$400,000-plus Awanui flood protection work looms

11 Jan 2016, 11:00 AM

More than $400,000 worth of protection work designed to better protect Kaitaia and the wider Awanui catchment from the effects of flooding is due to get under way next month.

The Northland Regional Council recently let two contracts; the first for roughly $150,000 to modify the existing Whangatane Spillway weir and the second for approximately $250,000 to build a stock crossing bridge about 2.5km downstream from the weir.

Councillor Joe Carr, who chairs the regional council's Awanui River Liaison Committee, says Far North Roading Ltd expects to begin an eight-week contract to modify the weir early next month.

"This work will see the existing weir modified to a split level, which will allow floodwaters to enter the spillway from the Awanui River much earlier during a flood."

Councillor Carr says part of the weir intake will be raised to 12 metres, with another part lowered to 9.5m which means during a large flood, water will enter the lower section when the Awanui River flow is 20 cubic metres per second. (At the moment, water only enters the current intake when the river's flow is more than 42 cu m per second.

"That change will reduce the flood risk to urban Kaitaia by lowering peak flood level at the spillway intake and upstream along the Awanui River through Kaitaia," he says.

"It should reduce the 'backwater effect' at bridges across the Awanui River through Kaitaia itself, as well as help floodwaters drain more quickly from Lake Tangonge."

Councillor Carr says floodgates on the Awanui River downstream of Kaitaia will be able to be open for longer before floods peak, as more water will flow down the spillway during the flood's early stages.

"It will also allow floodgates along the lower Awanui River to open sooner once the flood peak has passed."

Meanwhile, the second tender will see a 54-metre long, three span stock bridge built by Steve Bowling Contracting Ltd over about eight weeks from mid-February.

"The bridge is being built so an existing dairy farm operation spanning the Whangatane Spillway will not be adversely affected by the increased frequency of flow that will occur in it once the weir is modified."

Councillor Carr says the Whangatane weir and spillway are located on the north-east bank of the Awanui River, about 260 metres upstream of State Highway One's Waikuruki bridge. It flows for about 14km and discharges directly to the Pairatahi Stream, then into Rangaunu Harbour.

"The initial part of the spillway runs on the eastern side of an industrial area protected by a stopbank; it then flows through a number of farms."

Water that does not flow over the intake weir travels along the lower Awanui River for about 24km, before discharging to the harbour at Unahi.

Councillor Carr says the upcoming works are the latest in a series of scheme improvements the regional council and river liaison committee have approved on behalf of the local community in recent years.

"In addition to the latest weir and bridge works, we've also allocated another $350,000 in the current financial year for maintenance and other improvements to the existing scheme, including ongoing monitoring and works associated with stabilising the Bell's Hill slip."