avifauna risk assessment - gisborne district€¦ · avifauna risk assessment . march 2017 report...

Appendix 1

Avifaunal Risk Assessment

Avifauna Risk Assessment Gisborne Wastewater Wetlands Phase 2A

Prepared for Gisborne District Council

30 March 2017

CONTENTS

1.0 Introduction 1

1.1 Scope 1

1.2 Background 1

2.0 Methodology 3

3.0 Current State of Environment 3

3.1 Bird habitats and communities 3

3.2 Bird-strike at Gisborne airport 6

3.3 Existing Mitigation 6

4.0 Avian Risk Assessment 7

4.1 Wetland Type 7

4.2 Wetland Location 8

5.0 Recommended Mitigation 10

6.0 Wetland Ecological Benefits and Design Considerations 11

7.0 Limitations, Assumptions and Knowledge gaps 12

8.0 Conclusions and reccomendations 12

AVIFAUNA RISK ASSESSMENT

March 2017 Report No. 1702004 1

1.0 INTRODUCTION This report1, prepared by Ecology New Zealand Limited (’ENZL’) and Morphum Environmental Limited

(Morphum) for Gisborne District Council (‘the client’), presents an Avifauna Risk Assessment (ARA) for a

proposed wastewater wetland that will potentially be located in close proximity to the Gisborne airport,

Awapuni, Gisborne (‘the site’). The findings of this assessment are intended to be used by the client in a

multivariate assessment on wastewater management options that include consideration of potential avifaunal

risks associated with Gisborne airport.

1.1 Scope

The specific scope of this report is to address the following project requirements:

Assessment of both existing and future habitats, bird communities, and risks to the airport;

Assessments of bird communities to consider presence/absence, abundance, behaviour, seasonal

migrations, and local movements; include reporting rates where available;

Review of flight paths, including approach distances, elevations, relative use, and relevance to potential

bird strikes;

Mitigation strategies; Assess risk before and after mitigation and identify residual impacts that will remain

after implementation of mitigation;

Potential ecological benefits of new wetlands, including brief description of wetland design measures to

maximise ecological gains;

Provide conclusions and maps on relative risk depending on site location; and

Identify any assumptions and limitations that have informed the study or gaps in knowledge that have

become apparent.

1.2 Background

In December 1964, an outfall pipe was installed to discharge Gisborne’s untreated wastewater 1.8 km out into

Poverty Bay, Te Moana o Turanganui a Kiwa (the Bay). This system of wastewater disposal continued until early

January 2011. In June 2009, a consent variation was granted and in December 2010 a new treatment plant

was commissioned at Banks Street. With this came a consent requirement for the phased introduction of

additional treatment and disinfection processes.

A further variation to the consent for the wastewater treatment plant was granted in 2014. The primary driver

for the variation was to allow a more effective, sustainable and affordable wastewater management system

to be further investigated, confirmed and implemented. Significant amounts of work have been undertaken in

this space, including Council approval to investigate a constructed wetland process as a means of secondary

treatment post the 2010 wastewater treatment plant. Alternative use and disposal methods are also a

fundamental focus of this investigation.

Numerous trials and desktop exercises have been carried out to query the feasibility of alternative systems,

processes and technologies. The project is now in Phase 2A, which requires further refinement of feasible

options, to enable community consultation after June 2017. A key component being considered for the

wastewater management system is a wastewater treatment wetland with associated habitat values being

incorporated where possible.

The scope of investigations has accordingly been broadened to include areas of land that could be suitable to

locate a treatment wetland. Ecological support services are required to support the decision making process to

select a fit-for-purpose implementable system.

1 This report is subject to the Report Limitations provided in Appendix A.

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2.0 METHODOLOGY A preliminary literature review and GIS investigations were carried out to compile relevant avian information

from existing ecological studies in the area. The results of these investigations were used to guide on-site

habitat assessments undertaken by two ENZL ecologists on –the 5th and 6th of March 2017. Habitat assessments

targeted areas directly surrounding the Gisborne airport and encompassed several proposed wetland sites

(Figure 1). These investigations were used in conjunction with discussions with airport management personnel

and local ornithological experts to assess the significance of the area’s birdlife values and to assess whether

the risk of increased bird-strike impacts may arise as a result of constructing the proposed wastewater wetland.

3.0 CURRENT STATE OF ENVIRONMENT

3.1 Bird habitats and communities

Five notable habitat types exist within the surrounds of the Gisborne airport and proposed wastewater wetland

areas. These habitats are described as agricultural farmland, urban, watercourses, shoreline and

wetland/open water areas (Figure 3). This mosaic of landcover provides suitable habitats for a range of native

and exotic bird species, however bird communities across these local areas are generally dominated by a

select number of bird species. Based on observations recorded by ENZL ecologists, together with information

provided by local experts, these species include masked lapwing (Vanellus miles novaehollandiae), Southern

black-backed gull (Larus dominicanus dominicanus), swamp harrier (Circus approximans), pukeko (Porphyrio

melanotus melanotus), mallard (Anas platyrhynchos), paradise shellduck (Tadorna variegata), house sparrow

(Passer domesticus), Australian magpie (Gymnorhina tibicen), rock pigeon (Columba livia) and red-bill gull

(Larus novaehollandiae scopulinus).

With the exception of swamp harrier and Australian magpie, the above listed species are known to aggregate

in large numbers in areas of suitable feeding, roosting or breeding habitat. This was observed during the site

assessment where mallards were noted feeding in high numbers across large open water and watercourse

habitats. Notable local movements of congregating birds include nightly movements of pigeons into Gisborne

city2 and black backed gulls onto open farmland south of the Gisborne airport. Seasonality effects may also

act to influence these aggregations. For instance, during winter months and/or during high rainfall events, the

habitat provided by the paddocks along the eastern shoreline change as they become waterlogged. During

these times these areas have been known to attract species such as pied stilt (Himantopus himantopus) and

geese (Anser anser) which may locally increase in numbers and replace species such as masked lapwing

which require dryer habitats2.

A recent spike in black-backed gull abundance and activity around Gisborne Airport has been investigated

by Airport management and has been found to be associated with liquid vegetable waste being discarded

adjacent to the airport. The discharges are currently not occurring and as a result, the spike in gull abundance

has tapered off.

No migratory birds (namely shorebirds in large numbers) were discussed by airport management as currently

being a bird strike issue. Discussions with local bird experts reveal that migratory shorebirds do not actively use

the shoreline to the south of Gisborne airport which intensively used by beachgoers, vehicles and dogs2. The

closest habitat used by these migratory birds is located >6 km southwest of the Gisborne airport at Karaua

Stream Lagoon

2 Pers.Comm. Murry Cave (9 March 2017) and Sandy Bull (6 March 2017).



Figure 2: Flooded pasture along eastern shoreline following a summer rainfall event

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March 2017 Report No. 1702004

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3.2 Bird-strike at Gisborne airport

On a descending scale of severity, very large bodied flocking species such as geese pose the greatest bird-

strike risk to airports whilst very small and solitary bird species pose the lowest (Table 1). Bird-strike rates at

Gisborne Airport have historically been among the highest in the country, with reported strike rates as high as

11.5 per 1000 flights3. Discussions with airport management revealed that the key bird species currently posing

risks to aircraft bird-strike are ‘masked lapwings’ and flocks of ‘small birds’. Documented bird-strike rates for

these bird groups between 2010 and 2016 where on average 3.4 masked lapwing strikes and 9.3 small bird

strikes per year4. Other bird species documented within Gisborne airports bird-strike data include swamp

harrier, ‘gulls’ (assumed to include both black-backed and red-billed gulls), pigeon, ‘duck’ and magpie. These

species posing bird-strike risks for the Gisborne airport are associated with using habitats on and nearby the

airport as well as intersecting with aircraft approach distances and elevations.

3.3 Existing Mitigation

In recent years, bird management under taken by airport management and contractors have enabled

Gisborne airport to more effectively manage bird-strike. The current mitigation strategies employed by

Gisborne airport include grass maintenance, driving at birds and shooting. Though a range of techniques have

been trailed including poisoning, gas scare guns and kites, these are not sustainable as birds quickly become

habituated to the interventions.

The maintenance of grass on the airport involves maintaining grass heights at approximately 150-180 mm3. This

height aims to reduce shorter grass habitats preferred by species such as masked lapwing which often

increase in numbers immediately following grass maintenance. A contractor is used to produce hay

approximately six times a year from grassed areas adjacent to the runways. The timing of grass maintenance is

scheduled to additionally commence before grass produces seed to avoid small birds from feeding in these

areas.

Shooting has proved to be one of the most effective means of controlling birds to mitigate the risk of bird strike

at Gisborne airport. Onsite airport shooting is currently undertaken by two airport staff members with pump

action shot guns on an as required basis. Gisborne airport have additionally contracted assistance from AgFirst

Consultants NZ Ltd who control birds outside of the airport with on average 518 birds shot a year between 2010

and 2016. This offsite shooting is undertaken in accordance with a permit from the Department of

Conservation and is primarily undertaken across land immediately south of the airport.

Table 1: Risk and severity of bird strike associated with species identified on site

Species Risk of bird strike34 Severity of bird strike5

Australian Magpie Medium Level 4

Black-backed gull Medium Level 2

Mallard Low Level 2

Paradise shellduck Low Level 2

Pukeko Medium Level 3

Red-billed gull Medium Level 3

Sparrow/Finch/Yellow hammer High Level 5

Sasked lapwing High Level 3

Swamp Harrier Medium Level 4

Starling Medium Level 4

Pigeon Medium Level 3

3 Murry Bell – Gisborne airport Manager, pers com. 6 March 2017

4 Bird-strike and mitigation information provided by provided by Gisborne airport Management

5 Sowden, Richard; Kelly, Terry; and Dudley, Stewart, "Airport Bird Hazard Risk Assessment Process" (2007). 2007 Bird Strike Committee USA/Canada, 9th Annual Meeting, Kingston, Ontario. Paper 8.



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4.0 AVIAN RISK ASSESSMENT

4.1 Wetland Type

The selected wetland type for this project should act a means of passive mitigation which avoids creating

habitat types suited for high risk bird-strike species (Table 2). This would specifically mean aiming to reduce

open water habits for larger bodied flocking species such as geese and ducks. Additionally, larger and diverse

vegetation would provide more suitable roosting and nesting habitat for small to medium sized birds. The

avoidance of creating these habitats will be increasingly crucial the closer the wetland is located to the

Gisborne airport. The wetland types identified by GDC for consideration are listed below.

Dense Raupo / Schoenoplectus / Machaerina

Salt marsh

Diversity wetland (variable structure)

Kahikatea Swamp Forest / Manuka

A swamp wetland type, which results in the creation of open surface water, would provide suitable habitat for

larger bodied waterfowl which pose the greatest risk for airport bird-strike. The extent of open surface water

provided by the wetland would be the primary factor which would determine the number of waterfowl

supported by the wetland. Areas of pastural grass in close proximity to areas of open surface water would

further increase habitat suitability due to the provision of feeding areas.

A design incorporating larger and/or diverse vegetation could provide higher biodiversity values and habitat

complexity. Woody terrestrial vegetation would provide roosting, feeding and breeding habitat for a range of

smaller to medium bird species. Small and medium sized birds in flocks do pose a high risk to airport bird-strike.

Large numbers of sparrows and finches were noted in trees surrounding a wetland/pond area approximately

1.3 km east of the airport which provides evidence that this may occur with a design of this nature.

A saltmarsh wetland type would typically provide densely vegetated areas interspersed with areas of surface

water. This would provide an intermediate between a swamp forest and heavily vegetated sedge wetland.

The creation of a wetland type of this nature would be reliant on saltwater influence. Larger waterfowl could

be attracted to open surface water areas and additionally nest in any ‘dryer islands’ that may be formed by

vegetation.

A raupo and/or sedge dominated wetland would likely provide densely vegetated habitat which lacks areas

of open surface water. Raupo dieback occurs during winter. This is likely to result in the creation of open water

areas in locations dominated by raupo. Additionally, the annual deposition of large amounts of biomass

associated with raupo dieback provides additional pressure on the capacity and life expectancy of the

proposed treatment wetland. Therefore, its suitability should be deliberated. Birds which are likely to use this

habitat include pukeko, small birds during periods when sedges are seeding, and possibly cryptic native birds.

A sedge dominated wetland, with minimal open water, is the preferred wetland treatment option with respect

to reducing the potential to increase the risk of bird strike. Initial recommendations for the design and

operational maintenance of such a wetland are discussed in section 5 below.



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Table 2: Relative increase in bird strike risk associated with the different wetland type proposed

Wetland type Relative risk of increased bird strike

Schoenoplectus / Machaerina reed sedgeland (designed and

maintained with recommendations outlined in section 5) Low

Dense Raupo / Schoenoplectus / Machaerina reed sedgeland Medium

Salt marsh Medium

Diversity wetland (variable structure) High

Kahikatea Swamp Forest / Manuka High

* Table 3 considers the location of wetland in isolation of the type and relative footprints

* Note the above considers relative risk, the overall risk of all options is considered low

4.2 Wetland Location

Aircraft flight paths at Gisborne airport are captured by the airport protection overlay area (APOA) within the

current Gisborne District Plan (Figure 1). Large aircraft are restricted to the main north-south runway whilst

smaller aircraft utilise smaller grassed runways (Figure 1).

Additionally, the GDC operative plan rules seek that no structure or activity in the APOA shall, singularly or

cumulatively attract birds onto Gisborne Airport or into the APOA that may compromise aircraft safety

(8.10.1c).

The three central proposed wetland locations are almost entirely within the airport protection overlay and

intersect aircraft runways (Figure 1). A wetland in any of these locations would require placement either

adjacent to a runway or would almost directly adjoin a flight path/s. It is without a doubt that the risk to bird-

strike will be positively correlated with decreasing distance to the Gisborne airport, therefore it is paramount

that the relative risk of creating any wetlands in these locations are reduced through design and size.

The creation of a wetland to the south of the airport is more likely to pose increased risk to bird-strike if it

provides open water feeding, roosting or nesting habitat for waterfowl and/or shorebird species.



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Figure 4: Numbered wetland locations

Table 3: Relative increase in bird strike risk associated proposed wetland locations

Wetland locations Relative risk of increased bird strike

1 Low

2 High

3 High

4 High

5 Low

6 Medium – High

7 Medium - High

8 Low

9 Low

* Table 3 considers the location of wetland in isolation of the type and relative footprints

* Note the above considers relative risk, the overall risk of all options is considered low

1

2

3

4

5 6 7 8

9



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5.0 RECOMMENDED MITIGATION Mitigation measures currently employed by Gisborne Airport management include grass management,

shooting and driving at birds. These have proven to be the most effective and sustainable methods for the

airport. At this point in time, no alternative methods of mitigation at the airport have been identified to

mitigate the risk of bird strike from the proposed wetland.

The amount and nature of mitigation techniques are dependent on the design and location of the proposed

wetland. These may include (but not be limited to) the following considerations for the design and operational

maintenance of the proposed wetland. Note, these recommendations do not constitute a full operations and

maintenance plan, and relate only to mitigation of the potential increase of bird strike:

Wetland design mitigation

Minimise open water areas. This option may be constrained by the following functional requirements.

Oxidation and sludge settling ponds, if required as part of the wastewater treatment process, would

create open water areas. These areas would have to be actively managed as 'bird-free' areas', with

proven robust and effective management measures.

Emergency forebay that can be maintained following accidental overflows of high sediment loads

from prior treatment processes should the process present this risk.

Consideration of discharge concentrations of E. coli, nitrogen and/or dissolved oxygen. Additional

treatment and remedial processes may be required post wetland treatment prior to discharge to the

receiving environment to ensure these parameters are within an acceptable range. This may include,

rock rip rap shutes and/or UV treatment.

Avoid using woody terrestrial vegetation in the wetland design. This may require consideration of any

requirement for landscape screen planting for any of the proposed wetland locations.

Permanent netting and/or deterrents to avoid access to required open water areas.

The wetland design should allow for each ‘cell’ of the wetland to be completely ‘drawn down’. This will

minimise the period that open water is present during operational maintenance involving plant

replacement. Incorporating a means to achieve intermittent draw down depths are also advised.

Water levels should be progressively raised as vegetation establishes at a rate that limits the amount of

visible open water bodies.

Woody terrestrial vegetation should not be planted on either external or internal bunds of the wetland. It

may be appropriate to plant the bunds in dense reeds and sedges that are tolerant of dryer soils.

Raupo (or other species with annual die back) should not be specified for planting within the wetland

Initial planting of the wetland should occur between November and December (early in the wetland

planting season) with a shallow water level (at or near (5 mm)) the wetland surface. This is to ensure rapid

vegetation growth in ideal warm summer conditions.

Larger grade (≥2 L) plants should be specified to provide more rapid establishment.

Damage and mortality to vegetation due to pukeko and other water fowl should be carefully managed

during the establishment period to ensure complete vegetation establishment and cover occurs. This

may require the use of:

Exclusion netting



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Electric fences

Shooting

Replacing any significant areas of unsuccessful plantings

Operational maintenance

Proactive control and removal of areas of natural raupo colonisation. Follow up planting of rush and

sedgeland species specified in the design of the wetland immediately post raupo control and removal.

Should any bunds be designed to be grassed, maintenance of these grassed areas should involve

regular mowing or grazing to avoid grass seeding.

Over time vegetation may become ‘clumped’ and/or experience attrition resulting in preferential flow

paths and areas of open water. Small areas of open water should be infilled with additional planting

(especially within the first 5 years of operation). Older established reed and sedge wetland beds may

require complete removal and replanting to ensure proper functioning of the wetland treatment system.

This should be undertaken by first completely drawing down the wetland cell to be maintained and then

following the recommendations of pant establishment outlined above.

Cyclical maintenance of vegetation removal and replanting should be implemented to limit the areas of

open water that are available at any one period.

6.0 WETLAND ECOLOGICAL BENEFITS AND DESIGN CONSIDERATIONS As discussed, a reed or sedgeland wetland type is preferred to reduce the potential increased risk of bird strike

as this type provides less favourable, and lower diversity of, habitat for avifauna. Recommendations regarding

design and maintenance are outlined in section 5. More diverse wetland types are not advised (both in terms

of vegetation assemblages and habitat diversity). The inclusion of woody terrestrial vegetation on any bunds is

also not advised. These considerations limit the potential ecological values of the proposed wetland in regards

to biodiversity, however, the proposed wetland will still provide ecosystem services and other ecological

benefits including:

Diversity of habitat on a landscape level

Creation of an (albeit artificial) nationally and regionally rare ecosystem type

Habitat for wetland macroinvertebrates and other fauna including, fish and bird species(mainly pukeko

and cryptic species such as fern bird)

Maintaining and buffering groundwater and surface water levels

Ecosystem services including:

Flood attenuation

Contaminant removal

Carbon sequestration

In addition to the above ecological values there are also cultural, social and economic values associated with

the creation of wetland areas.



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7.0 LIMITATIONS, ASSUMPTIONS AND KNOWLEDGE GAPS

It is reasonable to assume that the Gisborne airport will not want to adopt or modify their current bird-

strike risk management at their cost.

Avian data for the proposed wetland areas and surrounds are based discussions with local experts,

general species ecology and behaviour, bird observations from online databases, and data provided by

GDC and Gisborne airport management. This data was verified over a two day site visit by ENZL and

Morphum in collaboration with GDC.

Although migratory birds do not seem to pose an issue to Gisborne airport, the actual flight paths these

birds may take was not determined.

The risk associated with each proposed wetland type is based on general characteristics of these

wetland systems.

Bird-strike elevation and location data is not currently recorded by Gisborne airport.

8.0 CONCLUSIONS AND RECCOMENDATIONS The proposed wetland locations and wetland types have been ranked in regards to the relative potential

increase in risk of bird strike. However, it should be noted that the overall risk of all options is considered low.

As the proposed location of the wetland increases in relative risk category a greater effort to incorporate

mitigation to reduce the potential of bird strike into the design and operational maintained of the wetland is

required.

A reed or sedgeland wetland type (designed and maintained with recommendations outlined in section 5) is

the preferred wetland type with respect to reducing the potential increase risk of bird strike.

The maintenance of vegetation within the wetland requires careful consideration. The required periodic

replacement of reeds for example will result in the temporary creation of open surface water areas. Options

for mitigating this risk are provided in section 5 of this report.



Report limitations



Report Limitations This Report/Document has been provided by Ecology New Zealand Limited (ENZL) and Morphum

Environmental (Morphum) subject to the following limitations:

i) This Report/Document has been prepared for the particular purpose outlined in ENZL’s and

Morphum’s proposal and no responsibility is accepted for the use of this Report/Document, in

whole or in part, in other contexts or for any other purpose.

ii) The scope and the period of ENZL’s and Morphum’s services are as described in ENZL’s and

Morphum’s proposal, and are subject to restrictions and limitations. ENZL and Morphum did not

perform a complete assessment of all possible conditions or circumstances that may exist at the

site referenced in the Report/Document. If a service is not expressly indicated, do not assume it

has been provided. If a matter is not addressed, do not assume that any determination has been

made by ENZL or Morphum in regards to it.

iii) Conditions may exist which were undetectable given the limited nature of the enquiry ENZL and

Morphum was retained to undertake with respect to the site. Variations in conditions may occur

between investigatory locations, and there may be special conditions pertaining to the site which

have not been revealed by the investigation and which have not therefore been taken into

account in the Report/Document. Accordingly, if information in addition to that contained in this

report is sought, additional studies and actions may be required.

iv) The passage of time affects the information and assessment provided in this Report/Document.

ENZL’s and Morphum’s opinions are based upon information that existed at the time of the

production of the Report/Document. The Services provided allowed ENZL and Morphum to form

no more than an opinion of the actual conditions of the site at the time the site was visited and

cannot be used to assess the effect of any subsequent changes in the quality of the site, or its

surroundings, or any laws or regulations.

v) Any assessments, designs and advice made in this Report/Document are based on the conditions

indicated from published sources and the investigation described. No warranty is included, either

express or implied, that the actual conditions will conform exactly to the assessments contained in

this Report/Document.

vi) Where data supplied by the client or other external sources, including previous site investigation

data, have been used, it has been assumed that the information is correct unless otherwise

stated. No responsibility is accepted by ENZL and Morphum for incomplete or inaccurate data

supplied by others.

vii) The Client acknowledges that ENZL and Morphum may have retained subconsultants affiliated

with ENZL and Morphum to provide Services for the benefit of ENZL and Morphum. ENZL and

Morphum will be fully responsible to the Client for the Services and work done by all of its

subconsultants and subcontractors. The Client agrees that it will only assert claims against and

seek to recover losses, damages or other liabilities from ENZL and Morphum and not ENZL’s and

Morphum’s affiliated companies. To the maximum extent allowed by law, the Client

acknowledges and agrees it will not have any legal recourse, and waives any expense, loss,

claim, demand, or cause of action, against ENZL’s and Morphum’s affiliated companies, and their

employees, officers and directors.

viii) This Report/Document is provided for sole use by the Client and is confidential to it. No

responsibility whatsoever for the contents of this Report/Document will be accepted to any person

other than the Client. Any use which a third party makes of this Report/Document, or any reliance

on or decisions to be made based on it, is the responsibility of such third parties. ENZL and

Morphum accepts no responsibility for damages, if any, suffered by any third party as a result of

decisions made or actions based on this Report/Doc

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