ATTACHMENT 5

Geological Assessment (Tonkin & Taylor)

Job No: 1007709 10 January 2019 McConnell Property PO Box 614 1140

Attention: Matt Anderson

Dear Matt

Orakei ONF Assessment 1- 3 Purewa Rd, Meadowbank

Introduction McConnell Property is proposing to undertake the development of a multi-story apartment building at 1 - 3 Purewa Road, Meadowbank. The property is located within an area covered by the Outstanding Natural Feature (ONF) overlay of the Auckland Unitary Plan. The overlay relates to the volcano located to the west of the property. The ONF overlay requires consent for the earthworks and the proposed built form associated with the development of the site. McConnell Property has commissioned Tonkin & Taylor Ltd (T+T) to provide a geological assessment of the property with respect to both the ONF overlay and the geological characteristics of the property. The purpose of the assessment is to place the property in context of the significant geological features identified by the ONF overlay, and to assess the geological effects of the proposed development.

Proposed Development The proposal (as shown in the architectural drawings appended to the application) is to remove the existing houses and much of the vegetation from the site, and to develop the site with a new four- storey residential apartment building with a single-level basement for parking. The development will involve excavation of the site, which will require cuts of up to approximately 6m below existing ground level (bgl). The cut depths vary across the site, resulting in the average cut depth being less than 6m bgl.

Site Description The site is located at the end of the eastern arm of the ridgeline that encloses the Orakei Basin (Figure 1). The property is set back approximately 25 m from the edge of the Orakei Basin and is currently occupied by two semi-detached houses (Figure 2). The property slopes moderately towards the west. Immediately west of the property boundary the topography steepens significantly as it descends to the Purewa Creek. This is illustrated in a sketch cross-section through the property presented as Figure 3.

Tonkin & Taylor Ltd | 105 Carlton Gore Rd, Newmarket, Auckland 1023,

PO Box 5271, Wellesley St, Auckland 1141 P +64-9-355 6000 F +64-9-307 0265 E [email protected]

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Some modification of the site appears to have occurred as a result of developing these houses and sub-basement levels.

Published Geology The Orakei Basin represents the flooded remains of an explosion crater formed from a phreatic (steam) eruption bought about from basaltic magma encountering groundwater at a relatively shallow depth. The explosion(s) created the existing 800 m diameter explosion crater through a combination of material being ejected into the air and from the surrounding country rock and ejecta collapsing back into the crater as a series of landslides. The ejected material was deposited upon the surrounding landscape to form a tuff ring approximately 1 km wide. The published geology of the Orakei Basin1 and its surrounds is shown in Figure 4. It can be seen that the subject property is located with the inside edge of the tuff ring. The tuff ring itself extends approximately 700 m further to the east of the property. In total the tuff ring covers an area of approximately 6 km2 and covers parts of Meadowbank, Orakei and . The Orakei Basin volcano appears to have ceased activity upon the completion of the phreatic eruption stage of the basaltic eruptive sequence, not advancing to the stage of scoria cone or lava flow development. There are a number of other similar explosion craters in Auckland such as the , Onepoto volcano, volcano, Pukaki volcano and Mangere Lagoon volcano.

Orakei Basin Volcano A 3D topographic model of the Orakei Basin and surrounding area is presented in Figure 5. It illustrates the following notable features:  The explosion crater is approximately circular in shape and defines the general size and shape of Orakei Basin;  The inside slopes of the tuff ring have collapsed back into the explosion crater. This is particularly clear in the southern part of the crater;  The Purewa Creek developed or re-established its main west-east channel and its southern tributary channel around northern and eastern edges of the explosion crater once eruption activity ceased;  Erosion along the flanks of the Purewa Creek appears to have removed the northern and eastern sides of the explosion crater to below current sea level. Recently completed geotechnical boreholes undertaken by T+T at the subject property has proven the presence of variably welded tuff to a depth of at least 11 m. It is apparent from this, the topography model (Figure 5) and the view from Kepa Road (Figure 6) that the property at 1-3 Purewa Road is located within the tuff ring but lies some distance outside of the original explosion crater. The most distinctive topographic feature associated with the subject property is the west-facing slope that extends to the Orakei Basin. Although this slope appears to be a continuation of the explosion crater when viewed from across the basin, this slope is set back from the explosion crater and is entirely non-volcanic in origin. The topography of the site, and the west facing slope in particular, has in fact been formed by the southern tributary of the Purewa Creek cutting down into the tuff ring. The land surrounding the Orakei Basin has been developed with residential housing. Because of its urbanisation, the presence of the wider tuff ring is almost entirely obscured and is indistinct from

1 Kermode, L.O. 1992. The geology of the Auckland urban area. Scale 1:50,000. Institute of Geological and Nuclear Sciences.

Tonkin & Taylor Ltd 10 January 2019 Orakei ONF Assessment, 1-3 Purewa Road, Meadowbank Job No: 1007709 McConnell Property

3 the surrounding undulating terrain underlain by the marine sediments of the East Coast Bays Formation (ECBF).

Orakei Basin ONF The Outstanding Natural Features (ONF) and Outstanding Natural Landscapes (ONL) overlays are included in Chapter D10 of the Auckland Unitary Plan – Operative in part (AUP). The extent of the Orakei Basin volcano ONF overlay is shown on Figure 7. Its eastern boundary has been set to align with the western limit of Puroto Street. The northern boundary of the ONF has been set within the railway corridor, thus incorporating Purewa Road. The ONF includes the eastern bank of the southern tributary of the Purewa Creek, even though this is a non-volcanic topographic feature formed after the cessation of volcanic activity. It can be seen from a consideration of the geological deposits (Figure 4) and the extent of the ONF (Figure 7) that the ONF encloses only a small part of the overall tuff ring. Its outer boundary corresponds to property and road boundaries and not geological features. Schedule 6 of the AUP presents details of the overlay that are specific to each ONF. This is reproduced in Table 1. From the description provided in Schedule 6, it appears that the Orakei Basin volcano ONF reflects the presence of the explosion crater and part of the surrounding tuff ring, but not specific geological features of note such as an exposure or outcrop. The property is located some 230 m north-east of the nearest exposures of the explosion crater. There are no outcrops or exposures of the volcanic deposits that are visible to the public, with the exception of those limited exposures present within the southern cliffs of the explosion crater and the limited number of small exposures adjacent to the pedestrian path that follows part of the basin edge. There are no exposures present within the subject property or any other unique or notable geological features.

Table 1: Entry in Schedule 6 of the AUP for the Orakei Basin volcano

ID Name Location Site Description Unitary Type Plan Criteria 143 Orakei Orakei V Ōrākei Basin is a volcanic explosion crater and a, c, d, e, f, Basin Basin large tuff ring (1km in diameter). The tidal h, i, l, b, k volcano inlet was formed when the sea entered Purewa Creek valley and breached a former freshwater lake that occupied the crater. Subsequently, the basin was closed off by the railway embankment and the water level and flushing of the basin is now controlled. Sediment cores taken from Ōrākei Basin revealed 90 ash layers deposited by eruptions from other volcanoes over the past 90,000 years

Tonkin & Taylor Ltd 10 January 2019 Orakei ONF Assessment, 1-3 Purewa Road, Meadowbank Job No: 1007709 McConnell Property

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Assessment

Scheduling of the Orakei Basin Volcano ONF The factors set out in B4.2.2(4) of the AUP have been used by Council to schedule ONF’s. Council has assessed that criteria a, c, d, e, f, h, i, l, b, k (underlined below) apply to the Orakei Basin volcano ONF: a) the extent to which the landform, feature or geological site contributes to the understanding of the geology or evolution of the biota in the region, New Zealand or the earth, including type localities of rock formations, minerals and fossils; b) the rarity or unusual nature of the site or feature; c) the extent to which the feature is an outstanding representative example of the diversity of Auckland's natural landforms and geological features; d) the extent to which the landform, geological feature or site is part of a recognisable group of features; e) the extent to which the landform, geological feature or site contributes to the value of the wider landscape; f) the extent of community association with, or public appreciation of, the values of the feature or site; g) the potential value of the feature or site for public education; h) the potential value of the feature or site to provide additional understanding of the geological or biotic history; i) the state of preservation of the feature or site; j) the extent to which a feature or site is associated with an historically important natural event, geologically related industry, or individual involved in earth science research; k) the importance of the feature or site to Mana Whenua. It is noted that there is no criterion ‘l’ in B4.2.2(4). We provide our assessment against the relevant criteria as follows: (a) Orakei Basin is one of a number of water-filled explosion craters (maar) in Auckland. Whilst the Orakei Basin itself contributes to the overall understanding of the (AVF), the subject site does not as the landscape in this area is largely of non-volcanic origin having been formed by the Purewa Creek cutting through the tuff ring post-eruption. The sequence of volcanic eruptions recorded within the sediments of the marine basin are of geological significance, however these are not present on the subject site. Furthermore the tuff deposits that underlie the site are not of geological significance as these are present over large areas of the Auckland isthmus; (b) As noted previously, the Orakei Basin is one of a number of similar features in Auckland. Other examples include the Panmure Basin, Onepoto volcano, Tank Farm volcano, Pukaki volcano and Mangere Lagoon volcano. We do not consider the Orakei Basin to be a rare or unusual geological feature in an Auckland context; (c) As for (b) the Orakei Basin is one of a number of similar features in the AVF. It does not contain any geological feature that we would consider to be outstanding, however the volcanic feature does contribute to the overall diversity of Auckland’s natural land forms and features. The subject property does not contain any geological features of note. Indeed its most obvious characteristic (its western slope) is not volcanic in origin, and is not remarkable in the context of the volcanic geology of the Auckland isthmus; (d) The basin is recognised as being one of a number of similar features within the AVF; (e) Not a geological issue; (f) Not a geological issue;

Tonkin & Taylor Ltd 10 January 2019 Orakei ONF Assessment, 1-3 Purewa Road, Meadowbank Job No: 1007709 McConnell Property

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(g) While this is not a factor for which the ONF has been scheduled, the value of the site to public education is negligible given the lack of exposures or other geological features within the site; (h) The educational value of the site is limited given the lack of exposures and the topography and geomorphology reflecting post-eruptive erosional processes rather than volcanic activity; (i) The site has been modified as part of previous urban development; (j) This is not a factor for which the ONF has been scheduled; (k) Not a geological issue.

Assessment of effects of the proposal on the ONF Section D10.4.2 of the AUP requires that any development of buildings and structures (Activity A1) is a Restricted Discretionary activity. Section D10.8.2 states that Council will consider the relevant assessment criteria in D10.8.2. We interpret that criteria (1) and (3) are relevant to geological aspects: (1) The extent to which the nature, form and extent of the proposed use or development adversely affects the criteria or values for which the feature was scheduled taking into account all of the following: a. whether the use or development will result in increased erosion, of the feature; b. whether the use or development will result in increased compaction or erosion of the feature, or changes to the vegetation will adversely affect the values for which the feature is scheduled; c. whether the use or development will result in ground disturbance or earthworks that will affect the values for which the feature is scheduled; and d. whether the use or development will interfere with natural processes associated with the feature. (3) The extent to which the proposed use or development will cause any significant loss of geological value of a feature, taking into account the extent of a feature has already been modified and whether further modification will cumulatively result in a significant loss of geological value.

In relation to criterion (1): a) The proposed use or development will not result in increased erosion; b) The proposed use or development will not result in increased compaction or erosion of the feature; c) The proposed magnitude of the earthworks will not affect the values for which the feature is scheduled because the earthworks will primarily be within the footprint of the building and therefore will therefore not in itself be visible. No exposures or features of a geological nature are present on site and therefore cannot be removed; d) There are no natural processes of note occurring on the current site. This will not change as a result of the proposed development.

In relation to criterion (3), it has been established from the assessment presented above that:  The proposed development will require excavation into the top of the very broad tuff ring that covers some 6 km2 of the surrounding suburbs of Meadowbank, Orakei and Remuera, not all of which has been scheduled as the Orakei Basin volcano ONF;  The proposed development will not require any modification of the explosion crater as the subject property is located some 230 m beyond its nearest occurrence;

Tonkin & Taylor Ltd 10 January 2019 Orakei ONF Assessment, 1-3 Purewa Road, Meadowbank Job No: 1007709 McConnell Property

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 The distinct topographic feature of the Purewa Road area is the vegetated slopes that border Orakei Basin. This slope has been formed by the Purewa Creek and does not represent a volcanic landform. As such, the explosion crater will not be modified by the proposed development;  While the subject site is located within the tuff ring, the spatial extent of the Orakei Basin volcano ONF has been arbitrarily defined by cadastral boundaries rather than by geological features. Had the mapping of the ONF been restricted to the definable explosion crater and a small strip of immediate tuff (as is the case with the rest of the Orakei Basin volcano), the subject site would not have been affected by the ONF overlay;  No geological exposure or outcrop exists on the property and therefore none will be modified or lost as a result of the development;  The site does not contain recognisable geological features nor does the current landform reflect volcanic activity. The site’s geomorphology reflects post-eruptive erosional processes that are reflected in a significant part of the surrounding land that has not been included in the ONF overlay. We therefore do not consider that a loss of geological value will result, as the geomorphology that is associated with post-eruptive processes (and where these processes have interacted with eruptive processes/geomorphologies) will continue to be appreciable in the area. This is the same for the other properties in this area, both inside and outside of the ONF overlay. We therefore do not believe that the proposed development will result in cumulative loss of geological value.

In addition to the above, section E12.4.3 of the AUP requires that any earthworks that exceed 2m3 are a restricted discretionary activity (Activity A39). Section E12.8.2(2)(d) provides the assessment criteria that are specific to earthworks within an ONF overlay. Those that are considered to be relevant to geological matters are underlined: (i) whether the nature, form and extent of the proposed works or activity adversely affects the feature or features for which the item was scheduled; (ii) whether the activity will interfere with natural processes e.g. hydrology or adverse effects on nature and form of sand dunes; (iii) whether the proposed works or activity cause adverse visual effects or adversely affect landscape values; (iv) the degree to which the feature or features have already been modified so that further modification will not cause significant additional loss of geological value; (v) the extent to which the proposed works will protect the feature from further damage, such as erosion protection, or remediate it from previous damage. This excludes potential damage from the activity for which consent is sought; (vi) whether the proposed land disturbance is for an activity which has a functional or operational need to be in the location proposed; and (vii) the objectives and policies in D10 Outstanding Natural Features Overlay.

We provide our assessment against the relevant criteria as follows: (i) the ONF overlay primarily encapsulates part of a terrain formed by volcanic activity. It has been demonstrated above that the site’s physical characteristics (i.e. the site’s slope) do not actually reflect this volcanic origin. The site’s landform is derived from the interaction of post-eruptive erosion processes with the volcanic geology, which is not considered to be outstanding or particularly remarkable in the context of the geology of the AVF (or of Auckland generally). The resultant landform from this interaction is

Tonkin & Taylor Ltd 10 January 2019 Orakei ONF Assessment, 1-3 Purewa Road, Meadowbank Job No: 1007709 McConnell Property

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clearly represented in the steeper landform to the west of the site within the Council reserve, which will be retained in the future as this land is in public ownership. The site does not contain any geological features of note. As such we do not consider that any volcanic features will in fact be adversely affected by the proposed development; (ii) the only natural process occurring on the site at present is the infiltration of rainwater and the surface flow of stormwater towards Purewa Creek. The proposed development will manage stormwater by intercepting and discharging it in a controlled manner into Purewa Creek. This will not fundamentally affect the overall natural process, although it potentially has the benefit of reducing soil erosion and sediment discharge into Purewa Creek during large storm events. This process is not relevant to the features for which the ONF was identified; (iv) the site has already been modified for use as a residence, and the wider ONF contains significant human modification in the form of residential development around the majority of the eastern, southern and a portion of the western slopes of the Orakei Basin crater. Given the absence of any geological feature of note on the site, we consider that no significant additional loss of geological value will result, and the geological features of the ONF that are of note will not be adversely affected by the proposal.

Summary and Conclusions A geological assessment of the property at 1 – 3 Purewa Road has been undertaken. Available evidence indicates the following:  The property is located within a gently undulating landscape representing the eroded tuff ring surrounding the Orakei Basin volcano. The tuff ring extends some 700 m beyond the property and the defined limit of the ONF;  The property is located some 230 m to the north-east of the explosion crater, the defining volcanic feature of the area;  The west-facing slope that extends from the subject property to the Orakei Basin has formed as a result of post-eruption erosional activity of the Purewa Creek. The slope is not a volcanic landform;  The ONF encloses the subject property and therefore only a very small part of the tuff ring. The vast majority of the tuff ring is not included in the ONF;  The lateral extent of the ONF is determined by property boundaries and not geological features;  There are no geological features (outcrops or exposures) of note on the property.

We conclude that the proposed development will not result in a material loss of a geological feature.

Yours sincerely

Kevin J. Hind Technical Director, CMEngNZ (PEngGeol)

Tonkin & Taylor Ltd 10 January 2019 Orakei ONF Assessment, 1-3 Purewa Road, Meadowbank Job No: 1007709 McConnell Property

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Tonkin & Taylor Ltd 10 January 2019 Orakei ONF Assessment, 1-3 Purewa Road, Meadowbank Job No: 1007709 McConnell Property

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Site

Figure 1: Orakei Basin area with 1 – 3 Purewa Road indicated (source: GIS)

Figure 2: Aerial photograph of property showing existing dwelling and proximity to Orakei Basin with 0.5m contours (source: Auckland Council GIS). Section line refers to Figure 3

Tonkin & Taylor Ltd 10 January 2019 Orakei ONF Assessment, 1-3 Purewa Road, Meadowbank Job No: 1007709 McConnell Property

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West East

Proposed Apartment Building Orakei Basin

Figure 3: Sketch cross section through 1-3 Purewa Road

Figure 4: Geology of eastern Auckland from Kermode (1992). The location of the subject property is indicated by the arrow. The purple colour enveloping the subject site represented tuff of the Auckland Volcanic Field.

Tonkin & Taylor Ltd 10 January 2019 Orakei ONF Assessment, 1-3 Purewa Road, Meadowbank Job No: 1007709 McConnell Property

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Figure 5: 3D model showing the location of the site relative to the explosion crater and Purewa Creek. Blue arrows indicate the location of the Purewa Creek channels

Site Southern tributary

Explosion crater

Figure 6: View of the site and Orakei Basin explosion crater from Kepa Road. This illustrates the separation of 1-3 Purewa Road from the basin by the presence of the southern tributary of the Purewa Creek

Tonkin & Taylor Ltd 10 January 2019 Orakei ONF Assessment, 1-3 Purewa Road, Meadowbank Job No: 1007709 McConnell Property

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Orakei ONF overlay

Figure 7: The extent of the ONF overlay (stippled green) to the east of the Orakei Basin is shown. The property boundary of 1 – 3 Purewa Road is shown in red

Tonkin & Taylor Ltd 10 January 2019 Orakei ONF Assessment, 1-3 Purewa Road, Meadowbank Job No: 1007709 McConnell Property