Late Holocene channel discontinuity and adjustment in the lower Macquarie River, central New South Wales

    Research output: Chapter in Book/Report/Conference proceedingConference abstract

    Abstract

    Downstream declines in discharge and stream power are inherent features of many Australian lowland rivers that experience channel breakdown and floodplain wetlands on their lower reaches. The Macquarie Marshes are an alluvial system of anastomosing and discontinuous channels with wetlands on the lower Macquarie River. While contemporary processes of avulsion in the system are relatively well understood, this research investigated mechanisms of channel discontinuity (i.e. channel breakdown and reformation) and channel adjustment in the southern Macquarie Marshes. Morphometric analysis of discontinuous reaches of the Macquarie River using digital terrain data derived from a light detection and ranging (LiDAR) survey was coupled with sedimentological analysis and optically stimulated luminescence (OSL) dating of a late Holocene meander cut-off to determine the characteristics and timing of channel adjustment. Sinuosity declined from X to XX, channel depth declined from X to XX, and cross sectional area declined to less than 10 m2 in the breakdown zone of each reach. Channel reformation occurs where floodplain gradients allow small tributaries to rejoin and form another section of the trunk stream. Sediment deposited in the breakdown zone of each reach forms a lobe-shaped splay with a steepened downstream end, which can instigate knickpoint retreat and reconnection of reaches of the river. Overall, there has been a shift from a combination of lateral and vertical accretion as a means of channel adjustment to a dominance of vertical accretion with periodic avulsion in the system. The cut-off was actively meandering 1.25 ± 0.199 ka, so this shift has occurred within the last ~1000 years and is unrelated to European settlement and disturbance in the catchment. Long-term patterns of river adjustment can provide insight into the response of systems like the Macquarie Marshes to future changes in sediment regime or hydrology related to human impacts or climate change.
    Original languageEnglish
    Title of host publication15th Australian and New Zealand Geomorphology Group Conference
    Subtitle of host publicationprogram and abstracts
    Number of pages1
    Publication statusPublished - 2 Dec 2012
    EventAustralian & New Zealand Geomorphology Group Biennial Conference (15th : 2012) - Bundanoon, NSW
    Duration: 2 Dec 20127 Dec 2012

    Conference

    ConferenceAustralian & New Zealand Geomorphology Group Biennial Conference (15th : 2012)
    CityBundanoon, NSW
    Period2/12/127/12/12

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  • Cite this

    Larkin, Z., & Ralph, T. (2012). Late Holocene channel discontinuity and adjustment in the lower Macquarie River, central New South Wales. In 15th Australian and New Zealand Geomorphology Group Conference: program and abstracts