Opening the lake

An aerial view showing a lake opening. Photos supplied by Environment Canterbury.

Earlier this month you may have noticed something a little out of the ordinary at Te Waihora/Lake Ellesmere.  Machinery was working hard to create an access way for water to flow between the sea and the lake.

Leigh Griffiths, Environment Canterbury Senior Engineering Advisor says the lake was opened from 1 July till 18 July and naturally closed in a southerly swell.

“There is a large range of cultural and environmental reasons for opening the lake and in this instance it was to allow the lake to be at a lower level before potential winter rains,” says Leigh.

“July and August rains can result in a big rise in the lake, so opening it can reduce the risk of flooding.”

“This is the first time the lake has been opened since September 2015,” says Leigh.

The opening process is an important part of ensuring lake levels are managed appropriately, and it is not done without appropriate consultation.

Te Rūnanga o Ngāi Tahu and Environment Canterbury jointly hold the resource consents to open Te Waihora/Lake Ellesmere to the sea. Before the final joint decision is made by Kara Edwards (Te Rūnanga o Ngāi Tahu, General Manager Te Ao Tūroa) and Don Rule (Environment Canterbury, Director Operations), eight stakeholder groups are consulted: Te Taumutu Rūnanga, Department of Conservation, the Rating District Liaison Committee, Fish and Game, Commercial Fishermen’s Association, Selwyn District Council, Christchurch City Council and the Waihora Ellesmere Trust.

Machinery working on the opening.

Machinery working to open the lake.

According to Environment Canterbury, it is estimated that, should there be no human intervention to open the lake, the lake level would rise to a range of 2.7 to 3.6 metres above mean sea level before the beach was naturally breached.

Many things need to line up for an opening to be successful: the lake needs to have reached minimum levels required in the Water Conservation Order/Resource Consents; the sea needs to be relatively calm, and machinery needs to be mobilised and able to gain safe access to the site.

“The next time we may look to open the lake could be around September to help the Spring fish migration into the lake. An opening at that time will help species like pātiki (flounder) and tuna (eel),” says Leigh.

NIWA freshwater fish ecologist Shannan Crow has said that if the lake is closed at the wrong time it can restrict fish species from coming into the lake

“The lake opening regime is critical to fish numbers within the lake,” he says.

More information on the lake opening process can be found here and if you have any questions contact Leigh: leigh.griffiths@ecan.govt.nz