Dropping water levels in Palmerston North's Hokowhitu Lagoon have sparked concerns the water may be draining through channels opened up by the Wellington Anniversary Day earthquake.
The levels, at their lowest since a bore was installed in 2009, have also put into jeopardy a national canoe polo competition scheduled for next month.
The Palmerston North City Council's began to suspect the January 20 earthquake was to blame after the Ashhurst Wetlands drained early this month.
Council leisure assets officer Brian Way said yesterday that whereas the wetlands took just two weeks to drain, the lagoon, which he estimated was more than 50 centimetres lower than normal, would take longer because the bore was still operating.
"There's water running into it at 20 litres per second, 24 hours a day, so it's not like there's not water going in there," he said. "But since that bore's been running the level has never gone down before.
"We think, and hydrologists have supported the theory, that something's shaken up underneath there in the earthquake and just opened up channels for water to drain away."
He said hydrologists had told him there was a "huge layer of gravels" under the area.
"So there's quite a permeable layer not far below the surface. The suspicion is the earthquake has shaken that up, loosened all the fine silt, sand and clay particles that are sealing off the top of the gravels and just letting the water flow away."
Mr Way said the council would work with hydrologists to assess the situation.
"We'll turn the bore off and we'll monitor over a few days and see what the actual rate of discharge is without any water going in."
However, if it was draining, he did not think there was anything anyone could do.
"This is nature."
It was hoped that rain would bring dirty water off the road, with new fine material that might seal it.
"We can only watch with interest over the winter and see what happens."
The low levels are already affecting canoe polo training.
Paddle Blacks captain James Mitchell, who is also the national competition chairman, said yesterday the walkway side of the lagoon was too shallow to use.
"We can't actually paddle on that side of the courts, which is affecting training for national league," he said.
"And the big concern we do have is that we are hosting the A-grade national league in the middle of April and so there's concern that the water level won't come up again. We won't be having enough rain to bring up the water level before then, in which case we'll have some big problems.
"The reason we moved here is because we can play on two courts at the same time. There's not a lot of other facilities around the country. The only option historically has been to use pools and run tournaments from 6am to 10pm."
The pool that would normally be used was in Wellington and it was too late to book it for a weekend.
Mitchell hoped it would rain so water levels would rise.
"It's one of three rounds. Best guess is that we perhaps just cancel the round and hopefully people travelling from Australia and out of town will have travel insurance."
- Manawatu Standard
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