Twenty years after bypassing the estuary, the effects on local kaimoana were starting to be felt, with calls for the river to be reinstated starting in 1979.
"It's taken four decades for this project to come on stream," admits de Monchy.
Work to redirect waterflows began in June 2018 and is due to finish five months ahead of schedule, with a public ceremony on February 12.
"Probably the biggest development has been the creation of a new channel that extends a kilometre upstream from Ford Road, to divert quite a lot of fresh water into the estuary.
"It's 60 metres wide and then that water passes through 12 massive 2.5 by 2.5 metre squared culverts with automatic stainless-steel control gates on them. Inside the estuary there have been quite a few causeways removed to allow tidal and river flushing to recur as it did before."
In addition to a new man-made channel, new boat ramp and the 12 culverts, the project also included the renovation of 20ha of saltmarsh wetland for local birds.
The culverts were tested last week to make sure they were working for the official opening on February 12. Nine out of the 12 culverts will open first, so the council can monitor the effects.
"Consent conditions say we need to monitor what happens after that for 12 months before we open all 12 of them – just to be certain that there's no unexpected, negative effects that we haven't thought of," said de Monchy.
"In the longer-term, the council directed staff about six years ago to keep looking at ways of getting more of the river into the estuary, because of course this will redivert only a portion of the flow, about 20 per cent. And that could be done in the future as part of some coastal defences work or adaptation to climate change but at the moment this is the bulk of the work."
It currently takes 15 tidal cycles for all of the water in the estuary to be replaced from the river. But once the culverts open, that will be reduced to just two-and-a-half cycles.
The total cost of the project is $16.6 million, which includes everything from planning and construction to 3D tidal modelling and the acquisition of 45ha of land.
Getting the project over the line has also taken some good old-fashioned team work.
"The original group that tried to make this happen was called the Maketū Action Group, formed from tangata whenua and members of the local Maketū community.
"Since the resource consent was granted, we've been working closely with six different Te Arawa Iwi and meeting with them about every three months to make this project a success. They've been a big part of the planning, implementation and also the monitoring of results," said de Monchy.
A special celebration to mark the end of the project will take place on Wednesday, February 12 from 9am.
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