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Te Awarua-o-Porirua Harbour and Catchment Programme

http://www.gw.govt.nz/te-awarua-o-porirua-harbour-and-catchment-programme

Te Awarua-o-Porirua Harbour and Catchment Programme

Updated 27 October 2021 1:50pm

Greater Wellington Regional Council works in a collaborative partnership with Porirua City Council, Wellington City Council, Ngāti Toa Rangatira, and a number of other agencies to address the issues of sedimentation, pollution, and habitat loss with the aim of improving the environmental health of Te Awarua-o-Porirua Harbour.

Figure 1. Looking out across the Pāuatahanui arm of the Harbour from the Pāuatahanui Wildlife Reserve.

Te Awarua-o-Porirua Harbour

Te Awarua-o-Porirua Harbour is the largest estuarine system in the lower North Island and encompasses two estuaries; the Onepoto arm and the Pāuatahanui arm, both situated northeast of Porirua City. The wider catchment covers an area of 18,470 ha and is a mix of rural farmland, lifestyle blocks, urban settlement, parkland, railway and roads. Water from this catchment flows into the Harbour, which is a nationally significant wildlife area that holds substantial cultural, recreational, economic, and ecological value.

The Pāuatahanui arm in particular provides a significant nursery area for fish, habitat for a range of coastal and wetland birds, and hosts one of the largest cockle concentrations in New Zealand. Salt marsh and seagrass habitats of regional importance also grow in and around the Pāuatahanui Wildlife Reserve.

Figure 2. Te Awarua-o-Porirua Harbour with an outlet to the sea to the west, the Pāuatahanui arm to the east, and the Onepoto arm to the south (Photo: Aidan Wojtas).

Issues

Urban and rural development in the Te Awarua-o-Porirua Harbour catchment over the past 150 years has had a big impact on the health of this estuarine system. Urban expansion, aging stormwater and wastewater infrastructure, forestry, rural intensification and roading continue to negatively affect the Harbour ecology.

The three key issues facing this valuable environment have been identified as excessive sedimentation rates, pollution and ecological degradation. The collaborative partnership are currently delivering a range of activities to address these issues, and to implement the Te Awarua-o-Porirua Whaitua Implementation Plan and accompanying Ngāti Toa Rangatira Statement.

Monitoring and research

We monitor estuarine sediment quality every year to understand the natural variation within the environment and the impacts of human activities. Our priority research areas are measuring sedimentation rates, identifying the main sources of sediment, and modelling where that sediment settles in the Harbour.  

This information helps us to identify which land-based activities contribute the most sediment and help to develop targeted solutions. Repetitive monitoring allows us to measure the health of the environment and if degradation is detected, we can use this information to implement preventative measures over the long-term. 

To achieve these objectives, we have:

  • Installed buried sedimentation plates throughout the Harbour,
  • Installed turbidity sensors at the bottom of the three largest streams to provide information on the volume of sediment entering the Harbour, and
  • Established a programmes for habitat mapping and monitoring sediment quality and marine invertebrate health.

Figure 3. Collecting environmental samples at intertidal sites in Te Awarua-o-Porirua Harbour for the January 2020 ecological survey (Photo: Salt Ecology).

Overall, the health of the Harbour is in gradual decline, largely due to the increased pressure of sedimentation. Our monitoring reveals a long-term harbour-wide increase in the extent of mud-dominated sediments indicating that targeted investigations and remedial action is urgently required.

Whaitua objectives were set by the Te Awarua-o-Porirua Whaitua Committee in 2019 to address the most pertinent problems facing Te Awarua-o-Porirua Harbour and implementation is ongoing through numerous community projects as summarised below.

For more information on environmental research in Te Awarua-o-Porirua Harbour please view the Te Awarua-o-Porirua Monitoring webpage and the annual data reports.

Project implementation

Mahi Waiora, which means ‘wellbeing of water’ is a programme aimed at developing a coordinated approach for implementing our goals on water quality and biodiversity.

Started in 2015, this programme was later expanded to include carrying out of some of the non-regulatory recommendations in the Whaitua Implementation Programme (WIP) for the Pouewe Water Management unit, situated north-west of the Pauahatanui Inlet.

The connecting of ideas, approaches and methods ensures our ability to deliver successful environmental outcomes at a catchment level. This multi-disciplinary approach encourages teams to co-design catchment plans and results, share information between groups, and set clear directional targets. Time-bound targets for water quality and biodiversity improvement are identified, and our catchment team with community members work towards achieving the defined targets.

A key objective of the Mahi Waiora programme is for us and mana whenua partners to collaborate in an integrated way to improve water quality and biodiversity.

In this programme, our catchment team with community members work towards achieving time-bound targets for water quality and biodiversity improvement.

If you have any questions or would like to be added to our mailing list for updates please email the team at mahiwaiora@mail.gw.govt.nz.

Restoration and community involvement

We support the restoration of our native biodiversity and habitats in a number of different ways.

Environmental restoration by community volunteers

We support community restoration activities throughout the Whaitua area, which encompasses the Te Awarua-o-Porirua Harbour catchment, by means of the Community Environment Fund. This fund supports a range of local groups to restore, maintain and protect our local taiao (environment).

Projects include native planting, weed removal, pest animal control, creation of lizard habitat, environmental education, and propagating plants in community nurseries for restoration projects.  

Figure 4. Weed clearing in Taupō Swamp (Photo: Friends of the Taupō Swamp and Catchment) and native planting efforts by Friends of Maara Roa (Photo: Christine Jacobson Photography).

School based environmental education and restoration

In addition to community restoration groups, we also support schools in teaching students about the Harbour and its waterways, and support students in undertaking projects to improve the health of their local environment. Student projects have included plantings, environmental clean-ups, fish passage restoration, and community engagement events and initiatives. We achieve this by:

  • Funding Mountains to Sea Wellington to run the Healthy Harbours programme, which can see students snorkelling in our harbour and assisting with monitoring of stream health.
  • Lending monitoring kits to schools to measure stream health and quantify marine biodiversity.
  • Funding student transport on fieldtrips to learn about harbour and stream health.
  • Funding student projects to improve harbour and stream health.
  • Supporting the Harbour Educator Network, which consists of a range of agencies working with schools on environmental education initiatives.

Rural landowners reducing sediment

The Pāuatahanui arm of Te Awarua-o-Porirua Harbour is surrounded by rural farms and lifestyle blocks. Land management activities on rural land contributes significantly to sedimentation of the estuary so we support rural landowners to reduce sediment runoff through a range of initiatives such as:

  • Developing farm plans on large farms to determine how best to reduce erosion.
  • Riparian management including fencing, planting and weed control to reduce stream bank erosion.
  • Retirement of steep land from grazing with either forestry, planting or natural regeneration to stabilise the soil.
  • Pole planting on steep slopes to stabilise vulnerable areas such as gullies, particularly during storm events.

Biodiversity protection

In addition to supporting community groups, schools, and rural landowners to improve the health of the Te Awarua-o-Porirua Harbour and its waterways, we also work directly on the ground to reduce pest plants and animals threatening native biodiversity in the catchment.

Working together with our partners Porirua City Council and a range of local pest free and predator free groups, we manage a large pest animal trap and bait station network to keep the nationally important wetland bird habitat around the Pāuatahanui Inlet safe for birds to feed and breed.

Over half of the wetland bird species recorded in the Harbour are either threatened or at risk, and a number of particularly rare species nest on the ground, so predator control is critically important for these birds.

For more information on biodiversity work in the Te Awarua-o-Porirua Harbour and catchment, please contact us at biodiversity@gw.govt.nz. For more details around each project supported by the Community Environment Fund, view the Community Environment Fund webpage.