Here is a joint update from Porirua City Council and Wellington Water on the status of the project to reduce flood risk in the Karehana catchment.

As previously advised, Porirua City Council has put this project on hold because there is not an affordable solution at this time.  Wellington Water’s ongoing investigations and design work have shown that it is not possible to achieve the original targets with the available budget.  

We understand this will be frustrating and disappointing for residents concerned about flood risk.

You have an opportunity to comment through the Council’s Long-term Plan process, which was approved by Council today, with consultation opening next week (26 March). Specifically, you will find a reference to this project as one of a number of projects the Council is putting on hold because of financial constraints and concerns that investigation and design work to date has been unable to find an affordable solution that meets the outcomes sought for the project.

Council and Wellington Water are planning some targeted work to improve operational management and safety in the catchment. A sum of $800,000 is allocated for this in the Council’s Long-term Plan.

Background information

In 2021 Council approved a $16.9m option that was expected to deliver a significant improvement to the flood protection in this catchment. However, as Wellington Water progressed the design of this work, they re-estimated the actual cost to be between $32m and $41m.

A reduced scope option to deliver the most effective components of the project within the originally approved $16.9m budget was found to only benefit about 6 homes in a 30-year flood (a similar flood to the flooding in November 2020).

Click on the links below to view recent reports with further explanation on the options, effectiveness and costs of the proposed works. These documents informed Council’s decision to put this project on hold:

• PCC Karehana catchment recommendations 19 October 2023
• Wellington Water Karehana Council report 6 Oct 2023 (Attachment 1 to the PCC paper)
• Karehana planning stages 1 and 2 scope  (Attachment 2 to the PCC paper)

Next steps

Council is inviting community feedback on its Long-term Plan from Tuesday 26 March until 26 April. Please visit poriruacity.govt.nz/haveyoursay to find out how to make a submission.

Please get in touch if you have any questions.

Olivia Dovey, Porirua City Council

olivia.dovey@poriruacity.govt.nz

Lyndie McMillan, Wellington Water

Lyndie.McMIllan@wellingtonwater.co.nz

In 2021 Porirua City Council approved a $16.9m option that was expected to deliver an improvement to the flood protection in this catchment. However, as Wellington Water progressed the design of this work, they re-estimated the actual cost to be between $32m and $41m.   A reduced scope option to deliver the most effective components of the project within the originally approved $16.9m budget was found to only benefit about six homes in a 30-year flood (a similar flood to the flooding in November 2020).

Furthermore, this reduced scope had little resilience to the impacts of rising sea levels.  With this new information on the much higher costs of the planned upgrades and the limited effectiveness of a reduced scope,  Porirua City Council officers are recommending that this project should not procced in its current form at this time. Put simply, the money previously allocated to this project won’t deliver the outcome needed for the community.

What next?

Work has begun on the Porirua City Council Long-term Plan, and next year the Council will be making decisions on all its planned projects – including this one. Karehana residents can have their say on these decisions and are able to make individual and collective submissions as part of the consultation on the plan, which will begin at the end of March next year.

Further information will be provided early in 2024.

The investigations will take place over the course of four to five weeks during October and November. They will involve a series of ground investigations along Moana Rd, Cluny Rd, Airlie Rd, Firth St and the reserve, which will primarily include potholing and drilling bores. The results will inform design of improvements for the area.

The investigations will not be overly disruptive but we do apologise for any inconvenience.

This is a joint update from Porirua City Council and Wellington Water.

We are pleased to be able to confirm the work that will be going ahead in phase 1 of the Karehana stormwater improvements over the next year.

As outlined in June, Porirua City Council agreed to Wellington Water starting work within the existing budget of $16.9 million, while decisions on longer-term funding for the full scope of works were deferred.

Since then Wellington Water and its contractors have reviewed the programme and finalised Phase 1, work within the existing budget over the next year.  Phase 1 focusses on the eastern side of the catchment, Gordon Road and Airlie Road.

Gordon Road – late 2023 to 2024

Wellington Water and its contractors will be upgrading sumps in Gordon Road, to capture water and divert it more efficiently to the outlet behind the Plimmerton Boat Club. This will reduce the overland flow down to Airlie Road and across properties.

Construction will begin before the end of 2023. The team are currently completing the detailed design and finalising the construction contract arrangements.

Upper Airlie Road - first half of 2024

Wellington Water and its contractors will be upgrading the stormwater network in upper Airlie Road, with a bigger pipe and more inlets to divert more water into the main Airlie Road stormwater pipe, reducing the overland flow across properties to the stream.

The team are currently completing the detailed design. Construction contractors will need to be appointed and a traffic management plan approved before starting construction. We’ll let you know when we have a confirmed start date and provide information about any impacts on traffic and parking.

Airlie Road inlet – 2024

The Airlie Road inlet, from Karehana Park into the main Airlie Road stormwater pipe, will be improved to provide for greater flow and to reduce the risk of debris blockages. Detailed design will be discussed with neighbours in coming months and completed in mid-2024.  Wellington Water will have to obtain resource consent for this work. We are unsure how long that will take, but the aim is to start construction in 2024.  We will keep you informed about the resource consent process.

Airlie Road outlet – 2024-2025

An improved outlet will provide for greater flow out to sea.  As with the inlet, Wellington Water will have to obtain resource consent for this work, and we can’t be sure how long that will take, but we aim to start construction in 2025. We will keep you informed about the resource consent process.

Geotech investigations in Karehana Park – September/October 2023

The budget also covers geotechnical investigations in the park which will inform details in the design of future phases including the pump station.

Longer term funding for future phases

As we set out in our June update, the costs of the project have increased and additional funding is required for future phases of work.

Porirua City Council now intends to develop a priority list for investment in water infrastructure, including Karehana stormwater improvements, as part of the Long Term Plan (LTP). The LTP will be out for public consultation in early 2024, so residents will have the opportunity to express their views to council and local councillors as part of that discussion.

The LTP priority list would then be passed on to a new water entity.

Council will keep residents informed of the LTP process and the opportunities for input.

We are aware that it feels like everything is taking a long time, and we appreciate the community's ongoing patience.

Ngā mihi

David Down (Porirua City Council Manager Water and Waste)

Lyndie McMillan (Wellington Water Project Director, Karehana)

This is a joint update from Porirua City Council and Wellington Water.  

As you are aware from our previous updates, Porirua City Council has been considering recommendations from Wellington Water on stormwater works to reduce flood risk in the Karehana and Taupō Stream/James St catchments. 

Wellington Water presented an update on the Stormwater Improvements projects across the Plimmerton area to Councillors in April. This included an update on Karehana scope and cost estimates which are currently higher than the $17.9 million already committed for flood mitigation work. This also included an update on the Taupō Stream/James St catchment study and resulting scope and estimates. Following the workshop a recommendation paper was prepared for consideration by Council. 

You can find more information about Wellington Water’s recommendations on the Council website:  

• View the Plimmerton Stormwater Improvement Update from Wellington Water which appeared at a Workshop of Council on 27 April 2023. 
• Read the DRAFT Technical report providing advice to Porirua City Council following the above workshop (27 April 2023), noting this has not yet been considered by Councillors. 

The Council deferred consideration of these recommendations while it worked through the Annual Plan process, which has involved looking at all expenditure in the light of affordability for ratepayers across Porirua.  Council has not included any extra budget for Karehana or Taupō Stream/James St in the Annual Plan, deferring this issue for further consideration. 

Longer-term funding decisions are complicated by the Affordable Water Reforms process, as there is not yet clarity about the timelines for establishing the new water entity in this region, entity “G”. 

What this means for Plimmerton residents is that Wellington Water will continue works within the existing approved budgets, but unfortunately it will take some time to get clarity on additional longer-term funding for the full scope of works recommended. 

The $17.9 million already committed to this work includes $1 million for debris catch nets in the reserve. Work on the debris catch nets is underway.  

Karehana recommendation 

Wellington Water recommended continuing with all works except the widening of the stream above the park. Following the concept design, and more detailed survey and investigation work it has been determined that similar benefits may be achieved without the need for the stream works. This option is more cost effective with similar benefits to the original recommended option. 

The estimate for this work (at a concept design level) is currently approximately $31 million. This estimate and scope will continue to be refined as we develop the detailed design. Currently the work is expected to benefit approximately 20 habitable floors in a 30yr rainfall event (with climate change).  

Taupō Stream/James St recommendation 

The results of Wellington Water’s investigation in this catchment are that it would cost an estimated $40-$63m to resolve flooding of 20-25 floors + SH59 road in a 30 year rainfall event. 

Wellington Water has identified a three stage approach: 

• Stage 1: East. An initial stage of work is recommended (circa $10m - $16m) to reduce overland flow from Camborne around James St + Greys Rd buildings by upsizing the existing Greys Rd pipes and James St intakes/outlets. 
• Stage 2: West. The second stage (circa $14m - $22m) is to ‘open up’ the choke points in the Taupo stream (primarily two vehicle bridges and the overgrown stream banks) so it is ready for the increased flow from the northeast. 
• Stage 3: North. The third stage (circa $14m - $22m) is to allow increased flow from the northeast to the Taupo Stream by constructing additional box culverts under SH59 and Ulric St and to attenuate the northwest flow from the Taupo Swamp by constructing a retention bund at the south end of the Plimmerton Domain fields. 

Wellington Water recommended progressing with design and consenting and Stage 1 works. 

Next steps 

The next step is to review what can be achieved within the existing budget, while continuing to work on proposals for longer-term funding. 

We recognise that this is not what the community wants to hear and apologise for the lack of certainty about the long-term future. Wellington Water and Porirua City Council will continue to work together to make progress where we can. 

Please contact Olivia Dovey at Porirua City Council on Olivia.dovey@poriruacity.govt.nz if you have any questions. 

Ngā mihi 

Olivia Dovey (Chief Advisor to GM Infrastructure, Porirua City Council)  

Lyndie McMillan (Wellington Water Project Director, Karehana)  

Terry Sage (Wellington Water Project Director, Taupō Stream/James St) 

Porirua City Council deferred consideration of Wellington Water’s recommendations on stormwater works to reduce flood risk in the Karehana and Taupō Stream/James St catchments while it heard from submitters and considered their comments on the Annual Plan.

Council will be considering the Annual Plan, including the budget, at its Te Puna Kōrero meeting next Thursday 8 June.

These budget decisions will set the overall framework for stormwater work in your communities.  We’ll be able to provide more detail once these important decisions are made.

The Council committee paper will be loaded on the Porirua City Council website as part of the agenda papers on Monday 5 June.

You can choose to speak at the start of the meeting on Thursday 8 June – details of how to do that are on the Porirua City Council website.

We thank you for your patience as Wellington Water and Porirua City Council go through all the necessary processes.

Porirua City Council will be considering the new recommended works in the Karehana catchment and required funding at its next Te Puna Korero meeting on 25 May.

The same meeting will also consider recommendations relating to reducing flood risk in the James Street/Taupō Stream area. The papers will be available on the Porirua City Council website.

Wellington Water will not be proceeding with the initial proposal to widen the stream above the park which included increasing the capacity of the culverts under Firth Road.  However we do plan to be making improvements around the culverts to make sure the upgraded network functions well as a whole.  We are still working through the detailed design and will share more details as we progress.

Here is the latest update on our planning for reducing flood risk in Karehana. 

During the concept design process, a careful and comprehensive review of the mitigations for reducing flood risk has resulted in Wellington Water concluding that it is not necessary to widen the stream above Karehana Park.  

Instead, we are working on optimising the work in Airlie Road to increase the capacity of the stormwater network to capture more rainfall before it flows overland to the stream. 

This means we are no longer planning to extend the stream width above the park into private property. 

Our latest modelling shows that increasing capacity in the Airlie Road network, together with optimising the planned improvements across the rest of the catchment, will have a similar benefit of preventing houses being flooded in a 1 in 30-year flood (a similar level to the 2020 event) as the previous option. 

We listened to your concerns about the potential impact of widening the stream, and to your experience that flooding from overland flows (down the sides of the valley and across the roads) was often more of a concern than the stream overflowing.   

We have gathered more information, including new hydraulic modelling, to understand the impact of proposed stormwater diversions in upper Airlie Road and upper Cluny Road.   

As you’re aware, we have also done more investigations around the catchment, including a survey in parts of Gordon Road. 

I want to thank you all very much for your patience while we have gathered more information during the development of the concept design, have gone back over the options and refined the design.  

I recognise that this work has taken longer than initially expected and I accept that this may have caused some frustration.  But I am confident it has been worthwhile to ensure we are maximising the benefits of the proposed work.  

We are now asking Porirua City Council to confirm the new recommended works and required funding. And we are continuing with the design works while we are seeking these approvals. 

Porirua City Council will consider this at a meeting in coming weeks, I’ll let you know when the timing is confirmed.  As always, council papers will be available before the meeting and you have the opportunity to speak at the start of the meeting – details of how to do that are on the Porirua City Council website. 

Below is an overview of the refined package of works.  As previously discussed, we expect to progress the work in stages, and are aiming to start on ‘package 1’ in coming months.  

Contractors will be undertaking topographical surveys on Gordon Road and Upper Airlie Road.

On Gordon Road, the survey will help us to confirm how stormwater flows are captured, and ensure planned improvements are as effective as possible.

The survey will be conducted in the road reserve, but there will be some traffic management for health and safety purposes.  We will do our best to maintain vehicle access up Gordon Road, but there may be some delays. We apologise for any inconvenience while this important work is underway.

In Upper Airlie Road, the survey will measure levels around manholes and sumps, and survey the inlet at the top of the pipe and the ground around the inlet.

We’ll be directly in touch with residents if we need to access any properties.

You may also see some geotechnical investigations happening, which will help to characterise the subsurface soil conditions, which will then inform the design of various structures.

This may include:

• Drilling of boreholes: Machine drilling to collect samples of soil and rock material up to 20 m. The boreholes will be approximately 100 mm to 200mm in diameter and drilled vertically to a maximum depth of 20 m below the ground surface.
• Cone Penetration Tests: Probing of the ground to evaluate the engineering properties of the soil. The test involves pushing a small electronic cone with rods of about 30 mm to 50mm diameter into the ground to determine soil parameters, such as the strength. The testing is relatively low-impact, and no samples are taken.
• Window Sampling: Handheld rig investigation that provides information on layers of soil at shallow depths from the ground surface.

Again, we will be directly in touch with residents if we need to access any properties for any of these investigations.

We are planning for the work to happen in phases and are close to decisions on where and when the first phase will get underway.

We will provide a further update in the next month.

Wellington Water is making significant progress on plans for the Karehana Catchment stormwater project. 

Work underway includes a beach morphology study to understand the levels and slope of the beach. This detailed information will help design an outlet that is effective in the long term, taking into account climate change.

There’s also modelling underway to assess the impact of proposed stormwater diversions in upper Airlie Road and Upper Cluny Road, which will inform what work is needed in the stream. It’s important to scope any work on the stream as accurately as possible because of the potential impact. The modelling will also help inform physical works sequencing, with the aim of realising benefits as soon as possible.

Resource consent planning for the upstream elements such as stormwater diversions, the flow path through the stream, the park and down Airlie Road, and the outlets at the beach, is also being undertaken.

By April next year, around Easter, we will be able to identify where and when we’ll be starting construction and share plans publicly.

Wellington Water advises Karehana residents that the detailed design of works to reduce the risk of flooding in the catchment is taking longer than previously advised.

Project Manager Lyndie McMillan has contacted residents directly to advise that there have been changes to the team working on the project, and it is taking longer than expected to be able to provide further detail.

Lyndie says the new team are working through information from the survey and feedback from residents as they review the width of stream channel required.  The team is also carefully working through the optimal combination of pipes and inlets to divert stormwater in the upper parts of the catchment before it reaches the stream or the park.  This will impact on the detailed design of works carrying stormwater from the park to the sea and the outlets at the beach.  

“I assure you that this project remains a priority for Wellington Water and Porirua City Council. Thank you for your patience.”  

About 40 Plimmerton residents talked with Wellington Water and Porirua City Council staff about the concept designs for infrastructure to reduce flood risk in the Karehana catchment.

A drop in session at the Plimmerton Pavilion on 15 June was a chance for residents to look at the concept designs and discuss how they would reduce the impact of heavy rain, such as that experienced over the weekend.

You can see the concept design posters attached below, the first file is an overall map and the second file has more detail.

If you have questions please contact Janice.rodenburg@wellingtonwater.co.nz

Documents

Concept designs 15 June

Overview map 15 June 2022

Concept designs 15 June 2022

Summary Karehana Park Options September 2021

Summary Karehana options 13Sept2021

Presentation Karehana Park Options September 2021

2021 09 08 Karehana SW Catchment Community Presentation 1Plimmerton FRP Posters 6 July.final

Plimmerton flood reduction - community update documents July 6 2021

Plimmerton FRP Posters 6 July.final 1

Plimmerton handout 6 July final

Plimmerton Stormwater Catchment Management Project - Overview March 2021

Plimmerton project overview March 2021 1

Taupō Stream James Street project overview

Taupō Stream James St project overview

Wellington Water is now moving ahead with assessing options for improving the stormwater network in School Road/Beach Road, Plimmerton. 

Some initial discussions have been had with some residents but there is more work to do before we can make a final decision on the preferred solution for improving the stormwater network in this area.  

We aim to report to Porirua City Council on options in coming months.

In the meantime, as we head into winter, our operations team is focused on maximizing the capacity of the current system and have already done some modifications to the outlet at the bottom of Beach Rd.

However, if there is an immediate risk of flooding, or you are aware of a stormwater inlet becoming blocked, please ring the Porirua City Council Contact Centre on 04 237 5089.

Wellington Water project team and Porirua City Council staff thank community members who joined a meeting on reducing flood risk in and around James Street on Sunday 27 March. 

An outline of the investigations into the issues and potential options for reducing flood risk was presented by Wellington Water Project Director Lyndie McMillan and Project Manager Josh Wright with the support of Porirua City Council Principal Advisor – Environment Ben Fountain, Porirua City Council Parks & City Services Operations Manager Mark Hammond and Porirua City Council Chief Advisor Olivia Dovey.

Project Director Lyndie McMillan says there was a lot of very useful feedback and input from those attending and this will be considered by the team.

To read a full summary of the meeting, including the challenges, what we know from modelling, the long list of options and next steps attached below:

Taupō catchment March 2022

Wellington Water project team and Porirua City Council (PCC) staff thank community members who joined a meeting on reducing flood risk in and around James Street on Sunday 27 March. 

An outline of the investigations into the issues and potential options for reducing flood risk was presented by Wellington Water Project Director Lyndie McMillan and Project Manager Josh Wright with the support of PCC Principal Advisor – Environment Ben Fountain, PCC Parks & City Services Operations Manager Mark Hammond and PCC Chief Advisor Olivia Dovey.

Project Director Lyndie McMillan says there was a lot of very useful feedback and input from those attending and this will be considered by the team.

To read a full summary of the meeting, including the challenges, what we know from modelling, the long list of options and next steps click here 

People in Airlie Road and Cluny Road whose properties back onto lower Karehana Park or the stream should have received a letter inviting them to meetings to discuss the initial concepts for the detailed design of stormwater improvements to reduce the risk of flooding, including a pump station and stream upgrades.

Wellington Water is keen to get the input of neighbours of potential works during this detailed design phase.  Meetings are:  

• Tuesday 25 January 6 pm, Karehana Park (by the petanque court) to talk primarily about the concepts for the lower end of the park. 
• Wednesday 26 January 6 pm, 43 Cluny Road, to talk primarily about the concepts for the upper stream upgrade. 

Engineer Kieron Thorpe will also be talking to individual property owners during the week, if you want to make a time to talk to Kieron, please contact  Janice.rodenburg@wellingtonwater.co.nz 

It was an awful end to spring for some of our community, when torrential rain caused flash flooding, damaging a number of properties.

The flooding, on Sunday 29 November, left 15 Plimmerton homes uninhabitable and two Whitby properties were evacuated due to a slip the following day.

Many more homes were flood-damaged and the clean-up effort saw the Council, Wellington Water, Downer, regional response agencies and an incredibly supportive community team up to deal with the aftermath of the storm.

Mayor Anita Baker says the very heavy and localised rain that fell on the Sunday morning in a short time coincided with high tide, leaving the water which usually runs out to sea with nowhere to go, overwhelming the system.

"We are aware our infrastructure is ageing, and climate change is causing more severe weather events. This is why we’re proposing to more than double our 3-Waters infrastructure investment in our next Long-term Plan to $800 million. On top of that we have also asked Wellington Water to identify the flooding hotspots with a view to additional funding for those as well. We’ll be asking your views about this additional expenditure early next year."

Mayor Baker was heartened to see the way the Plimmerton community responded to the emergency - with residents, the volunteer fire brigade and many others all rallying in support of their friends and neighbours.

"This was a huge clean-up job. We put out skips and helped residents load flood-damaged items onto trucks, and everyone just pitched in. Our teams worked really hard, and the whole community really came together in amazing ways," she says.

"Some families will be affected by this freak weather event for some time. 2020 just keeps throwing up challenges and we really feel for you."

With the weather continuously reminding us why this work is so important, we wanted to provide an end-of-year update on our work to improve the stormwater system.

Karehana design work underway 

Following Porirua City Council’s decision to invest $17.9 million in reducing the flood risk in the Karehana catchment, our consultant engineers Stantec are moving ahead with design.  

The council agreed to an integrated package of works including a pump station and ‘feeder’ channel in Karehana Park; stream upgrades above the park; a main pipe down Cluny Road; improvements to the Airlie Road culverts; and inlet improvements to reduce the risk of blockage from debris. 

Some residents may have seen indicative diagrams showing what these things might look like and where they could go. With design work now under way a much more detailed picture of what will be constructed is being developed and will be available.     

There’s been an initial discussion with representatives of the Residents Association and the Flood Action Group about how to minimise the impact of works on the park, while still removing stormwater at the volumes required and keeping within budget.  

We’ll be in touch with residents in the Karehana Park area after Christmas (likely from mid-January) to talk through the design work in more detail. We plan to hold a drop-in session for everyone interested in the first quarter of 2022. 

Our timetable is to complete design and obtain any necessary consents over the next year, with a view to starting the first phase of construction in 2023.  

Airlie Road inlet and pipe 

In November 2021, we investigated the state of the pipeline under Airlie Road, including removing built-up sediment, locating stormwater manholes and inspecting the pipelines via a camera. We removed a lot of sediment. There will be further investigations in this area, as we progress with design. 

James Street/Taupō Stream catchment 

We’re also getting under way with developing options for reducing flood risk around James Street and the State Highway, in the Taupō Stream catchment.  

Our engineer has been in touch with some residents and local businesses and a representative of St Theresa’s as part of investigations into what’s causing flooding in this area. He’s been looking at water flows from the Grays Road/Mo Street area and from the north as well as across the State Highway. Surveying is also being undertaken and will be completed over the next couple of months.   

Wellington Water aims to recommend a preferred option to the council by mid-2022.  

Keeping in touch 

If you have any questions about this project, please get in touch with Lyndie McMillan, Project Director Plimmerton Stormwater Catchment Management and improvements Project, Wellington Water Lyndie.McMIllan@wellingtonwater.co.nz or contact Janice.rodenburg@wellingtonwater.co.nz  

As always, if there is an immediate risk of flooding, or you are aware of a stormwater inlet becoming blocked, please ring the Porirua City Council Contact Centre on 04 237 5089, at any time of day or night. 

A new stormwater inlet grill has been fitted at Airlie Road in the Karehana Catchment with an onsite winch so it can be lifted during storm events to improve flood discharge capability.

When debris is clogging the inlet screen, lifting the grill can reduce the flooding impacts on upstream properties, especially in smaller flood events.

North of 22 Airlie Road, Plimmerton

When will it be used?

Lifting of the grill will happen under exceptional circumstances during storm events. The grill is there for safety reasons to prevent people being washed into the culvert and also to prevent blockages occurring within the culvert.

A water level gauge or ‘trigger’ point has been marked on the channel wall next to the grill. Wellington Water is also in the process of installing an electronic gauge, to enable remote monitoring.

Once the water level is close to the trigger point, a trained person will go to the site. They will check whether there is any blockage that can be removed by raking. If there is no blockage that can be removed and the water level reaches the trigger point, then the grill will be opened.

Who will operate the grill?

The stormwater inlet grill is hinged and can be lifted using a mechanical winch.

The winch and grill will be unlocked and operated by authorised people who are trained and equipped to work onsite during flood events. Currently Wellington Water staff are authorised, and once the electronic systems are up and running, the intention is to authorise Porirua City Council staff and local firefighters.

The authorised operators will have a standard procedure to follow and will remain onsite monitoring the flow while the grill is open. Once the water levels have subsided below the trigger point and no heavy rainfall is forecast, the grill will be closed.

Wellington Water and Porirua City Council are getting underway with investigating stormwater management options to reduce the risk of flooding in James Street and the area around St Andrews Road/the State Highway in the Taupō Stream catchment.

Wellington Water aims to recommend a preferred option to PCC by mid-2022.

The first step will be to survey ground and building levels. This will happen over the summer.  Residents will be contacted directly before surveying of building levels begins.

Find out more about this project below:

Concept designs 15 June

Overview map 15 June 2022

Concept designs 15 June 2022

Summary Karehana Park Options September 2021

Summary Karehana options 13Sept2021

Presentation Karehana Park Options September 2021

2021 09 08 Karehana SW Catchment Community Presentation 1Plimmerton FRP Posters 6 July.final

Plimmerton flood reduction - community update documents July 6 2021

Plimmerton FRP Posters 6 July.final 1

Plimmerton handout 6 July final

Plimmerton Stormwater Catchment Management Project - Overview March 2021

Plimmerton project overview March 2021 1

Taupō Stream James Street project overview

Taupō Stream James St project overview

Porirua City Council has committed $17.9m to reduce the flooding risk for homes in the Karehana area of Plimmerton.

Read more here

Porirua City Council will now make a decision on the options to help reduce the risk of flooding in the Karehana Catchment at the Council meeting on 4 November 2021.

The date has been pushed out because Councillors have asked for more information and need more time to consider that information.

We apologise about this change in timing, and understand it may be frustrating. However it is important that Councillors make well-informed and well-considered decisions. 

In feedback on the options, concerns were raised about the potential impact of a pump station and upgrades on Karehana Park. Should the Council decide to go ahead with a pump station as part of any solution, be assured that during the design process the impacts on the park will be carefully considered and the design team will talk to the community about how we could minimise these impacts.

We will let the community know what the Council decides.

Porirua City Councillors are considering 36 responses from the community on the options for mitigating the impact of flooding in the Karehana catchment.

Porirua City Councillors are considering 36 responses from the community on the options for mitigating the impact of flooding in the Karehana catchment.

Councillors also heard from a community representative at a meeting on 23 September. The Councillors want to make well-informed decisions and have asked for more information about some of the options presented to them. To give them time to adequately consider community  feedback and this additional information, decisions have been deferred to the Council meeting on 21 October 2021.

Options for mitigating the impact of flooding in the Karehana catchment have been presented to Porirua City Council and councillors are considering the information.

The Plimmerton Flood Management and Resilience (PFMR) Working Group and members of the Plimmerton community have the opportunity to give their views on the options, before the Council makes decisions on the next steps on 7 October.

There is a summary of the information presented to the Council available below:

Concept designs 15 June

Overview map 15 June 2022

Concept designs 15 June 2022

Summary Karehana Park Options September 2021

Summary Karehana options 13Sept2021

Presentation Karehana Park Options September 2021

2021 09 08 Karehana SW Catchment Community Presentation 1Plimmerton FRP Posters 6 July.final

Plimmerton flood reduction - community update documents July 6 2021

Plimmerton FRP Posters 6 July.final 1

Plimmerton handout 6 July final

Plimmerton Stormwater Catchment Management Project - Overview March 2021

Plimmerton project overview March 2021 1

Taupō Stream James Street project overview

Taupō Stream James St project overview

The Stormwater Catchment Management and Improvements Project Team also briefed the Plimmerton Flood Management and Resilience Working Group on Wednesday 8 September.

The PMFR Working Group is due to present its views to the council on 23 September.

Plimmerton community members who have  questions or comments can either talk directly to a member of the PMFR Working Group, email plimmertonfloodaction@gmail.com; or email Ben Fountain at Porirua City Council on PlimmertonFloodResponse@poriruacity.govt.nz 

Written submissions should be emailed to PlimmertonFloodResponse@poriruacity.govt.nz by Monday 20 September.

The PFMR Working Group members are Grace Alum, Dave Anderson, Kelvin Berryman, Richard Bradley, Alan Dodson, Karen Feint, Alicja Gear, Chris Griggs and Mel Troy.

We're pleased to advise that the new grill, and the winch to lift it during heavy rain, will be installed at the Karehana Park inlet on 6 September.

We're pleased to advise that the new grill, and the winch to lift it during heavy rain, will be installed at the Karehana Park inlet on 6 September.

This has taken longer than we all wanted. It’s fair to say we have found that getting one-off assets such as this manufactured is not as quick and easy as we had anticipated. 

We are making good progress on options for reducing flood risk in the Karehana catchment, but to make sure we put the best possible information in front of Porirua City Council, we have had to push the timeline out a few weeks.

Karehana catchment long term options – new dates

We are making good progress on options for reducing flood risk in the Karehana catchment, but to make sure we put the best possible information in front of Porirua City Council, we have had to push the timeline out a few weeks.

The Council is now scheduled to make decisions on 7 October 2021.

We know the community is keen to see rapid progress, and this extension of the timeline will be frustrating, but it is important that we get this right. 

There are two main reasons for the extra time.

• Due to the many factors contributing to flooding, the engineers are putting together packages of infrastructure options. It is taking time to fully assess the impact, effectiveness, risks and costs of a number of different combinations of options.
• The Council wants to know what the community thinks of the options before it makes its decisions.  This means finding time for you to consider and provide feedback on these.

The Plimmerton Flood Management and Resilience Working Group has been providing the Project Team with a valuable community perspective on the flooding hazards and the options to date, and will consider the options and be invited to provide feedback to Councillors.

We also want to give everyone in the community the opportunity to have a say. We will be providing information about the options online and at a drop-in session and inviting you to provide written feedback.

The timetable is:

• 2 September: Options presented to a Council workshop, and to Flood Working Group members
• 3 September: Options made public on Plimmerton Stormwater website and advisory email sent out
• 8 September (4 pm – 6.30 pm, Plimmerton Pavilion): Drop-in session where you can ask questions about the options
• 20 September: Feedback on options closes
• 23 September: Councillors consider written feedback and hear from Flood Working Group
• 7 October: Council makes decisions

We will send an email to the community on 3 September about the options and inviting your comments.

You can contact Project Lead Ben Fountain, Principal Advisor – Environment Kaitohutohu Matua - Taiao (Āhuarangi me te Wai) 
Porirua City Council by emailing  PlimmertonFloodResponse@poriruacity.govt.nz 

Meanwhile please remember if there is a risk of flooding, or you are aware of a stormwater inlet becoming blocked, please ring our Contact Centre on 04 237 5089, at any time of day or night.

We're working through the analysis of a short list of options. These options focus on three topographic areas.

Karehana update

In brief, the team are working through the analysis of a short list of options. These options focus on three topographic areas:

• • Primary (options to increase the flow from the lower end of Karehana Park to the sea)
  • Secondary (addressing network incapacity in the upper and mid catchment and improving the effectiveness of the primary options)
  • Tertiary (supporting options to enhance the primary and secondary options where suitable).

Multi-criteria analysis is underway right now to assess the impact, effectiveness, risks and costs of the options, individually and in combination. This means:

• • Specialists including engineers, environmental scientists and key Porirua City Council and Wellington Water staff are assessing the options against 10 criteria including impact, practicality and cost.

The preferred options/package of options will be recommended to Porirua City Council for their deliberation and a decision next month (19 August).

Karehana Park Airlie Road Inlet

Later in July the winch will be installed so the grill can be lifted up in the flood. We’re talking to the Fire Brigade about who will operate this. A new grill that is less prone to blockage is being designed and fabricated by Porirua City Council and is due to be installed next month (August).

Keeping in touch

Remember if there is a risk of flooding, or you are aware of a stormwater inlet becoming blocked, please ring the Porirua City Council Contact Centre on 04 237 5089, at any time of day or night.

You can contact Project Lead Ben Fountain by emailing  PlimmertonFloodResponse@poriruacity.govt.nz 

There was a good turnout at the community drop-in session on Tuesday 6 July, providing an update on progress in reducing the risk of flooding.

About 40 people attended to find out about the work underway to maintain and improve the stormwater network.

Porirua City Council and Wellington Water staff thank those who came along for their questions and comments.

The community update posters and handout from the session are available below:

Concept designs 15 June

Overview map 15 June 2022

Concept designs 15 June 2022

Summary Karehana Park Options September 2021

Summary Karehana options 13Sept2021

Presentation Karehana Park Options September 2021

2021 09 08 Karehana SW Catchment Community Presentation 1Plimmerton FRP Posters 6 July.final

Plimmerton flood reduction - community update documents July 6 2021

Plimmerton FRP Posters 6 July.final 1

Plimmerton handout 6 July final

Plimmerton Stormwater Catchment Management Project - Overview March 2021

Plimmerton project overview March 2021 1

Taupō Stream James Street project overview

Taupō Stream James St project overview

Plimmerton people are invited to drop in for an update on progress in reducing the risk of flooding.

Plimmerton people are invited to drop in for an update on progress in reducing the risk of flooding. We’ll provide information on stormwater network maintenance and where we are up to in planning for long-term solutions.

Our team will be on site to talk to you and answer questions through the afternoon/early evening, drop in when you can.

3.30 pm – 7 pm

Tuesday 6 July

Plimmerton Pavilion, Sunset Parade

Wellington Water and Porirua City Council invite you to a drop-in session on Wednesday June 13 where we will share concept designs for works to reduce flood risk, and answer any questions:

The session will be held at the Plimmerton Pavilion on Wednesday 15 June from 3.30pm to 7pm.

As a reminder, Porirua City Council agreed to an integrated package of works including a pump station and ‘feeder’ channel in Karehana Park; stream upgrades above the park; a main pipe down Cluny Road; improvements to the Airlie Road culverts; and inlet improvements to reduce the risk of blockage from debris.

You can see a summary of the Karehana Park Options presented to Council below:

Concept designs 15 June

Overview map 15 June 2022

Concept designs 15 June 2022

Summary Karehana Park Options September 2021

Summary Karehana options 13Sept2021

Presentation Karehana Park Options September 2021

2021 09 08 Karehana SW Catchment Community Presentation 1Plimmerton FRP Posters 6 July.final

Plimmerton flood reduction - community update documents July 6 2021

Plimmerton FRP Posters 6 July.final 1

Plimmerton handout 6 July final

Plimmerton Stormwater Catchment Management Project - Overview March 2021

Plimmerton project overview March 2021 1

Taupō Stream James Street project overview

Taupō Stream James St project overview

Published 09/06/2021

As we head into mid-winter, Porirua City Council and Wellington Water remain focused on reducing the risk of flooding in Plimmerton.

As we head into mid-winter, Porirua City Council and Wellington Water remain focused on reducing the risk of flooding in Plimmerton. We’re up to date with maintenance and have made the maintenance schedule visible on the website (more below).

We’re making sure there’s a pump on standby when heavy rain is forecast and our crews are ready to respond. If you are aware of a stormwater inlet becoming blocked please ring our Contact Centre on 04 237 5089, at any time of day or night.

And we are making progress on developing long-term solutions. 

Maintenance

In recent months we have been taking a much more coordinated approach to how we maintain the existing stormwater assets in the Plimmerton area.

The Plimmerton Flood Action Group requested Council and Wellington Water be more transparent with its maintenance plans and schedules. We agreed this was a good thing to do and we have been working together to pull our information into one place and work out the best way to share this with the community.

There is now a map on the Council's project page that details the maintenance schedule for our assets. This map is a work in progress and we’re very keen to hear from you if we have missed any assets or you think the map could do with any improvements to make it easier to understand.

You can view the maintenance webpage here

Karehana

The project team is currently doing detailed analysis on options packages – or ‘grab bags’ – that combine actions to reduce the flow and volume of water ponding in Karehana park in heavy rain and get the water out of the park more quickly. 

The analysis includes using a computer model of flooding, which can predict what is likely to happen in different rain events.  The Flood Management and Resilience Working Group (FMRWG) discussed the model in some depth at its last meeting.  While no model is 100 % accurate, the engineers working on this project consider this model a useful tool that will provide helpful information.

The short-list options packages will be assessed against a number of criteria and the FMRWG is providing input into how those criteria are weighted. The short-list of options packages will be shared with the community in July.

Once again, thanks to the Flood Management and Resilience Working Group members Karen Feint, Richard Bradley, Chris Griggs, Kelvin Berryman, Alicja Gear, Grace Alum, Mel Troy, Alan Dodson and Dave Anderson.

They are doing a good job of keeping the project team focused on what’s important to the community, including the need to move this work along as fast as we can.

Managing the Karehana Park grate

We’ve been talking to contractors about getting a redesigned grate at the Karehana Park culvert inlet at the Airlie Rd driveway. Unfortunately that has not delivered a solution so Porirua City Council is now taking over alterations to the grate.

A winch to lift the grate at times of heavy rain is on the way and should be ready to install around the end of June or early July. A concrete base will be constructed that the winch will sit on.

WaStop

We have carefully considered whether to remove the WaStop where the Airlie Road culvert flows out to sea.  It has been decided that the WaStop will not be removed due to the risk of the pipe filling with sand and the health and safety risks associated with someone having to crawl inside it to clean it out regularly.

However, a new WaStop rubber valve has been installed and will operate more efficiently than the old, worn one.

Taupō Stream Catchment

PCC and Waka Kotahi have worked together to organise drain clearing.  Blackberry and vegetation has been cleared from the drains down the western side of State Highway 1.  On the eastern side, drains have been cleared around James Street. Contractors will soon be completing drain clearing on the eastern side from the weigh station to the roundabout.

Wellington Water has met with representatives of St Theresa’s Church and School, and Jennian Homes, on long term plans to mitigate flooding and discussions will continue. A detailed project plan is currently under development.

We are on track towards decisions about reducing the risk of flooding in Plimmerton. 

Karehana

In the Karehana catchment, the Working Group has been providing useful and thoughtful input on a long list of options that would address a number of issues contributing to flooding:

• holding back water safely and releasing it downstream at a manageable rate (AKA ‘attenuation’)
• reducing the flows and volume of water reaching Karehana Park in order to reduce peak flood levels in the park
• improving flow capacity above Karehana Park in order to prevent water from ‘escaping’ the collection network
• increasing flow out of Karehana Park in order to reduce peak flood levels, ie. bigger and/or new pipes
• controlling, managing or eliminating 'overland flow' – that is water that has escaped from - or never made it into - the collection network
• protecting the network from potential blockages, such as plant matter, silt, and gravel
• a range of localised solutions that help out smaller groups of properties, ie. improved curb and channel in the road, bigger grates and pipes in specific areas.

The next step is for the specialist engineers to develop packages, or ‘grab bags’, of options that would work together to offer solutions across the top, middle and bottom parts of the catchment.

You see the minutes of the meetings here

Thanks to Working Group community members Karen Feint, Richard Bradley, Chris Griggs, Kelvin Berryman, Alicja Gear, Grace Alum, Mel Troy, Alan Dodson and Dave Anderson.

Managing the Karehana Park grate

One of the interim measures to better manage stormwater leaving Karehana Park is to design a system that will allow the grate covering the culvert inlet at the Airlie Rd driveway to be lifted when the stream is at full flow. [see main image]

Kenepuru Engineering have designed a winch to lift the grill. Wellington Water have provided some feedback and we are now waiting on a final price from Kenepuru Engineering before instructing them to start work on building the winch. Once we have a delivery date, we will share this with you.

We are also planning to sit down with the Plimmerton Fire Brigade and Wellington Water Operational team to talk through and document how to operate the winch and when it will appropriate to use it, and how we make sure that everyone stays safe when the grate is open.

James Street and State Highway 1

Porirua City Council and Wellington Water are meeting with St Theresa’s parish and school representatives on 2 May to discuss the next steps in addressing issues in this area.

In coming weeks, you will notice teams working in the drains beside State Highway 1 clearing blackberry and vegetation from the drains. Porirua City Council is managing this task, with the financial support of Waka Kotahi/NZTA.

Waka Kotahi/NZTA have also agreed to join the team working on the long term flooding resolution for the James St/Taupō Swamp Catchment Study due to kick off in July. We are please to have one of the major partners on board and contributing to the wider investigation programme.

Operational readiness

During recent heavy rainfall, Porirua City Council and Wellington Water staff turned out at 1am to follow up on a call received by our After Hours Contact Centre. The council staff member checked out the Karehana Park grate, noted that everything was flowing as expected. They also walked up Airlie Rd, across Firth Rd and down Cluny Road to check out reports of potential flooding. The Wellington Water on-call crew also visited the site and cleared a small amount of built-up debris from the grate.

If you are aware of a stormwater inlet becoming blocked, please ring the Porirua City Council Contact Centre on 04 237 5089, at any time of day or night.

For other non-urgent maintenance requests, email enquiries@poriruacity.govt.nz or download the “Antenno” app to log a job.

Consenting workshop

We held a drop-in clinic on 21 April for flood-affected residents with questions about building or resource consents as part of their repair process. We had about seven homeowners or families stop in and we talked through their individual situations and answered questions where we could.

Karehana

In the Karehana catchment, consulting engineers have been gathering information, including site visits and meetings with a number of people whose homes were affected by the November flood. 

The Flood Management and Resilience Working Group met for the first time on 23 March, for what members felt was a useful discussion on a long list of options for reducing the risk of flooding.

The project plan sees Porirua City Council making decisions on preferred solutions in August this year.

Karehana surveying

Surveyors will be working along Airlie and Cluny Roads and around Karehana Park in the next few weeks, to build an accurate picture of ground and building levels and pipe work. 

Some residents will have received a letter asking for permission to enter properties to carry out this important work.  Thank you to those who have already responded.  If you haven’t responded yet, I encourage you to do so as this will contribute to us having the best information to base decisions on.

James Street and State Highway 1

We are in discussion with New Zealand Transport Agency, as a first step in investigating and finding solutions for this area.  

Hongoeka

The team at Porirua City Council will be in touch with Hongoeka Marae representatives about options to address flooding and stormwater issues there.

Operational readiness

Porirua City Council has taken community feedback on board about maintenance standards. The PCC Parks team, Downers and Wellington Water have set up a project team to share information and understand what each team does. This is all being pulled together into a joined up Maintenance Plan and Schedule. We are on track to finish this piece of work by end of April, when we’ll share it with you.

In the meantime, if you think a maintenance task is outstanding please ring PPC's Contact Centre on 04 237 5089, email enquiries@poriruacity.govt.nz 

Consenting

To support flood-affected residents, PCC is planning for a consenting drop-in clinic to be held in mid-April, where the building and resource consent planners will be available to chat with and seek advice or feedback on any planned work at home. We’ll be in touch with more detail closer to the date.

Finally, we understand the importance of moving with urgency to reduce the risk of flooding, and we are making progress as quickly as we can, while balancing this with taking the time we need to properly assess the options.