Drying lagoon sparks debate on cause
Another case of a drying Manawatu lagoon has been linked to the Wellington Anniversary Day earthquake, though there is doubt about the cause.
Valhalla Seeds owner and former All Black John Callesen said yesterday the water in the Karere Lagoon - most of which is on his Longburn property - dropped soon after the January 20 earthquake to a low he did not think had been seen since his family acquired the property in 1870.
This followed recent suspicions that the earthquake was behind the Ashhurst Wetlands draining and falling water levels in the Hokowhitu Lagoon in Palmerston North.
Mr Callesen said he had been in Christchurch when the January earthquake, centred near Eketahuna, happened. "I came home and I thought, ‘Geez, you guys have had some dry weather.' I was away for 10 days."
It appeared that the water level, which had never fully recovered from last year's drought, had settled now and evaporation was in play, but two months ago the lagoon lost 150 millimetres in just two days, he said.
"I hadn't thought it was the earthquake until a friend mentioned it, and I thought ‘crikey'."
He read a news report saying it was believed the clay basin supporting the Ashhurst Wetlands had cracked, allowing the water to drain away, and he realised there might be a connection.
Mr Callesen said there were layers of gravel underground, similar to the Hokowhitu Lagoon.
Palmerston North City Council leisure assets officer Brian Way said last week it was suspected the Hokowhitu Lagoon was draining because the earthquake had loosened the silt, sand and clay particles sealing the top of the gravel beneath it, creating channels for the water to flow out.
Mr Callesen said he would inform Horizons Regional Council.
However, Horizons says the earthquake may not be to blame for falling water levels in the region.
"Lake and lagoon levels could be dropping at this time of year due to little rain," science manager Jon Roygard said.
"We know the Ashhurst Domain wetland has drained away due to the earthquake and we have also received a report about the Hokowhitu Lagoon levels dropping."
Dr Roygard said in the case of the Hokowhitu Lagoon, it was a geotechnical problem and the council had referred Palmerston North City Council to a geotechnical engineer to determine what could be done at the lagoon.