Urban

Occurrence

Many of New Zealand’s Urban Environments are located near water. Water provides for the basic needs of our communities and supports the natural and built environments that many of us call home. However, as our urban areas grow and change, we also need to be mindful of our impact on the water.

Nationally 0.71% or 186,700 ha of New Zealand is classified as Urban Environment. Auckland, Wellington, and Canterbury are the largest urban areas. Auckland also has the highest proportion of the region at 10.1% classified as Urban Environment.

Extent of the Urban Environment in New Zealand.

Region	Area (ha)	Regional (%)	National (%)
Auckland	49,505	10.10	0.19
Wellington	24,436	3.05	0.09
Canterbury	21,798	0.49	0.08
Waikato	17,918	0.75	0.07
Manawatu	13,888	0.63	0.05
Bay of Plenty	11,867	0.99	0.05
Otago	10,398	0.33	0.04
Taranaki	7,306	1.01	0.03
Northland	6,954	0.56	0.03
Hawkes Bay	6,768	0.48	0.03
Southland	5,988	0.19	0.02
Marlborough	2,247	0.21	0.01
West Coast	2,192	0.09	0.01
Nelson	2,101	5.00	0.01
Tasman	1,076	0.11	0.00

Water in the Urban Environment

In an Urban Environment, the natural hydrology has been significantly modified by impervious surfaces, such as roads, paving, housing, and other buildings. Infrastructure is built to transport drinking water, stormwater, and wastewater. In most urban environments, these waters are managed as separate networks.

Drinking water is sourced either from groundwater or from surface water takes and treated to drinking water standards to make it safe for consumption prior to distribution across a piped supply network to your tap.

Wastewater from residential, commercial, and industrial properties is transported through the sewer to the wastewater treatment plant. Treatment varies depending on the setup of the wastewater plant but typically follows these stages. Firstly, primary treatment removes solids through a screen and grit through settling, which is landfilled. Secondly the wastewater undergoes bacterial decomposition to reduce the organic composition and undergoes a secondary settling and filtration where the solid waste material is often spread to land. The last stage of the treatment process is disinfection, typically through chlorine or UV light to kill microbes. Treated wastewater is ideally discharged to land where the environment can provide additional treatment. However, in many Urban Environments treated wastewater is discharged to either surface water or directly into the sea. This limits our ability to interact with water near these locations, especially gathering mahinga kai and recreation. Improvements to infrastructure are being made in many places to reduce direct discharges to water.

The stormwater network collects local rainfall that falls on any impervious surface, such as roads, building roofs, and pavements. This water is rarely treated prior to discharge into a waterway or directly into the sea.

Landscape Characteristics

Urban Environments are under increased pressure from a wide range of pollutants. These pressures can be small, such as a spill or pollution incident, or large, created by the accumulation of contaminants over time. Pollutants in the Urban Environment include more than just the nutrients, sediment, and microbial contaminants typical of other Physiographic Environments. Common contaminants also include oils, grease, and hydrocarbons, heavy metals, pharmaceuticals, hormones, personal care products, pesticides, plastics, microplastics and wastewater. Urban Environments also produce a large volume of waste, which is landfilled.

In many Urban Environments around New Zealand, there are legacy problems related to how urban infrastructure networks and built environments have been developed. Cross contamination between the stormwater and wastewater networks may occur in areas with old infrastructure resulting in wastewater entering the stormwater network and discharged without treatment. Local councils monitor popular swimming spots, check with them if it is safe to swim, especially after heavy rainfall. Upgrades to stormwater and wastewater networks require significant investment and long-term planning to ensure that decisions made upstream protect downstream receiving environments. Common recommendations are to use nature-based or green engineering infrastructure solutions to mimic or work with processes found in the natural environment. This could include retaining, restoring, and enhancing existing elements of the natural drainage system, and integrate these elements into the urban landscape. This also has the added benefit of increasing resilience to natural hazards and climate change.

Contaminant Profile

Urban municipal wastewater has been treated through the wastewater treatment plant, however the degree of treatment is variable. The overall risk varies according to the waste composition, degree of treatment, and wastewater treatment plant effectiveness including disposal method. Discharges to land have a lower risk as there is potential for further land-based treatment relative to discharges directly to water.

Stormwater varies according to source area and degree of treatment. Treatment is not common practice in many Urban Environments.

Other contaminants also are present, including but not limited to heavy metals, hydrocarbons (petrol), oils and grease, pesticides, plastics, and microplastics, etc. Risk of loss is considered high as there is no removal of contaminants once they are transported.

Key Actions

In the Urban Environment it is important to conserve and reuse water resources. Drinking water, wastewater and stormwater are each valuable resources, and we should reduce their consumption and/or production and maximise their reuse. This includes increasing water-use efficiency by reducing drinking water demand and maximising the use of stormwater for irrigation of lawns and gardens. Don’t put anything down the stormwater drain you wouldn’t want to end up in your local waterway or beach. Reduce the amount of rubbish produced, especially non-biodegradable plastics and waste products that don’t easily breakdown in landfill.