Buller Infrastructure Acceleration Fund

The Brief

The $1 billion Infrastructure Acceleration Fund (IAF) invests in infrastructure that supports new housing developments in areas that face the biggest housing supply and affordability issues throughout New Zealand. 

We were initially engaged by Buller District Council to provide conceptual engineering design, design report, schedule of quantities and engineers' estimate to achieve IAF funding approval for a proposed growth area on the west side of the Buller River. 

What We Did

A team from Westport, Greymouth, Christchurch and Nelson successfully delivered the works under a strict time frame of just eight weeks. 

We assessed existing and future demand for three waters services, lighting, roading and utilities servicing. We coordinated specialist lighting, power and transportation engineering sub-consultants. 

Subsequently, after the IAF funding was approved, we provided the detailed design for four separate IAF work streams – the Westport Wastewater Treatment Plant Inlet Works Upgrade (WWTP); Alma Road water main extension, wastewater servicing and transportation and stormwater design, which included two intersection upgrades, a new 2-lane bridge at Lagoon Creek and a proposed shared pathway and crossings over State Highway 67. 

Challenges

Complex challenges due to the topography and elevation of the site were met through innovative solutions. 

• A low-pressure sewer (LPS) to support connections to properties below road level. LPS mitigates the risk of the WWTP overloading during stormwater events as it provides onsite storage during wet weather. 

• Dual sewer rising mains of different internal diameters that can be configured for demand to reduce hydraulic resident time (HRT) and ensure scour velocities when pipes are not at capacity. 

• As most of the rising main is downhill to the WWTP, a Pressure Sustaining Valve (PSV) at the LPS main keeps the PE main full and prevents odour expulsion and excessive air release and ensures low HRT and scour velocities. 

• A piped bypass and valve arrangement about the inlet screen and grit chamber provides easier maintenance of the PSV. 

To ensure the Lagoon Creek bridge design was to the correct freeboard above Lagoon Creek in a 1-in-100-year flood, we completed a hydraulic stormwater model for the large contributing catchment of Gillow Dam. This was also used to inform flood hazard identification for the Westport Master Plan.