WATER AND SEDIMENT MOVEMENT IN THE VICINITY OF LINEAR SANDBANKS - THE NORFOLK BANKS, SOUTHERN NORTH-SEA

Geophysical surveys, current meter measurements and fluorescent sand tracer experiments were undertaken in the vicinity of the Broken Bank. The data are used to establish localised and regional patterns of water and sediment movement. The results obtained confirm mechanisms proposed previously for sandbank growth, with particular reference to the North Sea; these include the clockwise circulation of water and sand, with convergence at the crestline. Secondary helical water circulations do not appear to be a dominant process influencing sandbank maintenance. However, such circulation may still be important in the initial formation of linear sandbanks and/or at some stages in the bank development. On a regional basis, residual currents, bedform asymmetries and tracer dispersion indicate an offshore sediment transport component. This observation supports the hypothesis of other investigators, formed on the basis of geomorphological observations and numerical model predictions, concerning the movement of sand under extreme conditions. Moreover, these transport pathways may persist under low wave and tidally-dominated conditions, as opposed to being restricted to storm activity.