bell bay pulp mill project appendix 4 of witness statement

Bell Bay Pulp Mill Project

APPENDIX 4 of WITNESS STATEMENT

Mr. David Balloch

Construction Impacts of the Effluent Pipeline Crossing of Donovans Bay

January 2007

EnviroGulf Consulting

i

EnviroGulf Consulting January, 2007

Table of Contents

1. INTRODUCTION .......................................................................................................................1

1.1 BACKGROUND..........................................................................................................................1 1.2 SUMMARY OF KEY ENVIRONMENTAL ISSUES ........................................................................1

1.2.1 Physical Environment Issues...........................................................................................1 1.2.2 Water Quality Issues........................................................................................................1 1.2.3 Aquatic Ecology Issues....................................................................................................3 1.2.4 Aquatic Resource Use Issues ..........................................................................................3

2. PROPOSED CONSTRUCTION ..............................................................................................5

2.1 BACKGROUND..........................................................................................................................5 2.1.1 Construction Concept ......................................................................................................5

2.2 ENVIRONMENTAL MANAGEMENT AND MITIGATION .............................................................9

3. ASSESSMENT OF RESIDUAL IMPACTS .........................................................................11

3.1 GENERAL................................................................................................................................11 3.1.1 Classification of Residual Impacts ...............................................................................11

3.1.1.1 Spatial Classification of Residual Impacts ........................................................................... 11 3.1.1.2 Temporal Classification of Impacts ...................................................................................... 12 3.1.1.3 Nature and Significance of Residual Impacts ...................................................................... 14

3.1.2 Draft IIS Assessment of Residual Impacts....................................................................14 3.2 PHYSICAL IMPACTS................................................................................................................15

3.2.1 Hydrodynamics ..............................................................................................................15 3.2.1.1 Existing Environment ............................................................................................................ 15 3.2.1.2 Mitigation and Management Measures................................................................................. 16 3.2.1.3 Assessment of Residual Impacts ........................................................................................... 16

3.2.2 Changes in Bed Morphology.........................................................................................16 3.2.2.1 Existing Environment ............................................................................................................ 16 3.2.2.2 Environmental Management and Mitigation........................................................................ 17 3.2.2.3 Assessment of Residual Impacts ........................................................................................... 17

3.2.3 Changes in Bed Sediment Transport ............................................................................17 3.2.3.1 Existing Environment ............................................................................................................ 17 3.2.3.2 Mitigation and Management Measures................................................................................. 18 3.2.3.3 Assessment of Residual Impacts. .......................................................................................... 18

3.2.4 Generation of Suspended Sediment Plumes .................................................................18 3.2.4.1 Existing Environment ............................................................................................................ 18 3.2.4.2 Mitigation and Management Measures................................................................................. 19 3.2.4.3 Assessment of Residual Impacts ........................................................................................... 19

3.2.5 Underwater Acoustic Impacts .......................................................................................20 3.3 WATER QUALITY IMPACTS....................................................................................................20

3.3.1 Existing Environment ....................................................................................................20 3.3.1.1 pH Regime .............................................................................................................................. 21 3.3.1.2 Water Temperature................................................................................................................. 21 3.3.1.3 Dissolved Oxygen .................................................................................................................. 21 3.3.1.4 Nutrients.................................................................................................................................. 21 3.3.1.5 TSS and Turbidity .................................................................................................................. 22 3.3.1.6 Bed Sediment Chemistry ....................................................................................................... 22

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3.3.2 Mitigation and Management Measures........................................................................23 3.3.3 Residual Impact Assessment .........................................................................................24

3.3.3.1 pH............................................................................................................................................ 24 3.3.3.2 Water Temperature................................................................................................................. 24 3.3.3.3 Dissolved Oxygen .................................................................................................................. 24 3.3.3.4 Total Suspended Sediments and Turbidity ........................................................................... 25 3.3.3.5 Potential Contaminant release from Resuspended Bed Sediments..................................... 26

3.4 AQUATIC ECOLOGY IMPACTS................................................................................................27 3.4.1 Draft IIS Assessment of Residual Impacts....................................................................27 3.4.2 Construction Impacts on Donovans Bay Habitats.......................................................27

3.4.2.1 Existing Environment ............................................................................................................ 27 3.4.2.2 Mitigation and Management Measures................................................................................. 29 3.4.2.3 Assessment of Residual Impacts ........................................................................................... 30

3.4.3 Construction Impacts on Aquatic Flora .......................................................................30 3.4.3.1 Existing Environment ............................................................................................................ 30 3.4.3.2 Mitigation and Management Measures................................................................................. 32 3.4.3.3 Assessment of Residual Impacts ........................................................................................... 32

3.4.4 Construction Impacts on Benthic Macroinvertebrates................................................34 3.4.4.1 Existing Environment ............................................................................................................ 34 3.4.4.2 Mitigation and Management Measures................................................................................. 35 3.4.4.3 Assessment of Residual Impacts ........................................................................................... 36

3.4.5 Impacts on Fish..............................................................................................................38 3.4.5.1 Existing Environment ............................................................................................................ 38 3.4.5.2 Mitigation and Management Measures................................................................................. 38 3.4.5.3 Assessment of Residual Impacts ........................................................................................... 39

3.4.6 Impacts on Marine Mammals .......................................................................................40 3.4.7 Impacts on Aquatic-dependent Birds............................................................................40

3.4.7.1 Existing Environment ............................................................................................................ 40 3.4.7.2 Mitigation and Management Measures................................................................................. 41 3.4.7.3 Assessment of Residual Impacts ........................................................................................... 41

3.4.8 Aquatic Resource Use Impacts .....................................................................................43 3.4.8.1 Existing Environment ............................................................................................................ 43 3.4.8.2 Mitigation and Management Measures................................................................................. 43 3.4.8.3 Assessment of Residual Impacts .......................................................................................... 44

4. REFERENCES ..........................................................................................................................45

4.1 LITERATURE CITED................................................................................................................45


1. Introduction

1.1 Background A 300-m section of the onshore effluent pipeline will cross the intertidal eastern side of Donovans Bay, which is a small estuarine embayment that is contiguous with the lower River Tamar estuary at Long Reach (Figure 1). Donovans Bay is located immediately to the northwest of the small promontory on which the Bell Bay Power Station is located.

A small-unnamed creek flows into the bay from the northeast, which divides the bay into a steeply sloping eastern side and a shallower western side characterised by an expansive intertidal mudflat. The creek is likely to be seasonal in flow with very low flows during the drier months of the year due to its small catchment. Within its catchment, the creek has two reservoirs, namely Lauriston and Howell Reservoirs. The foreshore of the Donovans Bay is rocky.

The proposed alignment of the onshore effluent pipeline across Donovans Bay will be parallel to and east of both the buried gas Tasmanian Natural Gas Pipeline (TNGP) and a Telstra communications cable, both of which were both installed more than four years ago. The existing cleared easement for the gas pipeline is visible from the road, as are pipeline and Telstra cable markers.

1.2 Summary of Key Environmental Issues

1.2.1 Physical Environment Issues

The following physical environment issues associated with the construction phase have been identified:

• Direct disturbance of bed sediments along the proposed pipeline alignment.

• Indirect disturbance of adjacent bed sediments by delayed settling of resuspended bed sediments.

• Interference of inflows from the small creek that enters the northeast corner of the Bay.

• Interference with tidal flows due to the installation and presence of a temporary sandbag cofferdam.

• Increased above-water and underwater noise generated by construction equipment and in-water activities.

1.2.2 Water Quality Issues

The following water quality issues associated with the construction phase have been identified:

Locaton map of the effluent pipelinecrossing of Donovans Bay 1

001Figure No: Job No:

File No:Bell Bay Pulp Mill Project

Gunns Limited

EnviroGulf Consulting 001-A4-F1

Source: Draft IIS (Attachment A in Appendix 54, Volume 16)

Bell Bay Pulp Mill Project APPENDIX 4 3 Construction Impacts of the Effluent Pipeline Crossing of Donovans Bay ________________________________________________________________________________________


• Increases in the concentrations of total suspended solids (TSS).

• Reduced water clarity brought about by increased turbidity in the water column.

• Potential release of nutrients from disturbed estuarine bed sediments.

• Potential release of dissolved and particulate-associated contaminants by estuarine bed disturbance.

1.2.3 Aquatic Ecology Issues

The following aquatic ecology issues associated with the construction phase have been identified:

• Direct disturbance of benthic habitats along the effluent pipeline alignment and adjacent areas.

• Indirect disturbance of adjoining estuarine bed habitats due to delayed settling from bed sediments resuspended by construction activities.

• Sedimentation effects on benthic flora and fauna and their habitats.

• Effects of TSS concentrations and turbidity on benthic flora and fauna.

• Potential reduction of light penetration by turbidity associated with suspended sediment plumes, with consequential impacts on photosynthetic flora of the water column (phytoplankton) and the seabed (benthic algae and seagrasses).

• Acoustic disturbance of estuarine fauna, such as fish and seabirds or other water-dependent birds, that either inhabit or visit Donovans Bay and the lower reaches of the River Tamar estuary.

• Potential effects of elevated concentrations of nutrients or contaminants from resuspended bed sediments.

• Potential effects of temporary exclusion of tidal influences in that part of Donovans Bay behind the temporary sandbag cofferdam during the period of trench excavation.

1.2.4 Aquatic Resource Use Issues

The following aquatic resource use issues associated with the construction phase have been identified:

• Potential direct and indirect disturbance of species of conservation significance within Donovans Bay and conservation areas in the lower River Tamar estuary.

• Potential effects on fish in Donovans Bay that are targeted by recreational fishers.

• Potential deterioration of water quality in the receiving waters of the lower River Tamar estuary with potential effects on existing marine aquacultural sites, such as



the Van Diemen Atlantic salmon farm and water abstractions for Seahorse World and the Garden Island abalone farm.



2. Proposed Construction

2.1 Background The onshore effluent pipeline will cross the intertidal eastern side of Donovans Bay from south to north between kilometre points 2.1 to 2.4 (i.e., 300 m long), just northeast of the Bell Bay Power Station (see Figure 1).

The effluent pipe will be 1,000 mm in external diameter and may be constructed of either glass-fibre reinforced thermosetting plastic (GRP) or high-density polyethylene (HDPE) having an approximate wall thickness of 100 mm. The effluent pipe will be buried in a 2-m deep trench within the upper tidal zone of Donovans Bay, which will be located to the east of both the buried Tasmanian Natural Gas Pipeline (TNGP) and Telstra communications cable.

All early works construction within Donovans Bay that have the potential to resuspend bed sediments will be carried out immediately after the high tide recedes (i.e., after the construction area is naturally dewatered) and during the first two-thirds of outgoing (ebb) tides. The latter will ensure maximum downstream transport and dilution of the generated suspended sediment plumes and any associated nutrients or contaminants within the lower River Tamar estuary and out to sea (Bass Strait). This mitigation avoids potential suspended sediment plume impacts on the main body of water within Donovans Bay and avoids any upriver transport of the plume to potentially sensitive areas, such as the Van Diemen Atlantic salmon farm opposite the existing woodchip jetties.

A temporary sandbag cofferdam will be constructed and, when in place, the main construction activities (i.e., trench excavation) that disturb the bay bed can then be undertaken behind the dewatered cofferdam independently of the state of the tide, since the construction area will be enclosed and separated from the remainder of the bay.

Appendix 54 in the Draft IIS (Volume 16) presents a Construction Environmental Management Plan (EMP) for the effluent pipeline crossing of Donovans Bay.

2.1.1 Construction Concept

Early works (pre-construction) activities will be carried out during the first two-thirds of outgoing tides. However, key construction activities (trench excavation) that cause the greatest amount direct bed sediment disturbance will be conducted behind a dewatered sandbag cofferdam, which isolates the construction area from the main body of water forming Donovans Bay.

Figure 2 shows a schematic of the construction concept.

Schematic of effluent pipelinecrossing at Donovans Bay 2



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The method of construction will involve the following preliminaries:

• Pre-construction surveys.

• Onshore clearance of approaches:

— An onshore Erosion and Sediment Control Plan will be implemented to intercept sediment-laden surface waters and divert them to the sediment detention basin. In addition, temporary soil diversion berms and silt fencing will be installed to avoid or greatly reduce offsite delivery of sediments to surface waters.

• Early works (i.e., pre-construction activities) will be carried out at low tide when the construction site is exposed and, or, during the first two-thirds of the outgoing tides.

• Construction of a temporary access road:

— A 300-m-long and 5-m-wide rubble access road over geotextile fabric will be built on the eastern side of the proposed trench, including the shore approaches and cross-bay alignment.

— A gap of between 5 and 6 m wide will be left at the lowest point within the access road crossing to allow for tidal flows and the creek outflow (if creek flow is present during the scheduled summer construction period).

• Construction of a temporary sandbag cofferdam:

— A 300-m-long and 2-m-wide medium profile cofferdam using bulk fill bags will be emplaced on the western side of the trench. The height of the cofferdam will be decided once detailed information on high water levels are known. The sandbags will be prepared offsite and filled with fresh sand that is clean (i.e., free of contaminants) and transported to site.

— A temporary gap of between 5 and 6 m wide at the lowest point within the cofferdam will be maintained to allow for incoming (flood) and outgoing (ebb) tidal flows, as well as the outflow from a small creek that enters Donovans Bay at its northeastern corner. This gap will act as a tidal gate.

— A submerged low profile cofferdam comprising bulk fill sandbags to a height of 300 mm will be installed within or just downstream end of the 5 to 6 m wide gap at the lowest point to trap coarse sediments transported as bed load. This mitigation measure will limit offsite sedimentation impacts on the bed of the central basin of Donovans Bay.

— During early works when the tidal gate is open, the resuspension of construction-disturbed and displaced bed sediments by tidal and creek flow (if present) will allow turbidity plumes to pass through the tidal gate, but only during the first two-thirds of outgoing tides of about 4 hours duration. This will ensure that the construction-generated suspended sediment plume is transported, diluted and dispersed downriver and out to sea. This mitigation measure avoids any possibility of upriver transportation of the generated suspended sediment



plumes, which could affect potentially sensitive resources such as the Van Diemen Atlantic salmon aquacultural facility.

• Trenching:

— To complete the last part of the trench excavation, the 5- to 6-m wide tidal gate in the temporary sandbag cofferdam will be closed off in the final stage of the trenching operation with additional sandbags, such that the construction area and trenching operation will be isolated from the main body of Donovans Bay. This will prevent the egress of both bed and suspended sediments to the bay.

— The trench will be excavated using hydraulic excavators located along the temporary access road. If rock is encountered, hydraulic rock breakers or rippers will be used although a geotechnical investigation indicates this is unlikely.

— Excavation of the trench will commence from both sides of Donovans Bay, thus shortening the period that the bay will be exposed to construction and the duration that the enclosed area of the bay may lack tidal influence. At this stage it is envisaged that only one high tide within the tidal cycle may be excluded from the enclosed area, owing to the anticipated short duration (about 1 day) of trenching operations.

— Trench spoil will be temporarily placed in the 5-m wide corridor (windrow) between the trench and the sandbag cofferdam.

• Lowering-in:

— Following trench excavation and confirming correct depth and profile, the pipe string (prepared on the northern or southern right of way) will be floated into the Bay at high tide by removing the sandbags in the 5- to 6-m wide tidal gate, and the pipe string sunk into the trench.

• Backfilling:

— The timing of trench backfilling will be timed to coincide with low tide, when the construction area is exposed. The duration of backfilling will be less than a few hours.

— The tidal gate will be closed temporarily by installing additional sandbags, prior to trench backfilling using excavators in the lowest area in the middle of the crossing (i.e., the small tidal creek that enters the bay). Excessively turbid water in the creek mainstem can be pumped to the sedimentation pond and the clarified (desilted) supernatant returned progressively to Donovans Bay.

— The remaining sections of the trench will then be backfilled using the excavators, which will commence backfilling operations in the middle of the crossing and work back to the shorelines on either side.



— The tidal gate will be re-opened to allow inundation by the next high tide, so that the construction area can receive tidal influence, which is required to maintain the flora and fauna of the bottom sediments and intertidal rocky shore.

• Dismantling and reinstatement works:

— Dismantling of the access road and removal of the sandbag cofferdam will be initiated when the construction site is exposed by the receding high tide and continue for the first two thirds of the out going tide.

— The temporary access road will be dismantled from the centre working back to both shorelines. Some of this material can be utilised as rip rap over the trench line, if required. Excess material will be removed to the shoreline and disposed of at an appropriately licensed landfill site or the inert construction waste cell of the solid waste disposal area of the pulp mill.

— The temporary sandbag cofferdam will be dismantled by removing the sandbags and disposing of them at a licensed landfill or the pulp mill’s own waste disposal site.

• Offshore bed morphology reinstatement:

— The cross-bay pipeline alignment will be reinstated according to the Donovans Bay Remediation Plan. The bed morphology of the pipeline alignment will be reinstated, as close as possible to the pre-construction profile, minimising the creation of raised areas likely to aid the spread and colonisation of spartina (rice grass). Note that this occurred after restoration and remediation of the gas pipeline right-of-way, as the post-construction profile left a raised area that was colonised by patches of rice grass.

• Onshore restoration and revegetation:

— The onshore construction areas will reinstated and revegetated according to the Donovans Bay Remediation Plan. The onshore pipeline right-of-way approaches site will be reinstated, as close as possible to the pre-construction profile.

Construction of the crossing will be undertaken in summer, when conditions are typically dry. This will assist with the control of surface water flows and inflows of the small creek that enter the Bay.

2.2 Environmental Management and Mitigation A detailed Construction Environmental Management Plan (CEMP) has been prepared for the pipeline crossing of Donovans Bay (Appendix 54, Volume 16). The CEMP details the following:

• The construction method to be used for the crossing.



• Proposed management measures to avoid or minimise environmental impacts resulting from construction activities.

• Proposed water quality monitoring program.

• An implementation timetable for key aspects of the plan.

• A Remediation Plan for Donovans Bay crossing

The overall plan is basically to follow the construction method used by Duke Energy International (now Alinta) to install the gas pipeline across Donovans Bay in 2002.



3. Assessment of Residual Impacts

3.1 General Section 11 of Volume 3 of the Draft IIS provides details of the potential impacts of the effluent pipeline crossing of Donovans Bay. This reviewer was asked to consider the residual impacts of constructing and installing the effluent pipeline within Donovans Bay and consider consequential direct and indirect residual impacts on the Bay as well as the lower River Tamar estuary.

This review process summarises the findings of the Draft IIS and presents constructive commentary and assesses the validity of the conclusions reached. Where this reviewer has assessed the residual impacts to be incorrect or incomplete, a re-assessment of the relevant residual impacts has been undertaken to address any uncertainties, fill any information gaps and predict the nature, magnitude and duration of the impact. In the case where this reviewer agrees with the Draft IIS assessment of residual impacts, corroborative evidence is given to support the conclusions reached in the Draft IIS.

3.1.1 Classification of Residual Impacts

Residual impacts have been classified at various spatial and temporal scales, so that the area and duration of impacts have a precise meaning. This reviewer considers that the terminology used to describe residual impacts should be clear and easily understood (i.e., non-ambiguous) by the reader.

The classification of effects by nature of the impact (e.g., positive, neutral or negative), magnitude or severity of the impacts (e.g., major, moderate, minor or negligible) and other impact assessment criteria (e.g., reversibility or recoverability) are given separately as resource-specific, residual impact assessment criteria in the individual sections of this chapter, where required.

The following subsections define the spatial and temporal scales and significance of residual impacts on the River Tamar environment.

3.1.1.1 Spatial Classification of Residual Impacts

Definitions of the spatial scale of residual environmental impacts on Donovans Bay and the lower River Tamar estuary are provided so that individual statements about the areal extent of residual impacts have a precise or specified meaning.

The aquatic environment of the lower River Tamar estuary presents a different environmental domain from that of the offshore environment, and residual impacts are evaluated in a longitudinal spatial context, which reflects the linear nature of river and tidal flows. Incoming flows are associated with flood tides and outgoing flows are



associated with ebb tides as well as river inflows. Due to the semi-enclosed nature of Donovans Bay, the whole Bay has been selected and classified as the site scale.

Residual impacts on the estuarine aquatic environment are evaluated at four spatial scales:

• Site scale: Whole of Donovans Bay and the Immediate estuarine environment up to 1 km downstream (i.e., outgoing ebb tide and/or river flow) or upstream (i.e., incoming flood tide) from the centre of the mouth of Donovans Bay. Site scale residual impacts are normally assessed at the end of the estuarine segment (i.e., at 1 km), although residual impacts within the site scale may also be described in context.

• Sub-local scale: Estuarine environment extending between 1 km and 2 km downstream or upstream extending from ‘site scale’ waters.

• Local scale: Estuarine environment extending between 2 km and 5 km downstream or upstream extending from ‘sub-local scale’ waters.

• Regional scale: Estuarine environment extending more than 5 km downstream or upstream extending from ‘local scale’ waters.

Subsequent residual impact assessment sections refer to the above spatial scale definitions, which are presented in bold and italicised text to emphasise their special use in this report. The spatial scales are shown in Figure 3.

3.1.1.2 Temporal Classification of Impacts

Definitions of the temporal scale of residual environmental impacts on the River Tamar estuary are provided so that individual statements about the duration of residual impacts have a precise meaning.

Residual impacts on the estuarine aquatic environment are evaluated at four temporal scales:

• Temporary: residual impacts generally lasting for the duration of a construction activity or generally less than 1 month.

• Short term: residual impacts that last for periods of between 1 month and 1 year.

• Medium term: residual impacts that last for periods of between 1 and 5 years.

• Long term: residual impacts that last for periods of more than 5 years.

Subsequent residual impact assessment sections refer to the above temporal scale definitions, which are presented in bold and italicised text to emphasise their special use in this report.

Classification of spatial scalesin the River Tamar estuary 3



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Bass Strait

Site Scale

Sub-local Scale

Local Scale

Regional Scale

SPATIAL SCALES

Proposed wharfBig Bay

Donovans Bay

Dirty Bay

Low Head

Long Reach

Bell Bay

0 1 2

km



3.1.1.3 Nature and Significance of Residual Impacts

The nature of a residual impact is defined as follows:

• Positive: residual impact that has a beneficial impact on the physicochemical aquatic environment, aquatic ecology or aquatic resource use.

• Negative: residual impact that has an adverse effect on the aquatic physicochemical environment, aquatic ecology or aquatic resource use.

However, to save on repetitive text, subsequent residual impact assessment sections only refer to the nature of a residual impact when it is a beneficial one, that is, a positive impact. In general, most potential impacts on the environment that are evaluated will tend to be negative; therefore, residual impacts assessed in this report should be assumed to be negative unless stated otherwise.

The significance of a residual impact is defined as follows:

Not significant means that the magnitude (i.e., intensity) of a residual impact is simply classified as negligible.

Significant means that the magnitude (i.e., intensity) of a residual impact is classified as major, moderate or minor.

Subsequent residual impact assessment sections refer to the above significance classifications, which are presented in bold and italicised text to emphasise their special use in this report.

3.1.2 Draft IIS Assessment of Residual Impacts

The Draft IIS does not present a detailed assessment of likely residual impacts on the physical environment (e.g., hydrodynamics or noise) or on the water quality of Donovans Bay, but does assess the likely impacts on ‘estuarine ecology’ as an entity (i.e., as a whole), without detailing specific impacts on key aquatic biological resources, such as fish, seabirds, and marine mammals. However, the Draft IIS does assess directly affected benthic environment and affected foreshore areas of Donovans Bay, in the immediate vicinity of construction activities.

Table 11-13 in Section 11.9 of the Draft IIS (Part 11, Volume 3) summarises the residual impacts (i.e., expressed as an ‘overall rating’) on ‘estuarine ecology’, which is reproduced in Table 1 below.



Table 1: Draft IIS impact summary for residual impacts on estuarine ecology of constructing and installing the effluent pipeline across Donovans Bay.

Potential impact Impact rating Proposed mitigation Mitigation impact

Overall rating

Impacts on benthic and foreshore environment during construction.

Moderate negative impact

Implement CEMP and Erosion and Sediment Control Plan.

Minor positive impact

Minor negative impact

Draft IIS conclusion: Overall, impacts on the estuarine environment are considered to be minor. Source: Table 11-13, Section 11.9, Volume 3 of the Draft IIS. Grey shaded area represents the Draft IIS assessment of ‘residual impacts’.

It is assumed that the Draft IIS conclusion presented in Table 1 above relates to the estuarine environment of Donovans Bay and not to the lower River Tamar estuary. Therefore, this reviewer concurs with the Draft IIS assessment of ‘minor negative impacts’ on the ‘estuarine environment’ of Donovans Bay. However, this reviewer considers that residual impacts on the lower River Tamar estuary are temporary and not significant, owing to the implementation of an appropriate level of mitigation and management measures including new measures recommended by this reviewer (see Section 3.4.2.2), which will avoid or reduce potential effects of the cross-bay construction and installation of the effluent pipeline.

Additional analysis and evaluation of the residual impacts of constructing and installing the effluent pipeline at the Donovans Bay crossing are given below to support the Draft IIS conclusions of ‘minor negative impacts’ within Donovans Bay and this reviewer’s conclusion of temporary and not significant residual impacts in the contiguous lower River Tamar estuary.

3.2 Physical Impacts Physical impacts on Donovans Bay are short term and specific to the period of cross-bay and shoreline construction. Predicted residual impacts on the physical environment are assessed below.

3.2.1 Hydrodynamics

3.2.1.1 Existing Environment

Donovans Bay is a shallow tidal embayment that is exposed at low tide to reveal an extensive mudflat. The tidal range downstream at Georgetown is around 3 m, so a similar tidal range may be expected at the mouth of Donovans Bay. At low tide, when the intertidal mudbanks are exposed, there is a permanent subtidal channel along the path of the small creek that flows westwards across the bay.



In summer, during the proposed period of construction, inflows from the small creek are expected to be baseline flows only (i.e., groundwater). Indeed, there may be no flow, as the creek has two water supply reservoirs within its catchment.

3.2.1.2 Mitigation and Management Measures

A detailed Construction Environmental Management Plan (CEMP) has been prepared for the pipeline crossing of Donovans Bay (Appendix 54, Volume 16).

Prior to completion of the temporary sandbag cofferdam, a 5- to 6-m wide tidal gate will be maintained in the lowest section of the cofferdam alignment to allow unobstructed incoming and outgoing tidal flows. However, during the last stage of trenching, the tidal gate will be temporarily blocked to enclose and isolate the construction area from the main part of the bay and, thus, prevent the ingress of incoming tidal flows to the construction area. Hence, construction can take place behind the dewatered sandbag cofferdam regardless of the state of the tide. Excessively turbid water behind the sandbag cofferdam will be pumped to a sedimentation pond and the clarified (desilted) supernatant water pumped back to Donovans Creek in a controlled manner.

3.2.1.3 Assessment of Residual Impacts

During early works construction activities, such as access road construction and sandbag cofferdam installation, the 5- to 6-m wide tidal gate will remain open. Therefore, there will be no obstruction to flows.

During the last stage of trenching, the closure of the tidal gate will cause an obstruction to tidal flows and creek flow (if present). However, the timing of construction activities in the summer is likely to coincide with zero or baseflows (i.e., mainly the groundwater component) in the creek.

Overall, no significant impacts on tidal flows into and out of Donovans Bay are anticipated because tidal flows to and from temporarily isolated construction area will only be stopped for a short period of about 12 hours to prevent turbid water generated by trench excavation and trench spoil runoff. The total construction area behind the cofferdam is 0.44 ha and this represents a small area of shallow water, such that the volume of water (about 2,300 m3 based on an estimated average depth of 0.5 m), forms only a small portion of the total tidal flows in and out of Donovans Bay.

3.2.2 Changes in Bed Morphology


The morphology of the bed of Donovans Bay in the vicinity of the proposed effluent pipeline crossing is shallow and exposed at low tide, except for the narrow channel that forms the mainstem of the creek that is inundated during low tides. This creek flows into the bay from the northeast, which divides the bay into a steeply sloping eastern side and a western side with an expansive intertidal mudflat.



The surface area of Donovans Bay is approximately 105,000 m2 (10.5 ha) and the area of temporary construction works is 300 m long by 12 m wide or 3,600 m2 (0.36 ha). For the purposes of this report, the surface area of the bed of Donovans Bay is also assumed to be 10.5 ha, although the actual area would actually exceed this area, if bed slope was taken into account.

3.2.2.2 Environmental Management and Mitigation

On completion of construction and lowering in of the effluent pipe, the trench will be backfilled and the temporary construction access road and sandbag cofferdam will be removed. Finally, the bottom topography will be reinstated to the pre-disturbance profile. Adoption of the pre-disturbance topography will ensure that the hydrodynamic environment is reinstated and that previous (i.e., pre-construction) levels of scour, bed sediment transport, and sediment deposition and resuspension, will continue as before.


The construction area of 0.36 ha will affect approximately 3.5% of the bottom topography of Donovans Bay and only for the duration of construction activity, pipeline installation, and site reinstatement, which will be about 2 to 3 days at most.

Once dismantling of the temporary access road and sandbag cofferdam and site restoration takes place, the bottom topography will be reinstated. Therefore, changes in bed morphology will be temporary and last only for the duration of construction. In the short and longer term, no significant changes in the bed morphology of Donovans Bay are anticipated due to the proposed reinstatement of the original topographic profile.

Previous crossings of Donovans Bay by the Tasmanian Natural Gas Pipeline (TNGP) and the Telstra cable will have had similar, temporary physical impacts on bed morphology and topography. However, full reinstatement of bottom topography appears not to have been achieved, since a raised area along the TNGP pipeline alignment is still evident. Nevertheless, the current topographic profile has been in place for over 3 years (TNGP was installed in 2002) and is assumed to be stable.

Overall, the residual impacts on Donovans Bay bed morphology (i.e., bottom topography) at the site scale are assessed to be temporary and not significant and will only last for the duration of the cross-bay construction and reinstatement activities. The consequential effects of direct bed disturbance on the bottom habitats, flora and fauna of Donovans Bay are assessed in subsequent sections.

3.2.3 Changes in Bed Sediment Transport


Bed sediment transport in the small creek that enters Donovans Bay delivers coarse-grained sediments that settle out within the bay due to reduced flows. In addition, the frequent high sediment loads carried by the River Tamar also contribute significantly to



sediment deposition within Donovans Bay, which is a backwater area of the lower River Tamar estuary.


A submerged sandbag cofferdam section of about 300 mm high will be installed within the 5- to 6-m wide tidal gate. This will serve to trap coarse sediments (e.g., >125 µm particle size diameter) that are transported as bed load and, thus, limit offsite sedimentation within the central basin of Donovans Bay. Accumulated coarse sediment deposits behind the low profile sandbag cofferdam within the tidal gate will be removed periodically by a backhoe (if required) and disposed of in the trench spoil corridor between the cofferdam and the access road.

3.2.3.3 Assessment of Residual Impacts.

During early works, construction of the temporary access road and sandbag cofferdam will be carried out during low tide when the intertidal zone is exposed. There will be no offsite sedimentation of Donovans Bay during this period. However, subsequent incoming (flood) tidal flows will inundate areas of loose and unconsolidated bed sediments that will have been disturbed or displaced by early works. On the outgoing (ebb) tide and creek flow (if present), bed sediment transport is anticipated but most coarse bed material (> 125 µm particle size diameter) is expected to be trapped behind the low profile sandbag cofferdam section within the tidal gate. Therefore, no significant offsite bed sediment transport or sedimentation within the central part Donovans Bay is expected.

Overall, no significant sedimentation within Donovans Bay is anticipated, owing to the installation of the low relief (300 mm high) sandbag cofferdam section within the tidal gate, which will serve to trap coarse bed sediments as they are transported from construction-disturbed areas by outgoing tidal flows. However, the efficiency of the submerged sandbag cofferdam section is not known and there is expected to be some spill over of coarse sediments, such that a minor sediment tongue may form immediately downstream of the submerged sandbag cofferdam section. This will be verified by monitoring program for Donovans Bay.

3.2.4 Generation of Suspended Sediment Plumes


The Draft IIS did not report any in situ water quality measurements or the results of water quality sampling within Donovans Bay. Therefore, water quality data from the lower River Tamar estuary have been used as a surrogate data set, since the Bay is largely influenced by marine (estuarine) rather than freshwater inputs (Smith 1997a, 1997b).

Background TSS concentrations in the adjacent lower River Tamar estuary are reported in the Draft IIS (page 2-40, Volume 2), to be in the range 5 and 10 mg/L.




The primary mitigation measure during the initial and early works phase of construction is to conduct cross-bay construction activities at low tide and during the first two-thirds of outgoing tides. This will ensure that any suspended sediment plumes in the tidal outflow waters are diluted as they pass through Donovans Bay and are further diluted within the receiving waters of the lower River Tamar estuary and ultimately dispersed in the sea. The large dilution afforded is expected to reduce TSS concentrations to low levels (<50 mg/L) within Donovans Bay and to background levels (5—32 mg/L) within the lower River Tamar estuary and Bass Strait (<5 mg/L).


The magnitude and areal extent of the generated suspended sediment plumes will depend on the volume of bed sediment disturbed and suspended, which is related to the size of the sediment particles disturbed and the direction and velocity of prevailing tidal and creek flows (velocities).

At low tide, the construction area will be free of standing water, except for some residual flow in the tidal creek channel that crosses the effluent pipeline alignment. Early works will commence as soon as the high recedes from the construction area and continue for the first two-thirds of the outgoing tide. During this period, the resuspension of the finer fractions (< 63 µm particle size diameter) of disturbed bed sediments will allow turbid water to enter the central basin of Donovans Bay and thence to the receiving waters of the lower River Tamar estuary.

Typical TSS concentrations in the initially generated suspended sediment plumes are anticipated to lie in the range 200 to 500 mg/L, which will be significantly diluted as it passes through the central part of Donovans Bay where the concentrations of TSS are expected to reduce to low levels of less than 50 mg/L. In the receiving waters of the lower River Tamar estuary, the residual suspended sediment plumes will be further diluted through mixing in a much larger volume of water, such that residual TSS concentrations are expected to be reduced to background levels (i.e., 5—10 mg/L) within the lower estuary and lower concentrations (<5 mg/L) in the sea (Bass Strait).

The Draft IIS in Appendix 54 (Volume 16, page 8) states that once the sandbag cofferdam is complete, there will be no need to work only on the first two-thirds of outgoing tides, as any turbid water will be held inside the sandbag cofferdam and cannot be released to the estuary. It is assumed that this applies mainly for trench excavation and backfilling operations, which have the greatest potential to resuspend bed sediments and mobilise them offsite in the tidal outflows. In this case, any excessively turbid residual water behind the sandbag cofferdam can be pumped to the sedimentation pond for settling with subsequent discharge of the clarified (i.e., desilted) supernatant water to the Bay.

Overall, the generation of suspended sediment plumes will be associated mainly with the early phase of construction prior to the full installation of the temporary sandbag



cofferdam. After the sandbag cofferdam is completed, suspended sediment plumes will be avoided downstream, as the construction area will be isolated from the remaining part of Donovans Bay. Dismantling of the access road and cofferdam after backfilling and bed reinstatement, there is expected to be some residual suspended sediment plumes generated until bed sediments are sorted and the reinstated bed is stabilised.

3.2.5 Underwater Acoustic Impacts

The Draft ISS did not address the residual impacts of construction noise associated with the effluent pipeline crossing of Donovans Bay. This reviewer concludes that noise is not an issue for the following reasons:

• The cross-bay construction activities are located on intertidal areas that will be exposed at low tide and the predominant substratum is soft sediments (tidal mudbanks).

• Most construction generated noise sources will be above-water rather than underwater due to the noise buffering effect of soft bottom sediments. Therefore, residual impacts of underwater noise are assessed as being negligible (not significant).

• The passage of sound from air to water and vice versa is greatly reduced by the Lloyd mirror effect, with a loss of about 63 dB. Therefore, air-borne sound will negligible in producing an underwater sound field in the receiving water environment of Donovans Bay.

However, notwithstanding the above reasons, the residual impacts of construction airborne noise on aquatic and aquatic-dependent birds is assessed in Section 3.4.7, as this reviewer was asked to address residual impacts of construction on estuarine and marine birds.

3.3 Water Quality Impacts

3.3.1 Existing Environment

Donovans Bay is largely affected by marine rather than freshwater influences (Smith 1997a, 1997b), which may be expected given its direct hydraulic connection with the lower River Tamar estuary. There is a low volume, freshwater discharge from a small unnamed creek that enters the bay, but the creek is ephemeral. The catchment of this creek contains two water supply reservoirs, which further diminish the downstream flow regimes of this creek. Therefore, for most of the time, the water quality of Donovans Bay will be similar to that of the lower River Tamar estuary during flood tides.

During high rainfall-runoff events and elevated flow regimes, inflows from the small creek may add a significant freshwater component to the bay and also deliver elevated concentrations of suspended sediments mobilised by overland flow, by riverbank erosion or by the reworking of in-stream sediment deposits.



3.3.1.1 pH Regime

The pH regime of Donovans Bay will mirror that of the lower River Tamar estuary, that is pH 8, which reflects the influence marine waters in the bay. However, during outgoing and low tides, lower pH values are expected to be present in the water of the tidal channel that forms the bed of the small creek within Donovans Bay. Here, the range in pH will vary from that of freshwater (around pH 6.5 to 7.5) to pH 8 as marine tidal waters inundate the bay.

3.3.1.2 Water Temperature

Since Donovans Bay is influenced mainly by marine water during flood tides, the temperature regimes of the lower River Tamar estuary will also be largely reflected within the bay. Therefore, water temperature will vary from 10°C in winter to about 20°C in summer (Foster et al., 1986). However, given the very shallow nature of the upper intertidal areas of the Bay, elevated water temperatures may be expected during the summer.

The Bell Bay Power Station discharges spent cooling waters to Donovans Bay via an outfall on its southern shore, which located adjacent to the power station. The elevated water temperature of the power station discharge will also affect the temperature regime within parts of Donovans Bay.

3.3.1.3 Dissolved Oxygen

Dissolved oxygen (DO) measurements in Donovans Bay were not presented or reported in the Draft IIS. However, since the embayment is influenced by marine rather than freshwater influence (Smith 1997a, 1997b), the DO regime of the adjacent lower River Tamar estuary may be used as a surrogate. DO concentrations measured in the lower River Tamar estuary between 1971 and 1996 by the Department of the Environment and Launceston City Council indicated the presence of oxygenated waters that were compliant with the ANZECC/ARMCANZ (2000) guideline value of greater than 6 mg/L (Pirzl and Coughanowr, 1997). DO regimes have improved progressively since 1992 in line with improvements to sewage treatment plants (STPs) within the River Tamar catchment. Since Donovans Bay receives fresh, well oxygenated waters from Bass Strait during flood tides, then high DO regimes (>80% saturation) are anticipated within this embayment.

3.3.1.4 Nutrients

Nutrient concentrations in Donovans Bay were not reported in the Draft IIS. Therefore, surrogate values have been adopted from the adjacent lower River Tamar estuary.

Ammoniacal nitrogen (NH3-N) concentrations range from 70 to 140 µg/L (Pirzl and Coughanowr, 1997). Median orthophosphate concentrations in Big Bay Point, just upstream in Long Reach, have complied with the ANZECC/ARMCANZ (2000) guideline value of 5 mg/L for estuarine systems, although the Draft IIS (page 2-41 in Volume 2) did not report the actual orthophosphate concentrations.



In the absence of readily available data available to this reviewer, water quality data from the South Esk River have been used as surrogate data for the lower River Tamar estuary. Median nitrate-nitrogen (NO3-N) concentrations may be expected to be 0.012 mg/L (range <0.002—0.146 mg/L and, for total phosphorus (TP), a median concentration of 0.12 mg/L (range 0.007—0.04 mg/L) may be expected (DPIWE, 2005).

3.3.1.5 TSS and Turbidity

Total suspended sediment (TSS) concentrations in Donovans Bay will be similar to that of the lower River Tamar estuary, especially during flood tides, as the bay is largely influenced by marine tidal inflows rather than freshwater inflows. Background TSS concentrations in Donovans Bay have not been determined for the Draft IIS, but are assumed to mirror those of the lower River Tamar estuary, which are reported in the Draft IIS to be in the range 5 to 10 mg/L (page 2-40, Volume 2), and generally increase with distance upriver. Flood events are a key driver for increased TSS concentrations in the River Tamar.

3.3.1.6 Bed Sediment Chemistry

Section 10.5.11 in the Draft IIS (Volume 3, page 6-268) states that contaminated sediments may be present in Donovans Bay according to a desktop study undertaken by Hydro Tasmania (2001). However, the actual sites or contaminant concentrations were not identified nor presented in the Draft IIS. Nevertheless, site-specific bed sediment sampling was undertaken at six sites within Donovans Bay (see Figure 1, Appendix 28, Volume 11) and a summary of the results for the main potential contaminants present (i.e., metals and metalloids) are presented in Table 2 below.

Table 2 Concentrations of metals and metalloids in bed sediment sampled from Donovans Bay. November 2005.

ANZECC/ARMCANZ (2000) Sediment

Quality Guidelines

Donovans Bay bed sediment sampling sites

ISQG-L ISQG-H

Parameter (mg/kg)

S1 S2 S3 S4 S5 S6 (mg/kg) (mg/kg) Arsenic 6 11 8 10 12 11 20 70 Cadmium <1 <1 <1 <1 <1 <1 1.5 10 Chromium 30 11 13 16 17 20 80 370 Cobalt 7 3 5 5 5 6 — — Copper 8 <5 6 7 7 10 65 270 Lead 10 <5 7 9 9 12 50 220 Manganese 199 72 107 161 290 232 — — Nickel 7 5 6 8 9 10 21 52 Vanadium 62 20 21 25 25 30 — — Zinc 36 41 59 74 56 89 200 410 Mercury <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 0.15 1 Source: Non-labelled table in Attachment (‘Appendix’) C of Appendix 28 of the Draft IIS. ISQG-L = low Interim Sediment Quality Guideline value; ISQG-H = High Interim Sediment Quality Guideline value (after ANZECC/ARMCANZ (2000). Grey shaded boxes represent exceedences of the low or high interim sediment quality guideline values; however, none is exceeded.



The main findings are summarised below:

• None of the potential sediment contaminants measured exceeded the low (ISQM-L) or high (ISQG-H) Interim Sediment Quality Guideline values presented in the Australian Sediment Quality Guidelines (ANZECC/ARMCANZ, 2000).

• The absence of contaminated sediments indicates that the catchment of the small unnamed creek that flows into Donovans Bay contains soils of low mineralisation.

• There is no evidence of migration of sediments from more contaminated areas of the River Tamar estuary via either bed sediment transport or the settlement of suspended sediments, subject to this reviewer’s confirmation proviso below.

Given the above summary of background concentrations of metals and metalloids in Donovans Bay, it can be said that the bed sediments are not contaminated. However, this reviewer questions the logic behind the selection of the bed sediment sampling sites shown in Figure 1 of Appendix 28 (Volume 28 of the Draft IIS), which are all located within the bed of the mainstem of the small creek that flows westerly across Donovans Bay. This sampling area represents the lowest point of the effluent pipeline crossing and does not extend into the large areas of exposed intertidal mudflat along the remaining, more elevated sections of the pipeline alignment. Sampling of the bed sediments within the creek mainstem is more likely to reflect the chemistry of sediment inputs from the catchment of this creek, which is most likely to have low mineralisation, given its use as a water supply catchment. Nevertheless, if contaminated bed sediments were present in the intertidal mudflats, residual contaminant concentrations would most likely still have shown up in the analysis of the creek bed sediments, owing to their direct proximity to the mudflats.

Recommendation

It is recommended in any future Donovans Bay environmental baseline and monitoring program that bed sediment samples should also be collected from the intertidal mudflats of the bay, which are more likely to be affected by marine and River Tamar estuarine waters that may have deposited transported contaminated suspended sediments.

3.3.2 Mitigation and Management Measures

Implementation of the Construction Environmental Management Plan (CEMP) for the effluent pipeline crossing of Donovans Bay, as well as the Remediation Plan and the Erosion and Sediment Control Plan for the onshore sections of the pipeline right-of-way will, to a large part, avoid or limit impacts on water quality of the Bay.

Early works will be conducted at low tide and where construction is necessary during ebb tides, then work will be conducted during the first two-thirds of outgoing tides, such that any suspended sediment plumes will be short-circuited across the Bay to the receiving waters of the lower River Tamar estuary, where dilution of the plume will be maximised.



No additional management measures or mitigation are proposed for the protection of water quality within Donovans Bay. The proposed water quality monitoring program will also serve to forewarn of any unforeseen water quality problems, so that remedial measures may be undertaken to restore water quality.

3.3.3 Residual Impact Assessment

The residual impacts of cross-bay construction and installation of the effluent pipeline within Donovans Bay may affect the following water quality parameters.

3.3.3.1 pH

Given the presence of oxic sediments within Donovans Bay, resuspension of bed sediments by construction activity is unlikely to significantly affect the alkaline pH of the mainly marine/ estuarine waters of the bay by the release of major anions and cations and due to the inherent high buffering capacity.

Overall, no significant impacts on the pH regime of Donovans Bay are anticipated during the short period of construction.

3.3.3.2 Water Temperature

Given the very short term nature of proposed construction activities within Donovans Bay, water temperature is not considered a water quality parameter that may be affected by the proposed construction activities and is, therefore, not considered further.

3.3.3.3 Dissolved Oxygen

The Draft IIS did not present any organic matter analysis or redox determinations of sediments within Donovans Bay; therefore, surrogate information has been obtained from the wharf site where redox potentials were measured.

Mitigation and Management Measures

The mitigation and management measures that include early works construction to be conducted during low tides or during the first two-thirds of outgoing tides, will ensure that the suspended sediment plumes and any associated putrescible organic matter will pass rapidly through Donovans Bay to the receiving waters of the lower River Tamar estuary. No further mitigation nor management measures are proposed nor required.

Assessment of Residual Impacts

Given that the neighbouring surface (0 to 50 cm) and deeper (>50 cm) bed sediments of the lower River Tamar estuary at the proposed wharf facility site are oxic (i.e., positive redox potentials in range +61 to +283 mV), it is unlikely that sufficient putrescible organic material is present in the bed sediments of Donovans Bay to exert an oxygen demand that would significantly impact upon the DO levels of the water column of the Bay



following resuspension of bed sediments disturbed by construction. The proposed water quality monitoring program will verify the validity of this assessment.

3.3.3.4 Total Suspended Sediments and Turbidity

One of the key water quality parameters likely to be affected by the cross-bay construction and installation of the effluent pipeline is total suspended sediments (TSS) and associated turbidity.

Impact Assessment Criteria

Four categories of residual impact on TSS loads and concentrations have been defined:

• Major: TSS loads and concentrations in the water column are continuously greater than 100% above background levels at average river or tidal ebb flow.

• Moderate: TSS loads and concentrations in the water column are continuously 50% to 100% above background levels at average river or tidal ebb flow.

• Minor: TSS loads and concentrations in the water column are continuously 15% to 50% above background levels at average river or tidal ebb flow. In general, project-induced changes in the TSS loads and concentrations of substances in this category are within the natural range and cyclic fluctuations.

• Negligible (not significant): TSS loads and concentrations in the water column are continuously less than 15% above background levels at average river or tidal ebb flow. In general, project-induced changes in TSS loads and concentrations of substances in this category are well within the natural range and cyclic fluctuations.

Mitigation and Management Measures

The general mitigation and management measures outlined in Section 3.3.2 above have been designed primarily to address fugitive sediments derived from early works construction disturbance of the bed sediments within Donovans Bay. No additional or site-specific mitigation measures are proposed nor are necessary.

Residual Impact Assessment Conclusion

Section 3.2.4.3 above indicated that during the initial and pre-construction phase (i.e., early works), suspended sediment plumes will be generated and transported by outgoing tidal flows, as early works’ construction activities will be timed to coincide with the first two-thirds of outgoing tides.

Typical TSS concentrations in the initial suspended sediment plumes are anticipated to lie in the range 200 to 500 mg/L. These TSS concentrations are expected to reduce rapidly by dilution as the plume passes through the central part of Donovans Bay, with expected TSS concentrations of less than 50 mg/L. As the ebb tide transports the suspended sediment plume downstream, TSS concentrations will be further reduced to



background levels (5—10 mg/L) by mixing with the large volumes of outgoing tidal water within the lower River Tamar estuary.

Overall, residual impacts of shore-end and cross-bay early works’ construction activities on suspended sediment transport are predicted to be significant within the site scale (see Section 3.2.4.3). However, the magnitude of the residual impact is greatly reduced owing the temporary nature of the early works’ construction-generated silt plumes. Once the temporary sandbag cofferdam is complete, there will be no discharges of suspended sediment plumes from the construction area behind the cofferdam. Excessively turbid water behind the cofferdam will be pumped to an onshore sedimentation pond and clarified (i.e., desilted) water will be returned progressively to Donovans Bay.

Overall, the residual impacts of elevated TSS concentrations on water quality are assessed to be temporary and negligible (not significant) at the site scale or greater, owing to their transient passage through Donovans Bay. The principal mitigation measure of conducting early works’ construction activities to coincide with the first two-thirds of outgoing tides reduces the duration (time) that elevated TSS concentrations will occur within the confines of Donovans Bay. The consequential effects of elevated TSS concentrations and turbidity on aquatic flora and fauna are assessed in subsequent sections.

3.3.3.5 Potential Contaminant release from Resuspended Bed Sediments

Construction disturbance of intertidal bed sediments within the effluent pipeline crossing in Donovans Bay has the potential to release bed sediment contaminants into the water column as a consequence of resuspension. The contaminants may be either particulate-bound or dissolved in the sediment interstitial (pore) water

Section 3.3.1.5 above indicated that the bed sediment concentrations of metals and metalloids were below the low and high interim sediment quality guidelines promulgated by ANZECC/ARMCANZ (2000), indicating that the bed sediments of Donovans Bay are not contaminated. Therefore, residual impacts of contaminant release from bed sediments on the water quality are assessed in both the short term and long term as not significant at the site scale or greater.

As recommended in Section 3.3.1.5, future environmental monitoring should undertake the sampling and analyses of bed sediments from the intertidal mudflats in addition to the bed of the creek (already sampled) that flows westerly across Donovans Bay. This expansion to the monitoring program will provide confirmation that there is an absence of bed sediment contamination along the entire intertidal section of the proposed effluent pipeline alignment.



3.4 Aquatic Ecology Impacts

3.4.1 Draft IIS Assessment of Residual Impacts

Table 1 in Section 3.1.2 above presented a summary of the Draft IIS assessment of residual impacts on estuarine environment, which was assessed as a ‘minor negative impact’. However, the spatial and temporal scales of the residual impact were not described. Therefore, this reviewer has re-assessed the residual impacts of proposed construction and installation of the effluent pipeline within Donovans Bay, as well as impacts on the receiving water environment of the lower River Tamar estuary, to corroborate the general findings and conclusions of the Draft IIS.

3.4.2 Construction Impacts on Donovans Bay Habitats


The principal estuarine habitats that will be disturbed by construction are the soft bottom sediments (i.e., mud banks) along the proposed alignment and the crossing of the two foreshore areas.

Previous Third Party Construction Disturbance

There are some changes to the general pattern of the habitat types evident in Donovans Bay that appear to coincide with the location of the Tasmanian Natural Gas Pipeline (TNGP). There is evidence of disruption to the pattern of zonation on the shoreline, as the rocky shoreline was not reinstated. In addition, the area bed sediment overlying that section of the TNGP alignment across the mudflats has surface sediments of a different composition compared to the adjacent and surrounding mudflat. This implies that a different backfill material may have been used or that coarser-grained material in the backfill (i.e., assuming trench spoil was the source of backfill) is now at the surface. These observations highlight the need for reinstating similar habitat types during construction and installation of the effluent pipeline across Donovans Bay (see Section 3.4.2.2 below). Plate 1 shows typical intertidal zonation of the shoreline and Plate 2 shows the rocky substratum of the upper shoreline.

Mudflat Habitats

The existing mudflat habitats are characterised by the presence of fine-grained sediments. While the Draft IIS did not describe the particle size distribution (PSD) of the sediment cores that were sampled, surrogate fine-grained bed sediment data from wharf site in the lower River Tamar estuary have been used. The use of fine-grained bed sediment data is relevant, since there are extensive mudflats within Donovans Bay, which reflects its low energy hydrodynamic environment and the absence of significant waves (except for wind-induced waves) due to the bay’s sheltered position.



Plate 1 Intertidal zonation of the eastern shore of Donovans Bay.

Plate 2 Upper intertidal rocky area to the west of the small creek inflow on eastern shore of Donovans Bay.



The very fine sediments that are expected to form the mud banks within Donovans Bay are likely to comprise very fine silts (<0.0078 mm PSD) and clays (<0.0039 mm PSD). These soft bottom sediments present habitat for a limited number of species of estuarine flora (Section 3.4.3.1) and fauna (Section 3.4.4.1).

Rocky Foreshore Habitats

The foreshore of Donovans bay is characterised by the presence of rocks that are covered with a thin layer of fine sediments, which also covers the coarse sand and shelly substratum underlying the rocks. This habitat is narrow but structurally diverse with the rock surfaces and interstices providing a variety of microhabitats and niches for a range of estuarine flora and fauna.


The Donovans Bay Construction Environmental Management Plan (CEMP) and Rehabilitation Plan will ensure that the pipeline alignment is restored to its pre-disturbance topographic profile, which includes reinstatement of the rocky foreshore.

Recommendations

In addition to the proposed environmental management measures and mitigation outlined in the Donovans Bay CEMP, the following management and reinstatement measures are recommended by this reviewer:

• Rocky foreshore reinstatement and rehabilitation:

— During initial clearing of the foreshore and its approach from land, rocks should be temporarily stockpiled in an adjacent emplacement area.

— After the trench has been excavated and the effluent pipe string lowered in, the trench should be backfilled with trench spoil and the pre-construction topography reinstated.

— After the foreshore bed profile has been reinstated, the temporarily stored rocks should be returned to finalise rehabilitation of the northern and southern foreshores directly disturbed by construction.

• Mudflat reinstatement to pre-construction topography and sediment type:

— During initial trench excavation, surficial soft sediments (i.e., mud) should be placed on the western side of the 5-m wide trench spoil corridor, which is located between the temporary access road and sandbag cofferdam.

— Trench spoil from deeper sediments within the trench should be placed on the eastern two-thirds of the trench spoil corridor.



— Backfilling should be in the reverse order, such that the final trench covering will be the soft sediments (mud) recovered from the western side of the trench spoil corridor.

By using the above procedures, final reinstatement of the foreshore and mudflats along the pipeline alignment will ensure that, as far as is practicable, the pre-construction bottom and foreshore topographic profiles are retained and that they are formed of similar sized materials as before.


Implementation of the Donovans Bay CEMP, Remediation Plan, onshore Erosion and Sediment Control Plan, and the additional mitigation and management measures (as recommended above) will ensure that the character of the rocky foreshore and mudflats are not changed substantially.

The area of disturbance compared to the remaining areas of the bay unaffected by construction activity, gives a measure of the areal extent of the physical impact and its significance. Assuming that the mudflats form about 75% of the area of Donovans Bay (105,000 m2), then the total area of mudflats is about 80,000 m2 (or 8 ha) The area of temporary construction works is 300 m long by 12 m wide or 3,600 m2, which is about 4.5% of the total area of mudflat habitat. Therefore, the residual impact on the mudflat habitat type is assessed in the very short term as minor within the site scale. In the short term and longer, the physical attributes (e.g., sediment composition, particle size distribution and organic matter content) of the reinstated cross-bay alignment will recover as tidal and creek flows redistribute sediments and as new sediments are deposited.

Following post-construction site reinstatement and rehabilitation, these two habitat types will stabilise and recover. The consequences of the temporary loss or degradation of the mudflat and rocky intertidal habitats on aquatic flora and fauna is assessed in subsequent sections.

3.4.3 Construction Impacts on Aquatic Flora


The key aquatic flora groups in Donovans Bay are phytoplankton, benthic algae and seagrasses, as well as emergent vegetation such as reeds and rushes.

Phytoplankton

The phytoplankton of Donovans Bay are predominantly marine species, since the Bay is affected by marine rather than freshwater influences (Smith 1997a, 1997b). A long list of phytoplankton species is not required, as the residual impacts of deteriorated water quality on phytoplankton are assessed as a whole, that is, treating phytoplankton as a



collective group of microscopic photosynthesising plants in the water column that have a common functionality and environmental requirements.

Marine phytoplankton are at the mercy of tidal flows and fresh standing crops are brought in with each flood tide. The freshwater component of phytoplankton (i.e., potamoplankton) will virtually be absent or a very minor component, owing to either the absence of flow or very low baseflow in the small creek that flows into Donovans Bay during the summer, when construction is scheduled.

Benthic algae

The Draft IIS does not give a detailed description of benthic algae inhabiting Donovans Bay or the lower River Tamar estuary. However, it assumed that benthic green (Chlorophyta), red (Rhodophyta) and some brown (Phaeophyta) algae are present, given the strong marine tidal influence and presence of sand and shelly grot at the mouth of Donovans Bay.

Seagrasses

The Draft IIS (page 6-278 in Volume 3 and page 9 of Appendix 28 in Volume 11) states that there is no seagrass present on the bed of Donovans Bay. However, Aquenal (2001 and 2002) identified the seagrass Zostera tasmanica as being present in Donovans Bay. The Draft IIS also presents the results of baseline surveys of estuarine habitats in Long Reach (Appendix 25, Volume 11), which showed the presence of patches of seagrass (Zostera tasmanica and Z. muelleri ) are present within the subtidal habitats of both Big Bay (0.5 km upriver) and Dirty Bay (1.0 km upriver), which are also contiguous with the lower River Tamar estuary.

Given the aforementioned information, this reviewer accepts that seagrass is present in Donovans Bay and most likely to be present on the coarse-grained bed sediments, such as sands, near the western part and mouth of the Bay.

Invasive Plant Species

Rice grass (Spartina anglica) is a Northern Hemisphere intertidal saltmarsh plant that was deliberately introduced to Tasmania between the 1930s and the 1970s. Rice grass was introduced for its potential benefits to coastal engineering and agriculture but the spread of rice grass has emerged as a serious problem, degrading Tasmania's estuaries. Rice grass is present in Donovans Bay and occurs in patches of varying size on the soft bottom sediments in the upper intertidal area. Plate 3 shows patches of rice grass on mudflats within Donovans Bay.

No introduced benthic algal species are known to be present.



Plate 3 Patches of rice grass (Spartina sp.) on mudflats in Donovans Bay.


No additional mitigation or management measures for avoiding or reducing impacts on aquatic flora of Donovans Bay are proposed nor are they required. Implementation of the CEMP and Rehabilitation Plans are considered by this reviewer as adequate to significantly reduce the potential for offsite sedimentation impacts and also limit the frequency and duration of suspended sediment plumes and associated turbidity in the water column of Donovans Bay and the receiving waters of the lower River Tamar estuary.


The residual impacts on the aquatic flora of Donovans Bay and the lower Rover Tamar estuary are assessed below.

Phytoplankton

The presence of construction-derived suspended sediment plumes in the water column of Donovans Bay during the first two-thirds of outgoing tides is not expected to deleteriously affect phytoplankton in the water column. Exposure of phytoplankton to elevated TSS concentrations and associated turbidity and any released nutrients is too short for significant effects to occur. The duration of cross-bay construction is 2 to 3 days with outgoing (ebb) tides occurring every 6 hours.



Overall, residual impacts on phytoplankton are assessed as not significant at the site scale or greater within the very short time scale of proposed construction activity in Donovans Bay.

Benthic Vegetation (algae and seagrasses)

Benthic vegetation may be affected by sedimentation and increased TSS concentrations and associated turbidity in the water column.

Sedimentation

Section 3.2.3.3 assessed that no significant sedimentation within Donovans Bay is anticipated, owing to the installation of the low relief (300 mm high) sandbag cofferdam section within the tidal gate, which will serve to trap coarse bed sediments as they are transported from construction-disturbed areas by outgoing tidal flows. However, a minor sediment tongue (i.e., area of higher sedimentation rates) may occur downstream of the tidal gate, which will essentially be confined to the intertidal and subtidal bed of the small creek that crosses Donovans Bay and passes through the tidal gate. The bed of this creek will be characterised by bed sediment mobility, which is not conducive to benthic plant colonisation or establishment. Therefore, sedimentation impacts on benthic vegetation are not anticipated due to their absence along the creek bed.

In addition, secondary sedimentation (i.e., delayed settlement of resuspended bed sediments or cascade suspension) is not expected to occur to any significant degree, as the construction-generated suspended sediment plumes will be carried through Donovans Bay by the outgoing tidal flows. Note that the deliberate coinciding of construction activity with the first two-thirds of outgoing tides is a mitigative measure that also serves to avoid or limit delayed settlement of suspended sediments within Donovans Bay, as well as the lower River Tamar estuary.

Overall, residual impacts of sedimentation on the benthic vegetation (i.e., algae and seagrass) are assessed as negligible (not significant) at the site scale or greater.

Suspended Solids and Turbidity

Section 3.2.4.3 above indicated that typical TSS concentrations in the initial suspended sediment plumes are anticipated to lie in the range 200 to 500 mg/L. These TSS concentrations are expected to reduce rapidly by dilution as the plume passes through the central part of Donovans Bay, with expected TSS concentrations of less than 50 mg/L. As the ebb tide transports the suspended sediment plume downstream, TSS concentrations will be further reduced to background levels (5—10 mg/L) by mixing with the large volumes of outgoing tidal water within the lower River Tamar estuary.

The turbidity in the water column will be intermittent and of very short duration as construction-derived suspended sediment plumes pass through Donovans Bay during the first two-thirds of outgoing tides. The intensity, frequency and duration of elevated turbidity are insufficient to cause any significant decrease in primary productivity that could affect the growth of benthic vegetation. Potential effects will also be countered by



the shallowness of Donovans Bay, which allows photosynthetically active light penetration of the entire water column, even in the presence of the predicted low levels of turbidity.

Overall, the residual impacts of increased TSS concentrations and associated turbidity in the water column on the benthic vegetation of Donovans Bay and the lower River Tamar estuary are assessed as not significant at the site scale or greater.

Invasive Plant Species

After the effluent pipeline has been installed and the trench backfilled, the pre-construction topographic profile will be reinstated. However, the final surface overlying the buried pipeline will be characterised by ‘bare’ mud, which offers new habitat for colonisation by invasive species, such as rice grass. There is little than can be done to avoid this occurring, as previous cross-bay pipeline and telecommunication cable installations have resulted in the inadvertent establishment of rice grass patches.

Overall, the residual impact of providing new habitat areas for potential rice grass colonisation is assessed in the short term or longer as minor within the site scale (i.e., Donovans Bay), and not significant at the site scale or greater. Recovery from this negative residual impact can only be achieved by active intervention (see below) as rice grass has a high propensity for successfully competing with native saltmarsh vegetation.

Recommendation

This reviewer recommends that Gunns liaise with the Rice Grass Advisory Group (RGAG) to seek advice and direction on rice grass management within Donovans Bay and in relation to the project’s construction-disturbed area. Depending upon the advice received, a commitment to early control techniques to reduce rice grass infestation within in cross-bay construction area may be undertaken.

3.4.4 Construction Impacts on Benthic Macroinvertebrates


A brief outline of rocky intertidal and sift bottom sediment macroinvertebrates fauna, as well as marine pests and species of conservation significance, is given below.

Rocky Intertidal Invertebrate Fauna

The rocky intertidal areas of Donovans Bay are characterised by the presence of a small number of gastropods and barnacles on the upper surfaces of the rocks. The barnacle (Eliminius covertus) is commonly found on the rocks of the upper intertidal zone, as is the dark-mouth conniwink (Bembicium melanostoma). There is no evidence of widespread algal cover on the rocks. Underneath the rocks and within rock crevices, the mudshore crab (Helograpsus haswellianus) is commonly observed. A large band of the Pacific Oyster (Crassostrea gigas) occurs across the lower end of the rocky intertidal.



Soft Sediment Intertidal Invertebrate Fauna

The surface of the mudflat is characterised by the widespread presence of the sentinel crab Macropthalmus of which two species are present, the soldier crab (Mictyris platycheles) and the gastropod Polinices sp.

Marine Pests

There are no records of any introduced marine pests within Donovans Bay, except for the Pacific oyster (Crassostrea gigas), which forms a band along the lower section of the rocky foreshore. The Draft IIS (page 6-282, Volume 3) indicates that another introduced species, a spionid polychaete worm (Boccardia proboscides) may be present in the lower River Tamar estuary, but is considered a marine pest of low priority in Australia (Hayes et al., 2005

Macroinvertebrates of Conservation Significance or Protected Species

In addition to the Tasmanian TSP Act list of threatened species, there are a number of marine macroinvertebrate species that are protected under the Living Marine Resources Management Act 1995. Protected species include limpets in the superfamilies Fissurellacea, Patellacea and Siphonariacea. No representatives of these limpet groups appear to be present within Donovans Bay. However, one species of limpet, Siphonaria diemenensis, was recorded in the lower River Tamar estuary (page 31 in Appendix 25 in Volume 11 of the Draft IIS).


Implementation of the Construction Environmental Management Plan (CEMP), Rehabilitation Plan and onshore Erosion and Sediment Control Plan will aid in avoiding or limiting the areal extent and magnitude of potential effects on the macroinvertebrate fauna of Donovans Bay. In addition, the recommendation that backfilling of the trench should be conducted using the trench spoil with final grading using stockpiled fine sediments initially excavated from the trench line surface sediments, will aid in rapid colonisation and re-establishment of macroinvertebrates.

Trench excavation will be undertaken behind the dewatered temporary sandbag cofferdam. Therefore, it is recommended that only one high tide within the tidal cycle be excluded from the construction area, thus avoiding or limiting desiccation damage and potential mortality of macroinvertebrate fauna of the upper intertidal mudflats and rocky foreshore.

No additional site-specific mitigation or management measures are proposed to limit construction effects on the macroinvertebrate fauna of Donovans Bay, given the low likelihood of residual impacts.




The principal effects on macroinvertebrates stem from the loss or degradation of benthic habitats and burial of macroinvertebrates along the trench line, access road and cofferdam, as well as lateral sedimentation impacts and increased TSS concentrations in the water column.

Loss or Degradation of Macroinvertebrate Habitat

Construction of the temporary access road, sandbag cofferdam and trench spoil corridor represents a total temporary loss of 0.36 ha (see Section 3.2.2.1) of benthic macroinvertebrate soft bottom (mud) habitat in the upper intertidal area of Donovans Bay. The total area of unaffected, similar upper intertidal habitat within Donovans Bay is about 3 ha, hence construction will affect about 12 % of this type of habitat, which represents a moderate impact at the site scale. in the very short term. However, placed in perspective, this type of upper intertidal habitat is widespread along the lower River Tamar estuary, including other embayments. In the short term and longer, macroinvertebrates will recolonise this area of disturbed mudflat habitat.

There is a high potential for full recovery of the intertidal habitat in the medium to long term, as has been shown following the installation of the Duke Energy natural gas pipeline about three years ago. The Draft IIS (page 8 in Appendix 28 in Volume 11) states that ‘there appears to have been a recolonisation of areas disturbed after the construction of the gas pipeline with densities of infauna relatively similar to those found elsewhere in the lower Tamar. It would appear that disturbance to the mudflat is likely not to pose a particular threat to the fauna.’

Recovery

Recolonisation of construction-disturbed bed sediments is expected to occur rapidly. Mobile macroinvertebrate fauna will move in from surrounding undisturbed or less-disturbed habitats within the short term (i.e., weeks or months). Larval recruitment of new individuals to the restored construction zone will also contribute to recolonisation and population re-establishment in the medium term. The rates of benthic macroinvertebrate recolonisation and population establishment will also vary depending on the material used to backfill the pipeline trench. At this juncture, it is proposed to backfill the trench with trench spoil, which should promote rapid recolonisation because of the existing organic and microbial biomass. If backfilling with clean sand (i.e. low organic matter content, nutrients and microbial biomass) were to occur, recolonisation would be a slower process.

Suspended Sediments

Section 3.2.4.3 above assessed that typical TSS concentrations in the initial suspended sediment plumes are anticipated to lie in the range 200 to 500 mg/L. These TSS concentrations are expected to reduce rapidly by dilution as the plume passes through the central part of Donovans Bay, with expected TSS concentrations of less than 50 mg/L. As the ebb tide transports the suspended sediment plume downstream, TSS



concentrations will be further reduced to background levels (5—10 mg/L) by mixing with the large volumes of outgoing tidal water within the lower River Tamar estuary.

Short-term exposure of benthic macroinvertebrates to the construction-generated suspended sediment plumes in the water column of Donovans Bay is not expected to deleteriously affect their survival or growth owing to the predicted low TSS concentrations that will be present in the plumes. Many of the benthic macroinvertebrates present in Donovans Bay and the lower River Tamar estuary are sediment-tolerant species, which is to be expected given that the estuary is frequently turbid.

Overall, residual impacts of suspended sediments on benthic macroinvertebrates are assessed to be not significant at the site scale or greater.

Invasive Species

Construction disturbance of the intertidal areas may create new habitat that introduced marine species may colonise and establish viable populations. The risk is high for the Pacific oyster (Crassostrea gigas), which already has well-established populations within Donovans Bay. However, the risk is considered low for the polychaete worm (Boccardia sp.), which is known to present (from one observation) in the Bay and lower River Tamar estuary.

Pacific Oysters

Pacific oysters populations are already well established in Donovans Bay, being found in dense bands in the lower sections of the intertidal rocky shoreline. After reinstatement of the rocky foreshore, this species is expected to recolonise and re-establish viable populations on the rock surfaces of the restored shoreline. This is a successful species and there is little that can be done to prevent this from happening. Therefore, the residual impact may be classified as neutral, since the status quo will be re-established.

Boccardia

The Draft IIS states that ‘the only introduced species that may have been recorded from the present survey is a somewhat damaged specimen of the spionid polychaete Boccardia proboscidea, which is a North American species that has colonised marine waters of Victoria (Blake and Kudenov, 1978). However, it is considered a marine pest of low priority in Australia (Hayes et al., 2005).’

While construction disturbance of the intertidal areas may create new habitat for this introduced marine species to colonise, the risk however appears low. There is already evidence of substantial transport and movement of sediments throughout the Tamar estuary. Therefore, it would be expected that there is a relatively continuous creation of new habitat and that the disturbance resulting from the cross-bay construction is unlikely to create any particular new environment that may allow for colonisation of this marine pest.



Macroinvertebrates of Conservation Significance

Previous sections indicate that the residual impacts of sedimentation and suspended sediments on benthic macroinvertebrates are assessed to be not significant at the site scale or greater. Therefore, residual impacts on the one species of the protected limpet, Siphonaria diemenensis, which occurs within local scale in the lower River Tamar estuary are also assessed as not significant.

3.4.5 Impacts on Fish

The generalised effects of effluent pipeline construction within Donovans Bay on fish populations result from changes in sedimentation (habitat degradation), water quality (increased TSS concentrations), and indirect impacts on fish food resources (changes in macroinvertebrate populations, algae and detritus).

Residual impacts of constructing and installing the effluent pipeline in Donovans Bay are assessed below.


The Draft IIS gives a list of fish species inhabiting or expected to be present in the River Tamar estuary. However, a sub-list of species typically occurring in the lower estuary (and which may occur in Donovans Bay) is difficult to ascertain from the Draft IIS.

A total of 110 fish species have been documented in the River Tamar estuary (Pirzl and Coughanowr, 1997). The distribution of these fish species was related to salinity tolerance and availability of habitat. Most species are found in the lower and middle reaches of the estuary. The most common fish species known to inhabit the estuary include the yellow-eyed mullet (Aldrichetta forsteri), pufferfish (Sphareroides hamiltoni), garfish (Hemiramphus melanochir), flounder and cod (Pirzl and Coughanowr, 1997). The protected Australian grayling (Prototroctes maraena) is found in the upper reaches of the estuary and migrates through the lower estuary. This species is of high conservation significance and is listed under both the EPBC Act and the TPS Act. The introduced mosquito fish (Gambusia holbrocki) is present in the River Tamar estuary.

The Draft IIS (page 9, Appendix 28 in Volume 11) states that the absence of seagrass habitat in Donovans Bay renders this embayment unlikely ‘to provide any nursery areas for commercial finfish’. However, this is not the case, as seagrass does occur within Donovans Bay (Aquenal 2001, 2002).


Implementation of the Construction Environmental Management Plan (CEMP), Rehabilitation Plan and onshore Erosion and Sediment Control Plan will aid in avoiding or limiting the areal extent and magnitude of potential effects on the fish fauna of Donovans Bay.



No additional site-specific mitigation or management measures are proposed to limit construction effects on the fish fauna of Donovans Bay, given the low likelihood of residual impacts as assessed below.


The generalised effects of constructing and installing the effluent pipeline within Donovans Bay a on fish populations result from the physical alteration of subtidal fish habitats (sediment deposition), changes in water quality (increased suspended sediment concentrations), and indirect impacts on fish food resources (changes in macroinvertebrate populations, algae and detritus). The principal impacts of in-stream sedimentation and increased TSS concentrations on fish are assessed below.

Sedimentation

Section 3.2.3.3 above indicated that significant sedimentation of intertidal and subtidal habitats within Donovans Bay are not expected because of the installation of the 300-m low profile sandbag cofferdam section within the tidal gate with the resulting upstream entrapment of coarse sediments. Therefore, significant sedimentation of fish benthic habitats is not expected. Therefore, residual impacts of sedimentation on fish are assessed as not significant at the site scale or greater. Within the site scale, limited sedimentation in proximity to and downstream of the tidal gate will be small in areal extent and highly localised. Post-construction recolonisation of deposited sediments by fish food organisms (e.g., benthic macroinvertebrates) is expected to be rapid.

Suspended Sediments

Numerous studies have documented the effects TSS and deposition of the settleable solids component on fish populations (Alabaster and Lloyd 1982; Ryan 1991; Peters 1965; Bruton 1985; Waters 1995; Newcombe and MacDonald 1991; Caux et al. 1997; Berry et al. 2003). The generalised effects of suspended solids on fish may be considered both directly and indirectly at the both species and population level. Lethal effects include mortality of fish and eggs and sub-lethal effects include suppression of growth and productivity, and behavioural avoidance.

Section 3.2.4.3 above indicated that typical TSS concentrations in the initial suspended sediment plumes derived from early works construction activities are anticipated to lie in the range 200 to 500 mg/L. These TSS concentrations are expected to reduce rapidly by dilution as the plume passes through the central part of Donovans Bay, with expected TSS concentrations of less than 50 mg/L. As the ebb tide transports the suspended sediment plume downstream, TSS concentrations will be further reduced to background levels (5—10 mg/L) by mixing with the large volumes of outgoing tidal water within the lower River Tamar estuary.

Section 3.3.3.4 above indicated that the residual impacts of elevated TSS concentrations on water quality are assessed to be temporary and not significant at the site scale or greater, owing to their transient passage through Donovans Bay.



Fish exposed to the above transient TSS concentrations for intermittent periods during outgoing tides over 2 to 3 days are not expected to be affected, given that they experience a wide range of elevated TSS concentrations in the lower River Tamar estuary (including Donovans Bay).

Overall, residual impacts of elevated TSS concentrations on fish are assessed as not significant at the site scale or greater. The mobility of fish also implies that they may leave or not enter bay or river reaches containing elevated TSS concentrations.

3.4.6 Impacts on Marine Mammals

Potential impacts on marine mammals that visit the lower River Tamar estuary are only likely to arise from construction-derived suspended sediment plumes present during outgoing tides. Section 3.3.3 indicated that impacts on water quality within the lower River Tamar estuary are not significant at the site scale or greater. Therefore, no significant deterioration in water quality is envisaged in the receiving waters of the lower River Tamar estuary where marine mammals may be found.

The frequency of visitation by marine mammals to Donovans Bay and the adjacent reach of the lower River Tamar estuary at Long Reach is probably low, given the industrialised nature of this reach of the river. Nevertheless, humpback whales, southern right whales, killer whales, bottlenose dolphins, common dolphins and fur seals are regularly sighted.

Previous sections of this report indicate that construction-derived suspended sediment plumes will be diluted to low TSS concentrations (i.e., similar to or just above background levels of between 5 and 10 mg/L) within the lower River Tamar estuary and only occur during the first two-thirds of outgoing tides.

The presence of suspended sediment plumes on the first two-thirds of outgoing tides within the lower River Tamar estuary are most unlikely to affect any marine mammal, since the animal would be exposed to TSS concentrations similar to background levels. Therefore, residual impacts on marine mammals are assessed in the very short term or longer as not significant at the site scale or greater.

Overall, no significant impacts on marine mammals listed under the EPBC Act or the TSP Act are envisaged.

3.4.7 Impacts on Aquatic-dependent Birds

This section assesses the residual impacts of cross-bay construction on the avifauna of Donovans Bay.


The mudflats and shoreline of Donovans Bay present suitable habitats for feeding and roosting of some wading and shore birds. The Draft IIS database search suggested that



there were few records of wading or shorebirds in the bay. However, there are extensive mudflats along the River Tamar estuary that do provide habitat shorebirds, which are also recognised as being significant areas for migratory species.

The Draft IIS (Appendix 28, Volume 11) indicates the presence of several bird species that may visit or frequent Donovans Bay. These are:

• Ruddy turnstone (Urinaria interprets) • Latham’s (Japanese) Snipe (Galliano Hardwick) • Great Egret (Area alba) • Cattle Egret (Area ibis)

In the absence of a bird checklist for Donovans Bay, surrogate data for the Tamar Islands Wetland Reserve are presented in Table 3, which serves to highlight the presence and relative abundance of native and migratory bird species that may be present in Donovans Bay and the lower River Tamar estuary from time to time.


The Donovans Bay Construction Environmental Management Plan (CEMP) and Rehabilitation Plan will ensure that the pipeline alignment is restored to its pre-disturbance topographic profile, which includes reinstatement of the rocky foreshore. This will provide similar bird habitat and foraging areas as before construction. However, food resources will be reduced until the estuarine ecology is re-established at pre-disturbance levels.

The duration of cross-bay construction activity is scheduled to last only for a few days, which will minimise the time that birds are exposed to the physical presence of the workforce and to aerial noise generated by construction equipment.

No additional or site-specific mitigation or management measures to further minimise construction effects and disturbance on seabirds and aquatic dependent birds are proposed.


Most seabird species, because of their adaptation to remote areas, are susceptible to human disturbance, which includes direct human contact with the birds and their habitat, disruption to foraging areas and aerial noise from construction or nearby activities. In the case of Donovans Bay, this embayment should not be considered as a remote area, since the proposed area of effluent pipeline construction is adjacent to the Launceston to Georgetown highway nearby.

During construction and installation of the pipeline, estuarine birds and aquatic dependent birds that use the shoreline of Donovans Bay will be temporarily displaced by pipeline construction activities, aerial noise, and the presence of construction workers and mobile machinery.



Table 3 Checklist of bird species at Tamar Islands Wetland Reserve to indicate the types of birds and their relative abundance that may occur within or visit Donovans Bay.

Common name Latin name Relative abundance

Seabirds: Little Pied Cormorant Phalacrocorax melanoleucos C Little Black Cormorant Phalacrocorax sulcirostris C Great Cormorant Phalacrocorax carbo C Silver Gull Larus novaehollandiae C Pacific Gull Larus pacificus C Caspian Tern Sterna caspia C Crested Tern Sterna bergii UC/M Shore, Estuary and Lagoon Birds: Black Swan Cygnus atratus C Australian Shelduck Tadorna tadornoides C Pacific Black Duck Anas superciliosa C Australian Shoveler Anas rhynchotis C Grey Teal Anas gracilis C Chestnut Teal Anas castanea C Australian Wood Duck Chenonetta jubata C Tasmanian Native Hen Gallinula mortierii EC Purple Swamphen Porphyrio porphyrio C Eurasian Coot Fulica atra UC Great Crested Grebe Podiceps cristatus UC Hoary Headed Grebe Poliocephalus poliocephalus UC Great Egret Ardea alba C Cattle Egret Ardea ibis UC/M White Faced Heron Egretta novaehollandiae C Spotless Crake Porzana tabuensis UC Spotted Crake Porzana fluminea UC Red-necked Stint Calidris ruficollis UC/M Common Greenshank Tringa nebularia UC/M Black Fronted Dotterel Elseyornis melanops C Common Sandpiper Actitis hypoleucos UC Sharp-tailed Sandpiper Calidris acuminata UC/M Curlew Sandpiper Calidris ferruginea UC/M Australian Pelican Pelecanus conspicillatus UC Masked Lapwing Vanellus miles C Australian Bittern Botaurus poiciloptilus UC Source: Parks and Wildlife Service Tasmania (2003). C= Common; UC = Uncommon; M= Migratory; and EC = Endemic.

Overall, there is not expected to be any significant long-term effects to bird species that use Donovans Bay or the lower River Tamar estuary. The conclusion of low residual impacts on estuarine birds or water-dependent birds is corroborated by the fact that there have been two previous crossings of Donovans Bay, one for a gas pipeline and the other for a cable, and bird assemblages have re-established.



The cross-bay trench will cross minor feeding grounds along the foreshore, shoreline and intertidal mudflats of the eastern part of Donovans Bay. Therefore, there may be temporary effects on birds during the 2 to 3 day construction period. Displaced birds are likely to select other areas of Donovans Bay or the lower River Tamar estuary during the construction period.

3.4.8 Aquatic Resource Use Impacts


Recreational and Commercial Fishing

Recreational Fishing

Recreational fishing mainly occurs along the shores of and from boats in the lower River Tamar estuary, and Donovans Bay does not appear to be a significant recreational fishing area.

Commercial Fishing

There is no commercial fishing within Donovans Bay.

Conservation and Protected Areas

In accordance with the Living Marine Resources Management Act 1995, the Scalefish Fishery Policy Document (1998) and the Scalefish Fishery Management Plan (2004), there are restrictions on commercial and recreational fishing in areas of special conservation significance or particular vulnerability, such as the Shark Refuge in the River Tamar.

The Shark Refuge covers the entire River Tamar estuary from a line between Low Head and West Head in the north to the end of the estuary at Launceston in the south. This area has been set aside as important habitat where all species of sharks and rays can breed and find refuge. Within this area, there are restrictions on fishing activities.


The short duration of proposed construction activities within Donovans Bay and the implementation of the Donovans Bay Construction Environmental Management Plan (CEMP) and Rehabilitation Plan will ensure that residual impacts on the aquatic environment and resource use are either avoided or limited.

A key mitigation measure adopted to coincide early works construction with the first two-thirds of outgoing tides. This was initially considered as a means to avoid construction-derived sediment plumes from being transported upriver, as would be the case for incoming flood tides, and potentially affecting the Van Diemen Atlantic salmon farm located opposite the existing woodchip export facility.



No additional site-specific mitigation or management measures are proposed to avoid or limit potential construction impacts within Donovans Bay on aquatic resource use.


Residual impacts on aquatic resource use have been assessed.

Recreational Fishing

Section 3.4.5.3 indicates that no significant impacts on fish in Donovans Bay or the lower River Tamar estuary are expected. Therefore, residual impacts on recreational fishing are assessed in the short term or longer as negligible (not significant) at the site scale or greater.

In the very short term during active cross-bay construction, there may be a temporary access restriction to Donovans Bay, but this is assessed as a temporary nuisance rather than a negative impact on recreational fishers.

Aquacultural Facilities

There are two onshore aquacultural facilities located within the lower River Tamar estuary. These are Seahorse World at Beauty Point (7 km downstream) and the Garden Island Abalone aquacultural facility at Clarence Point (8km downstream). Both these facilities depend on the abstraction of fully saline water during high tides.

Early works construction-derived suspended sediment plumes will be transported out to sea during the first two-thirds of outgoing tides. This management procedure avoids the possibility of any upriver transport of the plumes. Hence, deteriorated water quality due to effluent pipeline construction will not be experienced at the Van Diemen Atlantic salmon farm.

Overall, residual impacts of Donovans Bay construction activities on aquacultural sites within the lower River Tamar estuary are assessed in the very short term or longer as not significant at the local scale (i.e., outside Donovans Bay) where they are located.

Conservation and Protected Areas

Section 3.4.5.3 indicated that no significant impacts on fish of Donovans Bay or the lower River Tamar estuary are expected. Therefore, residual impacts on the shark refuge are assessed in the very short term or longer as not significant at the site scale or greater.



4. References

4.1 Literature Cited Alabaster, J.S. and Lloyd, R. (1982). Water quality criteria for freshwater fish: 1. Finely

divided solids. Food and Agricultural Organisation, Butterworths, London.

ANZECC/ARMCANZ 2000. Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Australian and New Zealand Environment and Conservation Council.

Aquenal. 2001. Bell Bay Power Station: biological survey of Donovans Bay. Report for Hydro Tasmania.

Aquenal. 2002. Biological survey of Donovans Bay, Bell Bay Power Station. Report for Bell Bay Power Pty Ltd, September 2002.

Berry, W., Rubinstein, N., Melzian, B. and Hill, B. 2003. The biological effects of suspended and bedded sediment (SABS) in aquatic ecosystems: A review. Atlantic and Midcontinent Ecology Divisions of the National Health and Environmental Effects Laboratory, Office of Research and Development, U.S. Environmental Protection Agency. Internal report. August, 2003.

Blake, J. A. and Kudenov, J.D. 1978. The Spionidae from southeastern Australia and adjacent areas with a revision of the genera. Mem. Nat Mus Vict 39: 171-280.

Bruton, M.N. 1985. The effects of suspensoids on fish. Hydrobiologia, 125: 221 241.

Caux, P., Moore, D.R.J. and MacDonald, D. 1997. Ambient water quality guidelines (criteria) for turbidity, suspended and benthic sediments. Technical Appendix. Prepared for British Columbia Ministry of Environment, Lands and Parks April, 1997.

DPIWE. 2005. Waterways Monitoring Report: South Esk Catchment. Department of Primary Industries, Water and Environment, Government of Tasmania. 15 pp.

Foster, D.N., Nittim, R. and Walker, J. 1986. Tamar River Siltation Study. Report prepared for the Tamar River Improvement Committee, October, 1986.

Hayes, K., Sliwa, C., Migus, S., McEnnulty, F and Dunstan, P. 2005. National priority pests. Part II, Ranking of Australian marine pests. CSIRO.

Hydro Tasmania. 2001. Tasmanian Natural Gas Project Development Proposal and Environmental Management Plan. Stage One. April, 2001.

Newcombe, C.P. and MacDonald, D.D. 1991. Effects of suspended sediments on aquatic ecosystems. North America Journal of Fisheries Management 11:72 82.



Parks and Wildlife Service Tasmania. 2003. Wildlife: Tamar Island Wetlands Bird checklist. A WWW publication at www.parks.tas.gov.au/factsheets/wildlife/ TamarBirdlist.pdf. Accessed on 5 November, 2006.

Peters, J.C. (1965). The effects of stream sedimentation on trout embryo survival. In "Biological problems in Water Pollution Control. 3rd Seminar. US Department of Health, Education and Welfare, Division of Water Supply and Pollution Control, Cincinnati, Ohio.

Pirzl, H. and Coughanowr, C. 1997. State of the Tamar Estuary: A review of environmental quality data to 1997. Supervising Scientist Report 128, Office of the Supervising Scientist, Canberra.

Ryan, P.J. 1991. Environmental effects of sediment on New Zealand streams: A review. NZ Jour. Mar. Freshwat. Res. 25:207-221.

Smith, B.J. 1997a. Tamar Intertidal Invertebrates. An atlas of common species. Queen Victoria Museum and Art Gallery. Launceston.

Smith, B.J. 1997b. Invertebrate Fauna of the Tamar Estuary, Northern Tasmania. Proceedings of the Royal Society of Victoria. 56:475—482.

Stanford, G. 2006. Manager, Environmental Information Systems, Gunns Limited. Telephone call of Thursday 7th December, 2006.

Waters, T.F. 1995. Sediment in streams: Sources, biological effects and control. American Fisheries Society Monograph 7. America Fisheries Society, Bethseda, MD.

bell bay pulp mill project appendix 4 of witness statement

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