Gorge slip repair plan questioned

01:30, May 10 2012

A regional councillor has questioned whether it would have been wiser to push fallen earth from the Manawatu Gorge slips into the river below rather than spending millions of dollars clearing the debris.

During a meeting of the catchment committee in Palmerston North yesterday, engineers told councillors that falling debris from last year's slips would not adversely affect the Manawatu River.

Senior river engineer Graham Doull said the soil under the roadway would be washed away in a small flood or high river flow, but it would not damage the river as the river bed had degraded over time, allowing more room for river gravel between Ashhurst and Karere Rd, south of Longburn.

John Barrow, the Tararua representative for Horizons Regional Council, asked if it would have been smarter to push the dirt over the side to wash away rather than bench the slip, which has seen the gorge road closed for all but three days since August 18.

"Could we have bulldozed it in? Would it not have been a better idea to have pushed the slip into the river instead of carting it away?"

Horizons chief executive Michael McCartney said money had been saved as agencies used the dirt as fill and for other purposes.


But Cr Barrow said the whole exercise had cost a lot of money and if there was an option in the future for things to be done differently, it should be looked at.

"It's been a God-awful expense," he said. "We need to have a strategy for if, or when, this happens again."

Cr Barrow said he was concerned the decision to not dump the dirt in the river was made because it would have had an effect on the water quality.

"If we are concerned about a bit of dirty water, have we been held to ransom by some environmentalists?" Mr Doull said this had not been the case, but too much soil in the river at one time could have blocked the water course.

NZ Transport Agency Palmerston North state highways manager David McGonigal said the idea of pushing the soil into the river had not been discussed.

"Some has gone over the side, but in consultation with the council. We don't want to have an adverse effect on the river and, to be honest, that amount of dirt would just create a dam."

Mr McGonigal said the benching of the slip was in the last stages and the agency had finished its assessment of the damaged roadway. He expected the information about the state of the road to be released late today.

Horizons has been working for several years to keep silt out of the Manawatu River through its sustainable land use initiative that aims to prevent hillside erosion, which causes siltation of rivers. The councillors were told the silt would be washed away first and, after a while, only the large boulders would be left, creating rapids, for kayakers.

Manawatu Standard