A planned project to flood-proof part of the Ōpāwaho Heathcote River may not go ahead.
Following severe flooding along the Ōpāwaho Heathcote River in July 2017, Christchurch City Council resolved to investigate the technical feasibility of installing low stopbanks along the river between Colombo Street and Radley Street to reduce the flood risk.
Council says the stopbanks were one part of a comprehensive suite of floodplain management works.
“Those investigations have found that while it technically feasible to install low stopbanks for frequent smaller flood events, it is not feasible to install stopbanks for large flood events,” it said in a statement.
Based on those findings, Council staff are now recommending the Council not proceed with the stopbank project and remove it from the Long Term Plan.
They say the floodplain management work the Council has done since 2017 has substantially lowered the flood risk along the Ōpāwaho Heathcote River and building low stopbanks – at a cost of between $22 million and $58 million – may not deliver the benefits sought.
“Since the July 2017 floods, Christchurch City Council has allocated more than $80 million to floodplain management in the Ōpāwaho Heathcote River catchment. This has included buying the most frequently flooded houses, dredging, bank widening and strengthening, as well as beginning construction on four major flood basins.”
“These works have significantly reduced the risk of above floor flooding in properties along the river,” Council said.
A report prepared for the 5 May Council meeting stated that while there was still a risk of flooding along the lower reaches of the Ōpāwaho Heathcote River, adding low stopbanks was not a priority given other flood management needs in the city.
“Due to the low priority of the project, the Council made the decision last year that it would push out the budget for the stopbanks in the Long Term Plan to 2041.”
The report says that other Council workstreams, such as the Coastal Hazards Adaptation Planning Programme, will address flooding in areas affected by sea level rise.
“As such it is considered appropriate to cancel the current [low stopbank] project and for it to be included in future floodplain management projects if it is considered an appropriate response.’’