Stead Street pump station replacement
Environment Southland is replacing the Stead Street pump station with a new facility housing two new fish-friendly pumps. The pump station is part of a comprehensive flood protection scheme that helps to protect Murihiku Southland’s largest urban centre, Waihōpai Invercargill (population 57,000 +) and nationally critical infrastructure (Invercargill airport) from inundation. Stead Street also provides an important road between Invercargill and Otatara.
While much of the city is low-lying, Invercargill Airport is close to sea level. Because of this, the airport is surrounded by a comprehensive drainage network, including stop banks, ring drains and pumps. Several of these assets are owned and maintained by Invercargill City Council, and some are managed by Environment Southland.
In 1984 the airport was extensively flooded to depths up to 3m through the terminal buildings. The primary sources of that floodwater – the Waihōpai River, Waikiwi Stream and Oreti River – underwent significant flood protection upgrades following the 1984 flood.
Drawing of what the new pump station will look like.
In March 2016, a phenomenon known as storm surge caused the sea to spill onto Stead Street, resulting in road closures and surface flooding of the land surrounding the airport. Storm surge occurs when sea levels rise during intense weather events. Climate change-induced sea level rise will increase the frequency and severity of these events.
The need to replace the Stead Street pump station is also driven by the age of the existing infrastructure, which was installed in the early 1960s. The new pump station is being built beside the existing structure and will house two new fish-friendly pumps manufactured by a supplier in the Netherlands. It aims to protect the area from inundation for the next 50 years. This pump station is critical to the 116 properties in the immediate area and is a lifeline for the airport, supporting 320,000 passengers plus freight each year.
Unlike the original pumps, the new pumps allow for the safe passage of native fish, including large tuna or freshwater eels. Their design is based on Archimedes' screw pump technology, where fish are transported up through the pump without getting harmed. They are very light, so don't require a lot of power to operate, and are simple, requiring much less maintenance.
The work
The new pump house is being constructed alongside the existing pump station, which will remain operational until the new pumps have been fully commissioned. The outlet pipes run under the road to a pair of electronically controlled flap gates which can be closed during extreme tide or storm events.
There will be some disruptions to the movement of traffic, cyclists and pedestrians while the work is underway.
From 11 April through to August 2023, traffic will be restricted to one lane, operating under traffic lights from either side of the new pump station site to manage vehicle traffic while the outlet pipes are laid across the road. A temporary speed limit of 30kph will be in place for approximately 300m between the traffic lights while this work takes place.
From June to August 2023, the shared pathway will be closed opposite the pump station to allow for the construction of a viewing platform over the flap gates. At this time, cyclist and pedestrian traffic will be diverted to the northern verge of Stead Street.
Funding
In 2020, Environment Southland secured $2.25 million of funding from central government as a contribution to assist in replacing the ageing Stead Street pump station, one of the council’s six climate resilience projects co-funded in the region.
The new Stead Street pump station is a Resilient River Communities project. Resilient River Communities is a joint initiative between Kānoa - the Regional Economic Development & Investment Unit, regional councils, and local authorities focused on developing and upgrading vital river management and flood protection schemes in Aotearoa New Zealand.
The initial bid for government funding in 2020 was based on replacement axial flow pumps and a modest pump house at an estimated cost of $3.5 million. The original pump station design was unsuitable for these new-generation pumps.
Design works for the upgraded pump station mean that the contract price for the pump station is $8.3 million. This brings the projected total construction cost, including design and provision of fish-friendly Archimedes screw pumps, to $11 million.
Council will borrow the required funds to ensure works can begin immediately, with initial plans to repay debt over a minimum of 25 years. Council is investigating options for increased third-party funding to ensure ratepayer contribution is minimised.
Benefits
- Increased protection for our homes, communities, and critical infrastructure
- Project delivered with central government funding
- Greatly enhanced fish passage
Project update (17 March 2023)
- Design for a new station to house the pumps completed and works contracted September 2022
- New pumps designed, built and delivered to Invercargill September 2022
- Whakawātea/cultural blessing to mark the beginning of the construction of the new pump station
- Fulton Hogan on site from October 2022
- Drain realignment and fish salvage operation undertaken in November 2022
- Pump station foundations: first pour completed February 2022; sheet piling cofferdam and foundation slab completed March 2022
- Supervisory Control and Data Acquisition (SCADA) design and coordination underway
- Concept plans for cultural narrative artwork underway
Next steps
- Construction of new pump house walls
- Concept plans for cultural narrative artwork to be presented to Council in April 2023
- Laying of outlet pipes from April 11 to August 2023
- Construction of viewing platform above the flap gates and overlooking the estuary from June to August 2023
