Potential drainage trial concern

UNCERTAINTY: A potential trial at Sumner's Burgess St drain outlet to prevent flooding may not be able to fix flooding issues of drains within the Southshore estuary.

A potential flood prevention measure may not be a silver bullet for solving drainage issues at the Southshore estuary.

The city council will trial a groyne in Sumner to prevent problems there. If that works it will then be trialled in Ebbtide St, Southshore.

But doubt has been cast over whether the trial to place a temporary groyne at the drain in Burgess St, Sumner, will work at the estuary.

Coastal Ward city councillor David East, said the Sumner waves and the estuary at Southshore are “totally different conditions.”

“In the meantime, we have just got to carry on with a bit of experimentation with some options and get the problem sorted once and for all,” he said.

It comes after the Coastal-Burwood Community Board raised concern over inefficient stormwater drains in Southshore filling up when it rains heavily and the water being unable to flow out to the estuary.

Board deputy chairman Tim Sintes said he also has doubts the trial will work at Ebbtide St, but leaving it as it is was “not an option.”

City council land drainage manager Keith Davison said while staff are looking at the trial on Burgess St, there are no firm plans at this stage.

The temporary groyne would aim to artificially lower sand levels on one side which, if placed next to an outlet, may help clear it.

But a city council report said there would need to be natural tidal waves to move the sand laterally.

It said while natural tidal effects are expected at Sumner, there is no certainty it will work at drain outlets in the estuary such as Ebbtide St.

The board recently inquired with city council staff about the status of Ebbtide St drain after concerns it was not working properly when it rained.

Mr Davison said during a heavy rain event when the tide is high, the drain will be below the tide level which means it occasionally has to send a temporary pump out.

He said when there is a rainstorm the city council will ensure the drain is clear of sand and isn’t blocked.

“At this stage we will continue this method and monitor the effectiveness of it,” he said.

Placing a temporary groyne at Ebbtide St will be dependent on how successful the trial is at Sumner and if the estuary conditions are suitable, Mr Davison said.