Reducing the effects of impervious surfaces

Proposed Plan Change 22 and Variations 2, 3 and 4

The proposed plan changes and their associated variations were publicly notified on 12 April 2007. Submissions closed on May 18, 2007. A summary of submissions is currently being prepared for each proposed plan change.

Urban development has many effects on the environment, especially the way in which it affects stormwater runoff. Rainfall over an urban environment is affected in the following ways:

• Hard surfaces such as roads, driveways and roofs prevent water from soaking into the soil.
• Nice smooth pipes and channels are constructed which causes stormwater to run off more quickly.
• Vegetation is removed. Vegetation takes up water for its own use as well as intercepting rain before it hits the ground helping to reducing runoff and erosion.
• The soil is compacted, making it more difficult for water to soak into the ground.
• Many pollutants are carried into the environment by stormwater, especially from roads and earthworks.
• Hot bitumen and concrete roads and parking areas heat up stormwater affecting fish and other aquatic organisms in the streams and estuaries.
• Less water soaking into the ground means streamwaters dry up with no groundwater reserves to feed the watercourses during summer months.

One third of the city’s 13,000 hectares is now covered by impermeable surfaces. North Shore City has even been described as ‘Turtle City’ by a visiting overseas consultant. Yet the same amount of rainfall occurs as when the city was completely uninhabited by humans.

There is a continuing demand for land to develop and to add more impervious surfaces as more and more people move into North Shore City.

The traditional approach to stormwater management was to get rid of stormwater as quickly and efficiently as possible out to sea. This has had serious effects on our environment including increased risk of flooding, serious erosion of our streams, reduced water quality and a loss of biodiversity and amenity.

Our response was to engineer solutions using larger pipes and lots of concrete.

Proposed Council approach

Many people including the council now realise that the old methods of stormwater management are no longer acceptable and that a new more sustainable approach is required. The new approach aims to address the cause rather than treat the symptoms. We need to bring the rates and volumes of our stormwater flows back to a more natural and manageable level that the streams and waterways can cope with. Our strategy is to:

• Focus stormwater management requirements on those areas which are the most sensitive and where the most benefits will be achieved.
• Take a multi-layered approach of - minimising hard surfaces and disturbance, managing stormwater on individual properties, and providing communal stormwater treatment systems to cope with the rest.
• Encourage methods for on-site stormwater management which provide multiple benefits such as:
  • Raintanks - which collect rainwater from the roof for use in the toilet and laundry. These serve more than one purpose as they collect and slowly release water at a more manageable and natural rate to the streams and out to sea, plus they reduce the total volume of stormwater running off the site, and reduce the demand for water which has to be piped in from elsewhere.
  • Rain gardens - specially designed gardens with free draining soil and drains beneath them. These reduce the volume of stormwater runoff as well as slowing it down and also filtering out contaminants. These also act as normal gardens around the property.
• Take a long term approach to the improvement of stormwater and stream management across the city by requiring better management of stormwater on individual sites when people develop or re-develop their properties.

Useful links
Proposed Plan Change 22 and Variations 2, 3 and 4 PDF (151 KB)

• Map 1 (1.34MB)
• Map 2 (1.90MB)
• Map 3 (3.53MB)
• Map 4 (1.32MB)
• Map 5 (1.32MB)
• Map 6 (2.33MB)
• Map 7 (1.29MB)

Stormwater management areas
Stormwater GIS Viewer

For more information

Please contact Susan Andrews, Environmental Policy on:

Telephone:	09 486 8600
Email:	Actionline@northshorecity.govt.nz