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The $1.2b Central Interceptor is a giant underground wastewater tunnel running 14.7 kilometres from Māngere Wastewater Plant Treatment to Grey Lynn.
Older parts of Auckland, have a combined water and stormwater network. In wet weather, the system is engulfed by rain and overflows occur into neighbouring waterways. The Central Interceptor will store as well as convey flows to the treatment plant for processing. The tunnel will enable other projects, such as a replacement Western Interceptor to take place. Once finished, they will prevent around 80 percent of wet weather overflows to inner city beaches and waterways and see significant improvements to water quality in the Manukau Harbour and Hauraki Gulf.
The fossils were found during the early phase of construction when a hydrofraise machine was excavating the main launch shaft for Hiwa-i-te-Rangi, the Tunnel Boring Machine, which is digging the Central Interceptor tunnel. The material was discovered in a five-metre-thick shell layer in the geological Kaawa formation some 35 metres below ground.
The image on the right shows the super-sized Central Interceptor tunnel being built. Construction is due to finish early 2026.
Although the bulk of the sediment discovered consists of sand and crushed shell fragments, the layer has yielded more than 200 different species of molluscs and other fossils to date, many of which are in very good condition. Most importantly, a number of these species are new, previously unknown to science, including two fossil flax snail species.
The Ghella Abergeldie Joint Venture (GAJV)*/Watercare partnership have agreed that any unique or important material unearthed during the excavation of the Central Interceptor shaft will be lodged with Auckland Museum where, in Phase One of this project, the Museum will collect, identify and accession the Māngere Kaawa Formation fossils into the collection.
The Maoricardium spatiosum, a giant extinct cockle, from 3-4 million years ago. The large cockle measures 17cm wide, with a height of 15cm. It has a depth of 8cm. AWMM MA126260.
Similar molluscan fossils were recovered in the 1940s from a well sunk by the then-Waitemata Brewery at their site at Ōtāhuhu. Its manager, Mr Morton Coutts, contacted scientists to evaluate the spoil heaps and consequently fossil specimens representing at least 60 new species were lodged with Auckland Museum, Auckland University and the New Zealand Geological Survey (now GNS Science).
The number of fossil species found in the sediments excavated at Māngere exceeds the number found at Ōtāhuhu. To date, they appear to be more complete and better preserved. The spoil continues to yield new species and the Māngere material therefore presents a unique opportunity to shed further light on the story of Auckland’s geological history. It will substantially enhance knowledge of the fauna that inhabited the region’s seas and forests 3.5 million years ago.
Shown here is the Maoricrypta profunda, slipper limpet. The specimens represent a growth series and show the variation in the species from relatively juvenile to adult. The largest Maoricrypta measures: width 4cm, height 5cm and depth 1.5cm. AWMM MA12605.
With funding from Watercare, two collection technicians, Nathan Collins and Thomas Stolberger (pictured), have been recruited to the Museum providing an opportunity to enhance our knowledge of these taonga, as well as providing valuable training and development for these recruits.
The specialised collection technicians are using their museum practice and academic knowledge to carry out further field collecting, processing, identifying, housing and archiving of fossils into the Museum’s collections. They are working with Auckland Museum staff who are delivering project oversight, leadership and assisting with fossil processing and archiving, publication, and will establish access for mana whenua and the scientific community.
The identification of some of the fossils will require a visit to GNS Science in Wellington for expert advice and access to comparative material. The specimens will then be divided between the Auckland Museum collection and other national collections, mana whenua and educational outreach.
From the size of the machinery to the quantity and quality of fossils that were unearthed, almost everything about this story is over-sized.
In this blog, Wilma Blom (Curator, Marine Invertebrates) details Watercare's ground-breaking Central Interceptor Project and some of the significant specimens it uncovered.
Image: Watercare Central Interceptor Executive Programme Director Shayne Cunis holding two of the specimens in May, 2020. Photo Courtesy of Watercare.