GUARDIANS
OF PAUATAHANUI INLET
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| GUARDIANS
OF PAUATAHANUI INLET |
Proposed Western Corridor Plan 30 October 2005 Summary
1. The Guardians do not support the Coastal Route upgrade, principally because we wish to see a reduction of traffic through the Inlet catchment area on roads that are not able to be equipped to deal with the problem of particulate and dissolved materials reaching the Inlet.
2. The Guardians support the development of Transmission Gully because it will achieve a reduction of traffic on the roads surrounding the Inlet.
3. The Guardians most strongly represent that any new or upgraded roads must by the adoption of ‘best practice’ design and technology control and reduce the release of sediments and prevent particulate and dissolved materials reaching the Inlet.
4. The Guardians most strongly represent that any further bridging at the mouth of the Inlet be supported by the necessary prior research to ensure a neutral effect on the hydrology of the Inlet and on the tidal regime.
The Guardians wish to be heard on this submission.
Guardians of Pauatahanui Inlet The Guardians of Pauatahanui Inlet is an incorporated society, established in 1991 and currently with about 200 financial members. The Society’s primary objective is:
To encourage, promote, protect, maintain and foster the natural, historic and cultural values of the Pauatahanui Inlet.
To this end the Guardians have conducted triennial surveys of the state of the Inlet cockle population since 1992, and run a quarterly monitoring programme on the health of the Inlet catchment streams. We have made submissions on behalf of the Inlet in planning processes, have produced an education kit for use in schools and run a number of educational and promotional activities.
Guardians were also instrumental in initiating, promoting and supporting the development of the Pauatahanui Inlet Action Plan. This plan sets out a programme that will assist in the management of the Inlet and its catchment to achieve its objective to:
Manage the Pauatahanui Inlet and its catchment to enhance the quality of the environment by protecting the integrity of existing ecosystems and by restoring degraded ecosystems wherever possible.
The Action Plan is endorsed by the Guardians and we are working closely with the Pauatahanui Inlet Community Trust to promote its implementation.
We draw your attention to the endorsement of the Action Plan by parties heavily involved in the development of a Western Corridor transport strategy – Porirua City Council, Greater Wellington Regional Council and, significantly, Transit NZ. This endorsement behoves these parties to take every precaution to ensure that the environment of the Inlet is not adversely affected by the design, construction and operation of existing and new roads within the Inlet catchment.
The Significance of Pauatahanui Inlet Pauatahanui Inlet is identified in the Wellington Regional Coastal plan as an Area of Significant Conservation Value and is recognized by the Department of Conservation as a Site of Special Wildlife Interest and classified as being a site of National Significance.
The impact of roads on the Inlet Currently the greatest threats to the ecological values of the Inlet from the presence of roads in the catchment are:
· Release into the Inlet of sediment from earthworks and road construction. Modern technology and design concepts are capable of reducing this to negligible levels. We would expect any resource consent to insist on the application of ‘best practice’ in this regard. We understand that Transit NZ and the Greater Wellington Regional Council have already factored this approach into the development of the route for Transmission Gully.
· Release into the Inlet of particulate and dissolved matter from road surfaces. This mainly derives from vehicles, e.g. tyre and brake pad dust, oil and fuel residues, accidental spillages. Carried into the Inlet and its catchment streams by rainfall, these toxic contaminants, especially the heavy metals, accumulate in the sediment on the bottom of the Inlet and in the animals that feed there. They pose a direct threat to these animals and can be passed up the food chain to humans. Again, modern technology can prevent these materials from reaching the Inlet. We would expect incorporation of appropriate technology to be a condition of any resource consent for new and upgraded roads.
Our major concern is with existing roads. The high cost of retrofitting existing roads inhibits the authorities from taking action. Meanwhile the concentration in the Inlet sediments of some of these pollutants is at or just below the level at which they become a risk to the fauna and flora.
The volume of traffic on the major roads in the catchment (SH1, SH58, Grays Road, Paekakariki Hill Road) is projected to increase dramatically in the next decade and the pollution problem will increase proportionately. The Guardians' objective must be to seek a reduction in traffic through the Inlet catchment on roads that are not able to be equipped to deal with this problem.
For this reason the Guardians support Transmission Gully over the Coastal Route.
It is a misconception that Transmission Gully will be more of a problem than the Coastal Route because it has a much greater proportion of its length within the catchment. This is true, but it is located some distance from the Inlet edge, and provided that ‘best practice’ technology is used to treat road runoff the effect of the Gully road will be negligible.
· Reduction of ecological, social and cultural values through the modification of roads around the Inlet. This will happen if SH58 and/or Grays Road are modified to deal with increased traffic flows. Both are narrow with severe bends. In particular the widening and rerouting of Grays Road as depicted on the Transit NZ planning map would destroy valuable wildlife reserve land and an important area of native bush. It would clearly diminish the ecological value of the Inlet, as well as have adverse social and economic effects on the local farming community.
The present traffic volume severely compromises the safety of recreation cyclists and pedestrians and diminishes the recreation value of the Inlet – throughout the day and weekends, and not just at peak rush hour times.
Grays Road, SH58 and Paekakariki Hill Road together form the major east-west link between SH1 and SH2 in the north Wellington region. All are increasingly heavily used. Current daily flows are about 5,300 vehicles on Grays Road, 3,400 on Paekakariki Hill Road and 8,000 using SH58 for this link (plus a further 6,000 coming out of Whitby-Paremata). Increases of up to 40% are anticipated by 2016.
These roads will continue to provide this function if the Coastal Route is upgraded without an alternative east-west link in the northern section being provided. It is totally unreasonable to believe that upgrading of at least Grays Road will not be necessary in the near future. In this respect we draw your attention to the Transit technical report (May 2005) environmental assessment of a significant upgrade to Grays Road: "Assessment of positive effects on the environment Assessment of negative effects on the environment + Major ecological effects associated with earthworks + Loss of indigenous forest remnants + Permanent effects on up to 4ha of native vegetation, stream habitat, and saltmarsh + Potential for impacts on the Inlet and its wildlife reserves through + There is no room between the road and the estuary to implement
Transmission Gully would reduce traffic flow along these roads. Despite predicting a increase of 15% in the total volume of traffic flowing through the Inlet catchment, the Pauatahanui Inlet Community Trust’s analysis forecasts a reduction of about 45% on the roads surrounding the Inlet –SH1 at Mana by 40%, Grays Road by 76%, SH58 by 84% at Pauatahanui Bridge and 39% at Paremata.
· Bridges across the Inlet mouth. The Guardians are seriously concerned that yet another bridge is proposed – apparently without any plan for prior research on its effect on tidal flow and flushing cycles of the Inlet.
No prior research was done on the potential effects of the third bridge. It is now apparent that it has caused changes to sand deposition and movement patterns in the entrance channel. The effect of these on the tidal prism is as yet unknown. It is critical that this not be allowed to happen again.
Recent research by the Greater Wellington Regional Council confirms that the outgoing tidal flow exports a large volume of sediment that otherwise would be deposited in the Inlet. This has significantly mitigated the effect on the Inlet of the increased sediment input due to catchment development. Any reduction of this exported volume will have serious consequences for the future of the Inlet for recreation and as a visual amenity for the community.
It is the continuing high level of sediment export over the centuries that has maintained the Inlet as a subtidal estuary (with the majority of its area remaining underwater at low tide) in contrast to the much more common intertidal estuaries (where only a small minority of the area remains underwater at low tide).
It is this availability of a large spread of water at all states of the tide that gives the Inlet its special aesthetic appeal and its diverse ecological and wild life value. It also allows it to support significant levels of aquatic recreational activity at any state of the tide.
It is worth noting here that before the Environment Court in 2000 Transit NZ made a “commitment to the local community” to “demolish the existing Paremata bridge ….. in conjunction with the opening of TGM”. We ask if this commitment will still apply in conjunction with the completion of the Mana section of the Coastal Route. If so, or if not, this needs to be factored in to the research on the hydrology of the Inlet that Transit must be compelled to carry out prior to designing any further bridge over the Inlet.
We most strongly affirm that any new bridge required for the Coastal Route upgrade must be designed to have a neutral effect on the hydrology of the Inlet and its tidal regime. Prior research will be required to achieve such a design.
John Wells
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| Last updated: Sunday, November 13, 2005 |