Characterising stormwater quality

Urban stormwater can contain a variety of contaminants at a wide range of concentrations, collected as the rainwater runs over impervious surfaces.

Urban stormwater can contain a variety of contaminants at a wide range of concentrations, collected as the rainwater runs over impervious surfaces.

Contaminants include:

  • sediment
  • trace metals such as copper, lead and zinc
  • hydrocarbons from petrol and oil
  • pesticides
  • pathogenic bacteria and viruses
  • and trace organics such as phthalates and surfactants.

The amounts of these can vary between residential, commercial and different industrial land uses.

NIWA's scientists can help answer questions such as:

  • what is in the stormwater from this site?
  • are the contaminant concentrations higher or lower than typical?
  • is the stormwater likely to cause adverse impacts in downstream receiving environments?
  • how do I collect representative samples?

Stormwater quality can be difficult to characterise as storm events are intermittent, flows fluctuate and concentrations vary with time, with many sites exhibiting a first flush. Our approach is to install flow monitoring equipment to trigger automatic sampling during several rainfall events to ensure that collected samples are representative.

NIWA has considerable experience in stormwater characterisation around New Zealand including the following projects:

  • Characterising stormwater quality in the industrial land use catchment of Haytons Stream, Christchurch, by sampling under dry conditions and storm events.

Read the full report: Haytons Stream catchment water quality investigation 

  • Characterising road runoff quality and investigating differences in the amount of sediment, copper and zinc from heavily used roads compared to low trafficked roads.

Read the full report (#395): Enhancing the control of contaminants from New Zealand's roads: results of a road runoff sampling programme (PDF 2.7 MB)

  • Characterising stormwater quality and stream water quality from residential, industrial and commercial land uses for councils to gain resource consent for their stormwater networks. 
  • Reviewing particle sizes of sediments in Auckland stormwater and their associated settling rates to improve understanding and design of stormwater treatment systems. 

Read the report: Fall Velocities of Stormwater Sediment Particles: Literature Review (PDF 756 KB)

  • Monitoring sediment concentrations discharged from earthworks on small sites.
  • Measuring contaminants in sediments collected in catchpits from small industrial sites to screen for metals and organic contaminants from different industries. 
  • In addition, NIWA is currently leading the development of a national database for holding and reporting urban stormwater quality.

Find out more about our urban stream and stormwater quality database

Haytons stream stormwater quality characterisation. Credit: NIWA
Road runoff characterisation. Credit: NIWA
Stormwater and stream water quality characterisation. Credit: NIWA
Sediment particle size characterisation. Credit: NIWA
Earthworks sediment discharge concentration monitoring. Credit: NIWA
Catchpit-collected sediment characterisation. Credit: NIWA