Paekakariki Seawall Options, Pros and Cons

The Paekakariki Seawall replacement project is under discussion and involving the community in consultation.

The community is invited to participate by adding their ideas and input to the Feedback Form. Feedback deadline originally due by 15 May 2015 has been extended to 29 May 2015

We will display pictures, ideas, and information about the options as they become available.

We invite discussion and will add lists of advantages and disadvantages to each option listed.

The following information has been put together by:

John Mills and Shane Murland, two principle seawall builders of the Kapiti Coast

Also with help and advice from BECA Ltd., Ross Titchener NZCE (civil) REA, Caleb Pinfold BSc, Geoff McNelly BENG LBP IQP.

Send your ideas by clicking on and writing in our comments page.

STEPPED CONCRETE OPTION

SteppedConcreteOption1

Stepped Concrete Option

May 8, 2015

Advantages of Stepped Concrete compared to the Vertical Timber Option

  • Increased public safety: No unballastered high walls.
  • Future proof/long life: more than three times the minimum life span of timber.
  • Reduced wave reflection: Reduces storm surge and high tide impact on the seawall.
  • Reduced scouring: Scouring less likely due to the reduced storm surge allowed by the sloped design of the steps.
  • Increased foundation depth: Washout risk to the support material greatly reduced/eliminated by increased depth of the proposed sub wall apron.
  • Increased foundation support: No requirement for seaward support piles. The subterranean panelled wall apron eliminates need for the seaward row of support piles giving 6.6 times the ground bearing capacity of the proposed support piles.
  • Cantilevered strength: provided by the sub wall apron eliminates/reduces the need for expensive tie backs.
  • Reduced construction impact: The stepped concrete option is far less labour intensive at the site. Precast units constructed off site, craned/jetted into place eliminates the need for large untidy on-site timber construction in the wet.
  • Reduced construction time: The stepped concrete option would be over all 2 times faster than the wall option constructed in timber.
  • Reduced maintenance: Virtually eliminates maintenance. Bolted timber becomes increasingly costly over time.
  • Affordability: Contractors estimate $8,200,000 (within the allocated budget)
  • Enhanced beach accessibility:
  • Multiple height single walk levels:
  • Seating at beach level: Allows continuous seating along the beach whatever the tide level.
  • Grandstand like usage: Observation platform for water and beach sports. Allows continuous multiple height seating along the entire wall whatever the beach level.

 

Disadvantages of Stepped Concrete compared to the Vertical Timber Option

  • Aesthetically not pleasing to some: Large concrete footprint.
  • Accommodates too many people if the preference is for Paekakariki to become an exclusive back water.

Please add comments to be added to these advantages and disadvantages.

VERTICAL TIMBER WALL OPTION

TimberOptionLongWall

Timber Wall Option

May 8, 2015

 Advantages of Vertical Timber compared to the Stepped Concrete Option.

  • Light in weight. Support piles not required.
  • Affordability: Costs are unlikely to exceed the allocated budget.
  • Aesthetically pleasing to some, and for the most part mirrors the current seawall.
  • Vertical wall provides maximum space for plantings, rock gardens, and pathways between the top of the wall and the road.

 

Disadvantages of Vertical Timber compared to the Stepped Concrete Option

  • Limited Future proofing: Has only a guaranteed 50 year deteriorating life span the end of which requires complete replacement compared to much longer with concrete.
  • Greater vulnerability to wave action: Mass reinforced concrete has greater inherent strength and weight to resist the forces of wave impact.
  • Increased wave reflection: Provides a solid barrier which increases wave turbulence and the resultant beach scouring.
  • Longer construction time: At least 2 years for the timber wall compared to 1 year for the stepped concrete proposal.
  • Untidy beach front for an extended period: Construction site materials strewn around the moving work area as packets of timber are prepared for use and installed. Whereas concrete components are manufactured off site and most of the work is performed by machinery.
  • Beach inaccessibility: As with the existing wall there is at least a 1.5 meter drop to the mean beach level, and at certain times of the year the drop can be up to 2.5 meters at some places.
  • Limited seating: Seating only at the points where it is provided along the top of the wall, compared to continuous seating with the SC.
  • Increased maintenance over time: Over time bolted timber strength is reduced by salt and water penetration into the wall even with the heaviest of tantalising treatment.

Please add comments to be added to these advantages and disadvantages.

 

2 thoughts on “Paekakariki Seawall Options, Pros and Cons

  1. The concrete option seems to be more practical, longer life, easier access to the beach and if/when sand builds up will blend in more. Don’t like big rocks, don’t think the wooden option is cost efficient or visually ascetic or accessible. I am more interested in what ever option is built causes minimum halm on the environment, sand is not lost no impact on the wildlife.

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