Should lakes have been opened before farms flooded?

Tuesday, 6 May 2025

Farmer says opening Lake Forsyth ahead of the forecast storm could have prevented flooding.

Coastal lakes in Canterbury could have been opened days before surrounding farmland and the township of Little River was flooded during last week’s deluge.

But a Federated Farmers’ spokesman said only one lake opening would have made a difference to the floodwaters that saw Selwyn and Christchurch City enter states of emergency last week.

Te Waihora Lake Ellesmere and Te Roto o Wairewa Lake Forsyth’s lake levels were high enough to open days before they were approved by local councils.

By the time they were given the green light it was too late, and the subsequent flooding has left some farmers frustrated their land will be unusable for months.

Farmers across the region say they warned Environment Canterbury (ECan) to open Te Waihora and Christchurch City Council to open Te Roto o Wairewa Lake Forsyth days in advance of the incoming rain, to no avail.

Kinloch farmer Tom Power walks through a mess of debris left by the floodwaters.

Tom Power’s Kinloch farm is on the edge of Lake Forsyth. He said he won’t be able to use his land for months due to the flooding.

“The basic frustration is the lack of sort of foresight.

Farmer Tom Power says council refusing to open Lake Forsyth to drain ahead of heavy rain helped cause his farm to flood.

“The [council] told us that they were going to wait for the next storm to go through, and here we are now, after 300mm of rain, cleaning up the mess.”

Lake Forsyth’s consent says the lake can be opened to the ocean once levels reach 2.7m above sea level or if an extreme weather event is forecast.

Aerial footage from Tai Tapu shows floodwaters covering farmland following heavy rain in Canterbury. Paddocks are submerged and nearby waterways remain swollen, with cleanup expected to take days.

Lake levels reached that level at 7.45pm on Wednesday. The council gave the order to open it on Friday.

According to section 330 of the Resource Management Act, the local authority, can open the lake without consultation if there is “sudden event” likely to cause “serious damage to property”.

Power said the Christchurch City Council’s statement that flooding at Little River was not solely due to the high lake level was “rubbish”.

“If you're a local, you know for a fact that it's got everything to do with it,” Power said.

“They keep telling us that it's problems higher up in the catchment, but they can't tell us what these problems are and we can't get any answers from them.”

In an emailed statement, the Christchurch City Council said conditions prevented the opening of Lake Forsyth during the storm and on the days preceding it. “The southerly and swell would have pushed water back up the canal opening and may have closed the opening.”

Even if the lake had been opened, the council said, it may have had only a temporary improvement on drainage for Little River. “Given the existing stormwater network through the township and volume of rain it is likely it still would have seen flooding“.

Flooded farmland near Ataahua, near Te Waihora Lake Ellesmere, on Monday.

The council said it would review its response and the factors that contributed to flooding in the Little River community.

Mayor Phil Mauger told RNZ he wanted to explore mechanical options for opening Lake Forsyth, which currently had to be manually opened by excavators.

Te Waihora-Lake Ellesmere

Federated Farmers North Canterbury president Karl Dean agreed Lake Forsyth could have been opened to prevent flooding, but it would not have made a difference at the nearby Lake Ellesmere Te Waihora.

Dean, who has 400 dairy cows, 400 ewes and about 200 lambs at his farm on the edge of Te Waihora Lake Ellesmere, said his farm was 40% underwater due to the rain. Since the rain subsided it was 10% underwater due to the lake.

Environment Canterbury deputy chair Deon Swiggs posted pictures online of the opening of Te Waihora Lake Ellesmere.

“The lake is not actually the impacting issue, it’s purely the fact that we had an unprecedented, once in 1000-year rainfall event. Most farmers have never seen 160mm [of rain] in 36 hours.”

Opening Te Waihora was costly, Dean said, and it would have closed over again, even if ECan had done it earlier.

It costs between $20,000 and $150,000 to open the lake each time, a spokesperson for ECan said.

ECan’s deputy chair Deon Swiggs said crews had successfully opened the lake on Monday after two false starts at the weekend.

Crews were unable to do it earlier due to rough seas, .

Mayor Phil Mauger: ‘We should listen to locals’

Christchurch Mayor Phil Mauger acknowledged to RNZ that not opening Lake Forsyth earlier had “caused grief”.

“You're right, over there is totally different and they'll go, 'That silly bugger, he doesn't know what he's talking about',” Mauger told the broadcaster.

'ECan and Selwyn have got a good system for opening Lake Ellesmere. It is a lot bigger, of course, it holds a lot more water.

'Lake Forsyth, we don't seem to have the same joined-up approach and I feel we should listen more to locals. It hadn't reached the level that we're allowed to open it.'

Mauger told RNZ he understood how frustrating that situation was for residents.

'We've got to look at a better system to make sure that stuff doesn't happen again,' he said.

'They say, 'Open the lake, open the lake' and we're going, 'Oh, we aren't up to the level of the consent'. That'd grind anyone's boat, so we've got to work better to just go, 'Right, let's move quicker on those things'.'

The council would investigate options to ensure the process ran smoother in future and Mauger was keen to explore the possibility of a mechanical solution, as the lake currently had to be opened manually by excavators.