Harbour research & publications

The Porirua Harbour and Catchment Management Programme has undertaken research and generated publications about the harbour and its catchment.

Key findings for Porirua harbour

  • Sedimentation is getting less
    Between 2009 and 2015, our underwater sediment survey (called a bathymetric survey) has shown a reduction in sedimentation in Porirua Harbour. Check out the survey results (1.58MB pdf). Recent floods may have increased sedimentation rates, at least in the short-term.
  • Steady improvement in the health of the cockle population 
    The Cockle Survey 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
  • Recreational water quality continues to be of concern
    The Porirua Harbour Trust annual 'scorecard' assess the implementation of the Porirua Harbour Strategy 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.

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

Research findings

A series of annual and longer-term research projects have been 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 condition, particularly in Pāuatahanui Inlet,
  • moderate levels of heavy metal contamination in parts of the Onepoto arm, largely from roads and stormwater systems,
  • algal growth spreading throughout the harbour, indicating nutrient enrichment,
  • high nutrient levels preventing seagrass from being restored,
  • big opportunities to improve the quality of streams affected by sediment and contaminants,
  • dredging would make little improvement to harbour flushing and not last long,
  • the harbour still has the basis of a sound ecology that would benefit from reductions in sediment, contaminants and nutrients,
  • reducing sediment from rural erosion and urban development is key to protecting and improving the harbour’s health.

Read the reports

Plans and reports

Public seminar presentations

Current harbour conditions

What other organisations are doing