Cox's Creek improvement project

Background | Options assessment | Proposed works | Expected benefits

Image of Cox's Creek. 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.

Brief history

Mangrove pinch point, where water is held
back by mangroves.

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.