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Lake level management

Te Waihora aerial view

Te Whakatūwhera i te Hāpua/Opening the lake

Te Waihora/Lake Ellesmere has no natural outlet to the sea. This means that the lake must be opened artificially to manage lake levels and keep the lake connected to the sea for migratory fish, enabling mahinga kai and maintaining wildlife and wetland vegetation.

To find out more and learn about the many factors that are taken into account before opening Te Waihora to the sea, visit the Environment Canterbury website.

Horse cart Te Waihora
The first openings where by horse carts and scoops. North Canterbury Catchment Board Methods of Opening Lake Ellesmere 1868

The lake was opened by generations of Ngāi Tahu before Pākehā arrival

Openings would be created once the lake reached around 2.5 – 3 m above sea level, to protect the settlements around Te Waihora and support the abundant fisheries. These openings were constructed at the western end of Te Korua, the lagoon near Hone Wetere Church. The openings were created by a team of people digging a small pilot channel through the shingle barrier.

Once water began to flow, the channel would quickly scour out to form a much larger channel. It is likely these openings were created once every two to three years. 

Wooden Culvert Te Weihora
Bottomless timber culvert. North Canterbury Catchment Board Methods of Opening Lake Ellesmere 1868

This continued until the 1860s when European settlers began opening the lake much more frequently. This was done to lower the lake level to help drain the surrounding land to allow farming. The first written settler's record of an artificial opening between the lake and sea was in 1852. Since then, it has been opened more than 300 times. Selwyn County Council first let tenders in 1877 to artificially open the lake using horse-drawn scoops.

There have been two attempts to create permanent culverted structures to manage and control the opening of Te Waihora to the sea. The first, in 1904, was known as Dobson’s culvert. Unfortunately, the structure failed after a storm in 1908.

The second, constructed in 1908, was Pannett’s culvert. This structure operated with mixed success until it was seriously damaged by storms and destroyed in 1925.

Today there is a legal process to go through before the lake can be opened to the sea.

The image supplied on the left is an example of a bottomless timber culvert structure. The images below are examples of tractors being used to deepen the channel, and make the final cut through. 

Bulldozer Te Weihora
Bulldozer deepening the channel. North Canterbury Catchment Board Methods of Opening Lake Ellesmere 1868

Bulldozer working on seaward end of cut

Bulldozer working on seaward end of cut. North Canterbury Catchment Board Methods of Opening Lake Ellesmere 1868

Te Whakakāti i te Hāpua/Closing the lake

The Water Conservation Order allows for the lake to be artificially closed when it reaches 0.6 metres above sea level between 1 October and 31 March. This could be considered beneficial in summer if lake levels were very low and sea conditions were too calm to create natural closure. However, in practice, the level of Te Waihora has to be managed relative to mean sea level.

Sea level rise as a result of climate change is making it more difficult to achieve a successful opening at lower lake levels and no attempt has been made to close the lake artificially.