Te Awarua-o-Porirua Harbour FAQs

Image showing Porirua Harbour and Pauatanaui Inlet.

This page answers some of the most frequently asked questions about Porirua Harbour and the Porirua Harbour and Catchment Management programme.


Stormwater Bylaw - what does this mean for me?

Porirua City Council adopted its first Stormwater Bylaw on 27 August 2015. What does this mean for me?

It is now illegal to tip, wash or flush many common pollutants down our street and other stormwater drains. Up until now, Council had little control over what went into the stormwater system and then into the harbour.

The particular contaminants covered by the bylaw include the following:

  • Cleaning products - including detergents and disinfectants, such as bleach and '30 Seconds'
  • Water blasting waste
  • Paint - including paint wash
  • Solvents - including paint stripper
  • Liquid fuels - petrol, diesel etc
  • Oil & grease
  • Radiator coolant
  • Cooking oil
  • Cement wash, cement slurry, concrete cutting waste - this includes wash from new exposed aggregate driveways

These contaminants will either need to be collected and disposed of to appropriate facilities, or the run-off redirected to lawn, gardens or compost if only small amounts.

In the case of vehicle washing, washing on grass is a good option as it filters out most of the contaminants. Otherwise placing a small diversion (towels, compost sock, etc) to collect and channel runoff to lawn or garden will work.

Car wash fundraisers can contact Council for advice and assistance.

Small amounts of most other contaminants can be tipped down your laundry sink. This goes to the wastewater system for treatment.

The Council will exercise a 12 month grace period from 27 August 2015 while people get used to the new rules and Council undertakes a public education programme.

The other personal impact of the bylaw will be a significant contribution towards cleaning up Porirua Harbour and other sites around our coast, meaning we will be able to enjoy a healthier environment.

If you are interested in more information, watch a couple of short videos you might enjoy from Australia on stormwater and carwashing.

Some answers to more specific questions:

    • Doesn't road-run-off go into the drains anyway when it rains? So why bother with controlling carwash? Wet weather road run-off is a significant contributor to harbour contamination, one that Councils and the NZ Transport Agency are aware of and also seeking ways to deal with. There is however, an important difference between road run-off and carwash: Road run-off arises almost solely from rainfall events. The contaminants are therefore diluted by rainwater and there is also a greater possibility of them being flushed out of the harbour. By comparison, carwashing generally happens when the weather is fine and the carwash gets less dilution and also less possibility of being flushed out of the harbour. The reality is, that both sources need to be dealt with.

What can I do to help to clean-up the harbour?

At home:

  • Avoid putting soil, paints, solvents, oil, cleaners and other chemicals down the street drain or into the street gutter (these actually drain to the nearest stream then into the harbour. They don't go to treatment).
  • Dispose of leftover paints, solvents, oil, cleaners and other chemicals to landfill, your nearest disposal outlet (eg many garages take used oil), or you could tip small amounts onsite to lawn or compost dump.
  • Wash cars on grass wherever possible. This will filter out some of the contaminants. Other options include using a carwash facility, making a simple filtration sock or barrier to channel carwash to lawn or garden (avoid carwash entering street gutters or drains).
  • Avoid littering. Dispose of rubbish in your council bags or rubbish bins. Larger items of solid waste should be taken to the landfill.
  • Special mention needs to be made of road cones and shopping carts – not only do they make our streams and harbour unattractive, they interfere with the natural stream and harbour systems. Leave the cones and carts where they are meant to be – our roads and shops.
  • Report pollution incidents immediately to the 24hr Environment Hotline on 0800 496 734. That way the source can be tracked down and remedial action taken.

In the community:

Consider joining one of the local environmental groups (e.g., Pauatahanui Wildlife Reserve Management Group, Friends of Maara Roa Reserve (upper Cannons Creek), Whitireia Park Restoration Group, Friends of Tawa Bush ReserveGuardians of Pauatahanui Inlet (GOPI), Porirua Harbour Trust (PHT)).

Consider joining a restoration event. Opportunities for helping with vegetation planting and stream or harbour clean-ups are generally advertised.

Read our Stormwater Bylaw and Washing Your Car FAQs for more detailed information and view our car washing video to see what you can do to help.

The harbour has a 'new' name?

Yes. As part of the Ngati Toa Rangatira Treaty of Waitangi Settlement, a number of original names were restored to locations within the harbour catchment, including the harbour itself. On 1 August 2014 the New Zealand Geographic Board officially gazetted the 'new' name - Te Awarua-o-Porirua Harbour - including the use of the hyphens. As well as being the traditional name for the harbour, Te Awarua-o-Porirua is also the name of the harbour taniwha. Maori mythology describes how Te Awarua-o-Porirua carved out the harbour during his run-up in an attempt to fly. When he eventually succeeded, he then crash landed on Mana Island which resulted in flattening its top. Te Awarua-o-Porirua is now content to remain on the ground and live peacefully in the harbour.

Which part is actually ‘Te Awarua-o-Porirua Harbour’?

Both arms of the harbour officially make up ‘Te Awarua-o-Porirua Harbour’. This is the name officially gazetted by the New Zealand Geographic Board (NZGB) on 1 August 2014 as a result of Ngati Toa Rangatira's Treaty of Waitangi Settlement. NZGB also advises that 'Pauatahanui Inlet' is a 'recognised' name for the eastern arm of the harbour, and should be identified as 'Te Awarua-o-Porirua Harbour (Pauatahanui Inlet)' where appropriate. NZGB recognises no officail name for the southern arm of the harbour which is locally known as the 'Onepoto Arm'. The Council encourages the use of 'Te Awarua-o-Porirua Harbour (Onepoto Arm)' where appropriate.

The harbour stinks – why?

During the summer season some parts of the harbour can give off strong unpleasant smells. There are two reasons for this:

  • Algae decay. As an estuary Porirua Harbour is a great place for marine algae to grow. Warm temperatures and an abundance of nutrients promotes the growth of algae such as the bright green sea lettuce Ulva sp. Part of the algae life cycle includes die-off. The decayof the algae creates strong odours. The strength of the odour is dependent on the year to year amount of algae growth, temperature and, of course, wind direction.
  • Smelly mud. The Okowai Lagoon (the first lagoon on the right of State Highway One north of the City centre) has particular issues in summer resulting from a build-up of smelly muds. The smell is more noticeable depending on temperature and wind direction. The Council, agencies and local developer are considering options for improving the situation.

To dredge or not to dredge?

The possibility of dredging the harbour raises a number of interesting questions:

Why don’t we just dredge the build-up of silt in the harbour?

An important point to remember is that by their very nature all estuaries, including Porirua Harbour, are sediment traps. Their relatively calm environment allows the accumulation of sand coming in from the outer coast and silt from the land. This means that all estuaries eventually fill-in. It is the excessive rate of filling that is concerning about Porirua Harbour.

Can we improve the situation? Coastal scientist from agencies such as NIWA have advised against dredging until the excessive amounts of sediment coming into the harbour from the catchment have been significantly reduced. Otherwise, like digging a hole in the beach and going back after the tides been in to see it filled in again, the same will happen with harbour dredging. Dredging would also destroy shellfish beds and other sea life. Another serious issues would be where to dispose of any dredged materials, especially since some of it contains contaminants. At this stage, dredging would be ineffective, short-term and very expensive.

The joint councils have developed, and are now implementing, a catchment-wide Sediment Reduction Plan to reduce sedimentation rates to more natural and manageable levels.

Wouldn’t dredging the harbour help increase its flushing capacity and also make it healthier?

Dredging is unlikely to make much difference to the harbour flushing capacity. Target areas for dredging, for example to improve navigability, are below low tide. Technically, this means that such dredging would not improve the ‘tidal prism’ – the water that comes in and out of the harbour between high and low tide - which is critical for the flushing ability.

Some areas of the harbour are contaminated. Why don’t we clean them up by dredging them?

Firstly, any dredging work would also re-suspend and spread those contaminants further. Secondly, there would be a major issue around where to dispose of the contaminated sediments. It is unlikely a resource consent would be granted to dispose of dredged materials at sea since these could contaminate fishing grounds. Disposal to land (say, in a landfill) may require a purpose-built facility. This would be very expensive.

Current best practice is to leave the contaminated sediments undisturbed, reduce the amount of contaminants entering the harbour, and allow future accumulation of sediments cover over and ‘seal’ the existing sediments.

The joint councils are committed to reducing contaminants entering the harbour.

The sand bar is so shallow, why don’t we dredge to improve boat access?

Comparisons of all bathymetric surveys of the harbour since 1847 show that the height of the bar has changed very little over the past 160 years – fluctuating + or – 5cm in that time. This is consistent with the normal dynamics of a harbour bar. A harbour bar protects the inner harbour from much of the extreme impacts from coastal waves and storm events. The sand on a bar will also respond to sand removal by refilling any gap. Best practice and science advice recommends not disturbing the bar. Dredging would be ineffective, temporary and expensive.

The sand banks around the harbour seem to be growing

The sand banks are all made from marine sand. This is important. It means that the sand has come from the outer harbour. Research shows that very little new sand is now coming into the harbour. The apparent spread of sand banks occurs for two main reasons: King low tides happening during the day so that more sand bank is visible, so it seems they are 'growing'; Secondly, what we are seeing is a reworking and redistribution of the sand already in the harbour. This is a natural phenomenon and part of an estuary's dynamics. The earliest survey of the harbour by the HMS Acheron in 1847 strongly suggests that Pauatahanui Inlet was widely shoaled, even then. Also anecdotal evidence from long-time local boatees/engineers agrees with the science, that what we are seeing now is a redistribution of sand already in the harbour.

Meanwhile, the extension of the sandbank into Browns Bay is being monitored.

There are so many dead cockle shells around the harbour – is the harbour water killing them?

This is a natural occurrence, not related to contaminants. One reason Ngati Toa Rangatira settled around the harbour was large amounts of cockles. Cockle shell banks and beaches used to be widespread throughout the harbour. However, edge development for road, rail and reclamations destroyed many of these, particularly in the Onepoto Arm. Significant concentrations of cockles still exist in the subtidal and intertidal areas of both arms of the harbour - The harbour still has the highest concentration of cockles of any estuary in New Zealand. Natural mortality and the action of tide and waves washes cockle shells to the harbour edges, particularly sheltered embayments.

The 2013 3-year Cockle Survey undertaken by the Guardians of Pauatahanui Inlet (GOPI), showed a steady increase in cockle numbers since the first survey 1995. The numbers have increased 85% since then, and 21% since the previous survey in 2010. This trend indicates reduced sediment entering the Inlet, and a healthier harbour. The 2016 survey was completed in December and results from this should be available in March 2017.

The Harbour is so brown today, why?

There is no doubt that Porirua Harbour has a sediment problem – most of this washing in from the land. Floods carry a lot of sediment and do turn the harbour brown. However, this is not unique to Porirua. This is common in most estuaries and even the open coast.

The occasions when the parts of the harbour go brown and there has been no flooding are due to wave action stirring up bottom sediments – mud and fine silt – and keeping them in suspension until the wind and waves die down.

Is it safe to swim?

As a general rule, yes, for all beach areas.

Places like Plimmerton Beach and Karehana Bay, as well as Dolly Vardon Reserve at Mana, are some of the most popular and safe beaches in the Wellington region. These are closer to the harbour entrance and open coast where the water quality is understandably higher.

The harbour is widely used by various watersport groups – waka ama, sailing, powerboating, kayaks, paddleboarding and wind surfing are some of the common activities around the harbour. Various watersport schools prefer using Porirua Harbour because of its protected and safe environment, particularly for learners.

There are a number of areas signposted with health warnings. These areas are, however, either unattractive for swimming or where swimming is discouraged. These places are generally adjacent to stormwater pipes originating from industrial zones, particularly at the southern end of the Onepoto Arm. Swimming is also generally discouraged for three days after a storm/rainfall event. These events tend to wash contaminants off roads and into the harbour. Such contaminants are then generally flushed out of the harbour within three days.

What about fishing?

This raises two questions: Are there any fish? And are they safe to eat?

While the fishing in the harbour is not as good as historically, there are definitely fish. Fishers particularly enjoy the entrances to both arms of the harbour. Shellfish are safest to take from these same areas.

Fish taken from the harbour entrance are generally safe to eat. Testing of fish detects no concerning levels of chemical contaminants. One caution would be any taking fish or shellfish from around stormwater outfalls, particularly adjacent Porirua Stream and the City centre. There is a danger from faecal and other pathogenic matter. Keep to the harbour entrance and outer harbour.

What’s the impact of Transmission Gully Motorway on the harbour?

There may be short-term impacts on the harbour from sediment during the construction phase of the motorway. However, the evidence suggests that the motorway, once built, will provide long-term benefits to the health of the harbour. The use of best practice controls during the construction phase and then the operating phase, will minimise sediment and contaminant run-off into the harbour.

The state of the harbour and the performance of these control measures will be closely monitored.

If it’s that bad, why bother cleaning up the harbour?

Firstly, it’s not “that bad”. There are a few known areas of the harbour that are not in good condition, but otherwise the harbour has the basis of a sound ecology, is intensely used as a regional as well as local recreational resource and remains the centrepiece of Porirua City. Further, the science is telling us that the health of the harbour generally, including the bad bits, can be significantly improved: Which is what the Porirua Harbour and Catchment Strategy is all about.

The harbour is an important home and habitat for wildlife and fish. Cleaning up the harbour will improve this further. Clearly, we all love the harbour and the community wants it cleaned up.

What is the Council doing about the harbour?

The short answer… implementing the Porirua Harbour & Catchment Strategy.

The joint Porirua City, Wellington City and Greater Wellington Regional councils along with key partner, Ngati Toa Rangatira, are implementing the Porirua Harbour and Catchment Strategy which was developed with, and agreed to by, the Porirua catchment communities.

Key elements of the implementation of the Strategy are:

  • Sewer and stormwater upgrades
  • A catchment-wide Sediment Reduction Plan
  • A Porirua Stream mouth enhancement plan
  • A targeted school, business and community education programme
  • Reviewing regulatory provisions to better control sediment and contaminant run-off
  • Improved litter management
  • Maintaining a research and extensive monitoring programme

How long before we see any positive changes?

When you are dealing with nature most things take time. It is no different with the restoration of Porirua Harbour. Significant reductions in sediment and contaminants entering the harbour will, in some instances, take decades as we increase vegetation in the catchment and reduce pollution sources.

However, the 2013 Cockle Survey of Pauatahanui Inlet showed a steady increase in cockle numbers since 1995. This includes a 20% increase since the 2011 survey. The size of cockles is increasing too. These are indicative of sediment reduction and improved ecological health in the Inlet. The 2016 Survey was completed in December, and results should be available in April 2017.

One other area where a significant improvement has been made already is the cleaning up of the constant accumulation of litter (including shopping carts, road cones and car tyres) around the harbour.

Useful links

Do you have any other questions?

If you have any other questions, please contact Keith Calder on (04) 237 3598 or email kcalder@pcc.govt.nz.