Mutton Cove – Investigation and review of potential Living Shorelines projects

Ecologist Peri Coleman has finalised a report Investigation and review of Living Shoreline projects at Mutton Cove for the Estuary Care Foundation.

In 2015, prior to the breaching of the seawall at Mutton Cove, it was proposed to attempt to protect the eroding remnant mangroves, and establish young forests along the exposed areas of the seawall, using ‘Living Shorelines’ approaches.

The Foundation, with support from Adelaide and Mount Lofty Ranges Natural Resources Management Board, remains keen to see if the plans drafted then, ‘Mutton Cove: Draft project proposal for mangrove rehabilitation’, are still achievable.

ECF sought advice from Peri about possible ‘Living Shorelines’ rehabilitation methods to:

• build skill in mangrove protection and rehabilitation,
• improve blue carbon outcomes through protection of remnant mangrove and saltmarsh habitats and creation of new areas of those habitats, and
• minimise risk to existing infrastructure within the Cove and to the north and west.

There are now four breaches of the seawall at Mutton Cove with more pending, and the southern two breaches allow water to enter the Cove on a daily basis, so this is integral to the options now available.

Peri advises that inside the Cove, where the inner embankments were never rocked, the sand that forms these embankments is slumping with every tidal inundation. Further erosion of the western and northern banks has occurred and it seems likely that erosion will continue, albeit at a slower pace, until the embankments are reduced to the appropriate angle of repose right around the site, as shown in the diagram below.

    Sand slumping sketch by Peri Coleman

Peri’s report considers two options

• Repairing the seawall and reinstating the tidal pipe infrastructure
• Not repairing the seawall and using remedial actions along the landward embankments of the Cove to halt erosion

The report notes that ‘it is highly likely that unexpected eventualities may arise from either course of action.’