Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project
State Highway 10, Kaeo
12 July 2019
Prepared for:
New Zealand Transport Agency -c/o Aurecon Level 4 139 Carlton Gore Road New Market Auckland 1023
Prepared by:
Geometria Limited PO Box 1972 Whangarei 0140 Page 2 – Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. Executive Summary
This report is an archaeological assessment of the Kaeo Bridge project, to replace the existing single lane bridge on State Highway 11 north of Kaeo at Whangaroa. This assessment has recorded one archaeological site on or in the vicinity of the designation for the project, however historic records suggest that other features may be present, and may provide information on the archaeology and history of the area.
One previously unrecorded subsurface shell midden is located just outside the southern end of the designation, on the Pahuhu Stream, and other features associated with the late 19th/early 20th century Pahuhu settlement are nearby on the eastern side of the highway. Construction of the new Kaeo Bridge will not modify the recorded site or the Pahuhu settlement.
An area used as a camping ground and landing by Maori in the same period near the western end of existing bridge may be modified by the new Kaeo Bridge. An archaeological authority under the Heritage New Zealand Pouhere Taonga Act 2014 is recommended to manage any potential effects on archaeological sites and features in this area.
Archaeological monitoring guided by an archaeological site instruction during the early stages of enabling, site establishment and construction earthworks in the archaeologically sensitive area is recommended as an appropriate mitigation strategy, along with on-call protocols to manage other eventualities.
The results of any archaeological investigation and analysis will be provided in reports to stakeholders such as the Tangata Whenua, Heritage New Zealand Pouhere Taonga and Far North District Council, and may be presented through public open days, media releases and interpretation where appropriate.
Geometria Ltd Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. - Page 3 Quality Information
Document: Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo.
Ref: 2017-107
Date: 12 July 2019
Prepared by: Jonathan Carpenter
Revision History Revision Revision Date Details Authorized Name Client draft 0.1 24 October Issued to Aurecon/NZTA J. Carpenter 2017 Client draft 0.2 26 October Minor revisions. Issued to Tangata Whenua J. Carpenter 2017 Client draft 0.3 7December Minor revisions J. Carpenter 2017 Client draft 0.4 29 April 2019 Minor revisions due to design change J. Carpenter Client draft 0.5 14 June 2019 Minor revisions due to design change J. Carpenter Client draft 0.6 12 July 2019 Minor revisions due to design change J. Carpenter Final for submission 1.0 13 December Archaeological management plan added J. Carpenter 2019
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Geometria Ltd Page 4 – Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. Contents Executive Summary ...... 2 Quality Information ...... 3 Contents ...... 4 Figures ...... 5 Tables ...... 6 Glossary...... 7 1.0 Introduction ...... 8 1.1 The Heritage New Zealand Pouhere Taonga Act 2014 ...... 8 1.2 The Resource Management Act 1991...... 9 2.0 Location...... 9 3.0 Proposed Development ...... 9 4.0 Assessment Methodology ...... 10 5.0 Archaeological Context...... 11 5.1 Recorded Archaeological Sites in the Vicinity ...... 12 5.2 Archaeological Investigations in the Kaeo River Area ...... 14 5.3 Summary of the Archaeology of the Kaeo Area ...... 15 5.4 Other Heritage Listings...... 15 6.0 Historic Background ...... 16 6.1 Ngāti Uru, Pohue and Te Ara ...... 16 6.2 William Spickman in Kaeo ...... 16 6.3 Review of Historic Maps and Plans - Te Huia, Pahuhu and Waikukupa Blocks 20 6.3 The 1906 Bridge ...... 22 6.4 Summary of the History of the Waikukupa-Te Huia-Pahuhu Area...... 22 7.0 Field Survey...... 31 7.1 Overview...... 31 7.2 P04/775 Midden, Pahuhu Stream ...... 36 8.0 Significance Assessment...... 38 8.1 Assessment Criteria ...... 38 8.2 Significance Assessment of Midden P04/775...... 39 9.0 Stakeholder Consultation ...... 41 9.1 Te Rununga o Whaingaroa and Ngāti Uru ...... 41 9.2 Heritage New Zealand ...... 41 10.0 Assessment of Effects ...... 41 10.1 Alternatives Analysis...... 42 11.0 Recommendations and Mitigation ...... 43 12.0 Summary ...... 45 13.0 References...... 46 13.1 Published and Unpublished Reports and Books ...... 46 13.2 Published and Unpublished Maps, Plans, Photographs and Paintings...... 47 Appendix A - Site Record Forms ...... 48 Appendix B – Draft Archaeological Management Plan ...... 49 B.1.0 Purpose and Methods ...... 49 B.2.0 Management of Archaeological Effects...... 49 B.2.1 Briefing ...... 49 B.2.2 Earthworks and other Ground Disturbing Activity ...... 49 B.2.3 Features and Feature Recording...... 50 B.2.4 Analysis...... 51 B.2.5 Expected outputs...... 52 B.3.0 Personnel...... 52 B.4.0 Timeframe...... 52 B.5.0 Finds Management and Curation ...... 52
Geometria Ltd Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. - Page 5 B.3.0 Operational Guidance...... 54 B.3.1 Stand Down Periods...... 54 B.3.2 On-Call Procedures ...... 54 B.3.4 Koiwi Tangata/Human Remains Discovery...... 55 B.3.5 Taonga Tuturu Discovery Procedure ...... 55 B.3.6 Dispute Resolution...... 56
Figures Figure 1: Project area...... 10 Figure 2: Kaeo Bridge designation and indicative footprint July 2019...... 11 Figure 3: Archaeological sites in the vicinity of the project area (Project area in blue; ArchSite GIS)...... 13 Figure 4: Sites on the Ratcliffe Subdivision, west of the Kaeo Bridge project area (From Johnson 1988: 7)...... 14 Figure 5: OLC 3182 (1875) showing Te Huia and the Kaeo Bridge project area and Pahuhu reserve (circled)...... 23 Figure 6: ML 3312 (1875) showing Pt NW Waikukupa and Kaeo Bridge project area (circled)...... 23 Figure 7: Detail from OLC 69 (1875) showing Spickman’s Maungawhero Block purchases (Pahuhu and Hepara (Kohepara) Streams circled)...... 24 Figure 8: SO 6362 (ca. 1890). Note "Native Camping Ground" on the spit of land extending past the location of the existing bridge, and that Section 7 (now Waikukupa J Block) is covered by tides at this time and what would become the highway has not been formed or surveyed...... 24 Figure 9: ML 1736 (1879) showing a subdivision of part of the Te Huia Block and the road from Kaeo to Whangaroa...... 25 Figure 10: Detail from SO 16033 (1912) showing 1906 bridge and causeway road over Section 7 (now part of Waikukupa J Block) across mudflats and marsh. Note the spit of land extending past the bridge...... 26 Figure 11: ML 11137 (1918) showing the subdivision of the Pahuhu Block and features at the southern end of the project area...... 27 Figure 12: The opening of the Kaeo River bridge. Auckland Star, 26 November 1906. .28 Figure 13: Opening of the 1906 concrete Kaeo Bridge (Auckland Weekly News. 6 December 1906. APL)...... 29 Figure 14: 1906 concrete Kaeo Bridge (Auckland Weekly News. 6 December 1906. APL)...... 29 Figure 15: The 1906 concrete bridge, in 1913 (23 January 1913, Auckland Weekly News. APL)...... 30 Figure 16: Detail from the Geology of the Whangaroa Subdivision (1908) showing the spit of land and mudflats on the western side of the existing bridge...... 30 Figure 17: NZMS 003 aerial mosaic N11-1 (1954; photography from 1950)...... 31 Figure 18: Archaeological features observed in 2017 and historic features recorded from land plans in the immediate vicinity of the Kaeo Bridge project area as proposed in 2017...... 33 Figure 19: Panorama of project area, looking south to west (left-to right) across drained/reclaimed flats west of the existing bridge...... 33 Figure 20: Looking west along existing bridge over road causeway and drained/reclaimed flats...... 34 Figure 21: Looking north along river and stopbank over reclaimed/drained flats...... 34 Figure 22: Looking north towards highway, past toe of ridge which ascends to Taita trig...... 34
Geometria Ltd Page 6 – Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. Figure 23: Looking north east over drained/reclaimed flats towards highway and existing bridge...... 35 Figure 24: Looking south over low-lying ground on eastern side of river, immediately south of SH10/Whangaroa Road intersection towards Pahuhu Stream...... 35 Figure 25: Looking east across Eucalyptus plantation towards SH10, in vicinity of Pahuhu cultivations...... 35 Figure 26: Looking along Pahuhu stream re-alignment towards outfall to Kaeo River. .36 Figure 27: Looking north along SH10 with vicinity of Pahuhu cultivations to left and Pahuhu settlement right, with urupa on hill in centre right of frame...... 36 Figure 28: Location of midden...... 37 Figure 29: Shell midden exposed in section...... 38 Figure 30: Detail of shell midden...... 38 Figure 31: Indicative State highway realignment and bridge options in late 2017...... 43 Figure 32: Areas proposed for archaeological monitoring (outlined red)...... 44 Figure 21: Potentially archaeologically sensitive areas for monitoring (red polygons). All other areas on-call procedures apply...... 50
Tables Table 1: Significance assessment of Midden P04/775...... 40
Geometria Ltd Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. - Page 7 Glossary Classic The later period of New Zealand settlement Fire scoop Fireplace used for various reasons (cooking, warming, etc.) Hangi An earth oven for cooking food Midden The remains of food refuse usually consisting of shells, and bone, but can also contain artefacts Pa A site fortified with earthworks and palisade defences Pit Rectangular excavated pit used to store crops by Maori Radiocarbon Method of absolute dating using known rates of decay of a carbon isotope Terrace A platform cut into the hill slope used for habitation Wāhi tapu Sites of spiritual significance to Maori
Geometria Ltd Page 8 – Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. 1.0 Introduction
Aurecon Ltd commissioned Geometria Ltd on behalf of the New Zealand Transport Agency to undertake an archaeological assessment for the proposed new Kaeo Bridge on State Highway 10, north of Kaeo. No archaeological sites were recorded in the vicinity of the Project area prior to the preparation of this report, however given the location an archaeological assessment was recommended in the early planning stage of the project.
Under the Heritage New Zealand Pouhere Taonga Act 2014 (HNZPTA) all archaeological sites are protected from any modification, damage or destruction except by the authority of Heritage New Zealand Pouhere Taonga (HNZPT).
This assessment uses archaeological techniques to assess archaeological values and does not seek to locate or identify wāhi tapu or other places of cultural or spiritual significance to Maori. Such assessments may only be made by Tangata Whenua, who may be approached independently of this report for advice.
Likewise, such an assessment by Tangata Whenua does not constitute an archaeological assessment and permission to undertake ground disturbing activity on and around archaeological sites and features may only be provided by Heritage New Zealand Pouhere Taonga, and may only be monitored or investigated by a qualified archaeologist approved through the archaeological authority process.
1.1 The Heritage New Zealand Pouhere Taonga Act 2014
Under the Heritage New Zealand Pouhere Taonga Act 2014 (previously the Historic Places Act 1993) all archaeological sites are protected from any modification, damage or destruction except by the authority of Heritage New Zealand Pouhere Taonga (previously the Historic Places Trust). Section 6 of the HNZPTA defines an archaeological site as:
" any place in New Zealand, including any building or structure (or part of a building or structure), that—
(i) was associated with human activity that occurred before 1900 or is the site of the wreck of any vessel where the wreck occurred before 1900; and
(ii) provides or may provide, through investigation by archaeological methods, evidence relating to the history of New Zealand; and
(b) includes a site for which a declaration is made under section 43(1)”
To be protected under the HNZPTA an archaeological site must have physical remains that pre-date 1900 and that can be investigated by scientific archaeological techniques. Sites from 1900 or post-1900 can be declared an archaeological site under section 43(1) of the Act.
If a development is likely to impact on an archaeological site, an authority to modify or destroy this site must be obtained from the local Heritage New Zealand Pouhere Taonga office under section 44 of the HNZPTA. Where damage or destruction of archaeological sites is to occur, Heritage New Zealand usually requires mitigation. Penalties for
Geometria Ltd Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. - Page 9 modifying a site without an authority include fines of up to $300,000 for destruction of a site.
Most archaeological evidence consists of sub-surface remains and is often not visible on the ground. Indications of an archaeological site are often very subtle and hard to distinguish on the ground surface. Sub-surface excavations on a suspected archaeological site can only take place with an authority issued under section 56 of the HNZPTA issued by the Heritage New Zealand.
1.2 The Resource Management Act 1991.
Archaeological sites and other historic heritage may also be considered under the Resource Management Act 1991 (RMA). The RMA establishes (under Part 2) in the RMA’s purpose (section 5) the matters of national importance (Section 6), and other matters (section 7) and all decisions by a consent authority are subject to these provisions. Sections 6e and 6f identify historic heritage (which includes archaeological sites) and Maori heritage as matters of national importance.
Councils have a responsibility to recognise and provide for the relationship of Maori and their culture and traditions with their ancestral lands, water, sites, wāhi tapu, and other taonga (Section 6e). Councils also have the statutory responsibility to recognise and provide for the protection of historic heritage from inappropriate subdivision, use and development within the context of sustainable management (Section 6f). Responsibilities for managing adverse effects on heritage arise as part of policy and plan preparation and the resource consent processes.
2.0 Location
The Kaeo Bridge project area is to the north of the Kaeo township, and south of the existing single lane bridge and the intersection of Whangaroa Road and SH10. The project area is roughly triangular and generally bounded by the existing highway to the north and east, and by the higher ground on the western side of the Kaeo River. The area is approximately 500m long north-south and 700m long west-east.
3.0 Proposed Development
A full description of the Project, including its components and construction, is contained in the Assessment of Environmental Effects (AEE) for the Kaeo Bridge project. However, the project generally consists of a bridge spanning the Kaeo River with the bridge abutments located outside of the river, earth embankments up to the bridge, associated services, stormwater, and landscaping, and tying in the new alignment to the existing State Highway 10 via a new roundabout. The removal of the existing bridge will also be a part of the project.
The archaeological effects of these works based on the indicative designation, bridge and road alignment was assessed between July and October 2017. Archaeological and heritage issues, along with other factors, were fed into analysis of four different options for the bridge and highway in September 2017.
Additional areas and proposed works for flood mitigation were provided and assessed in November-December 2017, outside the designation for the new Kaeo Bridge. These include removing trees, stopbank and lowering the flood plain in the south-eastern part of the project area adjacent to the Pahuhu valley, removing the stopbank and lowering
Geometria Ltd Page 10 – Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. the flood plain along the western bank of the Kaeo River and constructing a new stopbank to the north of the old Kaeo Bridge, and installing and additional overland flow paths and overflows.
In April and June 2019, a revised design was provided and forms the basis for this version of the assessment.
4.0 Assessment Methodology
The methods used to assess the presence and state of archaeological remains in the Project area included both a desktop review and field survey. The desktop survey involved an investigation of written records relating to the history of the Project area. These records included regional archaeological and historic publications and unpublished reports, New Zealand Archaeological Association Site Record Files (NZAA SRF) downloaded via the ArchSite website, and historic survey plans and aerial imagery.
The field survey involved pedestrian survey of the construction envelope. Probing but
no spade testing of potential archaeological features or other areas of interest was undertaken.
Figure 1: Project area.
Geometria Ltd Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. - Page 11
Figure 2: Kaeo Bridge designation and indicative footprint July 2019.
5.0 Archaeological Context
An archaeological desktop assessment was undertaken by Opus International Consultants Ltd in mid-2016 (Jamieson 2016; the report also included assessments of two other Northland bridge projects at Taipa and Matakohe). That report indicated that despite the despite the important history of the area, no archaeological sites were recorded nearer than about 1.5km to the project area. The nearest recorded sites were Pohue Pa on the south-east side of Kaeo, the historic Spickman house on the north side of Kaeo, and two ridge pa to the south west of the project area.
The Opus report indicated a historically attested Maori camp dating to the late 19th century at the intersection of SH10 and Whangaroa Road, and local reports of human remains eroding out of the road cuttings immediately east of SH10. The report notes that the original bridge over the Kaeo River was built in 1871 although the exact location is unknown, with a replacement concrete bridge in 1906, with the existing bridge built in the 1950s. The report also noted that flood control works around the base of Pohue Pa in 2014 revealed intact subsurface Maori archaeological features below the plough zone and alluvium deposited by flooding around the base of the pa. (Opus 2016: 5-9).
The 2016 Opus report suggested that the there was a small or low risk of encountering archaeological sites during geotechnical testing due to the possible presence of subsurface features under flood-born alluvium and that such testing could be undertaken with an accidental discovery protocol in place or alternatively, a
Geometria Ltd Page 12 – Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. ‘precautionary’ authority (Opus 2016: 91). The ultimate advice in the report was that work around the SH10/Whangaroa Road intersection had a medium risk of having archaeological effects but outside this area the risk was low, and that work could proceed with an accidental discovery protocol (Opus 2016: 14).
The methodological statement for the Opus assessment refers to making use of ArchSite, the Heritage New Zealand List and District Council Schedules, archaeological reports, local historical reports, historic maps, plans and aerials and national digital archives. However there is only a single reference for Kaeo in the bibliography and no indication that any other sources other than ArchSite, HNZ and District Council databases were referred to or used to inform the recommendations for that area.
5.1 Recorded Archaeological Sites in the Vicinity
Archaeological sites in the vicinity of the Kaeo Bridge project area are illustrated in Figure 3 but as noted above, they are all at least one kilometre from the project area. The closest sites are two pa recorded near the high point known as Taita, to the west of the Kaeo River, P04/235 and 262.
P04/235 was recorded from the road side in 1965 by R. Lawns, an avocational archaeologist. It was described as a well-shaped terraced knob on a main ridge with a small summit platform or tihi and approximately five terraces below and was under gorse and fern which had been periodically burned off. P04/262 was recorded in the same manner by Lawns, in 1968. That site consisted of several terraces near the Taita trig, ½ a mile north east of P04/262. The area was otherwise under scrub, gorse and fern with native bush in the gullies and had been burned over.
The sites were never walked over and were not added to the site record file until 1973. They have not been visited since they were recorded and are not visible in available aerial photography. The pa sites are too far distant to be affected by the Kaeo Bridge project but the ridgelines north east of Taita Hill descend in that direction to meet the Kaeo River on the south side of the project area, and this area may have provided convenient access to those sites from the river.
Eight hundred metres to the south of the project area, on the south side of the river, is the Spickman House P04/754, erected by early European settler William Spickman sometime in the 1850s. Spickman was one of the earliest if not the earliest European recorded to have settled in the Kaeo area. The Spickman House was recorded by the author of this report in 2012 as a result of a proposal to re-pile the house as part of flood mitigation works in the Kaeo area. P04/765 on the edge of the Kaeo village is the Spickman/Nesbit family private graveyard, with headstones for Spickman’s two wives, son, daughter and son-in-law; Spickman himself is also probably buried there but no headstone remains.
Further south again is the prominent and significant Pohue Pa P04/238 on the eastern side of the Kaeo village centre.
Pohue Pa was built by Ngāti Uru and was the home of Te Ara, instrumental in the burning of the Boyd in 1808, dating the latest stage of occupation of the pa to the proto-historic
1 Following consultation with Heritage NZ, geotechnical testing was undertaking under an accidental discovery protocol.
Geometria Ltd Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. - Page 13 period. The site is a prominent landmark and a detailed plane-table and alidade map was produced by DOC archaeological J. Robinson in the 1990s. Parts of the site were subsequently excavated by S. Bedford (Bedford 2013).
Another site is associated with the Wesleydale Wesleyan mission of the mid 1820s, P04/633. The Wesleydale mission was established by the Rev. Samuel Leigh and Rev. William White in 1823, under the auspices of Ngāti Uru and opposite a Ngāti Uru kainga on the south side of the River, and west of the main settlement at Pohue Pa. The station had a house, barn, carpenters workshop, other outbuildings and at one stage had four acres of flat ground under cultivation. It was abandoned in 1827 under threat of muru or retribution as a result of tribal tensions in the Whangaroa area, at which point it was razed to the ground. The mission re-established at Mangunu on the south side of the Hokianga.
There is a somewhat denser archaeological landscape one kilometre to the west and north of the northern end of the project area, where intensive, development driven survey has occurred. L. Johnson (1988) recorded a large number of sites on the then Ratcliffe family subdivision of the Pt NW Waikukupa Block (Figure 4). More than 25 sites were recorded between SH10 and Taupaki Point, where the Kaeo River empties into the upper reaches of the Whangaroa Harbour. This included one pa, seven terrace sites, sixteen shell midden, a historic house site and a single pit site. The property was revisited by D. Nevin (1997) and sites relocated in advance of subdivision by the new owners, the Perrots.
In general the archaeological record of Kaeo and the Kaeo River catchment, in contrast to the wider Whangaroa Harbour area, is sparse.
Figure 3: Archaeological sites in the vicinity of the project area (Project area in blue; ArchSite GIS).
Geometria Ltd Page 14 – Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo.
Figure 4: Sites on the Ratcliffe Subdivision, west of the Kaeo Bridge project area (From Johnson 1988: 7).
5.2 Archaeological Investigations in the Kaeo River Area
Given the occupation of the area by Ngāti Uru from the 1700s and the relatively early European settlement of the area by William Spickman and other European arrivals and it’s role in the economic development of Northland and Auckland through the early establishment of the kauri industry, the lack of information about the archaeology in the area is surprising and can be contrasted with investigations at Mangonui, Kerikeri and Russell/Kororareka. It can be surmised that the coastal development boom in those areas from the 1980s has largely bypassed Kaeo due to its position further inland. For this reason there have only been a few archaeological excavation in the Kaeo area, chiefly on Pohue Pa (Bedford 2013), on the low lying land at the base of the pa (Shakles et. al. 2015), and at the Spickman House (Gibb 2015).
Excavation at Pohue Pa occurred against the backdrop of a proposal to develop a reconstruction of the pa on the site as a tourism destination. A detailed survey of the site had been undertaken by J. Robinson of DOC in 1993, followed by District Plan and Historic Places Trust scheduling/registration and the negotiation of a lease over the pa in favour of Ngāti Uru by 1999. In 2001-2002 two small excavations were undertaken by the then Historic Places Trust in collaboration with Ngāti Uru in order to feed into any future interpretation, reconstruction and/or management.
The results indicated that settlement was focused on the lower terraces and tihi, with no evidence for permanent occupation found on the upper terraces. Neither was there any evidence for defensive ditches or storage pits on the pa. Rather, the upper terraces were largely archaeologically sterile and may have been purely defensive. This was in contrast to the archaeological features and artefacts on the tihi which indicated that
Geometria Ltd Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. - Page 15 more regular, and possibly ceremonial activity took place there with more permanent occupation on the lower parts of the pa with easy access to the defended hilltop (Bedford 2013: 72). Whilst the artefacts recovered were limited, European material was found in almost all of the excavated areas which suggest that occupation was limited to the early historic period (Bedford 2013). Dating of obsidian and one radiocarbon determination indicated settlement of the pa sometime between AD1750 and 1850 (Jones 2003b; cited in Bedford 2013), aligning with Ngāti Uru’w own histories of when the site was established.
The investigation of the Spickman House was rather less noteworthy but did result in evidence that the house, the third occupied by Spickman in Kaeo, was probably established in the 1850s. A small collection of underfloor artefacts retrieved during the re-piling and dating to the 1850s-1920s and the recording of the subfloor structure of the house indicated it was largely original with a few more-recent concrete piles. 3D terrestrial laser scanning of the exterior of the house was also undertaken prior to re- piling (Gibb 2015).
The most extensive and most recent archaeological investigation in Kaeo came as a result of flood mitigation works near Pohue Pa in late 2013 and early 2014 (Shakles et. al 2015). Monitoring and machine testing of a number of areas was undertaken including testing the route of a haulway, and monitoring earthworks for silt traps, spillways and areas stripped for material to create stopbanks (Shakles et. al. 38-40). Three separate areas of archaeological features were revealed at different points north and south of the River and west, south and east of the pa, on the level river terrace.
Archaeological features and occupation layers were found up to 70cm deep, and lying below alluvial deposits. This included two cooking areas represented by clusters of earth ovens and a number of associated post and stakeholes, a storage pit complex, and the remnants of field boundaries. Radiocarbon dates from features suggested occupation from the late 16th into the early 19th century and structural features within one of the pits indicated it was a formal storage structure, probably for kumara and potentially other cultigens as well. Artefacts retrieved, largely from the fills within pits, included obsidian and chert flakes, hammerstone and sandstone grinder, and some mid-19th century European artefacts (Shakles et. al. 85-87).
5.3 Summary of the Archaeology of the Kaeo Area
This limited review of local archaeological investigations and site locations suggests that there is great potential for further research in the area to shed light on the history and archaeology of the Kaeo area, and that given the lack of prior research and the few sites recorded, any additional archaeological finds and research will be important.
5.4 Other Heritage Listings
With regard to other historic heritage resources in the area, a review of the Far North District Plan and Northland Regional Council Schedules of significant historic and cultural sites, and Heritage New Zealand List was undertaken.
A single historic place in Kaeo is on the Heritage New Zealand List, namely the War Memorial Library (List no. 7393) with the wahi tapu north of Pohue Pa also listed(List no. 7459). There are several scheduled historic places in Kaeo in the Far North District Plan including the War Memorial Library (Appendix 1E No. 235), the Wesleydale Memorial Cairn (Appendix 1E No. 236), Pohue Pa and Waahi Tapu (Appendix 1F No. MS06-16),
Geometria Ltd Page 16 – Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. and the Kaeo Waahi Tapu (Appendix 1F No. MS06-21). There are no scheduled places in the Regional Plan in the Kaeo area. None of the listed or scheduled places will be affected by the Kaeo Bridge project, as they are more than two kilometres to the south and south east.
6.0 Historic Background
6.1 Ngāti Uru, Pohue and Te Ara
Kaeo, named after a freshwater shellfish, is in the rohe of Ngāti Uru. Ngāti Uru originally lived in the southern Bay of Islands, but following the fallout from the deaths of the French Captain Marion Du Fresne and crew in 1772, they migrated to Whaingaroa2 and established themselves at Pohue Pa at Kaeo under Chief Te Ara, also known as George (Bedford 2013: 61).
European ships are recorded at Whaingaroa from 1805 as whaling vessels came to trade European goods for fresh food and water. In December 1809, the Brigantine Boyd was attacked by Ngāti Uru under Te Ara, who had been mistreated by the Captain of the ships during its voyage from Port Jackson, to New Zealand. The Boyd was perhaps only the second or third European ship to visit the harbour, and its captain was on his first voyage through the south Pacific. In early 1810 Captain Alexander Berry of the City of Edinburgh travelled up the Kaeo River to Pohue, making the first written record of the area, in search of survivors.
The subsequent rescue of four survivors from the Boyd by Bay of Islands Chief Te Pahi led to resentment and conflict between Whaingaroa and Bay of Islands tribes for several years. Following the intercession of Samuel Marsden in 1814 the tribes settled their differences and promised to never again harm a European. However the Boyd massacre helped cement the idea of New Zealand as the “Cannibal Isles” and travel advisories of the day suggested avoiding the place at all costs.
In 1820 the HMS Dromedary visited Whaingaroa, and cut kauri spars from around the headwaters of the Mangaiti Stream (or one of its tributaries), which flows north in to the Kaeo River just west of the town. The crew of the Dromedary spent five months at Whaingaroa, and created a track alongside the stream and which runs parallel to what is now Hospital Road and which included several bridges over deep streams. Captain Cruise of the Dromedary stated that the stands of tall Kauri were one and a quarter miles from Te Ara’s village (Pohue Pa) in a steep valley or ravine.
The next major European activity in the area was the establishment of the Wesleydale Mission from 1823-1827 as discussed briefly above. Following its destruction by Hongi Hika and Ngati Pou Europeans did not return to the area until the mid-1830s, with the arrival of William Spickman.
6.2 William Spickman in Kaeo
The following account of William Spickman’s life and association with Kaeo is based on the account provided in Prokohnik (1991) with additional material from Sale (1986) and Pickmere (1994), and Lee (1983). Material from the Daily Southern Cross and Auckland
2 Whaingaroa is the traditional Maori name for the area and is used instead of Whangaroa in this section.
Geometria Ltd Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. - Page 17 Star was sourced from the Papers Past website of the National Archives (www.paperspast.natlib.govt.nz). Historic land plans were accessed in electronic form from scans by Land Information New Zealand.
William Spickman (also written as Spickeman, or Spikeman) was born at Devizes, Wiltshire, England, on 15 October 1800. In 1819 he was convicted and transported to New South Wales, Australia, for his role in the theft of a handkerchief from a patron leaving Covent Garden. The handkerchief was valued at ten pence but he was later pardoned. He worked first as a carter in New South Wales and was then assigned to a landowner where he displayed some skill at managing cattle.
In 1823 he accompanied Reverend Samuel Marsden on his fourth visit to New Zealand on board the Brampton. He was engaged by the Church Missionary Society as a herdsman at Kerikeri and Waimate, under the charge of James Kemp. He undertook general farm duties and worked as a ploughman until returning to New South Wales to receive his ticket of leave in 1826.
After marrying Mary Ann Noonan at Sydney, Australia, he returned with her to the Bay of Islands on the Active in 1831. Mary was originally from County Cork, Ireland and had voluntarily emigrated to Australia, according to a testimonial signed by the Lord Mayor of Sydney in 1832. William Parrott who would go on to build the Stone Store and Kemp House for the Church Missionary Society, and then go into business with Spickman, was another passenger.
Spickman worked at the Te Waimate Mission Station until 1834 at which time he and Parrott formed a partnership, having purchased a 100 acre block at Kaeo and established themselves as sawyers. At that time they were the only Europeans in the area.
Spickman and Parrot purchased the 100 acre Pitakatahi Block for the price of a double barrelled gun (the original deed, see below) or for cash and goods worth £44 or two double barrelled guns (as stated in evidence presented to the Land Commissioners during the investigation of the purchase). The land was purchased from the local paramount Chief Te Ururoa. The original deed (Turton 1877) states:
“Wangerowa New Zealand 23rd Novr. 1833.
I Rivva well known by the name of Huhuroa Chief of Wangerowa hereby acknowledge to have sold to William Parrot and William Spickman the whole of that ground with the whole of the Wood contained thereon known by the name of Petuckitikie. Pitakatahi. Bounded on the North Urrakinna for the front. On the South by Bookatotarra, for Parrot and Spickman. the Back. On the East by Wheeronewee for a side, on the West by Toueetoto the Boundaries. other side, and contigues to a small creek known by the name of Moungaete. And I hereby bind and oblige myself to give up all claim and tittle to the said ground and wood contained thereon to the said William Parrot and William Spickman and for which ground and wood contained thereon I have received from the said William Parrot and William Spickman One Double Barrel Fowling Piece as full value of the fore mentioned Receipt. ground and wood contained thereon. As Witness my hand this the Twenty-third day of November in the year of our Lord One thousand eight hundred and Thirty-three years.
Huhuroa x his mark.
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Alexander Stephen.
Daniel Brown.
Tareha.
Paid to Taitaoro x his mark, one double barral Gun. 27 April 1835. Rd. Baker Witness.
Na Torotoro Kaeo.”
Spickman and Parrott then purchased another piece of land between the Waikara and Waitangi Creeks and the river for £53.2.0. They levelled an area on a prominent point near the river and built a whare of raupo (Prokhovnik states the area is still visible). Ralph Hodgskin visited them a month after the purchase and noted the “snug little cottage on an eminence within 200 yards of, and facing the river –all, excepting the front of their dwelling, sheltered by the forest and its lofty trees”. Another visitor, a missionary named Wade, visited in 1835 and noted that the former Wesleyan mission was located on the opposite side of the river.
The next two Spickman purchases in 1834 and 1835 totalled about 1000 acres of mixed character with some Kauri for £88 from Ururoa and others. In 1838 Parrot sold his share to Spickman and returned to New South Wales. Spickman then sold the original Pitakatahi purchase to James Kemp that same year for four head of cattle.
In January and May 1840 he purchased another 420 acres of agricultural land including a small flat to afford to keep for working bullocks. At the time his timber business employed a dozen men and he was supplying timber to Auckland and elsewhere. By the time the third Spickman child was born in November 1841 the family were well established, respectable settlers with a comfortable six roomed Kauri house and were known for their hospitality (Prokhovnik 1991 89-92).
At the time of the investigation of Spickman’s land claim in 1840-42 he valued his six room plus loft weatherboard house at £600 pounds, with working men’s houses and sheds nearby values at £50, eight acres of wheat in cultivation, with six cattle and 60 goats. His total claim was for 1420 acres of land valued at £562.8.6 with improvements of £1030.8.6 and he stated that “The subscriber has resided constantly on these lands since 1834 carrying on the timber business and has a European wife and three children”.
When he appeared before the Commissioners at Whangaroa on 20 December 1840 he had five witnesses on his behalf including the Maori chief Toro who witnesses the original purchase from his Uncle Ehaka, and Hare Hongi and Ururoa, the later having been one of the original sellers of the land.
In Spickman’s land claim file OLC 878-880 his statement by letter to the Land Claims Commissioner on 18 December 1840 states that his 3rd of four claims consisted of:
“Agricultural land situate on the opposite bank of the [Kaeo] river and bounded on the back or S by the top of the first hills and by the Mangaiti creek on the East and the Kohepara on the West containing in all about
Geometria Ltd Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. - Page 19 400 acres 250 of which –arable land—little or no timber—extensive swamps and hills barren.
Purchased in goods and money on Jany 4th 1840 for £86.0.0”
An itemised account of the 400 acre purchase included tobacco and cash, along with gunpowder, textiles and clothing, blankets and soap (Prokhovnik 1991 Appendix II). This property was noted as being to the west of his first and second purchases which was in the valley of the Taiawarua creek with the Waitangi creek to the east and hills to the west (Prokohnik 103-4). The reference to Kohepara Creek and Mangaiti Creek place this purchase on the southern side of what would become the Waikukupa Block where the third Spickman House still stands; Kohepara is shown on OLC 69 (1861), the plan of Spickman’s Maungawhereo Block at Kaeo, running into the Kaeo River on the western side, at what is now the southern end of the project area.
Spickman’s land claim was granted in 1842, as published in the Gazette of 17 August 1842. Mary Anne died at the age of 28 on 30 September 1842 and was buried near the site of the first house, above the river.
By around 1846 Spickman was living with Mary Mangatae, a daughter of Uroroa but did not marry her until 1869 or 70 (Prokohnik 1991: 119,123). In 1852 his 15 year old daughter Mary Ann married Alexander Nisbet and Prokohnik (1991: 125) states there is some evidence that he moved to a new house at this time and gave some of his land and the old house to Mary Ann and her new husband and moved across the river to a new house. The source of this information is not cited. Alexander Nisbet, who would ultimately come to live at the Spickman homestead on the other side of the river, arrived in Mangonui in 1850 on the South Boston and worked in the Kauri trade for several years before following the gold rush to Australia. He returned in 1853 and undertook various road and bridge contracts in the Whangaroa area. He had ten children with Mary Ann and became a prominent local citizen, Justice, Oddfellow, Mason, Orangeman and Wesleyan Church trustee,
Spickman set up a store in the mid-1850s and in 1857 became the post master, holding the position until 1874 (Prokohnik 1991: 126-7). In 1858 his original grant was cancelled and resurveyed, resulting in a reduction to 1549 acres, although on application to the waste lands commissioner and supporting statements from Te Uroroa some 300 acres land was returned at the back of the Taraire Block. This grant is illustrated on Old Land Claim plan OLC 69 which shows the 1549 acres plus additional 300 acres. Several buildings are shown on the north side of the river in the vicinity of where earlier accounts placed Spickman’s first and second houses, but there is no building illustrated in the vicinity of the Dip Road property. A place name, Kurukuru is indicated in the vicinity, however.
In 1862 the Spickman residence was being advertised as a polling place for the election of the Supervisor of the Province of Auckland but by 1863 and again in 1866, Spickman was attempting to sell his entire holdings at auction. The Daily Southern Cross of February 1863 and February 1866 both advertise almost 2000 acres, largely in kauri but with a frontage on the Kaeo River
In 1871 the property was again advertised for sale in to lots, with the smaller 247 acre Allotment 54 Parish of Kaeo which also belonged to Spickman were auctioned in Auckland by Samuel Cochrane and Sons (Daily Southern Cross, 29 September 1871).
Geometria Ltd Page 20 – Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. The land is described as partially cleared and cultivated with the remained in kauri, and including a “comfortable homestead, occupied by Messrs Spickman and Nesbit”.
By the 1870s Spickman was still with Mary, with the Nisbets living behind in a two storeyed cottage (at the time of writing her book the latter dwelling had been reduced to one storey’ and other houses on dip road belonged to three Nesbit grandchildren).
William Spickman died on 14 June 1881 of old age. His death was noted in a short obituary suggesting that at the time of his death he was one of the oldest of the original settlers, and probably undertook the first ploughwork in the country. He was probably buried in the family plot near the first house where the two Mary Annes (Wife and daughter), son-in-law Alexander Nesbit, their baby son Andrew, his son Arthur and four other grandchildren are buried (Prokohnik 1991: 130-131.
Following the death of William Spickman, the house was occupied by Samuel Hare and then Dick Whitehead. Samuel Hare was the ninth son of Joseph Hare Senior, who arrived in New Zealand on the Lancashire Witch in 1865 and settled in Kaeo shortly thereafter.
The Hare family were prominent settlers in Kaeo and became scions of the Seventh Day Adventist faith, Joseph Senior having converted in 1885. European settlement in the Kaeo area continued to expand along with the timber industry, and the deforestation involved had marked effects on the build-up of alluvium on the valley floor (see Richardson et. al 2014 and Shakles et. al. 2015 for a comprehensive discussion of the changes to the Kaeo River valley environment following initial settlement, and then the arrival of Europeans).
6.3 Review of Historic Maps and Plans - Te Huia, Pahuhu and Waikukupa Blocks
Early land sales and occupation of the Kaeo River area was focussed on the middle and upper reaches of the river, with its access to the fertile and cultivable alluvial flats and stands of workable timber in the hinterland beyond. Downstream in the vicinity of the Kaeo Bridge project area, land remained in Maori ownership into the 1870s. The Kaeo Bridge project area covers parts of what would later become known as the Waikukupa, Te Huia, and Pahuhu land blocks which were surveyed and progressively sold, subdivided and developed in the years after 1874. Waikukupa is the original block on the western side of the river in the vicinity of the project area, with the much larger Te Huia Block on the eastern side of the river, enclosing the much smaller Pahuhu Block.
Crown Land Purchase Agent Lieut.-Colonel Mcdonnell wrote to Land Commissioner Mr. H. T Clarke on 28 November 1874 to say that he has paid a deposit of £50 on several blocks of land at Whangaroa, including the Te Huia Block of 4000 acres (Turton 1883; Figure 5). There was some valuable timber on the block and the price paid was Is. 3d. per acre. The Te Huia Block was purchased from Wiremu Waihi and others with £10 paid as a deposit but the price still to be fixed. The land was described as broken, with some timber, and one half with good soil, the other half indifferent.
In 1888, Wi Warena Tuoro and others petitioned the Crown over the sale of the Te Huia Block, stating “that the block of land called Te Huia, situated at Whangaroa, was sold by Te Pahii to a European, and is now in the possession of the Government. They say the land belongs to them, and they wish to regain possession of it” (AJHR 1888: Petition 113 p 16). In 1901 Wi Warena again petitioned the Crown stating the land was taken illegally (AJHR 1901 Petition 1181, p14).
Geometria Ltd Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. - Page 21 In the meantime, the Pahuhu Native Reserve had been reserved out of the Te Huia Block. The title of the Pahuhu Block was investigated by the Native Land Court on 25 May 1894. In 1908, the Pahuhu Block Nos 1, 2, and 3 were recommended to be reserved for Maori occupation under the Native Settlements Act of 1907. At the time, the blocks had 2, 1 and 4 owners respectively (Northern Minute Book, 13: 131-132; 134). The Block was partitioned in July 1898 (Northern Minute Book 18: 29-30; 81) and the partition appealed in November 1898 (Minute Book 28: 64-69; 70-73). The name Pahuhu is shown on OLC 69 (1875), the survey of Spickman’s Maungawhero Block claim.
The initial claim to Pahuhu by He Haruia [illeg.] states - “I know the map before the Court. It is “Pahuhu” Land. It is [illeg]. I claim [illeg.] occupation. Te []imakau – Nahi (or Mahi) – Tane – Self. I have always lived on this land and [illeg.] Hill.”
The later partition discussed in Minute Book 18: 81 states “Pahuhu. This block to be divided into two parts by a line running from a point B on the Kaeo River to the W boundary of the Block, the division to the N of such line to be known as Pahuhu No. 1 and that to the S as Pahuhu No.2 The acreage to be ascertained of each respectively”.
A copy of a memo by Judge Clendon on the matter states. “This land is so broken that unless a survey or was on the ground no point can be given as the back boundary line, but it is understood that the line continuing from B at the river side must run so as to include Wiri Roiho’s house in No. 1. No. 2 cannot contain the same acreage as No.1 but this was a matter of arrangement between the natives. James Clendon Land Commissioner.” The subsequent appeal (Minute Book 28) covers issues of access to the river, cultivations, buildings and urupa that needed be addressed to satisfy the claimants. A number of the features discussed are illustrated on plans of Pahuhu from the early 20th century and included below.
In October 1876 one Arama Te Puhi of Ngāti Pukahi/Pakahi claimed the 1114 acre Waikukupa Block on the western side of the river for himself and 19 others from the Ngātiuru and Ngāti Pukahi/Pakahi hapu at a hearing of the Maori Land Court. He stated that the land was subdivided into five parts amongst himself, William Spickman, and 18 others of the tribe. No other claimants appeared and there was no opposition, the claim was granted, fees one pound for the hearing and one pound for the memorial of ownership were assessed. The Pt NW Waikukupa Block was originally three blocks known as Tapaka, Waitawari and Tenoako, but were added to the main Waikukupa Block to the south. The western side of the project area lies specifically within the Waikukupa J Block, originally mudflats and later drained/reclaimed and added to the Waikukupa Block which was originally purchased by William Spickman and abutted his adjoining purchases to the south.
The Waikukupa Block was progressively alienated from the late 19th century into the 20th century, with title to land created by accretion/reclamation of the mudflats behind and then beyond the stopbank upon which what would become SH10 established by the Crown and on-sold to neighbouring landowners from 1905-1906 when the river was bridged. G. Roke was farming Waikukupa J in the 1930s and applied for title to the reclaimed mudfats north of the highway (Section 11) and south of the highway adjacent to the river (Section 12 Kaeo Block 11) in 1937-38. Roke was a keen golfer and owned a caterpillar bulldozer. He established the original Whangaroa Golf Club on the Pt NW Waikukupa Block and several of the level terraces originally recorded by Johnson in 1988 were apparently tees created by local P. Hayes. A clubhouse was established north of the highway and the area was used for summer golfing for approximately 20
Geometria Ltd Page 22 – Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. years until 1952, when it was club moved to another property to the west (Nevin 1997: 1).
6.3 The 1906 Bridge
Prior to 1906 the overland route from Kaeo to the western side of Whangaroa was via a circuitous route from Kaeo along the old Dromedary Road/Dip Road and across the south side of the Taita hill to Pupuke, with numerous streams requiring fording and several major hills to climb. This route is shown on the 1908 geological survey plan. In the early 20th century a causeway was pushed across the mudflats and marsh from west of the Pupuke River eastwards to the western side of the Kaeo River, and towards the road on the eastern bank from Kaeo to Whangaroa. The 1906 bridge was 180 feet long and cost £650. Five hundred people attended the opening on 19 November 1906 at what was, at that time, known as Tapu Point. At the time it was the longest ferro-concrete bridge in New Zealand and the longest span could carry 150 tons. The new route between Kaeo and Pupuke cost £3000 altogether (Northern Advocate, 26 November 1906) and allowed a considerable saving in time and effort in contrast to the old route to the south.
The 1908 geological survey plan of Whangaroa shows the bridge and the highway/causeway crossing the mudflats on the western side of the project area. By 1950, the mudflats and marsh on the southern side of the project area had been reclaimed and drained and several houses established, with a partial reclamation of the land on the north side of the highway. This is shown on the aerial photo mosaic for the area.
6.4 Summary of the History of the Waikukupa-Te Huia-Pahuhu Area.
On the basis of the brief review above, it seems that the Pahuhu Stream and valley area and the outfall to the Kaeo River was occupied at least as early as the 1890s, if not earlier based on the 1875 reservation of the Block from the Crown purchase and its establishment as a “Native Reserve”. By 1918 there were extensive cultivations between the highway and river, and a church, urupa, houses and outbuildings on the eastern side of the highway.
It seems unlikely that there was any permanent occupation of the western side of the project area which was in mudflats, mangroves and marsh until 1906 or latter, with the exception of the spit of land extending northwards along the western side of the river and which was evidently used by Maori as a camp site. This spit of land would have provided access to the ridgelines to the south west and thence to Taita and Kaeo if the tides were against travellers making for those areas.
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Figure 5: OLC 3182 (1875) showing Te Huia and the Kaeo Bridge project area and Pahuhu reserve (circled).
Figure 6: ML 3312 (1875) showing Pt NW Waikukupa and Kaeo Bridge project area (circled).
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Figure 7: Detail from OLC 69 (1875) showing Spickman’s Maungawhero Block purchases (Pahuhu and Hepara (Kohepara) Streams circled).
Figure 8: SO 6362 (ca. 1890). Note "Native Camping Ground" on the spit of land extending past the location of the existing bridge, and that Section 7 (now Waikukupa J Block) is covered by tides at this time and what would become the highway has not been formed or surveyed.
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Figure 9: ML 1736 (1879) showing a subdivision of part of the Te Huia Block and the road from Kaeo to Whangaroa.
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Figure 10: Detail from SO 16033 (1912) showing 1906 bridge and causeway road over Section 7 (now part of Waikukupa J Block) across mudflats and marsh. Note the spit of land extending past the bridge.
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Figure 11: ML 11137 (1918) showing the subdivision of the Pahuhu Block and features at the southern end of the project area.
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Figure 12: The opening of the Kaeo River bridge. Auckland Star, 26 November 1906.
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Figure 13: Opening of the 1906 concrete Kaeo Bridge (Auckland Weekly News. 6 December 1906. APL).
Figure 14: 1906 concrete Kaeo Bridge (Auckland Weekly News. 6 December 1906. APL).
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Figure 15: The 1906 concrete bridge, in 1913 (23 January 1913, Auckland Weekly News. APL).
Figure 16: Detail from the Geology of the Whangaroa Subdivision (1908) showing the spit of land and mudflats on the western side of the existing bridge.
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Figure 17: NZMS 003 aerial mosaic N11-1 (1954; photography from 1950).
7.0 Field Survey
7.1 Overview
The project area was visited on four occasions between July and December 2017. J. Carpenter, R. Gibb and D. McCurdy undertook an initial visit on 19 July 2017 and walked over the publicly accessible, central part of the project area. J. Carpenter undertook a second visit on 10 August 2017 and walked over the southern and western parts of the project area and met iwi representatives. A third visit was undertaken on 16 October to inspect a suspected midden reported by project ecologist T. Barnett; this feature was subsequently confirmed as a midden. A fourth visit was made by D. McCurdy on 29 November 2017 to inspect the areas where additional flood mitigation measures were proposed. The project area and results of the assessment are divided into three general areas for descriptive purposes and are presented below.
The western part of the project area between the western bank of the Kaeo River and the rising ground at the western end of the project area was found to be low-lying and very wet, under short, grazed and heavily pugged pasture. Parallel swales and deeper drains running north to the roadside drain and weir on the south side of the highway, and from there into the river. Due to grazing, pugging and the presence of the drains the surface visibility was relatively good.
A small amount of fragmented shell was noted in the roadside drain on the south side of the highway west of the river, in several of the field drains and in other patches on the pasture. However recent aerial photography indicated that imported fill appeared to be added to the pasture over the last decade. Along with the historic research suggesting that the flats either side of the road are a post-1905 reclamation and prior to that time were a mix of tidal mudflats and salt marsh, the shell would appear to be a recent addition and archaeological features are generally unlikely in this area.
The western river bank was traversed but has been modified by farm race, fencing, and earthworks to create a stopbank, along with the existing Kaeo Bridge. The toe of the ridges rising up to the Taita hill were also walked over and examined but no archaeological sites or features were observed. The western ridge is under plantation
Geometria Ltd Page 32 – Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. pine and rises steeply from the flats with several bulldozed tracks and much cattle tracking present. The south-western ridge is under regenerating native bush and also rises steeply from what was the old sand spit shown on historic plans. The old spit and the ridges are more archaeologically sensitive than the intervening/surrounding flats.
On the eastern side of the bridge the river bank, and road cuttings on the eastern side of the highway, were inspected. Ground conditions for survey were poor to average, with the river bank heavily vegetated and under waist high grass, and the cuttings under regenerating native bush. There was no sign from the road edge of archaeological features such as shell midden, occupation layers, or other suspect pits or fills in the top of the road cuttings. The abutments of the existing bridge over the river are made of stacked dry stone and may remain from the original 1906 bridge; they are not archaeological but are of minor heritage value.
At the southern end of the project area on the western side of the highway, the area has been developed and landscaped for a restaurant which now serves as a private dwelling, and a eucalyptus plantation. Ponds have been excavated in the vicinity of the low lying marshy area shown on the historic survey plans and making use of the old drain to the river. The eucalyptus plantation lies over the area of the historically attested Pahuhu valley settlement cultivations. Surface visibility was poor across the area and the water level in the stream was high during the first inspection in August and the suspect midden reported later and described below was not noticed at the time.
East of the highway on the flat ground at the Pahuhu valley mouth, survey conditions were also poor due to the ground conditions and no features were observed in this area, although structures from the late 19th to early 20th century Pahuhu settlement are known to have been in this area.
Historically attested features, and the observed midden are illustrated below in relation to the project area (Figure 18).
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Figure 18: Archaeological features observed in 2017 and historic features recorded from land plans in the immediate vicinity of the Kaeo Bridge project area as proposed in 2017.
Figure 19: Panorama of project area, looking south to west (left-to right) across drained/reclaimed flats west of the existing bridge.
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Figure 20: Looking west along existing bridge over road causeway and drained/reclaimed flats
Figure 21: Looking north along river and stopbank over reclaimed/drained flats.
Figure 22: Looking north towards highway, past toe of ridge which ascends to Taita trig.
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Figure 23: Looking north east over drained/reclaimed flats towards highway and existing bridge.
Figure 24: Looking south over low-lying ground on eastern side of river, immediately south of SH10/Whangaroa Road intersection towards Pahuhu Stream.
Figure 25: Looking east across Eucalyptus plantation towards SH10, in vicinity of Pahuhu cultivations.
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Figure 26: Looking along Pahuhu stream re-alignment towards outfall to Kaeo River.
Figure 27: Looking north along SH10 with vicinity of Pahuhu cultivations to left and Pahuhu settlement right, with urupa on hill in centre right of frame.
7.2 P04/775 Midden, Pahuhu Stream
A single archaeological site was recorded on the Pahuhu Stream, approximately halfway between the highway and the stream outfall to the Kaeo River. The site consists of a layer of shell midden exposed in-section in the lower part of the northern stream bank. The eight-metre-long layer of midden consists of dense, whole cockle with some pipi, abundant charcoal and a few fire cracked rocks, under one metre or more of alluvial silt. The midden itself is up to 30cm thick in section. Probing into the bank suggests the midden extends at least 40-50cm in the bank, but it was too deeply buried by alluvium to follow by probing or spade from the ground surface above. Above the midden and still within the largely homogenous alluvium is a layer of charcoal and burned soil perhaps suggesting a later fire event, perhaps a purposeful burn off. Otherwise the thick layer of alluvium above the midden was homogenous, grey brown sandy silt.
Geometria Ltd Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. - Page 37 From the location of the midden downstream towards the river, occasional pipi and cockle shell are present on the bottom of the stream, having eroded out of the exposed section. The eastern end of the section has been recently modified by a fallen eucalyptus which has been undermined by the flow of water and fallen across the stream, taking part of the midden with it.
No other midden or other archaeological features could be discerned on the opposite side of the stream, or in the banks on either side between the highway and the outfall. The blocked-up original course of the stream was present approximately 15m south of the midden but was holding water. No other archaeological features were observed in the adjacent banks of the Kaeo River north of the Pahuhu Stream.
Given the alignment of the Pahuhu Stream through this area is artificial it seems likely that the midden was modified when the channel was cut in the late 19th or early 20th century to realign the stream through the culvert under the highway. Prior to this time the midden may have been further away from the stream. The midden slopes downwards from east to west with a noticeable drop on the western side, and the midden may have been deposited over the edge of an old alluvial terrace.
Richardson et. al. suggest that floodplain sedimentation rates accelerated across Northland following Polynesian settlement and initial forest clearance events, with aggradation rates in the vicinity of 3.3–10.1mm yr−1 increasing to an average rate of 8– 13.5mm yr−1 since European settlement when extensive deforestation caused by the demands of the timber industry ensued. With those rates in mind it is possible that the midden was deposited little more than one hundred years ago, but may of course be much older.
The site is located as Easting Northing (NZTM) and has been recorded in the ArchSite database as site P04/775.
Figure 28: Location of midden.
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Figure 29: Shell midden exposed in section.
Figure 30: Detail of shell midden.
8.0 Significance Assessment
8.1 Assessment Criteria
The archaeological significance of the archaeological site recorded as P04/775 is assessed using criteria derived from guidance issued by Heritage New Zealand (New Zealand Historic Places Trust 2016).
The first set of criteria assess the potential of the site to provide a better understanding of New Zealand’s past using scientific archaeological methods. These categories are focussed on the intra-site level. x How complete is the site? Are parts of it already damaged or destroyed?
A complete, undisturbed site has a high value in this section, a partly destroyed or damaged site has moderate value and a site of which all parts are damaged is of low value.
Geometria Ltd Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. - Page 39 x How diverse are the features to be expected during an archaeological excavation on the site?
A site with only one or two known or expected feature types is of low value. A site with some variety in the known or expected features is of moderate value and a site like a pa or kainga which can be expected to contain a complete feature set for a given historic/prehistoric period is of high value in this category. x How rare is the site?
Rarity can be described in a local, regional and national context. If the site is not rare at all, it has no significance in this category. If the site is rare in a local context only it is of low significance, if the site is rare in a regional context, it has moderate significance and it is of high significance it the site is rare nationwide.
The second set of criteria puts the site into its broader context: inter-site, archaeological landscape and historic/oral traditions and community association. x What is the context of the site within the surrounding archaeological sites?
The question here is the part the site plays within the surrounding known archaeological sites. A site which sits amongst similar surrounding sites without any specific features is of low value. A site which occupies a central position within the surrounding sites is of high value. x What is the context of the site within the landscape?
This question is linked to the one above, but focuses onto the position of the site in the landscape. If it is a dominant site with many features still visible it has high value, but if the position in the landscape is ephemeral with little or no features visible it has a low value. This question is also concerned with the amenity value of a site and its potential for on-site education. x What is the context of the site within known historic events or people, or existing communities?
This is the question of known cultural association either by tangata whenua or other descendant groups. The closer the site is linked with important historic events or people the higher the significance of the site. This question is also concerned with possible commemorative values of the site.
An overall significance value derives from weighing up the different significance values of each of the six categories. In most cases the significance values across the different categories are similar.
8.2 Significance Assessment of Midden P04/775
Based on the criteria noted above, the midden recorded as P04/775 is assessed as being of moderate archaeological significance. This assessment is based largely on its local rarity and uniqueness and the possibility that it might provide information about the archaeology of the northern Kaeo area in general, and the occupation of the Pahuhu Stream valley in particular. Investigation of the feature may yield useful information on the environmental history of the area to augment what has already
Geometria Ltd Page 40 – Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. been derived from sites investigated upstream. While midden sites are ubiquitous in coastal Northland and large numbers of such sites are recorded elsewhere in the Whangaroa area, none have been recorded along the Kaeo River and only a single discrete midden is recorded in the catchment. Any information which P04/775 might provide may be significant, especially given the depth of alluvium above the feature.
Table 1: Significance assessment of Midden P04/775.
Significance Value Comment Category
Integrity, Condition Medium The midden feature exposed in the bank of the Pahuhu Stream has and Information been modified by the realignment of the stream from its original Potential course to the south, through a culvert and along the current channel in the late 19th or early 20th century, and from subsequent erosion from the water flow. However the intact part of the feature appears in relatively good condition, with a dense layer of whole shell and charcoal which appears to extend north into the bank. Any other features associated with the midden nearby are buried under a metre of alluvium and may have been relatively protected from subsequent flooding, and land management practices including the establishment of the eucalyptus plantation. The feature may provide information on chronology of occupation, subsistence strategies, and vegetation and flood history of the area, and associated features could provide additional information on the occupation of the Pahuhu Stream and valley, and the utilisation of the alluvial fan at the outfall of the stream to the Kaeo River.
Diversity Low/ The feature consists of a single eight-metre-long, 30 cm thick midden deposit exposed in section in the river bank, with a possible Unknown separate layer or lens associated with a vegetation burnoff above. Other associated subsurface features such as garden soils, occupation layers, earth ovens and fire scoops, and postholes may be present nearby and buried under the alluvium.
Rarity and Medium No other archaeological sites are recorded in the vicinity and the Uniqueness next nearest known sites are more than one kilometre away. Few sites are recorded in the Kaeo River catchment and in general the archaeology of the Kaeo area is poorly known, so any archaeological features recorded in Kaeo are somewhat unique.
Archaeological Low The feature is probably associated with the use and occupation of Context the Pahuhu Stream and valley area by Maori in the late prehistoric or ‘classic’ period, but potentially it may be from the more recent historically attested occupation of Pahuhu in the late 19th and early 20th century. Alluvial soils are excellent growing mediums for traditional Maori cultigens like kumara, yam and taro and the alluvial fan may have been used seasonally to grow these crops, and later European introductions. The lack of other recorded archaeological sites nearby does make it difficult to put this feature into context.
Landscape, Visual Medium The features is not visible in the landscape and is not amenable to and Other Amenity on-site interpretation. However the results from any investigation Values would be locally significant and suitable interpretation opportunism may be available at the local museum or nearby as part of the development of visitor facilities.
Geometria Ltd Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. - Page 41
Historical, Low-medium The site is not directly associated with any known historical Community and personality or event but the site may be significant to the Tangata Cultural Whenua of Kaeo. However given its location and despite its depth Associations below the current ground surface it may relate to the late historic Pahuhu valley settlement attested in historic records.
9.0 Stakeholder Consultation
The key stakeholder parties for consultation regarding archaeological sites and historic heritage for the Project are Te Rununga o Whaingaroa and Ngāti Uru, and Heritage New Zealand. Consultation is ongoing with the stakeholders.
9.1 Te Rununga o Whaingaroa and Ngāti Uru
The author of this report attended a site visit with the wider project team and Tangata Whenua on 10 August 2017. The Pahuhu settlement and importance of the urupa was discussed at this time, along with the presence of early 20th century cultivations and other features at the south end of the project area. This was followed by two hui on 28 September to discuss the preliminary results of the archaeological assessment, with T. Faneva and W. Epiha of Te Rununga o Whaingaroa, and then with V. Walker and B. Smyth. At this time, midden P05/775 had yet to be identified and raised as a matter for consideration.
Iwi have subsequently participated in landscape planning and ecology fieldwork for the project.
Engagement with Iwi will be ongoing in the course of the project, through the provision of this archaeological assessment, other environmental assessments, hui, participation in developing the Archaeological Management Plan, landscape design and cultural monitoring and participation in any archaeological investigation.
9.2 Heritage New Zealand
Heritage NZ was appraised of the project in early 2016 and was involved in early discussions about geotechnical testing in the area, which later occurred under an accidental discovery protocol. Heritage NZ were appraised of the initial results of the assessment and the likely need for an archaeological authority.
10.0 Assessment of Effects
Archaeological sites and features may be affected at the western landing of the existing bridge where a Maori camping ground was indicated in the 1891 survey plan of road taking (the exact position on the northern end of the spit being indeterminate). The removal of the existing bridge and any flood mitigation work on the river bank to the north and south may affect any remaining features of the Maori camping ground or earlier, similar use of the spit in this area (although this area has been highly modified by the construction of the 1906 bridge, causeway, weirs/drains and stop bank during the early-mid 20th century).
The current design for the Kaeo Bridge project and associated flood mitigation works will not affect recorded archaeological site P04/775 and any other subsurface archaeological features which may remain on the alluvial flats at the mouth of the
Geometria Ltd Page 42 – Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. Pahuhu valley where cultivations were evident at the turn of the century on the western side of the highway, with the settlement itself to the east.
To the south of the existing bridge on the western side of the river, the construction of the new bridge and flood mitigation works may affect archaeological sites and features which may remain on the narrow spit of land which once made up the western bank of the river and extends north to the camping ground noted above.
The current plan will not affect the higher ground that rises to Taita on the western side of the river.
10.1 Alternatives Analysis
In deciding the preferred alignment of the new Kaeo Bridge, archaeological and heritage issues, along with other factors, were fed into analysis of four different options for the bridge and highway in September 2017. These options are shown in Figure 32 below.
The more northern Option 1 and Option 2 were considered least likely to have archaeological effects as they largely avoided the sensitive area around the Pahuhu Stream.
The southernmost Option 3 was the least preferred alignment in archaeological terms as it cut across the sensitive Pahuhu area on the eastern side of the river and into the higher ground on the western side of the river. It was considered to have the most likelihood of affecting archaeological features and would destroy midden P04/775 and anything else remaining in the vicinity.
Option 4, which was the preferred alignment in late 2017, would have affected any subsurface features remaining from the Pahuhu cultivations and midden, but only cut across the northern edge of the historically cultivated area. It also largely avoided the toe of the western ridgeline on the west side of the river.
The preferred option as of June 2019 is similar to the earlier Option 1 and 2 and is less likely to have archaeological effects than the southern alignments.
Geometria Ltd Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. - Page 43
Figure 31: Indicative State highway realignment and bridge options in late 2017.
11.0 Recommendations and Mitigation
1) The New Zealand Transport Agency should apply for a general archaeological authority under the Heritage New Zealand Pouhere Taonga Act 2014 to modify unrecorded subsurface archaeological sites and features which may be affected by the Kaeo Bridge project and undertake this work in accordance with a suitable archaeological site instruction.
2) Given the lack of definite archaeological effects an archaeological management plan will suffice and no research strategy is recommended due to the lack of specific archaeological features to be investigated. The archaeological management plan will include a standard approach to investigation and analysis of any accidental archaeological discoveries. This will be aimed at providing baseline information with regard to site use, chronology, and paleo environment.
3) The New Zealand Transport Agency should continue to undertake consultation with Tangata Whenua in light of the findings and recommendations from this report, as part of the archaeological authority process and should develop protocols around the appropriate tikanga for Maori archaeological sites and features and discuss opportunities for cultural monitoring of earthworks.
4) As plans are developed in consultation with the Tangata Whenua of Kaeo, an area should be designated with the Project area for the deposit of
Geometria Ltd Page 44 – Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. archaeological materials which do not need to be retained, and potentially any koiwi tangata (human remains) which might be encountered.
5) As construction plans are developed, they should be reviewed by the archaeologist in order to prepare the archaeological site instruction, and to inform the final assessment of effects required for the archaeological authority application.
6) Earthworks for the project are likely to require monitoring by an archaeologist in the archaeologically sensitive area in the vicinity of the old spit on the western side of the river, as identified in Figure 32 below. This would include the removal of the existing stopbank and modification of any underlying landform along the river edge, the removal of the stone bridge abutments, and removal of existing pavement adjacent to the western abutment.
7) The stone abutments of the 1906 bridge should be recorded prior to removal.
8) Opportunities should be investigated for interpreting the history and archaeology of the Kaeo Bridge Project area, either within the Kaeo Museum or in a public area adjacent to the Highway; during construction with open days and media releases as appropriate if archaeological materials are uncovered.
9) Any additional works proposed outside of the area where field investigations have been undertaken may require additional assessment.
Figure 32: Areas proposed for archaeological monitoring (outlined red).
Geometria Ltd Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. - Page 45 12.0 Summary
A single archaeological site has been identified to the south of the Kaeo Bridge designation. The observed feature, midden P04/775 will not be affected by the proposed new bridge and road alignment. Several other areas within the designation have been identified through historic research where archaeological effects are possible, although relatively unlikely.
Due to the possibility of archaeological effects, the Kaeo Bridge project will require a general archaeological authority to modify any sites and features which may be affected.
Recommendations have been made to mitigate the effects of the project on sites and features which may be present. As is common for projects where archaeological sites will be modified or destroyed, proposed mitigation involves the archaeological monitoring of sensitive areas, investigation, recording, analysis, reporting of sites under an archaeological authority issued by Heritage New Zealand Pouhere Taonga. Additional mitigation includes public interpretation of affected sites. This mitigates the loss of archaeological information, but not the destruction of sites themselves.
Geometria Ltd Page 46 – Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. 13.0 References
13.1 Published and Unpublished Reports and Books
AJHRS, 1888. Reports of the Native Affairs Committee. Government Printer, Wellington.
AJHRS, 1901. Reports of the Native Affairs Committee. Government Printer, Wellington.
AJHRS, 1908. G-01j Native Lands and Native-Land Tenure: Interim Report of Native Land Commission, on Native Lands in the Counties of Whangarei, Hokianga, Bay of Islands, Whangaroa and Mangoni. 1 January 1908. Government Printer, Wellington.
Bedford, S. 2013. From Paeroa to Pohue Pa: remnant landscapes of events that once shook the world, in M. Campbell, S. Holdaway and S. Macready (eds), Finding our Recent Past: Historical Archaeology in New Zealand. New Zealand Archaeological Association Monograph 29: 59-76.
Bell, J.M.; Clarke, E. de C. 1909 The geology of the Whangaroa subdivision, Hokianga division. Wellington: Government Printer. New Zealand Geological Survey Bulletin 8
Carpenter, J., 2012. Archaeological Assessment of the Re-piling of the Spickman House, Dip Road, Kaeo. Unpublished report for L. and W. Tyrrell. Geometria, Whangarei.
Gibb., R. 2015. Spickman House Re-piling - Final Report. Unpublished report for L. and W. Tyrrell. Geometria, Auckland.
Jamieson, B., 2016. Northland One Lane Bridges Project. Archaeological Desktop Review. Unpublished report for the New Zealand Transport Agency. Opus International Consultants, Auckland.
Johnson, L., 1988. Archaeological Site Survey of the Ratcliffe Residential Subdivision, Whangaroa. Science and Research Internal Report No. 17. Department of Conservation, Auckland.
Lee., J. A., 1983. I have Named It the Bay of Islands. Hodder and Stoughton, Wellington.
Nevin, D., 1997. Archaeology of the Proposed Subdivision of Lot 1 DP 137855. Unpublished report for C & D Perrot. D. Nevin, Whangarei.
Pickmere., N. P., 1994. Kerikeri. Heritage of Dreams. Northland Historical Publications Society, Kerikeri.
Prokhovnik, R. M., 1991. A reluctant pioneer : the story of William Spikeman, his life and times. Northland Historical Publications Society, Kerikeri.
Richardson, J.M., I.C. Fuller, K.A. Holt, N.J. Litchfield and M.G. Macklin. 2014. Rapid post- settlement floodplain accumulation in Northland, New Zealand. Catena, 113 (2014): 292–305.
Sale, E. V., 1986. Whangaroa. Whangaroa Book Committee, Whangaroa.
Geometria Ltd Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. - Page 47 Shakles, R,. S. Phear and R. Clough, 2015. Flood Mitigation Scheme Kaeo, Northland. Final Archaeological Monitoring and Excavation Report (Sites P04/760 and P04/761. Unpublished report for the Northland Regional Council. Clough and Associates, Auckland.
Turton, H. H., 1883. An Epitome of Official Documents Relatives to Native Affairs and Land Purchases in the North Island of New Zealand. George Didsbury, Wellington.
13.2 Published and Unpublished Maps, Plans, Photographs and Paintings
DP 25442 (1934).
DP 32504 (1944).
ML 2224 (1871).
ML 2320 (1871).
ML 2321 (1871).
ML 2322 (1871).
ML 3312 (1871).
ML 6255 (1890).
ML 11137 (1918).
ML 12039 (1923).
OLC 38 (1843).
OLC 69 (1861).
OLC 3182 (1875).
SO 1736 (1879).
SO 26835 (1932).
SO 28679 (1936).
SO 30005 (1938).
SO 31453 (1940).
SO 32245 (1941).
Geometria Ltd Page 48 – Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. Appendix A - Site Record Forms
Geometria Ltd NEW ZEALAND ARCHAEOLOGICAL ASSOCIATION
NZAA SITE NUMBER: P04/775
Site Record Form SITE TYPE: Midden/Oven SITE NAME(s):
DATE RECORDED:
SITE COORDINATES (NZTM) Easting:1669717 Northing: 6117056 Source: On Screen
IMPERIAL SITE NUMBER: METRIC SITE NUMBER: P04/775
Scale 1:2,500
Finding aids to the location of the site In the north bank of the Pahuhu Stream, midway between State Highway 10 and the stream outfall to the Kaeo River. At the point where the stream turns to the south.
Brief description
Recorded features Midden
Other sites associated with this site
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SITE RECORD HISTORY NZAA SITE NUMBER: P04/775
Site description Updated 24/10/2017 (Field visit), submitted by jonocarpenter , visited 20/10/2017 by Carpenter, Jonathan Grid reference (E1669717 / N6117056)
The site consists of a layer of shell midden exposed in-section in the lower part of the northern stream bank, The layer of midden is eight metres long and consists of dense whole cockle with a few pipi, abundant charcoal and a few fire cracked rocks, under one metre or more of alluvial silt. The midden itself is up to 30cm thick. From the location of the midden downstream towards the river, occasional pipi and cockle shell are present on the bottom of the stream, having eroded out of the section.
The eastern end of the section has been recently modified by a fallen eucalyptus which has been undermined by the flow of water and fallen across the stream, taking part of the midden with it. Probing into the bank suggests the midden extends at least 40-50cm in the bank, but it was too deeply buried by alluvium to follow by probing from the ground surface above.
Above the midden and still within the largely homogenous alluvium is a layer of charcoal and burned soil perhaps suggesting a later fire event, perhaps a purposeful burn off. Otherwise the thick layer of alluvium above the midden was homogenous, grey brown sandy silt.
No other midden or other archaeological features could be discerned on the opposite side of the stream, or in the banks on either side between the highway and the outfall. The blocked-up original course of the stream was present approximately 15m south of the midden but was holding water. No other archaeological features were observed in the adjacent banks of the Kaeo River north of the Pahuhu Stream. Condition of the site Updated 24/10/2017 (Field visit), submitted by jonocarpenter , visited 20/10/2017 by Carpenter, Jonathan
Site will continue to erode from the flow of the stream and may be affected by the proposed replacement of the single lane bridge over the Kaeo River to the north, and which will tie into the existing highway alignment near the Pahuhu Stream culvert.
Statement of condition
Current land use:
Threats:
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SITE RECORD INVENTORY NZAA SITE NUMBER: P04/775
Supporting documentation held in ArchSite
Detail of midden
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3 of 5 NEW ZEALAND ARCHAEOLOGICAL ASSOCIATION Looking north towards the site
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4 of 5 NEW ZEALAND ARCHAEOLOGICAL ASSOCIATION Midden exposed in north bank of Pahuhu Stream
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5 of 5 NEW ZEALAND ARCHAEOLOGICAL ASSOCIATION
NZAA SITE NUMBER: P04/262
Site Record Form SITE TYPE: Pa SITE NAME(s):
DATE RECORDED:
SITE COORDINATES (NZTM) Easting:1668825 Northing: 6116429 Source: CINZAS
IMPERIAL SITE NUMBER:N11/65 METRIC SITE NUMBER: P04/262
Scale 1:2,500
Finding aids to the location of the site
Brief description PA
Recorded features
Other sites associated with this site
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SITE RECORD HISTORY NZAA SITE NUMBER: P04/262
Site description
Condition of the site may be P04/235
Statement of condition
Current land use:
Threats:
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SITE RECORD INVENTORY NZAA SITE NUMBER: P04/262
Supporting documentation held in ArchSite
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NZAA SITE NUMBER: P04/235
Site Record Form SITE TYPE: Pa SITE NAME(s):
DATE RECORDED:
SITE COORDINATES (NZTM) Easting:1668525 Northing: 6116528 Source: CINZAS
IMPERIAL SITE NUMBER:N11/7 METRIC SITE NUMBER: P04/235
Scale 1:2,500
Finding aids to the location of the site
Brief description RIDGE PA
Recorded features
Other sites associated with this site
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SITE RECORD HISTORY NZAA SITE NUMBER: P04/235
Site description
Condition of the site may be P04/262
Statement of condition
Current land use:
Threats:
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SITE RECORD INVENTORY NZAA SITE NUMBER: P04/235
Supporting documentation held in ArchSite
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3 of 3 Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. - Page 49 Appendix B – Draft Archaeological Management Plan
B.1.0 Purpose and Methods
The purpose of this Archaeological Management Plan is to manage the effects/possible effects of the Kaeo Bridge project on recorded and unrecorded archaeological features.
The Kaeo Bridge project may have archaeological effects on Maori archaeological sites or features from the prehistoric and historic period. Due to the high degree of existing modification to the area from natural processes and the establishment of the highway, bridge and causeway, drainage/reclamation of the adjacent wetlands and mudflats, and establishment of stop-banks and drainage works, it is not possible to identify archaeological sites and features which might remain below the existing modification, and the effects the project may have on them.
The most likely location for such archaeological sites and features to exist, and be affected, is on the western bank of the Kaeo River during the removal of the existing bridge, establishment of the western landing of the new bridge, and associated works. This will occur on what was a narrow spit of land originally flanked by mudflats to the west and the river to the east. This spit was used by Maori as a camping area at the end of the 19th century, as attested by historic records, if not earlier.
B.2.0 Management of Archaeological Effects
B.2.1 Briefing The archaeologist will attend the pre-start briefing/site induction prior to works commencing for the Kaeo Bridge project. The archaeologist will provide a briefing on the known archaeological sites and features in the project area, recognising archaeological sites and features during earthworks, and the protocols contained in this document. At this time it will be useful to identify excavator operators who will work with archaeologists and kaitiaki during earthworks in sensitive areas. Consideration should be given to identifying and assigning roles to operators who have prior experience working with archaeologists/archaeological sites. The archaeologist and kaitiaki will work with the Project Manager to plan and schedule the required monitoring. It is preferable to undertake this work in the archaeologically sensitive areas at the commencement of the project as part of the initial enabling works.
B.2.2 Earthworks and other Ground Disturbing Activity
The archaeologist will: x Monitor earthworks in the identified areas (see Figure below). x Monitoring in sensitive areas will continue to archaeologically sterile or otherwise natural subsoil is reached. x There is no need to monitor in archaeologically sensitive areas once sterile subsoils are reached and bulk removal of subsoil/clay does not require monitoring. x Monitoring any other ground disturbing activity that may be required from time to time and not otherwise specified in the construction plans, in the archaeologically sensitive areas. x Investigate archaeological features as they are encountered.
Geometria Ltd Page 50 – Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. x Respond according to the on-call procedures for archaeological or potential archaeological finds occurring in the absence of the archaeologist, and/or outside the identified sensitive areas.
Archaeologically sensitive areas for the Kaeo Bridge project include: x The western abutment of the existing bridge and the western landing and any associated works for the new bridge x The eastern abutment of the existing bridge.
Note: Archaeological features may be encountered anywhere within the designation or areas outside the designation which might be used for temporary works including sediment control, hardstands and yards, and will require investigation accordingly.
Figure 33: Potentially archaeologically sensitive areas for monitoring (red polygons). All other areas on-call procedures apply.
B.2.3 Features and Feature Recording All features, profiles, layers, sample locations and artefact find spots will be recorded using a Leica RTK GPS tied to the NZTM 2000 map grid. Particularly significant features or details may be 3D laser scanned. Obvious 20th century features will be recorded as disturbances. Feature, layer, find acquisition, find discard and photographic information along with spatial data for those elements will be recorded in a Geographic Information System (GIS) or spatial database. A comprehensive written, hand-drawn and photographic record of features, complex feature sets, profiles and other relevant information will be created. Plans and
Geometria Ltd Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. - Page 51 stratigraphic profiles will be described, drawn and photographed and registered to surveyed points. The stratigraphic relationships of the different elements and evidence of disturbance to the deposits will be recorded. A mix of field forms, registers and notebooks will be used to record the work.
Maori archaeological features are not expected but may include: x Midden/faunal material. x Fire scoops and earth ovens. x Postholes from whare, cooking shelters, drying racks, palisades or other structures. x Pits/bin pits for storage x Koiwi Tangata/burials. x Artefacts including worked lithic, shell and faunal material,
Maori archaeological features will be excavated and sampled using standard techniques for the feature types encountered. Human remains and taonga tuturu as defined under the Protected Objects Act 1975 and including waterlogged wooden artefacts from wet areas are always a possibility and will be managed according to the specialised requirements of such finds.
European features and artefacts may be encountered and may include: x Foundations and postholes from buildings, outbuildings and other structures. x Wells and cisterns. x Drains and sumps. x Rubbish pits and privies. x Curtilage including paths, paving, postholes from fence lines and the remains of domestic gardens x Artefacts including bottles and bottle glass, crockery, ceramic sherds and stoneware, metal cutlery, tools and implements, miscellaneous domestic and farming items. x Historic midden/faunal material such as animal bones.
These features will be investigated using standard archaeological methods for historic sites.
Samples of building materials such as brick, wood, corrugated iron, ceramic drain pipes and concrete will be taken from features where they are encountered. Other materials such as soft furnishings like paint/paint chips, wallpaper and carpet may also be present. Sample locations will be recorded.
B.2.4 Analysis
Maori archaeological features and materials are possible. If such features are encountered they may require specialist analyses including lithics (e.g. stone artefacts), midden, radiocarbon dating, charcoal wood species identification, and osteoarchaeology (human remains) may be necessary for any excavated materials, and these may take some time to complete.
Maori archaeological materials analysis would be expected to include: x Up to four radiocarbon dates with samples selected from secure archaeological contexts or features as a first preference, to be undertaken by the University of Waikato Radiocarbon Dating Laboratory. The goal would be to date the earliest and most recent occupations of observable features, or other potentially significant features which might be encountered.
Geometria Ltd Page 52 – Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. x 10 litre midden samples from different archaeological contexts as necessary. x Charcoal wood species identification from midden, postholes, fire scoops and earth ovens as available. x Microfossil analysis as necessary, depending on finds. x Lithic or other artefactual analysis as necessary, depending on finds.
B.2.5 Expected outputs
Expected outputs of any investigation include: x Written descriptions of observed archaeological features. x GIS-based maps and plans. x Measured drawings including annotated plans, elevations, and details of archaeological features. x Photographic record. x Finds inventory and analysis. x Features inventory and analysis. x Photo inventory. x Radiocarbon dates for key features. x Analysis of midden and artefacts. x Preliminary and Final Reports on the results of the investigation. x Re-assessment of site significance of sites as necessary. x Identification of intact archaeological sites and features remaining on the property at the conclusion of works. x Preliminary report within 20 days of the conclusion of the investigation outlining initial findings including maps, photographs and descriptions of subsurface features and extents and their significance. x Final report within one year of the conclusion of the investigation containing the results of analysis.
B.3.0 Personnel
J. Carpenter supported by R. Gibb and D. McCurdy of Geometria will undertake any required archaeological monitoring and excavation.
B.4.0 Timeframe
TBA. The preliminary and final reports will be delivered within the timeframe specified by the relevant authority conditions.
B.5.0 Finds Management and Curation
Following the conclusions of fieldwork, excavated materials will be housed in the Geometria facilities in Auckland and Whangarei, in the first instance during the analysis and reporting stage. Some material may be transferred to sub-contractors for specialist analysis at their respective premises.
Any historic European artefacts will be offered to the landowner in the first instance following analysis. If the landowner does not wish to retain the materials they may be offered to the Kaeo Museum.
Maori artefacts and ecofacts (midden, charcoal, soil samples, unworked lithic material etc) deemed not to be Taonga Tuturu will be temporarily housed at the Geometria premises for recording and analysis and will then be offered to the Kaeo Museum in the
Geometria Ltd Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. - Page 53 first instance following analysis, or (in the case of ecofacts) be returned to the site if an appropriate area for disposal is available.
Koiwi Tangata (human remains) will be managed according to B.3.4 below and any particular tikanga as determined by the Tangata Whenua. Options may include re- interment at an appropriate urupa or local cemetery, or the remains may be left in place if development will not impact them, or taken for further analysis.
Maori artefacts which are identified as Taonga Tuturu will be managed according to B.3.5 below and any particular tikanga as determined by the Tangata Whenua as they are removed from the site, and the Ministry of Culture and Heritage notified per the requirements of the Protected Objects Taonga Tuturu Act 1975. Taonga will be temporarily housed at the Geometria premises for initial recording and analysis, and then stored at the Whangarei or Waitangi Museum while the Ministry of Culture and Heritage determines custody/ownership under the processes of the Taonga Tuturu Act.
Copies of any reports will be provided to Heritage New Zealand, NZTA, Te Rununga o Whaingaroa, Te Whaingaroa Maori Trust Board, Ngati Uru, the Far North District Council University of Auckland and Otago library systems, and the New Zealand Archaeological Association
B. 6.0 Key Contacts
Role Name Representa Primary Email tive Phone
Client NZTA TBA
Project Manager TBA TBA
Archaeologist Geometria Jonathan 021 893063 [email protected] Carpenter
Earthworks TBA contractor
Tangata Te Rununga o Whenua Whaingaroa,
Te Whaingaroa Maori Trust Board
Ngati Uru
Kaitiaki/Cultural TBA monitors
NZ Police Kaeo Police 09 4050147 Station
Geometria Ltd Page 54 – Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo.
Ministry of Nancy Watters 04 4994229 protected- Culture and [email protected] Heritage
Heritage New James Robinson 027 4284990 [email protected] Zealand
B.3.0 Operational Guidance
B.3.1 Stand Down Periods
Time delays should only occur if archaeological features, koiwi/human remains, or taonga are discovered during track construction. The length of the delay will depend on the nature and the extent of any finds and weather. Generally, the site Project Archaeologist will attempt to isolate the affected area and shall take reasonable steps to minimise any delays to construction. Most anticipated archaeological remains should require no more than 2-3 days to be cleared. Exceptional, complex or extensive remains may require additional time and periods of delay will be negotiated with the project manager and the contractors.
B.3.2 On-Call Procedures
All staff and contractors should be alert for archaeological sites/features in the course of their duties. These may take the form of unusual surface or subsurface features (holes, pits, other cuts and fills or unusual soil formations), natural features out of context (shell in piles or layers, water rolled or fire-cracked rocks, charcoal smears or concentrations) and items of human manufacture (glass and ceramics, metals and plastics, concrete and brick, worked timber).
In the event of the discovery of sites/features by anyone on-site the following protocol and any additional measures required by the Tangata Whenua will be followed:
1) All work within 10m of the discovery will cease until the Project Archaeologist advises it is appropriate to proceed, except in the case of human remains/koiwi tangata where work will cease within 20m of the discovery.
2) The Project Archaeologist and Tangata Whenua representative will be informed immediately if not present.
3) The Project Archaeologist will carry out archaeological investigation as quickly as possible according to conditions of the authority and the contents of this site instruction.
4) If human remains are discovered the Koiwi Discovery Protocol set out below in 5.3 will be followed.
5) If taonga are unearthed the protocol set out below in 5.4 will be followed.
In the event that significant archaeological features or artefacts are found in-situ, a stand down of up to three days in the immediate vicinity of the remains may be required to inform and receive a response from the HNZPT. HNZPT may require an archaeological
Geometria Ltd Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. - Page 55 investigation. Work may resume when the Project Archaeologist advises that the work is complete.
B.3.4 Koiwi Tangata/Human Remains Discovery
In the event of the discovery of koiwi tangata (human remains) the following protocol and any additional measures required by the Tangata Whenua will be followed:
1) All work on site will cease within 20m and the remains are not to be further disturbed in any way of the authority.
2) If it is not clear whether the bone is human, work in the immediate vicinity will cease until a reference collection and/or a specialist can be consulted and identification made.
3) The Project Archaeologist or Tangata Whenua representative will be notified if not present, along with HNZPT and Police.
4) The area containing the koiwi will be secured in such a manner as to protect the remains from further damage.
5) A site inspection by Tangata Whenua and appropriate statutory agencies (Police, District Health Board) will be arranged and they will determine whether the discovery is likely to be extensive and whether a thorough site investigation is required.
6) Koiwi will be handled in accordance with wishes and protocols requested by the Tangata Whenua. If requested, this may include the removal of the remains for analysis prior to reburial.
7) If the remains cannot be removed by Tangata Whenua or their authorised agent within the stand down period, the Project Manager may request the Project Archaeologist to remove the remains and deposit them at the mortuary or appropriate repository until other arrangements are made.
8) The Project Archaeologist will give clearance for work to proceed in consultation with the Tangata Whenua representative, once the remains are removed.
In the event that koiwi tangata are found, a stand down of up to three days may be required to confirm the identification, consult with affected parties, observe protocols and remove remains. Work may resume once the remains are removed from the site and protocols have been observed.
B.3.5 Taonga Tuturu Discovery Procedure
In the event of the discovery of taonga (treasures) such as carvings, stone adzes and greenstone objects, or other objects falling under the definition of “Taonga Tuturu” under the Protected Objects Act 1975, the following protocol and any additional measures required by the Tangata Whenua will be followed:
1) If necessary the area of the site containing the taonga will be secured in a way that protects the taonga as far as possible from further damage (or theft), consisted with the conditions of the Authority.
Geometria Ltd Page 56 – Archaeological Assessment of the Proposed SH10 Kaeo Bridge Project. State Highway 10, Kaeo. 2) The Project Archaeologist will inform the NZ HNZ and nominated Tangata Whenua representative so that appropriate actions (both archaeological and cultural) can be determined.
3) If the Project Archaeologist is not present he will be contacted immediately and informed of the find.
4) If the object is determined to be Taonga Tuturu under the Protected Objects Act 1975, the Project Archaeologist will notify the Ministry of Culture and Heritage within 28 days as required under the Act.
The Ministry for Culture and Heritage, in consultation with Tangata Whenua, will decide on custody or ownership of the Taonga.
5) If the taonga requires conservation treatment (stabilisation), the Ministry will be informed and will arrange and pay for this to be undertaken by the Department of Anthropology, University of Auckland. It would then be returned to the custodian.
In the event that taonga are found, a stand down of up to three days may be required to consult with affected parties and undertake archaeological investigation as required. Work may resume when the Project Archaeologist or HNZ advises the Project Manager that work is complete.
B.3.6 Dispute Resolution
Most disputes are a result of poor communication between the parties and can be avoided if sufficient details of the archaeological requirements and the various parties’ responsibilities are included in tender and work management documentation, and understood. Disputes usually arise on-site as a result of conflicting expectations for when/how fast areas of archaeological interest can be cleared by the archaeologist and when development may continue.
In the event of a dispute relating to archaeological issues a meeting between the authority holder’s representative, contractor(s) and Project Archaeologists should be convened as early as possible to resolve the dispute. If appropriate the Tangata Whenua representative should also participate. Stand down periods, which are the most common cause of dispute, are to allow for archaeological investigations are provided for in the HNZPT authority.
If the dispute cannot be resolved representatives of the HNZPT should be consulted to resolve the dispute as the HNZPT is responsible for resolving disputes relating to matters arising from authority conditions.
Geometria Ltd
Aurecon New Zealand Limited T +64 9 520 6019 Level 4, 139 Carlton Gore Road F +64 9 524 7815 Newmarket Auckland 1023 E [email protected] PO Box 9762 W aurecongroup.com Newmarket Auckland 1149 New Zealand
Memorandum
To Don Mackintosh From Stanley Howell Tom Hurdley, Claire Cunningham, Copy Reference 254914 Timothy Dee Date Pages 2019-07-17 (including this page) 2
Subject NESSoil Applicability to the Kaeo Bridge Realignment and Replacement
This technical memorandum summarises site contamination assessment considerations for the construction works associated with the Kaeo Bridge Project. A draft Preliminary Site Investigation (PSI) was prepared by Aurecon (254914-3000-REP-NN-0008) in 2017 at the concept design phase of the project. Since 2017, the bridge alignment has been revised to reflect the planned approximate construction footprint indicated in the attached drawing, 254914- 3000-DRG-KF-0001 (‘the site’). The draft PSI identified activities or industries described in the October 2011 edition of the MfE Hazardous Activities and Industries List (HAIL) in the vicinity of the site. None of the HAIL sites identified in the draft PSI are within the proposed site (ref. drawing 254914-3000-DRG-KF-0001).
Resource Management (National Environmental Standard for Assessing and Managing Contaminants in Soil to Protect Human Health) Regulations 2011 The MfE Resource Management (National Environmental Standard for Assessing and Managing
Contaminants in Soil to Protect Human ealth) Regulations 2011 (NESSoil) apply ‘when a person wants to do an activity … on a piece of land described in subclause (7) or (8) [of Regulation 5 of the NESSoil]’. Subclause (8) concerns production land; the site is not considered production land. Therefore, for the
NESSoil to apply to the site, the site must be considered a ‘piece of land’ under Regulation 5(7). Table 1 summarises these criteria and our assessment of these criteria, based on the findings of the draft PSI.
Table 1 Land covered by the NES – Regulation 5(7)
Criteria Assessment The piece of land is a piece of land that is described by 1 of the following: (a) An activity of industry described in the An activity of industry described in the HAIL has not, HAIL is being undertaken on it; is not or more than likely to not have been identified within the proposed disturbance footprint. (b) An activity of industry described in the HAIL has been undertaken on it; Not a piece of land.
(c) It is more likely than not that an activity or industry described in the HAIL is being or has been undertaken on it.
Based on the findings of the draft PSI, a HAIL activity is not being undertaken, has not been undertaken, and it is not more likely than not that a HAIL activity is or was undertaken on it.
Therefore, the site is not a ‘piece of land’, and the NESSoil should not be considered further for the Kaeo bridge realignment and replacement project. The following Planning documents have also been considered in this assessment:
Project 254914 File App G Contamination Assessment Memo July 2019.docx 2019-07-17 Revision 0 Page 1
Proposed Regional Plan for Northland
Regional Water and Soil Plan for Northland
Regional Coastal Plan for Northland
Far North District Plan Rules set out in these plans are generally aligned with but are not more restrictive then the standards set by the NESSoil for managing contaminated land. The NESSoil prevails over local plans in relation to the discovery of contaminated land or undertaking activities that have potential to contaminate land.
Therefore, if the site is not considered a ‘piece of land’ under the NESSoil, these local plans are unlikely to require additional resource consents beyond what is required for a permitted activity.
Conclusion Based on the planned approximate construction footprint and the findings of the draft PSI, site works are unlikely to require a resource consent under the NESSoil. It is noted the former restaurant immediately south of the site was identified in the PSI as HAIL activity E1, where asbestos containing materials in a degraded condition may be present. Should the structures associated with these buildings require alteration or demolition, or earthworks be required in the vicinity of these buildings, pre-demolition asbestos building survey and detailed site investigation works should be undertaken to better understand potential human health and environmental risk associated with historical site activities. The outcomes of these investigations may trigger requirements for consideration of the NESSoil.
Project File App G Contamination Assessment Memo July 2019.docx Revision 0 Page 2
SH10 Kaeo Bridge Project
Assessment of Coastal Processes Effects
Prepared for Aurecon NZ Ltd and NZTA
December 2019
Prepared by: Rob Bell
For any information regarding this report please contact: Rob Bell Principal Scientist Coastal and Estuarine Physical Processes +64-7-856 1742 [email protected]
National Institute of Water & Atmospheric Research Ltd PO Box 11115 Hamilton 3251
Phone +64 7 856 7026
NIWA CLIENT REPORT No: 2019366HN Report date: December 2019 NIWA Project: AUR18201
Quality Assurance Statement
Reviewed by: Dr M. Allis
Formatting checked by: Alison Bartley
Approved for release by: Scott Stephens
This report should be referenced as: Bell, R.G. (2018) SH10 Kaeo Bridge Project: Assessment of Coastal Processes Effects. NIWA Client Report 20180366HN, prepared for Aurecon NZ Ltd and the NZ Transport Agency:
© All rights reserved. This publication may not be reproduced or copied in any form without the permission of the copyright owner(s). Such permission is only to be given in accordance with the terms of the client’s contract with NIWA. This copyright extends to all forms of copying and any storage of material in any kind of information retrieval system.
Whilst NIWA has used all reasonable endeavours to ensure that the information contained in this document is accurate, NIWA does not give any express or implied warranty as to the completeness of the information contained herein, or that it will be suitable for any purpose(s) other than those specifically contemplated during the Project or agreed by NIWA and the Client.
Contents
Executive summary ...... 6
1 Description of the Project ...... 8 1.1 Project Background ...... 8 1.2 Purpose of this Report ...... 10
2 Assessment Methodology ...... 13 2.1 Desktop ...... 14 2.2 Site survey ...... 14 2.3 Assessment criteria, national policies and regional plans ...... 19
3 Description of the existing environment ...... 27 3.1 Estuarine/river environment ...... 27 3.2 Tides and storm tides ...... 31 3.3 Hydrodynamics ...... 39 3.4 Tsunami ...... 40 3.5 Geology and river-bed sediments ...... 41 3.6 Geomorphic features ...... 43 3.7 Existing SH10 bridge ...... 45
4 Assessment of effects and mitigation ...... 46 4.1 Operational effects ...... 46 4.2 Temporary effects (construction and de-construction) ...... 52 4.3 Risk screening assessment ...... 56 4.4 Assessment against regulatory standards or technical criteria/guidelines ...... 59
5 Summary and conclusions ...... 60 5.1 Summary of effects and mitigation measures ...... 60 5.2 Suggested coastal monitoring conditions ...... 61
6 References ...... 63
Tables Table 1-1: Project drawing references. 10 Table 2-1: Decadal increments for projections of SLR (metres above 1986–2005 baseline) for the wider-NZ region for four future scenarios from Figure 2-8. 26 Table 3-1: The dominant tidal constituents extracted from 2-year periods of water level measurements at NRC's Harbour and Whangaroa Rd gauge sites. 34 Table 3-2: Present-day coastal storm-tide 1% and 0.1% AEP elevations (m; OTP-64) in Whangaroa Harbour and Kaeo tidal creek based on recent historic water level data (KWH, WGFC). 37 Table 3-3: Increase in coastal water levels in the Kaeo creek section from relative SLR for 2070 (50 yrs) and 2120 (100 yrs). 38 Table 4-1: Risk screening assessment for potential environmental effects on coastal physical processes from the 100-year operational phase of the Project. 57 Table 4-2: Risk screening assessment for potential environmental effects on coastal physical processes from the construction phase of the Project. 58
Figures Figure 1-1: Project extent and proposed road layout for the SH10 re-alignment (yellow) and new bridge over the Kaeo River in relation to the existing bridge and adjacent stopbanks (at the head of the Whangaroa Harbour). 9 Figure 2-1: Geographic context for the tidal section of Kaeo River, annotated with sampling sites (A-C), the Project area (yellow ellipse) and the NRC tidal gauge site (KWR). 15 Figure 2-2: Channel edge on east bank of Kaeo River at site A – sediment sample and salinity measurements undertaken. 16 Figure 2-3: View looking west across channel at site B (left) and (right) channel edge on east bank of Kaeo River. 16 Figure 2-4: Looking upstream on east bank of Kaeo River at site C - with large coarser-grain mid-channel bar – with muddy silts in exposed bank evident on opposite side. 17 Figure 2-5: Classification of coastal management units for the Kaeo River and upper Whangaroa Harbour. 18 Figure 2-6: Indicative present CMA boundary and cross-river CMA boundary at the existing SH10 bridge, with designated natural character areas. 21 Figure 2-7: Marine Management Area Units - upper Whangaroa Harbour and Kaeo River. 22 Figure 2-8: Four scenarios of New Zealand-wide regional SLR projections for use in New Zealand, with extensions to 2150. 25 Figure 3-1: Kaeo River catchment and Whangaroa Harbour, with locations of the NRC water-level gauge sites. 27 Figure 3-2: River flooding over SH10 during ex TC Cook (13 April 2017) looking west from the existing Kaeo Bridge. 28 Figure 3-3: Whangaroa Harbour features and depths and intertidal flats (relative to Chart Datum). 29
Figure 3-4: View of western bank - coastal river section of Kaeo River at site B. 29 Figure 3-5: Kaeo River cross-sections 1–3 upstream of the existing bridge, looking seawards into the page (top panel) and location of transects (bottom panel). 30 Figure 3-6: Water levels in Whangaroa Harbour (blue) and at Kaeo at Whangaroa Rd (green) for the period 1-Jan to 30-Apr-2011. 32 Figure 3-7: Water levels at 3 gauges for period 15-Jan to 2-Feb-2011, showing influence of storm-tides and Kaeo River floods. 32 Figure 3-8: High-tide exceedance distribution at the Whangaroa Harbour Wharf by the Game Fishing Club relative to OTP-64 (excludes any weather or climate effects). 35 Figure 3-9: Coastal Flood Hazard Zones in Natural Hazards GIS viewer based on storm-tide levels from T + T (2016). 39 Figure 3-10: NRC Tsunami Evacuation Zone map. Orange areas could be impacted by a 1.5 m tsunami wave height, Yellow Zone is for a much lower probability tsunami scenario. 41 Figure 3-11: Primary geology units in the lower Kaeo River catchment – with Project area highlighted by the yellow ellipse. 42 Figure 3-12: Grain-size histogram distribution for sediment sample at site A (Section 2.2.1). Blue curve and values on right axis are the cumulative distribution. 43 Figure 3-13: Lateral intertidal shoal just upstream from the existing SH10 Bridge looking from site B. 44 Figure 3-14: Mid-channel bar looking downstream from site C in the coastal river section. 44 Figure 3-15: Existing one-lane SH10 bridge over the Kaeo River - viewed from the east bank looking upstream on the ebb tide around 1.5 hours after local high tide. 45 Figure 4-1: General arrangement for the new 2-lane bridge for SH10 over the Kaeo River with plan view (top panel) and elevation looking seaward (bottom panel). 47 Figure 4-2: Stormwater discharge points (blue ellipses). New stopbank (red line) on the left (western bank). The present stopbank (dotted line) is adjacent to the vegetation along the channel bank. 49 Figure 4-3: General layout of temporary construction platforms, haul road and lay-down area (top panel) and side elevation looking downstream of relativity of staging to the new bridge substructure (bottom panel). 52
Executive summary The New Zealand Transport Agency (NZTA) is currently planning a range of improvements centred around specific one-lane bridges in Northland. Aurecon NZ Ltd have been contracted by Fulton Hogan to provide engineering design services and secure resource consents for the various projects in the Northland Bridges programme.
The Project is the upgrade of the section of the State Highway 10 (SH10) north of Kaeo, primarily the replacement of the one-lane bridge crossing the Kaeo River and associated re-alignment of road covering both sides of a new 110-metre two-lane bridge, approximately 45 metres further upstream from the existing bridge.
The rationale for the Project is to improve traffic flows (dual-lane bridge), road safety (eliminating the perpendicular bend and adjacent Whangaroa Road junction) and to reduce the upstream backwater effect during river flooding through lengthening the new bridge and waterway underneath it.
This AEE technical report assesses the effects that the Project has with respect to coastal physical processes in the coastal environment and assumes the relevant coastal river section is in the Coastal Marine Area (CMA) even though currently the CMA boundary is legally defined at the existing bridge site. (In any case, the CMA will migrate upstream with ongoing sea-level rise).
Both temporary effects during construction and those effects that may accrue over the 100-year operational life of the Project were considered separately. No reclamations or impoundments, such as causeways or sheet-piling are planned in the CMA or the coastal river section.
In assessing coastal effects (excluding marine ecology, ecological effects of mangrove removal, landscape/natural character, stormwater water quality and river flood hydrology effects), the main elements of the Project that were considered was the new bridge (mainly the substructure including piers in), the benefit of widening the floodplain on the left (western) bank to provide more room for river floods under the new bridge (requiring a new re-curved stopbank) and the temporary staging platforms, which will partially require temporary occupation of the CMA.
Summary of effects on coastal physical processes and mitigation measures With respect to coastal physical processes, the Project activities and permanent works (as per the specimen design) will only have minor or negligible effects or risks, provided the suggested mitigation measures for design features or construction are followed (Section 4, Table 4-1 and Table 4-2). The latter could be incorporated into the Construction Environmental Management Plan (CEMP), given the final detailed design and as-built methodology will depend on the selected contractor.
There are also some benefits arising from the Project, particularly the wider waterway and additional floodplain width under the new bridge, which will reduce flood elevations. Also, no piers or piles will be present in the deepest section of the channel, which means a more freely flowing river and unimpeded recreational navigation.
The only potential long-term issue is the soffit level in the specimen design of the new bridge, which on average is at a similar height as the present single-lane bridge. This will lead to a moderate risk on the bridge (and ensuing flood effects) towards the end of the 100-year design life from high storm- tide levels alone (with normal river flows) riding on the back of an upper-range sea-level rise
6 SH10 Kaeo Bridge Project
projection (representing continuing high global carbon emissions). For this situation, the minimum freeboard allowance of 0.6 m recommended in the NZTA (2018) Bridge Manual, would not be met (or apply) during high storm-tide events for the top two of four sea-level scenarios recommended in the Ministry for the Environment coastal guidance (MfE, 2017).
The effects of river floods, which explored sensitivity to sea-level rise and increased rainfall, are considered separately in the Stormwater Hydraulic Modelling Technical Report (Aurecon, 2019). These modelling results indicate that river floods dominate the combined water level at the proposed new bridge, with the present-day 1% AEP1 flood water level reaching 3.7 m Reduced Level (David Hughes, Aurecon, pers. comm.), compared with the new bridge soffit levels that slope from 3.04 m (western abutment) up to 3.65 m (eastern abutment). This means a large present-day river flood acting alone, will produce a higher water level than a future 1% AEP storm-tide (+ sea-level rise), which would reach 3.0 m Reduced Level. From experience modelling such large flood events in coastal rivers, where the channel is confined, the larger river floods will mostly wash-out any coinciding storm-tide effect, leaving the river flood to dominate the total water level at the Project site. However, rising sea level will increase the baseline mean tide level in the coastal river, which could lead to a combined event of a moderate river flood and high storm tide that may also reach close to the proposed bridge soffit (although not modelled). In any case, a major river flood presents the highest risk to the performance and serviceability of the new bridge.
Some adaptive design features could be considered in the final detailed bridge design to provide future flexibility if the bridge deck is required to be lifted, if SLR effects on both storm-tides and river floods reduces the level of service towards the latter part of the operational life of the new bridge.
Overall, if the proposed mitigation measures for the construction and de-construction phases are included, the effects of the temporary construction activities on physical coastal and estuarine processes would be minor or negligible. The environmental risks are best managed adaptively via a CEMP for all construction or de-construction areas.
Some monitoring conditions are suggested in relation to coastal physical processes, mostly for information, check surveys and record keeping (Section 5.2).
1 AEP = annual exceedance probability (the chance an event will be reached or exceeded in any year)
SH10 Kaeo Bridge Project 7
1 Description of the Project
1.1 Project Background The New Zealand Transport Agency (NZTA) is currently planning or undertaking a range of improvements centred around specific one-lane bridges in the Northland Region. Aurecon NZ Ltd have been contracted by Fulton Hogan to provide engineering design services and secure resource consents for the various projects in the Northland Bridges programme.
This assessment of coastal physical processes applies to the section of the State Highway 10 (SH10) north of Kaeo, primarily the replacement of the one-lane bridge crossing the Kaeo River and associated re-alignment of road covering both sides of a new 110-metre two-lane bridge approximately 45 metres further upstream (Figure 1-1).
The rationale is to improve traffic flows, road safety (eliminating the perpendicular bend and adjacent road junction) and to reduce the upstream backwater effect during river flooding through lengthening the bridge and increasing the flow capacity of waterway underneath it. The Kaeo Bridge Project (the Project) covers an approximately 550 m section of SH10 plus the new linking intersection to join with Whangaroa Rd (Figure 1-1).
We understand that the key elements of the Project are:
Providing increased traffic capacity on SH10 centred on the Kaeo Bridge as follows:
í New realignment of SH10, appropriate for an open road speed limit. Starts 220 m back from the perpendicular bend onto the existing bridge (north of Kaeo), with a new bridge across the Kaeo River, to re-join the existing SH10 carriageway 280 m west of the existing one-lane bridge.
í New two-lane bridge (~110 m long) with sufficient height to pass low-probability river floods and storm-tides and include an allowance for sea-level rise in the next 100 years. The lowest soffit2 level of the proposed bridge design is 3.04 m OTP-64 (RL)3 at the left bank (western) abutment and 3.65 m RL at the right-bank abutment (David Hughes, Aurecon, pers. comm.). This compares with 3.4 m RL for the existing bridge soffit (Aurecon, 2019).
Providing improved safety on SH10 by moving the existing intersection, of Whangaroa Rd with SH10, further south to allow a new higher standard intersection with SH10 to be constructed using a roundabout.
Re-configuration of stopbanks on the left bank (western side) to curve in further on land (tying in at each end with the existing flood stopbank – see Figure 4-2) and a longer bridge in the Project area to widen the waterway under the bridge to improve conveyancing of river floodwaters.
De-commissioning the existing 55-m one-lane bridge over the Kaeo River and removal of the existing right-bank bridge abutment (east side) and all the left-bank (western)
2 The soffit is the level of the bottom (underside) of the girders supporting the bridge decking, which is the highest level for unimpeded river flow under the bridge. 3 Reduced Level (RL) is equivalent to One Tree Point-1964 vertical datum (OTP-64) – which defined in section 3.2.
8 SH10 Kaeo Bridge Project
embankment (Figure 1-1), which will reduce the local hydraulic constriction in flood flows. Note: while the existing SH10 western embankment will be removed (which lies on the adjacent flood plain), the existing stopbank seaward of the present abutment will not be modified, other than tying into the new curved section under the new bridge.
Figure 1-1: Project extent and proposed road layout for the SH10 re-alignment (yellow) and new bridge over the Kaeo River in relation to the existing bridge and adjacent stopbanks (at the head of the Whangaroa Harbour). Source: adapted from Drawing DRG-WD-1452-A, Stormwater Layout Plan, Aurecon NZ Ltd (8 Aug 2019).
A full description of the Project, including its components and construction, is contained in the Assessment of Environmental Effects (AEE) for the Project.
1.1.1 Design and construction Conceptual drawings for the bridges have been developed by Aurecon NZ Ltd to show the bridge span arrangement, section depths, overall height and clearances, and structural form of the bridge. In addition, the construction methodology has been developed to show the major temporary staging components. The key project drawings relevant to coastal processes assessment are shown on drawings indexed by Aurecon NZ Ltd and dated 8-Aug-2019 (Table 1-1).
SH10 Kaeo Bridge Project 9
Table 1-1: Project drawing references. Source: Aurecon NZ Ltd
Drawing index Description
BB-1401- B Bridge Plan and Elevation
BB-1406-A Bridge Construction Staging
RR-0402-0404, RR-0101, 0102, 0201 Kaeo SH10 Plan and Longitudinal sections (7 Sheets)
WD-1401, 1451-1452 Kaeo stormwater and catchment plans (3 sheets)
These form the specimen design for the consenting process, but detailed design and exact details of the construction method cannot be confirmed until the construction process is tendered but are expected to remain in general accordance with the construction methodology staging (e.g., Drawings BB-1406-A). The proposed construction methodology outlines a temporary staging platform for bridge construction on the downstream (north) side to construct the three piers and supporting pile. Once the new bridge is completed, a narrower staging platform will be set-up on the upstream side of the existing bridge to provide pedestrian access for construction personnel.
The critical construction phase, in terms of the effects of the project on coastal processes and water quality, will be removing the current flood stopbanks adjacent on the true left-bank Kaeo River upstream of the existing bridge (up to 135 m upstream and under the new bridge) to re-establish designed stopbanks further back from the channel edge to widen the floodplain in the vicinity of the new bridge (Drawing: DRG-WD-1452-A).
1.2 Purpose of this Report This report is one of a suite of technical reports that has been prepared as appendices to the Assessment of Environmental Effects Report (AEE) for the Project.
The particular focus of this report is an assessment of the effects of the Project with respect to physical processes in the coastal and river/estuarine environment, both temporary effects during construction and those effects that may accrue over the long-term operational life. This also includes effects from removal of a section existing river stopbank under the new bridge and de-construction of the present one-lane bridge and adjacent abutments. Effects are also assessed in line with requirements of the Resource Management Act (RMA), the NZ Coastal Policy Statement 2010, referred to as “NZCPS” (DoC, 2010), the operative (2004) Regional Coastal Plan for Northland (Northland Regional Council) and the Proposed Regional Plan (Northland) – July 2019 Appeals Version.4
In assessing coastal physical effects, the main elements of the Project that were considered are the:
A. effects during the operational lifetime e.g.,
í bridge (and support structures, such as piers/piles)
í the adjoining road embankments
4 https://www.nrc.govt.nz/newregionalplan
10 SH10 Kaeo Bridge Project
í realigned stopbank (left bank) that will be established to also enhance floodplain management.
B. during the construction phase, the effects of:
í temporary staging platforms on piles
í disturbances within the river channel
í removal of existing ~140-metre stopbank section (left bank) and reconfiguration of a new curved 165-metre section of flood stopbank
í de-construction of the existing one-lane bridge and adjacent abutment embankments.
The scope of this coastal processes report includes consideration and assessment of the effects of the Project on the existing coastal environment, mainly on:
tidal processes (e.g., currents, flushing, impedance of flows)
natural flood hazards (e.g., conveyancing of combined storm-tide and river flood flows and bridge deck levels, exposure to tsunami inundation5)
any additional sedimentation and scour of the seabed, or general geomorphic change
turbidity from seabed or riverbed disturbances (e.g., pile driving, excavation, removal of riverbank stopbanks, de-construction of the existing bridge and adjoining abutments and turbid de-watering discharges), and
effects of climate change, particularly sea-level rise (SLR).
These processes need to be factored into the overall design of the current Project and any future staging in order satisfy the requirement under the RMA to consider the effects of climate change, and over a period of at least 100 years as stipulated in the NZCPS (Policy 24).
Specific matters not considered in this Report are: a) effects of operational stormwater discharges on the receiving environment; and b) physical effects of mangrove removal. This Report also does not cover erosion and sediment control measures that will be part of the Construction Environmental Management Plan (CEMP).
The existing SH10 bridge will be dis-established and demolished, so consideration of the environmental effects of its removal is also required.
Relevant requirements from NZTA Appendices to Principal’s Requirements: Northland Bridges (9 September 2014) project that relate to the coastal processes’ assessment are (with some subsequent updates noted):
A3.2.1:
í The NZTA Requirements stipulated the use of the 2008 Ministry for the Environment coastal guidance. [Update: For this Report, the more recent 2017
5 Note: tsunami was not included in the design of the Project (NZTA decision), so only the potential exposure to tsunami is provided.
SH10 Kaeo Bridge Project 11
update of the Guidance, Coastal Hazards and Climate Change (MfE, 2017) will be used instead.]
A3.3.4 (generally used for the Northland Bridges programme):
í Waterways under the bridge crossings must be able to cater for the 1% Annual Exceedance Probability (AEP) flood event6 and must account for a rise in mean high water spring (MHWS) in 2100 from sea-level rise.
í Bridge crossings must be wide enough as to not funnel flows to an extent resulting in long term scouring downstream and sedimentation upstream (although in a tidal situation can be in both directions).
í Crossing must not negatively impact on fish passage, maintaining the low tide/low flow channel and during higher flows.
A.3.5.10.3:
í A numerical hydraulic model was developed for the Kaeo project (see report Aurecon, 2019). The original option of flood diversion works as one of the proposed mitigation strategies was not pursued.
A5.4.1:
í The design life of all bridges and related structures shall be 100 years.
A5.4.2:
í Kaeo Bridge shall meet the requirements of Tables 2.1, 2.2 and 2.3 of the NZTA Bridge Manual (NZTA, 2016) for an IL 3 structure.
A5.8:
í Tsunami effects shall be considered for Taipa Bridge and Kaeo in accordance with section 5.6 (now section 5.8 in 2018 3rd edition) of the NZTA Bridge Manual (which is now NZTA, 2018).[Update: NZTA have decided not to proceed with a full design of the new bridge to withstand damage to tsunami events propagating up through Whangaroa Harbour].
A5.9.2 c): Kaeo Bridge
í Vertical clearances to be confirmed in relation to the design flood level relative to the bridge superstructure soffit, which requires a 1% AEP flood level be used for assessing the Serviceability Limit State 2 (SLS 2).
H3 – types of resource consents required for Kaeo Bridge – see AEE Report.
6 Equivalent to a present-day 100-year average reccurrence interval (ARI) event
12 SH10 Kaeo Bridge Project
2 Assessment Methodology This Technical Report describes both the existing river/estuarine environment of the area around the new and existing bridges and the associated highway realignment works, focusing on coastal physical processes and the potential effects on these processes that may arise from construction and long- term operation of the new two-lane bridge and from de-construction of the existing SH10 bridge and abutments at the intersection of Whangaroa Road.
There are no quantitative assessment criteria for assessing the degree of effects on hydrodynamic and sedimentation processes or estuarine geomorphology, so this assessment relies on expert appraisal (using a coastal expert and reviewer), supported by desktop research, a walk-over field survey and sampling exercise and water-level data from Northland Regional Council.
The investigations into assessment of effects on coastal physical processes of the Kaeo Bridge replacement and the existing bridge de-construction were undertaken through a mix of:
1. Desk-top reviews of previous reports/papers (e.g., Tonkin + Taylor coastal hazard report (T&T 2016), Aurecon (2019) flood hazard report, Ahsan & Howse, 2011), field data (e.g., Northland Regional Council water level gauges) and aerial photography.
2. Field investigation limited to 1-day sediment and salinity sampling.
3. Assessment of potential effects of the Project based on expert appraisal, informed by the above analyses and information, including the analogue of long-term morphological change resulting from the present SH10 bridge across the Kaeo River and embankments.
4. Assessment aligned with NZTA Principal’s requirements, NZTA Bridge Manual (NZTA, 2016), the Coastal effects assessment guideline for transportation infrastructure (NZTA, 2017), the Coastal Guidance (MfE, 2017) and the implementation guidance for the hazard policies in the NZCPS (DoC, 2017).
In the coastal-river reach of the Kaeo River and Whangaroa Harbour, the coastal waters are designated as a Marine 2 (Conservation) Management Area in the Regional Coastal Plan for Northland or RCP-N (operative since 2004). 7 The RCP-N states that Marine 2 (Conservation) does not preclude the provision for appropriate new uses and development but the objective is to manage these remaining areas in such a way as to conserve and, where practicable, enhance ecological, cultural and amenity values. The southern waters and intertidal flats of Whangaroa Harbour (adjacent to SH10 further west from the bridge) are also to be designated as an area of Outstanding Natural Character in the proposed Northland Regional Plan (PRP) – September 2017 (NRC, 2017).
Relevant assessment criteria for discretionary activities related to coastal physical processes in the RCP-N cover (as examples):
Cumulative effects on the coastal environment.
Preserving natural character e.g., morphology, natural sediment substrate, and natural water and sediment movement patterns.
7 http://www.nrc.govt.nz/resources/?url=/Resource-Library-Summary/Plans-and-Policies/Regional-plans/Regional-Coastal-Plan/
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Extent to which structures and embankments can cause erosion and/or siltation.
Extent to which provision has been made in the design of the proposed embankments to minimise restrictions on natural movement of coastal water or floodwaters, including provision of culverts, floodgates, or bridges.
Effect of sea-level rise.
2.1 Desktop The desktop analysis for the existing environment included a review of the following information:
Aerial imagery (verticals) spanning the previous decade. Imagery dates: 2003 (LINZ Data Service), 12-Jun-2004, 7-May-2007, 12-Oct-2009, 5-Sep-2013, 12-Jan-2016 and 7- Oct-2016 (Google Earth). The latter 3 dates were recorded when the tide was higher.
Project drawings (see Table 1-1).
Relevant maps and charts:
í Hydrographic chart NZ5114 of Whangaroa Harbour (LINZ 2017).
í Whangarei QMAP Geologic Map (Edbrooke and Brook, 2009).
í Topographic maps (1:50,000 series).
Operative Regional Coastal Plan for Northland, which covers the region’s “coastal marine area” or CMA, which straddles the area of marine and coastal waters from 12 nautical miles offshore through to the mean high-water spring (MHWS) mark, and someway up river mouths.
Proposed Regional Plan (Northland) -September 2017 and July 2019 Decisions/Appeals Version (GIS Map Viewer).
2.2 Site survey A field reconnaissance survey of the bridge site was undertaken by the Author on 18 December 2017, making observations during part of the ebb (outgoing) tidal cycle. The three sites (A–C), shown in Figure 2-1, were examined from the east (right) bank covering the river reach from downstream of the existing bridge to well upstream of the new bridge. However, in the few areas where safe vehicle parking was available, the soft steep banks prevented walking access to the main tidal channel other than at site A. However, water and salinity sampling were possible and access to the channel edge at site A enabled a surficial sediment sample to be collected (Figure 2-2).
The purpose of the site survey was to become familiar with the general site, undertake sufficient measurements to establish the coastal hydrodynamic characteristics, background turbidity levels, riverbank sediment characteristics and identify important geomorphic features for the assessment.
The field survey of 18 December 2017 commenced at site A at 1035 hrs (NZDT) – 1.5 hours after local high water and ended at site C at 0140 hrs around 2.5 hours before local low tide. The 1.5 m tide range that day was average between a spring and neap tide.
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Figure 2-1: Geographic context for the tidal section of Kaeo River, annotated with sampling sites (A-C), the Project area (yellow ellipse) and the NRC tidal gauge site (KWR). Background image: Northland Rural Aerial Photography (1.25 m), 2003, LINZ Data Service.
2.2.1 Surficial sediments Surficial sediment at the water’s edge (east bank) at mid-tide (Figure 2-2) had the following characteristics:
10-percentile: 4.3 μm
Median: 31 μm
90-percentile: 54 μm
In terms of Wentworth sediment size classes, size ranges by volume in the sample were: 9% clay; 10% very fine silt; 11% fine silt; 20% medium silt; and 50% coarse silt (Figure 3-12). Therefore, the shoreline sediments are classified as a muddy silt (refer to particle size distribution graph - Figure 3-12). These sediments on the channel edge are more likely to be those disturbed during construction of the river stopbanks than sediments in the main sub-tidal channel.
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Sediments on the channel edge at site B (Figure 2-1) – halfway between the new and existing bridges – also visually looked to be similar muddy silts (Figure 2-3). Sediments at site C were coarser silts with some sands, and a coarser sand/gravel veneer on the mid-channel banks (Figure 2-4).
Figure 2-2: Channel edge on east bank of Kaeo River at site A – sediment sample and salinity measurements undertaken. Photograph taken at 1100 hrs NZDT, 18 Dec 2017. [Credit: R. Bell, NIWA]
Figure 2-3: View looking west across channel at site B (left) and (right) channel edge on east bank of Kaeo River. Photograph taken at 1252 hrs NZDT, 18 Dec 2017. [Credit: R Bell, NIWA].
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Figure 2-4: Looking upstream on east bank of Kaeo River at site C - with large coarser-grain mid-channel bar – with muddy silts in exposed bank evident on opposite side. Photograph taken at 0131 hrs NZDT, 18 Dec 2017 [Credit: R Bell, NIWA].
2.2.2 Salinity and water temperature A YSI hand-held salinity meter was used to measure salinity and temperature during the mid to late ebb tide at the three sites.
Salinity measurements are in units of part per thousand (ppt) and measure the salt concentration. For comparison, open ocean salinity is generally around 35 ppt and freshwater around 0–0.5 ppt, with intervening values classed as estuarine or brackish waters. The sensor was deployed in the channel-edge waters on the east bank.
At site A (just downstream of the existing bridge) the surface water salinity decreased from 15.7 ppt at 1.5 hours after local high water as the tide flow ebbed, to 13–13.5 ppt at 2 hours after high water. The salinity lower in the water column would be higher but was unable to be measured off the existing bridge (due to safety reasons). Surface water temperatures on the channel edge were around 22.9–23°C.
Further upstream and later at site B, the surface salinity varied from 12.5–13 ppt (2.3 hrs after local high water) to 9.7–9.9 ppt (3 hours after high water) as the freshwater flow from the river becomes more dominant approaching low tide. Surface water temperatures were similar to site A.
Further upstream at site C, the surface salinity was down to 2.2–2.6 ppt at 4.5 hours after high water (or 2.6 hours before local low tide). In the latter part of the ebb tide, the waters passing this site are essentially freshwater. Surface water temperatures were slightly higher at 23.6–24°C, as expected for a river inflow to an estuary in summer.
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These salinity measurements align with the classification of sections of Kaeo River in the Proposed Regional Plan (NRC, 2017; 2019) of a tidal creek, downstream of the existing bridge (e.g., site A), and a coastal river, between Dip Road bend (Figure 2-5) and the existing bridge (encompassing sites B and C).
Figure 2-5: Classification of coastal management units for the Kaeo River and upper Whangaroa Harbour. [Source: Proposed Regional Plan - Sep 2017 maps, NRC GIS server – no change with the Decisions Version of the Plan – May 2019].
2.2.3 Turbidity and visual clarity Two water samples were gathered at the water’s edge ate sites A and B and analysed in the NIWA Water Quality Laboratory (Hamilton) for turbidity (using a turbidimeter calibrated against Formazin standards).
At site A, at 1.75 hours after local high water, the turbidity was 4.8 NTU, with a visual clarity (using a black rod vertically suspended) of 0.65–0.7 m. Two hours later at site B upstream, the turbidity had increased to 12.4 NTU. The visual clarity was around 0.6 m (Figure 2-3).
2.2.4 Flow velocities Limited manual observations of surface tidal flows (average tide) from the east bank during the survey, timing travel distance using a 1 m rod, showed that moderate tidal velocities of 0.26–0.3 m/s occurred at the channel edge at peak ebb tide at site A on an average tide. The main sub-tidal channel occupies the eastern half of the waterway near this bank, with flow velocities estimated to be up to 0.35 m/s in mid channel based on estimates of surface debris movement.
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Later in the ebb tide (3.25 hours after local high water) at site B, the surface tidal velocities had decreased to 0.14–0.17 m/s. River flows were low following a relatively dry December period.
2.3 Assessment criteria, national policies and regional plans See the AEE Report for full description and consideration of the relevant criteria, plans and policies. The key relevant plans and policies for coastal physical processes are summarised below.
2.3.1 Resource Management Act (1991) requirements The key relevant sections of the RMA in relation to coastal physical processes are:
Part II, Section 6(h) — In achieving the purpose of the Act, “… the management of significant risks from natural hazards”.
Part II, Section 7(i) — In achieving the purpose of the Act, “… shall have particular regard to … the effects of climate change”.
Sections 5(2)(c) and 17— A duty to avoid, remedy, or mitigate any adverse effect on the environment arising from an activity ….
2.3.2 NZ Coastal Policy Statement (2010) The key relevant Objectives and Policies in the NZCPS which relate to either assessment of effects on coastal physical processes or management of the effects of coastal hazards and climate change on the Project are:
Objective 1— Safeguard the integrity, form, functioning and resilience of the coastal environment …. By maintaining or enhancing natural biological and physical processes in the coastal environment and recognising their dynamic, complex and interdependent nature …
Policy 1 (Extent and characteristics of the coastal environment). Sub-section (2): Recognise that the coastal environment includes: …
í (c) areas where coastal processes, influences or qualities are significant, including coastal lakes, lagoons, tidal estuaries, saltmarshes, coastal wetlands, and the margins of these
í (d) areas at risk from coastal hazards
í (i) physical resources and built facilities, including infrastructure, that have modified the coastal environment.
Policy 10 (Reclamation and de-reclamation). Sub-section (1) Avoid reclamation … unless there are no practicable alternatives; and the reclamation will provide regional or national benefit. Sub-section (2) where reclamation is considered a suitable use … have particular regard to … the effects of climate change over 100 years, the use of appropriate materials (avoiding contaminated materials) …, the ability to remedy or mitigate adverse effects … , the ability to avoid consequential erosion and accretion. Sub-section (3) consider the extent to which the reclamation and intended purpose would provide for efficient operation of infrastructure …
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Policy 22 (Sedimentation)— Requires that … development will not result in a significant increase in sedimentation in the CMA …
Policy 23 (Discharge of contaminants)— Sub-section (1) applies to the discharge of contaminants (which generally includes fine silts and muds) and the need to avoid significant adverse effects after allowing for reasonable mixing.
Policies 24 and 27 (Coastal hazards, climate change and protection of significant existing development)— Requires assessment of the effect of coastal hazards and climate change over at least a 100-year timeframe, taking into account national guidance8 and the best available information on the likely effects of climate change on the region or district.
Policy 27 also recognises that hard protection structures may be the only practical means to protect existing infrastructure of national or regional importance, and to meet the foreseeable needs of future generations.
Further, the Department of Conservation released implementation guidance in 2017 for the natural hazard policies 24–27 (DoC, 2017).
2.3.3 Regional Coastal Plan–Northland (RCP-N) The operative RCP-N applies predominantly to managing effects on the Coastal Marine Area (CMA) at or below MHWS.
For river mouths, the RMA (s. 2) defines the landward extent of the CMA up rivers or creeks as the lesser of either 1 km upstream from the defined river mouth or the point upstream calculated by multiplying the width of the river mouth by 5. The relevant present-day CMA boundaries of Whangaroa Harbour river mouths were defined in 1994 defined in Appendix 1.3 of the RCP-N9 using NZMS 260 Map series references (which were converted to WGS-84):
Kaeo River mouth and CMA boundary defined as P04 803 796 (–35.0819qS, 173.7612qE), being just seaward of the existing SH10 bridge site (Figure 2-5 and Figure 2-6). No upstream CMA boundary is defined.
In the Proposed Regional Plan (NRC, 2017; 2019), the site is referred to as the “cross-river coastal marine area boundary” taking into account the river mouth definition of the CMA – see Figure 2-6.
The existing SH10 bridge is presently designated as the inland extent of the CMA, which will be used by Northland Regional Council and this Project’s AEE report to assess the effects and implications specifically on the CMA (e.g., the coastal waters, seabed and the airspace above). However, with ongoing rising sea level, the future CMA boundary will need to be moved upstream at some point, but for this assessment of applicable impacts on the CMA in relation to the RCP-N, the present cross- boundary demarcation line along the existing bridge alignment will be used. However, through the NZCPS (Objectives 1–2), the integrity, functioning, resilience and preservation of natural character is to be applied to the wider coastal environment which includes areas where coastal processes and influences are significant e.g., tidal estuaries, tidal creeks, saltmarshes, wetlands and the margins of
8 Generally accepted that this would apply to the recent MfE coastal guidance (MfE, 2017) 9 NRC (1994). Agreement to define river mouths and record landward boundaries of the Coastal Marine Area (Far North District), 19 Dec 1994 https://www.nrc.govt.nz/media/10764/farnorthdistrictrivermouthboundaries.pdf – also Appendix 1.3 of the Northland Regional Coastal Plan (Far North District).
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these (Policy 1). Therefore, in assessing the effects of the Project on coastal processes, it is assumed in this Report that coastal processes, as evidenced by field measurements, are present within the Project Extent of the proposed new bridge (Figure 1-1), and are assessed accordingly, irrespective of whether the Project area is not deemed to be in the CMA. Measurements such as high salinity (Section 2.2.2) and tidal characteristics (Section 3) confirm that coastal processes within the upstream coastal environment need to be considered in terms of effects as required by the NZ Coastal Policy Statement (Objective 1 & Policy 1) and by inference, is implied from the definition by NRC of this stretch of Kaeo River as a “coastal river” (Figure 2-5). In any case, with ongoing rising sea level over the 100-year life cycle of the Project, this stretch of the “river” will become increasingly coastal (brackish), other than during high river flood flows.
Areas of Outstanding and High Natural Character are shown in Figure 2-6 from the Proposed Regional Plan (2019), with the closest designated area (of Outstanding Natural Character) adjoining SH10 further west of the bridge in the upper reach of Whangaroa Harbour, some 2.7 km downstream of the existing bridge along the tidal flow path.
Figure 2-6: Indicative present CMA boundary and cross-river CMA boundary at the existing SH10 bridge, with designated natural character areas. Triangles mark NRC tide gauge sites. [Source information: Proposed Regional Plan – Decisions Version May 2019, (NRC, 2019)].
For the upper Whangaroa Harbour and Kaeo River, the CMA is designated as a Marine 2 (Conservation) Management Area in the RCP-N (Figure 2-7). This zone applies generically to any part of the CMA of Whangaroa Harbour which is not otherwise covered by any of the other five classes of management area as indicated on the Coastal Plan Maps (RCP-N) including areas of natural character (Figure 2-6). The other three classes relevant to the Project are: Marine 3 (Marine Farming) – oyster farms; Marine 4 (Mooring); and Marine 6 (Wharves) Management Areas, as shown in Figure 2-7.
The closest designated areas, other than Marine 2 (Conservation), is the Marine 3 (Marine Farms) Management Area (Figure 2-7), which is around 3.5 km downstream via the tidal flowpath from the existing SH10 bridge.
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Figure 2-7: Marine Management Area Units - upper Whangaroa Harbour and Kaeo River. [Source information: Coordinates GIS Map server – operative Northland Regional Coastal Plan].
The RCP-N states that Marine 2 (Conservation) does not preclude the provision for appropriate new uses and development but the objective is to manage these remaining areas in such a way as to conserve and, where practicable, enhance ecological, cultural and amenity values. The RCP-N states that:
“Generally, little or no comprehensive information exists to assist the Northland Regional Council in deciding resource consent issues for the Marine 2 (Conservation) area, though it does contain significant amenity, visual and intrinsic values. The underlying values are natural processes such as sand movement, tides and currents that provide the integrity of coastal ecosystems as a whole (recognised in the NZCPS).
The Marine 2 (Conservation) Management Area will ensure that use, development and protection of the coastal marine area is appropriate by, among other things, ensuring that adequate information regarding any proposed activity is supplied so that the effects of the activity on the coastal marine area can be determined prior to any decision being made.”
Objective 1 for Marine 2 (Conservation) [Section 26.3, RCP-N] is:
“Subdivision, use and development occurring in such a way as to maintain, and where practicable, enhance, the existing natural, cultural and amenity values in the Marine 2 (Conservation) Management Area.”
22 SH10 Kaeo Bridge Project
Relevant Policies (26.4) for Marine 2 (Conservation) for assessing coastal physical processes in the RCP-N are:
Where there is a lack of knowledge about coastal processes and ecosystems in the Marine 2 (Conservation) Management Area, to adopt a cautious approach to decision- making.
To recognise that different areas within the Marine 2 (Conservation) Management Area have distinct natural, cultural and amenity values that should be maintained and where possible enhanced (e.g., consider unique attributes).
To provide for sustainable, use and development whilst ensuring that the intensity, character and scale of use and development is compatible in relation to the character (including natural character), heritage and amenity values of the adjoining coastal environment.
Rules for assessing coastal physical processes (excluding stormwater effects) in Marine 2 (Conservation) Management Areas [Section 31.4] include:
The erection or placement of any new structure, and the occupation of space for, and use of, a new structure is a Discretionary Activity (17.5.9).
Any new reclamation is a Discretionary Activity (18.5.2). Note: the proposed Project design does not currently include any requirement for reclamation of the CMA (or coastal river waterbody).
Any new impoundment10 is prohibited, other than that which is associated with any marina or port development or for public road realignment (which are Non-Complying Activities). Note: the proposed Project design does not currently include any requirement for temporary impoundment within the CMA (below mean high water springs) or permanent impoundment (causeway) in the CMA as temporary sheet piling or coffer dams will not be required.
Relevant general assessment criteria for discretionary activities related to effects on coastal physical process in the RCP-N are [Section 32.1, 32.2.1 and 32.2.2]:
The extent to which the proposal will add to the cumulative adverse effects of use and development on the coastal environment, including those associated with similar existing uses or developments within the same locality.
The extent to which cumulative effects on the coastal environment can be minimised.
The effect of the proposed activity on the natural character of the site or area within which the activity is proposed and the measures to be undertaken to ensure that natural character will be preserved, particularly in relation to: a) the topography or bathymetry within the site or area; b) the natural substrate composition within the site or area; c) the natural water and sediment movement patterns.
10 Defined in RCP-N as “permanent or temporary impounding, of water within any part of the coastal marine area by means of the construction of a causeway, bund, seawall, other similar solid structure ...”
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The extent to which the proposed activity adversely affects natural systems acting as a defence against natural hazards and the extent to which the activity has potential to require future hazard protection works.
The extent to which the proposed structure will create erosion or siltation and the likely effectiveness of any avoidance or mitigation measures proposed.
The extent to which sea-level rise has been taken into account in the location and design of the proposed structure.
The extent to which sea-level rise has been taken into account in the location and design of the proposed reclamation or impoundment.
A summary of these assessment criteria is used later in this assessment report to ascertain the degree of effects of the proposed works on coastal physical processes, both in the coastal marine area and the wider coastal environment (that includes the coastal river section – Figure 2-5).
Further, the nearby Outstanding Natural Character area (Figure 2-6) comprising the mangrove area of the upper Harbour, is connected to the Project site with a 2.7 km flowpath on the ebb tide . Therefore, any effects on this area also need to be considered when assessing potential turbidity effects of the Project (the potential environmental impact is further considered in the Marine Ecology report).
2.3.4 Sea-level rise guidance Under Policy 24 of the NZCPS coastal hazards including climate change effects are to be assessed over at least 100 years, which for this Project effectively means out to 2120. Policy 24 also requires assessments to take into account national guidance and the best available information on the likely effects of climate change on the region or district.
The operative coastal guidance provided by the Ministry for the Environment (MfE) is the 2017 edition of Coastal Hazards and Climate Change –Guidance for Local Government (MfE, 2017).11 This Guidance provides four sea-level rise (SLR) scenarios (Figure 2-8) to stress-test options for land-use planning and infrastructure design to ensure sufficient flexibility is provided to adapt to the widening uncertainty in rates of SLR and avoid locking in investment or path dependency based around trying to choose and design to a future “best estimate”.
This widening uncertainty in the rate of SLR, towards the latter part of this century and beyond, relates mainly to the trajectory of future global carbon emissions and the non-linear effect of polar ice-sheet instabilities – especially if global mean temperatures exceed ~2°C (above pre-industrial levels).
The SLR scenarios are based on different representative concentration pathways (RCPs)12 by the Intergovernmental Panel on Climate Change (IPCC) in their 5th Assessment Report (Church et al. 2013) and the upper curve from projections by Kopp et al. (2014).
11 http://www.mfe.govt.nz/publications/climate-change/coastal-hazards-and-climate-change-guidance-local-government 12 IPCC assessed 4 RCPs, ranging from RCP2.6 (where global emissions are reduced to a net of zero by 2075) to RCP8.5 (which represents continued high carbon emissions with little effective reductions in global emissions). RCP 6.0 was not used for the SLR scenarios as close to the projection for RCP4.5.
24 SH10 Kaeo Bridge Project
Figure 2-8: Four scenarios of New Zealand-wide regional SLR projections for use in New Zealand, with extensions to 2150. Excludes any local vertical land movement. [Source: Chapter 5, MfE coastal guidance (MfE, 2017)].
By 2070 (50 years from 2020), sea-level rise could range from 0.32 to 0.6 m (or possibly higher), while by 2120, rises could range from 0.55 to 1.36 m (or possibly higher), relative to MSL averaged over the period 1986–2005 (Table 2-1).
For the Whangaroa-Kaeo area, the ongoing vertical land movement is uncertain, due to a lack of a continuous GPS station in the area, but likely to be relatively small. Based on MfE, 2017 (Figures 20– 21) and the associated GNS Science Report (Beavan & Litchfield, 2012), with the nearest continuous GPS gauges in the GeoNet/LINZ network13 some distance away at Kaitaia (0.3 mm/yr subsidence over a 4.5-year record) and further afield in Whangarei (0.3 mm/yr uplift over a 9-year record). Therefore, until further data and analysis is undertaken, the vertical land movement to add to the NZ SLR scenarios (Figure 2-8) is assumed conservatively to be an ongoing subsidence rate of 0.5 mm/yr. This assumed rate is applied with the NZ SLR projections to estimate future storm-tide levels relative to the soffit levels of the new bridge in Section 3.2.4 and Table 3-3.
For this Report, the ranges in SLR to 2070 and 2120 for the four scenarios are used to stress test clearances under the proposed bridge soffits for storm-tide (tide + storm surge) levels only. River flood contributions to water level with sea-level rise are considered separately in the hydrology/stormwater technical report (Aurecon, 2019) but are summarised where relevant in Section 3.3.2.
13 https://www.geonet.org.nz/data/gnss/map
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Table 2-1: Decadal increments for projections of SLR (metres above 1986–2005 baseline) for the wider-NZ region for four future scenarios from Figure 2-8. In Section 3.2.4, an assumed 0.5 mm/yr subsidence is applied to these NZ-wide scenarios. [Source: Chapter 5, MfE coastal guidance (MfE, 2017)].
NZ SLR scenario NZ RCP2.6 M NZ RCP4.5 M NZ RCP8.5 M NZ RCP8.5 H+ (median) (median) (median) (83 percentile) Year [m] [m] [m] [m] 1986–2005 0 0 0 0 2020 0.08 0.08 0.09 0.11 2030 0.13 0.13 0.15 0.18 2040 0.18 0.19 0.21 0.27 2050 0.23 0.24 0.28 0.37 2060 0.27 0.30 0.36 0.48 2070 0.32 0.36 0.45 0.61 2080 0.37 0.42 0.55 0.75 2090 0.42 0.49 0.67 0.90 2100 0.46 0.55 0.79 1.05 2110 0.51 0.61 0.93 1.20 2120 0.55 0.67 1.06 1.36 2130 0.60* 0.74* 1.18* 1.52 2140 0.65* 0.81* 1.29* 1.69 2150 0.69* 0.88* 1.41* 1.88
2.3.5 Transport Agency requirements and coastal risk screening There is a requirement within the RMA and therefore by the Transport Agency to avoid or, where it is not practicable, adequately remedy or mitigate adverse effects on water quality, in this case caused by stormwater discharges and land-disturbing activities. From a construction or de-commissioning perspective, methodologies for the management of erosion and sediment, concrete, dust and other contaminants as well as construction related run off will be required to mitigate potential effects on adjacent land, in-stream, coastal river environments and the CMA.
The Transport Agency has also developed a Coastal Effects Assessment Guideline, based around a risk-screening approach of the effects of roading works on coastal environments (NZTA, 2017). Aspects of the risk-screening approach from this guidance were adopted for this Report to summarise the relative risks from various effects on coastal physical processes and also coastal hazard risks to the new two-lane bridge and associated works.
26 SH10 Kaeo Bridge Project
3 Description of the existing environment In considering environmental effects of the Project, the existing environment is the baseline that is considered for assessing effects, including the existence of riverbank stopbanks and the existing SH10 bridge crossing (see Policy 1(i), NZCPS). Consequently, the effects from the proposed structures and construction and de-commissioning works within the CMA and adjoining coastal environment will be considered for the coastal permit applications.
3.1 Estuarine/river environment The proposed new bridge crossing is located 40–45 m upstream of the existing SH10 bridge in the coastal river reach of the Kaeo River, which drains into Whangaroa Harbour (Figure 3-1). The site lies between the townships of Kaeo and Whangaroa (Whangaroa Rd intersection is currently adjacent to the east (right) abutment of the present bridge).
The Kaeo River drains a catchment area of 126 km2 (Figure 3-1), with a total stream network of 90 km (Ahsan & Howse, 2011). River floods have been a significant hazard in the lower catchment including a history of flooding of Kaeo township and low-lying parts of SH10 in or adjacent to the Project area e.g., ex tropical cyclone Cook in April 2017 (Figure 3-2).
Figure 3-1: Kaeo River catchment and Whangaroa Harbour, with locations of the NRC water-level gauge sites. Blue outline marks the Project site. Gauge sites: KFS = Kaeo at Fire Station; KWH = Kaeo at Whangaroa Rd.; WGFC = Whangaroa at Game Fishing Club. [Map source: NIWA River Environment Classification].
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A peak flow of 330 m3/s at Kaeo township was estimated for the large Kaeo River flood in July 2007 (Ahsan & Howse, 2011). Details on river flooding and the effect of the existing and proposed bridges on river flooding are in Stormwater/Hydraulic Technical Report (Aurecon, 2019).
Figure 3-2: River flooding over SH10 during ex TC Cook (13 April 2017) looking west from the existing Kaeo Bridge. [Source: TVNZ footage on YouTube: https://www.youtube.com/watch?v=7fiY1UnbwX4].
Whangaroa Harbour (Figure 3-3) covers a surface area of 19 km2 at high tide. The surface area of the harbour is reduced at spring low tide, with the exposure of broad, low-gradient tidal flats and banks covering 5 km2, particularly in the upper arms of the Harbour, more so in the inlet that the Kaeo River drains into (Figure 3-3). At the wharf, adjacent to the Game Fishing Club, the tidal range is 2.2 m at mean spring tides and 1.3 m at neap tides – slightly smaller than the tide ranges at Marsden Point (the nearest LINZ Standard Port). The tidally-exchanged volume14 of the Harbour is 33 Mm3 on a spring tide and 23 Mm3 on a neap tide (Heath, 1975).
As described earlier (Figure 2-5), the proposed Regional Plan (NRC, 2017; 2019), classifies the lower Kaeo River as a coastal river, from Dip Road (near gauge site KFS - Figure 3-1) to the existing SH10 bridge, and a tidal creek from there seawards into Whangaroa Harbour. Mangroves line the banks of the tidal creek section, becoming the dominant flora a few hundred metres downstream of the existing bridge while reeds, flaxes and fringing mature mangroves line the banks upstream, such as at site B (see Figure 2-1) just upstream from the proposed bridge crossing (Figure 3-4).
Various tide levels were established at the Kaeo at Whangaroa Road gauge site (KWH) in Section 3.2, but this site is 1.7 km downstream from the existing bridge, so a vertical offset will be needed to extrapolate the levels from KWH (see Section 3.2).
14 Tidal prism volume is the total volume of water that flows out of the harbour on an ebb tide (or in on a flood tide).
28 SH10 Kaeo Bridge Project
W
Figure 3-3: Whangaroa Harbour features and depths and intertidal flats (relative to Chart Datum). [Source: Hydrographic Chart NZ5114, LINZ].
Figure 3-4: View of western bank - coastal river section of Kaeo River at site B. [Credit: R Bell, NIWA].
SH10 Kaeo Bridge Project 29
River channel widths at the Project site at mean high water spring15 vary somewhat, ranging from 50–60 m wide in the section of coastal river upstream from the proposed bridge site (Figure 3-5), widening to 50–80 m in the tidal creek downstream from the existing bridge site. The channel is deeper on the true right bank side, reaching depths of 1.4 m below present MSL near the existing bridge and slightly shallower at 1.1 m at the proposed bridge site - see yellow line for Section 2 (Figure 3-5). The 1% annual exceedance probability (AEP) storm tide level is defined in Section 3.2.4).
3.0
2.0 Storm-tide (1% AEP) MHWS-10 1.0
present MSL 0.0
Section 1 -1.0 Section 2
-2.0 Elevation (OTP-64; m RL) Section 3
-3.0 90 80 70 60 50 40 30 20 10 0 Chainage [m] from SH10 on right-bank (east side of river)
Figure 3-5: Kaeo River cross-sections 1–3 upstream of the existing bridge, looking seawards into the page (top panel) and location of transects (bottom panel). Elevations in OTP-64 (RL). Water levels for MSL, MHWS- 10 and 1% AEP storm-tide for the Project site are marked by dashed lines. [Survey data: Aurecon NZ Ltd].
15 See Section 3.2.3 for definition
30 SH10 Kaeo Bridge Project
The steep banks and dense fringing mangroves in the tidal creek section (seawards of the existing bridge), together with the 90° bend approaching Whangaroa Harbour (Figure 3-3) means the wave climate in the Project area is benign, with little penetration of waves from the main Harbour, but some wave setup may propagate upstream from the Harbour (see Section 3.2.4).
3.2 Tides and storm tides
3.2.1 Mean sea level Vertical or reduced levels in Northland are usually defined in terms of One Tree Point Datum-1964 (OTP-64), which was established as the then mean sea level (MSL) at Marsden Point from four years of sea level measurements collected between 1960 and 1963. The historic MSL set in 1964 was +1.676 m relative to local Chart Datum at Marsden Point. An artefact of the OTP-64 datum is that present-day average sea level at Marsden Point over the past 19 years (1998–2016) is 0.086 m below the local datum, compared to other local vertical datums around New Zealand where present sea level is somewhat higher than the datum set several decades earlier.
To derive the present MSL for the Whangaroa Harbour and the lower Kaeo River, an analysis was undertaken of the water-level records from the two NRC gauges that exhibit a regular tidal signal (with locations shown in Figure 3-1):
a) Whangaroa Wharf at Game Fishing Club (WGFC) – covering 21 August 2008 to 7 March 2017, with gauge zero at -1552 mm relative to OTP-64 (supplied by Jason Donaghy, NRC).
b) Kaeo at Whangaroa Rd (KWH) – covering 29 Jul 2008 to 24 May 2015, with gauge zero at - 1285 mm relative to OTP-64 (supplied by Jason Donaghy, NRC).
For Whangaroa Wharf, the average MSL for the nearly 9-year period (2008–2017) was 1.601 m above tide-gauge zero (or +0.05 m OTP-64). At the Kaeo gauge, adjacent to Whangaroa Road, the average MSL for the nearly 7-year period (2008–2015) was 1.326 m above tide-gauge zero (or +0.04 m OTP- 64). These MSL values are similar, so for this Report, a MSL offset of 0.07 m above OTP-64 is used adding an estimated further 3 cm for the setup in mean tide level and river flow effects in the more confined channel up to the Project site.
Note: the mean tide level in the upper Whangaroa Harbour and Kaeo River is set-up higher by several cm than the open coast, probably due to tidal friction in shallow water, as shown by the MSL at the open coast site of Marsden Point being 0.086 m below OTP-64.
3.2.2 Tides and river floods Figure 3-6 shows the measured water levels (relative to OTP-64) over the first 4 months of 2011. This example period saw the highest storm-tide level over the record reached on the morning of 23-Jan- 2011 and six days later the highest river flood in the data record since 2008. A closer view of both the coastal event, that also coincided with a flood event in the Kaeo River, and the large river flood on 29-Jan-2011, are shown in Figure 3-7.
Firstly, the tide undergoes further distortion as it passes into and through the tidal creek section of the Kaeo River – with the ebb-tide (falling tide) becoming considerably longer, while the flood tide is shorter and steeper – as shown by the Whangaroa Rd gauge record (Figure 3-7; top panel). The lag in high water at this KWH site, relative to the Harbour ocean entrance is about 12–25 minutes, whereas the low water can lag by between 1 hour 20 minutes up to 2 hours 10 minutes after low water occurs
SH10 Kaeo Bridge Project 31
on the open coast. This distortion is caused by frictional dissipation of the tidal wave as it propagates through shallow water depths, slowing at lower tide levels, and assisted by the outgoing river flow.
WL gauges: Whangaroa Harbour and Kaeo at Whangaroa Rd 2 Storm-tide (1.63 & 1.59 m) 1000 hrs 23-Jan-2011 1.5
1
0.5
0
-0.5 Water level (m; OTP-64) level Water
-1
01/01/2011 01/02/2011 01/03/2011 01/04/2011 01/05/2011
Figure 3-6: Water levels in Whangaroa Harbour (blue) and at Kaeo at Whangaroa Rd (green) for the period 1-Jan to 30-Apr-2011. Height relative to OTP-64. The highest storm-tide level reached in the entire record was 1.63 m at Whangaroa Harbour gauge and 1.59 m at the Kaeo gauge during the coastal-storm event of 23-Jan 2011. [Gauge data source: NRC].
2 Storm tide (23-Jan-2011) 1.5
1
0.5
0
-0.5 Water level (m; OTP-64) level Water
-1
4
3.5
3
2.5
2
1.5
1 Water level (m; Gauge Zero) Gauge (m; level Water 0.5
0 16/01/2011 23/01/2011 30/01/2011
Figure 3-7: Water levels at 3 gauges for period 15-Jan to 2-Feb-2011, showing influence of storm-tides and Kaeo River floods. (Top) Comparison of Whangaroa Harbour (blue) and Kaeo at Whangaroa Rd (red); (Bottom) Kaeo at Whangaroa Rd (red) and Kaeo at Fire Station-KFS (black). [Data source: NRC]
32 SH10 Kaeo Bridge Project
Secondly, the comparisons between gauge sites reveal several characteristics of the tide and interactions with Kaeo River floods that are important to consider when assessing flooding hazards and setting the MHWS level. These characteristics are:
The tidal range observed at the Kaeo at Whangaroa Rd gauge site is smaller than in the body of Whangaroa Harbour, and is further dampened during larger spring tides (e.g., 21-22 Jan) when the water level at low tide doesn’t drop below a lower threshold level (Figure 3-6). This will be due to the shallow shoals at the outlet of the Kaeo River (evident in Figure 2-1) acting as a sill to pond water during the lower low tide periods during spring tides – a feature common in tidal creeks.
The high-tide water level is generally slightly lower than that measured at the Whangaroa Harbour gauge (and similarly will apply at the Project site) – but for this AEE assessment, the Harbour high-water levels will be adopted to be conservative (excluding river floods). Note: during large river floods, such as the 29-Jan-2011 event, which was the largest flood level reached in the record since July 2008 at the Kaeo at the Fire Station gauge, the high-tide water level at Whangaroa Rd gauge site is only slightly higher than the Harbour water level by 6 cm. Therefore, river floods have a negligible effect on tide levels in larger water bodies such as the Whangaroa Harbour.
Occasionally during spring tides and low river flows, a small high-tide influence can be seen in the Kaeo Fire Station record (e.g., 21-22 Jan) – around 6 km upstream from the river confluence with Whangaroa Harbour.
The storm-tide event on the 23-Jan 2011 was generated by a low-pressure system to the NE that coincided with larger perigean-spring tides. This event caused coastal flooding in Auckland, where the storm-tide level at the Port of Auckland was the highest on record – calculated to be nearly a 1% Annual Exceedance Probability (AEP) event (or nearly a 100-year average recurrence interval). The storm-tide level reached 1.63 m OTP-64 at the Game Fishing Club gauge, the highest in the short 9-year record – but may have had a similar AEP ranking to Auckland. This storm-tide level is also used in the coastal hazard report for NRC (Tonkin + Taylor, 2016). The Kaeo River was also in flood during this 2011 event (Figure 3-7), but only shown to noticeably affect water levels at lower tides, whereas the high-water level was dominated by the Harbour storm-tide level.
River floods have a major influence on the low-tide levels measured within the river arm (but not in the Harbour itself – refer to Bullet 2 above) due to the dominance of larger river flows at low tides. This is evident at the Whangaroa Rd gauge site (KWH) at the peak of the 29-Jan flood where the low-tide level was only ~0.6 m below the measured high-water level (meaning the tide range was only 0.8 m compared to the 1.4 m expected). During the long falling limb period following the flood peak, the low water elevations gradually ease back down to the expected low tide baseline.
SH10 Kaeo Bridge Project 33
The highest river flood level measured since 2008 at the Kaeo at the Fire Station (KFS) gauge at was 3.89 m above gauge zero on 29-Jan-ϮϬϭϭĂŶĚǁĂƐƐƵƐƚĂŝŶĞĚĂƚшϯ m levels for 16.25 hours. The next largest was a more recent flood on 13 April 2017 caused by ex-Tropical Cyclone Cook, where the river level reached 3.68 m and ƐƵƐƚĂŝŶĞĚĂƚшϯ m levels for 13 hours. This more recent event (Figure 3-2), caused flooding of SH10 at the western end of the Project area. A slightly elevated new western embankment off the new bridge will only partially reduce the extent of surface flooding closer to the bridge, but the low-lying section of SH10 will remain.
3.2.3 MHWS and maximum HW An analysis was undertaken on the tide-only component in the data records from Whangaroa Harbour (WGFC) and Kaeo at Whangaroa Rd (KWH) gauges provided by NRC.
Tidal analysis was completed for 2-year periods, and tidal constituents extracted as shown in Table 3-1. Tides explain 98.9% of the variance in the measured water levels at Whangaroa Harbour, decreasing slightly to 96.9% at Kaeo at Whangaroa Rd. The fortnightly spring-neap cycle occurs when the solar tide (S2) and the primary lunar tide (M2) move in and out of phase (i.e., in phase for spring tides on a Full/New Moon, out of phase for neap tides on the Moon’s Quarters).
The N2 tidal constituent, arising from the 27.4-day elliptical orbit of the Moon around the Earth, generates one set of larger monthly tides when the Moon reaches its perigee (closest distance to the
Earth) in the month. For Whangaroa, the N2 tidal constituent is larger than the S2 solar tide, resulting in a tidal pattern of alternating higher perigean-spring tides and lower spring tides in a month (e.g., Figure 3-6; top panel).
The decrease in the primary tidal constituents from the Harbour up into the entrance channel of Kaeo River occurs due to frictional dissipation of the tide wave as it propagates in and out over the shallow shoals – but is partially compensated by the shallow-water overtide M4 increasing at the Kaeo at Whangaroa Rd site – manifest as a distortion of the tide with a longer ebb-tide period and a shorter, steeper, incoming tide. The difference in tidal phases for the dominant lunar tide (M2) between the two sites translates into a lag of 8.5 minutes for the average high tide to propagate from the Wharf up to the Whangaroa Rd site.
Table 3-1: The dominant tidal constituents extracted from 2-year periods of water level measurements at NRC's Harbour and Whangaroa Rd gauge sites. Constituents are defined as an amplitude of a best-fit sine (or half tide range) and a phase when the peak tide occurs (in degrees of a tidal period for NZ Standard Time).
Whangaroa Harbour wharf Kaeo at Whangaroa Rd Tidal constituent half-range (m) HW phase (°) half-range (m) HW phase (°)
M2 (12.4 hr lunar tide) 0.806 217.7 0.684 221.8
S2 (12.0 hr solar tide) 0.147 279.8 0.108 289.5
N2 (12.66 hr lunar elliptical orbit) 0.167 184.8 0.119 189.1
M4 (6.2 hr shallow-water tide) 0.002 75.6 0.097 49.1
34 SH10 Kaeo Bridge Project
For the Whangaroa Harbour gauge site, the tidal constituents can be used to predict all the high tides for, say, the next 50 years (excluding weather and climate effects and SLR) and therefore establish various high-water marks. Figure 3-8 shows the cumulative exceedance distribution of all possible high-tide levels relative to OTP-64 after adding in the MSL offset of 0.05 m (Section 3.2.1) but excludes any SLR at this stage. The key high-tide marks (relative to OTP-64) annotated in the plot are:
Maximum HW: 1.353 m.
MHWPS = 1.169 m exceeded by: 5.8% of all predicted high tides.
Pragmatic MHWS for 10% exceedance (MHWS-10): 1.117 m.
MHWSn = 1.002 m - exceeded by: 23.0% of all predicted high tides.
Minimum HW: 0.483 m.
When a SLR of 0.63 m is reached (i.e., MHWS-10 of 1.117 m minus the minimum HW of 0.483 m = 0.63 m), all future high tides in Whangaroa Harbour will exceed the present-day MHWS-10 level.
Figure 3-8: High-tide exceedance distribution at the Whangaroa Harbour Wharf by the Game Fishing Club relative to OTP-64 (excludes any weather or climate effects). High water marks: MHWPS = mean high-water perigean spring tide (M2+N2+S2); MHWS-10 = high water exceeded by only 10% of high tides; MHWSn = nautical definition of MHWS (M2+S2); MHWNn = nautical definition of mean high-water neap (M2-S2); MHWAN = mean high water apogean neap (M2-N2-S2).
The MHWS-10 level of 1.03 m OTP-64 at the Kaeo at Whangaroa Rd (KWH) site is slightly lower than the Harbour site of 1.117 m (as described earlier for the lower high-water in Figure 3-6 and Figure 3-7), arising from bed-friction dissipating the tidal wave as it propagates upstream (eventually reducing to near zero up at Kaeo fire station – KFS). However, to be conservative, allowing for a river- flow component in the water level, a value for “MHWS” for the Project area should adopt a MHWS- 10 value of 1.05 m OTP-64 which uses the same value from the KWH site and includes a present-day estimated MSL of 0.07 m OTP-64 at the Project site. The maximum high-water (tide-only without weather effects) for the Harbour site (WGFC) is 1.35 m OTP-64.
SH10 Kaeo Bridge Project 35
3.2.4 Storm tides (coastal storm flooding) Storm-tides occur when a storm surge coincides with a spring or higher perigean-spring (aka “king”) high tide. Storm surge is the temporary elevation in sea level, generated by low-pressure weather systems (the inverted-barometer effect)16 and up-harbour winds (strong N to NE winds for Whangaroa) causing harbour waters to pile up (setup) above the predicted tide, which could reach an additional 1 m or more. During the 23-Jan-2011 storm-tide event (Figure 3-6), the storm surge component was ~0.55 m on top of a perigean-spring high tide at Whangaroa Rd gauge site, making the total water level 1.58 m OTP-64 (and 1.63 m at Whangaroa Harbour Wharf).
Additional contributions to the setup in total water level can arise from wind waves (wave setup) and variations in the monthly MSL, which can be higher than average due to natural variability of climate cycles e.g., during a La Niña climate episode and warmer late-summer months, which was the situation during the 21-Jan-2011 flood event.
Analyses of extreme events and their occurrence probability is undertaken by calculating extreme- value distributions from annual maxima (or the largest few events per year) for total water levels. Generally, storm-tide levels are expressed as an annual exceedance probability (AEP), which is the probability (in percent or a decimal fraction) of that level being exceeded in any year e.g., 1% and 2% AEP storm-tide levels are those exceeded with probabilities of 1% and 2% (or 0.01 and 0.02) in any year and are equivalent to an average recurrence interval of 100 and 50 years respectively.
The current Bridge Manual (NZTA, 2018; Table 2.1), requires a 1% AEP flood level be used for assessing the Serviceability Limit State 2 (SLS 2)17 for flooding risk for bridges on Level 3 routes (Primary Collector Road). It marks the threshold for the bridge becoming temporarily unfit for its intended use. The predominant effect on water levels in the Project area arises from either storm- tides for these tidal-creek and coastal river environments or river flood levels, or a combination of both, as occurred on 23-Jan-2011 (Figure 3-7) in the Kaeo River. Only storm-tide is assessed in this coastal processes Report, but the effect of an additional river flood contribution is considered in the hydrology/stormwater technical report (Aurecon, 2019).
The average recurrence interval (ARI) for the recorded 23-Jan-2011 event for the recent historic record was around a 50-years or a 2% AEP event (Stephens et al. on line - in review). The 1% AEP or 100-year ARI was estimated to be only 0.04 m higher (Stephens et al. on line - in review). This means the 1% AEP storm-tide level at the Whangaroa Rd gauge site (KWH) is estimated to be 1.62 m OTP- 64.
While not specifically required for the Northland bridges programme (see Section 1.2), the NZTA Bridge Manual (Table 2.1) also defines an Ultimate Limit State (ULS) for floodwaters for a Level 3 route of 0.1% AEP (or 1/1000–year event), which can be compared to the 1% AEP design requirement for the Kaeo Bridge. While measurements of tidal levels in the Whangaroa Harbour are not long enough to establish the storm-tide water level of such a rare event (even the longer Marsden Point record), it is estimated that such a 0.1% AEP storm-tide level would add 13 cm higher than the 1% AEP level at the Project site (Stephens et al. on line - in review). This modest additional storm-tide height for the ULS for storm-tide only (excluding river floods), is because the extreme
16 Inverted barometer (IB) effect is the setup in sea level during a storm, where every 1 hPa drop in pressure below the average barometric pressure (1016 hPa at Whangarei Airport) lifts sea level by approximately 1 cm e.g., 980 hPa would generate IB of 0.36 m storm surge (excluding wind setup). 17 SLS 2 – NZTA Bridge Manual defines this as the event where the structure should remain operationally functional for all highway traffic during and following flood events
36 SH10 Kaeo Bridge Project
value distribution tapers off to an asymptote for rare combinations of storm surge and high tides in coastal areas (see Jan 2011 example in previous paragraph). This arises as both components (storm surge and high tide) are physically constrained by the largest tide possible (every 18.6 years due to the Moon and Sun) and the lowest storm central pressure that can be experienced in New Zealand (as we don’t experience tropical cyclones). In any case 13 centimetres of additional water level for the ULS storm-tide at 0.1% AEP is a secondary effect compared to SLR over the next 100 years of between 0.55 m to 1.36 m plus vertical land movement as well as the river flood contribution.
Table 3-2 lists the estimated storm-tide levels in Whangaroa Harbour and Kaeo tidal creek from a coastal hazards report prepared for NRC (Tonkin + Taylor, 2016) for the 1% AEP event (1/100 yr ARI) and compared with the 0.1% AEP (1/1000 year ARI) from Stephens et al. (on line - in review). These levels include the storm-tide component (high tides, storm surge, and variability in MSL). The Tonkin + Taylor (2016) report also produced a second estimate for total static water level to account for local wind-wave setup – but this value is not appropriate to use well upstream in a sheltered tidal creek/river such as the Project site, where wave setup generated in Whangaroa Harbour will have dissipated. The 1% AEP storm-tide level of 1.6 m OTP-64 in Table 3-2 matches the above independent analysis.
The 1% AEP storm-tide water level for the present-day (Table 3-2) should be used, along with the range of SLR scenarios (Figure 2-8) from the MfE coastal guidance plus the assumed vertical land movement estimate of 0.5 mm/yr of land subsidence to estimate the relative SLR for the area, as listed in Table 3-3. Note the future storm-tide levels increase in a linear fashion with the rise in the underlying relative SLR, assuming that future changes in storm surge is minor. These future coastal water levels can then be used to test the proposed new bridge soffit levels, abutments and stopbank levels in the engineering design for coastal storm-tide plus SLR alone (excluding river floods) – see section 4.1.4.
Further allowances for the 1/1000-year (0.1% AEP) storm-tide level if an ULS storm-tide design level were to apply, would add a further 0.13 m to the 1% AEP storm-tide level (Stephens et al. on line - in review) before adding in the local relative SLR.
Table 3-2: Present-day coastal storm-tide 1% and 0.1% AEP elevations (m; OTP-64) in Whangaroa Harbour and Kaeo tidal creek based on recent historic water level data (KWH, WGFC). [Source: 1% AEP: Appendix C, Tonkin + Taylor (2016); 0.1% AEP estimate: Stephens et al. (online–in review)].
Present-day 1% Present-day 0.1% AEP estimate AEP (no SLR) Site No. Name (no SLR) Storm tide only Storm tide only (m; OTP-64) (m; OTP-64) 34 Whangaroa Settlement 1.6 1.78 35 Kaeo Estuary 1.6 1.73
SH10 Kaeo Bridge Project 37
Table 3-3: Increase in coastal water levels in the Kaeo creek section from relative SLR for 2070 (50 yrs) and 2120 (100 yrs). Note 1: combines SLR from the MfE coastal guidance (Table 2-1), an assumed vertical land movement of 0.5 mm/yr subsidence, which are then added to the 1% AEP values for present-day in Table 3-2. Note 2: Add 0.13 m for comparison with the estimated 0.1% AEP event for an ULS coastal water level.
Coastal 2070 (50 years) 2120 (100 years) water level (OTP-64) RCP2.6 M RCP4.5 M RCP8.5 M RCP8.5 H+ RCP2.6 M RCP4.5 M RCP8.5 M RCP8.5 H+
1% AEP storm-tide 1.95 1.99 2.08 2.24 2.20 2.32 2.71 3.01 only (m)
Combined storm-tide and river flooding Estimating combinations of joint storm-tide and flood flows in the Kaeo River at the proposed bridge site (e.g., 23-Jan 2011 is probably a low joint probability event for these purposes - Figure 3-7), requires estimation of the storm-tide and flood level upstream of the Whangaroa Rd (KWH) gauge and incorporating the river flood results from the Hydrology/Stormwater report Aurecon (2019).
The Aurecon modelling shows that river floods dominate the combined water level at the proposed new bridge, with the 1% AEP flood water level reaching 3.7 m OTP-64 (David Hughes, Aurecon, pers. comm.). From experience modelling such large flood events in coastal rivers, the river flood will mostly wash-out any coinciding storm-tide effect, leaving the river flood to dominate the total water level at the Project site. However, rising sea level will increase the baseline mean tide level on which the river floods. The Aurecon (2019) report used a SLR allowance of 2 metres in a sensitivity model test to determine that the change in backwater (afflux) effect from the new bridge configuration was minor.
Coastal-storm flooding hazard maps (NRC) Based on the 1% AEP storm-tide levels in Table 3-2, NRC commissioned hydrodynamic modelling, using LiDAR topography survey data, to map Coastal Flooding Hazard Zones (CFHZ) after ascertaining the extent of coastal-flooding exposure (excluding high river flows). The mapped zones were:
CFHZ 0 (present 1% AEP storm-tide).
CFHZ 1 (present 2% AEP storm-tide and 0.4 m SLR).
CFHZ 2 (present 1% AEP storm-tide and 1.0 m SLR).
The hazard maps are available online at: https://www.nrc.govt.nz/floodmaps/#View%20the%20maps%20online
Figure 3-9 shows these Coastal Flood Hazard Zones for the Project Area, with much of the low-lying coastal and river plains already exposed to present-day extreme storm-tide flooding (blue areas). Some additional small areas would be exposed with a 0.4 m SLR (CHFZ 1) – mainly upstream of the proposed new bridge crossing including the flat area on the western side of the River (view shown in Figure 2-5). Further, areas flanking the river and south of Dip Road would be flooded with a 1 m SLR (Figure 3-9). Of note is the deck elevation of the existing bridge, which is above these coastal flood hazard levels, however sections of SH10 heading west beyond the existing bridge would be subject to
38 SH10 Kaeo Bridge Project
increasing frequency and depth of coastal flooding as the sea rises, but may only require occasional closures of 1–3 hours around high tide (excluding any coincident river flood or intense rainfall).
During the recent ex TC Cook (13 April 2017) there was coastal flooding over SH10 (Figure 3-2), however during the recent 5-Jan 2018 storm-tide event, there was no apparent coastal flooding of SH10 in the Project area (although even further to the west, SH10 was flooded in the section north of Weber Road and Waitaruke, which is adjacent to Whangaroa Harbour (Jason Donaghy, NRC, pers. com.).
Figure 3-9: Coastal Flood Hazard Zones in Natural Hazards GIS viewer based on storm-tide levels from T + T (2016). Note: CFHZ 1 includes a single 0.4 m SLR; CHFZ 2 includes a single 1 m SLR. Source: NRC GIS map server - https://www.nrc.govt.nz/floodmaps/#View%20the%20maps%20online
3.3 Hydrodynamics Peak surface current velocities of 0.26–0.3 m/s were observed close to the edge of the main channel early in the ebb tide at site A (Section 2.2.4) adjacent to the existing bridge, with flow velocities estimated to be up to 0.35 m/s in mid channel for this average tide and normal river flows. The existing bridge site has a sand bar that is exposed at low tide on the western side of the channel, which partially deflects flows to the eastern side of the channel. Note that the present channel/bar configuration may change during or following river flood flows as bars migrate downstream with sediment transported during floods and from river bank erosion.
SH10 Kaeo Bridge Project 39
The existing pier heads do not appear to unduly constrict the tidal flow as the individual supporting piles are exposed well before the peak ebb or flood tidal flows occur.
The site for the new bridge crossing has a slightly wider effective channel width (also with a shallow bar on the western bank), so peak ebb-tide velocities on an average tide in the main channel will be similar to site A.
On perigean-spring tides (not observed), peak velocities early in the ebb tide will be higher – estimated to be around 0.5 m/s, with even higher velocities when river floods occur.
The incoming (flood) tide was not surveyed, but given it flows over a shorter period at the Project sites, the peak velocity reached early in the flood tide will be somewhat higher than the peak ebb tide velocities estimated above.
Wave conditions at both bridge sites will be benign, with few opportunities for substantial wind waves to form as both sites have narrow and sinuous channels (longest fetch is 1.2 km downstream of the new bridge site) and are surrounded by steep banks and further downstream, dense mangrove forests to dampen local winds.
3.4 Tsunami Tsunami are long-period (5-30 minute) waves created by a disturbance that is transferred to the water column. Tsunami are most often generated by rupturing and displacement of the sea floor from earthquakes or from disturbances of the water column produced by either: a) underwater volcanic eruptions and caldera collapses, or b) from underwater landslides on steep escarpments or canyons.
Northland’s east coast faces exposure to tsunami from local, regional and remote (Pacific-wide) sources. Local sources (within 1–2 hours travel time to the coast) pose the greatest hazard risk, which are predominantly located on the Kermadec Ridge (including volcanoes) or the more likely Kermadec Trench from large subduction-zone thrust earthquakes.
A number of moderate-to-large tsunami have impacted Northland's coast, both historically and prehistorically, as recorded in oral traditions, written accounts and geological evidence. In last 150 years, four moderate-to-large tsunami events have impacted Northland’s east coast. Pre-historically, one large event, or a series of large, closely-spaced events, occurred around 600 years ago, along with other events around 3000 and 6500 years ago (NRC web site)18.
The latest NRC tsunami evacuation/inundation zones are shown in Figure 3-10, with orange areas outlining the extent of inundation from a 1.5 m tsunami height at the coast. The orange tsunami zone encompasses the Project area but covers much the same low-lying area as the map for coastal flooding (Figure 3-9) and similarly for river flooding. However, compared with coastal flooding, tsunami flooding will be more vigorous with higher overland velocities in this location, although subject to substantial dissipation through Whangaroa Harbour and mangrove stands before reaching the Kaeo River.
The NRC mapping is based on Power (2014), which re-analysed the probabilistic extreme wave height distributions around New Zealand’s open coast from the National Tsunami Hazard Model. For the open coast off Whangaroa Harbour (Section 14: Cavalli Islands), the estimated median tsunami wave
18 https://www.nrc.govt.nz/Environment/Coast/Tsunami/
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heights (above the local water level at arrival) are 4.5 m, 8 m, and 15 m for an average recurrence interval (ARI) of 100, 500, 2,500 years respectively. The threats for lower ARI events are about 40% from local/regional sources (mainly the Kermadec Trench) and 60% remote sources in the Pacific, while the 2,500-year ARI event would be mainly derived from either a large event associated with the Kermadec Trench or a very large magnitude event off Peru.
The design specification for the Kaeo Bridge was revised by NZTA, with the bridge structural design no longer being required to include strengthening against tsunami. Overall, tsunami inundation is likely to affect the low-lying areas in the vicinity of the Project site that are also exposed to coastal flooding and ongoing SLR – but with more vigorous current speeds than a coastal flood event. It is not known what the heights of a tsunami would be for the 100 or 500-year ARI at the proposed bridge site – but public safety can be managed through timely warnings, evacuation and bridge closures.
Figure 3-10: NRC Tsunami Evacuation Zone map. Orange areas could be impacted by a 1.5 m tsunami wave height, Yellow Zone is for a much lower probability tsunami scenario. Source: https://northlandcdem.maps.arcgis.com/apps/webappviewer/index.html?id=00bf741d369b4eb7802021004d1 23e3b.
3.5 Geology and river-bed sediments Like other Northland harbours, Whangaroa Harbour is an old river system, drowned when the sea level rose during the early Holocene period around 6,000 years ago. The Whangaroa area is characterised by distinctive ancient volcanic rock outcrops.
To the southeast of Whangaroa Harbour that includes the Project area, the Whangaroa Subgroup volcanics are underlain by Paleozoic–Mesozoic Waipapa Terrane greywacke (Waipapa Group) and
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Cretaceous–Paleogene autochthonous19 and allochthonous20 sedimentary cover rocks (Te Kuiti Group) as shown in Figure 3-11 (Conning, 1999).
There are extensive low-lying Holocene estuarine and alluvial flats at the head of Whangaroa Harbour and perched basins of Pleistocene–Holocene alluvial deposits in hill country to the northwest and southeast of the Harbour (Conning, 1999).
Figure 3-11: Primary geology units in the lower Kaeo River catchment – with Project area highlighted by the yellow ellipse. Source: QMAP, Whangarei, GNS Science (Edbrooke & Brook, 2009).
Only limited sampling of surficial river-bed sediments was feasible during the site survey. A sediment sample was taken from the edge of the tidal creek section of Kaeo River, just downstream of the existing SH10 bridge surface on the eastern bank. The particle size distribution was analysed by laser (EYE TECH) with the grain size distribution shown in Figure 3-12. The sediment is classified as a muddy silt. The sample had an organic estuarine odour and quickly oxidised. The very fine clay sized particles (< 2 microns) were a small fraction at <3% of the total volume of sediment.
Erosion of the catchment geological units, especially mudstone (and overland soil runoff) manifests in the small particle sizes of the sampled sediment and mixed with estuarine silts.
19 formed in its present position 20 moved from its original site of formation, usually by low angle thrust faulting
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very fine fine mediummedium coarse clay/mud sands silt silt siltsilt silt
Figure 3-12: Grain-size histogram distribution for sediment sample at site A (Section 2.2.1). Blue curve and values on right axis are the cumulative distribution. Top bar shows Wentworth sediment size classes. [Method: Laser analyser – analyst: R. Ovenden, NIWA].
3.6 Geomorphic features In the general vicinity of the proposed and existing bridge area, the observed geomorphology of the coastal river section of Kaeo River is characterised by a deeper channel (down to ~1.5 m below MSL) hugging the right bank (east side) and an intertidal shoal along the western half of the channel up to the left bank (Figure 3-13 and Figure 3-5). These bars were present during the field survey (Dec-2017) and are also shown in the historic aerial photograph from 2003 in Figure 2-1. Surficial sediments in the shallows next to the banks and the intertidal shoal comprise muddy silts while the deep channel bed is likely to be lagged coarser sands (particularly after high river flow events). The banks are steep, especially on the right bank, comprising unconsolidated alluvial material and silts.
Further upstream, the channel morphology transitions to more riverine characteristics, such as site C, where the intertidal shoal is lagged with coarser sands/gravels, but with muddy silts near the banks (Figure 3-14). The river-bank vegetation also matches this estuarine to riverine transition changing from mangroves to reeds and flaxes.
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Figure 3-13: Lateral intertidal shoal just upstream from the existing SH10 Bridge looking from site B. [Credit: R Bell, NIWA, 18 Dec 2017].
Figure 3-14: Mid-channel bar looking downstream from site C in the coastal river section. [Credit: R. Bell, NIWA, 18-Dec-2017].
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3.7 Existing SH10 bridge The existing 55-metre one-lane SH10 bridge, which spans a 50-m channel over the Kaeo River, is part of the existing environment (Figure 3-13 and Figure 3-15). Some local scour was observable around the most western pier and supporting pile at lower tides (Figure 3-13) but is very localised within the broader low-tide sand bar. The existing bridge and its supporting piers and piles are destined to be removed, along with the abutment embankments on both sides, once the new bridge and road re- alignment are completed.
The existing bridge comprises four spans, supported by concrete piers founded in piles, which are exposed around mid-tide (for lower river flows). The soffit level is around 3.4 m (OTP-64; RL) based on Aurecon (2019; Section 3.1.1), which is nearly 2.4 m above present-day MHWS-10.
Figure 3-15: Existing one-lane SH10 bridge over the Kaeo River - viewed from the east bank looking upstream on the ebb tide around 1.5 hours after local high tide. [Credit: R Bell, NIWA, 18-Dec-2017].
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4 Assessment of effects and mitigation
4.1 Operational effects This section covers the assessment of potential effects of the Project on coastal physical processes, during its 100-year operational lifetime. It applies more stringent tests applicable to the coastal marine area (CMA) for assessing the effect of the new bridge on coastal processes , even though the present-day CMA cross-river boundary currently sits across the existing SH10 bridge crossing.
Coastal physical processes encompass: tidal processes and hydrodynamics (e.g., currents, flushing, impedance of flows), natural flood hazards, sedimentation and scour and the effects of climate change and sea-level rise (SLR) - see Section 1.2.
The longer-term effects of climate change on the Project performance are also covered in this section.
The proposed new Kaeo bridge design (Figure 4-1) requires construction of two piers in the CMA, with a third pier set on land on the floodplain adjacent to the left bank. Bridge spans will be 30 m, apart from the shorter 18-metre span adjacent to the right bank to support the edge of the roundabout. No reclamation or impoundment in the CMA or upstream in the Project area is required.
The effects arising from the bridges or abutments/stopbanks are addressed separately, as the latter will be constructed outside the CMA or the upstream coastal river waterbody (but still in the adjoining coastal environment).
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Figure 4-1: General arrangement for the new 2-lane bridge for SH10 over the Kaeo River with plan view (top panel) and elevation looking seaward (bottom panel). The existing bridge is shown at the top of the plan view. Source: Drawing DRG-BB-1401-A (Aurecon NZ Ltd).
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4.1.1 Bridge substructure The proposed bridge is supported by 3 piers, each supported by 2 piles, with short pier caps above the present MHWS-10 level (i.e., seldom in the flow). Individual piled columns are to be 1.5 m diameter with a cross-sectional area = 1.77 m2 (Figure 4-1).
Two of the pier sets will be located in the coastal river as shown in Figure 4-1 requiring a total permanent riverbed occupation area of 7 m2 by the 4 piles. This occupation area is approximately three times the area of riverbed occupied by the thinner 3-pile groups supporting the existing one- lane bridge but is offset by the pier caps being set much higher for the new bridge, compared with than the existing piers (Figure 3-15), and therefore would not impede normal mid- to high-tide flows as much.
The width occupied by the new bridge piles in the CMA (two sets) is ~5% of the effective channel width (3 m) and along with the small area occupied by the piles, comprises a relatively small portion of the riverbed – being necessary to support the new two-lane bridge. The piles are not located in the deepest section of the channel (Figure 4-1; bottom panel) and the two-pile groups are aligned with the flow direction, with both factors reducing the potential effect on flow impedance.
Therefore, the proposed configuration of the new bridge substructure is expected to have a negligible long-term effect on coastal physical processes, such as tidal prism21 and tide range, sedimentation processes and the coastal river hydrodynamics (assuming the existing bridge and abutments will be removed).
Minor local scouring is anticipated in the vicinity of each bridge pile, caused by the local acceleration and down-welling flows around each pile during higher tidal flows (mid incoming and outgoing tides) or river flood flows. Depending on the substrate strength below the riverbed, the depth of local scour anticipated at the new bridge site will be of a similar or higher scale to local scour around pile groups at the existing SH10 bridge, as the pile diameter for the new bridge is greater, but the effective waterway under the new bridge is considerably wider, which will reduce extreme river flood velocities and therefore constrain local scour. Local scour will principally occur during the higher tidal flows during larger spring tides or during river floods and will be transitory over a period of months to years (depending on extreme flood occurrences) until it reaches a new equilibrium locally around the pile groups.
Localised scour around piles is an unavoidable effect, but of minor consequence to the wider estuary sedimentation and hydrodynamics in this section of the Kaeo River. This is supported by the analogue of the existing bridge, with no discernible evidence of general channel scour of the geomorphology around the existing bridge sub-structure (which includes piers in the flow when water levels are above MSL).
Assessment: The proposed substructure of the new 110-metre two-lane bridge (45 m upstream of the existing one-lane bridge) will have negligible long-term effect on the coastal physical processes in the coastal river section of the Kaeo River (assuming the existing bridge and abutments will be removed).
21 Volume of water entering the stretch of river on the incoming tide
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4.1.2 Bridge abutments and reformed stopbank
New SH10 upgrade A wider waterway will be created from the new two-lane bridge, which is ~110 m long, albeit with a similar average soffit height to the existing one-lane bridge (55 m long). The new bridge abutments will be further back than the existing bridge abutments on both right and left banks – more so on the left (west) bank which will be a further 28 m further away from the channel (Figure 4-2).
Widening the adjacent floodplain on the left bank will entail the removal of the existing stopbank and constructing a new section of stopbank further back from the channel bank to provide more room for the river under the new bridge (Figure 4-2). The existing stopbank along the vegetated left bank will be removed, with the new curved stopbank tying back in with the existing stopbank at either end of the marked red line (Figure 4-2).
Figure 4-2: Stormwater discharge points (blue ellipses). New stopbank (red line) on the left (western bank). The present stopbank (dotted line) is adjacent to the vegetation along the channel bank. The crosshatched area is a new farm race on the property to replace the existing one. Source: Drawing DRG-WD- 1452-A, Aurecon NZ Ltd.
This widening of the waterway to give more room for the river is beneficial to improving the hydraulic capacity under the bridge for both coastal and riverine (fluvial) flood flows (and to some extent moderate tsunami flows), with the new abutments and stopbanks imposing less impedance on flows compared with the hydraulically-constrained waterway under the existing bridge (refer to Aurecon NZ Ltd (2019) for details on hydrodynamic flood modelling).
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The raised western approach embankment will be similar or slightly higher than the present embankment (Figure 3-2), but essentially will not materially change the exposure of the adjacent land to coastal and fluvial flooding beyond the western Project extent (Figure 1-1), as exemplified by the flood in 2017 of this area (Figure 3-2).
De-construct abutments of existing bridge The river flood report (Aurecon, 2019) demonstrates the effect of the constrained waterway under the existing bridge crossing on the backwater effect of extreme floods e.g., the 1% AEP river flood. There would be improvement in reducing the backwater effect on adjacent land by removal of the existing bridge, the western abutment and particularly the right-bank (eastern) abutment which acts as a hydraulic control.
The main benefit for de-commissioning the existing bridge and the eastern abutment relates to extreme fluvial floods, rather than coastal storm-tide flows propagating upstream, given the flow velocities for the latter will be substantially slower than for large river floods.
Assessment: This widening of the waterway through a longer bridge and moving back a section of stopbank to provide more room for the river is beneficial to improving the hydraulic capacity under the bridge for both coastal and riverine (fluvial) flood flows (and to some extent moderate tsunami flows), with the new abutments and stopbanks imposing less impedance on flows. The main benefit for de-commissioning the existing bridge and the eastern abutment relates to extreme fluvial floods, rather than coastal storm-tide flows propagating upstream.
4.1.3 Stormwater discharges (effect on coastal processes excluding water quality) The Stormwater technical report (Aurecon, 2019a) describes the terrestrial capture, transmission, and discharge of stormwater from within the Project extents during the operational life of the Project and is outlined in Drawing 254914-3500-DRG-WD-1452-A (Aurecon NZ Ltd), which is partially reproduced in Figure 4-2 (ellipses show stormwater discharge locations).
Most of these outlets would not discharge directly into the CMA and provided the outlet area of overland flowpath is sufficiently protected from soil erosion (e.g., rip-rap), the physical discharge of additional freshwater via the stormwater drains would have negligible effect on coastal physical processes within the channel. This assessment does not include the in-situ water quality aspects relative to the level of stormwater treatment at source (see Stormwater technical report, Aurecon, 2019a).
Assessment: Most of these outlets would not discharge directly into the CMA and provided the outlet area of overland flowpath is sufficiently protected from soil erosion (e.g., rip-rap), the physical discharge of additional freshwater via the stormwater drains would have negligible effect on coastal physical processes within the channel. This assessment does not include in-situ water quality aspects relative to the level of stormwater treatment at source.
4.1.4 Climate change (sea-level rise) Section 7(i) of the RMA, together with Policy 24 of the NZCPS, require the effects of climate change to be assessed for at least 100 years for coastal hazards.
Ongoing sea-level rise (SLR) for several centuries will become the dominant influence on coastal hazards, raising tides, storm surges and tsunami above the rising base mean sea level.
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Secondary effects of climate change for coastal processes will be changes in storm surge (waves are not relevant at the Project site), however changes to storm surges are likely to be modest in the range 0–5% from previous analysis done by NIWA (unpublished) and not considered further in this assessment.
Rainfall will become more intense, which has been included as a sensitivity testing for the river flood modelling (Aurecon, 2019).
As discussed in Section 2.3.4, the 2017 MfE coastal guidance recommends stress-testing infrastructure for the effects of coastal climate change for a range of four SLR scenarios (Table 2-1). For this assessment, these four NZ-wide SLR scenarios were combined with: i) an assumed extrapolated subsidence in vertical land movement of ~0.5 mm/yr (see Section 2.3.4); and, (ii) 1% AEP storm tide levels (SLS2 design requirement – section 3.2.4), to stress test clearances under the new bridge soffits for storm-tide levels only (in the absence of high river floods), as listed in Table 3-3.
The range of design storm-tide water elevations for the 1% AEP storm tide (excluding river floods) combined with these four SLR scenarios is 1.95–2.24 m OPT-64 by 2070 (50 years) rising to 2.20– 3.01 m OPT-64 by 2120 (100 years). The new bridge soffit levels in the proposed sloping-deck design range from 3.04 m (western abutment) up to 3.65 m (eastern abutment).
The new Kaeo bridge substructure will therefore just have sufficient clearance to not impede tidal flows during large storm tides with the range of projected SLR up to ~1.5 m SLR but does not include any hydraulic freeboard allowance22 (e.g., for local waves, debris dams) or coinciding river floods.
In contrast, the 1% AEP river flood level on a spring high tide (without SLR) would reach 3.7 m OTP (Aurecon NZ Ltd, 2019), and thus reach above the soffit, especially at the western end of the bridge. In terms of storm-tide and river flood combinations, these more extreme river flood events will tend to mostly “wash out” the storm-tide influence within the confined tidal river stretch through the Project area (which is about halfway between the Kaeo Fire Station gauge (KFS), with little tidal influence and the more open estuary gauge at Whangaroa Road (KWH). Therefore, the combined effects of coastal and river flooding under the bridge were not considered further, with river floods dominating and more critical for effects assessment. Note that there may be combined river and coastal flooding effects on water levels in the wider floodplain e.g., west of the western embankment similar to the situation in Figure 3-2, but any combined effects beyond the Project area would occur despite the new bridge development.
Therefore, leaving aside a freeboard allowance, there is just enough clearance beneath the new bridge soffits for the 1% AEP coastal storm-tide flows to pass unimpeded under the bridge girders for a SLR up to ~1.5 m (which could occur at the end of the 100-year design life). However, if a 0.6 m freeboard allowance is factored in (as recommended in the 2018 NZTA Bridge Manual), the new bridge could only accommodate a SLR of 0.9 m as the base MSL for a 1% AEP storm-tide event, which could occur from 2090 onwards (MfE, 2017; Table 11).
Assessment: The soffit levels of the proposed bridge design provides just enough clearance for the 1% AEP coastal storm-tide flows to pass unimpeded under the bridge girders for a SLR up to ~1.5 m (which could occur at the end of the 100-year design life). However, if a 0.6 m freeboard allowance is
22 Normally the minimum advised freeboard clearance under the soffit is 0.6 m if large trees are unlikely to jam against the bridge – NZTA (2018; Table 2.4)
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factored in, the new bridge could only accommodate a SLR of 0.9 m as the base MSL for a 1% AEP storm-tide event – a threshold that could be reached from 2090 (70 years) onwards if present high global carbon emissions continue unabated.
In terms of storm-tide and river flood combinations, more extreme river flood events (e.g., 1% AEP event) will tend to mostly “wash out” the storm-tide influence within the confined tidal river stretch in the Project area, so combined effects of coastal and river flooding under the bridge were not considered further, with river floods likely to dominate extreme total water level (leaving aside tsunami).
4.2 Temporary effects (construction and de-construction) This section provides an assessment of the main effects on coastal physical processes that could arise from temporary works associated with the construction or de-commissioning activities.
Temporary staging structures to support working platforms are required for construction of the new bridge piers and piles and fitting precast girders in place (see orange areas of Figure 4-3). Sections of these piled platforms will temporarily occupy the riverbed and the airspace above the river in the CMA. Temporary access to the new bridge construction is proposed via a temporary haul road from the western extent of the Project alongside the proposed western embankment (Figure 4-3).
A narrower, lighter temporary staging platform will be installed on the upstream side of the existing one-lane bridge for pedestrian access for the de-construction team (red area in Figure 4-3).
Figure 4-3: General layout of temporary construction platforms, haul road and lay-down area (top panel) and side elevation looking downstream of relativity of staging to the new bridge substructure (bottom panel). Source: DRG-BB-1406-A (Aurecon NZ Ltd).
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4.2.1 Temporary platform structures A temporary staging platform is proposed for access for construction machinery and personnel from the western side across the main river channel to the eastern pier site of the new bridge, but not across the deepest section of the river near the right bank (where access via crane will be from the eastern abutment).
The proposed construction of the main staging platform includes driving individual piles (diameter to be determined, but considerably smaller than the 1.5 m diameter permanent columns) at approximately 7–8 m spacing (Figure 4-3).
Temporary piles will also support smaller platforms adjacent to the piers to facilitate construction of the pier caps and pile columns for the new bridge – with two of the staging platforms in the CMA – the other being on land (Figure 4-3).
There is potential for local scour around these temporary piles positioned within the main tidal channel, noting the piles nearer the centre of the channel will be driven deeper to mitigate the effects of local scour on the integrity of the temporary structures. Once the piles are removed after construction, any remnant local scour holes in the riverbed will be covered over by sediment transport and sedimentation induced by higher spring tide flows and/or river floods. Therefore, the effect of staging-platform piles on causing local scour will be a temporary minor effect.
The piles supporting the staging platforms will cause some temporary modification to the channel flow at all tidal and river flood elevations for the duration of construction. This reflects a reduction in the net flow area in this location when considering the cumulative flow blockage of the temporary staging piles, together with the permanent column piles of the new bridge as they are successively built. We understand that the de-construction of the existing bridge will occur after all temporary staging for the new bridge is removed.
The mitigation measures factored into in the construction methodology (Figure 4-3) to minimise the flow impedance are:
i) to avoid placing piles in the deepest part of the channel on the eastern side where the strongest tidal and flood flows occur
ii) aligning pile groups and the staging platforms with the river flow direction, which means they will need to be placed at approximately 20° angle relative to having them normally perpendicular to the bridge deck (as shown schematically in Figure 4-3)
iii) installing the pedestrian-access staging platform, for de-construction of the existing bridge and removal of the eastern abutment, after the main staging platforms for the new bridge are removed (to avoid having piles from 4 bridges cumulatively impeding the river flow at the same time).
These mitigation measures will thereby reduce the overall impedance of the tidal and flood flows during construction and also reduce the local scouring effect as far as practical, with pile groups in line with the river flow. With such measures in place, the temporary-staging piles would present a 5– 6% reduction in flow cross-section below MHWS-10 – using the average flow area from Figure 3-5 and assuming temporary pile diameters of ~0.6 m aligned with the river flow. The effective flow impedance of these piles would be less than the 5–6% reduction when weighted by the main flow through the deepest section of the channel, where there would be no staging platform. Therefore,
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the effect of the temporary-staging piles on flow impedance would be minor, assuming no staging platform is located in the deeper part of the channel and pile groups are aligned with the river flow direction.
The soffit of temporary staging platform in the indicative construction methodology (Figure 4-3; bottom panel) is shown to be around or above the soffit level of the permanent pier caps at approximately 1.35 m OTP-64, which is 0.3 m above MHWS-10 at the Project site (Figure 3-5), and is equivalent to a 2-year ARI storm-tide event (not considering river floods). There is a modest chance of such an event occurring in a 9–12 month construction period, but any effects on the temporary staging and personnel safety can be further mitigated through responding ahead of storm-tide forecasts (noting the most serious storm-tides occur during high perigean-spring or “king” tides which are predictable23) and there is no staging across the deeper channel section where the main flow occurs. Additional effects on coastal physical processes of such an overtopping event (if it were to occur) in relation to the temporary staging platforms would be minor, other than potentially local scour around the piles or river-flood debris effect being exacerbated.
Any impedance on recreational boating from the temporary staging is likely to be negligible (other than closing of area while de-construction takes place or new-bridge girders are being installed).
Assessment: There will be a minor effect on flow impedance from temporary piles within the main channel as the effect has been minimised by: i) aligning the pile groups for the temporary platforms to the river current-flow direction; ii) having no main staging platform or piles across the deepest part of the river cross-section; iii) installing the pedestrian-access staging platform (for de- construction of the existing bridge and removal of the eastern abutment) after the main staging platforms for the new bridge are removed.
There would be only minor effects on coastal physical processes such as sedimentation and tidal flows if the staging platforms were overtopped by a storm-tide event exceeding the 2-year ARI level during the relatively short construction window (but not considering river floods). Any effects on the temporary staging and personnel safety can be further mitigated through response procedures ahead of storm-tide forecasts. Further, there is no major staging across the deeper channel section where the main flow occurs (apart from the smaller-scale pedestrian-access platform adjacent to the existing bridge).
4.2.2 Sediment run-off and disturbances during floodplain works (west bank) Potentially, one of the key environmental risks to coastal physical processes and aquatic habitats is the potential for sediment runoff to the CMA or the upstream coastal river during the removal of the present stopbank along the left (western) bank (see dotted line in Figure 4-2), after the new stopbank is constructed, set back further on the floodplain. During the removal process, no works are envisaged in the CMA or coastal river waterbody, so there would be no direct disturbances to the riverbed. Some vegetation removal may be required.
Fortunately, the potential risk of sediment runoff, causing elevated turbidity downstream (depending on the tidal flow direction), can be mitigated to the level of a minor effect, provided:
23 See NIWA’s red-alert tide days calendar: https://www.niwa.co.nz/natural-hazards/physical-hazards-affecting-coastal-margins-and-the- continental-shelf/Storm-tide-red-alert-days-2019
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Heavy-duty silt fences are installed to ring-fence the exposed earthworks and for the transition period while new vegetation (grasses) are established.
Where possible, the earthworks nearest the river channel are largely undertaken during the lower tide periods (below MSL), and the area secured if river flooding or storm-tide events are forecast.
Any necessary mangrove removal on the flank of the channel is undertaken by hand (cut off at base) at lower tides (below MSL) to minimise sediment generation and dispersal, with removed plants to be disposed off-site.
The new stopbank (Figure 4-2) is constructed and grassed plus the new farm raceway completed before the existing stopbank is removed, which will considerably reduce the risk of sediment runoff during construction of these two elements of the Project.
Assessment: Potentially, one of the key environmental risks to coastal physical processes and aquatic habitats is the potential for sediment runoff to the CMA during the removal of the present stopbank along the left (western) bank. The risk of causing elevated turbidity downstream (depending on the tidal flow direction), can be mitigated to the level of a minor effect, provided comprehensive sediment and erosion control measures are in place, planning when earthworks, and any mangrove removal required, is to be undertaken adjacent to the river channel and staging the construction of the new stopbank and farm race earthworks before removal of the existing stopbank.
4.2.3 Disturbance of seabed – piles and sheet-piling Disturbance of the seabed within the CMA will occur during the following works:
a. Driving of piles to support the temporary staging or foundation works for the permanent column piles or new eastern abutment.
b. Extraction of piles and any associated sheet-piling to remove the temporary staging.
These potentially adverse activities, while localised in extent and short-lived, will still require work practices and erosion/sediment control measures that minimise seabed disturbance and hence release of suspended-sediments to the receiving waters, thereby minimising the effects on existing water clarity from increased turbidity.
The disturbance of the seabed on installation and subsequent removal of the temporary works is expected to be minimal (including turbidity after allowing for reasonable mixing) and full restoration of the seabed from the disturbances is anticipated within weeks (especially on spring-tides) or higher river flows, due to both the limited area of disturbance and the moderate peak tidal flows that are present at this location.
Assessment: Potentially, pile or sheet-pile driving or extraction activities could cause localised release of suspended-sediments to the receiving waters from riverbed disturbances. Work practices and erosion/sediment control measures (detailed within the CEMP) that minimise seabed disturbance would minimise the effects on existing water clarity from increased turbidity to the level of being a minor, short-lived effect.
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4.2.4 De-construction and removal of eastern abutment The de-construction of the existing one-lane bridge (after vehicles commence using the new bridge) will need to be undertaken with careful planning given it occurs over the CMA, with potential for construction debris and dust to affect the aquatic environment.
Bridge de-construction is a specialist area of expertise and there are a number of methodologies that could be employed. The contractor will develop their own preferred methodology and mitigation measures (e.g., dust and debris controls) for removal of the bridge superstructure. However, it is envisaged that the contractor will install a temporary staging platform for personnel and light machinery access on the upstream side of the existing bridge (Figure 4-3) and with heavy machinery working from the existing bridge and/or existing abutments. The bridge superstructure will be removed span by span through supporting and saw-cutting sections of the deck to be lifted out by crane positioned on the existing bridge or abutments, the pile caps will then be supported and removed.
The existing piles will be very difficult, if not impossible, to completely remove as this would require pulling them out of the seabed where they have been in place for decades. If they cannot be removed with modern vibrating machinery, the intention would be to cut them as close to bed level as possible. If the removal is undertaken by clamping the pile above and below the cut point, avoiding disturbance of the seabed by keeping the bottom section of the clamp will mean the cut level to be slightly above the existing bed. However, it is probable that local scour holes exist around these long-standing piles, so sedimentation would tend to eventually cover the remnant pile stumps protruding above the bed level (but maybe temporarily re-exposed during extreme river floods posing a negligible effect on the coastal-river geomorphology).
Removal of previous fill or concrete works on the abutments to the existing bridge is necessary, especially on the eastern abutment. Similar to bridge de-construction, the contractor will develop their own preferred methodology and mitigation measures (e.g., dust and debris controls) for removal of the previous fill and structural elements in the abutments, which are above MHWS, to return to the original land or rock outcrop contours.
Assessment, both sites: Minor effect on coastal physical processes, for removal of the bridge and adjacent abutments, if debris and dust controls are in place to minimise discharges to the CMA (through mitigation measures and works practices to be defined in the CEMP) and the existing piles are cut at or just above the existing riverbed.
4.3 Risk screening assessment To summarise, a risk-screening exercise was undertaken on impacts of the Project and the completed form of the bridge/causeway works on coastal physical processes, adapting the methodology outlined in the Coastal Effects Assessment Guideline (NZTA 2017). Environmental or natural hazard risk or impact is described in terms of both the likelihood of impacts as well as the possible consequences, which are both qualitatively assessed.
The risk-screening assessment for the operational phase of the Project for the Kaeo River bridge Project are provided below in Table 4-1.
Overall, the potential environmental risks with respect to coastal processes are low if the proposed mitigation measures and specimen design features are implemented.
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Table 4-1: Risk screening assessment for potential environmental effects on coastal physical processes from the 100-year operational phase of the Project. Risk screening components [Risk = likelihood x consequences]. Likelihood [Unlikely, Likely, Very likely] Consequences [Low, Medium, High] Risk [Low, Moderate, High].
Risk screening assessment
Works/activities Description of environmental Risk mitigation or effects assumptions/comments Risk Risk Likelihood (mitigated) Consequence
Bridge structure, Alteration of waterway flow A beneficial effect with the wider piers/piles in the capacity e.g., tidal prism, tide waterway (and removal of eastern CMA and range. abutment of the existing bridge). existing-bridge Modification of natural water flows Unavoidable – minor impact through abutments and sedimentation processes. local scour around the new column removed. piles, but negligible effect at the cross- section scale.
Impact on changes in flows Beneficial effect from the wider bridge affecting recreational boating. span over the deepest channel section. Effects of coastal climate change Moderate risk on the bridge (and flood e.g., sea-level rise and storm-tides effects) towards the end of the design over the 100-year operational life from storm-tide levels or combined lifetime (to 2120). storm-tide and river flood levels, if high global carbon emissions continue and the soffit level if the specimen design is retained and requires invoking a freeboard allowance (e.g., 0.6 m, NZTA Bridge Manual). Other detailed design features could be to built in to improve the future flexibility for adaptation to SLR to support a jacked-up bridge deck in the future as required. Stormwater Additional sediment load causing Minor impact with mitigation e.g., discharges increased turbidity and overland flowpath from outlets is sedimentation rates on intertidal sufficiently protected from soil erosion shoals and banks. (e.g., rip-rap) and sufficient treatment of stormwater at source (see Stormwater Report).
All Cumulative adverse effects on local Negligible cumulative impact – and regional waterways. beneficial for flood hazards from a wider waterway perspective.
The risk-screening assessment for the construction phase of the Project for the new SH10 Kaeo Bridge and de-construction of the existing one-lane bridge and abutments are provided below in Table 4-2.
Overall, the potential environmental risks with respect to coastal physical processes are low if the proposed and suggested mitigation measures are implemented via a Construction Environmental Management Plan (CEMP).
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Table 4-2: Risk screening assessment for potential environmental effects on coastal physical processes from the construction phase of the Project. Risk screening components [Risk = likelihood x consequences]. Likelihood [Unlikely, Likely, Very likely] Consequences [Low, Medium, High] Risk [Low, Moderate, High].
Risk screening assessment
Works/activities Description of environmental Risk mitigation or (bridge No.) effects assumptions/comments Risk Risk Likelihood (mitigated) Consequence
Temporary Alteration of waterway flow Negligible impact bridge structure capacity e.g., tidal prism, tide piers/piles or range. sheet-piling. Modification of natural water flows Potential impedance of the flow from and sedimentation processes (e.g., multiple piles and local scour. local and general scour). Mitigation: i) design avoids placing temporary piles in the deepest part of the channel; ii) aligning pile groups under the staging platforms with the river flow direction; iii) installing the pedestrian-access staging platform, for de-construction of the existing bridge, after the main staging platforms for the new bridge are removed – thereafter a minor impact. Temporary impact on recreational Negligible impact (other than closing of boating. area while de-construction takes place or girders being installed). Physical disturbance of seabed/ Minor impacts from short-lived pile or turbidity plumes. sheet-pile driving or pile extraction activities, which could cause localised release of suspended-sediments to the receiving waters from riverbed disturbances, but likely to produce limited effects from turbidity after allowing for reasonable mixing. Sediment run- Potential for sediment runoff to the Mitigated to the level of a minor effect, off and CMA during the removal of the provided comprehensive sediment and disturbances present stopbank along the left erosion control measures are in place, during (western) bank causing turbidity planning when earthworks, and any floodplain works and sedimentation. mangrove removal required, is to be (on west bank). undertaken adjacent to the river channel and staging the construction of the new stopbank and farm race earthworks before removal of the existing stopbank. De-construction Potential for sediment runoff or Minor impact on coastal physical of existing SH10 debris and dust being discharged to processes, for removal of the bridge bridge and the CMA. and adjacent abutments, if debris and removal of dust controls are in place to minimise eastern discharges to the CMA (through abutment. mitigation measures and works practices to be defined in the CEMP) and the existing piles are cut at or just above the existing riverbed.
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4.4 Assessment against regulatory standards or technical criteria/guidelines Arising from the risk-screening and assessment processes for assessing environmental risks from the long-term operation of the new SH10 bridge across Kaeo River, the permanent (operational) risks or effects are minor or negligible, in relation to coastal physical processes both presently and with sea- level rise up to ~1.5 m (which could occur at the end of the 100-year design life) or a lesser 0.9 m sea- level rise if a 0.6 m hydraulic freeboard allowance is required to be implemented in the design.
It has been assumed that combined extreme river flood and storm-tide events coinciding will be dominated by a large river flood – with the flood assessments covered in the Aurecon (2019) stormwater and hydraulic modelling report in relation to NZTA Bridge Manual requirements.
Given the existing one-lane bridge will be removed along with the eastern abutment (which acts as a hydraulic control point of flood levels), the new longer bridge (albeit at a similar soffit height) provides an improvement with the wider waterway including the set-back of the stopbank on the western bank.
Similarly, the risk-screening process for assessing environmental risks arising from construction of the new SH10 bridge across the Kaeo River in the short-term (construction), environmental risks or effects on coastal physical processes are minor or negligible, provided the proposed mitigation improvements are implemented in the construction phase. This includes mitigation of the potential risk of sediment or debris/dust run-off, using robust erosion and sediment control, during removal of the section of the present stopbank on the western side (after the new re-curved stopbank is completed) and debris/dust management measures during the de-construction of the existing bridge and removal of the eastern abutment. As such, there would be negligible turbidity effects on designated areas in Whangaroa Harbour of outstanding or high natural character (Figure 2-6) and the Marine 3 (Marine Farm) management Areas (Figure 2-7).
This assessment considered the discretionary activities described the RCP-N (see Section 2.3.3) and in general accordance with statutory criteria and national guidance such as the NZCPS and the 2017 MfE Coastal Guidance, notwithstanding it is not practical in this situation to re-locate this critical road link and associated bridge away from areas of hazard and climate-change risk (Policy 25(d) - NZCPS).
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5 Summary and conclusions The Kaeo Bridge Project proposes to re-align a 550 m section of SH10 and construct a new longer 100-m dual-lane bridge across the Kaeo River, approximately 45 m upstream from the existing single- lane bridge.
This report assesses the effects that the Project has with respect to coastal physical processes in the coastal environment and assumes for the purposes of the assessment that the coastal river section upstream of the existing bridge has essentially similar coastal/tidal characteristics to the CMA just downstream of the existing bridge (noting the CMA boundary will eventually be moved upstream with ongoing sea-level rise). Both temporary effects during construction and those effects that may accrue over the 100-year operational life of the Project were considered separately. No reclamations or impoundments, such as causeways, are planned in the CMA or coastal river section.
In assessing physical coastal effects (excluding marine ecology, ecological effects of mangrove removal, landscape/natural character, stormwater water quality and river flood hydrology effects), the main elements of the Project that were considered was the new bridge (mainly the substructure including piers), the benefit of widening the floodplain on the left (western) bank to provide more room for river floods under the new bridge (requiring a new re-curved stopbank) and the temporary staging platforms, which will partially require temporary occupation of the riverbed.
5.1 Summary of effects and mitigation measures With respect to coastal physical processes, the Project activities and permanent works (as per the specimen design) will only have minor or negligible effects or risks, provided the suggested mitigation measures for design features or construction are followed (Section 4, Table 4-1 and Table 4-2). The latter could be incorporated into the Construction Environmental Management Plan (CEMP), given the final detailed design and as-built methodology will depend on the selected contractor.
There are also some benefits arising from the Project, particularly the wider waterway and additional floodplain width under the new bridge, which will reduce flood elevations. Also, no piers or piles will be present in the deepest section of the channel, which means a more freely flowing river and unimpeded recreational navigation.
The only potential long-term issue is the soffit level in the specimen design of the new bridge, which on average is at a similar height as the present single-lane bridge. This will lead to a moderate risk on the bridge (and ensuing flood effects) towards the end of the 100-year design life from high storm- tide levels alone (with normal river flows) riding on the back of an upper-range sea-level rise projection (representing continuing high global carbon emissions). For this situation, the minimum freeboard allowance of 0.6 m recommended in the NZTA (2018) Bridge Manual(, would not be met (or apply) during high storm-tide events for the top two of four sea-level scenarios recommended in the Ministry for the Environment coastal guidance (MfE, 2017).
The effects of river floods, which explored sensitivity to sea-level rise and increased rainfall, are considered separately in the Stormwater Hydraulic Modelling Technical Report (Aurecon, 2019). These modelling results indicate that river floods dominate the combined water level at the proposed new bridge, with the present-day 1% AEP24 flood water level reaching 3.7 m Reduced Level (David Hughes, Aurecon, pers. comm.), compared with the new bridge soffit levels that slope from
24 AEP = annual exceedance probability (the chance an event will be reached or exceeded in any year)
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3.04 m (western abutment) up to 3.65 m (eastern abutment). This means a large present-day river flood acting alone, will produce a higher water level than a future 1% AEP storm-tide (+ sea-level rise), which would reach 3.0 m Reduced Level. From experience modelling such large flood events in coastal rivers, where the channel is confined, the larger river floods will mostly wash-out any coinciding storm-tide effect, leaving the river flood to dominate the total water level at the Project site. However, rising sea level will increase the baseline mean tide level in the coastal river, which could lead to a combined event of a moderate river flood and high storm tide that may also reach close to the proposed bridge soffit (although not modelled). In any case, a major river flood presents the highest risk to the performance and serviceability of the new bridge.
Some adaptive design features could be considered in the final detailed bridge design to provide future flexibility if the bridge deck is required to be lifted, if SLR effects on both storm-tides and river floods reduces the level of service towards the latter part of the operational life of the new bridge.Overall, if the proposed mitigation measures for the construction and de-construction phases are included, the effects of the temporary construction activities on physical coastal and estuarine processes would be minor or negligible. The environmental risks are best managed adaptively via a CEMP for all construction or de-construction areas.
5.2 Suggested coastal monitoring conditions The following coastal monitoring conditions are suggested to either:
Gather or document physical changes to the existing environment.
Best-practice construction or post-construction house-keeping.
Note that no requirement for compliance monitoring is recommended, such as field deployment of turbidity sensors, provided that the turbidity and sedimentation effects are mitigated through the CEMP and the development of the detailed construction methodology. Such compliance monitoring could be instigated as part of an adaptive monitoring approach if turbidity issues arise during construction, after allowing for reasonable mixing.
C.1 – The NZTA shall provide to the Northland Regional Council, plans and drawings including dimensioned, cross sections, elevations and site plans of all areas of permanent or temporary occupation of the CMA by permanent or temporary structures at least 20 working days before the proposed date of commencement of the construction including installation of temporary structures.
C.2 – The NZTA shall supply to the Northland Regional Council and the LINZ Hydrographic Services Office and LINZ Topographic Services Office (Chief Hydrographer, National Topo/Hydro Authority, Land Information New Zealand, Private Box PO Box 5501, Wellington 6145), a set of “as built” plans, final topographic and cross-sectional bathymetry data covering the finished works, including an underwater survey to confirm the cut piles of the existing bridge pose no recreational swimming or boating hazard. The appropriate certification should be supplied confirming that the new structures have been built in accordance with sound engineering practice, within 60 working days of the completion of all works.
C.3 – The NZTA shall maintain the site in good order and shall, as far as practicable, remedy all damage and disturbance caused by vehicle traffic, plant and equipment to the foreshores of the Kaeo River during construction, to the satisfaction of the Northland Regional Council.
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C.4 – Removal or pruning of vegetation in the CMA or river foreshores shall be limited to the areas of permanent and temporary occupation. Removal of any mangroves shall be by hand tools.
C.5 – The NZTA shall ensure the removal of all equipment, erosion and sediment control measures, surplus soil/fill sediment and construction materials from the CMA, the coastal riverbed or the river foreshores within 20 working days following the completion of the construction works, to the satisfaction of the Northland Regional Council.
C.6 – The NZTA shall maintain a log recording the source of any fill/rock material imported onto each reclamation or temporary and permanent occupation sites, with all fill to be clean fill as per MfE(2002) specification. This log shall be made available to the Northland Regional Council for inspection on request.
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6 References Ahsan, H., Howse, B. (2011) Kaeo River catchment flood risk assessment and option analysis. Paper presented to the Stormwater WaterNZ Conference, 2011. https://www.waternz.org.nz/Attachment?Action=Download&Attachment_id=1171
Aurecon NZ Ltd (2019) Northland Bridges – Kaeo. Stormwater Hydraulic Modelling Technical Specialist Report, Project 254914: 23. August 2019.
Aurecon NZ Ltd (2019a) Stormwater technical report, Aurecon NZ Ltd, Project 254914.
Beavan, R.J., Litchfield, N.J. (2012) Vertical land movement around the New Zealand coastline: Implications for sea-level rise. GNS Science Report 2012/29: 41. www.gns.cri.nz/static/pubs/2012/SR%202012-029.pdf
Church, J.A., Clark, P.U., Cazenave, A., Gregory, J.M., Jevrejeva, S., Levermann, A., Merrifield, M.A., Milne, G.A., Nerem, R.S., Nunn, P.D., Payne, A.J., Pfeffer, W.T., Stammer, D., Unnikrishnan. A.S. (2013) Sea level change. In: TF Stocker, D Qin, G-K Plattner et al. (eds) Climate Change 2013: The physical science basis. Cambridge: Cambridge University Press.
Conning, L. (1999) Natural areas of Whangaroa Ecological District Reconnaissance survey report for the Protected Natural Areas Programme. New Zealand Protected Natural Areas Programme No. 41, Dept. of Conservation, (Northland Conservancy): 194. https://www.doc.govt.nz/about-us/science-publications/conservation- publications/land-and-freshwater/land/northland-conservancy-ecological-districts- survey-reports/natural-areas-of-whangaroa-ecological-district/
DoC (2010) New Zealand Coastal Policy Statement 2010. Department of Conservation, Wellington: 28. https://www.doc.govt.nz/about-us/science-publications/conservation- publications/marine-and-coastal/new-zealand-coastal-policy-statement/new-zealand- coastal-policy-statement-2010/
DoC (2017) NZCPS 2010 guidance note: Coastal hazards, Objective 5 and Policies 24, 25, 26, 27. Published by the Department of Conservation, Wellington: 100. http://www.doc.govt.nz/Documents/conservation/marine-and-coastal/coastal- management/guidance/policy-24-to-27.pdf
Edbrooke, S.W., Brook, F.J. (compilers) (2009) Geology of the Whangarei area. Institute of Geologic & Nuclear Sciences 1:250 000 Geological Map. 2, 1 sheet + 68 p. Lower Hutt, New Zealand. GNS Science.
Heath, R.A. (1975) Stability of some New Zealand coastal inlets. New Zealand Journal of Marine and Freshwater Research, 9(4): 449-57.
Kopp, R.E., Horton, R.M., Little, C.M., Mitrovica, J.X., Oppenheimer, M., Rasmussen, D.J., Strauss, B.H., Tebaldi, C. (2014) Probabilistic 21st and 22nd century sea-level projections at a global network of tide-gauge sites. Earth’s Future, 2(8): 383–406. Retrieved from http://dx.doi.org/10.1002/2014EF000239.
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Land Information New Zealand (LINZ) (2008) Hydrographic chart NZ 5114; Doubtless Bay and Whangaroa Harbour. Published October 1977, new edition March 2017.
McKerchar, A.I., Pearson, C.P. (1989) Flood Frequency in New Zealand. Publ. 20, Hydrology Centre Christchurch (now NIWA).
Ministry for the Environment (2002) A Guide to the Management of Cleanfills. Publication ME418:65. https://www.mfe.govt.nz/publications/waste/guide-management-cleanfills
Ministry for the Environment (2017) Coastal hazards and climate change: Guidance for local government. Lead authors: Bell, R., Lawrence, J., Allan, S., Blackett, P., Stephens, S. Ministry for the Environment Publication No. ME 1341, ISBN: 978-1-98-852535-8. 279 p + Appendices. http://www.mfe.govt.nz/publications/climate-change/coastal-hazards-and- climate-change-guidance-local-government
NRC (2017) Proposed Northland Regional Plan and maps – September 2017 https://www.nrc.govt.nz/newregionalplan
NRC (2019) Proposed Regional Plan for Northland and maps – Appeals version 29 July 2019. https://www.nrc.govt.nz/newregionalplan
NZTA (2018) Bridge manual (SP/M/022), Third Edition, Amendment 3. Published by the NZ Transport Agency, effective from October 2018. ISBN 978-0-478-37161-1. https://www.nzta.govt.nz/resources/bridge-manual/bridge-manual.html
NZTA (2017) Coastal effects assessment guideline for transportation infrastructure. Version 004, NZTA Report, March 2017: 39. ISBN 978-1-98-851216-7. https://www.nzta.govt.nz/assets/Highways-Information-Portal/Technical- disciplines/Air-and-climate/Climate-change/Adaptation/Coastal-Effects-Assessment- Guideline-FINAL-March2017.pdf
Power, W. (2014) Tsunami hazard curves and de-aggregation plots for 20 km coastal sections, derived from the 2013 National Tsunami Hazard Model. GNS Science Report 2013/59, Jan 2014: 544. http://www.gns.cri.nz/static/WillPower/SR_2013-059.pdf
Stephens, S.A., Bell, R.G., Haigh, I. (online – in review) Spatial and temporal analysis of extreme sea level and storm surge events around the coastline of New Zealand. Natural Hazards and Earth System Sciences. https://www.nat-hazards-earth-syst-sci- discuss.net/nhess-2019-353/
Tonkin + Taylor (2016) Coastal flood hazard zones for select Northland sites. Final Report prepared for Northland Regional Council by Tonkin & Taylor Ltd (May 2016). Retrieved from: http://www.nrc.govt.nz/contentassets/53a645abaf944d6b9eddd85177b88565/tonkin- taylor-coastal-flood-hazard-assessment-report-2016-web.pdf
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