Detailed design work is set to proceed for flood mitigation improvements to the Wainui Te Whara Stream channel, following approval by the Whakatāne District Council’s Projects and Services Committee.

A report to the committee last week confirmed that the channel improvements proposed earlier this year are technically feasible and provided updated costings totalling up to $2.4 million for the various components.

The work programme will increase the Wainui Te Whara Stream’s flood flow capacity from 18 to 32 cubic metres per second, which will significantly reduce the possibility of overtopping during extreme weather events. The channel’s current capacity is designed to deal with a one-in-20 year flood event, and the upgrade aims to lift the level of protection provided to accommodate a one-in-100 year flood flow. Using the Ministry for the Environment’s guidelines for calculating the likelihood of a specific flood event, that flow capacity increase would see the chance of the stream overtopping at any stage during the next 50 years reduce from 93% to 39%.

Major components include:

• 1555 metres of channel deepening, widening and realignment earthworks
• The installation of bank retaining walls on both sides of the channel along a narrow, 175-metre section adjacent to Valley Road
• The upgrading of eight bridge structures

Further debris and sediment control structures will also be installed 400 metres upstream of the Valley Road bridge.

Committee Chairman Councillor Andrew Iles welcomed the update report and said the projects involved would “go a long way towards meeting the concerns” of the Wainui Te Whara Flood Affected Residents group and the wider community.

“The Council is committed to working with the residents group, and their input will be factored into the detailed design process,” he said. “With winter now upon us, these projects will be scheduled to avoid potential erosion impacts, with the major bridge works tackled first and the channel bank works undertaken in the spring when conditions are more suitable.”