Holding back rising river done in ‘drop of a hat’

While Paeroa’s community slept during the height of Cyclone Gabrielle, a small team was beavering away to dam the Ohinemuri River across State Highway 26 at the town’s Criterion Bridge.

Waikato Regional Council’s Hauraki operational staff were geared up and waiting well before the river level recorder upstream triggered the alarm that high water was on its way.

In the very early hours of Tuesday morning (13 February 2023), they rolled the blue floodgates across the rail on the road where it goes through the river’s stopbank and lowered them to create a seal against the encroaching floodwater.

“It was absolutely wild out there, it was wild, I’ve never been in anything like it ... I have no other words for it, it was just crazy,” says Works Supervisor Hayden McGregor (picture below).

“We knew the river was going to spill and it went really quickly. We were on site in shifts from before the gate closure right until the river was down enough at 8pm the next day to open the gates, clean up the remaining water and mud; huge day, huge hours, huge effort.” 

It was the first time the blue flood control gates, which span 22 metres and weigh 5500 kilograms each, have been used “in anger” since being installed in 2018.

Previously, the operational staff would have had to piece together heavy stoplogs like a jigsaw, nice across and three high, and it was always touch and go as to whether they’d be erected in time before the river came through.

“The river came up far quicker than what was expected so it was great to be able to close the gates in half the time and with only half the crew,” says Hayden, who stayed dry in a nearby shed because he’d lost his wet-weather leggings.

“I just stood there and let them deal with it and they did a fantastic job in the worst conditions.

“The river went up so quick and fast it showed what we can do at a drop of a hat.

“It’s a huge pressure situation. I’m really proud of the level of preparedness of the crew and how smoothly it went, and the monitoring of the incoming storm which allowed us to be ahead of the punch with closing the gates.

“Once closed, the water kept rising, rising, rising to peak at 400 millimetres below the top of the gates.  

“A lot of people were standing on the other side of the river looking across and seeing the river being contained; it really showed how awesome the gates were.”

Wooden stoplogs were erected to close the stopbank on the other side of the bridge, also, which is only necessary during really high-level event.

“That shows the scale of what we were dealing with.”

Elsewhere in the Hauraki area, the recently upgraded Mill Road pump stations were also put to the test.

Structural and telemetric upgrades of the two pump stations were completed in August last year.

“The new smartification of the pumps is worth its weight in gold,” says Hayden. The smartification programme means the pumps can be controlled by a mobile phone, and slowed down, rather than needing to be started and stopped all the time.

“We had farmers with an interest in the pump stations there checking it out and going ‘far out’. The difference between the land riverside and land side; land side, you wouldn’t even know there had been rain as it looked so dry.”