26 June, 2013
MEDIA RELEASE

Update on opening of Te Waihora/Lake Ellesmere

Environment Canterbury staff have reopened Te Waihora/Lake Ellesmere to the sea this morning in a second attempt after high tide and heavy seas closed the opening made yesterday.

“The connection will be monitored throughout the day and staff and machinery will remain on standby in case the conditions cause the lake to shut once again,” says Leigh Skerten, Environment Canterbury Senior Engineering Advisor. “There is still a large swell of about three metres at the opening site with a southerly front approaching; this could potentially close the connection again like it did last night.”

Approximately 80m of shingle was washed into the cut at high tide last night, blocking the connection.  This is nothing out of the ordinary and attempts at opening the lake can often take two to three days to be fully successful if the seas are calm.

Ms Skerten says the lake can close in a southerly or large swell, requiring Environment Canterbury to open it again.

“While technically we can say the lake is open once a connection is made to the sea, the cut can actually take a few days to scour out and fully develop.  It can close at any time during this stage; the sea will progressively close the channel over time in any event, it’s a natural process.”

To make the channel a cut approximately 15m wide and approximately 1.8m deep is made.  The length of the channel can vary from 100 to 300 metres, on this occasion it was 240m.

“We don’t usually declare the lake open publically until it survives two high tides,” explains Ms Skerten “It is very changeable situation that, especially in current circumstances, needs regular monitoring.”

Many things need to line up for an opening to be successful: the lake needs to have reached minimum levels in the Water Conservation Order; machinery needs to be mobilised and able to gain safe access to the site which heavy seas can restrict. 

In the first stage of the opening, machinery needs to be able to work safely within and adjacent to the lake; the final stage machinery needs to able to work safely in the surf zone.  Once the cut is opened it needs time to develop and remain open which is reliant on a relatively calm sea.  

With no further significant rainfall and if the channel from Te Waihora/Lake Ellesmere stays open, it should help ease the flooding around the margin of the lake.

ENDS

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