Lake Taupō and Waikato River vulnerable to Cyclone Gabrielle

The high level of Lake Taupō is causing damage to the foreshore at the southern lake township of Kuratau. Photo / Sandra Greenslade

Mercury Energy is preparing for flooding in the Waikato River and Lake Taupō.

Southern Lake Taupō communities are already grappling with significant erosion to lakeside properties and public reserves from prolonged high lake levels.

The company has had the control gates between the lake and the river fully open for the past 10 days to try and bring the lake down below the maximum level allowed under its resource consent, but that may not be enough to prevent further damage and downstream flooding.

With further significant rain forecast to hit the catchment next week, Mercury GM Portfolio Phil Gibson is warning that Lake Taupō and Waikato River levels could reach the high levels seen after the flooding of two weeks ago.

“We know the high water levels in Lake Taupō and the Waikato River have impacted some properties, and caused concern. While forecasting future weather patterns is known to be complicated, we still need to be ready for the possibility of more rain.”

With the ground already saturated from months of rain, there is potential for flooding and raised water levels in the Waikato River and its tributaries, he said.

The floodgates are fully open to drain as much water from Lake Taupō as possible ahead of Cyclone Gabrielle. Photo / Milly Fullick

“Our team are working hard to prepare for next week. We’re moving as much water as we can out of the lake and through the river system, using the Taupō Control Gates and eight hydropower dams in the Waikato Hydro System.

“We’re also lowering the level of the hydro lakes behind the dams in the mid-river to provide storage within our operating limits and help reduce flooding downstream of Kārapiro.”

He said the company was working with the Waikato Regional Council on an all-of-river approach to managing the flood with a focus on the well-being and safety of communities across the catchment.

“There’s only so much we can do with the amount of water entering the system.”

He said north of Karāpiro, varying water levels may mean that there will be a downstream impact on low-lying land including some pathways and the Grantham St carpark in Hamilton.

Further north, there is potential for greater impact with additional tributaries and in-flows to the river including the Waipa.

Taupō mayor David Trewavas said there has been some serious erosion of public reserves at the southern lake communities of Kuratau and Pukawa.

“A lot of those residents are concerned about losing their beaches. We are keeping pressure on Mercury to keep those gates open.”

Mercury has been criticised by southern lake community groups in the past for not maintaining the lake level at a lower level as a precaution against extreme weather events.

The Waikato River is flowing at full speed as Mercury Energy attempts to create flood capacity ahead of Cyclone Gabrielle. Photo / Merv Richdale

The company is required to keep the lake in a range from 355.85 - 357.25 metres above sea level. The lake has been above 357 metres since the beginning of September last year. The level was sitting at 357.20 metres on January 10 after peaking at 357.28 on January 31.

Trewavas said they would be having “a round table discussion” with Mercury and other stakeholders, including the Waikato Regional Council which is responsible for managing flood risk in the lake and the river.

He said the high lake levels and associated erosion were “becoming too common for our liking”.

“We are stakeholders in this because we are losing our reserves as well. It is getting eroded away.”

The flip side of keeping the lake at a lower level is that it may not leave enough storage to run hydro dams if it turns dry, leaving the country short on electricity.