Transmission Gully Motorway

Submission 1: 30 October 2011

Submission by the Guardians of Pauatahanui Inlet on the application for resource consents for the Transmission Gully Project.


Reasons for submission


Our submission relates to all applications for Notices of Requirement and Resource Consents or parts thereof that are relevant to the issues of sedimentation or contamination of the Porirua Harbour, particularly the Pauatahanui Inlet.


Our background


The Guardians of Pauatahanui Inlet (GOPI) is a community-based incorporated society, with about 190 financial members.


GOPI was established in 1991 to "consistently with its ecological values, encourage, promote, protect, maintain and foster the natural, historic and cultural values of the Pauatahanui Inlet".


In support of these aims we have conducted triennial surveys of the intertidal cockle population since 1992, we carry out quarterly monitoring surveys of the basic health of the major input streams and we instigate and take part in revegetation programmes within the Inlet catchment. We make submissions on behalf of the Inlet in planning processes and have produced an education kit and website tools for use in schools. The website also features general information on the history, natural history and ecology of the Inlet. GOPI was instrumental in initiating, promoting and supporting the development of the Pauatahanui Inlet Action Plan and the Porirua Harbour Strategy and Action Plan.


Pauatahanui Inlet is identified in the Regional Coastal Plan as an Area of Significant Conservation Value and is registered by the Department of Conservation as a Site of National Significance in the Sites of Special Wildlife Interest database. 


Potential concerns with this application


As indicated above, our sole concern in assessing developments in the catchment is to argue that they must have a negligible adverse affect on the ecological health of the Inlet.


Two major sources of pollutants from human activities within the catchment threaten its ecological health and its value as a recreational resource. One threat is the uncontrolled input of sediment from rural erosion and urban development. The other is the input of toxic chemicals, much of which derives from vehicles using roads in the catchment, especially SH 1, SH 58 and Grays Road, which ring the shores of the Inlet.


When the construction of a motorway through Transmission Gully began to be considered seriously about a decade ago, it appeared to be to the advantage of Inlet ecology. The motorway's relative remoteness from the Inlet shoreline, coupled with the reduction of traffic on the roads directly around the Inlet seemed to offer a potential for a radical reduction in the direct impact of vehicle-sourced pollutants, even though more vehicles would be travelling through the catchment.


We understood that strict controls (Transit NZ called them "advanced ecological mitigation") on sediment outflow during construction and on chemical contaminants in stormwater afterwards would effectively reduce the direct impact of these pollutants on the Inlet to zero. 


On this basis we adopted in 2000 a policy of strongly supporting the construction of the Transmission Gully Motorway.


We continue to support TGM. However, these current applications reveal that we were naïve in our assumption. The AEE and Technical Reports clearly show that even the very best current onsite and near-site methods of controlling sediment and contaminants will not be able to prevent them having an adverse cumulative affect on the Inlet over and above the current situation.


In this submission we ask that NZTA be required to consider the possibility of additional mitigation and offsetting measures to address our concerns.


Why are we concerned?


The Assessment of Environmental Effects Report (AEE) predicts that despite taking excellent precautionary measures the project will still deliver sediment and result in an increase in contaminant loads in the Pauatahanui Inlet.


According to the AEE, the predicted effects of sediment on the harbour during construction are as follows.

  • A Q2 rainfall event could add 200 tonnes of sediment to the harbour (5% above that expected if road not built), likely to be deposited in isolated pockets up to 5mm deep in already heavily impacted sub-tidal locations.
  • A Q10 event could add 270-650 tonnes (4-9% above that expected if road not built) deposited mostly in "less ecologically sensitive" sub-tidal areas.
  • An event at the upper end of the Q10 range (accompanied with wind at 35-40 kph) could induce deposition of up to 10mm, and affect inter-tidal areas adjacent to Kakaho stream mouth and the eastern end of the Inlet. There is a 4-23% chance that such a top-end Q10 event will occur during "peak construction".


The predicted longer term cumulative sediment effects of the works are as follows.

  • An additional 3,000 tonnes of sediment will enter the harbour, an increase of around 2% over a 20 year period. The majority will be deposited in the central sub-tidal basins of the Pauatahanui Inlet and in the southern sub-tidal area of the Onepoto Arm.
  • Up to 50mm of the sediment deposited in the sub-tidal basin areas could be attributable to the project, a maximum deposition of 2.5mm per year on average.
  • Overall the area that will accumulate more than 100mm of sediment in 20 years' time will increase from 61 to 62 hectares in the Onepoto Arm and from 204 to 207 hectares in the Pauatahanui Inlet (0.79% and 1.6% increases respectively).


In the longer term, the project is expected to result in reductions in contaminant levels for the Onepoto Arm due to a reduction in traffic along SH 1. For the Pauatahanui Inlet, however, TGM will result in a net increase in traffic volume through the Inlet catchment.


Because current stormwater treatment technologies (wetlands and proprietary devices) can remove only 77% or fewer of the contaminants (Technical Report 11, page 123; AEE, page 348) the project is predicted to result in increased levels of Zinc, Copper and Total Petroleum Hydrocarbons in the Inlet (2%, 1% and 20% respectively; AEE, Table 20.9, page 355) by 2031 and cumulative increases thereafter.


The reduction in traffic along SH 1 is predicted to reduce the flow of contaminants into the Onepoto Arm (AEE, Table 20.9) but this should not be allowed to be regarded as offsetting the increases in the Pauatahanui Inlet. While both are arms of the Porirua Harbour, all evidence suggests that there is no significant interchange of water or sediment between them. 


We are very concerned that NZTA seems to regard these results as reasonable and unavoidable.


We had hoped that the days were over when developers could argue that small increments to sediment and contaminant loads are not harmful, and long-term cumulative effects were ignored. Our belief is especially relevant when there are means available to offset these deficiencies by action elsewhere in the Inlet catchment.


The case for increased mitigation


GOPI accepts that with existing treatment methods and technology it is not possible to avoid all the adverse effects of the proposal directly. It is inevitable that storm events during or after construction and the limited effectiveness of the proposed contaminant treatments will mean increased sedimentation and contamination of the harbour attributable to the project.


We argue, however, that mitigating and/or offsetting measures sufficient to ensure that there is no overall adverse impact on the harbour in the long term should be taken.


While the AEE (Chapter 28) outlines measures that will be taken to mitigate sediment and contaminant problems, it is clear elsewhere in the AEE that these measures will be only partially effective during construction and do not address the longer term situation (see above).  


The only reference we could find in the AEE to any form of compensatory mitigation for sedimentation and contaminant effects on the Inlet is a proposed condition to provide "specialist funding in the case of a significant [extreme weather] event" which could involve "Funding for a community project in the event of a notable event occurring" (page 481).


Possible measures


Sediment: A condition of consent should be to require NZTA to contribute to plans contained in the Porirua Harbour Strategy aimed at

  • reducing sediment entering the harbour from sources other than the Transmission Gully project
  • restoring the tidal prism or increasing the flushing ability of the harbour.


Contaminants: A condition of consent should be that NZTA be required in mitigation to

  • continuously update TGM stormwater treatment methods
  • install treatment devices on stormwater run-off outlets from other roads in the Inlet catchment to offset the adverse effects from TGM.




That the Board of Inquiry approve the applications subject to the inclusion of conditions that require the applicants to undertake additional mitigating and/or offsetting measures sufficient to ensure that any increases in sediment or contaminants entering the Pauatahanui Inlet as a result of the proposal are completely offset by equivalent reductions elsewhere in the Inlet catchment.


John Wells


Guardians of Pauatahanui Inlet Inc.


Submission 2: 6 March 2012

Joint representation by Pauatahanui Inlet Community Trust and Guardians of Pauatahanui Inlet to the TGP Board of Inquiry



Brief background of GOPI and PICT

1.     The Guardians of Pauatahanui Inlet (GOPI) is a community based Incorporated Society with about 190 financial members.  It was established in 1991 to encourage, promote, protect, maintain and foster the natural, historic and cultural values of the Pauatahanui Inlet.


2.     The Pauatahanui Inlet Community Trust (PICT) was established in 2002. Its trustees include representatives from GWRC, PCC and Ngati Toa, plus 8 members from the community. PICT is charged with facilitating the implementation of the Pauatahanui Inlet Action Plan which was prepared by community groups and local authorities following concerns about degradation of the Inlet and the way it was being managed.


3.     A key objective for both organisations is to advocate for developments in the Inlet and catchment to have a negligible (if not positive) effect on the ecological functioning and other values associated with the Inlet


Reasons for Submission - Concerns for Welfare of Pauatahanui Inlet

4.     The 2 major sources of pollutants from human activities which threaten the ecological integrity and values of the Inlet are sediments from rural erosion and urban development, and input of toxic chemicals largely derived from vehicles using roads in the catchment.


5.     From an early stage we identified roading and traffic as having major impacts on the Harbour. One of PICT's first tasks, therefore, was to carry out a detailed assessment of the likely implications - for both arms of the Porirua Harbour - of proceeding or not proceeding with TGP.


6.     In brief, the analysis concluded that the current impacts on the Harbour from roads and traffic were unsustainable. The Harbour's ecological, recreational, amenity, cultural and economic values were already at real risk, and if the current situation were allowed to continue the future of the Harbour looked very grim.


7.     The assessment identified that construction of TGP had the potential for creating adverse effects on the Harbour and would attract more traffic through the Harbour catchment. However, it also noted that TGM would significantly reduce traffic levels in the immediate vicinity of the Harbour.


8.     It concluded that TGM, if accompanied by strict controls both during and after construction, should provide significant benefits in terms of contamination, recreational use, amenity and cultural values, and economic activity.


9.     Both organisations continue to support the concept of TGM.


10.  However, the current applications and supporting technical information reveal that our assumption that controls on sediment and contamination could be managed to produce a near zero impact was naive.


11.  It was expected that the "advanced ecological mitigation" required under the original designation, together with the ever-increasing sophistication of sediment control measures and the likelihood of very strict resource consent conditions would - by the time of eventual construction - result in minimal sediment problems (except perhaps in the event of extreme storm conditions).


12.  Similarly, it was believed that, despite TGM leading to an overall increase (estimated at 15%) in vehicle kilometres traversing the Harbour catchments, the reduction (estimated at 45%) in travel on roads directly beside the Harbour would actually result in a reduction in Harbour contamination.


13.  We are concerned that the Applicants regard the likely impacts as assessed in the AEE and supporting evidence to this hearing, as unavoidable and reasonable. This is reinforced by the view that impacts in the Harbour of sediment runoff will affect the Harbour primarily in areas of "low ecological value". 


14.  We view the predicted impacts as neither unavoidable nor reasonable, and we do not accept that the affected areas are of "low ecological value" and therefore able in some way to be sacrificed. I explain the basis for this view later


15.  We submit that the Applicants be required to consider additional mitigation and offsetting measures to more nearly approach a zero impact of both the construction and operating stages of the TGP.


The Context of Change

16.  We would point out that the issues which may arise as a result of the TGP need to be viewed in the context of ongoing changes to the Inlet through human activities since human settlement.


17.  We are well aware that changes we see in the Inlet are taking place as part of a dynamic set of processes and events which include an element of "natural" change.  This makes the consideration of threats from new sources (such as TGP) on an "incremental" basis very difficult - given that there is a tendency to "dilute" the significance of possible effects within the historical quantum of change. There are for example a number of statements in the Applicants' evidence that seek to compare % increases in sediment load from TGP to the estimated "natural" ( without the project) load. The "natural" load is, we submit, to a large degree unnatural, resulting from the historical modifications to the catchment.


18.  We would also like to point out that many of the impacts from TGP such as contaminant loading and increases in sediment loads in the Harbour are, for all practical purposes, irreversible.


19.  This leads to a need to focus on prevention of adverse impacts rather than remedy.


20.  There have been many past attempts (which are ongoing) to mitigate and remedy the impacts of sedimentation and contamination. Significant lessons have been learned as a result, which will be of great value in considering TGP impacts.


21.  We have an opportunity to manage TGM to achieve improvements on the current situation.


Evaluating likely effects of TGP on the Harbour

22.  The Assessment of Environmental Effects Report, and subsequent expert evidence, predict ongoing sedimentation throughout the construction phase and, despite installing current 'state of the art' treatment for stormwater run-off during the operational phase, an increase for the foreseeable future in contaminant loads in the Pauatahanui Inlet. In other words, the nature and extent of the proposed mitigation methods will not be sufficient to prevent short term or long term cumulative adverse effects on the Inlet ecology.


23.  There is a good deal of uncertainty in these assessments about the "background" loads as well as what might be generated as a result of construction.  This is understandable given the unpredictable nature of major storm events.

24.  Our concerns are heightened by the peer reviews suggesting that the NZTA methods of analysis and prediction could be serious underestimates.


25.  Moreover, a considerable degree of extra uncertainty arises because of a lack of data on existing loads, the nature of the geology of the area and the efficacy of sediment management techniques during construction.


Management of risk

26.  GOPI and PICT accept that it is probably not possible to avoid all adverse effects of the project. In particular, it is inevitable that storm events during or after construction and the limited effectiveness of the proposed contaminant treatments will mean increased sedimentation and contamination of the Harbour attributable to the works.


27.  We submit that there is a need to consider a different approach to risk management and avoidance and minimisation of sediments entering the marine environment from the approach indicated in the project application and documents and evidence.


28.  This arises because of:

a.     the significant unknowns and uncertainties in the assessment of effects;

b.     the irreversibility of many impacts;

c.     the limited effectiveness of methods for mitigating sediment runoff into streams and the Harbour during storm events during the construction phase;

d.     concerns about effectiveness of management and monitoring - based on past experience.


29.  This approach should be inherently conservative and involve management of sediment generation:

a.     that is designed for events which are less likely than currently assumed;

b.     that is triggered, in the event of predicted adverse events at lower thresholds than currently assumed;

c.     that is genuinely state of the art and continually reviewed.


30.  Whatever the probability of adverse events occurring a set of activities should be considered which are designed to reduce the overall sedimentation and contamination which may not directly result from the TGP activities.


31.  Such mitigating or offsetting measures should be sufficient to ensure that there is no net adverse impact on the Harbour in the long term arising from the construction and operation of TGP.


Methods for mitigating and managing sediment generation

32.  We acknowledge that a focus in the project development and assessment stages has been on measures to avoid and minimise sediment and contaminant problems.  This is proposed through the erosion and sediment control measures, the revegetation of riparian margins, retirement of land, controls on maximum areas of open earthworks and procedures for stabilising earthworks sites, particularly when a large rainfall is predicted. It is clear, however, that these measures will be only partially effective during construction and do not address the longer term situation.


33.  The only reference we could find in the AEE to any form of mitigation is "funding for a community project in the event of a notable event occurring" on page 481 as addressed in Condition M7. This relates solely to an extreme weather event where sediment is transported from construction areas to the Harbour resulting in significant negative impacts on the marine ecology.


34.  Such an approach would be totally ineffective in dealing with the impacts on the Harbour of an adverse event, however such an event might be measured and defined. There is no sense in waiting until an adverse event has occurred and been identified, because options for remedy or offsetting are very limited.


35.  The concept of offset mitigation is discussed further in the rebuttal evidence of Dr De Luca (para 57). She notes that "given that adverse effects are only potential at this stage, it is not reasonable to specify the offset mitigation required".


36.  We disagree. The nature of many potential adverse effects is very predictable, the only variables being scale and timing. It makes good sense to consider and implement offset mitigation in advance of likely events based on an appropriate consideration of risks mentioned above.


37.  In this context the concept of offsetting for habitat loss by creating new habitat, as considered in the Freshwater Plan, is neither appropriate nor possible. We are not dealing with a simple loss of habitat concept but a significant change to the ecological functioning of a system.


38.  We are aware, however, that practical opportunities for effective compensatory activites are likely to be very limited and we suggest that greatest weight needs to go on avoidance, minimisation and mitigation in advance of adverse events.


39.  In respect of sediment, a condition of approval should be to require NZTA to contribute to plans contained in the Harbour Strategy aimed at:

a.     reducing the sediment input into the Harbour from all sources other than the TGP, including riparian planting programmes and other land management measures;

b.     restoring the tidal prism or increasing the flushing ability of the Harbour, for example by:

- creation or deepening of strategic channels;
- removal of existing reclamations;
- removal of tidal restrictions;
- the dredging and disposal of sediment from the sub-tidal basins.


40.  We cannot be specific about particular measures at this stage because we think the first step is to extend the current modelling to enable the effectiveness of the various possibilities to be tested. The AEE (Chapter 20, page 345) mentions the benefits already gained from the detailed modelling done by NZTA to support this application. However we understand that more modelling will be required if the most effective additional mitigation measures are to be assessed. It seems appropriate that this be funded by NZTA and carried out in collaboration with the Harbour Strategy team as a matter of relative urgency.


41.  In respect of contaminants, although there seems to be little scope in the short term to further reduce contaminant inputs from the TGM and other roading in the catchment, it should be a condition of consent that NZTA be required in mitigation to:

a.     update stormwater treatment methods throughout the life of the road; and

b.     install treatment measures on stormwater run-off from other roads in the catchment to offset the adverse effects.


Estimation of Ecological Value

42.  The evidence presented by the Applicants comes to the conclusion that, under the assumptions and modelling parameters chosen, most sediment which is likely to enter the Pauatahanui Inlet will settle in the central basin area.

43.  The ecological "value" of this area is assessed as "low" and the conclusion which seems to be drawn from this assessment is that impacting this area in this way is not particularly adverse and is acceptable.

44.  Our view is that such conclusions are based on a naive definition of ecological "value".

45.  The assessments of ecological value are based, as far as we can tell, on a view that value is lower in areas of greater muddiness and a relatively low invertebrate diversity and abundance.

46.  Given that ecological functioning of systems is driven by relationships and connectedness between elements of the system it is misleading to view a subset of the system in isolation.

47.  There is not a lot of specific information available about the biological connections between the central basin of the Inlet and other parts of the system.  There are, however, likely to be significant connections between the basins and other parts of the Inlet, through fish and other more mobile organisms which use the extensive central basins for feeding, spawning or other purposes.

48.  Such connectedness will ensure that changes to the biological community in this supposedly low value area will have an impact on the other areas and fauna in the Inlet.   Dr Baber discussed this in his evidence - particularly as it might impact birds, for example. 



Last Updated: 14/12/2015 12:01am