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Trenching for pipelines and cables

If trenching is required within the CMA, there are two main scenarios:

  • The works are in the intertidal area above low tide and can be done incrementally between tides
  • Trenching is done below low tide level.
Design essentials

Intertidal area

  • Carefully plan the works so that you do a defined extent of work each tide. Include the removal of any loose excavated material from the site within that time.
  • Consider access to the work area to determine how to minimise damage. For a sandy or rocky foreshore, limited protection will be necessary, but for a muddy foreshore, you might need to install a temporary causeway/accessway or raised platform.
  • Consider the tidal range in the location of work. If the works are near the high tide level, you might need a low coffer dam or causeway/accessway over the work area.
  • Using silt fences is not considered an appropriate ESC in the CMA.

Below the low tide

  • Install a coffer dam to isolate the area and to do the works in dry conditions. This will largely depend on the depth of water at the work location and the necessity of doing the works in dry conditions.
  • Do the trenching as a dredging operation with the pipe laying or cabling undertaken remotely from the surface or by using divers. In this situation, the main way to limit any sediment discharge is usually by limiting the work area and duration.

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