Whakatāne River Floodbanks
At a glance
With decades-old floodbanks facing increasing risks, Bay of Plenty Regional Council needed clear and focused insights quickly. We provided a targeted risk-based assessment of the Whakatāne River floodbanks, identifying key areas to guide smart investment and strengthen future flood protection. The result is a clear plan that helps keep Whakatāne safer when it matters most.
The challenge
Many of the Whakatāne River floodbanks were built decades ago, using the best methods and materials available at the time. While they still meet design heights, their resilience during major flood or earthquake events isn’t guaranteed.
The Council needed to understand where these structures might be vulnerable – but with limited time and budget, a full-scale investigation across the entire network wasn’t realistic.
We were engaged to deliver a staged and focused response, one that would give the Council confidence in their next steps without overextending resources.
Our response
We broke the work into three key phases.
Phase one began with on-site inspections by our geotechnical specialists, who used their experience with flood protection assets to identify visible signs of distress and focus on the areas most at risk.
Phase two involved targeted geotechnical investigations in those priority zones. We conducted subsurface testing and analysed potential failure modes such as slope instability, seepage, internal erosion, liquefaction and lateral spread. From this data, we carried out a qualitative risk assessment, categorising each hazard as low, medium, or high risk to the floodbank height.
In phase three, we performed detailed quantitative analysis on the highest-risk areas. Our geotechnical and hydrogeology teams collaborated closely to model seepage and assess hazards including heave, piping and rapid drawdown. This deep dive gave us a comprehensive understanding of how the floodbanks would behave under normal and extreme conditions.
Throughout the project, we provided the Bay of Plenty Regional Council with clear, evidence-based insights, highlighting which sections were performing well and which required remediation. We also incorporated breach modelling to help prioritise investment decisions based on both risk and potential consequences.
Our response delivered practical outcomes for this project and built on our broader experience with flood protection assets, contributing to robust methodologies that can be applied across the region.
The impact