With the increase in extreme weather events across New Zealand, Tararua District Council (TDC) wanted to make sure their towns are safe and sustainable for the future by building reliable 3 waters infrastructure that can withstand these weather events.  

The Challenge 

The four largest towns in the Tararua district are experiencing unexpected rapid growth in recent years, ahead of forecast growth, which is putting pressure on areas of the existing infrastructure that are already capacity constrained.  

Given this rapid population growth combined with ageing infrastructure and more intense and frequent weather events, TDC needed to understand the performance of the existing 3 waters systems and identify future infrastructure upgrades to resolve existing capacity and flooding issues and cater for future growth. 

Wood’s Involvement 

Woods was involved in the masterplanning of 3 water infrastructure (stormwater, wastewater and water supply) in the townships within the Tararua district. Woods teamed up with WSP on this project, supporting the master planning for climate-resilient communities and proposing servicing to TDC around the current infrastructure.  

InfoWorks ICM was used to undertake a model build of the wastewater and stormwater systems. Through the model build and calibration process, Woods confirmed areas where wastewater and stormwater infrastructure networks operate as a combined system, with stormwater and groundwater entering the ageing wastewater infrastructure (inflow and infiltration) and contributing to the wastewater system being overloaded during extreme weather events.  

An inflow and infiltration issue can add strain to the integrity of water infrastructure and can cause even bigger problems in the event of a flood.  

After understanding the current condition of the infrastructure system, Woods carried out a Multi-Criteria Analysis (MCA) to identify the preferred upgrade options for resolving identified issues and catering for future growth. The analysis was conducted with the input of all stakeholders, considering environmental, economic, cultural and social criteria to determine the best upgrades to the stormwater and wastewater networks.  

Outcome 

Through a collaborative master planning process, Woods helped provide TDC with the knowledge necessary to understand the nature of the challenges associated with the current 3 waters infrastructure. Woods came up with a list of solutions to address the risks associated with anticipated population increases and unpredictable weather cycles.  

The goal is for the rapidly growing towns within the Tararua District to develop climate-resilient and sustainable infrastructure. Woods’ involvement in the master planning helped get Tararua District Council closer to that goal.