Harbour research & publications

The Porirua Harbour and Catchment Management Programme undertakes research and generates publications about the harbour and its catchment.

Key findings for Porirua harbour

  • Sedimentation rates are fluctuating
    Between 2009 and 2014, our underwater sediment survey (called a bathymetric survey) had shown a reduction in sedimentation in Porirua Harbour. Check out the survey results (1.58MB pdf). However, floods over 2015/2016, increased sedimentation rates - at least in the short-term. A more settled 2017 and an exceptional 2017/18 summer should be good news for relatively lower sedimentation rates.
  • Steady improvement in the health of the cockle population (until recently)
    The Cockle Survey of Pāuatahanui Inlet is done every three years by GOPI (Guardians of Pāuatahanui Inlet) and analysed by NIWA. Until the 2016 survey, cockle numbers steadily increased. A series of floods in 2015/16, including just before the 2016 count, showed the first decrease in cockle numbers. GOPI cockle survey. The first Shellfish Survey of the Onepoto Arm was done in November 2017. Results will be available mid-2018.
  • Recreational water quality continues to be of concern
    An annual survey of Harbour User groups and the Porirua Harbour Trust annual 'scorecard' assesses implementation of the Porirua Harbour Strategy, recreational water quality and general harbour health.
    Porirua Harbour Trust annual state of the harbour scorecard

Literature review

Our literature review of information published about the physical and natural history of Porirua Harbour and catchment.

All literature identified in the review is also available at Porirua Public Library. 

Research findings

A series of annual and longer-term research projects are being undertaken to monitor changes in Porirua Harbour. Critical aspects highlighted by these reports are:

  • sediment is the most significant threat to the harbour’s current and future health, particularly in Pāuatahanui Inlet,
  • moderate levels of heavy metal contamination exist in south-western parts of the Onepoto arm, largely from roads and stormwater systems,
  • recurring algal growth throughout the harbour, indicates nutrient enrichment,
  • high nutrient levels prevent seagrass from being restored,
  • big opportunities exist to improve the quality of streams affected by sediment and contaminants,
  • dredging would make little improvement to harbour flushing and public and ecological health,
  • the harbour still has the basis of a sound ecology that would benefit from reductions in sediment and contaminant inflows,
  • reducing sediment run-off from rural erosion and urban development is key to protecting and improving long-term harbour health.

Read the reports

Plans and reports

Public seminar presentations

Current harbour conditions

What other organisations are doing