A new way of making it easier to release floodwaters from the Wairoa River is being trialled by Hawke’s Bay Regional Council.
A 50m-wide overflow channel has been created by council contractors. It is being maintained at the centre of the Wairoa River bar, with a protective gravel bank on the seaward side to try to keep it intact.
A spokesperson for Hawke’s Bay Regional Council said a new method of bar management began after June 2024, when catastrophic flooding swamped 127 homes, and spilled into hundreds of other properties in the northern Hawke’s Bay town.
“Council is proactively maintaining a built overflow channel at the centre of the main Wairoa bar to release flood waters and enable the opening or relocation of the Wairoa Bar when optimal conditions arise,” the council spokesperson said.
“The gravel bank protects the channel from the effects of swell and tide, which could cause sediment to build up and limit its usefulness during a flood event.
“The purpose of the channel is to create a breach point in the bar so that during flood events the river can create a new exit point.”
During a rainfall and flood event, the Regional Council is then able to engage a contractor to open the gravel bank to pass water from the lagoon to the sea.
“The overflow channel also reduces the time spent on preparation works, should a mouth opening or relocation be carried out by contractors,” the spokesperson said.
Previous attempts to open the bar have required a lead-in time of a few days to mobilise and prepare the site, before attempting to open a new river mouth.
The spokesperson said the base of the channel sat at one metre above sea level, much lower than the ground along Kopu Road, which was about three metres above sea level.
The work is part of the council’s interim management plan for the Wairoa Bar, while medium to long-term options are developed jointly with the Tripartite group, HBRC, Tātau Tātau o te Wairoa, Wairoa District Council, and the Wairoa community.
It follows Cyclone Gabrielle in February 2023 and further flooding on June 26 this year when the Wairoa River overflowed.
An independent Government review into the June floods highlighted shortcomings around planning and management of the river mouth and bar and recognised the need for greater engagement from the Hawke’s Bay Regional Council with the Wairoa District Council and community on emergency preparedness.
The review also recommended actions to mitigate against similar future events, such as developing an operational plan for the management of the river mouth and bar, and improved monitoring, detection and early warning systems.
The HBRC spokesperson said there had been attempts to maintain an opening in the Wairoa River bar which aligns with the middle of the river channel, to the east of Pilot Hill.
“This has proved difficult due to a number of factors. Creating temporary new openings in advance of rainfall events is a complex undertaking.”
The council says it plans to appoint a representative from Tātau Tātau o te Wairoa to conduct a joint inspection of the bar and the channel once a week, with maintenance work carried out as required.
Tātau Tātau o Te Wairoa said it had yet to decide if a local representative from the Trust would be involved.
Chairperson of Tātau Tātau o Te Wairoa Leon Symes said they need to have an internal conversation before making a decision.
By Local Democracy Reporter Linda Hall
LDR is local body journalism co-funded by RNZ and NZ On Air
