Swollen Lake Taupō soaks up floodwaters to protect Waikato River communities

High rainfall means Lake Taupō is sitting at its highest level in more than a decade.

The level of Lake Taupō is managed by Mercury Energy via the Control Gates Bridge, a few hundred metres downstream from where the lake flows into the Waikato River.

Resource consent conditions stipulate the lake level should be kept at a range between 355.85 and 357.25 metres above sea level. Mercury was holding water back in Lake Taupō earlier this week to take pressure off flooded downstream catchments, including Lake Karapiro.

As a result, the level of Lake Taupō surpassed the maximum after the weekend’s rain, triggering a high flow management plan.

Mercury’s general manager portfolio, Phil Gibson, said the situation is being constantly monitored, but ultimately the lake could not be completely controlled.

“We can only have a limited impact on the lake level.”

At its peak over Auckland Anniversary weekend, 1 million litres of water were entering the lake per second. That’s over three times more than the 300,000 litres of water that can exit the lake when the control gates are fully opened.

The gates were not able to be constantly open throughout the high rainfall period, due to the potential for flooding further down the Waikato River.

“We reduced the flow out of Taupō for a short period to manage the flow.”

The influx of water, combined with a limited outflow, caused the lake levels to rise by more than 28 centimetres in under three days.

Rick Liefting, regional resilience team leader at Waikato Regional Council, said significant flooding had been avoided along the Waikato River.

The “unprecedented rainfall” triggered the high flow management plan for Lake Taupō once the lake level hit its maximum consented level.

This plan involves multiple agencies and is designed to contain the effects of excess water on local communities and infrastructure.

“It’s a very collaborative conversation with Mercury.”

He warned that although Taupō and Tūrangi got off lightly compared to Auckland and Te Puke, it was still crucial to be prepared.

“Neither of those events was predicted to be as bad as what they were.”

“Everyone gets their turn. It’s a question of when, not if.”

He also praised the dedication of the council departments, emergency services and other service providers who have been responding to the evolving situation.

“We worked all through the weekend. We have teams on call 24/7.”

The area had a total of 82.2 millimetres of rain between Friday and Sunday, with 58mm falling on Saturday alone.

The conditions caused disruption across the region, with Taupō Racecourse calling off Sunday’s planned race.

Fortunately, there was no lasting damage due to flooding at Taupō Racing Club.

Taupō Racecourse president Terry Campbell said the level of rain was unheard of.

“We’ve never had anything like it.”

Luckily, there was no lasting damage, but the course was temporarily flooded by the deluge.

The meet won’t be rescheduled, but Campbell remained optimistic about better upcoming conditions.

“Taupō drains brilliantly, so we’re back in action this Tuesday.”

Taupō District Council also had operational concerns, placing the whole region on a conserve water notice for about 24 hours between Sunday, January 29 and Monday, January 30.

In a statement, it said that although the southern and western communities had been hardest hit, the whole district had experienced very high levels of rainfall.

This led to concerns about the ability of stormwater and wastewater systems to cope with the onslaught of rain.

“Many of our pump stations and other infrastructure are flooded and underwater.

“The very real risk is that if they are overwhelmed, wastewater will spill into our stormwater gullies, waterways and possibly the lake.”

The notice asked residents and visitors to only use water as needed, and make moves to conserve water where possible, through measures like shortening showers and only running washing machines with full loads.

Mercury's data, captured as of the afternoon of Tuesday, January 31, shows Lake Taupo above its maximum consented level. Image / Mercury