Some maintenance repairs are needed along the Beach Road seawall.

Project status: Analysis & reporting
Open for feedback: 6th November 2019 - 27th November 2019
06 Nov 2019

Consultation has now closed

 

Consultation on Beach Road seawall repairs has now closed. People were able to provide feedback from 6 November 2019 to 27 November 2019. During this time we heard from 42 individuals and groups. 

The submission results table [PDF, 961 KB] is now available.

A staff report will be presented to Banks Peninsula Community Board for a decision. At this stage the report meeting is anticipated to be 20 April 2020 at 10.00am. However, Banks Peninsula Community Board use two venues; one in Akaroa and another in Little River.  Staff would like the report to be presented at a meeting using the Akaroa Board rooms so if the meeting on this proposed date gets scheduled for the Little River meeting room we will bring forward or postpone to the next available meeting date in Akaroa.

Beach Road section of seawall

Beach Road seawall was constructed from unreinforced stone between 1901-1904. Over time, wave action of the sea has been scouring out the mortar and sediments between the rocks and creating voids in behind. This has resulted in damage or slumping to the pavement behind the sea wall, and in some areas holes or pavement collapse is starting to appear. These sections of pavement have received patch repairs over the last few years. However, the damage is still deteriorating and some areas have had to be temporarily fenced for pedestrian safety. We have carried out a survey using ground penetrating radar (GPR) to assess the damage. The survey found damage but the seawall is still economical to repair.

 

Areas where undermining and voids have been detected

Areas where undermining and voids have been detected

Repair Plan

While a number of repair options are available some have been ruled out as either too expensive, or not suitable, because they may have an impact on aesthetics, heritage, ecological, or cultural values of Akaroa township. Constructability, stability and durability is also important. The other key consideration is any work done now needs to facilitate, and not prevent, future protection work to mitigate against possible sea level rise.

For these reasons the ‘stone revetment toe’ method of repair (where a rock base is added to the front of an existing wall) has been chosen as the best suited for this site. Advantages of this method are:

  • the ability to increase the sea wall height and the rock base protection at a later date
  • it dissipates wave energy and mitigates scouring from the base of the wall
  • it is easily maintained and a well-tested protection method
  • avoids deep foreshore excavations and wall undermining
  • a more natural look is achievable
  • heritage wall structures remain intact
  • moderate cost and disruption

 

A cross section diagram of the proposed method of protection for the seawall

A cross section diagram of the proposed method of protection for the Beach Road seawall

Description of work

Cracks and voids in the existing wall face would be cleared of loose material and filled with coloured mortar to match. The surface can be dressed with shells and stone to blend with and replicate the appearance of the current wall. An excavation below the base of the wall would be filled with concrete to improve stability. Once that concrete has set it will be possible to excavate behind the wall to fill in voids and refinish the surface with chip to match the current footpath. A stack of rocks will then be placed at the base of the wall, on the seaward side, to protect it from future wave action.

Image of current seawall along Beach Road

Artist impression with rock base added

Illustration of how wave action can undermine a wall

An example of rock base added at Beachville Road, Redcliffs

 

Images of other seawall repair options considered

1. Rock base added to an existing wall (preferred option)

2. Concrete bagwork toe added in front of a wall

3. Gabion basket toe

4. Sheet piled toe protection

5. Sprayed concrete over existing wall

6. Stone masonry and repointing

7. Injection grouting

 

What happens next?

Following Community Board decision we will apply for the resource consents that are required for our work. We plan to carry out the sea wall repairs during winter of 2020 so that it is completed before the busy summer visitor period.

 

Other seawall work coming up soon

The seawall near the old public slipway also requires some repairs.  This area is adjacent to the old landfill where land was reclaimed to form Akaroa Recreation Ground.  The repairs required are much less invasive than the Beach Road section. Soil testing is currently underway and if any contaminants are found then a resource consent will be required for this work.  A start work notice  with further information will be issued before this work begins to inform about dates and exact location of work.

 

 

 

Map location

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