Land drainage  |  22 May 2019

A $19 million land drainage scheme has reduced the flood risk for dozens of properties in the Woolston and Linwood area and created lasting legacies for the community.

“The flood mitigation work that has been done over the past two years in the Bells Creek catchment area has reduced the number of properties at risk of floor level flooding in a one-in-50-year event from 33 to one, Christchurch City Council Land Drainage Manager Keith Davison says.

The urban forest in Linwood.

Te Oranga Waikura Urban Forest in Linwood.

“An additional 88 properties also benefit from significantly lower flood risk.

“But what is really great about this land drainage scheme is the benefits that we’ve been able to bring to the community as a whole through providing new recreational and ecological spaces such as the Te Oranga Waikura Urban Forest,” he says.

Thousands of native trees and plants have been planted in the forest, which sits off Ferry Road and covers 2.75 hectares. The forest, which is open to the public, acts as a storage basin in heavy rain events, reducing the frequency and severity of flooding in the surrounding area.

Part of the forest has been adopted by nearby Te Waka Unua School, which uses it as a space for teaching and nature play.

“The forest is an amazing legacy for the city and will ensure that future generations have access to a forested wetland within a residential area,” Mr Davison says.

As part of the flood mitigation work, Bells Creek has also been realigned and naturalised through Linwood College.

The realignment of the creek means that Linwood College has additional buildable land that it can use to accommodate future growth.

Edmonds Park sports field.

The sports field at Edmonds Park can also be used as a stormwater basin.

At Edmonds Park, the sports field has been excavated by about one metre to form a stormwater basin which can be used to store excess water when it rains heavily.

A new stormwater pump station has also been built in Richardson Terrace. Its recent commissioning marks the completion of the Bells Creek flood mitigation work.

The pump station is important because it allows the catchment to drain when water levels in the Heathcote River are high.

“Without the pump station, the existing gravity outfall cannot discharge water from the catchment until the water level in the Heathcote drops lower than the outfall pipe, which means water backs up in the catchment causing flooding,” Mr Davison says.

“We have also spent $2.4 million installing a stormwater treatment device next to the pump station. The device is the biggest of its type in Australasia and should filter out about 20 per cent of the dissolved metals in the stormwater and about half of the sediment.

“That is going to improve the health of the Heathcote because it will mean there are less contaminants entering the waterway,” he says.

The flood mitigation work in the Bells Creek catchment area is part of the Christchurch City Council’s Land Drainage Recovery Programme, which is aimed at restoring the flood-risk across the city to pre-earthquake levels.