Recent sedimentation and geomorphical changes, Lake Illawarra, NSW, Australia

Abstract

Assessing recent changes in landforms associated with Lake Illawarra was achieved by identifying changes in geomorphological features observed in early mapping of the region, aerial photographs and satellite imagery. Quantifying rates of sedimentation associated with prograding fluvial bay-head deltas and within the central basin of Lake Illawarra was established within the framework of amino acid racemisation, radiocarbon, and cesium 137 dating. Results indicate that sedimentation rates associated with fluvial bay-head deltas range from 31 mm/yr proximal to the delta front and fall to between 3 and 7 mm/yr in the pro-delta region. This is a significant increase in sedimentation rate when compared to the underlying estuarine mud (<1mm/yr). Data obtained from the central lagoon facies also support a significant increase in the rate of sedimentation over the last 200 years with pre-European settlement sedimentation rates of ca. 0.3 mm/yr increasing to 0.52 m/yr for the period associated with initial settlement and a sedimentation rate of ca. 4.5 mm/yr for the past 50 years. As indicated by the aerial photos, remotely sensed imagery and post-European sedimentation rates, the sedimentary infill of Lake Illawarra and the morphological change associated with the fluvial influenced facies and inlet processes have increased significantly over the last 200 years. However, results only imply that recent morphological change and increased sedimentation is due to anthropogenic effects, and further research is needed to separate natural sedimentary processes as opposed to accelerated sedimentation due to human modification of the landscape.