Case study - Mangere sewage ponds restoration

The Mangere Waste Water treatment plant on Auckland’s Manukau Harbour once supported the largest oxidation ponds in the world, covering more than 500 hectares of intertidal foreshore and processing all domestic and industrial waste produced within a 40km radius. ²⁸⁴¹  With increasing volumes of waste from the fast-growing Auckland urban area, stress was placed on the plant, and this resulted in the need for a substantial upgrade.

With growing public awareness, and a need to future-proof the facility against the region’s inevitable growth, Watercare Services Limited embarked upon a period of extensive public consultation. This resulted in Project Manukau, New Zealand’s largest marine restoration effort. ²⁸⁴²  The project, supported by the public, ran from 1998 till 2005 when the foreshore was re-opened to the public as a coastal walkway.

The primary objective of the project was the removal of the oxidation ponds and restoration of 13km of coastline. Oruarangi Creek and Mangere lagoon, which had been closed off when the old sewage site was built, were reopened allowing them to flow into the sea for the first time in over 40 years. ²⁸⁴³  The length of foreshore was reconnected to the sea, restoring it back to being part of the intertidal zone. Extensive areas of white shell beaches were constructed, extending more than 13 kilometres, along which more than 270,000 native shrubs and trees which were planted with support from local community groups.

Water quality in the area has improved considerably with a notable decline in bacteria levels, to the point where it is now deemed to be of swimming quality, and odours and midges (which had plagued the area whilst the ponds were in operation) disappeared. ²⁸⁴⁴  Pipi beds re-established themselves as the estuarine ecosystems were restored. Previously destroyed fishing grounds have gradually replenished as aquatic life once again became established in the area. The native bush has provided habitat and food to an increasing number of wildlife and birds, particularly waders, which have been drawn back to the area by the expanse of beaches.

To further support the returning bird life, purpose-built roosting sites were placed in the harbour. These have attracted native and migrating birds, turning the area into an internationally-recognised roosting and feeding area. The area is now inhabited by 80 bird species, including a breeding flock of 12 New Zealand dotterels of which there are only 2000 left in the country. In peak season, the number of birds swell to an estimated 20,000 individuals, with half the worlds’ wrybill population using Mangere Bridge to roost. ²⁸⁴⁵  An extensive network of paths has been created for the public to enjoy the natural surroundings and rich diversity of life that has been restored.

Last updated at 2:11PM on February 25, 2015