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Coastal erosion protection works

What, and issues to look out for

What

Coastal erosion protection works usually involve placing a non-erodible material or structure within the CMA to prevent erosion of the coastal margin. For example, coastal protection rock is a stabilised product and can be placed directly into the CMA.

Depending on the degree of coastal protection works required, many of the operations may require an element of reclamation.

Issues to look out for

Construction issues may arise from the need to undercut an area that is to be lined with rock and is inundated by the tide. If you undercut a footing below the tidal level in marine mud, you may need a coffer dam to create a dry working environment, to:

  • Do the works in a way that minimises the discharge of sediment
  • Construct to the design (that is, attempting to excavate in marine mud underwater is no guarantee that any design levels had been achieved)
  • If you carefully place large rock rip-rap that settles into the marine muds to a stable point of ‘refusal’, you may not need undercutting or a coffer dam to create a dry working environment.
Design essentials
  • Plan the works to minimise both the extent and duration of the operation.
  • Consider in detail the design of the footing or toe of the protection works. Any detailed design works underwater will need a coffer dam to create a dry working environment.
  • Consider the design option of placing large rock rip-rap into the marine muds to ‘refusal’ (that is, to the point where the rocks have settled to the maximum level of settlement for the ground conditions) to avoid excavating underwater.
  • If works underwater are required and a coffer dam is installed, you then need to consider where you will pump the sediment laden water for treatment.
  • If the coastal protection works involve the construction of a structure within the CMA, you will usually need a coffer dam to enable the construction as well as for environmental control. Design for this from the initial design of the project.

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