Lake Taupo Erosion and Flood Strategy
There have been suggestions foreshore erosion around Lake Taupo is directly related to the lake’s level being kept high by electricity generators for the purposes of power generation. However, the facts do not support this notion and show the causes of erosion to be quite complex and varying.
The following information summarises the understanding of Waikato Regional Council about foreshore erosion.
During periods of high rainfall and inflows from run-off in surrounding catchments, Lake Taupo can rise very quickly.
Under the electricity scheme run by Mighty River Power, the gate outlet of Lake Taupo into the Waikato River is wider than the natural outflow point. That means more water can flow out than would naturally leave the lake.
Without this widened gate outlet and the intervention of Mighty River Power to increase flows leaving the lake during flood conditions, the level of Lake Taupo during flood events would usually be much higher (and therefore potentially in previous events have caused more damage and erosion).
During such flood events, Waikato Regional Council has well defined procedures for working with Mighty River Power and Genesis to help manage Lake Taupo levels and flows into the lower Waikato River. We don’t “favour” one area over the other, rather we work on what is best for the entire Waikato River catchment. This is a very difficult and challenging task.
So, to recap, the actual lake levels are predominantly influenced by direct rainfall and catchment runoff. Up to 3000 cubic metres a second can flow into the lake but only a maximum of 300 cumecs can be let out (but bear in mind this latter figure is higher than “natural”).
Analysis shows that the lake level has primarily been operated near its “natural” range over much of the past 70 years, during which the lake level has been influenced by electricity generation operations.
Mighty River Power manages Lake Taupo levels on a day to day basis. The company has freedom under its consent to manage lake levels for energy generation purposes within a 1.4 metre range of from 355.85 metres above mean sea level to 357.25 metres above mean sea level.
They must also manage the risk of these levels being exceeded in high rainfall events. If the lake level goes outside the consented range, Mighty River Power is obliged to get the level back within the range as soon as practicable. Waikato Regional Council recognises that the lake level may go as high as 357.5 metres above sea level at least once every 100 years. This is still less than would have occurred “naturally”, before the Taupo gates were installed and the new consent regime was introduced.
We will continue to monitor closely the operation of the consent regime by Mighty River Power.
Causes of foreshore erosion
Erosion around Lake Taupo’s foreshore is largely a natural process but is influenced by a number of interacting and complex factors. These include:
- “soft” geological material unique to Lake Taupo around the shoreline
- vegetation removal
- the effect of structures, such as dams and groynes, on the way sediment moves around in the lake
- developments near the shoreline
- seiching (water slopping)
- wind and waves
- the level of the lake under the consented lake management regime.
There is no evidence to suggest such erosion is purely “manmade” and primarily attributable to Mighty River Power keeping the lake level “too high”. Waikato Regional Council will continue to monitor the influence the impact of the various factors mentioned on foreshore erosion.
What’s being done about erosion?
Recognising that the factors contributing to erosion are complex and inter-related, the regional and district councils adopted the Lake Taupo Flood and Erosion Strategy in 2009.
The strategy, based on the best available science, was developed through a full and open public consultative process.
It established agreed roles and responsibilities for the councils and proposed an annual work programme, involving monitoring, asset maintenance and physical works.
Waikato Regional Council has already completed flood hazard mapping assessments for Lake Taupo’s foreshore. It is Taupo District Council’s responsibility to incorporate these assessments into land information memoranda (LIMs) and the district plan.
In addition to this, we have, in consultation with Taupo District Council, engaged a consultant to do beach monitoring and analysis to further develop the councils’ understanding of the situation.
Taupo District Council, meanwhile, has prepared an action plan regarding urgent repair work for a number of lakeshore assets including community paths, stormwater outlets and other structures damaged in the September 2010 and January 2011 storm events.
Finally, Waikato Regional Council and Taupo District Council are leading a programme looking at proposed new physical works at specific sites around the lake, including Kuratau and Taupo Bay, to either deal with the effects of erosion or stop it occurring. Options may include beach renourishment, beach slope contouring, and planting. Both councils are looking to jointly agree on a longer-term timeline for these works. Regional council staff will then use this planning, including budgets, to negotiate and formalise funding from councils and other stakeholders, such as Mighty River Power and King Country Energy.
We will look to update this information as work progresses under the strategy.
For more information, please contact us.
Download the strategy below.
Lake Taupo Erosion and Flood Strategy
(3532 kb, 504 seconds to download, 56k modem)
Several reports commisioned by the regional council and Taupo District Council helped in the development of the strategy. You can read these here:
You can also find out more on Taupo District Council's website.