Protecting Southland’s lifeline from floods

Built in the late 1950s, the pump drains an area of 1556 hectares in an area formerly known as Lake Hawkins – within a boundary of Currans Road, Bay Road, Stead Street and the Waihopai River. Lake Hawkins was reclaimed in the early 20th century and used to form part of the boys’ borstal farm.

Original efforts to drain the land into the estuary with floodgates were hampered by silt and plant build-up, leading to the need for the pump station.

“The pump station is well past its use-by date,” says Environment Southland catchment manager Paddy Haynes.

“It’s that old, we can’t get parts for the pumps anymore – we have to get them manufactured.

“It is very critical, not only for Invercargill, but also for the wider Southland region. The airport is a key connection to the rest of New Zealand so we need to make sure it is protected.”

The new pump will be built alongside the old one so there’s no interruption of service during the build. It will be more cost-effective to run and maintain, with a similar capacity for pumping water.

Sitting on low-lying land, the airport has its own drainage network, which includes stop banks, ring drains and a two-pump station that drains the immediate airport land into the surrounding Lake Hawkins area.

During the February 2020 floods that affected the entire region, Southland essentially became an island. Invercargill Airport general manager Nigel Finnerty says: “During the February floods, we were almost a lifeline for Southland. Our flights were full because that was the only way people could get in or out.

“We also had the military flying in, we had several evacuating aircraft, and we were directing people to welfare centres on arrival because they didn’t have anywhere to go. For a number of hours, we were it.

“It’s good to know that we have got robust infrastructure looking after our systems. The stop banks, particularly along Stead Street, and the pump station are critical to the success of our whole drainage network.”

The pump station is just one piece of Southland’s flood protection defence. Environment Southland owns and maintains more than 450kms of stop banks across the region to protect people, property and livelihoods.

The Government’s ‘shovel ready’ funding is paying 75 percent of the costs to upgrade the pump station and other flood infrastructure. This includes raising the stop banks in Invercargill (a joint project with Invercargill City Council), upgrading the stop banks on the Mataura River, and repairing flood damage on the Waiau River. The projects are expected to create more than 100 jobs over three years.

“With the Government funding, we're able to fast track improvements to our flood defences,” Paddy says.

“We know that Southland needs to be prepared for the impacts of climate change, and soon. This is an investment that’s essential for our communities, and that’s been shown by how well the stop banks performed during the floods across the region in February.”

Invercargill City Council manager - engineering services Jeremy Rees says raising the Stead Street stop banks is going to be a big job. The plan is to drive steel piles into the current Stead Street walkway, and raise it by about one metre to align with 2070 sea level rise predictions.

Environment Southland will then raise the banks of the Waihopai River and Otepuni and Kingwell creeks to match.

“Our stop banks work hand-in-hand, so there is no point raising one and not the other,” Jeremy says.

“Raising all of the stop banks in the city means that we have a consistent and coherent flood protection network in Invercargill.”

The Stead Street stop banks will look significantly different, and the Invercargill City Council is aiming to incorporate the heritage and culture of the area into the final design.

You can read the full Envirosouth magazine as a PDF online here.