Sedimentation near the mouth of Mullet Creek, Lake Illawarra

This study looks at sedimentation at the mouth of a small coastal delta. Its main aim is to describe and account for the decline in environmental quality at the stream\u27s outlet by examining the delta\u27s growth and form, sediment distribution and channel geometry, thereby gaining an understanding of processes occurring throughout the system with the aid of theoretical models. The result is an assessment of the most suitable means of overcoming the practical problem of sedimentation. Results showed that the cause of sedimentation was largely due to the introduction of a man-made channel, which has re—directed stream and sediment discharge away from the old stream mouth and into a shallow bay. Stream erosion and siltation have occurred as a result of these changes. Nevertheless, the artificial channel should remain open, as overbank flow during high discharges is common along the creek, and further restriction downstream would initiate a back—log of floodwaters upstream, causing extensive flooding to residential, commercial, industrial and rural properties. Instead, a proposal to dredge sediment accumulated in the bay and along the stream channel (to increase channel capacity) was put forward, noting that stricter controls and policing of land development in the creek\u27s catchment be immediately implemented. The study therefore demonstrated that a sound knowledge of channel form and dimensions, of flood behaviour, and of depositional patterns is essential if a deterioration of environmental quality is to be avoided. This knowledge needed to be based on and linked to the general theory of delta development as well as direct field observation