During the last three months we've been talking to the community about the Emerald Flood Protection Scheme and have received a number of questions.

What is the Emerald Flood Protection Scheme?

The Emerald Flood Protection Scheme (EFPS) was one of three potential structural flood mitigation options  pursued and included in an action plan in February 2014 and consists of six separate levee alignments to minimise flood impacts on Emerald.

The proposed scheme was developed during the completion of the Flood Management Study and was provided at the commencement of the Feasibility Study.

What is a Feasibility Study?

A feasibility study is commonly carried out for major infrastructure projects and is an engineering study based on field investigations and analysis. It identifies the technical, operational and financial feasibility of a project to determine whether or not a project should be advanced.

The Emerald Flood Protection Scheme Feasibilty Study is in accordance with the design development process outlined in the International Levee Handbook.

It is important to note that this feasibility study does not arrive at a final levee design suitable for construction as further design phases are still required if the project proceeds.

Who did the Emerald Flood Protection Scheme Feasibility Study?

AECOM Australia Pty Ltd a global engineering consultancy with offices in Cairns, Townsville, Mackay, Rockhampton, Sunshine Coast and Brisbane. 

More than 50 technical specialists in a range of discipline areas such as geotechnical, drainage, civil, environmental, visual amenity and structural engineering were involved in the study.

When was the feasibility study report received by council?

The report was received by council in December 2014 and was reviewed at its first meeting in January 2015.

The report discusses the field investigations and technical analysis carried out during the study with respect to the Emerald Flood Protection Scheme. It includes conclusions on the technical feasibility of the scheme and provides recommendations.

The report was not released until 18 March 2015 so as council could engage with landholders that landholders and key stakeholders that would be potentially affected by the report’s recommendations.

What process has the council followed?

2009-10 -  Flood Data Audit completed that  included hydrological and other spatial data, and flood studies available from multiple sources (government agencies, mining sector and private sector) to prepare a Floodplain Management Plan.

2011 - Flood data from largest flood in recent history was captured across a number of towns and catchments in the region.

2012 – July 2014 -  Floodplain Management Study completed that included flood modelling, flood mitigation investigations and further studies.

February 2014 -  Community engagement was conducted to obtain a vote on the  preferred option from  four  shortlisted options.  Option C, or levee scenario 15, was chosen by the community.

February 2014 - Council resolved to pursue three flood mitigation strategies:

  1. River improvement works in the Nogoa River
  2. Investigate upstream dam options
  3. Investigate feasibility of building levees – the EFPS

July 2014 - AECOM was appointed to undertake the Emerald Flood Protection Scheme Feasibility Study.

July 2014 - Funding was secured to carry out river improvment works.

During 2014 - Upsteam dam options were investigated in partnership with Sunwater, Department of Natural Resources and Mines, Department of Energy and Water Supply.

December 2014 - Council received the  Emerald Flood Protection Scheme Feasibility Study.

June 2015 - Council agreed to commence a staged procurement process to enable a decision to be made.

December 2015 - Council agreed to forego a fully engineered design for a concept plan, cost analysis, business case and risk analysis to enable a decision to be made around July 2016.

How many flood mitigation options have been assessed?

More than 40 different scenarios for flood mitigation have been assessed.

What is the ongoing timeframe of the project?

A prelimary concept plan, cost analysis, business case and risk analysis package is expected to be completed by July 2016. The council can use this information to make a decision as to whether the project is to proceed or not. If it is to proceed, discussions with all levels of government for funding options will commence. Completion of the project will depend on the availability of funding.

What consultation has been done with the community?

Tjhere have been numerous briefings with stakeholders and individual meetings with landholders since 2 March 2015. 

Detailed displays  at an Interpretive Space at Centro Shopping Centre (for three weeks), council’s Customer Service Centre, and online have enabled the  community to access key information about the project. 

Feedback forms enabledr the views to be shared about the outcomes of the study and  about  flood levees as a flood mitigation option for Emerald.

Workshops with key stakeholders such as state government representatives, Insurance Council of Australia and the banking sector were held. 

Presentations were also made with the Emerald Cotton Growers and Irrigators Association and Rotary Club members.

Briefings and workshops were held with Councillors to review the report recommendations, to be kept informed on the progress of the consultation activities and to meet directly with affected landholders towards the end of the engagement period.  Councillors also held workshops to progress other related work to do with advocacy for better insurance premiums, legal advice on land acquisitions options and scenario planning on options for the project.

What is a Flood Plain Management Plan?

A Floodplain Management Plan outlines a flood risk management process that provides information to support informed decision for land-use planning, emergency management and flood risk management for the region and its contributing catchments.

The primary objectives of the Floodplain Management Plan are to develop a detailed understanding of flooding in the region; reduce the adverse impacts of flooding by defining a holistic approach to floodplain management; develop an ongoing strategy that defines a number of management and mitigation actions; demonstrate likely costs of the management and mitigation actions; and put forward a sequence of actions and responsibilities.

Has council undertaken a Floodplain Management Plan?

Yes. In 2012, council engaged KBR to undertake a Floodplain Management Study & Plan to specifically to inform and update planning schemes, emergency management, evacuation planning and structural mitigation works.

Why does Emerald need flood levees?

A system of levees was identified as a potential structural flood mitigation option for Emerald during the Floodplain Management Study. This recommendation was based on detailed hydrologic / hydraulic modelling carried out by KBR, which was independently reviewed by GHD.

The feasibility study focussed on the further optimisation and subsequent assessment of the technical feasibility of a series of proposed levees along the eastern and western sides of the Nogoa River and to the north and south of the Vince Lester Bridge. 

What is the status of the other two options for Emerald?

Council has undertaken further investigation on options relating to the Fairbairn Dam.

Upstream dams and river diversions do provide flood mitigation benefits, but are estimated to cost in excess of $500 million and are unlikely to be economically viable. 

These are state government assets and have been forwarded for its consideration.

Council is implementing an excavation and vegetation management strategy for the Nogoa River at Emerald. It has state government approvals and works are continuing until late 2015. Selective thinning of immature trees at ten sites within the river has been completed.

Cultural heritage management agreements have been finalised with the two native title claimants. A controlled vegetation burn in the river adjacent to the golf club was held for final inspections and clearance. Some cultural heritage artefacts have been removed to a temporary keeping place. An amended environment management plan has been lodged for the clearing and excavation works for final approval by the state government. Engineering plans are completed and tenders are expected to be advertised in December 2015. River clearing works will be completed by June 2016.

River management approaches to flood mitigation, including enlarging bridge openings, undertaking environmental clearings and excavation works to enlarge the channel, all provide good local benefits, but are insufficient to reduce the overall flood risk to Emerald.

What are levees?

Levees are raised structures predominately made of earth. Their primary objective is to provide protection against flood events along the coast, rivers and artificial waterways. Earth levees generally form part of a flood defence system that may also include vertical flood walls, retaining structures, gate closure structures, pumps and interior drainage systems.

Do other places use levees?

Yes. Flood levees are a vital part of modern flood risk management. Most countries have existing levee systems. It is estimated that there are several hundreds of thousands of kilometres of levees in Europe and United States.

A number of towns and cities in Australia use flood levee systems, including Mackay, Roma, St George and Charleville.

Who will benefit from the levees?

Everyone! And it will provide an increase in reputation and business confidence for the region.

How long are the levees planned for Emerald?

Levee Length
Selma West 5239.96 m
Golf Course  4800 m
Moffat Road 3000 m
Lakeside 608.65 m
Rifle Range 2100 m
Codenwarra Road 2401.82 m

The accumulated length of the levee is approximately 18.15 km.

Where are the levees proposed to be located?

Selma West Levee begins in agricultural land west of the main township of Emerald and extends to the north-east along the Nogoa River to its termination point at the Capricorn Highway where the flood levee section joins with the Golf Course levee section.

Golf Course Levee continues on from the Selma West levee adjacent to the Capricorn Highway and extends north along the Nogoa River to its termination point at Moffat Road where the levee joins with the Moffat Road Levee.

Moffat Road Levee continues on from the Golf Course Levee and traverses in an east-west direction and parallel to Moffat Road, located north of the Emerald township.

Lakeside Levee is located in the southern part of Emerald, adjacent to the newly constructed water treatment plant.

Rifle Range Levee is located east of the Nogoa River as it passes through the main part of the Emerald Township and north of the Lakeside Levee.

Codenwarra Road Levee skirts the northern boundary of Emerald.

What are key focus areas?

Four key focus areas require more detailed investigation and consideration of different alignments and levee types. They are: Selma West, Slack Drive, Opal Street and Whitchurch Road.

To help council decide on the final alignment conceptual design and analysis has been carried out to compare the feasibility of several options in these areas. 

What are the different types of levees proposed?

This document has images of the different types of levees.

Earthen Embankment Levee

Where there is space, an earthen levee embankment provides protection against floodwaters. They are typically the most economical and incorporate an access track along the crest and landside drainage channels.

Road Levee

The Moffat Road Levee and Codenwarra Road Levees involve raising the existing road to provide flood protection and are similar to an earthen embankment levee, but have a wider crest for two-way traffic and flatter batters for safety.

Crib Wall Levee

A partial embankment section where existing space constrains the use of a full earth embankment levee. An earthen embankment extends to the waterside, while a concrete crib wall is located on the landside to reduce the overall levee footprint.

Concrete Flood Wall

Used where space is a premium, concrete flood walls are limited wherever possible due to visual amenity issues, cost, constructability and long-term maintenance difficulties.

Buttress Flood Wall Levee

A concrete flood wall with a buttress or structure built against a wall to strengthen or support it. These are extensive engineered structures that are used where typical concrete flood walls can’t be used due to ground conditions or the height of the structure.

Floodgates

Used where access is required through the levee structure, like road and rail crossings and where it is necessary to maintain access to community infrastructure (such as the botanical gardens and golf course) and properties outside the leveed area.

Temporary Flood Barriers

For use across the Capricorn Highway and the Central West Rail Line. 

Why can't we use temporary flood barriers?

A complete system of temporary demountable flood barriers is not feasible for because they: have limited resistance to flood borne debris; require permanent and secure foundations or prepared subgrade; have limited flood protection height; have issues with under-seepage and potential failure if ground surface not adequately prepared; require extensive storage, transport and erecting components; have a shorter asset life in comparison to permanent levee; require training of staff to implement systems safety and effectively; require time to erect with limited warning times, as is the case for Emerald; have security issues, including tampering and vandalism.

What would the levees look like?

Levees will be incorporated into the existing environment to minimise impacts on the visual amenity and character of Emerald’s landscape.

Levees are used throughout the world for other community benefits, such as walkways and recreational activities. 

What building code applies to levees?

The QLD Levee Regulations, which have a number of key criteria for the design and construction of large levee structures and outlines requirements after construction, including annual inspections and comprehensive reviews every twenty years. 

What would cause a levee to fail?

Hydraulic failure occurs when the area protected by the levee experiences water ingress, at a level lower than the planned protection level and can happen from an error in design and/or construction; environmental changes, such as river bed level changes or settlement of the levee; operational failure, such as a flood gate being left open; poor maintenance of critical levee infrastructure, such as flood gates and pumps; a structural failure.

Structural failure occurs when the levee is breached as a result of damage or defect and can happen from an error in design and/or construction; deterioration or damage caused by erosion or instability; poor maintenance; hydraulic failure.

What happens when a levee fails?

Breach analysis scenarios are analysed and incorporated in an emergency response plan and the local disaster management plan.

What happens if the flood level is larger than the levee?

Levees are designed to protect up to a certain flood height as it is not commonly economically feasible to protect against the probable maximum flood. If a flood event exceeds the design height of a levee, overtopping will result. 

Having levees gives more time to put into place emergency response plans and preserves Emerald’s western evacuation routes for longer. 

Are the size and height of the levees different?

The levee crest level (height) and footprint (width) vary along the system and are dependent on the levee design flood immunity level and the existing height of the topography along the levee alignment.

What enviroment and cultural considerations are there?

A range of environmental and planning approvals will be required and it has also been recommended that the Bidjara People #7 and the Western Kangoulu People, be consulted if the project proceeds.

Will there be more site investigations?

Yes. Two additional stages of geotechnical testing and a field survey will be required to finalise the design of the levee structures.  

Will property acquisition be required?

Property acquisition will be required and council has undertaken consultation with property owners that may be affected.  

What is the acquisition process?

The Emerald Flood Protection Scheme Acquisition Policy was adopted on 27 August 2015. The CEO, Scott Mason, and Councillor Gail Nixon have completed the majority of ‘one-on-one’ discussions with landholders likely to be directly affected by the levee project. All have been given the opportunity to obtain a property valuation now, although no decisions regarding acquisition will be made until the staged procurement process is complete and the environmental and financial considerations have been thoroughly assessed and a decision has been made to construct the levees.

How was the flood model developed?

By compiling a range of data in a computer-based model that simulates flood behaviour using numerical techniques. Outputs from these models give maps that show areas predicted to be inundated for various flood magnitudes.

Model input data includes: topographic data showing land contours, hills and waterway locations; hydrological assessment of the amount of rainfall expected in particular events; land use information; historical flood heights, stream gauge data and rainfall records; and hydraulic structures, such as bridges, culverts and weirs.

This information is entered into the modelling software, which is calibrated to record flood and mapping developed for various design flood events.

The surveyed flood heights from the 2008 and 2010/11 flood event were used to calibrate the Emerald flood model. The flood model was developed in 2012/13 by engineering consultants Kellogg Brown and Root Pty Ltd (KBR).

What flood height gauges have been used in the modelling?

A flood data audit was done during 2009 – 2010 to compile and audit hydrological and other spatial data and flood studies to prepare a Floodplain Management Plan for the region.

Data came from state government, catchment authorities, utility companies, mining companies and other private sector groups; and included earlier flood studies completed by the former Emerald, Peak Downs, Bauhinia and Duaringa Shires.

Historical data from numerous rainfall and river gauges throughout the region was compiled with recorded data during the 2008 and 2010/11 events.

How do I know the model is correct?

Engineering consultants GHD undertook an independent technical peer review of the regional flood studies and flood mitigation options and found the model to be acceptable.

What is a 1% Annual Exceedence Probability (AEP) event?

It’s the likelihood of a flood of given size or larger occurring in any one year and is expressed as a percentage. 

For example, a 1% AEP event means that there is a 1% chance that a flood event of this magnitude or larger will occur in any one year.

What is a defined flood event (DFE)?

The flood event magnitude/size selected for the management of flood hazard as determined in floodplain management studies and incorporated into floodplain management plans and development assessment codes.

What is the DFE adopted by CHRC?

The DFE is a 1% AEP, or a 1 in 100 year average recurrence interval, event in the year 2100assuming climate change induced changes to rainfall intensities have occurred. In other words, it has a 1% chance of occurring in the year 2100.

In 2015, the same flood magnitude is estimated to be a 0.5% AEP event, or a 1 in 200 year average recurrence interval. In other words, it has a 0.5% chance of occurring now on the basis that climate induced changes to rainfall intensity has not occurred. 

To provide a comparison, the 2010/11 flood event was approximately a 1% AEP event . However, as climate change progresses, the same flood magnitude is forecast to become a 1.7% AEP event, or 1 in 60 year interval, in the year 2100.

What level of flood protection is provided by the EFPS?

The levee footprint (width) and crest level (height) of the levee has been designed for three separate flood immunity levels.: the 2010/11 equivalent flood event levels; the Design Flood Event (DFE); the DFE minus 0.5 m.

The purpose of designing and comparing three different options is so that costs and economic benefits of each can be considered prior to confirming the level of flood protection offered by the EFPS.

What impact will the levee have on local flooding?

Approximately 27 local catchments have been mapped, their catchment areas determined, and preliminary analysis undertaken.

How the local drainage system is managed will depend on the final configuration of any levee system. Final design and analysis will be undertaken when the final levee alignment is chosen. The cost estimates for the EFPS include provisions for local drainage.

Will there be external flood impacts due to the EFPS?

Changes in water levels will occur upstream and downstream of the levees and is dependent on the flood magnitude and location within the floodplain.

How do I find out information about my property? 

Make an appointment to speak with a council representative who will show you the modelling electronically or via maps. 

How much will the levees cost?

The cost will depend on the level of flood protection adopted (flood size and hence final levee height), and the residual risk chosen.

Design Immunity Level Estimated Cost
  Original Alignment Alternative Alignment
2010/2011 $121.5M $105.7M
DFE minus 0.5 m $137.1M $121.2M
DFE $151.2M $134.4M

 

What do the cost estimates include?

  • Provision of a levee system to provide flood protection around Emerald.
  • Associated works, including the relocation of existing services where required.
  • Provision of temporary barriers to road crossings.
  • Three options of levee heights, with two alternatives for levee alignment within each option.
  • Cost of land resumptions required, including demolition costs to clear resumed land.
  • Inclusion of allowances for consultant fees and statutory authority fees.

 

What don't the cost estimates include?

  • Excavation in and removal of contaminated materials.
  • Excavation in rock and/or hard ground.
  • Provision of fill material from a commercial source not exceeding a 10 km distance from site.
  • Finance costs.
  • Funding application costs.
  • Escalation beyond the First Quarter 2015.
  • Goods & Services Tax (GST).

 

How much will it cost to maintain the levees?

Estimated to be $100,000 - $200,000 per annum.

What is a hybrid-style cost estimate?

Cost estimation has been carried out using Cost-X, an industry standard estimating software. The cost for the majority of the items has been estimated using First Principle Estimating Methods. Where the scope and detail in not clearly defined, unit rates have been adopted and benchmarked against historical cost data from similar works. 

How much did the 2008 and 2010/11 floods cost the council?

Total tangible flood damage costs  for Emerald were estimated to be $64,170,000 and $251,180,000 for the 2008 and 2010/11 flood events respectively.

Who will pay for the levees?

This is not a question we can adequately answer right now. 

The council is seeking considerable contribution from state and federal governments and will investigate if other private sector organisations with an interest in the region would be prepared to invest. 

The contribution and funding model is a task that will be explored during the next design stage.

Will the levees mean a rate increase?

Because the timeframes are currently unknown and the council is yet to decide on the final levee alignment, the how the project will be funded cannot be confirmed.

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