We’re working to develop a shared pathway between Wi Neera Drive and Onepoto and provide coastal resilience along the harbourside edge of Titahi Bay Road and Wi Neera Drive.
We've come a long way, but there’s still a lot of work to do – find out more below.
We welcome your feedback on where we’ve landed with the project so far and are happy to answer your questions. You can contact the project team at WiNeera2Onepoto@poriruacity.govt.nz
This image is an indicative only, artist's impression
Council has agreed to progress with a preferred option for the Wi Neera to Onepoto Shared Pathway and Coastal Resilience Project.
Delivery of the project is subject to resource consents and to securing external funding, so there is still a lot of work to do.
The preliminary concept design for the preferred option includes:
We believe this is the best solution to deliver on the project objectives; to improve cycling and pedestrian connection and address harbour edge erosion and coastal resilience. This preliminary concept design has been shaped by feedback from community and stakeholder engagement in recent years.
We’d love to hear your feedback on the preliminary concept design. Take a look at the information on this page and share your feedback by emailing us at WiNeera2Onepoto@poriruacity.govt.nz before Wednedsay 24 February 2021.
We also plan to hold public drop-in sessions in February to share details of the project. We’ll provide dates, times and location nearer the time.
The preferred option we are progressing with has an estimated construction cost of $10.7m; $4m for the pathway, $6.1m for coastal resilience alongside Titahi Bay Road, and $0.6m for Wi Neera Beach improvements. (30% contingency is built in.)
The final cost won’t be known until we have obtained resource consent, completed detailed design and expert costing reviews, and we have a preferred tenderer.
Council would need to contribute $3.6m to the project, which is being sought through the Long-Term Plan. Further funding is being sought from Waka Kotahi NZ Transport Agency ($3.9m) and external funding sources ($3.2m), beginning with applications in the new year.
If Waka Kotahi and external funding can’t be secured, the project will be closed, and the capital funding returned to the Transport renewal programme, and to City Partnerships to complete Wi Neera Beach (subject to resource consent). Coastal erosion issues along Titahi Bay Road would be managed through the business as usual transport maintenance programme.
We look forward to your feedback and will keep you updated, plus update this webpage, as we have more detailed information to share.
Hello
This is a quick update to let you know how this project is progressing.
We held a workshop with councillors last week (19 November) where we sought direction on a recommended option for the shared pathway and coastal resilience works, and possible funding approaches.
Based on feedback from councillors, the project team is now working to further develop a recommended option that will be presented to Council for approval at the next meeting on 16 December.
At that stage, we look forward to being able to share more information with you.
Thanks for your patience as we work through all the issues.
Update - Wi Neera to Onepoto Shared Pathway and Coastal Resilience project
Kia ora
In our last update to you we said we hoped to present Councillors with two preliminary concept options for the Wi Neera to Onepoto Shared Pathway and Coastal Resilience Project at a workshop in October 2020.
However work done to develop and cost those options has made it clear they would exceed the currently available budget of $3.6m. This work has helped us understand the full cost of the coastal resilience work, which is similar to that of the pathway development, and has understandably changed since we drafted budgets for the works some years ago.
As a result, the project team, including Ngāti Toa, will now regroup to review the two preliminary concept options, alongside other possible options, which will help ensure we:
This means, we have had to readjust our planned timeframes and will now workshop a preferred option/options with Councillors at a later date and not October as originally planned.
Following Council input we will be inviting feedback from stakeholders and the community on aspects of the proposal before final design decisions are made and consent is sought.
It’s important to stress that feedback received during the life of this project has helped us shape the preliminary concept options. The design is being guided by the themes raised during engagement with Ngāti Toa, community consultation in 2016, in feedback to the Long Term Plan, and the more recent 2019 community workshop.
These themes include:
We’re aware that this project has been ongoing for some time, and we appreciate your patience as we work through the challenging and complex issues it is presenting us with. Projects next to the sea are often complex and in this situation that is no different. It’s really important that we get this right, by coming up with best solutions and options for the city.
We hope to have more clarity around next steps and timings in the next few months and will keep you updated.
This update (30 July, 2020) is to let you know how the Wi Neera Drive to Onepoto Shared Pathway and Coastal Resilience Project is progressing.
We are now well on the way to preparing the information required for shaping the best design solution, and the consenting process, for this project along Titahi Bay Road and Wi Neera Drive.
The project includes construction of a shared cycling and pedestrian pathway between Wi Neera Drive and Onepoto, and erosion protection works to enhance coastal resilience along the coastal edge of Titahi Bay Road and Wi Neera Drive.
An experienced team has been assembled to ensure the design solution is appropriate for the area and to also understand what can be done to improve habitat quality within the inner harbour as a result of the project.
The design required for a comprehensive consenting process is significantly more complex than originally envisaged based on all the previous harbour-related works, and includes investigations into coastal processes, rates of erosion and sedimentation, tidal and sub-tidal ecology, and stormwater management.
On the foreshore, leading experts in coastal soft engineering and managing the effects of sea level changes, are investigating how coastal resilience designs can work to protect the harbour edge using bathymetry (seafloor) data, wave modelling and ecological analysis just offshore. Onshore, engineering specialists are investigating possible options for the pathway – and this will draw from the results of geotechnical investigations to help ensure the design will be resilient into the future.
Two preliminary design options are currently being developed and costed. These will be assessed at a workshop with Porirua City councillors and a preferred option identified for Council consideration and approval in October. Confirmation of a preferred option will clarify the project scope for the concept design and consenting stages that will follow.
The team is working closely with Ngāti Toa (who are supportive of the project and will have a representative on the project team) and we will also be inviting feedback from stakeholders and the public on aspects of the proposal before final design decisions are made.
Consenting is planned for 2020-21.
Once completed, it will create a unique, naturally vegetated coastal margin that will help improve the health of the harbour, establish a stunning natural landscape for residents in Takapūwāhia, Elsdon and Titahi Bay, and connect our city. The path will allow for coastal resilience, interaction with the harbour, and become a link between recreational activities on Wi Neera Beach and Onepoto Park.
We appreciate your ongoing patience and interest as we work through this complex project. We will provide ongoing updates as the project develops.
Next steps:
Our initial work included investigations into coastal processes, rates of erosion and sedimentation, tidal and sub-tidal ecology, and stormwater management.
On the foreshore, leading experts in coastal soft engineering and managing the effects of sea level changes investigated how coastal resilience designs could work to protect the harbour edge using bathymetry (seafloor) data, wave modelling and ecological analysis just offshore.
Onshore, engineering specialists investigated possible options for the pathway and developed two preliminary concept design options, taking local constraints such as the pohutakawa trees and seagrass into account and drawing from the results of geotechnical investigations.
These options were assessed and presented to Councillors at a workshop on 19 November 2020.
The Council direction at the workshop was to ask staff to provide further information on Option 1 for consideration at a Council meeting in December 2020.
Option 1 will:
This option currently has the support of our project partners – Ngāti Toa and Waka Kotahi NZ Transport Agency (and meets Waka Kotahi co-funding requirements).
The main parts of the preliminary concept design include:
The diagram below shows a typical cross section of the soft coastal resilience work which includes extensive areas of saltmarsh.
Pathway:
Harbour:
Amenities:
Other:
What you asked for |
Addressed in the preliminary concept design? |
How? |
---|---|---|
Pathway: | ||
Harbour edge pathway | ✔ | The pathway is located along the harbour edge. |
Provide crossing points (and access) onto the pathway along its length, e.g. at Te Pene Ave |
✔ |
Three crossing points (including raised cycle/ pedestrian islands) are proposed – north and south of Te Pene Ave and across Onepoto Road. (These islands will facilitate safe crossing in two movements when traffic volumes are heavy.) |
Provide a safety zone/separation) between traffic and shared pathway users |
✔ |
A 1.2m wide shoulder and a 0.5m wide buffer are provided between the southbound lane and the shared pathway. Possible ‘treatment’ options for the buffer (e.g. whether to plant it out or create a grassy swale) are yet to be assessed. (Also see below) |
Consider cyclist and pedestrian safety in the design and potentially reduce traffic speeds |
✔ |
The 3m wide concrete shared path will enable recreational cyclists and pedestrians to travel safely in opposite directions without conflict. The speed limit will be reduced to 50km/h along the full length of Titahi Bay Road (and thus reduce the risk to pedestrians crossing Titahi Bay Road and users of the shared path.) Narrowing the traffic lanes to 3.2m will also help slow vehicle speeds and reduce the crossing width for pedestrians. |
Accessible for all ages and abilities | ✔ |
The concrete pathway will be 3m wide and flat along the full length to enable recreational cyclists and pedestrians travelling in opposite directions to move safely and without conflict. |
Harbour: | ||
The harbour has special value and is a priority (within the project) |
✔ |
Our community wants our harbour to be restored. The saltmarsh replanted as a result of this project will have a huge positive effect on restoring this large and important part of our harbour margin. The habitat created is a key part of our work to protect the harbour for generations to come. |
Enhance the mana of Te Awarua-o-Porirua | ✔ | The coastal resilience works will begin to address the issues of harbour health. Ngāti Toa’s desire is to be able to obtain healthy kai moana and swim in the harbour. While a long term aspiration, this work will be a major step towards achieving it. |
Preference for a ‘soft’, resilient harbour edge solution – to protect the vulnerable coastal edge |
✔ |
‘Soft’ coastal resilience works will be provided along a significant proportion of the harbour edge (except some sections where a ‘hard’ (rock) edge is required to protect the seagrass). This combination of ‘soft’ and ‘hard’ coastal resilience will repair the existing erosion and dramatically improve the future resilience of the harbour edge. |
Minimise encroachment into the harbour, protect seagrass and kaimoana beds, improve harbour/ harbour edge habitat |
✔ |
The coastal works are to be only placed on what was part of the original reclamation in the early 1950’s. As the new rock sill and saltmarsh will not be located within the tidal mud flats this will help protect the slowly regenerating habitat that is left. |
Opportunity to improve stormwater management and filtration |
✔ |
Saltmarsh will play an important role in filtering contaminated stormwater and thereby reducing sediment, heavy metals and other contaminants going into the harbour. This will help improve water quality in the harbour. |
Ensure the work doesn’t worsen flooding within Takapuwahia |
✔ |
Water sensitive design features (which are part of the new coastal resilience works) will help slow flooding down and are intended to complement other stormwater management works in the surrounding catchments. |
Amenities: | ||
Improve connections to the harbour | ✔ |
People will be able to walk and cycle the length of the shared pathway and be able to watch the sea-life and coastal birds that will be using the new natural coastline just below the path. Where possible, pause points (incorporating seating, etc) will also part of the experience of connecting to our harbour. |
Retain the Pohutakawa trees if possible | ✔ |
As the shared pathway will be located on the landward side of the Pohutakawa trees, most will be able to be retained (unless diseased and otherwise requiring removal). The Landscape Concept Plan (once developed) will highlight proposed landscaping for the harbour edge (including replacement of vegetation requiring removal during construction). |
Consider beach creation at Wi Neera and opportunities to improve access for waka ama and other water-based events |
✔ |
The restored beach along Wi Neera Drive will enable people to walk along the water edge and watch waka ama events and waka launching at the waka ramp. It will also be more attractive for other water-based events and waterfront activations on the adjoining Wi Neera Reserve. |
Parking | ✖ |
There is no provision for parking along the length of the shared pathway. Users would be required to park at either end, along Wi Neera Drive or on the west side of Titahi Bay Road. |
Other: | ||
A desire for meaningful opportunities to have a say and provide feedback on the draft proposal |
✔ |
Feedback from previous engagement has guided the preliminary concept design (as outlined above). You can give us your feedback now and we’ll keep you updated as things progress. |
What you asked for |
When will this be addressed? |
Notes |
Provide a safety zone/separation) between traffic and shared pathway users |
In the detailed design stage |
While a 0.5m wide buffer is provided (alongside a 1.2m shoulder) in the preliminary concept design, we now need to assess possible ‘treatment’ options for this area. While two possible options could be to plant out the buffer (as requested by some) or create a grassy swale, we will need to consider ongoing maintenance requirements and associated costs. |
Lighting | In the landscape concept design and detailed design stages |
Lighting will be provided. The next steps are to assess lighting-related needs (for pathway and road users) and develop a lighting plan. |
Seating | In the landscape concept design and detailed design stages |
While not allowed for at this stage (in order to keep costs down) seating will be provided for through the landscape concept and detailed design processes so it can be added in future, as funds permit. |
Pause/stopping points |
In the landscape concept design and detailed design stages |
While not allowed for at this stage (in order to keep costs down) pause points will be provided for through the landscape concept and detailed design processes so it can be added in future, as funds permit. |
This project has a long history and affordability has been a key deciding factor along the way
The project began back in 2002 with a harbour-side boardwalk proposal jointly started by Porirua City Council and Ngāti Toa.
In 2007 the Takapuwahia Village Concept Plan included, among other things, a harbour-side timber boardwalk along Titahi Bay Road linking Onepoto to Wi Neera Drive.
There have also been a few feasibility studies exploring options to provide a path/cycleway and harbour edge erosion control works.
This is a complicated project. We need to look at erosion control, harbour ecology, climate change, road construction and maintenance and building a shared pathway. All of these matters need to be addressed through a resource consent process.
Taking community advice on board
During Council consultation on the project for the Long-Term Plan 2018-38, 73% of respondents who gave feedback on various pathway and coastal protection options supported a harbour-side path and erosion repairs to the harbour edge. The majority of feedback urged Council to complete the project sooner than proposed (at the time).
Key support decisions for the project
In 2019, Waka Kotahi NZ Transport Agency (NZTA) endorsed a 4-Stage Business Case for a shared pathway between the Porirua CBD and Titahi Bay. This project is stage two of that pathway.
In 2019 a coastal expert was engaged to develop a concept for the shared pathway, which saw the introduction of ‘soft’ coastal resilience/restoration works which people requested. Soft engineering is a significant departure from previous ‘hard’ (concrete & rock) engineering solutions.
This work, plus the earlier feasibility studies and option assessments and feedback from the community and stakeholders has informed how we have developed the current project and our assessment of the options.
The Onepoto Arm of Porirua Harbour has been extensively modified over the years. Almost all the present Onepoto harbour margin is reclaimed. The original coastline is 60-150 metres inland of the current coastline which was reclaimed during the 1950s. The rest of the Onepoto harbour arm has also been modified particularly with the development of SH1 and the railway lines, which have an ongoing impact on the health of the harbour.
The image below shows Titahi Bay road prior to reclamation
The image below shows the harbour margin pre and post the 1950s reclamation work
The images below show the current state of the seagrass beds
The images below show the current erosion issues along the Titahi Bay Road foreshore
There are three approaches we could take to protecting the harbour edge and addressing the erosion issues:
Localised and ongoing erosion mitigation works will be required to repair and protect the road if we don't implement the preferred option.
Given the current erosion damage, rock armour protection would need to be installed along approximately 511m of the coast where the current bank edge is within 2m of the Titahi Bay Road edge.
Ongoing maintenance would be required along the length of the harbour edge, and it would be just one storm away from substantial, further damage that could potentially undermine the road.
Hard patch repairs could have a flow-on impact leading to erosion in neighbouring areas. This is known as ‘end effects’.
Installing rock rip rap would not provide any ecological benefits for the harbour and would not allow for the reinstatement of nearshore habitats.
Resource consent and coastal permits would be required from Greater Wellington Regional Council for reclamation and discharge and ongoing repairs over time.
Example of ‘patch’ erosion repairs
Hard coastal engineering would protect the shoreline from the effects of erosion and sea level rise and would be long lasting.
Ongoing repairs could be required to the seawall following storm events.
Hard engineering would not provide any ecological benefits for the harbour and would not allow for the reinstatement of nearshore habitats.
The ease of consenting would depend on the footprint/reclamation required and a detailed assessment of the proposal. Hard engineering does present a more challenging consenting pathway (than for soft engineering). It is noted that both the proposed Porirua City District Plan and GWRC plans favour soft engineering (rather than hard) as a primary method to reduce damage from sea level rise and coastal erosion, protect coastal margins and preserve natural character.
Hard engineering works are harder to stage and in the longer term more costly.
The imagae below shows an example of harbour edge hard engineering alongside Portobello Road in Dunedin
The diagram below shows a typical cross section of a hard engineering approach
Soft engineering in coastal areas is used as a cost-effective way to protect shorelines from erosion and the effects of sea level rise associated with climate change. It also reduces the effects of flooding on marine environments and helps increase harbour health.
Small rock reefs (chenier) are placed just offshore and then saltmarsh is planted in between the shore and the reef. Natural examples can be seen around Pauatahanui Inlet where natural shell banks create the “rock reefs”. The rock reef and the saltmarsh dissipate wave energy. The larger the saltmarsh, the greater the wave energy dissipation. The rock reef is also called a sill.
The coastline along Titahi Bay Road is ideal for this type of coastal engineering (which has been used successfully around New Zealand and has worked since the early 1990’s). See more information about the benefits of soft engineering in the FAQ section below.
The advantages of this approach are that it creates a natural harbour margin that would protect the shoreline from the impacts of sea level rise and storm damage. It would also stabilise sediment entering the harbour and create habitat and be a food source for shellfish, fish, invertebrates and birds.
While more expensive to construct initially than patch repairs, it would cost about the same as hard engineering upfront. Longer term it would be cheaper to maintain, with repairs possibly only required after heavy storms. The ease of consenting would depend on the footprint/reclamation required. This approach could be staged.
The image below shows the shoreline of Pauatahanui Inlet, which is protected by soft coastal engineering - a wetland behind a chenier (a sandy beach ridge)
The image below shows a typical cross section of a soft engineering approach
Early consultation
Options development
Information on options for Council
Preliminary concept design and cost estimates for Council decision
Next steps:
How many options have been considered for this project?
Seven options have been assessed for this project, including:
The options were assessed through a two-step Multi Criteria Assessment process (explained in more detail below).
MCA is a tool to assist and document decision-making where there are multiple options.
It helps carry out a comparative analysis of options (against consistently applied criteria) to decide which best meets a range of objectives set by stakeholders and the community for a project.
The MCA criteria were based on desired project outcomes, Waka Kotahi investment objectives, and community feedback from earlier engagement – and these were reviewed by Waka Kotahi and Ngāti Toa representatives. The assessment was carried out in two steps including:
Options 1 and 3 scored the highest against the initial ‘sieve’ criteria (step 1) and progressed to step 2 alongside the project ‘Do Minimum’ option (option 4 - which included only essential erosion repairs, rather than full coastal resilience). Option 1 (the preferred option) was the highest scoring option in the detailed assessment (step 2), followed by Option 3 and option 4.
The Council decided to proceed with Option 1 (the preferred option). Council believe this is the best solution to deliver on the project objectives and will also:
The option also has the support of our project partners – Ngāti Toa and Waka Kotahi (and meets Waka Kotahi co-funding requirements).
A preliminary concept design is a more detailed look at an option after all options have been looked at by stakeholders, experts and funders.
At this point, the preliminary concept design (and initial cost estimate) includes the basic elements for the shared pathway and coastal resilience, such as:
‘Nice to have’ elements like seating and pause points (areas with signage or a seat for users to take a break) aren’t included at this point as we’ve tried to keep the costs down and don’t yet know how much external funding we’ll be able to source. These elements will be provided for as we develop the landscape concept and work through the detailed design processes in order that they can be added in future, as funds permit.
There is no provision for parking along the length of the shared pathway. Users would be required to park at either end, alongside Wi Neera Reserve, or on the west side of Titahi Bay Road.
While some aspects of the concept (such as the harbour-side route, pathway width and ‘soft’ coastal resilience) are unlikely to change, there’s more work to be done on other aspects such as the buffer zone (and treatments within that area), the location of crossing points, and lighting (through the developed design stage). Seating, cultural elements and pause points will be provided for as we develop the landscape concept plan and work through the detailed design process so they can be added later as funds permit.
We’ll progressively refine the details as we move through the resource consent and design processes and will be able to share more details and invite feedback on those elements in due course.
A shared pathway is a widened footpath (separated from the road) that may be used by pedestrians, cyclists, riders of mobility devices and riders of other non-motorised devices, at the same time.
Value engineering is a systematic, organised approach to providing necessary functions in a project at the lowest cost. It promotes the substitution of materials and methods with less expensive alternatives, without sacrificing functionality. That is – it’s a way of finding cheaper ways to achieve the same project outcome.
Current erosion damage is such that rock armour protection would need to be installed along approximately 511m of the project site where the current bank edge is within 2m of the Titahi Bay Road edge.
While ‘patch’ repairs would be cheaper initially, ongoing maintenance would be required along the length of the harbour edge, and it would remain just one storm away from substantial, further damage that could potentially undermine the road. ‘Hard’ patch repairs could also have a flow-on impact leading to erosion in neighbouring areas – known as ‘end effects’.
Four of the seven options we considered included essential erosion repairs (i.e. patching) to the harbour edge, instead of coastal resilience. As these options did not score well against the MCA criteria (or the other options) they didn’t proceed beyond the stage one initial ‘sieve’.
It’s also noted that this approach would not provide any ecological benefits for the harbour or allow for the reinstatement of nearshore habitats.
The recurring stumbling block has been the mis match between cost and available budgets.
The current (inflation-adjusted) budget in the LTP 2018-38 is $3.6m. (This includes $3.2m for the shared pathway and coastal resilience along Titahi Bay Road and $0.4m for Wi Neera Beach.)
The preferred option has an estimated capital construction cost of $10.7m (including 30% contingency).
Estimated construction costs for the key elements are: $4m for the pathway, $6.1m for coastal resilience alongside Titahi Bay Road, and $0.6m for Wi Neera Beach improvements.
The final cost won’t be known until we have obtained resource consent, completed detailed designs and expert costing reviews, and we have a preferred tenderer.
Council’s contribution of $3.6m to the project, will be considered as part of the Long-Term Plan. Further funding is being sought from Waka Kotahi NZ Transport Agency ($3.9m) and external funding sources ($3.2m). Applications will start in the new year.
We have a commitment in principal from Waka Kotahi. Further funding sources will be investigated over the next 12 to 18 months.
Yes. While the $10.7m does include 30% contingency, the cost estimates are preliminary and based on preliminary concept drawings. These costings will require an expert costing review, and at a later stage we may seek contractor input to explore potential construction-related efficiencies. The true final cost won’t be known until the tender for construction closes.
We have a Funding Plan which includes how we aim to request additional funding from other funding organisations.
If Waka Kotahi and external funding can’t be secured to meet the budget shortfall, the project will be closed, and the capital funding returned to the Transport renewal programme, and to City Partnerships to complete Wi Neera Beach (subject to resource consent). Coastal erosion issues along Titahi Bay Road would be managed through the ‘business as usual’ Transport maintenance programme.
Waka Kotahi (NZ Transport Agency) is one of our project partners and has been closely involved in, and helped shape, the project to date.
This project is stage 2 of the 4-stage shared pathway project (between the Porirua CBD and Titahi Bay) endorsed by Waka Kotahi in 2019. We are working closely with our Waka Kotahi Investment Advisor through the concept design process to further maximise the funding opportunities available towards the developed design and capital works stages of the project.
To date, Waka Kotahi has been very supportive of the harbour-side pathway proposal, along with the coastal resilience works to restore the harbour edge and protect the road.
Yes, feedback received over the years from Ngāti Toa, the community and other stakeholders has helped shape the preliminary concept design for the preferred option.
Yes, we have undertaken a safety audit of the preliminary concept design for the preferred option to ensure it is safe for all users. The traffic speed on Titahi Bay Road would also be dropped to 50kmph along the full length to improve safety and reduce the risk to people crossing the road and users of the shared path.
Feedback received on this project during community consultation on the 2018-38 Long Term Plan showed a clear and strong community desire for a cycle and pedestrian pathway linking Titahi Bay – with 73% of submitters on the project in Long-Term Plan expressing a preference for a harbour-side pathway.
Yes. One of the seven options assessed through the MCA process included a pathway on the landward side of Titahi Bay Road, with essential erosion repairs along the harbour edge. This option didn’t score as highly as other options through the MCA process and wasn’t progressed beyond the first (initial ‘sieve’) stage.
An audit of the trees along this stretch of Titahi Bay Road has revealed that some are diseased and will need to be removed – however our aim is to keep as many trees as possible.
Soft engineering in coastal areas is used as a cost-effective way of protecting shorelines from erosion and the effects of sea level rise associated with climate change. It also reduces the effects of flooding on our marine environments and helps increase harbour health.
To make a shoreline resilient, we create small rock reefs or “sills” which are placed just offshore and then plant saltmarsh between the shore and the reef. The rock reef and the saltmarsh dissipate wave energy and protect the shoreline. The larger the area of saltmarsh, the greater the wave energy dissipation. Natural examples can be seen around Pauatahanui Inlet where shell banks create the “rock reefs”.
The low tidal mudflats along Titahi Bay Road are ideal for this type of coastal engineering (which has been used successfully around New Zealand and has worked since the early 1990’s).
The present day Titahi Bay Road shoreline was formed by reclamation in the 1950’s and in many areas lies 60-150m seaward of the original natural shore. Just 2% of the original saltmarsh area (which was once extensive) is left in the Onepoto arm of the harbour, two thirds of which is now rock armoured.
If a soft engineering approach is taken, harbour water quality would be improved through stormwater filtration by the saltmarsh created along the harbour edge. These saltmarshes would reduce sediment, heavy metals and other contaminants going into the harbour and provide a significant habitat for our bird species which are currently declining. Salt marsh is a large food source for our coastal ecosystems in Porirua.
Capturing sediment
The present day Titahi Bay Road shoreline was formed by reclamation in the 1950’s and in many areas lies 60-150m seaward of the original natural shore. Two thirds of the coast around our harbour is rock armoured. Just 2% of the saltmarsh is left in the Onepoto arm of the harbour.
By replacing rock with salt marsh we can capture sediment and stop it from damaging other parts of habitat in the harbour.
Salt marsh is also a large food source for our coastal neighbours in Porirua. Each year, over 400 tonnes of food is provided through the salt marsh to our coastal species in Pauatahanui Inlet. The saltmarsh in Onepoto will also provide a significant habitat for our bird species which are currently declining.
This length of saltmarsh means a massive improvement for harbour health.
Water sensitive design
For this project we are using water sensitive designs to manage water. What this means is using swales and saltmarsh (coastal wetlands) to slow down and treat stormwater before it gets into the harbour. Swales and wetlands are natural wastewater treatment plants.
Saltmarsh as a wetland treatment for contaminants
Contaminants like heavy metals and organic compounds from our cars and trucks are deposited on our roads and then washed into stormwater when it rains. The contaminants have a significant, detrimental impact on harbour health.
Saltmarsh is a coastal wetland. As a wetland, it can filter out contaminants in our stormwater. The marsh absorbs heavy metals and stores them, which means they are no longer deposited on the tidal mudflats where lots of our harbour life lives. The saltmarsh also slows down the effects of heavy rain and flooding caused by stormwater.
Grassy swales
Along the shoreline next to the pathway we may also put in swales which are u-shaped areas to hold and filter water. The swales can be either grass or wetland plants to filter out contaminants and slow down flooding.
The slopes next to the shared pathway will be planted with coastal species naturally occurring around Onepoto. The salt marsh formed will turn into a landscape similar to that along Grays road at Kakaho Estuary (see below). Pause points or viewing areas will allow people to see the saltmarsh close up and in time, the many types of coastal bird species that people enjoy around Pauatahanui Inlet. Two types of marsh plants can be used – oioi (which is a lovely golden brown colour and is mostly seen in drier areas of mudflats) and sea rush (which is a blue grey colour and lives where there is around four hours of seawater at high tide).
Pauatahanui estuary