Memorandum - Auckland Council · replace an existing, smaller diameter culvert. The inlet and...

Memorandum

16212 Memorandum SH1 Widening S92 Response 15Oct18 (002)

Bioresearches Group Ltd 68 Beach Road, Auckland 1010 P O Box 2027, Auckland 1140 T 09 379-9417 Website: www.Bioresearches.co.nz

To: Jacobs GHD P2Wk-TAS Joint Venture Date: 15 October 2018

Attention: Shaun Hamilton Ref: 16212

Subject: State Highway 1 Widening S92 Response - Streamworks Ecology plus SEV

Bioresearches was requested to provide ecological information in response to a S92 request from

Auckland Council for the proposed widening of State Highway 1 (SH1) between Hudson Road, Warkworth

and the northern connection of the Pūhoi to Warkworth (P2Wk) motorway to SH1 (Figure 1).

Figure 1. State Highway 1 widening from Hudson Road to the Northern Connection of the Pūhoi to Warkworth motorway, north of Warkworth.

The proposal includes the addition of a southbound lane, and median islands as well as the intersection

with the proposed Matakana Link. Works will require the installation of culverts, identified as E180 and

E530 as illustrated in Figure 1. The SH1 project and this memorandum relates to the area to be widened

and excludes the P2Wk roundabout (Appendix I).

With regard to the ecology the S92 response requested:

An additional assessment of effects, including a qualitative assessment of the streams subject to

the proposed culverts, and a quantitative assessment of the proposed streamworks in relation to

the culverts, including any measures intended to address the loss of ecological habitat associated

with the culvert installation; and

an ecological assessment of the culvert E180 with respect to the proposed lack of fish passage.

Culvert E530

http://www.bioresearches.co.nz/

Memorandum : State Highway 1 Widening S92 Response - Streamworks Ecology plus SEV 16212 Memorandum SH1 Widening S92 Response 15Oct18 (002)

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Culvert E530 is proposed as a single barrel 1,350mm concrete culvert, 78m long with a rock apron, to

replace an existing, smaller diameter culvert. The inlet and outlet for Culvert E530 will designed for

unimpeded fish passage and the culvert base will be lined with baffles for fish passage (refer NX2

Stormwater plan P2Wk-DRG-SW-05-0052).

The stream immediately upstream SH1 was assessed in November 2017 as low quality aquatic habitat,

primarily due to land use practices, but it still maintained fish habitat. Although the habitat was poor,

with limited cover and shading, the potential of the stream for fish habitat was moderate, and twelve

shortfin eel (Anguilla australis) were recorded in a 100m stretch of the open watercourse immediately

upstream of SH1 in November 2017. Cattle had full access the watercourse at the time of the assessment.

The riparian vegetation in the vicinity of the proposed works area is very poor, limited to grazed exotic

pasture with occasional willow (Salix species), and pampas (Cortaderia selloana), with no native trees or

shrubs.

A quantitative assessment of the stream in the proposed works area was carried out on 9th October 2018

using the Stream Ecological Valuation (SEV) methodology (Storey et al., 2011)1. The SEV resulted in a low

score of 0.35 as a result of the highly impacted, low quality stream habitat, with limited cover, no shading

and poor macroinvertebrate and fish habitat. The SEV results are summarised in Table 1. These results

corroborate the results of the SEV carried out immediately upstream of the site in 2017 which also

resulted in a low SEV score (0.38), with the assessment finding the aquatic ecological potential of the site

to be moderate, with riparian planting and fencing (Bioresearches, 2018)2.

1 Storey, R. G., Neale, M.W., Rowe, D.K., Collier, K.J., Hatton, C., Joy, M.K., Maxted, J.R., Moore, S., Parkyn, S.M., Phillips, N., Quinn, J.M., (2011) Stream Ecological Valuation (SEV): a method for assessing the ecological function of Auckland streams. Auckland Council Technical Report 2011/009. 66p. 2 Bioresearches (2018). Assessment of Ecological Effects: Tūhonohono ki Tai / Matakana Link Project. Report prepared for Auckland Transport, September 2018.


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Table 1. SEV summary data – impact length 9 October 2018

Function category Function Variable (code) SH1

Vchann 0.37

Vlining 0.80

Vpipe 1.00

NFR = 0.51

Vbank 1.00

Vrough 0.20

FLE = 0.20

Vbarr 0.30

CSM = 0.30

Vchanshape 0.90

Vlining 0.80

CGW = 0.83

Hydraulic function mean score 0.46

Vshade 0.30

WTC = 0.30

Vdod 0.45

DOM = 0.45

Vripar 0.00

Vdecid 1.00

OMI = 0.00

Vmacro 0.49

Vretain 0.20

IPR = 0.20

Vsurf 0.59

Vripfilt 0.60

DOP = 0.59

Biogeochemical function mean score 0.31

Vgalspwn 1.00

Vgalqual 0.00

Vgobspwn 0.80

FSH = 0.40

Vphyshab 0.24

Vwatqual 0.09

Vimperv 1.00

HAF = 0.39

Habitat provision function mean score 0.40

Vfish 0.23

FFI = 0.23

Vmci 0.62

Vept 0.17

Vinvert 0.23

IFI = 0.34

Vripcond 0.10

Vripconn 1.00 RVI = 0.10

Biodiversity function mean score 0.22

Overall mean SEV score (maximum value 1) 0.35


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The potential of the stream habitat if the land use practices were improved is moderate. Although the substrate is very soft and mobile, with riparian planting and fencing the watercourse from stock, the stream would likely form a more defined channel with a reduction of fine sediment and inputs of woody substrate, providing higher quality habitat for both fish and macroinvertebrates.

Downstream of culvert E530, within the proposed alteration to designation, the aquatic environment is

highly modified. The bed and banks are lined with large rocks and the channel has been straightened and

deepened for stormwater and erosion control. There is limited or no access to the floodplain, no trees or

shrubs for shading or organic inputs and no connection to the riparian area. Impervious surfaces cover

the majority of the true left bank, with bare ground on the true right bank, and piped inputs are present

within the channel (Photos 1 and 2). The potential of the aquatic habitat could be improved slightly by

riparian planting of the true right bank, but as the riparian area of the true left bank is concrete slab and

the area is already fenced from stock, the potential for improvement in the habitat is minimal, without

extensive modification.

Photo 1. Current culvert outlet, to be replaced by outlet for culvert E530.


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Photo 2. View downstream from culvert outlet.

The primary adverse ecological effects of the proposed streamworks, with regard to culvert E530, are the

modification of approximately 30m of low quality stream habitat (Photos 3 and 4) upstream of the current

culvert, and the potential for increased sedimentation, both in the watercourse and downstream, during

the construction phase. The primary beneficial ecological effect of the proposed streamworks would be

the establishment of fish passage into the upper catchment and the treatment of the currently untreated

SH1 stormwater runoff.

Photo 3. Stream impact site for the culvert E530 (7 Sept 2018).


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Photo 4. Stream impact site for the culvert E530 (9 October 2018).

Potential sedimentation effects during and immediately after construction, will be addressed as per the

erosion and sediment control measures outlined in the submitted AEE document and the proposed

resource consent conditions, in particular proposed resource consent condition number 5 requiring an

Erosion and Sediment Control Plan, working to the best practice guidance as required by Auckland Council.

The culvert extension will result in the degradation of the natural character of the low quality farm stream.

Soft substrate will be replaced with hard substrate and the connection of that section of stream to the

adjacent ground and riparian area will be removed. However, the increase in shading and addition of

baffles will increase the ecological functioning of the stream, restoring and improving the upstream and

downstream connection for native fish and macroinvertebrates, cooling the water and providing for

variation in hydrology within the culvert. A SEV score for a culvert of this type, as accepted by Auckland

Council is 0.2 to 0.25. The stream as discussed above currently maintains a SEV score of 0.35, which would

equate to a minimal loss in ecological function. In the context of the approximately 2.5km stream habitat

upstream of the site, the modification of 30m (i.e. 1%) of the upstream habitat, while maintaining the

hydrological functioning of the watercourse and improving the ecological connection through the

provision of fish passage, is not assessed as a significant residual adverse effect on ecological functioning

or biodiversity.


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Culvert E180 – fish passage

The area subject to the proposed alteration to designation with respect to proposed culvert E180, lies to

the north of SH1, the property at 56 State Highway 1, Warkworth.

Culvert E180 is proposed to replace the current four small culverts draining the roadside drain and

upstream catchment. Approximately 50m upstream of SH1, water flow from the catchment has been

dammed and is retained in a small farm pond, limiting downstream flow to stormwater flow. The

potential aquatic habitat above the SH1 culvert is restricted to the grass roadside swales, the small farm

pond and its outlet.

The vegetation immediately adjacent to the highway in the vicinity of culvert E180 is of low quality. On

the south-west side of SH1 it is limited to exotic pasture grasses, and on the north-eastern side of the

highway to pasture and amenity plantings.

The culvert will be located in the upper extent of a catchment with no upstream fish habitat.

Although a constructed farm pond is present immediately up-catchment (outside of the proposed

designation), the pond is artificial, and it does not have any shading, undercuts or large debris to provide

quality habitat for native fish (Photo 4). The pond also has very limited connectivity with the downstream

catchment, with the associated drainage channels comprising overland flow paths and grass swales

(Photos 5 and 6). Although there was sheet flow of water off the site after recent rain (Photo 7), there

was no water flow in the grass channel downstream of the pond (Photo 6). The water collected by the

current series of culverts draining under SH1 is provided by the roadside drainage channels north-west

and south-east of the area, and by overland flow paths from 56 State Highway 1. Aside from the lack of

flow, pools or aquatic habitat between the farm pond and SH1, the embankment to SH1 provided a

complete barrier (Photos 8 and 9), with water flow from the property either flowing over the top of the

access track (Photo 7), or from groundwater.


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Photo 4. Farm pond on 56 State Highway 1, Warkworth.

Photo 5. Overland flow path on 56 State Highway 1 draining towards SH1


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Photo 6. Flow path draining the farm pond on 56 State Highway 1.

Photo 7. Lower catchment with surface flow over access track to SH1.


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Photo 8. Embankment from 56 State Highway 1 to the SH1 roadside drain.

Photo 9. Debris supporting access track – no culvert or connection with upper catchment


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Yours sincerely

BIORESEARCHES LTD

Treffery Barnett, M.Sc.(Hons) | Marine & Freshwater Biologist Bioresearches, a subsidiary of Babbage Consultants Limited +64 9 379 9417 | DDI +64 9 367 5282 | Mobile +64 21 285 4330 |


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Appendix I. Land included in proposed alteration to designation (blue).


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