Estimated reading time: 3 min
Why is the Whau River dirty?
Wastewater and stormwater drainage systems which date back to the early 1900s are still being used in suburbs surrounding the Whau River.
Wastewater and stormwater
Wastewater is water that has been contaminated by human use, and includes used water from any combination of domestic (bathroom, toilets, kitchen and laundry), industrial, or commercial activities. Wastewater can contain physical, chemical and biological pollutants.
Stormwater is water that originates from rain. Stormwater can soak into the soil (infiltrate), be stored on the land surface in ponds and puddles, evaporate, or contribute to surface runoff. Most runoff is conveyed directly to nearby streams, rivers, or other water bodies (surface water) without treatment. In the Whau River, unmanaged stormwater can create two major issues: one related to the volume and timing of runoff (flooding) and the other related to potential contaminants the water is carrying (water pollution).
The Whau River stormwater catchment drains to the Waitematā Harbour. Any water overflows within the Whau River stormwater catchment are discharged to the Whau River where the tide moves the water in and out of the estuary.
The drainage systems consist of separate wastewater and stormwater systems and includes combined sewer systems. Combined sewer systems consist of one pipe to convey both wastewater and stormwater, and are common in cities of a similar size and age to Auckland.
When it rains the overflow points within the Whau River discharge a dilute mixture of urban stormwater and wastewater into urban streams and also directly into the Waitematā Harbour. This can result in no swimming alerts at beaches, with impacts on important cultural and community values and risk of illness from swimming, triggered by enterococci bacteria in the water. The bacteria is common in animal and human faeces, and ends up in the water through animal and bird droppings, or from stormwater runoff and wastewater discharges.
Other water pollution
- The Whau catchment area contains a range of residential (covering 66% of catchment area), commercial (2.2%) and industrial (10%) land uses, all of which are sources of stormwater contaminants. Often there are unsafe practices, for example dumping rubbish in streams, washing cars on the road or accidental spills.
- Rainfall runoff from roads is a source of stormwater contaminants, including tail pipe emissions, oil dripping, as well as wear and tear including from tyres and brakes pads.
- Roof runoff can contain pollutants, such as metals from old or poorly maintained iron roofs.
- There are a number of closed landfills located in the Whau River catchment area. Many of these landfills are now public parks and sports fields. Landfills can create leachate. Although Auckland Council has programmes in place to control leachate, there may be a possibility of uncontrolled discharges from closed landfills going into the water.
Why the pathway will make the Whau River cleaner
One of the purposes of Te Whau Pathway project is to contribute to restoring the health of the Whau River and its environment.
A coordinated approach with mana whenua, the Henderson-Massey Board, the Whau Local Board, Auckland Council, Watercare and local communities will begin to bring the river back to its natural state. The first steps of this collaboration will create a plan called “Whau People. Land. Water. Plan.” This name was chosen to reflect the fact that our actions on land impacts the quality of our waterways.