The Peka Peka to Ōtaki (PP2Ō) Expressway Project involves the construction of 12.5km of four-lane expressway, 9.0 km of local road, ten bridges, and 1.6 km of rail realignment for Waka Kotahi New Zealand Transport Agency. The upgrade of Chrystalls Stopbank is being completed for Greater Wellington Regional Council as a separate but related project. Bringing the stopbank upgrade forward by two years avoided constructing an additional expressway bridge that would otherwise become redundant when the stopbank was upgraded later.  

The works involve modifications to the existing stopbank to reduce flooding in Ōtaki in the design event, a 1% AEP (or 100-year ARI) flood event with a mid-range climate change allowance to 2130. The stopbank runs along the true right bank of the Ōtaki River from the Ōtaki River rail bridge to a higher elevation terrace 2.3km upstream. A 650m section of the stopbank will be raised between 0 and 1.0m above the current stopbank crest level on the landside of the existing stopbank. A 700m section of the stopbank will be raised between 0 and 1.6m above the current stopbank crest level on the waterside of the existing stopbank.

Tonkin + Taylor was engaged by Fletcher Construction Company (FCC) as part of the wider design and build PP2Ō Expressway Project. T+T completed the detailed design and currently provides construction observation of upgrade works for the existing Chrystalls Stopbank.


  • Hydrology
  • Flood modelling 
  • Hydraulic design 
  • Detailed design
  • Geotechnical investigations and interpretation 
  • Geotechnical design
  • Earthquake engineering
  • Preparation of construction drawings  
  • Construction observation


  • Greater Wellington Regional Council (GWRC)


  • 2016 – 2022

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