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  Environment » Natural Resources » Water » Urban stormwater management

Urban stormwater management

Photograph of coastal stormwater drain outlet>> Go to stormwater management guidelines

Urban development in the Waikato region has had significant impacts on the natural water cycle in urban areas. Historically the drainage of urban areas focussed on conveying stormwater into receiving waters as quickly as possible to prevent flooding from occurring. This approach enabled urban areas to be established and to grow, however it has led to the degradation of natural waterways in our region.

Urbanisation results in the establishment of significant impervious surfaces such as roofs, roads and other hard surfaces that cover the land. These surfaces prevent rainfall from soaking into the ground and cause impacts related to the increased stormwater runoff from those surfaces.

Impervious surfaces also convey contaminants efficiently into drainage systems where they are transported to receiving environments, potentially harming aquatic ecosystems, plants and animal life and people’s health.

What causes stormwater quantity effects?

The creation of impervious surfaces in urban areas reduces the amount of water that soaks into the ground and hence changes the natural hydrological cycle. Urban development can also remove significant amounts of vegetation resulting in reduced plant moisture uptake, evapotranspiration and interception (where a plant’s leaves will intercept rainfall and reduce contact with the ground). These processes cause impacts related to the increased stormwater runoff from those surfaces, including:

  • Reduced base flow to streams
  • Increased flow rates, velocities and volumes of stormwater runoff, which can cause flood effects and can increase erosion of waterways and coastal environments.
  • Degradation of stream channel physical structure (increase in bank instability, structural constraints (stream crossings, channel reinforcement), incised channels and reduced connectivity with the floodplain).

What causes stormwater pollution?

When rain contacts the ground and drains downhill, a range of contaminants are entrained in the stormwater depending on the land use type, hence stormwater becomes polluted. Urban activities typically increase and introduce new contaminants when compared to runoff from natural areas, which can cause adverse effects in the receiving environment.

Some of the key pollutants associated with urban stormwater include: sediments, pathogens, total and dissolved metals, hydrocarbons and oil, organics and pesticides, nutrients and gross pollutants.

An additional impact of urbanisation is an increase in water temperature of stormwater runoff from contact with hard stand areas heated by the sun. Thermal effects of stormwater can have a significant adverse effect on aquatic species in downstream receiving environments.

A simple way to see stormwater effects is to walk along an urban stream and note the changes in the stream as the land use changes. Area with greater levels of imperviousness discharge higher quantities of contaminants and water volumes that quickly change the physical structure and quality of the stream. Effects are particularly evident where the upper reaches of a catchment are undeveloped and have native bush. A visual survey can document comparative downstream changes, such as channel erosion locations, fish passage blockages and areas of sedimentation.

Effects of stormwater pollution

People can get sick. Plant and animal life can get sick and die. Our beaches and waterways become dirty and degraded.

  • Drinking water can become contaminated.
  • Food sources such as shellfish, eels, koura, watercress and fish can become contaminated.
  • Bacteria and toxins can enter your body through water activities, such as swimming, especially just after rain.
  • Toxic substances, such as vehicle wastes, pesticides and paint, poison streams and waterways.
  • Plant material, sewage, and some chemicals starve water of oxygen, choking aquatic and marine life.
  • Large amounts of rubbish from stormwater ends up in waterways and on our beaches. It looks ugly, and it's bad for the environment.
  • Heavy metals from stormwater build up in the tissue of fish and seafood and cause poisoning.
  • Bacteria and viruses from untreated human and animal wastes are allowed to drain into natural waterways, making them unsafe for swimming and drinking.
  • Sediments from waterblasting, concreting, and earthworking operations affect water clarity.

Waikato Regional Council helps prevent and manage stormwater discharges

  • We have provisions and rules for stormwater discharges. Check out our policies and plans, especially our Regional Policy Statement, Waikato Regional Plan and Regional Coastal Plan.
  • We regularly monitor the water quality of our region's waterways and coastal areas. This helps us with policy making and resource consent decisions.
  • We regulate and monitor activities that impact on our rivers, lakes and coastal marine areas.
  • We provide advice and support for efforts to reduce the impacts of farming on waterways through fencing and planting waterway margins.
  • We support and advocate practices that try to reduce and prevent contaminated water run off.
  • We prohibit stock from accessing high priority waterbodies and coastal marine areas.
  • We support care groups. Their riparian management work, such as planting and fencing helps decrease sediment and nutrient runoff to estuaries and the coast via streams and rivers.
  • We support environmental education school programmes throughout the region.

Stormwater management guidelines

We have produced two guidelines on how to manage stormwater in the Waikato region.

The Waikato Stormwater Management Guideline has been developed to replace the use of Auckland Council’s ‘Stormwater Management Devices – Design Guidelines Manual, Technical Publication 10’ commonly referred to as TP10.

Waikato Stormwater Management Guideline [PDF, 9.9 MB]
(external link)

The Waikato Stormwater Runoff Modelling Guideline has been developed to replace the use of Auckland Council’s ‘Guidelines for Stormwater Runoff Modelling in the Auckland Region, Technical Publication 108’ commonly referred to as TP108.

Stormwater Runoff Modelling Guideline [PDF, 2.8 MB]

Managing your stormwater - what you can do

Stormwater drains are designed to carry clean rainwater into our waterways. Have a look around: there'll probably be drains right outside your front gate, in your own back yard or on your farm.

These drains are not a dumping ground for waste liquids and materials. But pollutants get into our streams and coastal water because people allow waste, contaminated water and rubbish to get into them.

Many normal everyday activities can pollute stormwater, if any related waste or dirty water gets into the drains. Washing your car or paint brushes, washing down spilt chemicals or letting livestock wander through drains. You need to remember that stormwater and wastewater systems are quite different:

  • Stormwater goes directly into waterways.
  • Wastewater is treated before it reaches waterways.

Only clean rainwater should enter stormwater drains and the region’s waterbodies. Don’t be afraid to ask for advice if you’re not sure about what you should be doing to stop pollution getting into them.

On the work site

  • Follow best work practices for managing any run off.

Around the home

  • Make sure that any contaminated water from your property doesn’t enter the stormwater drains.
  • Wash your car and boat on the lawn so that the soapy water and dirt doesn’t enter the stormwater drains, and wash your water-based paintbrush at an inside sink or on the lawn or garden.
  • Clean up any spills or dirt around the home by soaking up the mess or sweeping it. Don’t just wash it down the stormwater drain.
  • Don’t hose housewashing, concrete cleaning or any other chemicals down the stormwater drain.

Around the farm

  • Install proper holding ponds for farm animal wastes.
  • Fence off streams from cattle.
  • Plant riparian margins along watercourses within your property if you have any.
  • Consider fencing off and replanting natural wetlands within your property if you have any.

Other suggestions

  • Store your chemicals in a safe place.
  • Don’t tip unwanted paint, oil or any other substance down the stormwater drain. Dispose of them responsibly.

  Updated July 2018

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