MONITORING THE TEMPORAL BEHAVIOUR OF THE SUBMARINE SAND DUNES OF MISPEC BAY, SAINT JOHN, NB, THROUGH USE OF MONTHLY MULTIBEAM ACOUSTIC SURVEYS

A large submarine sand dune field in Mispec Bay is one of many headland-associated sand bodies (banner banks) that lie along the margins of the Bay of Fundy. Within these banks, highly mobile and particularly well-sorted sand exists in an otherwise sediment-starved seabed region. The aim of this research is to investigate the relationship that the pattern of bedform migration has with both the tidally induced gyrating flow found in the vicinity of the headland and the seasonally varying, predominantly seaward flow of the Saint John River. Previous studies of other similar banks have demonstrated their gross morphology and bedform migration patterns over time scales of a year or more. Through use of monthly repeat multibeam surveys we have been examining details of the sediment transport mechanisms to thus better understand the evolution of these banks. Using properly calibrated and integrated multibeam sonar systems, and taking advantage of improved availability and reliability of RTK – GPS, we now have the potential to examine fluctuations of the sediment water interface at scales of as little as a decimetre vertically and less than a metre horizontally. In addition, data from ADCP studies has supplemented the bathymetry data to build up a complete picture of the evolution of the local current field over an M2 tidal cycle. . Besides large-scale migration of long wavelength features, we are observing transient features indicative of locally enhanced sediment transport. This indicates that, whilst the bank appears to be mainly dominated by the M2 tidal current field, episodic events perhaps related to storms and or a period of high river discharge may be of more significance than previously realised.