Silty stop- banks are a win-win

23:00, Jan 25 2013

The river's own silt is being used to build stop-banks on the lower reaches of the Rangitikei River.

Part of a long-term project to bring the Parewanui stop banks up to a 100-year standard of flood protection, the work comes after extensive damage from flooding near Scotts Ferry in 2004.

Horizons Regional Council northern area manager Wayne Spencer said since then, about 1 kilometre of stop bank had been upgraded every year.

"By the end of the current construction season, 9.3km will have been raised to the new standard, leaving 5km to complete. A secondary stop-bank has also been built around houses at Scotts Ferry," Mr Spencer said.

"The project has been tendered out and we supervise the contractor as work progresses. This year's work began in November and is expected to be complete in February."

He said the stop-banks at Parewanui protected cropping and dairy farms on the highly productive Rangitikei River floodplain and the protection they provided was crucial to the economic viability of those operations.


The stop-banks also protect farm houses, the Scotts Ferry village, roads and bridges.

Mr Spencer said the stop-banks were built with silt deposited on the river berms that was reducing channel capacity.

"Using the silt results in a win-win situation. We have good material close to the job so costs are kept down, while removal of the silt slows the loss of channel capacity in the river.

"An area of land alongside the river is selected for silt supply and cleared of vegetation. The material is then burrowed with a tractor and scoop and carted to the works site where it is compacted before being shaped with an excavator and grassed down."

Horizons project engineer Lew Marsh said work was also underway to construct some large rock linings to prevent river bank erosion.

"Protection works were damaged at a number of sites in the November 2010 floods and repairs have been progressing since then. The last of this work is expected to be completed by this April," he said.

Manawatu Standard