Development Application Detailed Design Cradle Coastal Community Pathway

REQUEST FOR TENDER DEVELOPMENT APPLICATION AND DETAILED DESIGN OF THE COASTAL PATHWAY

10 MAY 2019

CRADLE COASTAL PATHWAY

Table of Contents 1.

2.

3.

Background Scope of Works Selection Criteria 3.1.

3.2.

4.

5.

6.

6 7 7

Underpass Structures Bridge Structures Retaining Walls Other Structures Drainage Geotechnical

7 7 7 7 8 8 8

Threatened Flora Threatened Fauna Threatened vegetation communities Reserves Declared weeds

8 9 9 9 9

Geoscientific issues 8.1.

8.2.

8.3.

8.4.

8.5.

9.

5 6

Environmental 7.1.

7.2.

7.3.

7.4.

7.5.

8.

Selection Criteria Weighting Project Milestones

Submission Enquiries Path Structures 6.1.

6.2.

6.3.

6.4.

6.5.

6.6.

7.

3 4 5

10

Geoconservation sites Geotechnical / Landslip potential Geotechnical Report Coastal Vulnerability Acid Sulphate Soils

10 10 11 12 12

Stakeholders

12

Preferred Alignment Maps TasRail Fencing Guidelines Pitt & Sherry Geotechnical Report 2012 Latrobe to Ambleside Design Drawings Prepared by DCC 2012 Latrobe to Ambleside

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1. Background In 2010, the Cradle Coast Authority (CCA) secured funding from the State Government's Trails and Bikeways Program to prepare a master plan to guide the construction of approximately 85km of continuous linear shared / cycling pathway which connects coastal-zone communities from Wynyard in the west to Latrobe in the east. It also includes around 24km of additional connecting links (a total of approximately 110km). The Plan was developed to inform each Council’s own local shared pathway planning and related funding applications.

The Pathway is being constructed in stages, with approximately 35kms (30%) complete. A Project Control Group (PCG) was established to focus on identifying the status of incomplete sections, with the aim of getting these sections development ready while funding was being secured.

Government funding provided in 2019 has allowed the project to proceed with planning, detailed design and construction of the pathway. Cradle Coast Authority (CCA) will coordinate the tender process and appoint all consultants/contractors for the duration of the project.

There are three sections of pathway which are to be completed prior to June 2022. Each of the sections are at different stages of development and so require varying amounts of work in order to get all three sections to a point where construction can proceed.

•

•

•

Latrobe to Ambleside – approx. 4kMs (Connecting Devonport and Latrobe LGA’s.) The Development Application is underway for this section. The next step is to develop the full design package, followed by a tender process contract a developer to construct and deliver the project.

Don to Leith – approx. 7kMs (Connecting Central Coast and Devonport LGA’s.) This section is not as progressed as the previous one and the Development Application also needs to be completed. In order to speed the process, it would be preferred that the DA be completed simultaneously with the Design.

Ulverstone to Penguin – approx. 4.5kMs. This section of pathway also has not commenced on the DA or the design work.

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2. Scope of Works In consideration that each of the path sections are not at the same stage of development CCA require that each Tenderer submit five separate tender prices as follows: 1.

2.

3.

4.

5.

Planning for Ulverstone to Penguin Planning for Don to Leith Design for Latrobe to Ambleside Design for Ulverstone to Penguin Design for Don to Leith

Tenderers must submit a tender for each of the above elements as a standalone price, CCA will award each element as the work falls due. Tenderers may be awarded all sections or a number of sections of the work.

Phase 1 – Preliminary Assessment of the Pathway sections, Coordination of investigations/reports, cost planning, approvals and design.

1. Review/Assess the preferred alignments outlined in the concept designs of the pathway sections. Assess the functional requirements considering the following Standards and Guidelines; • Austroads Guide to Road Design Part 6A – Paths for Walking and Cycling • Australian Standards including: o AS2156:2001 – Walking Tracks o AS5100:2017 – Bridge Design o AS2758.6:2009 – Aggregates o LGAT Standard Drawings • DIER Specifications – R22 earthworks and R24 Geotextiles 2. Assess and prepare a cost plan report on the likely construction cost based on the preferred alignment for all three sections of pathway.

3. Undertake consultative discussion with key Stakeholders (Section 9), obtain feedback and if necessary, adjust the design to obtain agreement and required permits for the Development Applications required.

4. Prepare the Development Applications (required sections) and submit on behalf of CCA. DA fees to be excluded as these will be waived by Councils. Note: sections do cross Local Government boundaries and therefore require dual applications.

5. Respond to matters which need addressing throughout the Development Application, note and manage conditions advised on the permit.

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Phase 2 – Detail Design & Tender Specification 1. Complete the detail design for the three sections.

2. Provide ongoing design support for the duration of construction.

3. Prepare a tender specification suitable for the construction stage of each of the three sections which conforms with the following Standards and Guidelines: • Austroads Guide to Road Design Part 6A – Paths for Walking and Cycling • Australian Standards including: o AS2156:2001 – Walking Tracks o AS5100:2017 – Bridge Design o AS2758.6:2009 – Aggregates o LGAT Standard Drawings • DIER Specifications – R22 earthworks and R24 Geotextiles 4. Identify/advise and document suitable selection criteria allowing assessment and scoring of tender responses including collaboration with the PCG. 5. Assist CCA in providing technical responses and information requested by prospective Tenderers through the tender phase.

6. Assist CCA in seeking clarification on Tender Submissions.

3. Selection Criteria The following Criteria will be considered in selection of the consultant: -

Capability and relevant experience Previous performance of similar projects in the region Demonstrated understanding of the scope of work Technical skills of key personnel Time performance, ability to meet deadlines Management systems Safety systems and practice Lumps sum price

3.1. Selection Criteria Weighting Item Capability and experience Ability to deliver works in a timely manner Local knowledge and understanding of the works Price

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% Weighting 40 20 20 20

5

3.2. Project Milestones

Item

CCA Target Date

1

Request for Submission

10 May 2019

2

Submission Close Period

31 May 2019

Nominate Consultant and engagement Deliver detailed design Latrobe to Ambleside Planning Ulverstone to Penguin

3 4 5 6

Planning Don to Leith

7

Design Ulverstone Penguin

8

Design Don to Leith

Consultants Commitment

14 June 2019 26 July 2019 Tenderer to Advise Tenderer to Advise

to

Tenderer to Advise Tenderer to Advise

4. Submission Submissions to be sent to tenders@cradlecoast.com Subject: Development Application & Detailed Planning of the Coastal Pathway Attention:

Project Control Group

Submission Closing time:

30 May 2019

All submissions shall include the following: a) Project Staff and Sub-Consultants Nominate the intended project staff b) Timing The submissions are also to state the ability of the consultant to meet the timelines as specified in this document, and to provide timelines as requested.

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5. Enquiries Enquiries concerning this brief should be made to: Mary Roddy Regional Economic Development Officer Cradle Coast Authority p: (03) 6433 8425 m: 0416 523 079 e: mroddy@cradlecoast.com

6. Path Structures 6.1. Underpass Structures Not in scope of this design work. However, consideration needs to be given to the alignment and the functional requirements of the structure in designing the approaches. The Underpass Structures will be a separate D&C contract.

6.2. Bridge Structures Not in scope of this design work. However, consideration needs to be given to the alignment and the functional requirements of the structure in designing the approaches. The Bridge Structures will be a separate D&C contract.

6.3. Retaining Walls Various small retaining wall structures are anticipated along the route, however most are expected to be less than 1.5m in height. The most significant retaining wall structure would be located around the high-level bench at Leith Headland 6.4. Other Structures A viewing area is proposed at the eastern end of Lillico straight at the top of the hill near the northern entrance of the rail underpass on the Don to Leith Section of pathway.

Council expressed a preference for some shelters to be constructed along the route for path users, suggesting a shelter would be useful at the viewing area at the eastern end of Lillico straight.

Several existing culverts under River Road (approx. 27no.) are identified as requiring extensions under the proposed pathway. In addition, the design has identified a further 13no. new culverts that are required for path drainage.

The existing culverts vary from 300mm diameter to 750mm diameter, whilst the new culverts are all 300mm diameter and typically 6m long.

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6.5. Drainage Various small culverts will be required along the route so as not to disrupt existing drainage flows. In particular, the section of pathway along Lillico Straight is in a low lying, swampy area which does not drain well, particularly in winter. Additional fill will be required to raise the path in these locations.

6.6. Geotechnical The preferred route is to use the existing high-level bench around Leith Headland on the southern side of the Bass Highway as an alternative to a new low-level pathway adjacent to the highway which would require significant earthworks, traffic barriers and retaining wall. A high-level site review of the bench has been undertaken and initial indications are this route would be suitable. However, a number of measures would need to be taken to protect path users.

7. Environmental Desktop environmental assessment, in conjunction with preliminary site reconnaissance investigation has been undertaken for the preferred alignments. A range of publicly available spatial datasets including the Tasmanian Natural Values atlas (DPIPWE) were searched for environmental values within proximity of the potential pathway alignments. The key findings are summarised below.

Environmental assessment has identified a broad range of issues and features which must be considered in detailed design including likely presence of threatened flora, habitat for threatened fauna and geoscientific issues including landslip susceptibility. The issues identified will require further on ground detail and specialist assessments but are considered manageable with appropriate risk assessment, mitigation plans and appropriate permits.

Cultural heritage record searches (including Aboriginal Heritage) have not been completed due to extensive use of public lands for which desktop search tools are unavailable. On ground surveying will be required, however, with use of existing infrastructure and most options assessed occurring within highly disturbed and/or developed lands it is likely that most issues identified in specialist assessments will be manageable with appropriate risk assessment, mitigation plans and appropriate permits.

7.1. Threatened Flora Threatened flora has previously been identified and reported in proximity to the proposed alignment.

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During detailed design an on-ground survey will be required to undertake a risk assessment for threatened flora species with permits to disturb/take required if identified. There is a risk of project delay while waiting for approvals to be obtained.

7.2. Threatened Fauna The proposed alignment for the entire length of the pathway is in close proximity to a number of locations where threatened fauna has been sighted.

Works undertaken for the pathway development will require habitat assessments during detailed design to determine any potential impact on the threatened fauna. There is a risk of project delay while waiting for approvals to be obtained.

7.3. Threatened vegetation communities There are several threatened vegetation communities listed under Schedule 3A of the Nature Conservation Act 2002 (Tas) which occur in proximity to the preferred alignment. These include: Wetlands Eucalyptus ovata forest and woodland Melaleuca ericifolia swamp forest Eucalyptus viminalis wet forest The detailed design will require consideration of the communities and avoidance or appropriate disturbance mitigation measures.

7.4. Reserves The potential alignment of the Ulverstone to Penguin section traverses the Three Sisters – Goat Island Nature Reserve.

The entire proposed section of Latrobe to Ambleside is situated on Public Reserve pursuant to the Crown Lands Act 1976 (Tas).

The potential alignment of the Don to Leith section traverses the Don Heads Conservation Area at the mouth of the Don River and approvals will be required. The Lillico Beach Conservation Area is located to the north of the potential pathway alignment and will not be traversed.

7.5. Declared weeds A range of declared weeds have been identified and reported in proximity to the potential pathway alignment. These include bridal creeper, boneseed, pampas grass, Spanish heath, fennel, montpelier broom, perforated St Johns wart, blackberry and gorse.

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A weed management plan will be required during detailed design to support any development proposal.

8. Geoscientific issues 8.1. Geoconservation sites Consideration needs to be given to Two geoscientific features of conservation significance have been mapped near the potential pathway alignment on the Don to Leith section.

Notable examples of the Don Heads basalt and landforms are mapped around the northern end of the Don headland.

Ulverstone to Penguin has three geoscientific features of conservation significance mapped near the potential pathway alignment.

An outstanding example of Goat Island Conglomerate is noted, unusual deposits of Penguin Megabreccia and Penguin pillow lavas are noted in the vicinity of the preferred alignment. The pathway alignment is likely to require a risk assessment and management plan for approval and permitting of the development.

It may be possible for the pathway to incorporate ‘interpretation’ signage to highlight the significance of the features.

8.2. Geotechnical / Landslip potential

Don to Leith Section The preferred alignment will traverse sections of the coast for which landslide hazards exist. Mapping indicates that the section of road cutting adjacent to the Leith turnoff comprises a mixture of low to medium rated risk areas. The section of railway track traversing between Lillico road and the Bass Highway overpass traverses an extensive section of low to medium rated risk sections and included some sections for which the risk is identified as medium-active.

Indications of active landslide features have been identified during the reconnaissance visits and the detailed design is likely to require a landslide risk assessment and report.

Ulverstone to Penguin Section The potential alignment between Ulverstone and Penguin will traverse sections of the coast for which landslide hazards exist. Mapping indicates that the CRADLE COASTAL PATHWAY

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section of road cuttings traverse a mixture of low to medium rated risk areas with a medium active risk noted between Tea Tree and Penguin Points.

The final alignment is likely to require a landslide risk assessment and management report.

Latrobe to Ambleside Section The preferred alignment between Latrobe and Ambleside will traverse sections of the coast for which landslide hazards exist. The 1:25,000 scale landslide hazard maps for the Devonport-Forth region published by MRT indicate the presence of 4 ‘possible’ landslides and 1 ‘active’ landslide within the study area.

Close examination of both the landslide hazard maps and aerial photographs shows the 4 ‘possible’ landslides to be located about the southern extent of Ambleside, somewhat distant from the proposed cycleway route, on the moderate to steep hillslopes above and to the west of River Road. The features are difficult to distinguish on the aerial photographs and appear typically small to moderate in size, possibly related to land clearing undertaken several decades or more ago.

The single ‘active’ landslide within the study area is located below River Road near Ch450m of the proposed cycleway route. The small circular feature appears from both aerial photographs and on-site inspection to have resulted from erosion and undercutting of an over steepened area of road embankment, with continued slow regression of the slope likely to occur into the future.

Indications of active landslide features should be identified during the detailed design and are likely to require a landslide risk assessment and report if found.

8.3. Geotechnical Report

Latrobe to Ambleside Section On the Latrobe to Ambleside section of pathway P&S undertook and geotechnical report of the area in 2012 and this is provided in Appendix D. The key findings relating to the pathway construction are: The risk of excessive amounts of soft sediments requiring removal before placement of fill is considered low.

There is a medium/low risk of existing embankment instability above the path between Ch.700 and Ch. 3100. Vegetation of the current embankments should be disturbed as little as possible to reduce this risk of instability.

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There are areas of deep-water channel adjacent to the river banks that may cause additional fill to be required, particularly between Ch.2600 and Ch.3100.

8.4. Coastal Vulnerability The pathway connecting Penguin to Ulverstone will require development in close proximity to the coast (within 30m of the high-water mark) and consequently must address the Development standard requirements of the Central Coast Council interim planning scheme section 10.6 of the E10 Water and Waterways Code.

The development will require assessment to ensure a minimised risk to the function and values of watercourses for a variety of issues including hydraulic performance, potential impacts on amenity and aesthetic appearance. The development must minimise immediate or cumulative adverse effects including for on coastal landforms, water movement processes and quality. The development must minimise adverse effects for risks from natural hazards including coastal erosion, sea level rise, storm surge and potential inundation because of climate change.

While most the preferred alignment is situated at topographic levels and distances sufficient to avoid any risk to waterways and will not adversely impact coastal waters or shoreline areas, any over water crossings will require further detailed assessment. Suitable designs will be required to minimise potential impacts.

8.5. Acid Sulphate Soils Acid Sulphate Soils (ASS) are common to Tasmania’s coastal regions. The areas of low topography adjacent to the Bass Strait coast have been mapped as low probability of occurrence of ASS. However, the intertidal estuarine environment at the mouth of the Don River is indicated to have high probability of occurrence. A monitoring and management plan will be required to ensure any potential for disturbance is identified and appropriate mitigation plans are in place to support development.

9. Stakeholders The length of this section of pathway means that inevitably several stakeholders will be affected by the development. These include: • •

Department of State Growth (Nick Brown, Lucy Thorne) TasRail (Jennifer Jarvis)

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• • • • • • • • •

Crown Land Services & DPIPWE (Anne Maginnity) Parks & Wildlife Service (Anne-Maree Smith) Adjacent Private Landowners (Residential and Commercial) Safer Roads for Cyclists Tasmania (Keith Price) Coastal Pathway Coalition (Andrew Leary) Bicycle Network (Alison Hetherington) Cradle Coast NRM The communities connected by the proposed infrastructure Relevant Councils (including engineering and planning departments)

In developing the proposed routes, we have tried to utilise Council and State Government infrastructure as much as possible, which is expected to provide the ‘path of least resistance’ to achieving the required stakeholder approvals.

Initial discussions have been had with key stakeholders to better understand their requirements and concerns. In general, these stakeholders have provided preliminary feedback only, and reserve the right to provide more feedback when the development application and detailed design are completed.

The successful Tenderer will need to ensure that all stakeholders are consulted throughout the planning/detail design process and that any concerns are incorporated into the planning and design of the overall pathway.

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Preferred Alignment Maps

CRADLE COASTAL PATHWAY

Leith to Don

Further detail available

N

Under investigation – future works

Under investigation – future works

Under investigation – future works

Possible route if funds available Under investigation – future works

Under investigation – future works

TasRail Fencing Guidelines

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TASRAIL STANDARD - FENCING

INF-TS-501 Fencing Standards Accountable Manager: Group Property and Compliance

INTERIM FENCING STANDARD v1.0 Boundary Fences

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INF-TS-501 Fencing Standards Accountable Manager: Group Property and Compliance

CONTENTS: 1

Purpose

3

2

References 2.1 Australian Standards 2.2 Other References

3 3 3

3

Definitions

3

4

Standard Designs – Fencing Types 4.1 General 4.2 Rural Fencing 4.3 Residential/Urban Fencing 4.4 Cycleways/Walking Track Fencing (Separation Fencing) 5 4.5 Fencing Distances Diagram

3-5 3-4 4 4-5

6

TasRail Managed Network – Map

7

5

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INF-TS-501 Fencing Standards Accountable Manager: Group Property and Compliance

1

Purpose

This document specifies the requirements for the design and installation of boundary fences on or bordering TasRail Managed Property.

Boundary fences are to: − provide a measure of security and safety by restricting unauthorised access to the rail corridor and rail infrastructure amenities and services; − discourage stock from entering the rail corridor; − mark the boundary to define the rail corridor and adjoining properties; and − discourage and limit illegal access to TasRail’s managed network.

Boundary fences shall be established, when required and at the discretion of TasRail, to separate land adjoining TasRail’s managed network with the exception of locations where natural boundaries exist.

New fences shall be designed and constructed in accordance with this Standard.

Existing fences that do not comply with the design requirements are to be upgraded when the fence is due for renewal, or when enhancement is required as determined by a risk assessment by TasRail.

2

References 2.1

Australian Standards

AS 1725 - 2003 Chain-link fabric security fences and gates AS 2423 - 2002 Coated steel wire fencing products for terrestrial, aquatic and general use

2.2

Other References

Section 6 of the Boundary Fences Act 1908 (Rail Land is Crown and therefore TasRail is not liable to contribute towards the cost of boundary fences).

3

Definitions

Rail Corridor – the entire parcel of land with which contains a portion of track; TasRail Managed Network – as described under the Rail Infrastructure Act 2007.

4

Standard Designs – (Fencing Types) 4.1

General

Adjoining land owners and other land users shall restrict access to the rail corridor and rail services by the provision of appropriate fencing.

There are three (3) types of fences: -

Rural Fencing Residential/Urban Fencing Cycleway/Walking Track Fencing (Pedestrian Separation Fencing)

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INF-TS-501 Fencing Standards Accountable Manager: Group Property and Compliance

There will be locations that require a site specific design and construction method. The design and construction methods used in the location shall be equivalent to or will exceed the prescribed performance levels detailed in this standard.

TasRail reserves the right to accept or reject any fencing proposals.

4.2

Rural Fencing

This standard is applicable to private lands or properties adjoining the rail corridor anywhere in Tasmania and shall apply only to rural areas and will not apply in suburban, built-up or within city precincts.

TasRail is NOT responsible for any cost or associated costs with rural corridor fencing, the full cost of fencing or any associated costs are the sole responsibility of the land owner or lease holder.

General Specification:  The type of fencing required should be of a suitable type and standard that will enable stock to be contained away from and kept off the rail corridor;  The fencing will generally be of a consistent standard;  Typically a farm type stock fence; th  Being of a minimum 6 strand single wire with barb-wire on a 7 top strand; or,  Alternatively use of Ring-Loc wire may be used;  All wires to be fixed and fully supported with appropriate strainers and bridging droppers to enable adequate tensioning so not to allow any area of the fencing to collapse and render it ineffective. This will include sustainability for inclement weather conditions; While there will be several variables that need to be considered, (ie: type of stock - cattle, sheep, pigs, deer, etc) when deciding to erect or replace any of the rural fencing. These variables will need to be determined on a case by case basis through agreement with TasRail.

A fundamental requirement is that TasRail expect that any rural fencing is of sufficient design and quality to contain stock under any conditions.

4.3

Residential/Urban Fencing

This standard is applicable to private lands or properties adjoining the rail corridor anywhere in Tasmania and shall apply only to Residential/Urban areas and will not apply in rural areas.

TasRail is NOT responsible for any cost or associated costs with residential/urban fencing, the full cost of fencing or any associated costs are the sole responsibility of the land owner or lease holder.

General Specification:  Standard residential/urban fence is a hardwood timber paling fence, or  A colorbond steel fence in accordance with manufacturers specifications may also be used,  Other fence designs may be considered, subject to TasRail assessment and approval  Residential/Urban fences shall be a minimum of 1800mm high.

While there will be several variables that need to be considered when deciding to erect or replace any of the residential/urban fencing. These variables will need to be determined on a case by case basis through agreement with TasRail.

A fundamental requirement is that TasRail expect that any residential/urban fencing is of sufficient design and quality to restrict access under any conditions.

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4.4

Cycleway/Walking Track Fencing (Separation Fencing)

This standard is applicable to Cycleways/Walking Track proposals that adjoin or form part of TasRail’s managed Network anywhere in Tasmania and may require further approvals and consultation from an authorised TasRail representative.

TasRail is NOT responsible for any cost or associated costs with rail corridor fencing, the full cost of fencing or any associated costs are the sole responsibility of the land owner or lease holder.

General Specification: Operational Network  1800mm high chain mesh fence with a minimum offset from the outer most rail of 5.7m, so an adequate safety refuge can be provided for rail persons and rail operations can be undertaken within the corridor. ., The 1800mm high plain chain-link fence is to be in accordance with AS 1725, that offers four (4) standard configurations including; -

Rail-less Top rail only Bottom rail only Top and bottom rail.

For fencing without a top rail, bracing panels or bracing stays shall be used on all ends, corners and gateposts. 

Any (Separation Fencing) within the Operational Network that is to be proposed within 5.7m must be negotiated on a case by case basis and additional approval by TasRail management must be sought. The building of a fence within 5.7m will be considered to impact negatively on rail and maintenance operations and potentially expose TasRail to increased risk and liability.

General Specification: Non - Operational Network  1200mm high chain mesh fence;  To be installed no closer than 5.7m from the outer most rail;  If the line becomes operational a 600mm ridged bar extension and chainmesh infill shall be installed giving a total height of 1800mm (as per operational Specifications and at installers/lessees cost).  Any (High Volume Pedestrian Fencing) within the Non-Operational Network that is to be proposed within 5.7m must be negotiated on a case by case basis and additional approval by TasRail management must be sought.

See diagram 4.5 for required fencing details between an operational and non operational line and Cycleway or (High Volume Pedestrian Separation Fence).

*Please note this fencing standard does not automatically mean your cycleway/walking track proposal will be approved by TasRail. Separate approval/authorisation must be sought via Licence Application.

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INF-TS-501 Fencing Standards Accountable Manager: Group Property and Compliance

DANGER ZONE – INFRASTRUCTURE NOT PERMITED

Operational 1800mm high plain chainlink fence in accordance with AS 1725.

TASRAIL INFRASTRUCTURE ONLY WITHIN 5.7m

Non-Operational A 1200mm high chain mesh fence, if line becomes operational a 600mm ridged bar extension with chainmesh infill, giving a total height of 1800mm must be added.

SAFE ZONE - NON RAIL INFRASTRUCTURE MAY BE LEASED OR LICENSED WITHIN THIS AREA

4.5 Fencing Distances Diagram

2.7m+

3m 5.7m

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TasRail Managed Network – Map

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Pitt & Sherry Geotechnical Report 2012 Latrobe to Ambleside

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Geotechnical Report: Devonport City Council Proposed Cycle Way Prepared for:

Devonport City Council

Date:

June 2012 RevB

t ransport inf rast ruct ure | communit y inf rast ruct ure | indust rial inf rast ruct ure | climat e change

Table of Contents 1.

2.

3.

4.

5.

Int roduct ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Mersey River Channel Est uary and Fluvial Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3. 1 Background Inf ormat ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3. 2 Current Condit ions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. 3 Hist orical Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. 4 Issues of Relevance t o Proposed Cycle Way . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Geological and Geot echnical Condit ions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. 1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. 2 Sit e Walkover Findings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. 3 Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4. 4 Geohazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4. 5 Issues of Relevance t o Proposed Cycle Way . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Recommendat ions and f urt her work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

© 2012 pitt&sherry This document was produced by pitt&sherry and may only be used f or t he purposes f or which it was commissioned and in accordance wit h t he Terms of Engagement f or t he commission.

Unaut horised use of t his document in any f orm is prohibit ed.

Prepared by:

____________________________ Drew Bedelph and David Oldmeadow

Date:

18 June 2012

Reviewed by: ____________________________ Derek Pennington

Date:

18 June 2012

Authorised by: ____________________________ Peter Douglas

Date:

18 June 2012

Report Revision History Rev No.

Description

Prepared by

pitt&sherry ref : LN12120 H001 Geot ech Rep 31P RevB. docx/ DT/ rw

Reviewed by

Authorised by

Date

1.

Introduction Devonport Cit y Council (DCC) has t endered f or geot echnical and environment al services f or a proposed cycle way in nort hern Tasmania.

DCC requires any geot echnical or environment al issues t o be ident if ied f or t he proposed cycle way.

This t echnical report has been prepared f or t he proposed alignment of t he cycle way which is depict ed below in Figure 1.

The proposed cycle way alignment f ollows t he bank of t he Mersey River f or a dist ance of approximat ely 3. 8km. St art ing at t he weir at Bells parade, t he f irst 600m f ollows t he alignment of an exist ing hist oric pavement which is approximat ely 4 – 6 m lower t han River Road.

However, f rom 0. 6 t o 3. 8 km it is underst ood t hat land reclamat ion ext ending approximat ely 10m int o t he Mersey River will be required and t he cycle t rack will be placed on t his reclaimed ground. This sect ion of t he cycle way t raverses a number of headlands and bays, indicat ing varying geology and/ or erosion hist ory along t he alignment .

2.

Approach In t his report , t he geot echnical risks, const raint s and issues f or t he proposed cycle way are considered.

The f ollowing approach was t aken:



Sit e walkover



Aerial phot ograph int erpret at ion of t he Mersey River along t he proposed alignment , using phot ographs f rom 1946, 2009 and 2010. This allows f or comment on changes in deposit ional and erosional pat t erns and geomorphological f eat ures.



A det ailed search of t he landslide regist er f or t he area as depict ed in t he Tasmanian landslide map series f or Devonport , shallow slide and f low suscept ibilit y Map 5.

3.

Mersey River Channel Estuary and Fluvial Environment

3.1

Background Information The proposed cycleway ext ends along t he right hand bank of t he Mersey River as shown in Figure 1.

This sect ion of t he Mersey is charact erised as a meso-t idal river est uary 1 (est uary zones 1 t o 3 in f igure 1), and a river delt a in t he upper part .

The meso-t idal river est uary is charact erised by t hree main zones2; zones 1 and 2 consist of ext ensive mudf lat s, wit h wat er dept hs at low t ide ranging f rom

1

Edgar, G. J. , Barret t , N. S. and Graddon, D. J. , 1999, A classif icat ion of Tasmanian est uaries and assessment of t heir conservat ion signif icance using ecological and physical at t ribut es, populat ion and land use. Tasmanian Aquacult ure and Fisheries Inst it ut e Technical Series Report 2.

2 R. J. Murphy, C. M. Crawf ord and L. Barmut a, 2003, Est uarine healt h in Tasmanian, st at us and indicat ors: Wat er qualit y, Tasmanian Aquacult ure and Fisheries Inst it ut e.

pitt&sherry ref : LN12120 H001 Geot ech Rep 31P RevB. docx/ DT/ rw

1

approximat ely 2 t o 5 met res wit hin zone 2, and 1 t o 2 met res wit hin zone 1. Zone 3 is predominant ly an art if icial rock wall wit h a channel over 10 met res deep.

The proposed cycleway rout e ext ends along t he bank of t he river delt a zone, and river est uary zones 1 and 2 (see Figure 1).

The Mersey River est uary is ident if ied as being of low conservat ion signif icance 3. The Nat ional Land and Wat er Resources Audit ident if ied t he Mersey River est uary as being an ext ensively modif ied, wave dominat ed est uary 4, and it has been classif ied as being severely alt ered f rom nat ural condit ion 5.

3.1.1 Key Events 

A port was est ablished in 1855, at t he sit e t hat is now known as Bells Parade, t he st art of t he proposed cycleway, which f ormed t he main port f or t he wider region at t his t ime. For a period in t he 1880’ s it was t he second maj or t rading port in nort hern Tasmania. The port had t o be regularly maint ained against t he accumulat ion of silt in t he river, as a result of land clearing and f arming upst ream.



In t he 1890s t he port was no longer viable, and was closed 6.



In 1968 Parangana Dam was built as part of t he Mersey Fort h Power Development , t o divert wat er f rom t he Mersey River int o t he Fort h River valley. This caused a signif icant reduct ion in t he f low of t he Mersey River at Liena.



In 1999 Hydro Tasmania agreed wit h t he Depart ment of Primary Indust ries Wat er and Environment (DPIWE) t hat it would increase t he riparian discharge f rom Parangana Dam, in order t o maint ain a minimum ` environment al' f low in t he Mersey River.



Comparison of t he average recurrence int ervals under ‘ nat ural’ (pre 1968) and current condit ions (including current ‘ environment al’ f low condit ions) shows t hat t he peak discharges t hat occur every 2, 5, 10, 20, 50 and 100 years are almost ident ical. Parangana Dam has had lit t le ef f ect on t he occurrence of high magnit ude f lood event s7, 8.



24 August , 1970, Record f looding occurred in t he Mersey River. One f at alit y was recorded and damage est imat ed in excess of $5m 9.



27 March, 1977, Maj or f looding occurred in t he nort h-west , leaving 4 houses at Penguin and 14 at Lat robe inundat ed wit h mud 10.

3

Edgar, G. J. , Barret t , N. S. and Graddon, D. J. , 1999, A classif icat ion of Tasmanian est uaries and assessment of t heir conservat ion signif icance using ecological and physical at t ribut es, populat ion and land use.

4 Nat ional Land and Wat er Resources Audit , 2002, Aust ralian Nat ural Resources At las - Wat er Resources Allocat ion and Use 5 Conservat ion Freshwat er Ecosyst em Values dat abase (ht t p: / / www. dpiw. t as. gov. au/ int ernnsf / WebPages/ CGRM-7JHVSJ?open).

6 2004, SKM, Mersey River Precinct St udy.

7 DPIWE, 1997, St at e of River Report on t he Mersey River, Flow St udy.

8 DPIWE, 2005, Mersey Wat er Management Plan.

9 Aust ralian bureau of st at ist ics (ht t p: / / www. abs. gov. au/ ausst at s/ abs@. nsf / Lat est product s/ 1301. 6Feat ure%20Art icle32000?open document &t abname=Summary&prodno=1301. 6&issue=2000&num=&view=) 10 Aust ralian bureau of st at ist ics (ht t p: / / www. abs. gov. au/ ausst at s/ abs@. nsf / Lat est product s/ 1301. 6Feat ure%20Art icle32000?open document &t abname=Summary&prodno=1301. 6&issue=2000&num=&view=)

pitt&sherry ref : LN12120 H001 Geot ech Rep 31P RevB. docx/ DT/ rw

2

3.2

Current Conditions The proposed cycle way alignment runs along t he right hand bank of t he Mersey River f or a dist ance of approximat ely 3. 8 km. The rout e t ravels t hrough t wo dist inct channel morphologies, a large open meso-t idal river est uary f or f irst 3200 met res, and a small river delt a f or t he last 600 met res.

The last 600m of t he proposed rout e f ollows alongside t he right bank of a narrow channel, approximat ely 20 met res wide, t hat f orms t he divide bet ween t he main land and Pig Island. At t he sout hern end of Pig Island t here are a number of small veget at ed islands, channels and backwat er environment s. The delt a area at t his locat ion is approximat ely 300-400 met res wide.

Toget her wit h Ballahoo Island, Snag Creek and Ballahoo Creek t o t he west , t he area f orms a series of t idal mud f lat s, channels and veget at ed islands t hat f orm t he head of t he meso-t idal river est uary proper. The mud f lat s, exposed at low t ide, ext end int o t he est uary f or approximat ely 400 met res f rom t he veget at ed islands.

The river est uary widens signif icant ly nort h of t he river delt a area, t o approximat ely 1km wide. The est uary is dominat ed by ext ensive mudf lat s and islands on t he lef t , and a deep wat er channel t owards t he right , near River Road.

The est uary shore line along t he right bank, t he proposed cycle way alignment , is charact erised by shallow bays and headlands. Tidal mud f lat s are associat ed wit h t he small bays. The main channel is only in close proximit y t o River Road in t he vicinit y of t he sewage t reat ment plant , in t he upper sect ions of t he meso-t idal river est uary proper.

Table 1 shows riverine landscape f eat ures along t he proposed cycleway.

Bank erosion, and prot ect ion, was evident in bot h t he upper river delt a zone and t he meso-t idal river est uary zone (Table 1). It is likely t hat t he erosional processes dif f er in t he t wo zones, wit h f luvial f orces dominat ing in t he narrow channel of t he river delt a zone, and aeolian processes and wave act ion dominat ing in t he est uary zone. Where t he main est uary channel is in close proximit y t o t he right bank near t he sewage t reat ment plant , a mix of erosive processes may be operat ing.

Table 1 Riverine landscape along t he proposed cycleway

Bank erosion along pat h in upper river delt a zone of proposed cycle way.

Failing bank prot ect ion in upper river delt a zone of proposed cycle way.

pitt&sherry ref : LN12120 H001 Geot ech Rep 31P RevB. docx/ DT/ rw

3

3.3

Main channel abut t ing bank in upper sect ions of t he meso-t idal river est uary zone.

Bank erosion along right bank of t he meso-t idal river est uary zone.

Shallow deposit ional area wit hin a bay in t he meso-t idal river est uary zone. Main channel t o right of phot ograph.

Shallow deposit ional area wit hin meso-t idal river est uary zone. Bank prot ect ion in f orm of rock rip rap t o t he lef t of t he phot ograph.

Historical Change Aerial phot ograph int erpret at ion allows f or t he analysis of phot ographs t hat have been t aken in t he past t hat can be cont rast ed wit h more recent phot os. This can give an insight int o how a part icular f eat ure, or set of f eat ures, has alt ered, eit her t hough ant hropogenic inf luences, nat ural event s, or bot h.

Aerial phot ographs of t he Mersey River over t he proposed cycleway rout e were obt ained f rom t he Geodat a Services Branch, Inf ormat ion & Land Services Division, Dept . of Primary Indust ries Parks, Wat er & Environment , t he Devonport Council and Lat robe Council, f or t he years 1946, 2009 and 2010.

The 1946 phot ograph covers t he ent ire proposed cycleway except t he very st art of t he rout e at Bells’ Parade.

The 2009 phot ograph ext ends f rom approximat ely half way along t he proposed cycleway t o t he nort hern end, wit h t he 2010 phot ograph covering t he beginning of t he cycleway at t he sout hern end t o approximat ely half way along. For t he int erpret at ion, t he 2009 and 2010 phot ographs were combined, wit h a small lengt h of bank along t he proposed cycleway, approximat ely 310 met res, not represent ed by t he phot ographs, and hence not included in t he int erpret at ion.

Glare was a limit ing f act or in some areas of t he phot ographs making it dif f icult t o view f eat ures, such as channels and deposit ional zones below t he wat er surf ace. It was an issue in t he nort hern part of t he 1946 phot ograph and part of t he sout hern area of t he 2010 phot ograph. The phot ographs were also t aken during dif f ering t idal periods.

pitt&sherry ref : LN12120 H001 Geot ech Rep 31P RevB. docx/ DT/ rw

4

Where glare was not an issue t he mudf lat s, normally exposed at low t ide, could be seen and delineat ed underwat er.

ArcMap sof t ware was used t o geo-ref erence and bind t he coordinat es t oget her, t o creat e a mosaic of images. The key geomorphic f eat ures of t he 1946 and t he 2009 and 2010 combined series were digit ised. The 1946 image represent s t he earliest available image of t he area, and provides a ref erence point f rom which t o assess t he level of change in t he syst em over a 63 year period.

The f ollowing error levels (RMS error) were associat ed wit h t he geo-ref erencing:



RMS error f or t he 1946 phot ograph was 5. 8 met res



RMS error f or t he 2010 phot ograph was 1. 15 met res



RMS error f or t he 2009 unknown (phot ograph was already geo-ref erenced)

The f ollowing key point s were not ed (see Figures 2, 3 and 4):

3.4



Overall t here has been lit t le change t o t he syst em over t he 63 year period, which includes t he const ruct ion of a Dam on t he Mersey River, diversion of f lows, and t wo record f lood event s. The 1946 syst em is generally as described in sect ion 3. 2.



The size and alignment of t he river delt a channel t hat f orms t he divide bet ween Pig Island and t he main land, along which t he cycleway is planned, and t he general locat ion of t he mud f lat s and posit ion of t he deep wat er channel in relat ion t o t he right bank in t he meso-t idal est uary proper, has remained largely unchanged over t he 63 year period.



There have however been slight alt erat ions in t he alignment of t he right bank along which t he cycleway is planned, near t he small headlands t hat ext end int o t he meso-t idal est uary (see Figure 1). These changes appear t o be localised and real, not an art ef act of geo-ref erencing error. The cause of t hese alt erat ions is unknown, but may be a result of bot h nat ural erosional/ deposit ional processes and ant hropogenic dist urbances, such as localised f ill and land reclamat ion.



The great est level of alt erat ion in t he syst em is associat ed wit h t he mudf lat syst em and veget at ed land on t he west ern side of t he meso-t idal est uary. There has been a small reduct ion in useable/ agricult ural land on t his side of t he est uary, as indicat ed by a ret reat in veget at ion and conversion of agricult ural land and vehicle t racks (observed in t he 1946 phot ograph) int o mud f lat s (where t he alignment of old vehicle t racks is st ill apparent , Figure 3).



Small areas of land reclamat ion have also occurred since 1946, convert ing mudf lat s int o useable t errest rial land surf aces on t he west ern side of t he meso-t idal est uary (Figure 3).



The small amount of land ret reat since 1946 maybe due t o a reduct ion in sediment supply and disrupt ion t o sediment t ransport cont inuit y along t he Mersey river syst em.

Issues of Relevance to Proposed Cycle Way 

The proposed cycleway will result in a small loss of deposit ional, mud f lat area due t o pot ent ial land reclamat ion along t he meso-t idal est uary sect ion. The impact on sediment dynamics wit hin t he syst em however is expect ed t o be negligible t o none.



The right bank along which t he proposed cycle way is planned is not prone t o adj ust ment , except wit h t he possibilit y of localised adj ust ment around t he small headlands. Not e, t he cause of t he localised channel alignment since 1946 in t he vicinit y of t he headlands is not known. Comment t heref ore cannot be made on t he pot ent ial f or f ut ure adj ust ment in t hese areas.

pitt&sherry ref : LN12120 H001 Geot ech Rep 31P RevB. docx/ DT/ rw

5



Erosion on t he right hand bank was not ed wit hin t he meso-t idal est uary and river delt a areas. The processes of erosion likely dif f er in t hese t wo areas, wit h f luvial f orces act ing on t he banks in t he narrow channels wit hin t he river delt a area, and wind and wave at t ack act ing on t he banks in t he meso-t idal est uary proper.



The key area f or considerat ion is t he right bank of t he upper est uary, immediat ely downst ream of t he river delt a zone, where t he deep wat er channel abut s t he bank (see Figures 1 & 3). Any reclamat ion of t he channel in t his area will involve large amount s of mat erial, which will be exposed t o f luvial erosive f orces during large f lood event s, and pot ent ially wind and wave at t ack during cert ain st orm event s.

Depending on t he amount of deep wat er channel reclaimed, it may also cause some reworking of t he mudf lat s t o t he west of t he channel, possible result ing in mobilisat ion and t ransport of sediment , and localised loss of mud f lat area. This mudf lat area would pot ent ially need t o be considered in any acid sulf at e soil assessment undert aken (see below).

4.

Geological and Geotechnical Conditions

4.1

General The assessment of geological and engineering aspect s of t he proposed development has been based primarily on inf ormat ion obt ained f rom t he det ailed sit e walkover, which was conduct ed over t he course of t wo days in May 2012.

The walkover was undert aken by Drew Bedelph, Engineering Geologist f rom pitt&sherry’ s Hobart of f ice, in t he company of Ian Cut e f rom Devonport Cit y Council, and comprised t he mapping of t opographic, geological and st ruct ural f eat ures along t he 4km lengt h of t he proposed cycleway rout e.

4.2

Site Walkover Findings The f indings of t he sit e walkover are summarised in Table 2 below, which incorporat es inf ormat ion on geology, indicat ive slope angles, ident if ied geot echnical issues and an assessment of likely f ill dept hs.

Table 2 Summary of Findings

Chainage Interval (m)

Geology

3940 – 3060 (walking t rack)

Colluvium/ sandst one

Indicative Slope Angle (deg) -

Anticipated Fill Depth Range (m) Localised f illing only required

Identified Geotechnical Issues -

3060 – 2600 (River Road)

Dolerit e/ Sandst one

30 wit h locally st eeper zones

Up t o 10

-

2600 – 1850 (River Road) 1850 – 1050 (River Road)

Sandst one/ Dolerit e Dolerit e/ Weat hered Dolerit e/ Sandst one

Sub-vert ical (erosion) 40 wit h locally st eeper zones

pitt&sherry ref : LN12120 H001 Geot ech Rep 31P RevB. docx/ DT/ rw

0-2

-

Up t o 5

-

Erosion/ scour Inundat ion Unst able areas upslope of t rack Poor drainage condit ions Large f ill volumes required Presence of sof t sediment s at t oe of f ill embankment Erosion/ Scour Erosion/ scour Large f ill volumes required Presence of sof t sediment s at t oe of f ill

6

-

1050 - 450 450 - 100

100 - 0

Sandst one/ Dolerit e Dolerit e

Dolerit e

Sub-vert ical (erosion) 30-40 wit h locally st eeper zones

-

0-2

-

Up t o 10

-

0

-

embankment Localised road embankment f ailures Erosion/ Scour Erosion/ scour Large f ill volumes required Presence of sof t sediment s at t oe of f ill embankment Erosion/ Scour No issues ident if ied

The exist ing walking t rack bet ween Ch3940m and 3060m is prone t o inundat ion and scour, as it is posit ioned direct ly adj acent t he river channel, and close t o wat er level.

This is evidenced by recent f ailures along t he edge of t he river, part icularly in t he vicinit y of t he weir at Bells Parade, and recent deposit ion of debris above t he high t ide level along bot h sides of t he channel. Two large sect ions of t rack, close t o Bells Parade, have also been recent ly ret ained t o prevent f ailure of t he weak colluvial mat erials on t he slope above t he t rack.

From Ch3060m t hrough t o CH100m, where t he cycleway is t o be const ruct ed along t he river side of t he exist ing pavement , t here are recurring issues of scour and f ailure of over-st eepened road embankment s, and drainage inf rast ruct ure t hat would require modif icat ion or re-rout ing. Large volumes of f ill mat erial would be required in several sect ions (Ch3060m – Ch2600m, Ch1850m – Ch1050m and Ch450m – Ch100m), wit h bat t ers likely t o be f ounded eit her part ially or wholly on sof t sediment s. Separat e ret aining st ruct ures may be necessary wit hin t hese areas, in order t o minimise t he pot ent ial f or erosion and set t lement of any proposed f ills.

The sourcing of suit able f ill t o const ruct t he cycleway may prove dif f icult , given t he pot ent ial volumes and coarseness required t o resist t he erosive f orces present in t he river environment . Most quarries in t he Devonport region supply sub-100mm sized basalt aggregat e, t ypically sourced f rom f inely columnar-j oint ed deposit s, whereas more massive (ie. Cobble t o boulder) sized mat erial would be required f or t he proj ect .

4.3

Geology The geology of t he st udy area is shown on Figure 5, which has been adapt ed f rom t he most recent series of 1: 25, 000 Mineral Resources Tasmania maps f or t he Tasmanian land area.

The st udy area is charact erised by Jurassic aged dolerit e, which underlies t he maj orit y of t he proposed rout e bet ween Ambleside(Ch0m) and t he sewage t reat ment plant near Lat robe (Ch3100m). The dolerit e body ext ends across t he hill slopes t o t he east of t he sit e, and st ret ching bot h sout h t owards Lat robe and nort h t owards Devonport , wit h higher elevat ions about Ambleside capped by Tert iary aged basalt .

Abundant exposures of dolerit e were not ed in road cut t ings and along t he f oreshore adj acent River Road, wit h t he mat erial t ypically appearing moderat ely t o ext remely weat hered in nat ure, and in places mant led by a t hin (<1m) layer of loose dolerit ic colluvium. Consist ent wit h t he geology map, a band of ext remely weat hered dolerit e was not ed in road cut t ings bet ween Ch1250m and Ch1450m.

Despit e it s weat hered nat ure, t he dolerit e generally appears compet ent and st able, wit h small, localised f ailures not ed t o have occurred in t he overlying colluvial layer rat her t han t he in sit u dolerit e mat erial.

pitt&sherry ref : LN12120 H001 Geot ech Rep 31P RevB. docx/ DT/ rw

7

Sout h of t he sewage t reat ment plant , t he si t e walkover revealed t he dolerit e t o be largely obscured by deposit s of Quat ernary aged colluvium, ranging f rom less t han a met re t o several met res in t hickness. The colluvium cont ains predominant ly angular t o subangular dolerit e clast s of generally cobbl e t o boulder size, wit h a mat rix of sandy, low plast icit y clay. The generally weak, non cohesive nat ure of t he colluvium is best evidenced by abundant shallow f ailures in cut t ings bet ween t he sewage t reat ment plant and Bells Parade, bot h upslope and down slope of t he road.

Permian aged sandst one was not ed in road cut t ings bet ween Ch880m and Ch1250m, and Ch2450 and Ch2780m, consist ent wit h t hose areas indicat ed on Figure 5. The sandst one in t hese areas present s as moderat ely t o ext remely weat hered, subhorizont ally bedded t o weakly cross-bedded, compet ent mat erial.

Despit e t he geology map indicat ing t he presence of Permian aged sandst one out crop adj acent t he river in t he vicinit y of Bell s Parade and Pig Island (Ch3270m-Ch3820m), only small exposures of sandst one were not ed in cut t ings along t he walking t rack alongside t he river. For t he most part , t he sandst one was observed t o be overlain by colluvium in t his area.

4.4

Geohazards

4.4.1 Landslides The 1: 25, 000 scale landslide hazard maps f or t he Devonport -Fort h region published by MRT indicat e t he presence of 4 ‘ possible’ landslides and 1 ‘ act ive’ landslide wit hin t he st udy area, t he locat ions of which are shown on Figure 5.

Close examinat ion of bot h t he landslide hazard maps and aerial phot ographs shows t he 4 ‘ possible’ landslides t o be locat ed about t he sout hern ext ent of Ambleside, somewhat dist ant f rom t he proposed cycleway rout e, on t he moderat e t o st eep hillslopes above and t o t he west of River Road. The f eat ures are dif f icult t o dist inguish on t he aerial phot ographs and appear t ypically small t o moderat e in size, possibly relat ed t o land clearing undert aken several decades or more ago.

The single ‘ act ive’ landslide wit hin t he st udy area is locat ed below River Road near Ch450m of t he proposed cycleway rout e. The small circular f eat ure appears f rom bot h t he aerial phot ographs and on-sit e inspect ion t o have result ed f rom erosion and undercut t ing of an over st eepened area of road embankment , wit h cont inued slow regression of t he slope likely t o occur int o t he f ut ure.

Int erest ingly, t he MRT maps show no landslides having occurred in t he weak, lowcohesion colluvial mat erials present bet ween t he sewage t reat ment plant and Bells Parade, despit e t he presence of recent small f ailures and creep-relat ed f eat ures on t he hillslopes above t he road.

4.4.2 Acid Sulphate Soils The st udy area has a high probabilit y (>70% chance of occurrence in mapping unit ) of Coast al acid sulphat e soils and Marine subaqueous and int ert idal acid sulf at e soils (Figure 6).

Acid sulphat e soils when dist urbed and exposed t o oxygen t hrough drainage or excavat ion can produce sulphuric acid in large quant it ies t hrough oxidat ion.

There is no legislat ion direct ly relevant t o acid sulphat e soils in Tasmania, however, pot ent ial impact s may come under t he “ general environment al dut y” sect ion of t he Environment al Management and Pollut ion Cont rol Act 1994, such t hat :

pitt&sherry ref : LN12120 H001 Geot ech Rep 31P RevB. docx/ DT/ rw

8

“ A person must t ake such st eps as are pract icable or reasonable t o prevent or minimise environment al harm or environment al nuisance caused, or likely t o be caused, by an act ivit y conduct ed by t hat person. ” 11 Given t hat t he st udy area has a high probabilit y of acid sulphat e soil occurrence, if t he proj ect will excavat e 100m 3 of soil or sediment , or will involve t he dumping or f illing of land wit h more t han 500m 3 of soil t o a dept h of great er t han 0. 5m t hen, a desk t op risk assessment should be undert aken12. All dist urbances t o t he groundwat er hydrology or surf ace drainage pat t erns in coast al areas below 20 met res AHD should be invest igat ed.

4.5

5.

Issues of Relevance to Proposed Cycle Way 

There is evidence of erosion and / or scour along t he exist ing river f ront age, and const ruct ion of t he proposed cycle pat h will have t o consider caref ully t he select ion and placement of mat erials t o count er t his.



At t he Lat robe end of t he proposed t rack, t here is evidence of inundat ion during f lood / t idal event s. This should be considered in t he cont ext of sea level rise and f inal levels of t he t rack.



Unst able areas bot h upslope and down slope of t he exist ing road been not ed bet ween in Table 2.



Poor drainage condit ions are evident wit h t he exist ing road way and upgrading t hese should be included in t he design of t he cycle way.



Since signif icant reclamat ion is required f or a large part of t he proposed t rack, large f ill volumes would be required. In producing t his report , no considerat ion has been given t o assessing t he soil condit ions over t he lat eral ext ent of t he proposed reclamat ion. It is possible / likely t hat t here is a signif icant dept h of sof t soil deposit s, and t hese will not only set t le as reclamat ion is carried out , but will also t ake a long t ime t o set t le.



At chainage 450 t here is a land slip t hat is likely t o cont inue moving, result ing in set t lement t hat may need remediat ion.

Recommendations and further work 

Consult wit h t he EPA t o det ermine t he need t o undert ake a risk assessment f or acid sulphat e soils;



Bank erosion is evident , and likely due t o dif f erent processes, depending on locat ion wit hin t he river delt a/ meso-t idal est uary syst em. Prot ect ion of t he proposed cycle way embankment s will be required. The level of prot ect ion will depend on t he processes involved and locat ion. An assessment of t he pot ent ial erosive f orces along t he lengt h of t he proposed cycleway, and appropriat e bank prot ect ion met hodologies, should be undert aken;



An assessment of channel reclamat ion will be required, account ing f or necessary bank bat t ers and erosion prot ect ion. This should t arget t he upper est uary where t he deep wat er channel abut s t he bank, and in part icular ident if y any loss or impingement t o t he deep wat er channel in t his area. Depending on t he pot ent ial f or alt erat ion t o t he deep wat er channel, an assessment of t he pot ent ial impact of t he cycleway on t he mudf lat s t o t he west of t he channel should be undert aken.



Carry out probing t o assess t he ext ent and t hickness of sof t sediment s t hat would underlie reclamat ion areas.

11

Tasmanian Acid Sulf at e Soil Management Guidelines, Depart ment of Primary Indust ries, Parks, Wat er and t he Environment Sust ainable Land Use. 12 Tasmanian Acid Sulf at e Soil Management Guidelines, Depart ment of Primary Indust ries, Parks, Wat er and t he Environment Sust ainable Land Use.

pitt&sherry ref : LN12120 H001 Geot ech Rep 31P RevB. docx/ DT/ rw

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

Obt ain bat hymet ric dat a where reclamat ion is required, and combine t his wit h probing inf ormat ion t o enable an assessment of required mat erial volumes t o be made. This is likely t o be large considering t his t o be a proj ect where reclamat ion may not be f inancially j ust if iable.



Assess t he likely cost of reclamat ion act ivit ies.



Consider and compare t he cost s of reclamat ion wit h ot her opt ions such as a light weight j et t y st ruct ure t hat runs f or t he chainages where reclamat ion would be signif icant .

pitt&sherry ref : LN12120 H001 Geot ech Rep 31P RevB. docx/ DT/ rw

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Est uary zone 3

Est uary zone 2

Est uary zone 1

River delt a zone

Figure 1: Location of the proposed cycle way alignment (see section 3. 1 for explanation of zones)

pitt&sherry ref : LN12120 H001 Geot ech Rep 31P RevB. docx/ DT/ rw

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Mudf lat s Veget at ed islands Slight change t o right bank near headlands

Mudf lat 2009/ 2010

Land reclamat ion Edge of mudf lat s

Mudf lat f eat ures 1946

Mudf lat s

Change in veget at ion Right Bank Sect ion of est uary where deep wat er channel abut s right bank â&#x20AC;&#x201C; key area f or considerat ion

Deep channel

Mudf lat channels

Veget at ed islands

Figure 2 â&#x20AC;&#x201C; Channel 1946 (Red dashed line) and 2009 (blue line north and west), 2010 (blue line south east) (Background photo is j ust for illustration, it was not used in the analysis)(Blue line shows extent of 2009/ 2010 photographs).

pitt&sherry ref : LN12120 H001 Geot ech Rep 31P RevB. docx/ DT/ rw

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Land reclamat ion General ret reat in veget at ed boundary

New channel since 1946

Remnant s of 1946 f arm road

1946 channel

Figure 3 â&#x20AC;&#x201C; Channel 1946 (red dashed line) and 2009 (blue line), northern end (Background photo is j ust for illustration, it was not used in the analysis).

pitt&sherry ref : LN12120 H001 Geot ech Rep 31P RevB. docx/ DT/ rw

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Edge of channel – right bank Sect ion of est uary where deep wat er channel abut s right bank and land reclamat ion is possible – key area f or considerat ion

Mudf lat s

Backwat er evident in 1946 and 2010

Veget at ed islands

Mudf lat channels

Mud f lat s (due t o glare 2010 boundary could not be det ermined) River delt a channels st ill in same general locat ion

Figure 4 – Channel 1946 (red dashed line) and 2010 (blue line), southern end (Background photo is j ust for illustration, it was not used in the analysis) (Blue line shows extent of 2010 photograph).

pitt&sherry ref : LN12120 H001 Geot ech Rep 31P RevB. docx/ DT/ rw

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Figure 5: Geology and geohazards of the study area

pitt&sherry ref : LN12120 H001 Geot ech Rep 31P RevB. docx/ DT/ rw

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Figure 6 â&#x20AC;&#x201C; Probability of Acid Sulphate Soil (within 500 m)

pitt&sherry ref : LN12120 H001 Geot ech Rep 31P RevB. docx/ DT/ rw

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t ransport inf rast ruct ure | communit y inf rast ruct ure | indust rial inf rast ruct ure | climat e change

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Design Drawings Prepared by DCC 2012 Latrobe to Ambleside

CRADLE COASTAL PATHWAY

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AMBLESIDE

01

0.00km

DARY

02

MUNIC

IPAL BO UN

03

1.00km 04

05

2.00km 06

07 08

09

WEIR

3.00km

3.90km

LATROBE

END

ROAD AHEAD

END

ROAD AHEAD

ROAD AHEAD EN D

R AH OA EA D D

ROAD AHEAD

END

END END END

1

3

1

16

2

152

152A

4

6

8

10

12

14

CRADLE COASTAL PATHWAY

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