Cox's Creek improvement project
Background |
Options assessment | Proposed
works | Expected benefits
Cox's Creek is a tidal channel that flows through Cox's Bay
Reserve before entering Waitemata Harbour. The creek is fed by a number of
stormwater outlets that drain the Grey Lynn catchment, and from time to time it
also receives sewer network overflows.
Poor water quality and odour have long been a problem at Cox's
Creek. Studies
have been undertaken to assess the causes of the pollution issues and the most
effective management options for the creek.
The
first step in solving the problem is to reinstate tidal flow in the creek, which
will help improve water quality. We will do this by removing polluted sediment
that has clogged the creek and clearing points of water constriction and ponding.
To
reduce the sewage overflows into Cox's Creek, Metrowater has installed grit
traps to help prevent wastewater pipe blockages, and will be separating some
local combined stormwater-wastewater pipes in the near future.
In the
longer term, Auckland City Council and Metrowater are working to separate the
major combined stormwater and wastewater networks in the city. These large scale
works are still some time away, as they will need to fit with the wider regional
drainage strategy being developed by Watercare Services Ltd.
Before
the first stage of works can take place (reinstating suitable tidal flow in
Cox's Creek), the council needs to obtain resource consents.
Project update
Stage 1 of the improvement works at Cox's Creek has
recently been completed. The design of Stage 2 has been revised slightly as a
result of feedback received from members of the public and Ngati Whatua. It is
now proposed to extend works up the Wharf Rd arm of Cox's Creek to mitigate
odour issues experienced in this area as well, and leave the pool adjacent to
Richmond Rd until the completion of Stage 2 (to determine if filling is actually
necessary to achieve the goals of the project). Extensive riparian restoration
planting is also proposed, and we look forward to the ecological and amenity
benefits that the project will bring to the creek and park.
Re -prioritisation
of projects has meant that Stage 2 works are now scheduled for the 2010/2011
earthworks season, subject to financial availability and obtaining resource
consents.
Brief history
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Mangrove pinch point, where water is held
back by mangroves. |
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Cox's Creek has been significantly modified during the last 100 years, including
the formation of a causeway (West End Road), land reclamation (Cox's Bay
Reserve) and channel alignment changes with a history of dredging and bunding.
In 1982 the reserve was opened for public use - incorporating playing fields,
parking, a road, walkways, a footbridge, a playground, the sports pavilion and
planting.
Over the years, Cox's Creek has accumulated road gravel and sediment from
stormwater flows and bank erosion. The build up of this material together with
the relatively flat slope of the creek, has resulted in ponding of stagnant
water.
Adding to this, the surrounding residential area is serviced by a combined
stormwater and wastewater system that is overloaded during larger rainfall
events. Sewage solids, organic matter, nutrients, bacteria, litter, heavy metals
and hydrocarbon contaminants are regularly discharged into the creek.
Although the interactions producing the unpleasant smell and visual disturbance
are complex, they are mainly caused by biodegradable pollutants in the water and
sediment, combined with a poor flushing regime (the wash out of sediment and
pollutants by tidal cycles and stream flows).
This problem is worsened by mangroves constricting certain sections of the
watercourse, the scour pools, and warm summer temperatures.
