Lake Ellesmere. Photo: CC Wikicommons
Banks Peninsula remains under a state of emergency days after heavy rain caused flooding in Canterbury.
And Environment Canterbury (ECan) officials are continuing to defend decisions made around when to empty a lake into the sea, which some say could have prevented flooding if done earlier.
On Sunday, Christchurch Mayor Phil Mauger said there was land instability and closed roads in Banks Peninsula which need to be monitored.
Banks Peninsula MP Vanessa Weenink was out in the community over the weekend, and said there remained "a whole lot of clean-up" to do and risks of landslides.
"In Akaroa, up on Lighthouse Road, there's a huge crack through the road - but that crack extends across the hillside. and that site was apparently… the site of a historical slip with similar issues back in the '90s," the National Party MP told RNZ's Morning Report.
"So this is something that was dealt with at that time, and geotechnical work was done in the '90s to mitigate it. But the volume of rain that's been through last week was pretty huge, nearly 300mm in Akaroa over three days, so that's the kind of volume that will stick into that soil and hold there."
Luckily the road saw little traffic, and locals had been evacuated from their homes.
"I think from that perspective it's not having a big impact on people, apart from those of course who have been evacuated and a business that's had to shut its doors, which is quite devastating."
Some residents were upset Lake Ellesmere and Lake Forsyth were not drained into the ocean in time to mitigate flooding risks.
Flooding at Banks Peninsula following heavy rains in the Canterbury region. Photo: Christchurch City Council
"Farmers around the shores of Lake Ellesmere and Lake Forsyth are pretty upset about the impact, because they had asked that the lake be drained earlier and for whatever reasons, probably quite technical and access reasons that hadn't been done," Weenink said.
"People are feeling as though they weren't listened to, and that's I think the frustrating part of it. Farmers around there are used to dealing with water on their land, living in the kinds of places that they do… I feel like that has made them more upset about the impact than they might have otherwise been.
"It's one thing to deal with water on your paddocks and the impact that has because it's not just about the water - it's about the fences, it's about the fact that stock has had to be moved and now they can't use some of those paddocks…
'Strict conditions'
ECan science director Tim Davie said there were "strict conditions set by the national water conservation order on when the lake can be opened".
"Those weren't reached until Tuesday of last week, and the storm came on Wednesday - so we were ready to go, but we weren't able to open it."
Tim Davie. Photo: supplied
The council used diggers to create a channel between the lake and sea at certain times, governed by a 1990 water conservation order and resource consents held jointly with Te Rūnanga o Ngāi Tahu.
ECan general manager of hazards Leigh Griffiths last week said consultation for a lake opening began on Monday 28 April, and by the following afternoon a joint decision had been made to open the lake once it reached the prescribed target height of 1.15m.
Once the lake reached that height however, it was too late - the storm making it too dangerous to open the lake, which takes three to seven days, possibly longer in rough sea conditions.
Davie said if there was an "absolute emergency" they could override the order, but the forecast for the local region ahead of the storm was not dire.
"There was an orange rain forecast. It wasn't particularly forecast for this area - it was actually North Canterbury, that was more of the issue.
"But even if we had been able to open it… it wouldn't have stayed open and we would have had the same issue" because of the rough seas.
"This lake doesn't open naturally to the sea. It has to be opened. If it was left naturally, it would go up at least another two metres before it opened.
"It's something that we're constantly working at, and we're trying to manage it for all the different values of the lake. Flooding is one of them, but there are numerous other values as well.
"We're constantly looking to improve and, and we'll, we'll look into this."
According to ECan's website, "Once the lake is opened, there is limited ability to control how long it stays that way. The length is determined by weather and sea conditions, and how quickly gravel is deposited by the sea to close the cut."
Davie said real-time updates on the lake levels were available on the ECan website.
"We've tried twice since the floods to open and it's closed every time. So on Saturday and Sunday, we had it open and then it closed again. This is a really difficult environment to open the lake."
Emergency Management Minister Mark Mitchell said he was confident officials had made the right call, but was prepared to hear more about the community's concerns over the the lake's management.
As of Monday 5 May, the lake height was 1.62m and closed to the sea.
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