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Sedimentation effects of salinity-control weirs in Illawarra streams

Conference Paper


Abstract


  • Macquarie Rivulet and Mullet Creek are the two main rivers draining the Illawarra escarpment west of

    Lake Illawarra, NSW. Both rivers have low run-of-river salinity-control weirs to prevent brackish water

    from Lake Illawarra penetrating upstream into the main agricultural areas.

    The weir on Mullet Creek has been in place since the late 1800s associated with a river crossing

    whereas the Macquarie Rivulet weir was only emplaced in 1963. Detailed GIS analysis of aerial

    photographs shows no signs of sediment build-up behind the weirs and no significant scouring on the

    downstream side of the weirs. This is especially apparent on Macquarie Rivulet when pre- and postweir

    construction could be analysed. The results show that channel surface areas and rates of

    change through time occur independently of the weirs with most change occurring after major floods,

    e.g. the 1984 flood on Mullet Creek.

    Surface sediment samples and vibracores were collected both upstream and downstream from the

    weirs in both rivers. Upstream from both weirs showed significant scouring with almost no sediment

    accumulation in the middle of the rivers and only minor accumulations of both coarse and fine

    material near the banks. During flood conditions when the river level is 2-3 m above the weir both

    coarse and fine material are entrained by the turbulence upstream of the weir and transported over

    the weir. Immediately downstream of the weir a scour pool is present with sediment deposition

    occurring 30-50 m below the weir. Coarse layers, up to 50 cm thick in bank-attached bars, represent

    flood deposits that may be separated by finer grained low flow deposits. The progressive fining of

    sediment downstream towards the mouth of the river is a function of the backwater effect caused by

    the lake. No anthropogenic pollution is being stored in fine material upstream of the weirs.

Publication Date


  • 2014

Citation


  • Skorulis, A., Jones, B. G. & Hopley, C. A. (2014). Sedimentation effects of salinity-control weirs in Illawarra streams. AQUA Biennial Meeting: Program and Abstracts (pp. 48-1-48-1). Australia: Australasian Quaternary Association.

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Abstract


  • Macquarie Rivulet and Mullet Creek are the two main rivers draining the Illawarra escarpment west of

    Lake Illawarra, NSW. Both rivers have low run-of-river salinity-control weirs to prevent brackish water

    from Lake Illawarra penetrating upstream into the main agricultural areas.

    The weir on Mullet Creek has been in place since the late 1800s associated with a river crossing

    whereas the Macquarie Rivulet weir was only emplaced in 1963. Detailed GIS analysis of aerial

    photographs shows no signs of sediment build-up behind the weirs and no significant scouring on the

    downstream side of the weirs. This is especially apparent on Macquarie Rivulet when pre- and postweir

    construction could be analysed. The results show that channel surface areas and rates of

    change through time occur independently of the weirs with most change occurring after major floods,

    e.g. the 1984 flood on Mullet Creek.

    Surface sediment samples and vibracores were collected both upstream and downstream from the

    weirs in both rivers. Upstream from both weirs showed significant scouring with almost no sediment

    accumulation in the middle of the rivers and only minor accumulations of both coarse and fine

    material near the banks. During flood conditions when the river level is 2-3 m above the weir both

    coarse and fine material are entrained by the turbulence upstream of the weir and transported over

    the weir. Immediately downstream of the weir a scour pool is present with sediment deposition

    occurring 30-50 m below the weir. Coarse layers, up to 50 cm thick in bank-attached bars, represent

    flood deposits that may be separated by finer grained low flow deposits. The progressive fining of

    sediment downstream towards the mouth of the river is a function of the backwater effect caused by

    the lake. No anthropogenic pollution is being stored in fine material upstream of the weirs.

Publication Date


  • 2014

Citation


  • Skorulis, A., Jones, B. G. & Hopley, C. A. (2014). Sedimentation effects of salinity-control weirs in Illawarra streams. AQUA Biennial Meeting: Program and Abstracts (pp. 48-1-48-1). Australia: Australasian Quaternary Association.

Start Page


  • 48-1

End Page


  • 48-1