The cost of upgrading the McAlister pump station in Whakatāne has increased by $275,000, largely as a result of a change in the construction method required to install a 3-metre x 1-metre box culvert gravity-bypass through the Whakatāne River stopbank.
Whakatāne District Council Infrastructure General Manager Tomasz Krawczyk says the pump station upgrading is the major component of a key project which aims to reduce the frequency and impact of surface flooding on properties and roads in the Apanui catchment.
“Our original budget for replacing the station’s three pumps with high-efficiency semi-submersible pumps, together with structural modifications to the station and intake, and installation of the gravity bypass culvert, was just under $3 million,” he says. “However, following a peer review of the proposed construction method for the box culvert, the resource consent for the project required a change in that methodology.”
Mr Krawczyk says the original proposal – to construct a sheet-pile wall to protect the embankment while the entire culvert was installed – was amended, and the work is now being undertaken in three phases, with full reinstatement of each section of stopbank completed before moving on to the next phase.
“That’s a much more complex process, which has extended the construction time and increased the cost for that part of the job by about $430,000. To offset part of that cost escalation, the project team has identified savings we can achieve by using alternative materials and methods, without affecting the project outcome. The net result though is still a potential nine percent budget overspend.”
The additional spending was approved by the Council in September and will be financed by loan funding.
Work on the installation of the gravity bypass culvert on the eastern side of the station is progressing well and is expected to be completed by December 2016, about six weeks later than had originally been planned. Work on the remaining project components is expected to be finished by April 2017.
The upgrading will significantly improve the drainage of the Apanui catchment (which encompasses the area between the river in the north and Landing/Domain Road in the south), both through increased gravity feed capability and a 60 percent increase in pumping capacity. The upgraded pump station will be capable of pumping up to 6000 litres of water per second (360,000 litres per minute, or close to 22 million litres per hour) from the stormwater channel into the Whakatāne River.