Lake Dennis Dam Emergency Action Plandata.dnrm.qld.gov.au/eap/lake-dennis-eap.pdf · Doc# 8191949-v8- Logan City Local Disaster Management Plan - September 2016 i . LOGAN CITY . LAKE

Doc# 8191949-v8- Logan City Local Disaster Management Plan - September 2016 i

LOGAN CITY

LAKE DENNIS EMERGENCY ACTION PLAN August 2019

INNOVATIVE, DYNAMIC, CITY OF THE FUTURE

WIDTJ

Text Box

Approved by the delegate of the Chief Executive, Department of Natural Resources, Mines and Energy until 1 June 2020

Emergency Action Plan for Lake Dennis Approved: 09 March 2018

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Lake Dennis - Emergency Action Plan

Registered dam ID: 1654 Current as at: 30 August 2019 Approved to: 1 October 2018

Dam Owner

Name: Logan City Council Date: 9 March 2018

Emergency Action Plan for Lake Dennis Approved: TBC


Approval and Authorisation

Prepared by Title Date

River and Catchment Engineering Program Leader 30/08/2019 Approved by Title Date

A/Local Disaster Coordinator

Chair Disaster Management Group

A/Chief Executive Officer, Logan City Council

Disclaimer The wording in this Plan is not intended to be relied upon as an exact statement of the requirements of the legislation, and users should refer to the relevant Acts when considering the legislative requirements.

Notwithstanding anything in the Plan that might be interpreted to the contrary, the provisions of the relevant Act prevail.

No responsibility is accepted for actions taken or any losses sustained based on reliance on an interpretation of this Plan to the exclusion of the relevant legislative provisions.

Emergency action planning shall be viewed as an ongoing continued improvement process that incorporates detailed disaster risk management principles and aligns with Local Government Disaster Management Plans.



Distribution List 1 The Lake Dennis Emergency Action Plan [‘EAP’] has been developed as part of Logan City Council’s comprehensive all hazards disaster management approach. The EAP is distributed as part of the Local Disaster Management Plan.

EAP distributed to Name and postal address Distribution copy no.

Dam Owner Chief Executive Officer

Logan City Council

150 Wembley Road, Logan Central QLD 4114

1

Emergency Contact Local Disaster Coordinator

Logan City Council


2

Local Disaster Management Group [‘LDMG’]

Logan City LDMG

Logan City Council


3

Dam Safety Regulator Director, Dam Safety

Water Planning and Regulation

Department of Natural Resources, Mines and Energy [‘DNRME’]

[email protected]

PO Box 15456, City East QLD 4002

4

Others District Disaster Coordinator

Queensland Police Service

11 Civic Parade, Logan Central QLD 4114

5

Duty Officer

Queensland Fire and Emergency Services

Emergency Services Complex

Corner Park Road and Kedron Park Road, Kedron QLD 4031

6

Director Community Services

Logan City Council


7

Manager, Parks

Logan City Council


8

Manager, Road Construction Maintenance

Logan City Council


9

1 Note that while the chief executive is required to give a copy of the approved plan to the emergency management chief executive, and publish the approved in the register of approved emergency action plans, s 352N(b) of the Water Supply (Safety and Reliability) Act 2008 (Qld) requires the Dam Owner to make it available to an individual –

(i) Who has a function under the plan; or (ii) Who, under the plan, is named and required to be personally notified of a dam hazard or emergency event.



Glossary Council Logan City Council

DCF Dam Crest Failure

DEWS Department of Energy and Water Supply

DM Act Disaster Management Act 2003 (Qld)

DNRME Department of Natural Resources, Mines and Energy

EAP Emergency Action Plan

EER Emergency Event Report

EMAF Emergency Management Assurance Framework (IGEM, 2012)

FIA Failure Impact Assessment (GHD, 2017)

FSL Full Supply Level

HIRA Hazard Identification and Risk Assessment

IGEM The Office of the Inspector General of Emergency Management

LDMG Local Disaster Management Group

LDMP Local Disaster Management Plan

LGA Local Government Area

PAR Population at Risk

PMF Probable Maximum Flood

PMFDF Probable Maximum Flood Dam Failure

SDF Sunny Day Failure

The Act Water Supply (Safety and Reliability) Act 2008 (Qld)

The Lake Lake Dennis



Table of Contents

1. Introduction ................................................................................................................................................ 7

2. Dam Information ........................................................................................................................................ 8

3. Dam Location ............................................................................................................................................. 9

4. Dam Owner Responsibilities.................................................................................................................... 10

5. Warning and Communication Plan .......................................................................................................... 11

5.1 Downstream Affected Properties (PAR) .............................................................................................. 12

5.2 Notification listing ................................................................................................................................. 14

6. Dam Hazard, Dam Hazard Event and Dam Emergency Event ............................................................... 16

7. Training .................................................................................................................................................... 17

8. Monitoring ................................................................................................................................................ 17

8.1 Telemetry ............................................................................................................................................. 18

8.2 Operations and Monitoring .................................................................................................................. 18

8.3 Inspections ........................................................................................................................................... 18

9 EAP Activation ......................................................................................................................................... 19

9.1 Emergency Management ..................................................................................................................... 20

9.2 Dam hazard event and emergency event escalation tables...................................................................... 21

9.2.1 Flooding Emergency ............................................................................................................................... 21

9.2.2 Embankment Failure Event .................................................................................................................... 22

9.2.3 Seepage ................................................................................................................................................. 23

9.2.4 Natural flooding only ............................................................................................................................... 24

9.2.5 Terrorist or High Energy Impact ............................................................................................................. 26

10 Emergency Event Report ..................................................................................................................... 26

11 Maps .................................................................................................................................................... 27

11.1 Dam Locality Map ................................................................................................................................ 27

11.2 Area Map ............................................................................................................................................. 29

11.3 Catchment Map ................................................................................................................................... 30

11.4 Dam Failure Inundation Maps.............................................................................................................. 31

11.4.1 Sunny Day Failure (SDF) compared to Natural Flooding ................................................................ 31

11.4.2 0.2%AEP Flooding with and without failure event ........................................................................... 31

11.4.3 PMF Flooding with and without failure event ................................................................................... 31

11.5 Contact List .......................................................................................................................................... 32

12 Other relevant drawings ....................................................................................................................... 34

12.1 Vulnerable Area Assessment .............................................................................................................. 34

12.2 Spillway at eastern end of embankment (Douglas Partners, 2015) .................................................... 35

12.3 Stability Analysis Results (Douglas Partners, 2015) ........................................................................... 36

12.4 Discharge ............................................................................................................................................. 37

12.5 Intensity Frequency Duration for rare rainfall events (BoM 2016) ....................................................... 38

12.6 Inspection Guide .................................................................................................................................. 39

Appendix A – Risk Assessment and Warnings Development ......................................................................... 41



1. Introduction 1.1 Background Subject Site Lake Dennis Park is located in Daisy Hill, a suburb in the north-eastern part of the Logan City local government area [‘LGA’].

The park is approximately 3.4 hectare in area and consists of a recreational walking track around a small water body of which is utilised by the residential community surrounding the park.

The water body referred to above, known as the Lake Dennis [‘the Lake’], expands over an area of 2.24 hectares, and has a capacity of 51.65ML. The Lake was constructed in 1951 by the Dennis family, the original land owners, for the purpose of irrigating their farm. The Lake has a dam wall which spans 110 meters in length and is approximately 4 meters high.

The Lake and the surrounding parkland is owned and managed by Logan City Council [‘Council’].

Legislation The Water Supply (Safety and Reliability) Act 2008 (Qld) 2 [‘the Act’] details the provisions for referrable dams, and the requirements for a Failure Impact Assessment [‘FIA’] as set out by the Guidelines for Failure Impact Assessment of Water Dams [‘the Guideline’]. 3

The Lake does not trigger a failure impact assessment, as detailed in s 343 of the Act, as it does not meet the following minimum specifications:

s 343. (1) A person who proposes to construct a dam must have the dam failure impact

assessed if the dam, after its construction, will be— (a) more than 10m in height and have a storage capacity of more than 1500ML; or (b) more than 10m in height and have a storage capacity of more than 750ML and

a catchment area that is more than 3 times its maximum surface area at full supply level.

Failure Impact Assessment Council commissioned a FIA as part of the implementation of the recommendations of the Lake Dennis Dam Stability Assessment. 4 The FIA was submitted to the Department of Natural Resources, Mines and Energy [‘DNRME’] for review and consideration, and was subsequently accepted by the DNRME Chief Executive and the Lake was registered as a referable dam.

1.2 Purpose of the Emergency Action Plan The purpose of the EAP is to ensure effective disaster management planning is in place to minimise the risk to people and property if a critical event was to occur. The EAP is to be implemented in line with the responsibilities of the Logan City Local Disaster Management Group [‘LDMG’] pursuant to the Disaster Management Act 2003 (Qld) 5 [‘DM Act’]. The EAP is intended to provide the relevant information and planning to support decisions of the LDMG for potential dam failure emergency scenarios.

Under the Act, the EAP is to document: • The identification, detection and management of dam hazards, as well as dam hazard and

emergency events; and • How effective warnings and notifications are communicated to those potentially impacted.

2 Water Supply (Safety and Reliability) Act 2008 (Qld), as at 1 July 2017. 3 Guidelines for Failure Impact Assessment of Water Dams (DNRME, 2012). 4 Lake Dennis Dam Stability Assessment (Douglas Partners, 2014). 5 Disaster Management Act 2003 (Qld), as at 3 July 2017.



The EAP is consistent with the comprehensive disaster management framework of prevention, preparedness, response and recovery as required under the DM Act.

The EAP is intended to be used in conjunction with the Logan City Local Disaster Management Plan and relevant dam safety documentation. The Emergency Management Assurance Framework 6

[‘EMAF’], prepared by the Office of the Inspector General of Emergency Management [‘IGEM’] has been used to ensure the EAP is an effective plan aligned with the elements of good practice disaster management planning.

2. Dam Information Dam name: Lake Dennis

Referable dam register no.: 1654

Owners name: Logan City Council

Owners phone no.: 07 3412 3412 (Council 24 hour number)

Emergency contact name: (if Dam Owner cannot be contacted)

Local Disaster Coordinator

Emergency contact phone no.: 07 3412 3412 (Council 24 hour number)

Stream name: Priest Gully

Reservoir name: N/A

Construction completed: 1951

Type of dam: Earth embankment

Purpose of dam: Initially built for irrigation and now part of public open space.

Storage capacity: 51.65ML

Dam Height: 4 metres

Dam Crest level: 76.43 mAHD (minor spillway concrete crest) 77.21 mAHD (embankment crest)

Full supply level (FSL): 7 76.16 mAHD

Surface Area at FSL 2.24 hectares

Embankment dimensions: 110m (L) x 4m (H)

Embankment slope: D/S – 1.2H:1V; U/S – 1.7H:1V

Spillway Type and width: Concrete crest and control section located on the east of the embankment. An unlined discharge channel runs down the eastern abutment and along the toe of the dam.

Incremental Population at Risk (PAR):

SDF: 0 DCF: 2.9 PMFDF: 11.6

Dam Consequence Category: LCC All Hazards Risk Rating: Low ANCOLD Rating: High C

6 Emergency Management Assurance Framework (IGEM, 2014). 7 Technical data extracted from the Lake Dennis Failure Impact Assessment (GHD, 2017).



3. Dam Location Latitude: 27o37’31.0” S

Longitude: 153o09’11.2” E

Physical address: 8A Lawnton Street, Daisy Hill QLD 4127

Lot and plan numbers: Lot 4 on RP116324

Figure 1. Location of Lake Dennis


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4. Dam Owner Responsibilities Pursuant to the Act, the Dam Owner is responsible for the following:

• Develop an emergency action plan (EAP) in consultation and collaboration with local government and disaster management group/s who may be affected by a dam hazard identified in the plan.

• Provide a copy of the EAP to each local government and disaster management group who may be affected by a dam hazard identified in the plan. These stakeholders have 30 business days to review the plan. The local government must provide a notice back to the dam owner within the 30 business days, the disaster management group may provide a notice, however it is not compulsory.

• The local government assessment notice of the EAP against the Disaster Management Plan and all notices received by the dam owner from the chairperson/s of the district (disaster management) group/s must be provided to DNRME at the time of EAP submission.

• Assess the EAP against the outcomes of the Office of the Inspector General of Emergency Management’s Emergency Management Assurance Framework. The Emergency Management Prioritisation Tool may be utilised for this purpose.

• Submit the EAP to the chief executive for assessment. The EAP must be accompanied by each notice given by a local government (must have), disaster management group for the plan (if received) and any notice responses by the dam owner.

• Maintain and update documents annually (before 1 October each year)

• Distribute current approved EAP to all parties listed in the distribution list.

• Respond in accordance with the approved EAP in all dam relevant incidents.

• Activate the EAP and maintain an incident log (including visual inspection of the dam and any notifications that have been made).

• Provide timely and accurate notifications to all relevant parties mentioned in the notification list in a relevant dam hazard event or emergency event.

• Report all incidents and failures in writing to the chief executive within forty-eight (48) hours of becoming aware of the incident or failure.

• Prepare Emergency Event Report (EER) and submit to the chief executive within 30 business days after the end of the emergency event.

• Ensure the Population at Risk (PAR) have an appropriate evacuation plan in the event of a dam failure.

• Ensure the Population at Risk (PAR) have an understanding of the purpose of the warning and notifications in the event of a dam emergency or dam hazard.

• Ensure appropriate training for all personnel with responsibilities under the EAP.

• Undertake periodic testing of EAP to ensure telephone numbers are correct and the notification priority list is logical. Make appropriate dam safety related decisions based on advice from a consulting engineer where appropriate. The dam owner is also responsible for authorising any immediate expenditure so that urgent repair work will not be delayed.

Undertake regular on-site monitoring and visual inspection of the conditions at the dam. The dam owner is responsible for conducting a safety evaluation of the dam and to identify any deficiency in the dam’s safety. Where deficiencies exist, the dam owner is required to take appropriate steps to minimise the potential risk of dam failure from these deficiencies.


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• Council has nominated the Local Disaster Coordinator as the standby operator, of whom will undertake all the roles and responsibility of this EAP in the absence of Council’s Chief Executive Officer.

5. Warning and Communication Plan There are high community expectations that all dam owners will provide timely warnings and notifications of a dam hazard event or emergency event. For this reason the Act requires the Dam owner to state within the EAP when and how PAR and relevant entities will be contacted in the event of a dam emergency (including priority order).

The purpose of emergency warnings is to inform the PAR of an impending or current threat and promote an appropriate responsive action.

Depending on the location of the dam and the number of PAR that may need to be notified of warning it may be appropriate that the warning is issued via a personalised phone call or personal visit.

Component 7 of the EMAF is that the key outcome of an effective warnings is that: • Communities at risk of impact from an event are defined and can be targeted with

contextualised warnings; and • Communities at risk of impact from an event, receive fit-for-purpose, consistent, accurate

warnings through all phases of events.

Council’s multi-modal communication framework will be utilised to disseminate warnings as necessary. In line with the Disaster Management Act 2008 (Qld), determination of the most fit-for-purpose communication method and implementation of warnings is the responsibility of the Logan City Local Disaster Management Group (LDMG). The multi-modal warning model for Logan City is outlined in Figure 2.

Multi-modal Communications Framework

General

More quickly disseminated

Frequently Used Logan-specific modes

Radio Media Release

Television

News bulletin

Internet/web-based Disaster Dashboard and Council website

Community notice boards Not considered effective in immediate instance for EAP

Newspapers Not considered effective in immediate instance for EAP

More slowly disseminated


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Specific

More quickly disseminated

Frequently Used Logan-specific modes

Telephone Emergency Alert Campaign

Computer EWN

Two-way

Loud hailers As per the activation and notification tables in Section 9.2 and Section 5.2 respectively. Door knocking

More slowly disseminated Figure 2. Logan’s multi-modal communications framework.

5.1 Downstream Affected Properties (PAR)

The Failure Impact Assessment 8 digitised 359 building footprints adjacent to the Priest Gully waterway downstream of Lake Dennis. In line with the Guidelines, a comprehensive two-dimensional hydraulic assessment was delivered to identify the failure impact zone.

Based on a GIS analysis, the Probable Maximum Flood Dam Failure [‘PMFDF’] scenario indicated up to 251 parcels may experience some level of inundation. On further inspection, 78 of these properties were identified as being publicly owned land (173 parcels privately owned).

The Act, and the supporting Guidelines require the Dam Owner to identify properties where flood inundation depth exceeds 300mm. The number of homes affected downstream of the dam is outlined in Table 1 below.

Table 1 - Downstream Affected Homes and Population

Failure Scenario

Likelihood of Coincident Rainfall

Homes at Risk (Number) Population at Risk (People)

Non-Failure

Failure Incremental Risk

Non-Failure

Failure Incremental PAR

SDF N/A N/A 0 0 N/A 0 N/A

DCF 500yr ARI 0 1 1 0 2.9 2.9

PMFDF ~10,000yr ARI 12 16 4 34.8 46.4 11.6

Note: The Failure Impact Assessment reported the PMFDF event would impact 17 homes (PAR = 49.3); however, the property at was noted to have been duplicated in the digitisation process. The EAP is based on corrected data.

The Probable Maximum Flood [‘PMF’] is based on probable maximum precipitation, and it is likely, that should such a rainfall event move across the city, the impact on surrounding catchments would be more significant than the impact of a PMFDF event.

A comprehensive hazard identification and risk assessment for the population at risk has been completed along with an assessment of communication modes and is detailed in Appendix A.

8 Lake Dennis Failure Impact Assessment (GHD, 2017).


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For the purposes of developing the Emergency Action Plan, the PAR within the failure impact zone has been identified. To ensure disaster planning is effective, Council’s unique property identifier - ‘Property Key’ has been adopted for the purposes of identifying affected properties. The Property Key is integrated into Council GIS and operational tools

Table 2 - Downstream Affected Properties (PAR)

Name Property Key Location Notification requirement

Engagement

Dam Hazard Event – ‘Watch and Act’ EA

Emergency Event – ‘Emergency Warning’ EA

Other multi-modal notifications as required

Engagement

Dam Hazard Event – Door Knock and ‘Watch and Act’ EA

Emergency Event – Door Knock and ‘Emergency Warning’ EA


Engagement

Dam Hazard Event – ‘Watch and Act’ EA

Emergency Event – ‘Emergency Warning’ EA



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5.2 Notification listing Table 3 – Agency Notification

Relevant agencies

Name Location Contact Details Notification Requirement Notification Responsibility

Dam Safety Regulator, DNRME

Brisbane

[email protected]

• Advise of details of activation of EAP to ‘Stand-up’ level of activation.

• Keep the Dam Safety Regulator informed of any changes in dam status as emergency situation develops.

• Notify any incidents or failures in accordance with safety conditions, if applicable, where applied to the dam.

River and Catchment Engineering Program

Local Disaster Management Group

Logan City LDMG, Chair –

• Advise of details of activation of EAP to ‘Stand Up’ level of activation

• Keep the LDMG informed of any changes in dam status as emergency situation develops

• Advise the LDMG of any infrastructure that may be impacted from the flows from the dam

• Notify of any incidents or failures in accordance with safety conditions applied to dam

Disaster Management Program

Logan City Council

Logan City Council

(07) 3412 3412 (Council 24 hr number)

• An emergency event that affects Council’s infrastructure Disaster Management Program

Queensland Police Service, District Disaster Coordinator (DDC)

Logan Logan Police HQ

• Advise of details of activation of EAP to ‘Stand Up’ level of activation

• Keep the DDC informed of any changes in dam status as emergency situation develops

• Advise the DDC of any infrastructure that may be impacted from the flows from the dam

• Notify of any incidents or failures in accordance with safety conditions applied to dam

Disaster Management Program

State Emergency Service (if relevant)

Logan SES 132 500 • Notify if assistance is required Disaster Management Program

mailto:[email protected]

mailto:[email protected]


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Relevant agencies

Name Location Contact Details Notification Requirement Notification Responsibility

Bureau of Meteorology

Weather radar

Rainfall and river conditions

Forecasts

www.bom.gov.au/qld

• No notification requirements

• Website to be used during a rainfall event to predict the impact of flows from the catchment into the dam

River and Catchment Engineering Program

http://www.bom.gov.au/qld

http://www.bom.gov.au/qld


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6. Dam Hazard, Dam Hazard Event and Dam Emergency Event

The EAP identifies each 'dam hazard event' and 'emergency event' and includes a table of actions for each event. The tables are provided in Section 9.2 and provide clear and concise instructions to enable dam operation personnel to complete the task during each 'dam hazard event' and 'emergency event'.

EAP must identify each ‘dam hazard event’ and ‘emergency event’ and include a table of actions for each event. The table should provide clear and concise instructions to enable dam operation personnel to complete the task during each ‘dam hazard event’ and ‘emergency event’.

Under the Act ‘dam hazard’ means a reasonable foreseeable situation or condition that may:

• cause or contribute to the failure of the dam, if the failure of the dam may cause harm to people or property; or

• require an automatic or controlled release of water from the dam, if the release of water from the dam may cause harm to people or property.

The main purpose of an emergency action plan is to minimise the risk of harm to persons and property if a dam hazard event or an emergency event for the dam happens. The difference between a ‘dam hazard event’ and an ‘emergency event’ will relate to the scale and severity of an event.

Under s 358A of the Act, a ‘dam hazard event’ is defined as:

‘dam hazard event, for a dam, means an event arising from a dam hazard if—

(a) persons or property may be harmed because of the event; and

(b) a coordinated response involving 2 or more of the relevant entities mentioned in paragraphs (b) to (d) of the definition relevant entity is unlikely to be required to respond to the event; and

(c) the event is not an emergency event.’

In other words, a dam hazard event is an event or a point in time, related to a dam hazard, when the dam owner plans to respond under the dam owner’s emergency action plan.

An ‘emergency event’ for a dam is defined under s 358A of the Act as:

‘an event arising from a dam hazard if—

(a) persons or property may be harmed because of the event; and

(b) any of the following apply—

(i) a coordinated response involving 2 or more of the relevant entities mentioned in paragraphs (b) to (d) of the definition ‘relevant entity’ is likely to be required to respond to the event;

(ii) the event may arise because of a disaster situation declared under the Disaster Management Act;

(iii) an entity performing functions under the State disaster management plan may, under that plan, require the owner of the dam to give the entity information about the event’.


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The Emergency Action Plan for Lake Dennis dam, considers the following specific dam hazard and emergency events relevant to the dam:

• Flood event (leading to overtopping) including flood routing of design flood events from 50yr ARI to PMF as well as failure impacts assessed for sunny day failure, 500yr ARI failure, 1000 yr ARI failure and PMF Failure; 9

• structural damage to the dam; • new seepage or increased seepage; and • terrorism or high energy impact.

7. Training Responsible personnel within Logan City Council will receive appropriate dam safety training based primarily around “on the job” training in the maintenance of the dam in combination with practical exercising from time to time.

The training will aim to ensure that responsible personnel understand:

• the location, construction and other relevant Dam Information;

• the Emergency Action Plan;

• their role in the monitoring and activation of the Emergency Action Plan; and

• the dam safety routine inspection and surveillance procedures.

Training will include, but not be limited to:

• internal training and desktop exercising to test the effectiveness of the EAP - annually; and

• exercising of the EAP will occur at least every two years.

8. Monitoring The watershed of the Lake Dennis catchment is approximately thirty (30) hectares, which is relatively small in comparison to the Lake Dennis surface area of approximately 2.5 hectares. As a result, the time of concentration is short and if there is extreme rainfall in the upstream catchment, there will be a short time between rainfall occurring and runoff reaching Lake Dennis. Due to the nature of the natural movement of flows upstream of the Lake Dennis catchment, it is important to consider available monitoring approaches for activation of the EAP and for community awareness and warning. Engagement with the PAR will included awareness of the relevant, available monitoring and warning tools.

Given the relatively short time of concentration, the primary monitoring approach will be the rainfall gauges near the Lake Dennis catchment. These gauges will provide the relevant intelligence on rainfall volumes and direction. The Lake Dennis Failure Impact Assessment (GHD, 2017) determined the Population At Risk (PAR) trigger is in events greater than 0.2 percent annual exceedance probability (0.2%AEP) rainfall in the upstream catchment, with coincident one percent Annual Exceedance Probability (1%AEP) in the downstream catchment. The Australian Rainfall and Runoff Guidelines (Engineers Australia, 2016) describe 0.2%AEP rainfall events as ‘rare’. The Bureau of Meteorology Intensity-Frequency-Duration chart (see Section 12.5) indicate the rare rainfall depths associated with the PAR are 472mm in 24 hours (1 day) with rainfall volumes

9 Lake Dennis Failure Impact Assessment (GHD, 2017).


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approaching 819mm in 96 hours (four days). Based on historical information for south-east Queensland, the rare rainfall volumes would most likely be associated with a slow moving low pressure system, generally the result of a Tropical Cyclone or ex-Tropical Cyclone. The EAP activation triggers outlined in Section 9 have been selected on a conservative basis to ensure an effective response to an emerging dam hazard or emergency event can be implemented.

Situational awareness of evolving events should be considered in combination with observed dam levels at the spillway.

8.1 Telemetry Rainfall telemetry stations are located across Queensland, with gauge readings publicly available through the Bureau of Meteorology. Council has additional telemetry and monitoring systems that are utilised during severe weather response as part of the Local Disaster Management Group’s standard operating procedures. Nearby telemetry stations (see map in Section 11.1) are:

• Underwood AL (Millers Road);

• Slacks Creek AL (Reserve Park); and

• Slacks Creek AL (Loganlea Road).

River and Catchment Engineering are Council’s flood intelligence lead within the Local Disaster Coordination Centre and will monitor the above rainfall gauges to provide telemetry intelligence as part of a potential emerging event under the scope of the EAP.

8.2 Operations and Monitoring The decision to activate the EAP should be guided by available information, including but not limited to:

• Condition assessments;

• Reading of the gauge board located at the spillway;

• Near-real-time stream closed circuit television of the spillway, monitored by River and Catchment Engineering as part of Council’s telemetry network; and

• Rainfall gauges.

Detailed monitoring and disaster operations are to be implemented in line with the Flooding Standard Operation Procedure, Logan City Local Disaster Management Plan.

8.3 Inspections In addition to the above monitoring process, routine inspections will be undertaken to minimise the risk of a dam hazard event occurring.

In determining the appropriate frequency of inspections, a range of guidelines and standard Council asset management protocols were considered. ANCOLD Guidelines on Dam Safety Management (2000a) are “applicable for water or tailings dams with the potential to cause loss of life or significant environmental or physical damage through operation or failure. Although prepared for dams which would normally be at least 10 to 15m high ANCOLD guidelines can also be used to assist with decisions on smaller dams, particularly where a dam or series or dams creates the potential for loss of life or significant damage.” Table 5.2 suggests Dams with a hazard category of High C should have the following inspections:

• Comprehensive: On first filling then 5 yearly; • Intermediate: Annual;


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• Routine Visual: Daily to Tri-Weekly; and • Special: As required.

ANCOLD Guidelines (Table 5.2) on Frequency of Inspection note that “Dam Owners may undertake a review to determine if a reduced or increased frequency of inspection is acceptable. The review should be carried out by a dams engineer and take into account such matters as Regulator requirements, dam hazard and risk, type and size of dam, dam failure modes and monitoring arrangements”.

Council engaged a suitably qualified dam engineer to develop Standard Operating Procedures (SOPs) and a Detailed Operation and Maintenance Manual (DOMM) for the Dam. The frequency of inspections outlined in the SOPs are in accordance with the dam safety conditions issued by the Queensland Government and are scheduled:

• Routine Inspection – monthly;

• Comprehensive Inspection – every five years; and

• Special - following forecast of extreme rainfall in the area, during and after a flooding or overtopping event, following a seismic event as as directed by the Dam Safety Regulator.

These inspections are undertaken by a suitably qualified and experienced engineer.

Considering the guidance provided by ANCOLD, the potential impacts identified in the Failure Impact Assessment and the SOPs and DOMM prepared by the dam engineer the above inspection frequency is considered fit for purpose.

Inspections should seek to identify and monitor potential indicators of structural damage to the dam. There are many potential indicators of the structural damage to a dam. The significance of these will depend on the particular event and the circumstances at the dam. If new instances of any of the following indicators are discovered at Lake Dennis Dam, the actions listed in Section 9.2.2 should be followed. A guide of potential indicators is contained in Section 12.6

9 EAP Activation This EAP will be activated when dam hazard or emergency event occurs at the dam and there is the potential for the dam to place persons and property at risk.

There may be no need to activate this EAP if minor incidents happen (e.g. cracking, small slips, sinkholes) if they will not endanger the integrity of the dam. However, minor incidents will be investigated, monitored and adequate works completed to prevent further deterioration.

The EAP has been structured as a ready reckoner to assist decision making as part of Council’s disaster management framework. Section 9.2 provides event escalation tables for possible dam hazard and dam emergency events.

Flooding/Flooding Failure is included in the EAP for completeness; however, it should be noted that there is no incremental population at risk due to Lake Dennis for generic flooding events. Flood information for flood events resulting from significant rainfall up to 1%AEP in the Priest Gully catchment are as per the Priest Gully Flood Study. This information is managed and maintained in line with Council’s standards for flood data management and disaster management planning procedures.

The EAP activation should be considered in light of other flooding which is occurring as a result of rare to extreme rainfall in the region. It is likely that river and creek catchments will be experiencing significant and widespread flooding if rainfall was occurring as considered in the assessment of dam failure scenarios.


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Council’s disaster management planning is considered effective – with effective planning to enable an adaptable, scalable and comprehensive emergency and disaster management. It takes a measured approach to response and warning to ensure the safety of people, property and infrastructure.

As discussed in Section 8, given the short response times of the catchment upstream of the dam, activation of the Lake Dennis EAP will generally be based on observed rainfall approaching the catchment and consideration of observed condition and dam levels.

9.1 Emergency Management

The purpose and responsibility of Emergency Management is as follows:

• Be alert to potential developments and maintain close vigilance during extreme events or perceived abnormal behaviour of the dam;

• Maintain safety requirements at all times during response actions;

• Take actions as outlined in the event escalation tables; and

• Maintain communication equipment is in working order.


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9.2 Dam hazard event and emergency event escalation tables 9.2.1 Flooding Emergency

The following activation table should be used in conjunction with the Inundation Maps for DCF (S11.4.2) and PMFDF (Section 11.4.3)

Triggers

Responsibility Accountable Officer Contact RCE River and Catchment Engineering Program Leader PO Park Operations and Maintenance Program Leader DM Disaster Management Program Leader RCM Roads Maintenance Program Leader LDC Local Disaster Coordinator

Table 4. Flooding Emergency Activation

Emergency level

Characteristics (Trigger) Actions

Dam Owner LDMG/LDCC R&CE DM Park Ops RCM

ALERT Dam is at full supply level and more than 400mm is forecast by the BoM in 24hrs in the upstream catchment.

Approve removal of baffle board.

Monitor rainfall gauges at Slacks Creek AL (Reserve Park) and Slacks Creek AL (Loganlea Rd).

Monitor water level rises at the dam spillway and provide updates to DM and Dam Owner every 12 hours.

Notify the LDC of potential to activate lean forward arrangements.

In consultation with the LDC liaise with emergency services to advise of potential future situation.

Inspect embankment and look for any signs of bank instability. Report to DM, R&CE and the Dam Owner.

Open spillway drop board

LEAN

FORWARD

No signs of embankment instability.

Rainfall radar intensities in the vicinity of the dam and in the direction of the dam exceed 400mm.

If signs of failure – refer to Section 9.2.2

Continue monitoring the issue.

Notify the LDMG of a change of activation.

As for the above, however provide updates to DM and the Dam Owner every 6 hours or when deemed appropriate.

Recommend to the LDC for activation of the LDCC if triggers are met. Liaise with emergency services at the direction of the LDC.

As above, updates expected every 24 hours or as determined by the LDC/LDMG.

Prepare to support with road closures if required.

STAND-UP No signs of embankment instability.

Recorded rainfall exceeds 400mm in the past 24hrs at Slacks Creek AL (Reserve Park) and Slacks Creek AL (Loganlea Rd) AND water level is greater than 76.9mAHD. - 0.4m above minor spillway - 0.7m above FSL - 0.3 below crest Refer to 0.2%AEP extent on DCF Map (S 11.4.2)

Consider notification of PAR as listed in Section 11.5.

Liaise with the Chair of the LDMG as appropriate.

Updates expected every 24 hours or as the situation changes.

Frequency to be determined by LDC/LDMG

As for the above, however provide updates every 4 hours or when deemed appropriate by the LDC/LDMG.

As above, with increased frequency as determined by the LDC/LDMG.

As above, potentially remotely, with increased update every 6 hrs or as determined by the Dam Owner and LDC.

Prepare to support with road closures if required.

As above, but water level reaches 77.1mAHD. - 0.6m above minor spillway - 0.9m above FSL - 0.1m below crest

Notify PAR as listed in Section 11.5.

Notify the Dam Safety Regulator of emergency event

Notify downstream PAR using watch and act alert

Updates expected every 12 hours or as determined by the LDC/LDMG.



As above, with increased update frequency as determined by LDC.

As above, but water level reaches 77.3mAHD - 0.8m above minor spillway - 1.1m above FSL - 0.1m above crest Relates to 0.01%AEP – Use PMF extent (S11.4.3)

Notify PAR as listed in Section 11.5

Notify the Dam Safety Regulator of emergency event

Notify downstream PAR using emergency warning alert

Updates expected every 6 hours or as determined by the LDC/LDMG.



As above, if safe.

STAND-DOWN

Rainfall ceases and dam levels falling Notify Dam Safety Regulator of ‘Stand Down’

Issue a final notification advising the end of the emergency event.

Advise DM and the Dam Owner that dam levels have fallen to full supply levels (76.2mAHD)

Complete the remedial works and confirm that there’s no risk of dam failure.

Post event inspection of embankment

Remedial works as required.


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Emergency level



Prepare emergency event report to the Dam Safety Regulator (see Section 10).

9.2.2 Embankment Failure Event

The following activation table should be used in conjunction with the Inundation Maps for SDF (S11.4.1), DCF (S11.4.2), PMFDF (S11.4.3). Consider in conjunction with 9.2.4.

Triggers

Responsibility Accountable Officer Contact Information RCE River and Catchment Engineering Program Leader

PO Park Operations and Maintenance Program Leader DM Disaster Management Program Leader RCM Roads Maintenance Program Leader LDC Local Disaster Co-ordinator

Table 5 – Failure Emergency Event Activation

Emergency level



ALERT • Identification during routine inspection of initial signs of embankment distress such as cracks.

• Earthquake • Terrorism or high impact event

Contact a suitably qualified dam engineer for advice and if necessary employ a contractor to perform adequate remedial works.

Review rainfall forecast. Report to DM and Dam Owner

Liaise with LDC and emergency service to advise of potential actions. Monitor and advise LDC of earthquake via Council’s DM network.

Inspect embankment and look for any signs of bank instability. Signs of cracking/ scouting/ slumping progressing. Open spillway drop board and report to Dam Owner, DM, RCE.

Undertake remedial action if practical. Report to Dam Owner, Parks and DM.

LEAN

FORWARD

Signs of cracks progressing. Cracking becoming more significant to the point where dam stability may be starting to be impaired. Lake levels at 76.4mAHD. Use Mapping and PAR for SDF (Section 11.4 and 11.5)

Consider notifying (door knock) downstream PAR, Section 11.5.

Consider stand-up of LDCC. Consider notifying downstream PAR. Updates expected every 6 hours or when deemed appropriate.

Monitor rainfall forecast and current rainfall records. If rainfall is occurring/forecast, monitor lake levels for WSL rises above 76.3mAHD - 0.1m above FSL In consultation with on-ground staff, advise DM, LDC and Dam Owner of water level rises. - If no rainfall: update every 24 hrs. - If rain <200mm per day, update every 12 hrs. - If rainfall > 400mm per day, update every 3 hrs.

Notify LDC/LDMG. Inform them of any downstream infrastructure or PAR that may be impacted by a dam failure. Monitor and advise LDC of earthquake via Council’s DM network. Updates expected every 24 hrs.

As above, with increased monitor as determined by the Dam Owner.

Upgrade efforts at remedial works or load reduction if practical.

STAND-UP Increasing in cracking to a state where the safety of the dam is significantly impaired. Water level approaches 76.4mAHD - 0.2m above FSL - at minor spillway level - Rainfall > 400mm in 24 hrs forecast Use Mapping and PAR for SDF (Section 11.4 & 11.5)

Continue monitoring the condition of the dam remotely. LDC to notify downstream PAR, relevant LDMG and the Dam Safety Regulator that the dam is likely to fail.

Implement Watch and Act Alert Updates expected every 4 hours or as the situation changes. Frequency to be determined by LDC/LDMG

As above, with increased update frequency as determined by the Dam Owner and LDC.

Notify LDC/LDMG. Inform them of any downstream infrastructure or PAR that may be impacted by a dam failure. Monitor for earthquake as above.

Continue monitoring the condition of the dam remotely. As above, updates expected every 6 hours or as determined by the LDC/LDMG.

Assist with road closures

Increasing in cracking to a state where the safety of the dam is significantly impaired. Water level above 76.5mAHD - 0.3m above FSL - above minor spillway level

LDC to notify downstream PAR, relevant LDMG and the Dam Safety Regulator of imminent dam failure risk.

Implement Emergency Warning Alert Updates expected every 2 hours or as the situation


Notify LDC/LDMG as required by the LDC. Monitor and advise LDC of earthquake via Council’s



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Emergency level



- Rainfall > 550mm recorded in 24 hrs Use PMFDF Mapping and PAR (Section 11.4 & 11.5)

changes. Frequency to be determined by LDC/LDMG

DM network. Updates expected every 12 hrs.

STAND-DOWN

Remedial works completed and there’s no risk of failure or it is determined that the issue is manageable and is not going to develop into a failure condition.

Notify Dam Safety Regulator of ‘Stand Down’ Prepare emergency event report to the Dam Safety Regulator (see Section 10).

Issue a final notification advising the end of the emergency event to previously notified entities


Notify LDC/LDMG as required by the LDC..

Post event inspection of embankment. Engage dam safety expert as necessary to confirm dam safe.

Complete remedial works

9.2.3 Seepage The following activation table should be used in conjunction with the Inundation Maps for SDF (S11.4.1), DCF (S11.4.2), PMFDF (S11.4.3)

Responsibility Accountable Officer Contact Information RCE River and Catchment Engineering Program Leader PO Park Operations and Maintenance Program Leader DM Disaster Management Program Leader RCM Roads Maintenance Program Leader LDC Local Disaster Co-ordinator

Table 6 –Seepage Emergency Event Activation

Emergency level



ALERT Identification of new areas of seepage or increase in existing seepage.

Notify downstream PAR, relevant LDMG and the Dam Safety Regulator.


Review rainfall forecast. Report to DM and Dam Owner

Liaise with LDC and emergency service to advise of potential actions.

Inspect embankment and look for any signs of bank instability. Signs of seepage identified. Open spillway drop board and report to Dam Owner, DM, RCE.

Undertake remedial action if practical.

Report to Dam Owner

LEAN

FORWARD

Significant seepage detected with signs of cloudy water in seepage.

No rainfall in catchment

Water level at full supply level (76.4 mAHD).

Use SDF Mapping (Section 11.4).

Consider notifying (door knock) downstream PAR.

Consider notifying downstream PAR

Updates expected every 6 hours or when deemed appropriate.

Monitor rainfall forecast and current rainfall records.

If rainfall is occurring/forecast, monitor lake levels for WSL rises above 76.3mAHD

- 0.1m above FSL In consultation with on-ground staff, advise DM and Dam Owner of water level rises.

If no rainfall update every 24 hrs. If rain <200mm per day, update every 12 hrs.

If rainfall > 400mm per day, update every 3 hrs.

Notify LDC/LDMG. Inform them of any downstream infrastructure or PAR that may be impacted by a dam failure.

Monitor the seepage and determine whether the seepage rate is increasing or monitor sign of cracks progressing.

Upgrade efforts at remedial works or load reduction if practical.

STAND-UP Increasing seepage discharge rate and clouding. Piping failure has initiated.

Progressive internal erosion of the embankment or foundation to form an open conduit or a pipe and the dam failure is likely.

Continue monitoring the condition of the dam remotely.

LDC to notify downstream PAR, relevant LDMG and the Dam Safety Regulator that the dam is likely to fail.

Implement Watch and Act Alert

Updates expected every 4 hours or as the situation changes. Frequency to be determined by LDC/LDMG



Continue monitoring the condition of the dam remotely.

Assist with road closures


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Emergency level



Water level approaches 76.4 mAHD.

As above, but water levels above 76.4 mAHD

If rainfall > 400mm per day is forecast refer to S9.2.2.

LDC to notify downstream PAR, relevant LDMG and the Dam Safety Regulator of imminent dam failure risk.

Implement Emergency Warning Alert

Updates expected every 2 hours or as the situation changes. Frequency to be determined by LDC/LDMG




Report to LDC/LDCC observations from field. Frequency as determined by the LDC/LDMG.

STAND-DOWN

Remedial works completed and there’s no risk of failure or it is determined that the issue is manageable and is not going to develop into a failure condition.

Notify Dam Safety Regulator of ‘Stand Down’

Prepare emergency event report to the Dam Safety Regulator within 30 Days (see Section 10).

Issue a final notification advising the end of the emergency event to previously notified entities

Prepare Emergency Event Report (EER) and submit to Director Dam Safety, DNRME within 30 business days after the end of the emergency event.


Complete the remedial works and confirm that there’s no risk of dam failure.

9.2.4 Natural flooding only (1%AEP Flood – Natural Flood) Consider in conjunction with 9.2.2 Responsibility Accountable Officer Contact Information RCE River and Catchment Engineering Program Leader PO Park Operations and Maintenance Program Leader DM Disaster Management Program Leader RCM Roads Maintenance Program Leader LDC Local Disaster Co-ordinator

Table 7 – 1%AEP Catchment flooding

Emergency level



ALERT Significant rainfall in catchment with lake levels rising towards FSL and a spillway discharge expected.

Lake level 77.0mAHD

Notify downstream PAR, relevant LDMG and the Dam Safety Regulator.


For a creek flooding scenario, standard LDMG/LDMP activation and operations prevail.

Operations monitor rainfall activity on the BOM radar and Environmon.

Dam inspection and recording of water level at regular intervals as per the Detailed Operating Maintenance Manual, Dam Safety Conditions.

Notify the LDC and LDMG (if applicable).

LEAN

FORWARD

Spillway flows increasing but as yet are unlikely to impact on downstream PAR and infrastructure.

Continue monitoring the issue.

Continue monitoring rainfall.

Dam Inspections and recording of water level at regular intervals in line with Reconnaissance Team Standard Operating Procedures and Duty Statement DM# 8190137 if rainfall continues over several days.

STAND-UP Spillway discharge increasing with flows. Use PAR Table for Natural Flooding in Section 11.5.

Continue monitoring the condition of the dam and the issue if safe to do so.

LDC to notify downstream PAR, relevant LDMG and the Dam Safety Regulator that the dam is likely to fail.

Dam Owner to continue monitoring rainfall in the catchment.

Dam Inspections and recording of water level at regular intervals if rainfall continues over several days.

Remove baffle board if rainfall exceeds 1%AEP for more than 3 days.


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Emergency level



STAND-DOWN

Flood levels receding with lake levels dropping back towards FSL and dam releases are unlikely to impact on PAR and downstream infrastructure.

Notify Dam Safety Regulator of ‘Stand Down’

Post event inspection of the wall as part of standard Dam Safety Condition requirements


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9.2.5 Terrorist or High Energy Impact

Any identified sabotage or vandalism should be treated seriously in line with the Logan City Local Disaster Management Plan and the following actions are recommended:

• Immediately report the incident to Queensland Police Service by calling 000. • Report the incident to National Security Hotline by calling 1800 123 400. • Take photographs of the damage or incident site • If possible and safe to do so, record and photograph unusual vehicle details including

registration, description, time, date etc. • Barricaded the area to enable the incident site to be inspected and investigated • Conduct a dam safety inspection.

10 Emergency Event Report In accordance with the Act and the Dam Standard Operating Procedures, the dam owner will prepare an emergency event report (EER) and submit it to the chief executive within 30 business days (or another period agreed in writing with the chief executive) at the conclusion of an emergency event which has resulted in the activation of the EAP, where:

a) a person or property has been or may have been harmed because of the event; and b) any of the following applies –

(i) a coordinated response involving two or more relevant entities; (ii) an event arose because of disaster situation declared under the DM Act; (iii) an entity performing functions under the State Disaster Management Plan, required the dam

owner to provide information about the event, An emergency event ends when the dam hazard, that triggered the event, no longer presents a material risk to persons or property.

The EER is to provide a timeline of events, including monitoring and inspection data (rainfall, storage level, seepage and etc.), which were used to make EAP activation decisions. The EER should also outline responsibilities associated with emergency communications between the dam owner, governments (local and state), disaster management groups (local and district) and the PAR and the wider community (if relevant). The EER should include photographs of the event.


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11 Maps 11.1 Dam Locality Map


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11.2 Area Map


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11.3 Catchment Map


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11.4 Dam Failure Inundation Maps

11.4.1 Sunny Day Failure (SDF) compared to Natural Flooding

11.4.2 0.2%AEP Flooding with and without failure event

11.4.3 PMF Flooding with and without failure event

Section 11.5 has been redacted


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12 Other relevant drawings 12.1 Vulnerable Area Assessment

Figure 3. High resolution impact assessment


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12.2 Spillway at eastern end of embankment (Douglas Partners, 2015)

Figure 4. Spillway at eastern end of embankment (Douglas Partners, 2015)


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12.3 Stability Analysis Results (Douglas Partners, 2015)

Figure 5. Stability Analysis Results (Douglas Partners, 2015)


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12.4 Discharge

Figure 6.Stage Discharge curves


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12.5 Intensity Frequency Duration for rare rainfall events (BoM 2016)

Figure 7. Intensity Frequency Duration for rare rainfall events (BoM, 2016)


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12.6 Inspection Guide


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Appendix A – Risk Assessment and Warnings Development 1. Community Profile The Failure Impact Assessment found that the highest number of persons at risk occurred in the PMFDF event. While the probability of a PMF event is far more rare and unlikely, the other failure scenario’s and the impact area of a failure event under PMF conditions has been used as a worst-case planning scenario for the development of the Lake Dennis EAP.

The population at risk has been profiled to identify specific vulnerable communities in the failure impact zone. The following factors were considered in the community profile:

• Land Use; • Building Structure type; • Ability to evacuate; and • Flood severity (hazard).

2. Land Use The community profile of the failure impact zone is predominantly low-density residential areas (30 properties) with two (2) environmental management and conservation properties, and one (1) recreation and open space property identified.

Within the PAR, downstream affected properties are entirely (16 parcels) low-density residential type properties.

Figure 8. Land Uses within the Failure Impact Zone

The building type on these residential properties is important to consider when determining the potential impact of dam failure events and ensuring that fit-for-purpose, consistent and accurate messages can be delivered.

2.1 Building Structure Type The nature of the buildings, those located within the failure impact zone, have been identified in line with the Guidelines.

The population at risk is represented by detached housing, which is standalone residential properties. Based on a severity rating established in the Reclamation Consequence Estimating Methodology, 10 the consequence associated with dam failure can be ascertained. The risk of

10 Reclamation Consequence Estimating Methodology (USBR, 2015).

0 10 20 30

Low Density Residential

Environmental Managementand Conservation

Recreation and Open Space

Failure Impact Zone - Land Use

0 10 20 30

Low Density Residential

Environmental Managementand Conservation

Recreation and Open Space

Population at Risk - Land Use


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structural damage has been considered as part of the Hazard Identification and Risk Assessment [‘HIRA’] and determining the appropriate warning approach and priority for warning for each failure scenario.

Figure 9. Building Nature

2.2 Flood Severity The flood severity categorisation for the PAR has been adopted from the Failure Impact Assessment and is summarised in Table 11 below. Flood severity definitions are as follows:

Table 11. Flood severity categories

Criteria Impact

(L-) Minor D<0.3m No significant damage

(L) Low 0.3<D<3 or DV<4.6m2/s No buildings washed off their foundation with depths generally less than 3m

(M) Medium D>3m and DV>4.6m2/s Homes are destroyed but trees or mangled houses remain for people to seek refuge in or on with depths generally greater than 3m.

(H) High DV>15m2/s and max rate of rise is 36m/hr or greater

Flood Sweeps the area clean and nothing remains. This generally associated with a dam that fails instantaneously.

Figure 10. Flood Severity for Failure Impact Zone and Population at Risk

0 10 20 30 40

Detached Housing

Semi-Detached, Row or…

Shops, Shopping Centres

Failure Impact Zone - Building Nature

0 5 10 15 20

Minor

Low

Medium

High

Failure Impact Zone - Flood Severity

0 5 10 15 20

Minor

Low

Medium

High

Population at Risk - Flood Severity

0 10 20 30 40

Standard Property

Strata Unit

Reserve

Population at Risk - Building Nature


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Table 12. Flood Severity for PAR

Property Key Primary Address Property Owner

Flood Severity

SDF DCF PMF

L

L

L

L

L- M L

L

L

L

L

L

L

L

L

L

L

L

2.3 Ability to Evacuate The failure impact zone includes one (1) property in the Elements Retirement Village on Dennis Road. Due to the higher vulnerability of elder persons, further assessment of the nature of flooding of the site has been undertaken. The Project 10 - Appropriate Safety Criteria for People 11 provides the criteria for flood risk for vulnerable sectors of the community.

Figure 11. Safety Criteria for People (Engineers Australia, 2010)

11 Project 10 - Appropriate Safety Criteria for People (Engineers Australia, 2010).


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Table 13. Peak Dam Failure Flood Characteristics at Elements Retirement Village.

Flood Characteristic SDF DCF PMDF

Peak Depth (D) Not Affected Not Affected 0.04m

Peak Velocity (V) Not Affected Not Affected 0.1m/s

Peak Hazard (DV) Not Affected Not Affected 0.004m2/s

Risk Not Affected Not Affected Safe

Based on the above information, the Elements Retirement Village does not require specific evacuation planning. The Failure Impact Assessment does not predict any above-floor impacts; however, Dennis Road is anticipated to be isolated for up to four (4) hours in PMDF. Section 9.2 provides evacuation plan in the form of an Area Map.

Evacuation planning for the downstream community is based on flood immune or low flood hazard as is outline section 9.2.

2.4 Hazard Identification and Risk Assessment Utilising the community profile and PAR information, a robust and replicable HIRA was undertaken in line with the methodology adopted in the Local Disaster Management Plan, Annexure D. 12

The risk-based assessment of warning and communication methods is consistent with Council’s adopted corporate risk management framework which is aligned to risk management standards and including AS/NZS 4360, ISO31000 and guidelines such as Emergency Risk Management: Applications Guide. 13

Council’s all hazards risk assessment considers atmospheric hazards which lead to flood events. The accepted risk assessment provides effective planning for rare flood and severe weather events that may be experienced or exceeded once in 100 years. As outlined in Table 13 below, based on Council’s adopted methodology, the dam failure scenarios have a probability with ‘extremely rare’ frequency or rarer. Table 14. Frequency Risk Assessment (Logan City Council, 2016)

The Lake Dennis failure HIRA follows the risk assessment criteria for consequence adopted in the LDMP. The consequence assessment is shown in Table 16 on the following page. Table 15. Definitions of Consequence (Logan City Council, 2016)

12 Local Disaster Management Plan, Annexure D (Logan City Council, 2016). 13 Emergency Risk Management: Applications Guide (Australian Institute for Disaster Management, 2012).


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The severity analysis in the Failure Impact Assessment can be related to the HIRA definitions of consequence based on the impact to people, property and the environment. Table 15 below, provides the relationship between the Failure Impact Assessment and the LDMP definitions for the purposes of determining the risk classification.

Table 16. HIRA Consequence Definitions

Lake Dennis Failure Impact Assessment Severity Classification

Adopted Hazard Identification and Risk Assessment Consequence Definitions

Minor Insignificant

Minor

Low Moderate

Moderate Major

Major Catastrophic

Council’s adopted risk matrix has been used to ensure a robust, replicable risk assessment is undertaken to inform disaster planning and selection of appropriate warning and communication methods. The key attributes assessed and considered include likelihood, consequence of flooding


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and available warning time for population at risk. The adopted definitions have been applied to the dam failure scenarios, with the results summarised in Table 18.

Table 17 Risk Matrix

Likelihood Consequence

Insignificant Minor Moderate Major Catastrophic

Frequent Low+ Medium+ High Very High Extreme

Occasional Low- Medium- Medium+ High Very High

Rare Negligible Low+ Medium- Medium+ High

Very Rare Negligible Low- Low+ Medium- Medium+

Extremely Rare Negligible Negligible Negligible Low- Low+

Table 18. Summary of HIRA

Failure Scenario Likelihood Consequence Risk Assessment

Sunny Day Failure Very Rare Minor Low-

Dam Crest Failure Extremely Rare Major Low-

Probable Maximum Flood Dam Failure Extremely Rare Moderate Negligible

Based on the hazard identification and risk assessment each property has been assigned a priority for warning and communication to be implemented by the EAP in the case of a potential failure event.

2.5 Flood Warning Options and Notification Requirements Selection of appropriate warning and communication methods was based on the priority for notification identified through the HIRA. An effective warning system utilises multiple modes of communication, depending on the location to the dam and the PAR that may need to be notified, it may be appropriate that the warning is issued via a personalised phone call or personal visit. Please refer to Figure 12 below.

Component 5 of the EMAF outlines the key outcomes for Public Engagement. The EAP deals specifically with the response phase of a potential emergency failure event at Lake Dennis; however, preparedness measures have been identified as part of Council’s community awareness program will also be implemented to help to minimise the risk of impact to people and property and to contribute towards increasing the resilience of the community.

An assessment of the available warning time for Dam Crest Failure and the failure scenarios affecting the population at risk, to determine the nature of Warning and Communication Systems considered fit-for-purpose in the case of a potential failure scenario. The EMAF requires warnings to be:

• Specific; • Accurate; • Reliable; and • Timely.


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Figure 12. Available General and Specific Warning Modes, Manual 21 – Flood Warning Australian Emergency Manuals Series (National Institute for Disaster Resilience, 2009)

With regards to timeliness, the Australian Disaster Resilience Handbook Collection – Manual 21 – Flood Warnings, 14 indicates that there is no convention in Australia for acceptable warning time; however, the guidelines provided in Manual 23 – Emergency Management Planning for Floods Affected by Dams 15 suggest:

‘warning time for evacuation needs to be considered in time blocks of not less than one hour to ensure that action plans can be realistically implemented’

The Failure Impact Assessment noted that Reclamation Consequence Estimating Methodology provided guidelines on warning times for dam failure planning, such that:

• No Warning Time: Less than 15 minutes.

• Some Warning Time: 15 minutes to one (1) hour.

• Adequate Warning Time: Greater than one (1) hour.

For disaster planning purposes, the available warning time and level of impact is presented in the following figures. Only one property has been identified at risk in a DCF scenario (see Figure 13 below), while the PMFDF (Figure 14) clearly shows distinct communities with similar warning times.

14 Australian Disaster Resilience Handbook Collection – Manual 21 – Flood Warnings (Australian Institute for Disaster Resilience, 2009). 15 Australian Disaster Resilience Handbook Collection – Manual 23 – Emergency Management Planning for Floods Affected by Dams (Australian Institute for Disaster Resilience, 2009).


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Figure 13. DCF Available Warning Time

Figure 14. PMFDF Available Warning Time Analysis of the PAR for the PMFDF scenario gives the following warning times for the downstream failure impact zone.


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Table 19. Summary of Available Warning Time for PMFDF scenario

Warning Time Number of Properties

Specific Areas

No Warning Time Less than 15 mins 3

Some Warning Time

15 mins – 60 mins 7

Adequate Warning Time

More than 60mins 6

The comprehensive two-dimensional hydraulic modelling completed as part of the Failure Impact Assessment included a local catchment inflow in the catchment immediately above the properties at

The small warning time is due to the PMF runoff from the local catchment rather than a dam failure flood wave impacting the properties. The PMFDF impacts to these properties occur more than one (1) hour after a potential dam failure and adequate warning is available for emergency warning and communications to be issued.

The Flood Warning Manual 16 provides guidance on the most appropriate warning modes for quick, specific dissemination of warnings, being telephone and computer. Given the highest risk areas identified in the HIRA are located within and have some warning time but less than sufficient time to realistically implement a warning message, Council’s disaster management planning will consider public engagement prior to the threat of an event occurring. The downstream communities in and are appropriate communities to benefit from a specific, timely and accurate telephone and email message.

2.5.1 Emergency Alert The Queensland Fire and Emergency Service provides the Emergency Alert service which allows phone messages and text messages to be distributed based on a specific area of impact. Council has registered an Emergency Alert Campaign for the downstream population at risk that may be used for dam failure scenarios.

An EA Campaign has been developed for Dam Crest Failure and PMFDF events, including:

• Watch and Act; and

• Emergency Warning.

Activation of an Emergency Alert will be at the discretion of the Local Disaster Coordinator as a member of the Local Disaster Management Group. An example of the Emergency Alert text is as follows:

Watch and Act

Voice Message

"This is a Watch and Act message from Logan City Council. Issue detected at Lake Dennis Dam which may lead to a dam failure emergency. Be on stand by and prepare to evacuate in the event of dam failure. You should warn neighbours. For more information listen to local radio or visit http://www.disaster.logan.qld.gov.au"

16 Flood Warning Manual (Australian Institute for Disaster Resilience, 2009).

http://www.disaster.logan.qld.gov.au/


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Text Message

“Watch and Act Message. Potential Lake Dennis Dam failure. Prepare to evacuate. Warn neighbours. Listen to local radio or visit www.disaster.logan.qld.gov.au"

Emergency Warning

Voice Message

“Emergency Emergency. This is a dam failure warning from Logan City Council. Lake Dennis Dam is at imminent risk of failure. Evacuate to higher ground. You should warn neighbours. For more information listen to local radio or visit www.disaster.logan.qld.gov.au”

Text Message

“Emergency. Lake Dennis Dam imminent failure. Evacuate to higher ground. Warn neighbours. Listen to local radio or visit www.disaster.logan.qld.gov.au”

The Emergency Alert system utilises the Emergency Alert polygon specifically developed for this purpose. It is targeted at the community downstream of Lake Dennis. The Emergency Alert polygon is shown in Figure 15. Limitations in the number of polygon vertices allowed by QFES under the Emergency Alert Guidelines mean any properties in the vicinity of the failure impact zone identified in the Failure Impact Assessment will receive specific warning message, with adequate time to evacuate or take refuge. This EAP has also undertaken evacuation route planning, that can be utilised by disaster managers as appropriate.


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Figure 15. Emergency Alert campaign polygon and threat direction

Documents

Lake Dennis Dam Emergency Action Plandata.dnrm.qld.gov.au/eap/lake-dennis-eap.pdf · Doc# 8191949-v8- Logan City Local Disaster Management Plan - September 2016 i . LOGAN CITY . LAKE