Whangaehu River bund, Crater Rim engineering, World Heritage status
Where is the bund located?
The 283m long bund is designed to
prevent the lahar from breaching the
bank of the Whangaehu River
The bund (stopbank) is located at the end of a ridge on the true left-hand side of the Whangaehu River close to the national park boundary. It is constructed in the location most suitable for preventing a lahar spilling over the Whangaehu riverbank into the Waikato Stream and ultimately into the Tongariro River.
What is the bund made of?
The bund is built from material recovered from the Whangaehu riverbed.
What are the bund dimensions?
The bund is approximately 285 m long, 20 m wide and a maximum of 4.6 m high.
Will deflecting the worst case lahar down the Whangaehu river create additional risks to infrastructure and people?
The increased risk is negligible. It is projected that flows down the Whangaehu would increase between about zero and seven per cent, or looked at another way, would increase the water level at Tangiwai by about 2.5 cm, or 0.5 %.
Why not cut a trench through the crater rim?
The Minister of Conservation has ruled out an engineering intervention at the Crater Lake. As well as raising technical and safety concerns, this option also raises several major conservation, cultural and legal concerns that would have to be addressed. The Crater Lake is the most significant natural, scientific and cultural site within Tongariro National Park. Any physical interference is regarded as unacceptable to iwi and indeed to many conservationists, scientists and recreationalists (as evidenced by submissions to the Assessment of Environmental Effects (AEE, see Fact Sheet 3) and subsequently) Making structures on the flood plain able to withstand lahars is a better solution which will provide long term mitigation of risks.
What are these concerns?
- An engineering solution runs counter to National Parks Act principles, the Tongariro National Park Management Plan, and the park’s World Heritage status.
- Engineering would compromise the first two widely agreed objectives of the Management Plan which include managing the park so that present natural processes (such as lahars) continue, and maintaining the cultural, spiritual and inspirational heritage of the mountains of the Park.
- Engineering would also compromise the natural and cultural World Heritage values.
back to top