Wade St Portland

Site Specific Landslip

Emergency Management Plan

June 2008

2

Contents Introduction ......................................................................................................................................................................3

History of Wade Street Landslip.....................................................................................................................................4

General Description of Wade St Landslip....................................................................................................................5

Potential Mechanisms of Failure ...................................................................................................................................6

Immediate actions ..........................................................................................................................................................7

Monitoring .........................................................................................................................................................................7

Infrastructure Damage ...................................................................................................................................................7

Remedial Actions.............................................................................................................................................................7

Emergency Response Plan ............................................................................................................................................8

Landslip Movement with no damage to infrastructure ...................................................................................... 8

Movement resulting in damage to road and public infrastructure ................................................................. 8

Landslip movement with potential damage to utilities ...................................................................................... 8

Movement threatening or causing damage to houses and structures .......................................................... 9

Municipal Emergency Management Control ...................................................................................................... 9

Geotechnical Support .............................................................................................................................................. 9

Media Involvement ................................................................................................................................................. 10

Recovery Arrangements ........................................................................................................................................ 10

Landslip Response Roles and Responsibilities ...........................................................................................................11

Police.......................................................................................................................................................................... 11

Glenelg Shire............................................................................................................................................................. 11

Council Geotechnical Consultant ....................................................................................................................... 12

Utilities Service Providers ......................................................................................................................................... 12

SES............................................................................................................................................................................... 12

DSE.............................................................................................................................................................................. 12

Property Owners....................................................................................................................................................... 12

Contact List .....................................................................................................................................................................13

Authorisation...................................................................................................................................................................14

Appendix 1......................................................................................................................................................................15

Water, Sewer & Storm water Services .................................................................................................................. 15

Appendix 2......................................................................................................................................................................16

Gas Services.............................................................................................................................................................. 16

Appendix 3......................................................................................................................................................................17

Power Services.......................................................................................................................................................... 17

Appendix 4......................................................................................................................................................................18

Telephone Services.................................................................................................................................................. 18

3

Introduction

This 'Site Specific Landslip Contingency Plan' forms part of the Municipal Emergency

Plan and should be read in conjunction with that plan.

The aim of this plan is to:

• provide a background to the Landslip,

• outline Agencies responsibilities,

• analyse consequences of future movements, and

• to provide a guide to resources likely to be required for response

and recovery.

The Shire has an obligation under the Emergency Management Act 1986 to provide

resources under its control at the request of the Municipal Emergency Response

Coordinator and to undertake the short and long-term recovery process from the

advent of an emergency.

The technical data included herein is sourced by the inspection and Assessment

report undertaken by Parsons Brinckerhoff in February 2008.

These contingency plans as with other similar plans will be reviewed as required and

thus continue to be an evolutionary document.

4

History of Wade Street Landslip

A landslip on the cliff face of Portland Bay, near the eastern extremity of Wade Street,

Portland was initially reported to Glenelg Shire on Wednesday August 15th when the

movement had extended vertically for approximately 300mm.

The area was monitored, barricaded off and pedestrian signage and barriers were

put in place on Friday 16th when it was apparent that the movement was continuing,

albeit slowly.

Public Notices for newspaper advertisements were prepared on Friday for publication

in the following Monday's paper and also in the following Friday's paper. The site was

inspected by both Council and DSE officers on Monday 19th August 2007.

A more dramatic slip failure occurred on the night of the 22nd August, where the

vertical movement was in the order of 6m. Loose soil and boulders spilled from the

base of the slip onto the beach below.

By the 3 September 2007, the vertical movement at the slip head scarp was in the

order of 8m. The Portland Foreshore cliffs are located mostly on Crown Land, however

the upper reaches of the cliff are situated in land dedicated for the purposes of a

road and parking area. The road, Clifton Court, is the only access to a number of

private properties located near the cliff top.

Glenelg Shire actions following the slip were to provide :

• fencing along the cliff crest

• a crash barrier between the vehicle turning area and the cliff crest

• cordons and signage on the beach north and south of the slip area

• a cordon on the Anderson Point stairs just to the north of the slipped area.

5

General Description of Wade St Landslip

There is little substantial vegetation on the cliff in the vicinity of Wade St, mostly grass

cover. The ground surface landward of the cliff crest in Wade Street is a bitumen

sealed road and parking/turning area and water infiltration should be minimal

through this surfacing. There were no tension cracks in the pavement directly behind

the head scarp and no distortion noted in the kerb/spoon drain on the cliff crest. No

erosion or scouring due to surface water is visible near the slip area.

The extent of the Wade Street slip was estimated to be 40 m wide and 50 m high. A

near vertical head scarp around 10 m high was the main feature of the slip, located

just to the south of Wade Street very close to Clifton Ct corner. A 200 mm wide tension

crack was noted to the north of the head scarp suggesting that the slip is

propagating northwards. This tension crack is running from the north end of the

slipped zone northwards towards the stairs.

There is potentially a slip developing there that may be larger than the current one.

This tension crack may be well developed vertically. It is possible that the whole area

is active and very dangerous and the potential slip to the north would likely destroy

the stairs.

A concrete slab which was the former footing for a bench seat is now right on the

edge

of the head scarp whereas, it was probably 3 m to 4 m inland from the cliff crest

before the slip.

Cobbles and boulders were observed rolling down the landslide debris suggesting

ongoing slide activity. The slip was noted to have occurred in the top two thirds of the

cliff face as the limestone present at the base of the cliff was inferred to be intact.

A cliff depletion area was noted between the current slip and the cliff stairs,

suggesting a slip has occurred there in recent geological time. Old landslide debris

was noted at the toe of the cliff slope near the base of the steps. Angles of the

natural slopes above the limestone to the south of the slip were measured by

Clinometer and found to be around 35 degrees from the horizontal.

6

Potential Mechanisms of Failure

Portland cliffs have experienced a large failure every 3 or 4 years. The general mode

of failure of slips in the area is that failure is thought to occur within the thin plastic

clays (Maretimo clay) located on the surface of the limestone. It is probable that

groundwater becomes perched above this relatively impermeable clay giving rise to

elevated pore water pressures and reduced shear strength. At the foreshore, the

groundwater level will be similar to sea level therefore a hydraulic gradient, of the

groundwater within the cliff must exist. This gradient, being towards the coastline, will

tend to promote slope failure.

In general, along the Portland cliff coastline, large slips have occurred where the

limestone and Maretimo clay are located below beach level. The difference with the

Wade St slip is that the limestone and overlying Maretimo clay are visible above

beach level, so the slip has occurred at a higher level than, say the Hanlon Parade

slip. This has meant that the slip is limited in size due to the presence of the stronger

limestone in the cliff face. This type and size of slip has been common at the Portland

cliffs through geological time but not in living memory.

There is evidence to suggest that the Wade St slip will be retrogressive meaning that it

is likely to propagate. This particular slip is likely to propagate inland, due to the over

steep head scarp and along the cliff line to the north, as is already occurring, and

possibly also to the south. Generally observed angles of slopes on the cliff face

provide evidence of more stable configurations and we observed slopes at or about

30 degrees.

Propagation of the Wade St slip landward is likely to begin with local failure of the

near vertical backscarp slope. This local movement is likely to stabilise when the cliff

profile above the limestone reaches an angle of around 30 degrees to the horizontal.

The slip is propagating northwards with the beginnings of a large slip which is moving.

The complication in the Wade St area is that the limestone surface dips down towards

the north and is not visible on the north side of the current slip. The large tension crack

noted running from the current slip towards the north is likely to be the beginnings of a

larger slip, as its slip surface could be deeper seated. This larger slip will likely destroy

the cliff steps to the north of Wade St and it’s run out could reach the sea.

The mechanisms of failure can be summarised as cliff material slipping on the

Maretimo

clay when the clay’s strength is reduced by water pressure. The trigger for the

landslide is not known, but it is likely that surface water has been percolating vertically

down through the weathered basalt and has been perched on top of the Maretimo

clay, reducing its strength until a critical strength has been reached.

7

Immediate actions Immediate actions to protect people in the area of the slip have been undertaken

with the whole area cordoned off with physical barriers and signage warning of the

danger. No one is allowed to be in the area of beach below the slip or on the stairs.

Monitoring The tension crack will be monitored regularly for movement. The monitoring system

has been set up by Glenelg Shire and results are showing spasmodic and infrequent

small movements.

Infrastructure Damage The assessment report indicates that there are no immediate threats to the properties

located on Clifton Court but this will change if further movement occurs. The

immediate threats are to the road surfacing and associated drainage at the eastern

extremity of Wade Street, the northern part of the cliff top access road and to the

beach access steps.

Remedial Actions Short term actions are required to mitigate risks associated with inland propagation of

the slide but events may overtake this process. Also the actions need to be reviewed

depending on the results of the monitoring.

The Glenelg Shire will consider and where appropriate implement generic long term

options possibly including upgrading of the drainage profile and the creation of a

retaining wall to regrade the area to a stable configuration. A combination of these

methods may be appropriate especially as there is an access pinch point at Clifton

Ct which may require a near vertical retention system.

If the slip continues to regress, tension cracks may form at the cliff crest or the head

scarp face could deteriorate. If any of these features occur then emergency

retention of the face may be required to protect infrastructure (i.e. road, drainage

and ultimately houses).

Should this further occur, the following land slip emergency response plan has been

developed for implementation.

8

Emergency Response Plan

Landslip Movement with no damage to infrastructure

• Ensure Shire Contact is notified

• Shire contact to advise Landslip Consultant

• Consider Increasing visual observations & remote measurement monitoring

• Notify public in circumstances of substantial measurements

•

Movement resulting in damage to road and public infrastructure

• Ensure Shire Contact is notified

• IMMEDIATE Site inspection and Assessment by Council & DSE

• Notify authority / agency responsible for utility infrastructure (e.g. gas, Power,

Telephone, Water)

• Council to review restricted access to landslip and barricading on road reserve

• Council to notify residents of alternate access requirements and/or restrictions

• Council & DSE to increase frequency of measured and visual observations

• DSE to review restricted access to low lying areas along foreshore and areas of

Crown land

• Council / DSE to continue public awareness campaign

• Shire contact to advise Landslip Consultant

• Council to review long term requirements for road & public infrastructure

services

•

Due to co-existence of gas and power services in close proximity to the road reserve

along Clifton Court, there is a possibility that ground movement could contribute to

the development of a fire from a ruptured gas service. Therefore in all circumstances

below consideration is given to the potential that power cables and gas mains may

have been compromised.

Landslip movement with potential damage to utilities

• Ensure Shire Contact is advised

• Shire Contact to evaluate potential of damage to service lines

• Shire contact to advise MERO where municipal emergency considered (e.g.

People dislodged, houses affected)

• Contact CFA should fire be present

• Contact Service Authorities to disconnect affected services

• Consider evacuation of residents in conjunction with CFA should threat be

likely to affect health of persons in the area

• Participate in coordination of evacuation or persons and return t normal

operations following completion of emergency

• Shire contact to advise Landslip Consultant

9

Movement threatening or causing damage to houses and structures

• Ensure Shire Contact is notified

• IMMEDIATE Site inspection and Assessment by Council & DSE

• Shire contact to advise MERO where municipal emergency considered (e.g.

People dislodged, houses affected)

• Evacuate adjoining households where threatened

• Shire contact to notify Landslip Consultant

• Council to review restricted access to landslip and barricading on road reserve

• Council to notify residents of alternate access requirements and/or restrictions

• Council & DSE to increase frequency of measured and visual observations

• DSE to review restricted access to low lying areas along foreshore and areas of

Crown land

• Council / DSE to continue public awareness campaign including liaison with

stakeholders

• Council to review long term access for road and infrastructure depending

upon continuation of landslip

Municipal Emergency Management Control

The Emergency Management Manual Victoria, Part 7, identifies the relevant Control

Agencies for Response. Landslip is not expressly identified within the Manual and

resultingly, the Control Agency is: Victoria Police -“Threat Other” (against person,

property or environment)

The Incident Controller will be a member of the Victoria Police Force of suitable rank

and experience.

The incident controller will determine the Incident Control Centre, at time.

Response Expectation of the Council

Assistance with resources will be coordinated through the Municipal Emergency

Coordination Centre during a response to an incident of landslip.

These resources include but are not restricted to:

· Technical Specialists

· Barricades for Traffic Diversion

· G.I.S., Town Planning Maps

· Heavy Plant

· Community Information

· Shelter

There will be a requirement for a Municipal Liaison Officer at the Incident Control

Centre.

Geotechnical Support

The Glenelg Shire Council shall remain the direct liaison with the preferred geo-

technical consultant. Any circumstances that require the expertise of the

Geotechnical Consultant, including emergency situations outside office hours

responded to by emergency services, are to be coordinated by the Glenelg Shire

Council contact.

10

Media Involvement

All releases of information to the media must be ratified by the incident controller prior

to release. Individual stakeholders are able to utilise their own specific media liaison

officers once the information has been approved.

Recovery Arrangements

Whilst residents are requested to develop their own emergency plan in the situation

involving damage and/or evacuation of premises, any further emergency

arrangements for any displaced residents will be coordinated by the Municipal

Recovery manager (MRM) in accordance with the Municipal Emergency

Management Plan.

11

Landslip Response Roles and Responsibilities

Police

a) Coordinate activity on the site. b) Call in and liaise with other emergency services as required. c) Clear people from above, below and adjacent to the landslide

area to a SAFE area. The defined location of the evacuation

assembly point will be determined by the incident controller,

depending on the severity of the slip and the prevailing

conditions at the time of the emergency.

d) Ensure landowners remain contactable. e) Have “eye witnesses” available to brief professionals. f) Engage MERC where required g) Contact utility services where required to turn off

electricity/gas/water

h) If emergency situation occurs at night have emergency lighting made available, consider SES, CFA

i) Ensure communications off-site are available.

Glenelg Shire

a) Supply barriers and materials to cordon off Council roads and infrastructure

b) Provide advice to other services on Council issues as required. c) Provide initial coordination of Council resources. d) Ensure safety of Council staff on site e) Contact the Councils Geotechnical experts if required f) Instigate short term drainage actions where required g) Set up monitoring system for Council infrastructure h) Have earth-moving contractor/staff on stand-by to move

material as required

i) Be able to identify other experienced contractors with

appropriate equipment that can get to site without delay.

j) Conduct preliminary assessment of the site including a preliminary

structural assessment of buildings. Assess structural integrity of

buildings as required by Shire building Surveyor.

k) Maintain public awareness program l) Re-establish access to residents if required

12

Council Geotechnical Consultant

a) Listen to brief from eye-witnesses b) Where requested by Council, conduct a preliminary review of the

landslide including assessing the type, size and likelihood of future

movements on or adjacent to the landslide, the potential areas

involved, and the risks to life and property.

c) Provide an initial briefing to Glenelg Shire. d) Possible involvement of a more detailed assessment of the site.

This more detailed assessment may require access onto the

danger areas in accompaniment of Search & Rescue person.

e) Document the results of the assessment.

Utilities Service Providers

a) Identify all services in proximity to slide area. b) Turn-off water, gas and electricity to the site as required. c) Have service repair crews on stand-by.

SES

a) Check for injured or trapped persons and initiate rescue / treatment

b) Have short-term emergency electricity generators and local lighting available if required.

c) Have plastic sheeting, etc. available on stand-by.

DSE

a) Advise on requirements in relation to the Crown land component

b) Supply barriers and materials to cordon off Crown land and associated infrastructure

c) Set up monitoring system for Crown Land d) Contact the DSE Geotechnical experts e) Maintain public awareness program

Property Owners

a) Need to develop their own emergency plan in the situation involving damage and/or evacuation of premises

13

Contact List

Portland Police Station

Officer in charge

5523 1999 - 000 in emergencies when Station unattended

Glenelg Shire Council Contact

Mr Mauro Boddi

Title: Senior Engineer Operations

Ph: 0403 607 517

MERO

Mr Malcolm Armstrong

Title: Infrastructure Engineer Glenelg Shire Council

Ph: 0407 836 347

Council Contact for Plant /Equip

Mr Wayne Frost

Title: Works Coordinator Glenelg Shire Council

Ph: 0408 386 002

State Emergency Services

Ph 132 500 (Storm Activity Only)

0407 052 722 Police or Local Controller

Wannon Water

Ph 1300 926 668

Powercor

Ph 132412

Gas leaks

Ph 132771

Dept Sustainability & Environment

Mr Ross Martin

Title Coastal / Environmental Planner

Ph 0428 343 501

Geotechnical Specialists

Parsons Brinkerhoff

Mr Allan Garrard

Ph: 03 9861 1111

14

Authorisation

This plan was endorsed by the Glenelg Shire Council Municipal Emergency

Management Planning Committee at a meeting held on 12th May 2008.

15

Appendix 1

Water, Sewer & Storm water Services

Legend

Storm water

Water Service

Waste Water

16

Appendix 2

Gas Services

17

Appendix 3

Power Services

18

Appendix 4

Telephone Services