Circulation patterns from seabed-drifter studies, Western Port and inner Bass Strait, Australia

Morphological evolution of a complex drift‐aligned prograded barrier

“…Their alongshore extension appears to be related to fairweather wave conditions forming ridges roughly parallel to the coast (Stapor, 1975; Tamura, 2012), whereas elevation variation between consecutive ridges seems to be a function of the availability of sediment (Shepherd, 1987). At SSP, bottom velocities of 2.9 cm s −1 have been measured with seabed drifters across the Middle Bank towards the shores of the barrier (Marsden, 1979) and a moored bottom‐current tripod located about 5 km to the southeast of Point Leo (Sternberg, 1979). These flood‐dominated tidally induced flow velocities exceed the threshold values required to cause sediment movement of fine and medium sands on the seabed (Harris et al, 1979), and transport grains to the shore.…”

“…Progradation of SSP barrier seems to have been sustained by intense sediment movement of the Middle Bank, the biggest individual sand body in WP (Harris et al, 1979), instead of the typical convex shoreface sand body that provides conditions for the cross‐shore supply of sediments (Anthony & Aagaard, 2020; Kinsela et al, 2016). Apart from the tide‐generated clockwise circulation that occurs there (Marsden, 1979), an eastwards net flood sand transport of 1–10 kg cm −1 year −1 was estimated to have supplied sand to the Cowes Bank (Figure 1), which prograded 1.5 km during the Holocene producing extensive sediment deposit in that region (Harris et al, 1979). A much more limited amount of sand also needs to be transported to maintain the North Arm (Harris et al, 1979).…”

“…Flood dominance prevails on the western flank of the bank, swinging east to southeast across the northern part, whereas ebb‐dominant transport prevails on the deeper channel to the east side of the bank (Marsden et al, 1979; Sternberg, 1979). This complex circulation is responsible for not only supplying sand from the Middle Bank to the beaches and other sandy environments to the north and east of the confluence zone (Harris et al, 1979) but also for creating a minor clock‐wise circulation around the Middle Bank (Marsden, 1979). These flow patterns are associated with the progradation of the Sandy Point Spit and the Cowes Bank complex, further to the southeast (Marsden et al, 1979).…”

“…Off Sandy Point, the coastline orientation changes and the waters entering WP bifurcate around French Island, in an area known as the Confluence Zone (Marsden, 1979). Partly exposed sand bars and shoals run out forming the Middle Bank, a large sandy bank approximately defined by the 6-m bathymetric contour (Marsden & Mallett, 1975), which extends for about 9 km in a southwestern direction.…”

“…Apart from the tide-generated clockwise circulation that occurs there (Marsden, 1979), an eastwards net flood sand transport of 1-10 kg cm À1 year À1 was estimated to have supplied sand to the Cowes Bank (Figure 1), which prograded 1.5 km during the Holocene producing extensive sediment deposit in that region (Harris et al, 1979). A much more limited amount of sand also needs to be transported to maintain the North Arm (Harris et al, 1979).…”