Project: Desilting of the Poutu Channel, Lake Te Whaiau and the Otamangakau Canal
Location: Turangi - Central North Island, New Zealand
The 361.8 MW Tongariro Power Scheme comprises three hydro power stations – Rangipo, Tokaanu and Mangaio and has a
catchment area of more than 2600 km2 in the North Island's central volcanic plateau. The scheme gathers water from the
mountains of the central plateau through what are known as the Eastern and Western Diversions of the Scheme. The water
passes through a series of pipes, lakes, canals and/or tunnels to the Mangaio, Tokaanu and Rangipo hydro power stations before entering Lake Taupo.
On eight occasions between 1981 and 2013 Heron dredged silts, sand and gravels from the Poutu channel, Lake Te Whaiau and the Otomangakau Canal which deliver water into Lake Rotoaira for the Tokaanu hydro power station for the then Government Corporation ECNZ and more recently Genesis Energy.
The cutter suction dredges Kotuku or Beaver were equipped with several booster pumps to pump the dredged material up to 2500 metres to the disposal areas.
The Poutu Channel, Lake Te Whaiau and Otamangakau Canal are all pristine freshwater waterways, culturally and spiritually
significant to the local Maori Hapu. These waterways are also renowned for their trophy fish, with fit and strong rainbow trout commonly exceeding 4 kilograms being caught.
For these reasons very strict environmental controls with regards to water quality, hydraulic oils and fuel storage/transfer were put in place to ensure that the dredging operation had a minimal effect on the surrounding environment.
Daily water turbidity testing at the dredge and the disposal overflow pipe was undertaken by Heron staff and local iwi
representatives to show that the turbidity limits in the Recourse Consents were not being exceeded. Panolin bio-degradable oil was used in all hydraulic systems and a rigorous equipment inspection and maintenance regime was implemented.
Not once did Heron breach any of the conditions or requirements of the Resource Consent conditions.