Lake Taupo erosion study findings released

A Lake Taupo Erosion Study has identified a range of options for managing erosion at nine high risk sites around the lake.



The recommendations focus on “soft” structural options like beach replenishment and re-vegetation along with further monitoring. The study indicates that no residential homes are at immediate risk however, portions of Council reserves along the foreshore are threatened. At Waitahanui, Kuratau, and between Four Mile Bay and Waipahihi service pipes within the reserves could be at risk in the future.



The technical study was carried out by consultant Beca Infrastructure Ltd for Taupo District Council and Environment Waikato. The initial investigation (Lake Taupo Erosion Study – Stage 3) determined the extent of erosion around the lake foreshore and identified contributing factors. The latest stage of the study (Stage 4) which was completed this month concentrates on further analysis of nine high risk areas around the lake – identifying what’s at risk in those areas and recommending a range of possible management options. The study also includes an action plan and indicative costs for a range of physical works and monitoring at the high risk sites.



The technical findings in the erosion study and a similar flood hazard study which is due for release at the end of March will be taken out for public consultation during April and May. The technical information and feedback from the community and stakeholders will then be used to develop a Lake Taupo Erosion and Flood Strategy. The Strategy, which is due for completion this year, will guide future management decisions, set out funding responsibilities and identify work programmes and timeframes.



The high risk erosion sites include Waitahanui, Hatepe, Motutere, Te Rangiita, Whangamata Bay (Kinloch) and Whakaipo Bay, Kuratau and Whareroa and the stretch of foreshore from Waikato River to Wharewaka Point – including Taupo Township.



The study explains that erosion is influenced by a combination of natural factors (geology and wind) and human factors (management of Lake levels, development, structures, a lack of sediment and vegetation removal). It says that although erosion is most evident during periods of high wind and high lake levels a lack of long term data and monitoring, coupled with the complexity of shoreline processes, make it difficult to establish the extent to which various factors are contributing to erosion. The study says a lake wide monitoring programme would provide the long term scientific data needed to assess how much each of the natural and human causes are influencing erosion.



The study also identifies a range of specific planning measures and physical works at each high risk site. The emphasis is on soft structural management options like beach replenishment and re-vegetation which will maintain the existing natural character of the shoreline. Indicative costings for a range of options have been included in the study to give people a general idea of the costs that could be involved. Further site specific investigation and community consultation is required to determine the true costs of each preferred option.



The options will be discussed with iwi and the community over the next two months to identify their priorities. These will be balanced with the technical recommendations during development of the Lake Taupo Erosion and Flood Strategy. The final Strategy will include an implementation plan and timeframes.



In a joint statement Taupo Mayor Rick Cooper and Environment Waikato’s Taupo representative Cr Laurie Burdett said the Lake Taupo Erosion Study provided a way forward.

“We now have recommendations for managing erosion at the nine high priority sites along with general estimates for a range of options that communities may want to consider.

“The challenge in developing the strategy is to work with our key stakeholders and the community and come up with equitable, affordable, and effective solutions for dealing with the erosion risk.

“The priority for us all is to get the final Strategy in place so we have a firm long term plan that will enable consistent management of erosion issues.”



Copies of the erosion report will be available from Council offices and libraries in Taupo, Turangi and Mangakino and on-line www.ew.govt.nz  or www.taupo.govt.nz  

Lake Taupo Flood and Erosion Strategy

March 7 2008


Key Facts Lake Taupo Erosion Study – Stage 4



Key Facts

Consultants have been employed by Taupo District Council and Environment Waikato to prepare technical reports on the erosion and flood risk around the Lake Taupo Foreshore
The technical findings will be used as a basis for development of a Lake Taupo Flood and Erosion Strategy
The Strategy is being developed during 2008 in consultation with key stakeholders, affected property owners and the public
The Strategy will clarify roles, responsibilities and funding and guide future management decisions.


Lake Taupo Erosion Study

The Lake Taupo Erosion Study – Stage 3 determined the extent of erosion around the lake foreshore and identified contributing factors
The Lake Taupo Erosion Study – Stage 4 concentrates on further analysis of nine high risk areas identified in the Stage 3 report (Waikato River to Wharewaka Point – including Taupo township, Waitahanui, Hatepe, Motutere, Te Rangiita, Whangamata Bay and Whakaipo Bay, Kuratau and Whareroa)
The Study identifies assets at risk, looks at the pros and cons of a range of management options and comes up with recommendations for managing erosion
The study includes an action plan and indicative costs for measuring and monitoring shoreline erosion
The technical options recommended by the consultant will be summarized in an issues and options paper and taken to iwi and the community for comment and discussion
Further feasibility assessments including field investigation, design and costings for the recommended management option will be carried out at high risk site to ensure they are viable. This work will need to be prioritized.


Assets at Risk

A site by site analysis of assets at risk indicates that portions of Council reserves on the foreshore are at immediate risk
No residential homes are immediately threatened, although residents may think otherwise
At Waitahanui, Kuratau, Four Mile Bay and Waipahihi there are service pipes within the reserves that could be at risk in future.


Technical background and findings

Factors contributing to erosion vary considerably from site to site
Erosion is influenced by a combination of natural factors ( geology, wind, tectonic subsidence) and human factors ( land use/soil conservation, lake level regime, development , structures, sediment removal)
In most cases insufficient historical monitoring makes it difficult to differentiate between short term fluctuations and long term erosion
Erosion is most evident during periods of high winds and high lake levels
The study recommends that monitoring be undertaken at each high risk site. ( beach profiling, water depth measurements, sediment sampling, wave height modeling, monitoring of erosion control options).
This is needed to help understand processes driving erosion and enable development of effective long term protection measures
A range of physical works and planning measures at each high risk site are also identified for further investigation.


Lake Level

The lake level is managed within a 1.4 metre range for use in the Waikato hydro electric scheme
Long term analysis shows that the controlled lake level is similar to what it would have been naturally if compared on a yearly basis
In recent years controlled lake levels have been higher than natural during summer months, which can coincide with extreme high wind events increasing the erosion risk at some locations
The study notes that in 2007/08 lake levels have been lower than the natural level during summer
Advice from consultants is that further long term data and site specific investigation would be needed to determine how great an impact the lake level regime has on foreshore erosion
Consultants have indicated that even if the lake level was to be lowered it might not solve erosion issues at all sites because of the complexity of lake processes and the range of factors that contribute to erosion e.g. vegetation removal, hard structures e.g. boat ramps and protection walls.


Costs

Estimated costings in the study for monitoring and other management options like physical works are only indicative
They will be used during consultation and development of the strategy to enable people to compare different options and combinations
Further site specific investigation will then need to be undertaken to finalise options and refine the actual costs
Councils will work closely with key stakeholders during development of the strategy to determine funding and responsibilities.