15 May 2014

Unearthing an Urban Stream

From Our Changing World, 9:06 pm on 15 May 2014

Stream restoration in La Rosa reserve in West Auckland

The La Rosa Reserve before and after the daylighting project to return two streams to the surface. (images: Auckland Council)

Auckland Council stormwater engineer Tom Mansell estimates Auckland loses up to 11 kilometres of stream each year through culverting. "We’ve spent many years just trying to put our stormwater and freshwater away so we can build over the top of it,” he says.

However, two previously piped sections of streams in West Auckland have now been opened up thanks, in part, to his design. Orignally culverted in the 1970s, the Parahiku and Waitahurangi (Avondale) streams were piped in La Rosa Reserve to make life easier for the park's maintenance contractors so they could mow the grass. But the site was prone to flooding and often became boggy in winter, making it all but inaccessible.

It was this disruption that became the catalyst for the reserve’s rejuvenation and made La Rosa Reserve the first dedicated stream daylighting project in Auckland. In all, 5,000 cubic metres of clay and 180 metres of pipe were removed and 600 cubic metres of basalt rock was imported to help form the new channels of the streams. Trees cleared on the site were also used for slope stabilisation, as well as in-stream woody debris features for enhanced habitat. Community planting days were held, with residents helping to plant the stream and establish a community orchard. Pa harakeke or flax plantings have also taken place along the banks, and it’s hoped it will be harvested for weaving in years to come.

Prior to opening the southern stream up, testing showed there were no traces of stonefly, mayflies or caddisfly – three insects that are good indicators of water quality. However, within two months of the project’s completion, four species of the insects were detected, along with shortfinned eels and whitebait.

While Tom Mansell is the first to agree that the project has been given the Rolls-Royce treatment, he believes that lower budget projects could be carried out across Auckland to make streams “part of people’s everyday lives”. And he says the community inclusion in La Rosa Reserve project has been paramount to its success.

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