Research - Site winds/tides/water quality

The Manukau Harbour is a large, tidally controlled inlet that opens to the sea via a relatively narrow
and deep channel. Mangere Inlet in the north-eastern corner of the Manukau harbour has an area of 6.6 km2 and a catchment of 34.5 km2

• the tide in Mangere Inlet ranges from around 2.0 m (neaps) to 3.4 m (springs) - one of the largest tidal range in NZ
• the volume which flows out of the manukau harbour between low and high tide is 450 million m3 (neaps) and 690 million m3 (springs).
• tidal flows dominate over freshwater inflows
• the mean residence time of water in the harbour is around 20 days

Prevailing wind = westerly

 The coastline of Mangere Inlet has a long history of contamination. Environmental quality improved after the Mangere Wastewater Treatment Plant (MWWTP) was built, but stormwater contaminants, unauthorized discharges from industrial sites and the discharge from the MWWTP still affect water and sediment quality.

• dominated by muddy sediments, which are moderately contaminated with copper and zinc on the northern shore of the inner inlet. In contrast, sites on the southern shore and outer inlet appear to have relatively good sediment quality.
• Historical data indicates that sediments within the inlet have always been muddy.
• extensive reclamation along the eastern shore was carried out in the 1960s during development of the Westfield rail yards. The southern shore is less modified; the Harania and Tararata Creeks are still largely intact, although the upper reaches of both creeks are dissected by high volume roads. Both creeks are heavily forested with mangroves.

• mussels, oysters and flounder collected from Mangere Inlet tend to have relatively high concentrations of organic contaminants in their tissues, and relatively high concentrations of lead have been found in the blood of South Island pied oystercatchers.

The area directly off Norana Reserve is classed as Coastal Protection Area (CPA) 23a, CPA Type 2 and is a significant feeding ground for the many thousands of international and NZ endemic wading birds which roost around the Ambury area.

KELLY, S., 2008. Environmental Condition and Values of Mangere Inlet, Whau Estuary and Tamaki Estuary. Prepared by Coast and Catchment Ltd for Auckland Regional Council. Auckland Regional Council Technical Report 2008/031.