Midge Point coastal protection designs, QLD

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Midge Point is a small coastal community in central Queensland that was hit by the Category 4 Cyclone “Debbie” in 2017. The resulting erosion was extreme, with the majority of beach swept away, and the township flooded from the associated storm tide. JBP undertook concept and detailed designs for a new beach nourishment, buried seawall constructed of geotextile sand containers (GSC), and dune revegetation. The sand and dune revegetation is designed to maintain coastal and ecological processes, with the GSC seawall providing a backstop defence against cyclonic erosion, with a 50-year standard of protection and 20 year design life before replacement is needed.

Figure 1: Post TC Debbie erosion at Midge Point

The new 3.6-metre buried seawall is made from 2000 GSC units, each holding 2.5m3 of sand with a weight of four tonnes. The associated nourishment will cover the full residential 900-metre shoreline, with 26,000m3 of sand imported to restore and raise the frontal dune. While the nourished beach will evolve with ongoing shoreline processes and erode over time, the sand is designed to offer increased protection from erosion and storm tides as it absorbs and spreads the waves’ energy in a storm. By including revegetation along the dune, grasses can capture wind-blown sand before it leaves the beach, with roots helping to stabilise the rear dune. The designs were approved by the State Government and recovery works supported under the Natural Disaster Relief and Recovery Arrangements.

JBPs work included the following tasks

  • Concept design and numerical modelling
  • Detailed design calculation for the GSC wall
  • Detailed design for sand nourishment
  • Safety in Design report
  • Technical Specification
Figure 2: Design overlayed on the completed works (background)