The influence of nearshore sandbars on coastal stability in Port Geographe, south-west Australia

Charitha Pattiaratchi, Sarath Wijeratne, Lucya Roncevich, James Holder

    Research output: Chapter in Book/Conference paperConference paperpeer-review


    The coastline of Geographe Bay, south-west Australia, is dominated by a system of shore attached oblique sand bars that are 1-3 km long, up to 1 km wide and extend from the shoreline to a depth of ~5 m. The Port Geographe coastal development, initially developed in the 1990s, included a residential canal estate and a marina. Subsequent to the construction of this system a series of coastal problems were encountered that included the accumulation of seagrass wrack upstream of the breakwaters and erosion of beaches downstream of the development at Wonnerup. In 2014, a reconfiguration of the marina breakwater layout was completed to enable natural bypassing of the seagrass wrack and sand. Hydrodynamic and morphological model output using the DHI MIKE21 numerical modelling suite together with repeated bathymetric surveys were analysed to determine the shoreline evolution subsequent to the completion of the new marina layout. Results indicated that the Port Geographe coastal environment is complex with a variety of features influencing sand transport in the region. This included sheltering from the large headland at Cape Naturaliste, presence of offshore sand bars with sand transport occurring predominantly during winter storms when relatively larger waves approach the coast from the northwest. Model predictions indicated that there were strong interactions between the incident waves and currents with the nearshore sandbars. The sandbars refracted the waves to create regions of high and low energy along the coastline and acted as an obstruction to the flow and thus currents were enhanced along the crests of the sandbars and in the nearshore. In combination, these features resulted in shoreline changes corresponding to the location of the sandbars and highlighted the importance of the sandbars in controlling nearshore sand transport.
    Original languageEnglish
    Title of host publicationAustralasian Coasts & Ports 2017
    Subtitle of host publicationWorking with Nature
    EditorsTom Baldock
    Place of PublicationBarton, ACT
    PublisherEngineers Australia
    Number of pages7
    ISBN (Print)9781922107916
    Publication statusPublished - 2017
    EventAustralasian Coasts & Ports 2017 conference - Cairns, Australia
    Duration: 21 Jun 201723 Jun 2017


    ConferenceAustralasian Coasts & Ports 2017 conference


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