Site works in a rapidly growing city

Proposed Plan Change 25

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.

On most days in the city, construction begins on five new building sites – starting with earthworks. This means thousands of tonnes of earth are potentially exposed to being washed away by rain – and on average one truck load of soil is washed off these sites and into the city’s streams and drains every day.

Once very fine particles of clay are picked up and‘suspended‘ in water, and travel down gutters and stormwater drains, it’s in our streams and marine environments of the Waitemata Harbour and Hauraki Gulf – where the problems occur:

Biological effects

• Reducing water clarity and visibility– preventing animals from eating if they are unable to see their prey.
• Smothering aquatic life and food sources.
• Damaging the gills and mouthparts of animals.
• Altering habitats and destroying spawning areas.
• Increasing heat absorption and water temperature – affecting aquatic life.
• Stopping light penetration slowing photosynthesis and algae (food) growth.

Other pollutants

• Sediment also attaches to and transports other pollutants such as lead, hydrocarbons, nutrients and toxic substances – into streams and harbours where they accumulate and affect aquatic life.

Stream blockages

• Deposited sediment can infill waterways, reducing their water carrying capacity and increasing the risk of flooding.

Consumable water

• Water extracted for irrigation, stock or domestic water supplies can be affected.

Aesthetic values

• Sediment in stream, lake or coastal waters detracts from their aesthetic qualities.
• Clean, clear water is more conducive to recreation than ‘dirty’ water.
• Scenic values of waterbodies such as the Waitemata Harbour are enhanced by good water clarity.

Damage to property and public utilities

• Lower lying properties and roads can be inundated with sediment if adequate measures are not put in place.

Council will introduce new regulations:

1. To ensure developers of sites take full responsibility for managing exposed earth – keeping clean water away from earthwork areas wherever this is possible and treating stormwater that does pick up sediments before it leaves the building site
2. To require additional protection on sites where earthworks are planned for steep sites with a gradient of 1:4 or more.

Regulations will also ensure ’decompaction’ of soils – where soils have been stripped back to clay and compacted during the development process – to ensure the areas of grass and other vegetation that are reinstated once construction is complete – are able to absorb rainwater that falls on it – and to stop these areas from acting just like another area of concrete.

Useful links

Proposed Plan Change 25 PDF (53 KB)

For more information

Please contact Susan Andrews, Environmental Policy on:

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