Chelsea Ponds - The Complexity of Water Quality Management of De Facto Stormwater Ponds

The Chelsea Ponds were created to provide a reliable fresh water supply for the Chelsea Sugar Refinery on Auckland’s North Shore. The freshwater habitat that they provide has historically supported numerous fish and bird species, as well as providing for various recreational human activities. With the increasing urbanisation within the catchment, these ponds have increasingly become de facto stormwater treatment ponds, leading to accumulation of sediment and associated pollutants.

This paper reviews the various water quality and ecological issues present at Chelsea Ponds, including eutrophication and avian botulism. The potentially complex aetiology of these issues is addressed, considering past and present land use, including the role of accumulated sediment, air discharges and, potentially landfill leachate in these processes. The ongoing environmental management of the ponds is discussed, with reference to the amenity value that the ponds potentially provide. In this respect, this paper touches upon the wider issue of providing increased public amenity from ponds that perform a stormwater treatment function.