There were grey skies and a bit of drizzle in Paeroa on June 4, but nothing to suggest any risk of flooding. Passersby might have been confused then, to see a 2.7 metre high floodgate closing in south of the Criterion Bridge.
The Criterion Floodgate, part of Paeroa’s flood protection system, was the subject of a training exercise by Waikato Regional Council workers to ensure as many staff as possible would be able to operate the gates in the case of an emergency.
Council’s scheme unit lead, Hayden McGregor, said it was important for redundancy.
“This is our number one critical element or asset that we need to look after, so having a range of people skilled in that responding space is good,” he said.
“For my team here, it’s their first priority, and if they are shut then people have to stay here and monitor it. [But] it’s a chance to get a batch of new young staff as well trained up, and able to respond if we do get people out of the local area for whatever reason.”
The Profile was invited along to get a first-hand look at the gate’s operation. For this exercise, only one half of the gate was shut to allow traffic to still traverse the bridge. However, the two sides operate in exactly the same way, and Hayden said it would take less than 20 minutes to completely close and seal the gate in a flood situation.
“[Cyclone Gabrielle] was the first time that we had used it… before that we used to have the big aluminium gates and they’re kind of like a big Lego kit. It used to take about 45 minutes to stack those things up and across everything else,” he said.
“It used to take 10-12 guys to close it, now we can probably do it with five.”
The actual operation of the gate was fairly simple: panels were removed to allow staff to connect the gate’s hydraulics; a winch was attached on both sides; and the gate was slightly raised before being slid forward.
Once it was fully extended it was bolted to the ground, and metal arms extended to brace the gate against the force of gushing floodwaters. The gate was also lowered again, forming a watertight seal at ground level.
When fully closed, the gate fills the gap in Paeroa’s defensive stopbank system where the road runs through. On the town side of the bridge, the stopbank gap would still need to be filled the old-fashioned way, with heavy timber stoplogs.
“They only go up in a one-in-100-year event – they obviously did go up during Gabrielle, but that’s my first time putting them up in the 10 years that I’ve been here,” Hayden said.
QUICK FACTS
The Criterion Bridge Floodgate was installed in 2018.
The two gates cost $1.02 million to construct and install.
Each gate is 10.8m tall, 2.7m high, and weighs 7 tonnes.
The gates were first used in February, 2023, during Cyclone Gabrielle, when the river rose to 400mm below the top of the floodgates.
