Eels given safe path to sea thanks to new pump
Innovative flood pump commissioned
An innovative fish-friendly flood pump commissioned by the Waikato Regional Council that aims to give eels a safe path to the sea for spawning has had a successful trial at the Huntly golf course pump station.
The prototype pump, developed to replace existing Macewans PPF axial pumps, successfully passed a 1.2 metre shortfin eel.
The new pump kicked into action at the end of January with the arrival of heavy rain, and seven eels, also known as tuna, passed through into a net attached to its outlet as part of the council’s monitoring programme to determine the pump’s success.
The council and funding partners put up $280,000 towards the research and development of the pump, including $120,000 from Waikato-tainui.
Pathways to the Sea programme manager Michelle White said the largest tuna was 1.2m long and weighed 4.2kg, while the other six ranged in size from 664mm to 878mm. The eels were released in the lower catchment and are now free to safely make their way out to sea to breed.
“This is an awesome first result,” said White.
“The big eel was a resident shortfin eel that had been living in the catchment for decades. This eel is a developing migrant and was in perfect condition after going through the pump.”
The council, which owns and operates more than 120 pump stations, many of them with Macewans pumps, started its journey to ensure safe fish passage in 2015 with an investigation that showed there could be significant mortality of tuna over 600mm long as they travel through existing flood pumps during migration to the sea.
In response to this finding, the council set up its Pathways to the Sea, a research and strategy development programme to help manage flood pump impediments to fish passage and the development of a regional fish passage strategy.
Macewans Pumping Systems general manager Tom Bailey says the challenge to build a fish-friendly
pump opened his eyes to the life cycle of New Zealand short- and longfinned eels, which breed only once, at the end of their life, and at sea.
“We’d been approached by councils to build fish-friendly pumps for a couple of years but to have Waikato Regional Council willing to be involved, and have funding for the project, that made the decision a much easier one,” said Bailey.
“I was so pleased with that big eel coming through! This has been a fiveyear endeavour with many challenges along the way, like Covid19 and labour shortages, so to have this result the first time the pump operated is such a relief.”
Bailey added the fish-friendly prototype has been designed to retrofit pumps with 24-inch (61cm) impellers that Macewans installed widely across New Zealand between the 1960s and 1980s.
“If this pump proves to be a success over the entire migration season, we’ll also look at changing out larger 30-inch [76cm] impellers.”
Features of the new pump include a slower rotation, having only two blades instead of four, and ensuring more space between the impeller (rotating blades) and stator (outer cavity).
The development of the pump, with design assistance by Callaghan
Innovation, included the creation of a scalesized pump and testing using 3D-printed rubber eels – scaled equivalents of 800mm eels, 1.2m eels and 1.5m eels.
High-speed videography shows even the 1500mm eels made it through in one piece.
The council’s integrated catchment management director, Greg Ryan, says the development of the pump is exciting and “innovation in action”.
“There has been a huge amount of research that has got us to this point and early indications are that this pump is working as we expected it to,” said Ryan.
“Our flood control schemes were built many, many years ago to safeguard lives and properties and enable productive use of the land. They knew what they knew back then when they put in this infrastructure, and not what we know now.
“The impact of these old pumps on these taonga species is something we want addressed.”
The council installed the country’s first fish-friendly pump at Orchard Road, Te Kauwhata, in 2017, and another at its Mangawhero pump station in 2021. Two fish-friendly pumps are due to be put in at the council’s Churchill East pump station, Hampton Downs, at the end of February.
“We’re replacing our pumps as they come to their end of life with fish-friendly ones, but no one was building them in New Zealand, so we’ve been having to look overseas,” Ryan said.
The council is monitoring the effectiveness of the pump until May, when the tuna migration season ends.