River dredging to be fast-tracked

A four-kilometre stretch of Christchurch’s Heathcote River will be dredged for the first time in more than 30 years to reduce flooding.

Christchurch City Council decided yesterday to fast-track a $16.5 million dredging programme that would remove about 60,000 cubic metres of material from the river by 2020. That was enough mud and silt to fill 24 Olympicsized swimming pools.

The fast-tracking was in response to residents in the floodprone area calling on the council to remove the silt that had built up over more than 30 years.

The first of three stages could begin as soon as May and would involve removing about 20,000cu m from a section of the river from Woolston’s Radley St to the end of Radley Park (Woolston Cut), at a cost of $3m.

The second stage, from Radley St to Opawa Rd, would be completed in 2018/19, instead of 2020. Stage three from Opawa Rd to Opawa’s Hansen Park, would start in 2019 and finish in 2020 instead of 2021.

However, the fast-tracking of the second and third stages was still subject to consenting and would mean other capital projects

"We'll be looking at what will have the least negative benefits, but we think this (the dredging) should be at the top of the list."

Council city services general manager David Adamson

would need to be deferred so rates were not impacted.

The work was part of a $72m plan to address flooding issues along the river. The council was also working on new storage basins in the Upper Heathcote and had agreed to buy up to 35 homes at risk of frequent flooding.

A number of homes along the river have frequently flooded above floor level since the 2010 and

2011 earthquakes. The number of homes at risk of flooding during a

one-in-50-year event was 222, compared to 175 before the tremors.

Councillor Pauline Cotter said it seemed logical to do the dredging at the same time as work to create storage basins in the river’s upper catchment area, because together the projects would provide maximum benefit.

Council city services general manager David Adamson said staff had not yet decided which projects in the $1.2 billion land drainage recovery programme would have to be delayed for the dredging.

‘‘We’ll be looking at what will have the least negative benefits, but we think this (the dredging) should be at the top of the list.’’

A staff report said the dredgedup material would be disposed of at existing waste-management facilities and could also be used to remediate land at locations including the former Bromley landfill, where post-earthquake settlement had left the ground uneven.

The report said care would be needed to manage the environmental effects of the dredging. Fish had been seen in the area and the dredging could impact inanga (whitebait) spawning areas. However, staff said that could be reduced by timing the dredging outside the spawning season from December to May.

There was also an opportunity to increase the spawning areas once the work was complete, especially along the section from Radley to Woolston Cut where very little spawning happened because of the existing steep banks, staff said.