Sedimentation of Tauranga Harbour is a natural process. Development however has increased the rate of infilling of the harbour, creating adverse effects on ecology, promoting the colonisation of the harbour with mangroves, and shallowing navigation channels. The rate of infilling has been increased by human activities on land associated with development.
For more information about Sedimentation in Tauranga Harbour read our Tauranga Harbour Factsheets.
Sedimentation issues affect many aspects of life in the harbour. Navigation channels have shallowed, mangroves have proliferated and there is evidence of widespread ecological losses eg. eel grass beds, juvenile fish areas, shellfish beds. The average mud content of many of the western estuaries, including Welcome Bay, Waimapu Estuary and the Waikareao Estuary, in particular has increased significantly. These changes are to a large extent driven by historical events when development took place with very little control.
Looking to the future, the Tauranga Harbour catchment will continue to face pressure as a result of urban growth and climate change. Bay of Plenty Regional Council commissioned a three year study by NIWA to investigate sediment sources and deposition processes in southern Tauranga Harbour. The Tauranga Harbour Sediment Study was completed in December 2009 and the reports are available below.
NIWA Technical Reports
- Tauranga Harbour Sediment Study: Assessment of Predictions for Management - Amended May 2010 (6MB, pdf), $25
- Tauranga Harbour Sediment Study: Catchment Model Results - Amended May 2010 (1.8MB, pdf), $12
- Tauranga Harbour Sediment Study: Harbour Bed Sediments (8.3MB, pdf), $12
- Tauranga Harbour Sediment Study: Hydrodynamic and Sediment Transport Modelling (2.7MB, pdf), $12
- Tauranga Harbour Sediment Study: Implementation and Calibration of the USC-3 Model (Final report - May 2009) (3.2MB, pdf), $15
- Tauranga Harbour Sediment Study: Sediment Load Model Implementation and Validation (2MB, pdf), $25
- Tauranga Harbour Sediment Study: Specifications of Scenarios (1.4MB, pdf), $10
- Tauranga Harbour Sediment Study: Predictions of Harbour Sedimentation under Future Scenarios - Amended May 2010 (850KB, pdf), $15
Land management around Tauranga harbour
The Regional Land and Water Plan governs earthworks for land development through the resource consent process, which places requirements to control sediment run-off. A review of the management rules and practices dealing with sediment generating activities is planned.
Land management programmes run by Bay of Plenty Regional Council, such as fencing of stream margins around the harbour, revegetation of steep land, and farm environment plans are important in reducing the amount of sediment entering the harbour. Coupled with the work of Estuary Care groups around the harbour, improved land management plays an important role in reversing the effects sedimentation.