Auckland’s single most environmentally beneficial stormwater management project

Auckland city’s Waiatarua Reserve, and its stormwater flows, has immense implications in the broader context of the Ellerslie Waiatarua catchment, the Orakei Basin and Waitemata harbour. As far back as the 1980s, the Reserve was recognised as playing a very important role in the management of stormwater from the surrounding land.

The Ellerslie Waiatarua catchment covers some 795ha – the area generally bounded by Remuera Road in the north, the Ellerslie Panmure highway in the south, Winstone quarry in the east and Great South Road in the west.

Currently, stormwater runoff threatens the habitable floor space of 190 homes in the catchment with predicted flooding in a rainfall event of a magnitude that could be expected to occur once in 100 years. Also, the sediment and contaminants contained in the stormwater runoff degrades the existing waterways in the reserve, increases the risk to public health in the Orakei Basin recreational water body, and contributes to the degradation of the wider receiving environment of the Waitemata harbour.

The harbour is the primary receiving environment for stormwater runoff from this catchment. The associated sediment and contaminants contribute over 70% of the pollutant load to Orakei Basin and some 7% from the entire Auckland isthmus’ stormwater runoff to the harbour.

In view of these significant public health and environmental issues, the Ellerslie Waiatarua Catchment Management Plan was developed with two major objectives, namely to improve stormwater drainage to reduce flooding of homes in the catchment and minimise the environmental impacts on the Waiatarua Reserve and Waitemata harbour receiving environments.

“Waiatarua Reserve constitutes the city’s single major opportunity to address stormwater quality on a sustainable basis throughout the catchment. Opportunities of this nature are rare in the life of a city - in Auckland, there is not another such opportunity of this magnitude,” says Councillor Bill Christian, chairperson of Auckland City Council’s Works Committee.

The proposed enhancement works involve the installation of engineered and natural sediment traps to clean the water before entering the central area of the reserve. These traps include the creation of a natural wetland that will provide a water polishing effect and a valued environment to support a wider variety of fauna and flora than presently exists.

The overall project will significantly reduce (by 80%) the amount of sediments and contaminants reaching the reserve’s wetland area and Waitemata Harbour, while at the same time make a more effective maintenance operation possible.

To date, and thanks mainly to the good weather Auckland has enjoyed since the start of the year, work on the installation of sediment traps in the main stormwater entry channels is progressing well and is expected to be completed in April, weather permitting.

Mr Christian, members of the Works Committee and Auckland City Council wish to thank all those residents who have contributed to the soon-to-be-completed landscape planting plan. Further consultation is programmed for later in the year on the landscape and maintenance plans, prior to implementation of the final stages of the project.

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