Alluvial sedimentation rates from southeastern Australia indicate post-European settlement landscape recovery

Abstract

Increased catchment sediment yields are common following the introduction of European-style agriculture to relatively undisturbed landscapes. Catchment erosion rates generally increase immediately after disturbance and then decline over time. Consequently, where a catchment currently sits along this disturbance-recovery sequence will strongly influence future catchment sediment yields and river morphology. In this study, field stratigraphy, optical dating, and hydraulic modelling are used to investigate changes in catchment sediment yield and storage in the Lake Burragorang catchment in Australia with emphasis placed upon changes occurring since European settlement in A.D. 1820. On the Southern Tablelands and the upper Cox's River subcatchment, a large volume of sediment was liberated by gully erosion early in the post-settlement period, much of which was deposited at break of slope positions below the catchment's headwaters or stored in alluvial benches adjacent to the channel but within the confines of older Holocene alluvium. A lack of substantial sediment deposition over the last 20 to 40 years is evidence that catchment sediment yields have strongly declined. This is consistent with both reduced erosion rates and re-aggradation of the incised gullies that, in their erosive phase, dominated the catchment's post-settlement sediment flux. Collectively, these characteristics indicate the catchment is undergoing a phase of landscape recovery.