Morphodynamics of Deeban Spit, Port Hacking.

Deeban Spit is in the estuary of the Port Hacking River. The data collected will be used to study the dynamics of Deeban Spit across three time scales: geological through a review of literature, engineering through GIS spatial analysis of changes in spit volume, and shoal and seagrass area through aerial photography. The aerial photographs were taken sporadically throughout the period from 1930 to 2006 and monthly throughout the four month period from March to July 2006 of the beach profile survey period. In the geological time scale, Deeban Spit has developed through sediment brought to the coast during the post glacial marine transgression (PMT), and the flooding of coastal valleys forming the estuary mouth. The sediment was then reworked into a flood tide delta, and waves, tides, and dredge spoil disposal caused the establishment of the spit itself. Decadally, the spit has oscillated according to shoal movement (which may be dredging and/or current induced) and major storm events, with a mean erosion trend of 117m3 /year. The storm events caused major changes in the beach profile, which varied between the locations along the spit. Similar profile adjustments were observed on a monthly scale, with a greater rate of erosion (mean rate of 18 650m3/year for the 4 month period) possibly due to the occurrence of a 6m storm wave event on 3/6/06) with the ability to cause most of this erosion in one event.