The Waitakere Ranges are a chain of hills in the Auckland Region, generally running approximately 25 km (15.5 mi) from north to south, 25 km west of central Auckland, New Zealand. The maximum elevation within the ranges is 474 m (1555 ft). The ranges and surrounding areas were traditionally known to local Māori as Te Wao Nui o Tiriwa (The Great Forest of Tiriwa). It is under the jurisdiction of the Auckland Council.
The western coastline of the ranges consists of cliffs exceeding 300 m (984 ft), interspersed infrequently with beaches. The rugged upstanding topography is formed from erosion-resistant ancient volcanic conglomerate and lava flows laid down in eruptions from the large Waitakere volcano to the west 12–25 million years ago. The ranges are covered in native forest, most of which is in the process of regeneration since extensive logging and farming in the mid–late 19th and early 20th centuries.
In 1894 a group led by Sir Algernon Thomas (the first professor of natural sciences at Auckland University College, now the University of Auckland) persuaded the Auckland City Council to preserve 3,500 acres (14 km2) in the Nihotupu area of the ranges as a bush reserve. In 1895 the national Government vested the land, and several other smaller areas of the ranges, in the City Council as "reserves for the conservation of native flora and fauna". The Waitakere Ranges Regional Park now contains about 39,500 acres (160 km2). The area is also protected under the Waitakere Ranges Heritage Area Act 2008.
Five reservoirs within the ranges supply water to the Auckland region, including the Waitakere Reservoir and the Lower Nihotupu Reservoir. Combined, the reservoirs supply approximately 26% of Auckland's potable water demand. The ranges receive an average of over 2,000 mm (78.75 inches) of rainfall annually while the corresponding rate in the city is less than half that. As weather systems approach across the Tasman Sea, their path is blocked by the ranges causing a small uplift sufficient to trigger orographic rainfall.
The area is home to kauri snails, glowworms and native long-tailed bats. Long-tailed and short-tailed bats are New Zealand’s only native land-based mammals. At the northern end of the ranges, Otakamiro Point is the site of one of New Zealand’s few mainland gannet breeding colonies. In the bush are many indigenous invertebrates, including kauri snail, weta and oviparous peripatus (Onychophora or velvet worms) with 14 pairs of legs, and ovoviviparous species of 15 and 16 pairs of legs, none of which are members of any of the five scientifically described New Zealand species.
Some of the ranges' main attractions are: the four popular surf beaches, Piha, Muriwai, Te Henga (Bethells Beach), Karekare; an extensive network of bush walks and tracks; and panoramic views of the east and west coasts and the city. A road, aptly named Scenic Drive, runs a good portion of the length of the ranges from Titirangi to Swanson. The Auckland Regional Council operates an information centre near the Titirangi end.
The beaches are typical of west coast beaches north of Taranaki in that they are all black sand beaches. They have a reputation of being dangerous for swimmers due to rips and large swells. Surf Life Saving Clubs patrol designated areas of the four most popular beaches during the summer months. Piha Surf Life Saving Club is the oldest of these, being founded in 1934.
On January 11, 2010, the Auckland Regional Council opened the Hillary Trail, a 77 km trail running roughly south-north from the Arataki Visitor Centre to Muriwai through the Waitakere Ranges, named in honour of the New Zealand mountaineer Sir Edmund Hillary.
The Ark in the Park conservation initiative, a partnership between Forest and Bird and the Auckland Council, is working to reintroduce some of the species made extinct in the Cascades Kauri Park section of the ranges. The project was started in 2003 and now covers 2,300 hectares (5,700 acres).