Best Practise

The following section highlights potential environmental effects of stormwater and wastewater and outlines the elements of best practise that can be adopted to reduce their impacts. This list is by no means exhaustive. 

1) In periods of heavy rain stormwater increases the volume of wastewater so that wastewater treatment plants cannot treat it all

  • Replace combined sewage/stormwater systems with separate networks
  • Monitor and maintain sewage pipes to prevent leakage

2) Earthworks generate increased sediment

  • Prepare catchment management plans to protect natural channels, restore wetlands and provide stormwater retention ponds
  • Require an erosion and sediment control plan as part of building consent applications and include strict conditions in resource consents to require adequate sediment detention methods to be used. These may include chemical sediment control (flocculation), silt fences, decanting earth bunds or sediment retention ponds.
  • Undertake major building works at times of the year when rainfall is unlikely to be heavy
  • Retain existing vegetation wherever possible and effect revegetation as soon as possible
  • Stabilise disturbed areas as soon as possible, and limit the area disturbed as much as possible
  • When considering zoning for plans, pay particular attention to the potential for the cumulative effects of earthworks in an area to cause significant sedimentation of the receiving marine environment

3) Development of urban areas releases large amounts of sediment 

  • Use sediment detention measures such as silt fences, earth bunds, sediment detention ponds and chemical sediment control (flocculation)
  • Avoid  major building works during times of the year when rainfall is likely to be heavy
  • Retain existing vegetation wherever possible and revegetate disturbed areas as soon as possible
  • Limit the size of the disturbed areas

4) Urban areas create large amounts of stormwater which transports toxic pollutants and sediment

  • Reduce the area covered by impervious surfaces. District plans can include maximum site coverage provisions and encourage the use of permeable paving
  • Use networks of swales and planted areas to reduce and filter stormwater runoff in urban areas
  • Restore wetlands
  • Collect and treat stormwater before discharge
  • Use roof rainwater collection tanks

5) Wastewater treatment works fail to remove organic matter, nutrients and micro-organisms from the effluent before it is discharged 

  • Use the best available technology (tertiary with UV pathogen treatment or similar) in wastewater treatment plants to ensure that the water discharged into the coastal marine area contains minimal amounts of organic matter, micro-organisms and nutrients
  • Plan the construction of wastewater treatment works so that they have the capacity to deal effectively with all the waste generated by the community, and with future or seasonal growth in the area.
  • Minimise stormwater ingress into the wastewater network.

6) Septic tanks 

  • Construct septic tanks only in areas where the soil is suitable
  • Construct septic tanks only where there is an adequate amount of land surrounding the property to cope with the amount of effluent generated
  • Adequately maintain septic tanks and soakage fields to ensure that they do not fail
  • Use the latest technology in designing effective septic tank systems

7) Wastewater enters the stormwater system and from there enters the catchment untreated

  • Prevent illegal connections
  • Include stormwater control measures such as permeable paving in new developments and modifications to existing urban areas
  • Adequately maintain piping
  • Use swales and planted areas as buffers to limit and filter stormwater run-off
  • Restore old wetlands to filter and limit the flow of stormwater to the sea

8) Industrial processes result in the discharge of effluent into the catchment 

  • Use the best available technology to minimise pollution, and instigate programmes for the reduction of waste
  • Constructed or restored wetlands are an alternative treatment and disposal system, they can be effective at removing nutrients as well as organic material

9) Heavy metal contamination in stormwater 

  • Phase in a prohibition on the use of unpainted zinc roofs
  • Reduce vehicle use through good urban design and provision of public transport, biking trails and pedestrian friendly routes
  • Require copper-free brake linings for vehicles and more chemical-friendly tyres

Last updated at 1:42PM on February 11, 2018