ASSESSMENT
OF
WATERCOURSES
AND
WETLANDS AT TWO PROPOSED LANDFILL SITES,
BLACKBRIDGE ROAD, DAIRY FLAT
R3653
ASSESSMENT OF WATERCOURSES AND WETLANDS AT
TWO PROPOSED LANDFILL SITES, BLACKBRIDGE ROAD,
DAIRY FLAT
Contract Report No. 3653
April 2015
Project Team:
Nick Goldwater - Project manager, field work, report author
Steve Rate - Peer review
Prepared for:
Norsho Bulc
C/- Hazel Hewitt and Associates
6 Glenvar Close
North Shore
AUCKLAND OFFICE: 97A MT EDEN ROAD, MT EDEN, AUCKLAND 1023
P.O. BOX 46-299, HERNE BAY, AUCKLAND 1001, Ph 09-377-4886
HEAD OFFICE: 99 SALA STREET, P.O. BOX 7137, TE NGAE, ROTORUA
Ph 07-343-9017; Fax 07-343-9018, email [email protected], www.wildlands.co.nz
CONTENTS
1.
INTRODUCTION
3
2.
METHODS
3
3.
VEGETATION AND HABITATS
3.1
Proposed Landfill 1
3.2
Proposed Landfill 2
3
3
5
4.
ECOLOGICAL VALUES
4.1
Intermittent streams
4.2
Freshwater wetlands
8
8
8
5.
POTENTIAL ECOLOGICAL EFFECTS OF THE PROPOSED LANDFILLS
8
6.
OPTIONS FOR MITIGATION
9
7.
CONCLUSIONS
9
ACKNOWLEDGMENTS
11
REFERENCES
11
APPENDICES
1. Site photographs
12
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Contract Report No. 3653
Reviewed and approved for release by:
_______________________
W.B. Shaw
Director/Principal Ecologist
Wildland Consultants Ltd
 Wildland Consultants Ltd 2015
This report has been produced by Wildland Consultants Ltd for Hazel Hewitt and Associates.
All copyright in this report is the property of Wildland Consultants Ltd and any unauthorised
publication, reproduction, or adaptation of this report is a breach of that copyright.
© 2015
Contract Report No. 3653
1.
INTRODUCTION
The client, Norsho Bulc, is seeking resource consent to construct two managed
landfills at Blackbridge Road, Dairy Flat (Figure 1). The proposed works will require
c.940,000 m3 of earthworks over c.10 ha, although the maximum area of earthworks
at any one time will be 3 ha. Initial investigations indicate that the footprints of the
proposed landfills contain intermittent watercourses and small areas of indigenous
wetland vegetation. Before resource consent can be granted, a detailed assessment of
the vegetation and habitats present at the site is required. The environmental effects of
the proposed landfills also need to be assessed and potential avoidance, remedy, and
mitigation measures for adverse effects identified.
To this end, Hazel Hewitt, on behalf of the client, commissioned Wildland
Consultants Ltd to undertake a site visit and prepare an ecological assessment of the
site, focusing on aquatic and freshwater wetland habitats.
2.
METHODS
A site visit was undertaken on 6 March 2015. The aquatic and wetland habitats within
the two gullies were described and assessed. The status of watercourses at the site were
determined as per the criteria in the working document entitled ‘Guidance for the
classification of drainage systems based on the Proposed Auckland Unitary Plan
definition’. A hand-held GPS device was used to record the coordinates for the
upstream extent of intermittent watercourses. Recorded calls of North Island fernbird
(Bowdleria punctata vealeae) and spotless crake (Porzana tabuensis) were played in
potential habitat and responses listened for. Representative site photographs are
provided in Appendix 1.
3.
VEGETATION AND HABITATS
3.1
Proposed Landfill 1
The proposed site for Landfill 1 comprises part of a sub-catchment drained by at least
four small gully systems (Figure 2). The main watercourse flows north-east through
the proposed landfill site. Despite the presence of pasture grasses and pugged soil, it
was possible to distinguish between stream banks and stream bed in the upper reaches
of the sub-catchment. The point where the bed and banks could no longer be
distinguished was considered to be the upstream extent of the intermittent watercourse
(Figure 2). Slightly downstream of this point, a wetland occurs in the channel.
Vegetation in the wetland comprises manuka (Leptospermum scoparium agg.)
shrubland over an understorey of dense swamp millet, frequent Machaerina
rubiginosa and soft rush (Juncus effusus), and occasional gorse (Ulex europeaus) and
swamp kiokio (Blechnum minus) (Plate 1; Figure 2). The substrate is very boggy
underfoot, which indicates the presence of hydric soils.
In the area earmarked for a sediment control pond (near the downstream extent of the
proposed landfills), the channel widens into a grazed wetland characterised by
abundant swamp millet with local manuka and Machaerina rubiginosa, frequent soft
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rush and lotus (Lotus pedunculatus), and occasional rautahi (Carex lessoniana).
(Plate 2; Figure 2). The vegetation differs in the small eastern arm of the wetland, and
includes abundant Eleocharis acuta with frequent swamp millet and soft rush, and
occasional water milfoil (Myriophyllum propinquum). Shrubland bordering the
eastern margin of the wetland comprises manuka with frequent gorse and occasional
woolly nightshade (Solanum mauritianum). No watercourses within the footprint of
Landfill 1 were classified as ‘permanent’.
3.2
Proposed Landfill 2
The gullies within the proposed site for Landfill 2 are dominated by exotic grassland
with frequent gorse (Plate 3). Two tributaries running in a northerly direction
converge into a main channel where the vegetation is characterised by a mixture of
dryland and wetland species. Both tributaries have been heavily impacted by stock
trampling and pugging. The channel in the western tributary is very wide in places (up
to 6 m) and contains abundant purei (Carex virgata) with frequent rautahi and
Eleocharus acuta with occasional giant umbrella sedge (Cyperus ustulatus) and
emergent mamaku (Cyathea dealbata), cabbage tree (Cordyline australis), and
manuka (Plate 4). Pasture grasses also occur in the channel, including brown top
(Agrostis capillaris), sweet vernal (Anthoxanthum odoratum), and paspalum
(Paspalum dilatatum). Other parts of the tributary are characterised by soft rush,
Yorkshire fog (Holcus lanatus), creeping buttercup (Ranunculus repens), lotus and
occasional jointed rush (Juncus articulatus) and swamp millet. Although no flowing
water or pools were present in the tributary - and despite the impacts of cattle - a
channel and thalweg could be discerned. Most of the western tributary is considered
to meet the definition of ‘intermittent’ (Figure 3). Some areas were boggy underfoot,
which indicates the presence of hydric soils (Plate 5).
The upstream extent of the eastern tributary is dominated by indigenous wetland
vegetation comprising frequent manuka over an understorey of locally common
rautahi-Machaerina rubiginosa sedgeland (Plate 6; Figure 3). Other species present
include occasional kiokio (Blechnum novae-zelandiae), and swamp willow herb
(Epilobium pallidiflorum). Approximately half the length of the eastern tributary is
considered to be intermittent (Figure 3). The upper point of the channel is deeply
incised and well-shaded by a mixture of kiokio, ring fern (Paesia scaberula), rank
grass, and gorse. There was no flowing water or pools present in the channel,
although the substrate was wet
Downstream of the confluence of the two tributaries, occasional pools of stagnant
water occur in the more incised reaches of the stream, all of which are shaded by
ferns. The largest pool observed was c.1 m wide and 0.2 m deep with a hard clay
substrate (Plate 7). It is well-shaded by gahnia (Gahnia setifolia), kiokio, karamu
(Coprosma robusta), and wheki (Dicksonia squarrosa). Frogs have previously been
observed in the pool (N. Roberston, pers. comm. 2015) and it also has the potential to
support indigenous fish such as eels (Anguilla spp.) and banded kokopu (Galaxias
fasciatus). Downstream of the pool the channel widens (up to 5 m) and becomes less
defined, and is characterised by soft rush, lotus and paspalum, with occasional Mercer
grass (Paspalum distichum), water pepper (Persicaria hydropiper), and rautahi.
No watercourses within the footprint of Landfill 2 were classified as ‘permanent’.
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4.
ECOLOGICAL VALUES
4.1
Intermittent streams
Intermittent streams can provide habitat for aquatic plants and animals. They also
provide important drainage and rainfall interception and infiltration in the catchment
headwaters, and can be a significant contributor of sediment when disturbed. In small
catchments, these headwaters can therefore have an important influence on catchment
hydrology. In term of aquatic biodiversity, intermittent streams have lower species
diversity than permanently flowing streams, but they do support viable communities
of aquatic invertebrates and may contain some rare species. Indigenous fish are also
able to survive in intermittent streams, moving in and out of stream reaches as they
flood and dry (Storey and Quinn 2007).
The downstream reaches of the surveyed intermittent watercourses may have the
capacity to support indigenous fish during winter months, although the intermittent
watercourse within proposed Landfill 2 is more likely to support fish year round
(given the presence of pools). However, both watercourses have been heavily
impacted by stock and the removal of riparian vegetation, and their aquatic values are
considered to be low.
4.2
Freshwater wetlands
Although the site contains very small areas of freshwater wetland vegetation, it should
be acknowledged that this is a nationally under-represented habitat type with only
10% of the original extent remaining. All wetlands perform important ecological
services such as the filtration of sediments, uptake of nutrients, and attenuation of
flood waters.
5.
POTENTIAL ECOLOGICAL EFFECTS OF THE PROPOSED
LANDFILLS
The proposed landfills will result in the loss of c.0.3 ha of indigenous freshwater
wetland vegetation, although these fragments are considered too small to support
threatened fauna species. The proposed works will also require the destruction of
c.350 m of intermittent watercourses in the western gully and c.160 m of intermittent
watercourse in the eastern gully. The proposed works will result in the loss of aquatic
habitat for small numbers of indigenous fish and aquatic macroinvertebrates.
No species of vascular plants classified as nationally or regionally threatened by
de Lange et al. (2013) and Stanley et al. (2005), respectively, will be affected by the
proposed works. Habitats within Significant Ecological Area (SEAs) will not be
affected by the proposed works.
Earthworks have the potential to generate large amounts of sediment, which could
potentially adversely impact on aquatic and freshwater wetland receiving
environments downstream of the proposed cleanfill.
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6.
OPTIONS FOR MITIGATION
In order to mitigate for loss of aquatic and wetland habitats, it is proposed to provide
additional protection for the extensive area of raupo (Typha orientalis) reedland (Plate
8) and aquatic habitat that occurs to the north of the proposed landfills, and is
included within a large Significant Ecological Area (SEA 6261). The wetland is in
relatively good condition and currently supports at least two pairs of spotless crake
(N. Goldwater, pers. obs. 2015). This cryptic indigenous wetland bird species is
classified as ‘At Risk - Relict’ by Robertson et al. (2013). The wetland also provides
good potential habitat for other bird species such as Australasian bittern (Botaurus
poiciloptilus) and North Island fernbird, both of which are considered to be
threatened. Similarly, the watercourse that runs though part of the wetland is likely to
support indigenous fish species such as banded kokopu (Galaxias fasciatus), longfin
eel (Anguilla dieffenbachii), and shortfin eel (A. australis).
The following measures are recommended to restore and protect the wetland and
watercourse:
(i)
(ii)
Either remove stock or construct a stock-proof fence at least 15 m from the
wetland margins.
Protect the wetland in perpetuity under a covenant or similar legal mechanism.
The total area of wetland and stream habitat to be fenced will comprise a minimum of
2.1 ha over a length of c.540 m (Figure 4).
7.
CONCLUSIONS
The client wishes to establish two managed landfills on a rural property at
Blackbridge Road, Dairy Flat. A field survey was undertaken of the natural areas at
the study site, with particular focus on the aquatic and wetland habitats.
The proposed landfills will adversely affect three small discrete areas of freshwater
wetland vegetation and c.510 m of intermittent watercourses. The loss of wetland
vegetation is unlikely to adversely affect indigenous fish and birds, although given
that freshwater wetlands constitute threatened habitat types, their loss will need to be
mitigated. Proposed measures for mitigation include protecting and enhancing the
large raupo reedland that occurs in the northern half of the property (currently within
an SEA) and includes a permanent watercourse. This wetland supports good numbers
of spotless crake and is likely to provide habitat for several other indigenous bird
species as well as indigenous fish.
To protect downstream receiving environments during earthworks, best practice
sediment control as per Technical Publication 90 (ARC 1999) should be implemented.
It is considered that the environmental effects of the proposed landfills will be no
more than minor if the aforementioned recommendations are implemented.
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ACKNOWLEDGMENTS
Nicola Robertson provided client liaison, site access, and site plans.
REFERENCES
de Lange P., Rolfe J., Champion P., Courtney S., Heenan P., Barkla J., Cameron E., Norton
D. and Hitchmough R. 2013: Conservation status of New Zealand indigenous
vascular plants, 2012. New Zealand Threat Classification Series 3. Department of
Conservation, Wellington. 70 pp.
Robertson H.A., Dowding J.E., Elliott G.P., Hitchmough R.A., Miskelly C.M., O’Donnell
C.J.F., Powlesland R.G., Sagar P.M., Scofield R.P., and Taylor G.A. 2013:
Conservation status of New Zealand birds, 2012. New Zealand Threat Classification
Series 4. Department of Conservation, Wellington. 22 pp.
Rowe D., Quinn J., Parkyn S., Collier K., Hatton C., Joy M., Maxted J., and Moore S. 2006:
Stream Ecological Valuation (SEV): a method for scoring the ecological performance
of Auckland streams and for quantifying mitigation. Auckland Regional Council
Technical Publication 302.
Stanley R., de Lange P., and Cameron E.K. 2005 :Auckland Regional Threatened and
Uncommon Vascular Plants List. Auckland Botanical Society Journal 60(2): 152-157.
Storey R. and Quinn J. 2007: When rivers run dry: invertebrate communities in intermittent
streams. Water & Atmosphere 15: 16-17. Published by NIWA.
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APPENDIX 1
SITE PHOTOGRAPHS
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Plate 1: Wetland comprising manuka shrubland over an understorey of swamp millet,
frequent Machaerina rubiginosa and soft rush. 6 March 2015.
Plate 2: Wetland characterised by swamp millet and soft rush
at the downstream extent of proposed Landfill 1. 6 March 2015.
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Plate 3: View north of the gully within the footprint of proposed Landfill 2.
6 march 2015.
Plate 4: Upstream view along the intermittent channel within the western
tributary (proposed Landfill 2). Note the presence of terrestrial plant species.
6 March 2015.
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Plate 5: Boggy hydric soils in the western tributary (footprint of proposed Landfill 2).
6 March 2015.
Plate 6: Rautahi and manuka dominate a wetland in the upper reaches
of the eastern tributary (proposed Landfill 2. 6 March 2015.
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Plate 7: Pool within intermittent stream, western gully (proposed Landfill 2).
6 March 2015
Plate 8: Raupo reedland proposed for protection. 6 March 2015.
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Plate 9: Gullies proposed for protection at the northern end of the property.
The raupo reedland runs east-west in the middle of the photograph.
6 March 2015.
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