Board pushing for increased flood defence maintenance

Looking toward Outram. PHOTO: ODT FILES
Looking toward Outram. PHOTO: ODT FILES
An imminent programme of tests for an Outram floodbank built in the 19th century has been welcomed but more work will be needed to satisfy the Mosgiel-Taieri Community Board enough is being done to maintain Taieri flood defences.

The board is pushing for water courses, drains and culverts to be cleared of obstructions "at all times", and for identified areas of concern to be dealt with urgently by the Otago Regional Council.

"The Mosgiel-Taieri Community Board believes that all flood protection assets on the Taieri should be maintained to at least 100% of their original design capacity," it said in a Facebook post this week.

Testing is to start next week on the Outram floodbank to provide information about its composition and help establish where maintenance will be needed.

Core samples will be taken from the 1.5km floodbank as part of a drilling programme that could start on Monday, depending on weather.

Otago Regional Council (ORC) engineering manager Michelle Mifflin said the work would reveal information about underground geology and hydrology, the floodbank’s material makeup and history.

"This work will help inform us on the floodbank integrity and confirm maintenance and replacement programmes in the future, which could span decades ahead," she said.

Taieri flood defences have been in the spotlight in the past month after a study found a massive deluge would cause widespread failure of the network.

Community board chairman Andrew Simms said the investigation proceeding at Outram was great news.

Mr Simms said the board had received feedback from Outram residents that heavy rain tended to result in water building up on the side of the floodbank that was not beside the Taieri River, suggesting porosity in the structure.

The Outram floodbank was built in the late-1880s, using horses and carts.

A variety of construction materials could have been used, the council said.

A mobile rig would drill 100mm-diameter holes and run cone penetration tests along the floodbank for about two weeks.

Test results would be analysed over several months.

The programme had been estimated to cost about $120,000.

The community board said in its Facebook post it was gravely concerned about levels of maintenance on flood protection assets.

It highlighted a 2019 report that explored the capacity of the Silver Stream.

"The report showed that several flood events across the Gordon Rd spillway that happened between 2006 and 2019 would not have happened had the Silver Stream been maintained to its original capacity, and that the last significant flood event in 2017 would have been far less severe," the board said.

It drew attention to community drop-in sessions about Taieri flood protection to be hosted by the council on Tuesday and encouraged people to "politely let the ORC know what standard of flood protection you want for your community".