Paremata Residents Association Presentation to TGP Board of Inquiry – 6 March 2012 1. My name is Russell Morrison and I am the Vice-President of the Paremata Residents Association which covers an area of about 2,100 households encompassing Papakowhai, Paremata, Golden Gate, Mana and part of Camborne. I have lived in residences right next to the Pauatahanui Inlet and used the harbour in many different ways since the age of two when my family moved to Browns Bay in January 1950. 2. Our Association strongly supports the TGP and has been prepared to go to the Environment Court on three occasions in the past to ensure, directly or indirectly, that TGP stayed on the books. We are asking, however, that the Board consider imposing conditions in a number of areas. Adverse Impacts on the Harbour 3. Our submission mentions our concerns about the harbour but does not go into much detail, opting instead simply to endorse the recommendations of the Pauatahanui Inlet Community Trust (PICT) entirely. I would like to elaborate on our views here. - Sedimentation 4. Quite a number of our members have lived next to the Porirua Harbour for many years. We recall the controversy when the initial Whitby subdivision was pouring sediment out onto the beach opposite what is now Postgate Drive. Many still mention the promises about retaining tidal flows when the highway was extended and the lagoons created between Porirua and Paremata. We remember the learned debates which took place when the National Roads Board proposed putting a 6 lane motorway on a causeway along the Dolly Varden beach and up through Camborne. So we became educated in a traditional wisdom which said that any reclamation or other reductions in the tidal prism (no matter how small) should be avoided because they will have a compounding effect on the rate of infill. Essentially, we were led to believe that the more the tidal compartment is reduced (i.e. the shallower the harbour is allowed to get), the faster it will infill. 5. As a result, when NZTA or other agencies have put forward projects which would reduce the tidal prism or restrict tidal flows, this Association has asked for conditions requiring the agency to take equivalent measures to maintain the tidal prism. Up until now, such requests have never been accepted – the usual response being “the adverse effects of the works are expected to be less than minor” , or something along those lines. The cumulative impacts of adopting such a stance have become more and more apparent in recent years. 6. What we have learnt from the experts or from observation over the years is that there are really three inter-related factors that determine the rate of infill (and thus the length of life) of our harbour: The amount of sediment or marine sand coming into the harbour; 1
The rate at which the tidal prism is being reduced by that sedimentation or by works such as reclamations, seawalls, etc; The extent of restrictions which affect the tidal flow and flushing ability of the harbour. We believe that all of these factors need to be considered when addressing issues around sedimentation. 7. The draft Porirua Harbour and Catchment Strategy and Action Plan identifies excessive sedimentation rates, pollution levels and degraded ecology as major issues affecting the harbour. Sediment rates over the past 35 years are said to have averaged about 6mm per year in the Onepoto arm and 9mm per year in the Pauatahanui Inlet. The Strategy sets targets to reduce sediment inputs from tributary streams by 50% by 2021, and to reduce the sedimentation rate (averaged over the whole harbour) to 1mm per year by 2031. The Action Plan affords immediate priority (over the next 3 years) to reducing run-off from terrestrial sources by, for instance, developing and implementing a whole-of-catchment re-vegetation plan. The investigation of options to reduce or compensate for the effects of harbour structures and other works on harbour dynamics is identified as medium priority (over the next 3-10 years). 8. As we understand it, the final Strategy is due to be launched in April and, regardless of what happens with the TG Project, the “key stakeholders” are committed to its implementation. 9. There still seems to be considerable uncertainty as to the amount of sediment which is likely to end up in the harbour as a result of constructing the TGP. Dr Murray Hicks in his Section 42A report thought that the sediment yield increases during relatively common events could be several (2- 5 times) greater than had been estimated by NZTA’s experts . His updated statement of 20 February 2012 states that “there remains an approximately factor - of-two uncertainty on the baseline mean annual sediment yields and a larger uncertainty factor still for event sediment yields” . 10. As I understand it, NZTA’s AEE forecasts that construction of the project will result in about 50 mm of sediment accumulating in the harbour. And yet Transit’s marine ecology expert, Dr De Luca, does not see a need for any measures to mitigate or compensate for accumulation of sediment within the harbour (other than if there is a major Q10 rainfall event during construction) because “the contributio n of the Project to the accumulation of sediment within the harbour is minimal compared to the baseline situation and has negligible additive adverse effects” . [Paragraph 55 of Rebuttal Evidence] 11. With respect, we strongly disagree with this assessment. If I have interpreted the information correctly, an accumulation of 50mm is equivalent to 50 years of sedimentation at the normally expected “natural” rate of 1mm per year. I am happy to be corrected, but that suggests to me that the sediment deposited as a result of construction of the TGP will effectively reduce the natural life of the harbour by 50 years . 12. Regardless, my Association believes (in simple terms) that if constructing this project deposits x tonnes of extra sediment into the harbour, then NZTA should be required to take 2
measures that will have the effect of removing the equivalent of x tonnes of sediment from the harbour – not in 20 or 30 years’ ti me, but either before or as soon as possible after the deposition. 13. We are aware of Dr De Luca’s concern (shared by other experts) that remedial action to remove sediment from ecologically sensitive habitats “is likely to cause more damage than benefit ” [Paragraph 131 of her Evidence]. However this need not necessarily preclude removal of sediment from areas of “ less er ecological importance” – perhaps the deeper central muddy basins where most of the sediment is eventually expected to settle out. [Mr Roberts - Page 475/6 of Transcript] 14. Nor would we want to rule out the possible deepening or creation of new channels within the harbour as a means of maintaining the tidal prism – notwithstanding the reported results of a recent modelling exercise by DHI Water and Environment Ltd which have been misrepresented by some local politicians as ruling out the viability of any dredging within the harbour. In fact the report merely purports to show that deepening of several existing channels would be unlikely to improve the flushing ability of the Inlet. It seems to us that, if the flushing ability cannot be improved, then early removal of any extra sediment being deposited in the harbour becomes even more important . 15. We also believe that the options should include the removal of some existing tidal restrictions if that could be shown to have some benefits equivalent to sediment removal. For instance, the removal of the obstructions under the northern end of the rail bridge and replacement of the walkway on piles should be seriously considered. Our observations suggest that this work, carried out when the ferry jetty was installed, has had a major influence in reducing the channel width and tidal flow in that vicinity. 16. On the matter of tidal restrictions, we are also aware of correspondence and discussions back in 1999/2000 relating to the possible effects of constructing the new Paremata Bridge on the infilling of the Inlet. At that time, one local “expert” - using the results of research on inlet tidal stability by Hume and Herdendorf published in 1985 – assessed that the effect of the new bridge in reducing the cross- sectional area of the estuary’s inlet could be to create a reclamation 2 metres deep with an area of 14.5 hectares. Despite my best efforts, it proved impossible to get any expert agreement on this matter, but if removal of tidal restrictions around the estuary’s entrance had even a fraction of the benefits suggested by that analysis, they would certainly be significant. (Having said that, I am not sure that removal of the old bridge should be included as mitigation for this particular project because it has already been used for that purpose in gaining consents for building the second bridge - and at this stage anyhow, there is no guarantee that the bridge will even be demolished.) 17. We note that the Expert Conferencing Report on marine ecology (paragraph 20) suggests some potential compensation including: Re-vegetation of stream margins in key catchments e.g. Duck Creek; Restoration of harbour margins to a more natural state e.g. de-reclamation and restoration of saltmarsh areas; and Seagrass restoration in suitable habitats. 3
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