Case study

Ākitio – river erosion resilience

Overview

In Ākitio, the Tararua District Council faced persistent erosion and infrastructure damage to the community’s primary access road, particularly after a major slip in 2021 and further degradation during Cyclone Gabrielle in 2023.

A collaborative effort between HEX-LOC®, Lattey Group, and the Tararua Alliance led to the implementation of a hybrid HEX-LOC® retaining wall system to restore and protect the critical roading infrastructure.

Challenge

  • Prolonged Search for Resilient Solutions: Tararua District Council had struggled for years to find a viable solution to ongoing erosion and slope instability.
  • Geotechnical Constraints: Steep slopes and dense papa soil ruled out conventional solutions like lime rock, sheet piling, and timber pole retaining walls.
  • Cost and Feasibility: Managed retreat and high-cost structural options were not viable due to land constraints and a 50+ meter rock face behind the road.
  • Environmental Sensitivity: The site is culturally and ecologically significant, requiring careful stakeholder engagement and environmental consideration.
  • Hydrological Impact: The road is overtopped by floodwaters 2–3 times annually. Water movement impacts the bank at a 90-degree angle, with flow velocities reaching up to 6.5 m/s during storm events – posing significant structural stress.

Project:

River Rd, Ākitio

Size:

1100 Modules

11 Tier’s High

Structure Size:

59 mtrs Length – Main Structure

162 mtrs Length – Road Edging

Completion:

May 2025

Client:

Tararua Alliance

Contractor:

Lattey Group & Agmar Tools

Solution

  • HEX-LOC® Modular System: 1100 interlocking concrete HEX-LOC® units were installed, to form a robust retaining wall and reinstate a double-lane road.
  • Design Innovation: Inspired by natural hexagonal forms, the geocell units feature castellations for interlocking strength and can be adapted to sloped terrain.
  • Anchored Foundation: The foundation layer was supported by a piling system at intervals along the bottom layer, anchored deep into the sandstone riverbank and providing critical structural stability.
  • Sustainability: Use of local fill significantly reduced the need for heavy truck movements carrying rock from outside the region – lowering both cost and carbon emissions.
  • Cultural Collaboration: Approved by local iwi (Rangitāne o Tamaki nui-ā-Rua and Kahungunu ki Tāmaki-nui-a-Rua), ensuring cultural and environmental alignment.

Result

  • Resilient Infrastructure: The road was successfully reinstated with a structure capable of withstanding frequent flooding, overtopping and extreme weather.
  • Community Confidence: The project gave the local community renewed confidence in maintaining access to their area during future weather events.
  • Environmental Harmony: The design supports ecological functions, including fish spawning in the nearby Marainanga Stream.
    Scalable Innovation: The success of this project has positioned HEX-LOC® as a leading solution for erosion-prone and high-impact river environments across New Zealand.