Heavy machinery caught in floodwaters at the Wairoa river mouth in June. Photo: Supplied / Siobhan Pryde
The flooding that devastated Wairoa might have been lessened if the river bar's crest had been lowered, as advised by a local contractor before the flood.
That is according to a review led by consultant Kyle Christensen. It was one of four different reviews into the flooding released this week, three of which were commissioned by the Hawke's Bay Regional Council.
Hundreds of homes flooded during the June incident, causing about $40 million of damage.
The review revealed that the contractor tasked with opening the river bar had advised the regional council of an alternative option of lowering the 'crest' of the gravel bar.
Pryde Contracting had texted the council, asking that an alternative beach crest lowering option be pursued, instead of the full mouth opening.
"Can you confirm that your request for the Wairoa Bar is that you want us to attempt a full open a new mouth and also attempt to close the existing. Or if we are removing sand from the potential new mouth spot to lower sand bar height?" the text read.
Another text from the contractor to the council said:
"Seems at this stage that, if HBRC were wanting to do anything, it's get a bulldozer into where the potential new bar mouth would be and push excess sand off the top of the bar down near sea level height..."
However, the report found that the message was misunderstood by the council.
Christensen said it "had not interpreted Pryde's suggestion as an alternative option, rather as the first step in full mouth relocation".
He said lowering the height of part of the river bar could have been a better use of resources, as levelling of the bar required far less earthworks than a full opening and mouth relocation.
If that action had been taken, or if the contractors had been deployed on the Friday before the flood, not the Monday, then the outcome could have been quite different, Christensen said.
"Having either option in place would have likely been better than nothing and at least provided the possibility of a breach occurring earlier in the event which might have reduced the extent and duration of flooding."
Christensen recommended that the council looked at how Whakatāne managed its river bar.
The town's much simpler strategy "either includes significant preparatory works whenever the river mouth is in an adverse position or just focuses on beach crest lowering", he said.
The report also found that if the river bar had not been breached naturally during the storm, then the floodwaters would have been half a metre higher, and lasted for 20 hours instead of seven.