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Conference
2006
Plants as infrastructure
Abstract:
Waiatarua
Wetland Restoration, Auckland City
GRANT
OCKLESTON
Auckland City has recently
completed the construction of a wetland stormwater treatment system
within the Waiatarua Reserve, east Auckland. The 41ha reserve used
to be home to a 22ha wetland formed around 9000 years ago when a
volcanic eruption isolated the catchment from the sea.
The wetland was utilised
by early Polynesian settlers as a source of food that was augmented
by clearance of surrounding land for additional crops. Significant
modification to the wetland occurred in the 1930s with the inclusion
of drainage channels that reduced the wetland size to around 6ha.
The channels and use of cattle for grassland and wetland margin
maintenance impacted public amenity and resulted in much of its
water purification and ecological value being lost.
Restoration of the wetland
involved significant public consultation and was constrained by
the need for flood protection of neighbouring residential dwellings
and challenging geology involving a thin surface crust underlain
by as much as 8m of soft peat. In designing work, it was necessary
to minimise the depth and extent of both excavation and filling,
and design hydraulic control structures that did not require substantial
stable foundations. Constructability was also a significant factor
in both design and contract structure.
This paper will set out
the broad treatment and flow design concepts, and the multiple objectives
required as design outcomes. It will describe the design approach
for the flow control structures and how construction was implemented.
The outcome has been a new, expanded wetland area, with improved
amenity and ecological values, and with an increased ability to
capture contaminants from urban stormwater runoff.
Grant Ockleston:
Manager Stormwater Projects, Auckland City Council
Email: grant.ockleston@aucklandcity.govt.nz
Graham Levy:
Senior Associate, Water and Environment, Beca
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