Finding sand to feed a growing city

Finding sand to feed a growing city

Auckland’s construction industry needs large quantities of sand for buildings and roads. Some of this sand is extracted from Kaipara Harbour.

In 1997, the Minister of Conservation issued Mt Rex Shipping and Winstone Aggregates with 20-year consents to dredge sand from the harbour entrance. Consent conditions included the requirement to undertake a study of the sand system and whether extraction is likely to cause adverse environmental effects over the term of the licence.

The Kaipara Sand Study Working Group (comprising the two extraction companies, Auckland Regional Council, Northland Regional Council, Ngati Whatua, and DOC) commissioned NIWA to do this work. We looked at the physical effects of the sand extraction, including whether or not extraction was causing erosion of the shores.

The 3 year study involved extensive technical investigations, using such diverse methods as sidescan sonar surveys, sediment sampling, and deployment of instruments in the harbour. We found the volumes of sand stored in the dunes, beaches, and seabed of the tidal inlet are vastly greater than the volumes of sand extraction. Large amounts of sand were coming into the harbour from the open coast to build banks and a large sand island in the extraction area. We worked out how much sand could be extracted from various sites with minor adverse effects, and recommended some changes to existing monitoring of the beaches and the position of the shoreline.

Research subject: Coasts