Before the Hearing Panel
In the matter
of the Resource Management Act 1991
And
In the matter
of
application
APP-2015200296.00
for
Resource
Consents (Land Use Consents):
ATH-2015200297.00,
ATH-2015200302.00,
ATH-2015200303.00,
ATH-2015200304.00,
ATH-2015200305.00,
ATH-2015200346.00,
ATH-2015200347.00
and Water Permits
ATH-2015200345.00
ATH-2015200345.00
by Manawatu Wanganui Regional Council trading as
Horizons Regional Council for
Lake Horowhenua Weed Harvesting Activities
Fish Pass at Lake Horowhenua Outlet
Arawhata Stream Sediment Trap Lake Horowhenua
Section 42A Report of Frances Forsyth,
Senior Ecologist for Wildland Consultants
A.
Qualifications and Experience
1. My name is Frances Mary Jean Forsyth. I hold the position of Senior Ecologist with Wildland Consultants Ltd, a role I have had since May 2012. I hold the qualifications Bachelor of Science and Post Graduate Diploma from Victoria University of Wellington. I am a qualified Stream Ecological Valuation practitioner and am also currently studying for a Master of Science by thesis. I am a member of the Wellington Botanical Society, the New Zealand Freshwater Sciences Society, and the New Zealand Plant Conservation Network.
2. This Section 42A technical report presents an audit of the following applications - Horizons Regional Council Resource Consent Application Nos. ATH-2015200297.00, ATH-2015200345.00, ATH- 2015200301.00, ATH-2015200302.00, ATH-2015200303.00,
ATH-2015200304.00, ATH-2015200346.00, ATH-2015200305.00, and
ATH-2015200347.00. These comprise water permits and land use consents sought for proposed weed harvesting and associated infrastructure on Lake Horowhenua, proposed fish pass at the outlet weir on Lake Horowhenua, and a proposed sediment trap on the Arawhata Stream - Lake Horowhenua, Levin. The application documents are dated June 2015.
3. My involvement with the application commenced on 17 June 2015. I have been engaged by the Manawatu Wanganui Regional Council – Regulatory Team. I am one of a team of consultants working with Hill Young Cooper Ltd on behalf of the Regional Council in its role as the consent authority. I visited all of the proposed sites on 1 July 2015.
B.
Introduction
4. The applicant Manawatu Wanganui Regional Council trading as Horizons Regional Council (Horizons) seeks consent to:
a. Harvest lake weed from Lake Horowhenua and to construct, operate and maintain two boat ramps on the southern and eastern sides of the lake, including associated vehicle access and minor earthworks;
b. Construct and maintain a fish passage structure located at the outlet weir between Lake Horowhenua and Hokio Stream; and,
5. I have audited the assessment of effects on the environment for the construction works associated with the weed harvesting and for the construction works associated with the fish passage structure and the sediment trap.
C.
Background
6. Lake Horowhenua is the largest natural lake in the Manawatu-Wanganui region, and on the west coast of the North Island. In 2010 Lake Horowhenua was ranked seventh worst out of 112 lakes monitored nationally. Two of its tributaries, the Arawhata and the Patiki Streams, rank as second and fourth highest (worst) in terms of median nitrogen concentrations in New Zealand.
7. In 2013 the Lake Horowhenua Accord was formed between Horowhenua 11 (Lake) Part
Reservation Trust (the “Trust”), HDC, HRC, the Horowhenua Lake Domain Board and the Department of Conservation (DOC).
8. The Lake Horowhenua Action Plan was completed by the Accord partners in 2014. The
Accord Action Plan includes projects as a part of the Lake Horowhenua Fresh start for Freshwater Clean-up Fund project (the Clean-up Fund). The projects for which consents are being sought are part of the Clean-up Fund work programme. These aim to improve the water quality, ecology and fishery of Lake Horowhenua in the following ways:
a. The fish pass is to provide access (which is currently being impeded by the weir) for migratory fish to and from Lake Horowhenua, thereby improving fish habitats and in turn, the ecological integrity of the lake’s ecosystem.
b. The seasonal harvesting of the lake weed will reduce the amount of sediment settling on the lake bed, as well as the ability of the weed to change the chemistry of the lake creating conditions suitable for cyanobacteria growth and high ammonia concentrations.
c. The sediment trap will reduce the amount of sediment entering Lake Horowhenua via the most consistent contributor of it, Arawhata Stream, and in turn, will improve water quality and clarity within the lake.
D.
Description of activities
9. A plan showing the design of the fish pass is on page 14 of the Fish Pass application. A description of the design, construction and maintenance of the boat ramps is contained in Appendix L of the weed harvesting application. The sediment trap layout plan is contained in Appendix B of the sediment trap application.
Fish Pass
10. The proposed fish pass is to be located on the north bank of the Hokio Stream, adjacent to the weir at the outlet to Lake Horowhenua. Access to the fish pass for construction purposes will be via an existing farm track from Moutere Road, which will be upgraded. 11. The fish pass is designed to allow fish passage around the outlet weir through a three
metre wide semi-circular concrete structure. The crest of the fish pass will be matched to the height of the weir to minimise any impact on the lake level. The fish pass will have a concrete foundation for stability, lined with a grouting of rough concrete and rock, with the rock exposed so as to provide a more natural stream environment for migrating fish species. The margins of the ramp will be planted with indigenous plant species.
Weed Harvesting
12. A weed harvester will be operated on Lake Horowhenua at key times of the year (for example during the months of spring) with the purpose of removing weed biomass by cutting the top off the weed.
13. A detailed weed harvesting strategy has been prepared and filed with the application. As well as informing an operating model, the strategy also informed the decision to have a primary boat ramp at the Arawhata site, and a second contingency boat ramp at the Lake Domain.
14. The primary boat ramp will be constructed on the lake shore close to the proposed sediment trap on land owned by HRC. Boat ramps are required for the launching and recovery of the weed harvester. They will be constructed from pre-cast concrete, and will be 7 m long and 18 m wide with a slope of 1 in 8 into the water. Some land disturbance and dredging within the lake will be required, although the primary site has been selected to reduce the need for dredging.
15. Harvested weed will be off-loaded from the harvester and moved to a hard-stand area to allow excess water to drain off before being moved off-site to the landfill. At the Domain, weed will not generally be stored overnight so that there is, as far as possible, limited disruption to recreational users of the Domain and to the public.
Arawhata sediment trap
16. The Arawhata sediment trap is a new drainage structure which is designed to reduce sediment flows into Lake Horowhenua. It is proposed to extend over about five hectares of land to the west of Arawhata Stream and will have four cells with cell dividing walls at increasing heights.
17. A culvert and associated head walls placed into the Arawhata Stream will act to divert water into the trap at times of high flow in the stream. Otherwise the water will pass through the culvert unimpeded.
18. A planting strategy has been developed for the cells which incorporates the requirement for removal of sediment from Cells 1 and 2 on an annual or biannual basis. Watercress will be established in Cell 1, closest to the stream diversion. Cell 2 will be planted with pasture species, Cell 3 with Carex secta and Schoenoplectus tabernaemontani, and Cell 4 with pasture species, excluding nitrogen fixing species.
E.
Scope of audit
19. My audit addresses the following matters: a. The background to the application,
b. Comments on the descriptions of ecological values at the four proposed construction sites,
c. Comments on the assessment of environmental effects provided for the four proposed construction sites,
d. Details of Council policy relevant to the application; and,
e. Comments on measures to avoid, remedy or mitigate any adverse effects; and what, if any, monitoring should be undertaken.
20. Key issues are:
a. Vegetation disturbance that may promote the establishment of invasive weeds, and plans to manage these throughout the restoration period;
b. The management of the swamp nettle population (threat status At Risk-Declining) at the Arawhata boat ramp site throughout the works and restoration period; c. Removal of indigenous vegetation and potential effects on the Nationally
Threatened New Zealand dabchick;
d. Identification of proposed restoration/rehabilitation planting areas; e. The choice and provenance of restoration plant material;
f. Sediment discharges during construction;
g. The harvesting and disposal procedure for raupō at the lake outlet weir; and, h. The use of CCA treated wood for the fish pass, boat ramp and wharves and its
F.
Summary of findings from the Applicant’s technical report
Descriptions of ecological values
21. Lake Horowhenua is described as being a regionally significant wetland, meeting the definition of a “Threatened” habitat type under Schedule E of Horizons’ One Plan. The lake is just over 300 ha in extent and is said to provide habitat for a number of indigenous wildfowl and fish species (Lambie 2015). Wildfowl species are not identified in the report. However, the eBird website identifies six species of wildfowl observed at Lake Horowhenua, along with an additional eleven indigenous species of various types. Fish species include common smelt, common bully, inanga, grey mullet, and longfin and shortfin eels. The lake is highly degraded with a classification of ‘hypertrophic’.
22. Values summarised below were confirmed during the 1 July site visit. I generally agree with the applicant’s evaluation of indigenous vegetation. However there could have been more in depth information, in particular regarding:
a. Kākahi (freshwater mussel) estimated population size and distribution along the lake shore, and
b. The potential for threatened indigenous birds to utilise vegetation at the perimeter of the lake.
Proposed fish pass site
23. Vegetation at the site of the proposed fish pass is described as rank grass with planted indigenous species. Aquatic vegetation at the weir comprises raupō (Typha orientalis) which is regularly cleared under the Hokio Drainage Scheme. The site contributes very little to the indigenous biodiversity of the lake margin.
24. Pest plants at the site include gorse and are described in a table in the memorandum from James Lambie to Jon Roygard (11 August 2015).
25. The lake has a total of nine freshwater fish species of which six are indigenous (shortfin eel (Anguillaaustralis), longfin eel (Anguilla dieffenbachii), inanga (Galaxiasmaculatus), grey mullet (Mugo cephalus), common bully (Gobiomorphus cotidianus) and common smelt (Retropinna retropinna); and three are exotic (goldfish - Carassius auratus, European perch - Perca fluviatilis, and koi carp - Cyprinus carpio) (Tempero 2013). Notably absent is the indigenous black flounder (Rhombosolea retiara), while populations of diadromous/migratory indigenous species may be at extremely low densities in the lake and in upstream tributaries. Other important freshwater fauna in the lake include kākahi and koura (freshwater crayfish).
Primary boat ramp site (Arawhata)
26. Vegetation at the proposed primary, Arawhata boat ramp is described as falling into ten zones including eight vegetation types: rank grassland with flax and other recently planted indigenous species, cyperus sedgeland, grass/cyperus sedgelend, raupō reedland, planted flaxland, willow treeland, grazed pasture, willow carex swamp; and grazed pasture.
27. The ecological report does not discuss the values of the site vegetation as habitat for wildfowl.
28. Two plants of the swamp nettle (Urtica linearifolia) were observed by James Lambie within the raupō reedland. This species has a national threat ranking of At Risk-Declining (de Lange et al. 2013).
29. Pest plants described include willows (Salix cinerea, S. fragilis and/or S. alba), blackberry (Rubus fruticosus agg.), wild carrot (Daucus carota), and yellow flag iris (Iris
pseudoacorus). Purple loosestrife (Lythrum salicaria) is said to be present in the
catchment (James Lambie, Section 92 response.).
30. Kākahi (freshwater mussel) were searched for briefly (20 minutes) across a 20 m radius area of the lake bed at the proposed site, but none were found. Kākahi are also mentioned as being present at this site in the technical report on sediment release from boat ramp construction (Brown 2015, Appendix H of the weed harvesting application). Anecdotal evidence regarding the presence of kākahi at the lake was provided by local iwi during the July 1 site visit.
31. Kākahi have a threat status of At Risk-Declining (Grainger et al. 2014). I consider that a higher level of effort could have been invested in the kākahi survey.
Second (contingency) boat ramp site
32. Vegetation at the Lake Domain (Muaupoko Park) boat ramp site comprises mown grass, planted flax (Phormium tenax) and planted Carex virgata. Aquatic vegetation comprises two exotic species, Canadian pondweed (Elodea canadensis) and curly pondweed
(Potamogeton crispus). The site vegetation contributes little to the maintenance of
biodiversity at the lake margin.
33. The technical report refers to this area as being a loafing ground for wildfowl, and the applicant considers that there are no significant habitat values at this site for wildfowl. I consider that this statement refers to geese, swans and ducks resting and grazing on the mown grass. I agree that there are no significant wildfowl habitat values at this site.
34. This site was not surveyed for kākahi. No explanation is given as to why a survey was not undertaken.
Arawhata sediment trap
35. Vegetation at the site of the proposed sediment trap comprises grazed pasture grasses interspersed with the indigenous leafless rush (Juncus australis). Such habitat is precluded from being classified as a rare, threatened or at risk wetland under Schedule F of the One Plan.
Review of Assessment of effects
36. Effects of the proposed works are described as including vegetation removal and disturbance, potential weed invasion, sediment release, potential loss of kākahi (freshwater mussel), and potential pollution.
37. The applicant’s information in the application regarding extent and type of vegetation removal and the mitigation proposed to address effects arising from the four projects is in my view confusing. I have provided a table, Table 1 (Appendix 1) which in my view summarises information from the application in a more useful format.
Proposed fish pass site
38. Vegetation along the route of the access track and in the vicinity of the site of the proposed fish pass will be removed. This vegetation comprises rank pasture grasses and low numbers of recently planted indigenous species. There is a proposal to relocate recently planted trees to nearby areas should they need to be removed from the construction areas.
39. Raupō (Typha orientalis) from behind the weir will be removed to facilitate construction of the fish pass. I understand that this classified as permitted activity under Rule 17-19(c) of the One Plan.
40. The methodology for the regular harvesting and removal of raupō is covered in the applicant’s S92 response. This describes the use of a long reach excavator that will require a five metre wide track extending up to 20 m upstream of the weir. It is proposed that the excavated material will be dispersed by the bucket load within the restoration planting area. Trees will be planted at 2 m spacings to accommodate future raupō disposal.
41. I consider it unlikely that two metre spacings will be sufficient to accommodate bucket loads of removed raupō and associated sediment, particularly once the trees have grown and a closed canopy is established. The placement of large volumes of vegetation and silt on the ground within the dripline of trees is likely to compact the soil, reduce oxygen at the tree roots and to cause the roots and possibly the trees to die. It is also likely to damage tree branches.
42. There is the potential for wet cement to affect kākahi, fish, kōura, and macroinvertebrates at the construction site if it were to spill from the fish pass during the construction process. Wet cement has a high pH and is know to cause injury and death to freshwater organisms.
43. The applicant acknowledges the issue of un-cured cement and proposes that pre-cast concrete be used where possible. Where raw cement is to be used the effects will be managed by bunding off the works area to ensure any cement wash does not enter the lake or stream. The applicant also proposes that trucks delivering concrete to site will be required to wash out the chutes back at their yards. No concrete wash-water will be disposed of onsite.
44. I recommend the following conditions:
a. Bunding is to be installed around works areas where wet cement will be used; and, b. No concrete wash-water is to be disposed of onsite, trucks delivering concrete to
site are required to wash out the chutes back at their yards.
Boat ramp sites (Arawhata and Lake Domain)
45. Vegetation along the Arawhata route to the lakeside will be removed or disturbed including that of seven vegetation types (Table 1, Appendix 1).
46. Vegetation clearance is a permitted activity under Rule 13-5 with the condition that (c)
“The activity does not occur on land that is in, or within 5 m of … (iii) the bed of a lake.”
This makes vegetation clearance within 5 m of the bed of the lake a discretionary activity. There is a proposal to relocate recently planted trees and flax to nearby areas should they need to be removed from the construction areas. Where effects on indigenous vegetation cannot be avoided or remedied these will be mitigated by restoration planting at a ratio of 1:1. I consider that this is an appropriate restoration ratio for the fast growing species that are to be lost.
47. There is potential for effects on the threatened swamp nettle population at the Arawhata site.
48. Some amenity plantings of indigenous plants at the Lake Domain site may be removed or disturbed during construction.
49. Vegetation disturbance may promote the establishment of invasive weeds.
50. I note that the technical report does not discuss the effects of vegetation removal or weed harvesting on bird species. New Zealand dabchick have been recorded at Lake Horowhenua (eBird online). This species is listed as Threatened – Nationally Vulnerable (Robertson et al. 2013). No other threatened birds have been recorded at Lake Horowhenua. Dabchicks nest on floating rafts of vegetation anchored to plants at the water’s edge (Heather and Robertson 2005) and there is potential for them to be nesting alongside raupō beds on the lake. Nesting birds could be affected by vegetation removal at construction sites and by a weed harvester working in close proximity to nests.
51. Concerns regarding threats to nesting New Zealand dabchicks could be mitigated by precluding works during the peak nesting season (June to December), by conducting a search for nesting birds prior to commencing works and avoiding the nest area until the end of the nesting season, and by avoiding weed harvesting within 100 m of raupō beds or trees overhanging the lake where dabchicks could potentially be nesting during the peak nesting season. I recommend conditions to this effect.
52. Kākahi (freshwater mussels) may be lost during the construction process. The measures proposed to relocate shellfish immediately prior to construction are appropriate.
53. Sediment will be released/re-suspended during the construction process. This is covered by erosion and sediment control consultant Graeme Ridley.
54. There is the potential for wet cement and pollutants from CCA treated wood to affect kākahi, fish, kōura, and macroinvertebrates at the construction site. The applicant proposes to avoid wet cement at the boat ramp sites by using pre-cast concrete. CCA treated wood is proposed for the construction of wharves and moorings at both sites.
55. The applicant cites a Ministry of Primary Industries (MPI) report (2013) regarding the toxicity of leached chemicals from CCA treated wood. I disagree with the applicant’s conclusions (including those in the S92 response) regarding the amount of CCA leaching from piles and other wharf materials and its effects. The MPI Industries report concludes that metals from treated timber are likely to bind to sediments after their release and be deposited locally. This is confirmed by Lebow and Foster (2010) who found that soil samples with elevated levels of copper and chromium were confined to directly under the dripline of a boardwalk and that arsenic was limited to within 0.3 m of the structure with concentrations reaching maximum levels after 60 months. Kākahi live directly in such sediment rather than in the water column as is the case with farmed shellfish, the primary subject of the MPI report. More recent research (Clearwater et al. 2014) shows that kākahi larvae are among those aquatic species most sensitive to acute copper exposure, and that kākahi juveniles would not be adequately protected by current ANZECC water quality guidelines for copper. I consider that a precautionary approach to the use of CCA treated timber should be adopted.
56. My concerns regarding the effects of CCA leaching on kākahi could be addressed by various mitigation measures e.g. encasing treated pile timbers in a protective sheath prior to pile driving, and painting wharf decking prior to installation. However, maintaining a protective paint cover in the long term would not be possible due to the difficulty of accessing the underside of the decking. Replacing the CCA treated timber with untreated hardwood is another option. Such timber would be particularly suitable for the wharf superstructure.
57. I recommend a condition requiring the encasement of CCA treated piles and moorings to prevent the effects of CCA leaching, and a further condition requiring the use of untreated hardwood timber for all wharf superstructure constituents (decking, joists etc.).
Arawhata sediment trap
58. With regard to whether or not the sediment trap site should be classified as significant wetland; Schedule F, Table F. 2(b) iii of the Horizons Regional Council One Plan (the One Plan) states that “paddocks subject to regular ponding, dominated by pasture or exotic species in association with wetland sedge and rush species are a habitat type that
is actively precluded from being classified as rare, threatened or at risk.”
59. There is potential for the release of sediment into Lake Horowhenua during construction of the proposed sediment trap. Exposed slopes will be stabilised using coconut matting, and instream works will take place during five day fine weather windows and incorporate steel plates and over pumping. This is covered in greater detail by erosion and sediment control consultant Graeme Ridley.
60. Watercress (Nasturtium officinale) is proposed for establishment in Cell 1 of the sediment trap. This plant will be re-established in the cell following routine mechanical clearance of sediment and vegetation. Watercress requires a sediment substrate for anchoring and supporting the plant structure. The plant obtains nitrogen and phosphorus from stream water. Where there are aerobic areas in the substrate there will also be soil nitrogen (Howard-Williams et al. 1982). A dense cover of watercress would shade the water, keeping it cool, and reducing the likelihood of anoxic conditions developing. However, watercress dies back in winter, especially following frost. This means that in order for the plant to perform an efficient job of removing nutrients and stabilising sediments the routine removal of sediments should occur during late summer. 61. I recommend that a consent condition be written stipulating that clearance of sediments
from Cell 1 only be undertaken during the months of February or March and that root plugs of watercress be replanted in the spring following clearance.
62. The applicant states that it may be difficult to eco-source sufficient Carex secta for Cell 3 of the sediment trap (S92 response). Any Carex secta sourced from within the Foxton Ecological District would be suitable for this project. A consent condition stipulating eco sourcing from the Foxton Ecological District for all indigenous plantings would be appropriate.
63. The applicant has not mentioned the potential for invasive weeds to become established within the cells of the sediment trap.
Consideration of alternatives
64. The applicant considered a number of potential sites for the boat ramps which are discussed in Gibbs et al. (2015). The route for the access road and the placement of the boat ramps will be adapted to avoid areas of high ecological value.
65. The fish pass is well sited on the true right Hokio Stream where there is an existing access track. The applicant has landowner permission to use and modify the access track.
66. The applicant has selected land owned by Horizons Regional Council which is at the bottom of the Arawhata Stream catchment for the sediment trap.
G.
Submissions
67. Submitter C. Rudd raises the issue of protection of birds at the lake. I have covered protection of the threatened New Zealand dabchick in paragraphs 50 and 51 above. I do not consider it necessary to protect introduced birds or indigenous species that are not threatened.
68. Submitter D.M. Rudd raises the issues of translocation of kākahi and vegetation removal from the boat ramp sites. I consider that the applicant has dealt with both of these issues adequately.
H.
Conclusions
69. I consider that the works proposed by the applicant are appropriate. Mitigation proposed by the applicant includes:
a. A construction effects and management plan will be developed post-consent to identify and mitigate disturbance of indigenous lake margin plant species;
b. Where effects on indigenous vegetation cannot be avoided or remedied these will be mitigated by restoration planting at a ratio of 1:1;
c. Existing amenity plantings at the Lake Domain that are lost or damaged will be replaced like for like or similar;
d. Planting and weed management plans will be produced outlining proposed mitigation planting;
e. Raupō losses will be off-set by tree planting at the lake outlet;
f. A staged management plan has been outlined (Lambie S92 response) for the threatened swamp nettle population;
g. Cement products will be either pre-cast or bunded and left to cure; h. CCA treated wood products will be pre-weathered to minimise leaching;
i. The positive consequences of the proposed works will enhance indigenous biodiversity in the lake and Hokio Stream and will mitigate any residual effects.
70. Conditions that I recommend include:
a. Bunding is to be installed around works areas where wet cement will be used; and, b. No concrete wash-water is to be disposed of onsite, trucks delivering concrete to
site are required to wash out the chutes back at their yards.
c. Construction works shall not take place during the peak nesting season of New Zealand dabchick (June to December);
d. A search must be conducted for nesting dabchicks prior to the commencement of works and if nests are found that area is to be avoided until the end of that nesting season;
e. Weed harvesting will be avoided within 100 m of raupō beds or trees overhanging the lake where dabchicks could potentially be nesting during the peak nesting season.
f. CCA treated piles and moorings to be encased in a protective coating to prevent the effects of CCA leaching on kākahi;
g. All wharf superstructure constituents to be constructed from untreated hardwood timber;
h. Clearance of sediments from Cell 1 of the sediment trap must be undertaken during the months of February or March and root plugs of watercress be replanted in the spring following cell clearance;
i. All indigenous plantings to be eco sourced from the Foxton Ecological District.
Frances Forsyth
30 September 2015
References
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