"It was done to protect the low-lying farmland from flooding and improve drainage, but the resulting loss of freshwater inflow has severely degraded wildlife, kaimoana, water quality and the mauri (life force) of Te Awa o Ngātoroirangi/Maketu Estuary," he said.
Construction work will start in July to return 20 per cent of the Kaituna River's freshwater flows back into the estuary and recreate at least 20ha of new wetlands.
Existing levels of flood protection and boating access at Te Tumu cut will be maintained.
The construction work included creation of a new channel to carry fresh water from the river into a new inlet structure at Ford's Cut. Existing stop banks will be shifted and upgraded.
Ford's channel will be widened and the Ford Rd boat ramp will be upgraded.
De Monchy said the project would improve fish and shellfish habitat and public facilities in the long term but to achieve that some temporary Ford Rd and boat ramp closures would be required from August 1.
"We'll be asking fishermen, boat ramp users and other locals to be patient with us and help by using alternative boat ramps, river and beach access points at Bell Road, Kaituna River Road, Maketu Rd or Karewa Parade, while the Ford Rd-end facilities are closed," he said.
Ford Rd end, from Ford's cut bridge to Te Tumu cut, will be closed from August 1 to December 20 and traffic restrictions will remain in place until June 2020. The Ford Rd boat ramp and the stopbank west of Ford Rd, will be closed to the public from August 1 2018 until June 30 2020.
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De Monchy said the Bay of Plenty Regional Council considered 18 different methods and options for re-diverting the Kaituna River and creating new wetlands before making a final decision based on thorough engineering, hydrology and ecology investigations, as well as iwi and community consultation.
"All of the resource consents and conditions for the project were finalised in an Environment Court decision issued in May 2016. Following two years of work on land acquisitions, detailed design and contract tender processes, a $13.5m construction contract to complete the project was awarded to J Swap Contractors Ltd on March 29 this year."