the direction of flow of the stronger ebb or flood tidal current. A series of these has been recognised, all of which parallel the peak current. Wreck marks on a sand floor, consisting of scour shadows, have been distinguished from those on gravel floors where sand plumes are prevalent. The occurrence of single or double wreck marks has been shown to reflect the orientation of the wreck with respect to the peak tidal current flow. The longitudinal wreck marks are valuable as accurate pointers to the direction of dominant tidal current flow and to the direction of net sand transport, particularly in regions where other indicators are lacking. © 1979.