Source: Environment Canterbury Regional Council
We have started the process of opening Te Waihora/Lake Ellesmere to the sea. Machinery is onsite and a sea connection will be made as soon as sea conditions allow in coming days.
Te Waihora/Lake Ellesmere is the largest lake in Canterbury and has no natural outlet to the sea. The lake is normally opened two to three times a year and closes naturally,
Openings are jointly managed by Ngāi Tahu and us and governed by the National Water Conservation Order and a suite of resource consents.
Opening Te Waihora/Lake Ellesmere
Consultation for a lake opening started on Monday 28 April and was completed by the afternoon of Tuesday 29 April, with a joint decision to open the lake when conditions were suitable. The same afternoon the lake height reached 1.13m, a level that permits opening, but it was not physically possible to carry out due to sea conditions.
The success of a lake opening depends heavily on favourable weather conditions. Wind strength, wind direction, sea swell, wave directions and the tides are all factors that can affect openings.
In difficult weather and adverse sea conditions, multiple attempts may be necessary, and a successful opening may take weeks or even months to achieve. An opening is considered “successful” when it persists for at least four days (the amount of time required on average to lower the lake level below the opening threshold).
Conditions now suitable for lake opening
With sea conditions slowly improving, we have started the process of opening the lake to the sea.
“While we’ve started the process of opening, current conditions including large sea swells mean the cut could still fill in. Opening the lake is a complex process of balancing values, safety and timing with the weather conditions,” said Leigh Griffiths, General Manager Hazards.
Attempting to open the lake at lower lake levels is also difficult as appropriate flow to the sea is required – any lower lake level opening before this event would have likely failed due to large sea swells.
“It’s not uncommon for the lake level to be high, and it isn’t always something we can prevent. Due to sea level rise and a changing climate, we will need to consider different solutions to increase flood resilience for the local communities.”
We are working collaboratively with Civil Defence, District Councils and other agencies and updating our flood warning webpage with the latest information.
For more information visit: Opening Te Waihora/ Lake Ellesmere
