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.
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.
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
- Developing a citizen science monitoring programme for Te Awarua-o-Porirua Harbour and catchment. (640 MB) Review of citizen science methodologies for monitoring freshwater and marine environments.
- Developing a citizen science monitoring programme for Te Awarua-o-Porirua Harbour and catchment. Summary of monitoring activities.
- The health of our Harbour and Streams.
- Restoring the health of our harbour and streams. Vision: By 2040 Te Awarua-o-Porirua Harbour is safe for marine life and swimming, with all catchments riparian planted.
- Porirua Harbour Intertidal Fine Scale Monitoring Report 2008–09 (4.4MB pdf) assessed the ecological health of selected locations by analysing sediment nutrients, toxins and biota.
- Broad-scale Habitat Mapping Report (6.7MB pdf) assessed the sediments and habitat within intertidal areas of Porirua Harbour.
- Ecological Restoration Priorities for the Porirua Stream and its Catchment (1.8MB pdf) identifies the native species and habitat in this extensive stream system, the threats to these and other natural resources, and makes recommendations for ecological restoration.
- Porirua Stream: Your stream, your catchment (415KB pdf) summarises the 'Ecological Restoration Priorities' report and provides a lift-out Best Bets planting guide (1.2MB pdf) for restoration plants.
- Porirua Harbour Bathymetric Survey March 2009 (1.8MB pdf) and the follow-up survey of 2015 (1.58MB pdf) describe the processes and results of the most comprehensive and accurate surveys of the harbour's seabed.
- Patterns and Rates of Sedimentation Within Porirua Harbour 2009 (2.6MB pdf) compares the 2009 bathymetric survey with previous surveys dating back to 1849. Particular analysis of sedimentation changes between the 1974 survey and today.
- Porirua Harbour Targeted Intertidal Sediment Quality Assessment (2MB pdf) provides detailed assessment of some specific areas of contamination.
- Porirua Harbour Intertidal Macroalgal Monitoring (1.5MB pdf) analyses the coverage and significance of algae growth (predominantly sea lettuce or ulva) within the harbour.
- Stormwater Contaminants in Urban Streams in the Wellington Region (813KB pdf) has significant references to the Porirua Stream.
- Porirua Harbour Subtidal Sediment Quality Monitoring (1.2MB pdf) records the results of the 2010 survey.
- Sedimentation Zones and Rates (1.38MB pdf) within Pāuatahanui Inlet and the Onepoto arm of Porirua Harbour identifies sedimentation rates in localised zones covering the whole harbour, to help with catchment modelling in 2011.
- Porirua Harbour – Assessment of Effects on Hydrodynamics from Proposed Dredging, 2011 (2MB pdf) looks at the effectiveness and physical sustainability of strategic localised dredging in Pāuatahanui Inlet.
- Porirua Harbour's Sediment Problems: causes and solutions (3MB pdf) (links to pdf) was a presentation by Dr Mal Green summarising harbour research over 2011 and its implications for harbour and catchment management.
- A Seagrass Restoration Assessment (1.9MB pdf, 35 pages full colour) (links to pdf) was completed by NIWA in May 2012 and identified the possibilities and priorities for seagrass planting.
- A Fish Survey is a joint effort between Ngāti Toa Rangatira and NIWA, involving a literature search, oral history and field surveys of fish and shellfish numbers.
- Porirua Harbour Community Environmental Perception Survey Report, 2014 (2.9MB pdf) was the baseline survey undertaken to establish awareness, attitude and behaviours of the communities within the Porirua Harbour catchment.
- Pāuatahanui Inlet Cockle Survey December 2013 (2MB pdf) shows a significant progressive improvement in cockle numbers and inlet health.
- Te Awarua-o-Porirua Harbour: Report of Survey & Verification of Sedimentation Rates 2015 (1.6MB) indicates that sedimentation rates were lower in both arms of the harbour five years after the 2009 survey.
- Porirua Stream Mouth and Estuary Enhancement Plan - PSMEEP (8Mb pdf).
- Map - Porirua Stream Restoration Priorities By Sub-catchment (234KB pdf).
- Land-based effects on coastal fisheries - Ministry of Fisheries.
- Report of Joint Hearing Committee on Draft Harbour Strategy (835KB pdf)
- Geographic Board’s gazetted description of notice of new and altered geographic names for Porirua Harbour and catchment areas.
Plans and reports
Public seminar presentations
Current harbour conditions
What other organisations are doing