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.
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:
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.
People can get sick. Plant and animal life can get sick and die. Our beaches and waterways become dirty and degraded.
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.
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 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:
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.
Updated July 2018