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TRANSCRIPT
Response to Additional Questions from the Environment and Natural Resources Committee, Inquiry into Flood Mitigation Infrastructure in Victoria
20 June 2012
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Table of Contents
BACKGROUND ........................................................................................................................................... 6 Q22 WHAT WAS THE SEQUENCE OF EVENTS THAT LED TO FLOODING IN 2010‐2011? HOW MUCH RAINFALL FELL, AND WHERE DID IT FALL? WHAT TOWNS WERE AFFECTED, HOW WERE THEY AFFECTED, AND WHAT IS THE ESTIMATED COST
OF THE DAMAGE?....................................................................................................................................... 7 Q1 WHAT IS THE CURRENT STATUS OF THE VICTORIAN FLOOD MANAGEMENT STRATEGY?........................... 11 Q20 HOW DOES DSE DEFINE FLOOD MITIGATION INFRASTRUCTURE? ......................................................... 12 Q3 GIVEN YOUR EXPERIENCE OF THE RECENT FLOODS AND THEIR IMPACTS, WHAT DO YOU THINK ARE THE BIGGEST
AREAS OF IMPROVEMENT REQUIRED IN FLOOD MITIGATION AND MONITORING IN VICTORIA?................................ 13 Q2 IN YOUR BRIEFING YOU MADE REFERENCE TO ‘BEST PRACTICE’ FLOOD MITIGATION. WHAT DOES DSE CONSIDER TO BE ‘BEST PRACTICE’ IN FLOOD MITIGATION AND MONITORING? ..................................................... 17 Q6 ON AVERAGE, HOW MUCH MONEY HAS BEEN SPENT ON FLOOD MITIGATION EACH YEAR OVER THE PAST
DECADE, AND WHAT ARE THE KEY AREAS WHERE EXPENDITURE OCCURS? AND HOW HAS FUNDING CHANGED, IF AT ALL, OVER THE PAST DECADE? ........................................................................................................................... 19 Q4 WHICH CMAS AND LOCAL GOVERNMENTS HAVE BEST ADDRESSED FLOOD MITIGATION AND WHAT HAS GIVEN
THEM THE LEADING EDGE?......................................................................................................................... 20 Q5 ARE COUNCILS REQUIRED TO TAKE THE ADVICE OF CMA’S REGARDING PLANNING MATTERS, INCLUDING DEVELOPMENT OF FLOODPLAINS, OR IS THIS DISCRETIONARY?.......................................................................... 20 Q8 WHAT ARE THE KEY STRENGTHS AND WEAKNESSES OF CURRENT FLOODPLAIN MANAGEMENT AND PLANNING
IN VICTORIA? ARE CMA’S AND COUNCILS ADEQUATELY RESOURCED AND SKILLED TO UNDERTAKE THIS PLANNING? . 22 Q23 YOU STATED IN YOUR BRIEFING THAT ‘IN RELATION TO THE PLANNING SYSTEM, WE ALREADY REALISE THAT
THERE ARE A LOT OF OPPORTUNITIES TO DO A LOT OF THINGS PERHAPS BETTER THAN WE ARE DOING THEM NOW’. WHAT ARE THE IMPROVEMENTS THAT COULD BE MADE REGARDING PLANNING?................................................. 23 Q7 WHAT IS THE ESTIMATED ANNUAL AVERAGE DAMAGE IN VICTORIA OVER THE PAST TEN YEARS? .............. 24 Q9 IN A 1995 REVIEW OF FLOODPLAIN MANAGEMENT IN RURAL AND PROVINCIAL URBAN VICTORIA (WATER
STUDIES PTY LTD), A NUMBER OF KEY FLOODPLAIN MANAGEMENT ACTIVITIES WERE IDENTIFIED. FOR LGA’S WHERE
FLOOD PROBLEMS ARE KNOWN OR EXPECTED TO EXIST, THESE ARE THE: NUMBER OF LGA’S WITH COMPLETED FLOOD
MAPS; NUMBER OF LGA’S WITH MAPS STARTED; NUMBER OF LGA’S WITH FLOOD STUDIES COMPLETED OR
UNDERWAY; NUMBER OF FURTHER FLOOD STUDIES REQUIRED BY LGA; PERCENTAGE OF LGA’S WHERE IDENTIFIED
STRUCTURAL WORKS HAVE BEEN COMPLETED; AND PERCENTAGE OF LGA’S WHERE FLOOD MAPS AND PLANNING
CONTROLS HAVE BEEN INTRODUCED. COULD YOU PLEASE PROVIDE UPDATED FIGURES IN RELATION TO THESE MATTERS? .............................................................................................................................................. 25 Q10 YOU MENTIONED IN YOUR BRIEFING THAT A FURTHER 25 FLOOD STUDIES ARE TO BE UNDERTAKEN ACROSS VICTORIA IN THE NEXT FOUR YEARS. WHERE SPECIFICALLY ARE THESE STUDIES TO BE UNDERTAKEN, AND WHAT MAKES
THEM PRIORITY AREAS?............................................................................................................................. 29 Q11 THE DEPARTMENT OF SUSTAINABILITY AND ENVIRONMENT IS TO UNDERTAKE A LEVEE AUDIT IN NORTHERN VICTORIA. WHAT IS THE SCOPE AND KEY OBJECTIVES OF THE AUDIT? WHEN WILL THE PROJECT BE COMPLETED, AND CAN THE COMMITTEE OBTAIN A COPY OF THE FINDINGS WHEN IT IS COMPLETED? ............................................... 30 Q12 THERE ARE MANY RURAL LEVEES IN VICTORIA WHERE OWNERSHIP AND MAINTENANCE IS CURRENTLY
UNCLEAR. YOU STATED IN YOUR INITIAL BRIEFING TO THE COMMITTEE THAT THE DEPARTMENT OF SUSTAINABILITY AND ENVIRONMENT HAS BEEN LOOKING AT THIS ISSUE FOR A NUMBER OF YEARS. WHAT POLICY OPTIONS HAVE BEEN
CONSIDERED BY DEPARTMENT OF SUSTAINABILITY AND ENVIRONMENT IN ADDRESSING THIS ISSUE, AND WHAT ARE THE
BENEFITS AND DISADVANTAGES OF EACH POLICY OPTION?............................................................................... 31 Q13 IN VICTORIA LEVEES HAVE BEEN BUILT BY COMMUNITIES AS PART OF EMERGENCY RESPONSE. WHO IS
RESPONSIBLE FOR OWNERSHIP AND MAINTENANCE OF THESE LEVIES AFTER THE EMERGENCY? WHAT POLICY OPTIONS
ARE AVAILABLE TO GOVERNMENT IN DEALING WITH UNAUTHORISED LEVEES, AND WHAT ARE THE BENEFITS AND
DISADVANTAGES OF EACH POLICY OPTION?................................................................................................... 36 Q15 IN YOUR BRIEFING TO THE COMMITTEE YOU MENTIONED THAT IN ABOUT 10 OF THE 82 TOWNS AFFECTED BY
FLOOD, THE CAPACITY OF THE CHANNEL THROUGH THE TOWN HAS EXERCISED INTEREST AND COMMENT. MOREOVER,
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SOME EVIDENCE HAS BEEN COLLECTED REGARDING THE CAPACITY OF THE CHANNEL AT CRESWICK AND THE VIEW THAT
‘A LOT OF THESE CHANNELS WERE CHOKED WITH WEEDS AND VEGETATION’. WHAT EVIDENCE CAN BE PROVIDED TO
THE COMMITTEE REGARDING THE CAPACITY OF THE CHANNEL AT CRESWICK AND OTHER TOWNS AFFECTED BY THE
RECENT FLOODS? ..................................................................................................................................... 37 Q14 WHO HAS RESPONSIBILITY FOR THE FLOOD MITIGATION ASPECTS OF WATERWAYS MANAGEMENT IN
VICTORIA? .............................................................................................................................................. 38 Q16 YOU MENTIONED IN YOUR BRIEFING THAT DSE IS PUTTING TOGETHER ‘A FEW REVIEWS’ REGARDING THE REVEGETATION OF WATERWAYS AND THEIR IMPACT ON FLOODING. WHAT IS THE SCOPE AND OBJECTIVE OF THESE
REVIEWS? WHO IS UNDERTAKING THESE REVIEWS, AND WHEN ARE THESE REVIEWS EXPECTED TO BE COMPLETE?..... 40 Q17 TO WHAT DEGREE ARE COMMUNITY VIEWS TAKEN INTO ACCOUNT REGARDING WATERWAYS CLEARING AND
MAINTENANCE? ....................................................................................................................................... 41 Q18 EARLY IN THE BRIEFING TO THE COMMITTEE YOU MENTIONED THAT ‘THEY [FLOODS] ARE PREDICTABLE OVER HUMAN LIFE SPANS TO A MUCH GREATER EXTENT THAT OTHER DISASTERS’, AND ‘WE CAN PREDICT THE FREQUENCY, THE LEVEL AND THE EXTENT OF FLOODING OFTEN TO WITHIN MILLIMETRES’. YET LATER IN THE BRIEFING YOU MENTION THAT
‘IT IS ACTUALLY REALLY HARD TO PREDICT FOR A PARTICULAR TOWN…THE SIZE OF THE FLOOD THAT IS COMING, WHERE
IT IS GOING TO GET TO…WHAT HOUSES ARE GOING TO BE FLOODED TO WHAT DEPTHS’. HOW DIFFICULT IS IT TO
PREDICT WHEN AND WHERE FLOODS WILL OCCUR? WHAT TECHNOLOGY IS CURRENTLY USED TO ASSIST FLOOD
PREDICTION AND WHAT CAN NEW TECHNOLOGY DO TO IMPROVE PREDICTIONS ABOUT FLOODING IN VICTORIA? ...... 42 Q19 WHAT IS THE ROLE, CONDITION, LOCATION AND PERFORMANCE OF VICTORIA’S RIVER GAUGES? .............. 43 Q21 WHAT DOES THE SOUTH EASTERN AUSTRALIAN CLIMATE INITIATIVE SAY ABOUT THE FUTURE LIKELIHOOD AND SIZE OF FLOODING IN VICTORIA? CAN WE PLEASE HAVE A COPY OF THEIR REPORTS THAT ADDRESS FLOODING?......... 44 ATTACHMENT 1: CRESWICK CASE STUDY ‐ THE EFFECT OF CHANNEL CONVEYANCE ON FLOODING IN CRESWICK CREEK 2010 AND 2011 ..................................................................................................................................... 45
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Introduction The information contained in this report is provided in response to additional questions directed at DSE by ENRC. The report provides further contextual information in support of the submission provided to ENRC in February 2012, which outlined policy and management options for the Committee’s consideration. This report reflects information and analysis as at August 2011.
Background Division 4 of the Water Act 1989 enables catchment management authorities and Melbourne Water to:
Determine the extent and height of floodwaters;
Declare flood levels, land liable to flooding, floodway areas, flood fringe areas, and building lines;
Develop and implement plans and take any action necessary to minimise flooding and flood damage, and
Control developments that are proposed or that have occurred. Recognising that prevention is better than cure, Victoria relies strongly on statutory planning and development controls to identify areas affected by flooding and to manage the flood risk. Any person wishing to develop land will usually be required to apply for a planning permit and/or a building permit from the relevant municipal council. If the land is known to have a flood risk this triggers a referral to the floodplain management authority – Melbourne Water or one of the catchment management authorities, who will assess each proposal on merits. In some cases a planning permit application will be refused because of the flood risk. However in most situations conditions are imposed on the planning permit to mitigate the risk. The planning system is strongly reliant on the delineation of the one in one hundred year probability flood extent or a best estimate of this extent1, and also on the corresponding flood levels. However this does not necessarily mean that other floods are not considered. Over many decades Victoria has built up a database of flood information such as flood photography and historic flood levels. In the absence of better information this has been used to delineate land subject to inundation overlays in planning schemes. Funding initiatives for flood investigations and flood data acquisition provide opportunities for continuous improvement. Flood studies and more detailed floodplain management studies (which look at a range of flood mitigation options such as planning controls, flood warning improvements, flood education and structural works to protect areas from flooding) often form the basis for improved planning scheme maps. They will usually require a range of floods to be investigated, not only providing better material to assess the flood risk, but also to better inform emergency management agencies on flood impacts. Planning controls are of limited value in treating the existing flood risk, until a property is redeveloped. Where development has already occurred in areas of flood risk, other measures to mitigate the flood risk must be found. Structural measures such as levees can provide some benefit, but they require consideration of the costs and benefits from an economic, social and environmental perspective.
1 The use of the one in one hundred flood in planning scheme controls is considered to be a reasonable standard for flood risk for planning purposes, regardless of the potential consequences of the flood. Larger floods do and will occur, and emergency management planning must take this into account.
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Other, less intrusive (and probably less effective) measures, such as improved flood awareness and education to empower people to minimise flood damages are often viewed by the community as preferable.
Q22 What was the sequence of events that led to flooding in 2010‐2011? How much rainfall fell, and where did it fall? What towns were affected, how were they affected, and what is the estimated cost of the damage? The sequence of events that led to flooding in 2010‐2011 According to the Bureau of Meteorology, the heavy rainfall events of late 2010 and early 2011 were driven by record warm sea surface temperatures to the north of Australia and one of the strongest La Niña events ever observed in the Pacific Ocean. On a number of occasions during this period, a developing low‐pressure system combined with a moist tropical air mass to form a significant weather event. Some of these systems contained intense thunderstorms that dumped large amounts of rain in very short periods. In 2010, Victoria recorded it’s the fifth wettest year on record and its wettest year since 1974. This led to major flooding across the north of Victoria in September. Further persistent rainfall through October, November and December meant that catchments were already wet before the record January rainfall. How much rainfall fell, where did it fall, what towns were affected and what is the estimated cost of the damage? From September 2010 through March 2011 Victoria experienced seven significant rainfall events resulting in flooding across river systems. The two maps below show cumulative rainfall distributions for 1 September 2010 to 30 November 2010, and 1 December 2010 to 28 February 2011. The distribution of rainfall and its impact for each month between September 2010 and March 2011 is outlined below.
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September 2010 floods The flood events of September 2010 were initiated by widespread heavy rainfalls of 50‐75 mm with localised falls of up to 250 mm across the north‐east and alpine areas of the state, and up to 100 mm in western Victoria were recorded during 4‐5 September, resulting in flooding throughout most of the State. Overall, 17 municipalities, 26 localities and 1,170 properties were affected.
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October 2010 flood During 30‐31 October 2010 widespread heavy rainfalls were recorded, with up to 150 mm in the north‐east of the state. This resulted in minor to moderate flooding across rural areas and short term road closures in the north east of the state. The Rapid Impact Assessment data indicated that only five properties at one locality (Healesville) were affected in the October event. November 2010 floods On 26 November 2010 intense thunderstorm cells originating in the north‐west swept across the state causing flash flooding. This weather pattern persisted through till 29 November 2010 with many locations receiving rainfall in excess of 100 mm. The heaviest rainfalls occurred in the north‐west and central areas of the state. The Rapid Impact Assessment data indicated that six municipalities, 10 localities and 29 properties were affected. December 2010 floods Severe weather began on 7 December 2010 with heavy rain and thunderstorms continuing through 9 December 2010. The north‐east of the state was worst affected with falls in excess of 150 mm. Data provided by the Rapid Impact Assessment team, coordinated by Office of the Emergency Services Commissioner, indicated that 16 municipalities, 21 localities and more than 150 properties were affected. January 2011 floods Low‐pressure systems associated with extraordinary tropical moisture led to Victoria recording its wettest January ever by the halfway point of January 2011. Heavy rainfall and flash flooding persisted between 9 and 15 January with rainfall totals of 100‐300 mm across two‐thirds of the state. Consequent major and moderate flooding spanned north, west and central Victoria. Record daily rainfall totals initially caused flash flooding across western and central parts of the state, with the cumulative effects of unprecedented multi‐day rainfall totals leading to major flooding in the Avoca, Loddon, Wimmera, and Campaspe River systems. Most river gauges in these catchments recorded river heights in excess of previous records, as indicated in the figure below. The Rapid Impact Assessment data indicated 27 municipalities, 96 localities, and 3,355 properties (of which 3,050 were residential) and 7,625 people were affected. There was also one fatality reported at Kialla West, where an eight year old boy drowned while swimming in a billabong which was estimated to be 10‐25 m metres deep in some areas. February 2011 floods Further severe weather occurred between 4 and 6 February 2011. This compounded the impact of the January 2011 floods in a number of towns in country Victoria. However, the greatest damages were caused by thunderstorm events leading to flash flooding in and around Mildura and suburban Melbourne. A record 190 mm of rain fell in Melbourne’s south‐eastern suburbs on 4 and 5 February2011. While Mildura received more than 100 mm of rain in two hours on 4 February 2011 and close to its average annual total of 220mm over two days. Overall 10 municipalities, 43 localities and more than 1,000 properties were affected in these events.
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March 2011 floods A complex low pressure system across Bass Strait produced thunderstorms and heavy rain over Gippsland on 22 and 23 March 2011. Wilsons Promontory was the worst hit area with 370 mm rainfall in less than 24 hours. Localities impacted the most were Fish Creek, Foster, Moe, Tidal River, and Toora. While parts of central Gippsland received up to 140 mm rain. In total the flood events that occurred between September 2010 and March 2011 affected a total of 172 towns or localities as recorded by the Rapid Impact Assessment data. Of these, 24 towns/localities were affected more than once, with some river side assets, nearby roads, and farmland affected many times. The table below provides monthly data on the number of towns, municipalities and properties affected.
Affected by flood Sept 2010
Oct 2010
Nov 2010
Dec 2010
Jan 2011
Feb 2011
Mar 2011
Municipalities 17 1 6 16 27 10 2
Towns/localities 26 1 10 21 96 43 5
Properties 1,170 5 29 >150 >3,500 >1,000 no data available
Further detail on the towns and localities affected is spatially represented in the attached map of Victorian Floods Sept 2010 – March 2011 (refer attachment A). Funding has been provided to the
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Department of Sustainability and Environment for a one year project to document flood impacts in 2011‐12. Estimated Cost of the Damage. Damage costs were estimated to be about $1.3 billion. However, this is likely to underestimate the final total cost of the damage.
Q1 What is the current status of the Victorian Flood Management Strategy? The Victorian Flood Management Strategy (VFMS) was completed in 1998 and remains in place until it is revised. The purpose of this strategy was to:
Enable effective flood management for the next 10 years, by providing a consistent statewide framework for the management of flood related issues by responsible authorities, agencies and groups;
Set out objectives, provide a statewide policy framework for best practice principles and guidelines, establish priorities for statewide action, and identify roles and responsibilities of key stakeholders;
Provide the statewide context for the development of regional floodplain management strategies, floodplain management plans and specific guidelines; and
Provide a process of continual assessment and improvement for flood management in Victoria, through the implementation and periodic revision of the strategy.
While most of the ten year targets associated with the 11 strategy programs have been achieved, the above policy framework and underlying approach to flood management are still relevant. The VFMS was expected to be revised within 10 years, but was delayed prior to the floods for a variety of reasons, including new pressures of climate change and variability, sea level rise, and lessons learnt from the Bushfire Royal Commission on emergency response. In addition, key stakeholders raised a number of complex longer term issues, e.g. the sustainable management of rural levees and the current and future roles of local government in flood management. The size and extent of the current floods means it is timely to review flood management arrangements in their aftermath. The revised Strategy will need to take into account forthcoming findings from both the Victorian Government’s, Review of the 2010‐2011 Flood Warnings and Response and the Environment and Natural Resources Committee of Parliament’s Inquiry into Flood Mitigation Infrastructure in Victoria. Until it is revised, the above objectives remain in place. In particular the:
Policy framework for the management of flood related issues, outlined in Section 4 of the Victorian Flood Management Strategy continues to be followed. This relies on the principle that flood management is a shared responsibility between the Commonwealth, State and local governments. Catchment Management Authorities and Melbourne Water have floodplain management functions, as prescribed in the Water Act, 1989, but partner with other agencies, and local government in particular, to develop processes and plans for implementation of many floodplain management activities.
Roles and responsibilities described in the Victorian Flood Management Strategy still apply.
Regional Floodplain Management Strategies have been developed by the Catchment Management Authorities and Melbourne Water to guide priority setting. The diagram below shows what they contain. The CMA regional strategies will need to be reviewed as part of the periodic adaptive process to maintain relevance.
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Q20 How does DSE define flood mitigation infrastructure? Flood mitigation infrastructure is regarded as structural measures that modify flood behaviour to protect the community and reduce flood damages. They can include:
Levees, which are raised embankments which protect flood prone areas from flooding, are usually the most economically attractive measure to protect existing development in flood affected areas.
Regulators and gated structures, which can control flow distributions. For example regulators may help control flows into bypass floodways or effluent streams, or they might be used to pass floodwater accumulating behind levees back into the river. While floodgates might be used to protect drainage pipes discharging into a waterway from back flooding.
Floodway bypasses, which divert some flows around a town, reducing the amount of water flowing through the town, and therefore flood levels.
Retarding basins and retention basins, which reduce flows downstream from these structures by temporarily storing flood water.
Large water supply storages, which can either reduce flows downstream from the dam structure or absorb floods upstream. However no dam in Victoria has been built specifically for flood mitigation purposes, and water in storages is fully allocated through water entitlements. Flood mitigation is regarded as an opportune benefit within the boundaries of safe dam operating procedures.
Channel modifications, flood proofing and house raising. While approved flood mitigation infrastructure is usually constructed to a standard, i.e. able to accommodate a 1% probability flood plus 600 mm freeboard, they are not failsafe. Further many roads, irrigation channels, railways and associated bridge and culvert works have been built on floodplains, and may obstruct or affect the distribution of flood flows. They are not regarded as flood mitigation infrastructure.
Regional Floodplain Management Strategy
Policy Framework
Vision, objectives, priorities
Management arrangements
Program responsibilities
Funding and cost sharing arrangements
Project prioritization criteria
Performance measurement, monitoring and review
Floodplain Characteristics
Flood conditions, risk levels
Floodplain uses
Floodplain assets
Available information
Detailed programs
Info management
Land use planning
Flood risk management plans
Asset management
Best practice, education & training
Emergency response
Flood warning
Community awareness
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Please refer to the DSE response to Question 3 for further explanations as to flood mitigation infrastructure.
Q3 Given your experience of the recent floods and their impacts, what do you think are the biggest areas of improvement required in flood mitigation and monitoring in Victoria? The background to and opportunities for future improvement in flood mitigation and monitoring are outlined below. Flood Mitigation Flood mitigation is regarded as measures to reduce the impact of flooding. Mitigation options may include a combination of:
1. Planning controls and development controls, which help to ensure that new development in flood prone areas is compatible with the flood risk. While in developed areas already subject to stormwater flooding it may be too expensive to retrofit drainage works that accommodate large flows, over time planning and development controls enable replacement houses to be built with higher floor levels, reducing the flood damage potential. If the flood risk is high, planning and development controls can prevent future development from intensifying.
2. Flood warning systems, which has six components that work together to ensure that vulnerable communities receive and are able to act on flood warning messages. These include the:
a. Collection of real time data via the network of stream flow and rain gauges and prediction of flood severity and time of onset of particular levels of flooding;
b. Construction of warning messages describing what is happening, predictions, expected impact;
c. Communication and dissemination of such messages; d. Interpretation of the prediction and other flood information to determine flood
impacts on the community; e. Response to the warnings by the agencies involved and the community to entice
protective behaviour; and f. Reviews of the warning systems and improvements to the system after flood events.
3. Projects to improve flood education and awareness, which provide communities with awareness as to the impacts of flooding and steps to reduce their individual flood damage, such as by relocating moveable assets out of the floodplain or above the 1% flood level and evacuations. Where communities rely on structural measures for flood protection such flood awareness is particularly important, as most communities are not aware that structural measures will fail when the design standard to which they have been constructed is exceeded.
4. Flood mitigation infrastructure, such as levees, channel modifications and retarding basins that benefits more than one property. These reduce the consequences of flooding by reducing flood levels at a particular location or protecting an area. They aren’t usually implemented unless they are shown to be cost effective and affordable, have no significant environmental impacts, are socially acceptable, and have arrangements in place for ongoing maintenance.
5. Individual structural measures that reduce the impact of flooding at the property scale, such as flood proofing of individual houses.
Flood Monitoring Water monitoring data is collected from the majority of Victoria’s regional river gauges under Regional Water Monitoring Partnerships for a range of purposes, including flood warning, water allocation and resource assessment.
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Monitoring for flood warning across all of Victoria is overseen by the Bureau of Meteorology and is conducted at a total of 585 surface water sites, of which:
The Regional Water Monitoring Partnerships manages 283 sites located in regional Victoria;
Melbourne Water operates those in the metropolitan Melbourne outside of the Partnership arrangements; and
Local government authorities and regional water corporations maintain a smaller number in regional Victoria outside the Regional Water Monitoring Partnerships.
Some additional sites are used to provide flash flooding information and are operated by other organisations, e.g. City of Greater Geelong, Melbourne Water and Goulburn Murray Water. Regional Water Monitoring Partnerships currently have 44 member organisations that share capital and operation and maintenance costs of flood monitoring. They include the Department of Sustainability and Environment, the Bureau of Meteorology, regional water corporations, local government and catchment management authorities. At an operational level it is important that flood monitoring is an on‐going and continuous process to ensure that the data series for flood warning sites are extensive and provide high quality information for future flood warning and preparation. Areas for Improvement Having regard to the recent flood events we believe the opportunities for improvement are required in the areas of: rural levees policy, flood warning and monitoring, processed for incorporating flood maps into planning schemes, updated flood studies and floodplain management plans, and improved flood intelligence. Rural levees policy Overall some 4,000 km of levees have been identified across Victoria. About 1 per cent of these are urban levees and 99 per cent are rural levees. Most levees are located on private land but some are located on public land, such as Crown land, land reserved for a state forest or park, or land vested in a public authority). Urban levees are generally owned by local councils or Melbourne Water. They are generally constructed to a high standard and are expected to be maintained as such. This is not the case for rural levees, which were often built without consideration of broader flood impacts on the flow of water on neighbouring landholders or within the levee systems. About 80 per cent of the rural levees have been constructed privately by landowners and are mainly located on private land. However farmers sometimes built levee systems at the boundary between public and private land, and it is difficult to determine whether they re located on private or public land. Most of the levees were built many decades ago, often after major floods in the 1980s, 1950s or earlier, well before land use planning controls were in place. The private rural levees have been constructed to varying standards and with little regard for the standard of protection. Their failure levels are unknown, and as landowners generally do not undertake maintenance on a regular basis, the standard of protection declines with time. About 20% of the rural levees have been constructed using government funding and resources. They include three well recognised systems totalling 520 km:
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Former Public Works Department (PWD) levees along the Murray River from Cobram to Ulupna Island;
Lower Goulburn levees downstream of Shepparton; and the
Tyntynder Flats levee downstream of Swan Hill.
Since their construction, 80 to over 100 years ago, the three rural levees have provided significant reductions in flood damages to adjoining landholders and government infrastructure. Their original design protection levels have been lost in time and with a lack of maintenance their ability to provide a level of protection against major floods is slowly diminishing with failures at specific locations over the years.
In addition to the three strategic levee systems mentioned above, a number of levees exist around that were built by former government agencies and other authorities such as the River Improvement Trusts. They are currently not being maintained by any authority and as such, are also slowly deteriorating.
Victoria therefore has a legacy of poor control over rural levees, most of which were constructed privately without consideration of the standard of construction or for long term maintenance requirements. Successive governments (State, Federal and local) have not accepted responsibility for managing rural public levees because of the large costs required to refurbish and maintain them, and the potential liability issues associated with their upgrade and the relatively low economic benefits. Flood warning and monitoring The flood warning system addresses five key elements, which are linked and interdependent. Failure to address any of the elements will result in a failure to provide warnings to the community. The five elements are: 1. Data collection, prediction and warning messaging; 2. Communication and dissemination; 3. Interpretation; 4. Protective behaviour; and 5. Community and agency consultation and review. The process to identify the requirements and priorities for a total flood warning system for Victoria is driven by two documents. The first document, Arrangements for flood warning services in Victoria (BOM Victoria, 2001), provides the background, principles and policies for flood warning services in Victoria. The second document, Flood Warning Service Development Plan for Victoria (Victorian Flood Warning Consultative Committee, 2005) provides a comprehensive review of the total flood warning system. The recommendations for improvements from the two documents have been aggregated into the Flood Warning System Implementation Plan. The ten themes, with the nominated lead agency (in brackets) are as follows:
Flood awareness roles and responsibilities (VICSES);
Flood planning at municipal level (Office of the Emergency Services Commissioner (OESC));
Linking flood studies to improved warnings (DSE);
Flood prediction – service level agreements (BOM);
Flood prediction – best practice in delivery (BOM);
Sustainability of flood warning systems (VICSES);
Coastal/estuarine flood prediction capability (BOM);
Post flood data management (DSE);
Flash flood prediction capability (BOM); and
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VFWCC – follow up actions (BOM). While this provides a reasonable process for ensuring the five elements of the flood warning system are addressed it is crucial that roles and responsibilities in flood warning monitoring are clearly defined and unambiguous to ensure efficient and appropriate ongoing resourcing. This includes roles, responsibilities and resourcing of, in particular, the operation and maintenance component of flood monitoring to ensure that flood monitoring data remains continuous, high quality and on‐going. The current framework relies on a process of mutual cooperation, which requires financial commitment and a desire to make things work from a number of stakeholders. An improved framework could require:
Clear, transparent and possibly simplified roles and responsibilities underpinned by a legal agreement.
A strategy for ensuring a reliable flood warning system for all Victorians across Victoria, including those areas that do not currently have a gauge network. This should include a minimum standard for key communities, agreed maintenance arrangements and a auditing process to ensure appropriate management during dry periods.
A prioritised and resourced flood warning upgrade program in place to manage and monitor progress. Floods can occur anywhere in the State at any time, even during droughts. While history shows that flood warning systems deteriorate over time if they are “optional.”
Simplify the process of incorporating flood maps into planning schemes Further consideration of planning scheme amendment processes for ensuring best available flood extent information is incorporated into planning schemes may need to be considered to ensure that these processes are less costly and more efficient. See answer to Q23. It is understood that those councils that have not incorporated flood information into planning controls have cited a number of reasons, including:
Concern that the information is of low reliability and requires detailed modelling;
Lack of sufficient resources within councils to undertake the planning scheme amendment process; and
Perception that flood controls will inhibit future development in their municipalities. For those floodplains not included in planning scheme controls councils have discretion in referring planning permit applications to catchment management authorities for their input. This then creates a risk of inappropriate subdivisions or houses being constructed close to the natural ground level. Councils’ assessment processes of development proposals where flood overlays are not in place needs to be reviewed to ensure that catchment management authorities are able to provide flood advice. Without planning controls, planning permits cannot be assessed by those with an understanding of flood impacts. Continue to support new and updated flood studies and floodplain management plans. Flood studies provide the basis for understanding flood behaviour for a range of flood events. They are informed by flood data, and provide the basic material for planning controls in planning schemes and advice to emergency management agencies on flood behaviour. Floodplain management plans provide a series of affordable, cost effective and socially acceptable flood mitigation options, structural and non structural, which are established in consultation with the community options. They allow for structural and non structural flood mitigation measures to be assessed and prioritised. Flood studies need updating every five to ten years, or after a severe flood, to ensure they remain relevant by taking into account the latest flood data, accommodating changes in roles and
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responsibilities and any changes in community aspirations. The recent floods affected areas that had not flooded for a very long time, and in some cases towns were flooded that were not expected to flood. For a town to be prepared for flooding it needs to understand what the risks are. After a major flood there is a tendency for municipal councils to respond through structural solutions, for example a levee built to withstand overtopping from a recent event, rather than ensuring that flood studies or floodplain management plans are updated. However, this approach can be counterproductive in that there is no provision to investigate alternative flood mitigation options, community aspirations, undertake updated modelling to establish the future frequency of overtopping, or to determine the standard of protection and arrangement for levee ownership or maintenance. The Department of Sustainability and Environment has received funding over four years to undertake up to 25 flood studies to inform a flood intelligence platform that will also be developed. This supplements funding provided through the Commonwealth Government’s, National Disaster Resilience Grants Scheme, which also funds floodplain management plans.
Improved flood intelligence. Flood intelligence combines forecasts of flood levels at a location with mapping of floods and information on people and assets. This intelligence can then be used to inform community warnings, flood response and recovery activities. Effective emergency response to flood events requires accessible and timely flood intelligence. During the recent floods a combination of consultants, as well as staff of the Department of Sustainability and Environment and catchment management authorities provided flood intelligence function. However, the timing and effectiveness of the provision of flood information was hampered by the limited availability and access to documents containing useful information. In relation to this need it should be noted that the Department of Sustainability and Environment has recently received substantial funding to improve the collation, documentation and assessment of flood risk, and to develop a computer based flood intelligence platform to improve the timeliness and effectiveness of providing flood advice to the emergency management agencies on flood impacts.
Q2 In your briefing you made reference to ‘best practice’ flood mitigation. What does DSE consider to be ‘best practice’ in flood mitigation and monitoring? ‘Best practice’ flood mitigation Elements of best practice flood mitigation include:
A risk management approach (see Figure below);
Appropriate risk treatment measures which include both structural and non structural measures;
Decision making frameworks for future investment which facilitates setting priorities for
competing projects;
Clear definition of roles and responsibilities of flood management stakeholders;
Clear definition of cost sharing principles;
Strategic planning framework at State, regional and local levels;
Legislative support for floodplain management functions (for Victoria they are listed in Section 202
of the Water Act 1989, and catchment management authorities and Melbourne Water have these
functions);
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A process for carrying out these functions (for example, developing floodplain management plans
and flood response plans and flood controls in planning schemes); and
Support systems including best practice manuals and guidelines for use by flood management
practitioners.
Figure: Flood Management in the Risk Management Context ‘Best practice’ flood monitoring ‘Best practice’ surface water monitoring, including flood monitoring, is specified in the Australian Standard 3778: Measurement of water flow in open channels ‐ Hydrometric determinations. This standard is identical to the relevant ISO Standards specific to the subjects. For example, ISO guidelines on measurement by current‐meters are described in AS 3778.3.1, a document that includes procedures for current meter measurements by suspension undertaken during high flows or floods. In addition to those standards there are four documents prepared by the World Meteorological Organisation for Guiding Hydrological Practices, including a manual on stream gauging. The Department of Sustainability and Environment ensures that these standards are implemented in service provider contracts under which a large component of flood monitoring is delivered across regional Victoria through the Field Services Contracts for the Regional Water Monitoring Partnerships. The Department of Sustainability and Environment also administers Victoria’s four Regional Water Monitoring Partnerships to ensure that data from Victoria’s regional surface waters is collected to a
Regional Flood Strategy (CMA) – Development of priorities
Flood Studies in priority areas to investigate flood behaviour incl. flood mapping
Floodplain management study to assess and prioritise mitigation options e.g. levees, planning controls, response plans, warning systems
Floodplain management plan developed containing agreed measures
Land use planning and building controls
Structural mitigation works e.g. levees, bypass channels etc
Emergency management plans
Flood warning systems
Stream management plans
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consistent standard and is of appropriate quality. This is implemented through the management of two service provider contracts (‘the partnership contracts’) associated with the collection of this data. Water data is also collected by other organisations for their own business purposes outside of the partnerships. This can include flood monitoring, such as the monitoring required for localised events. Data collection practices are specified in the contracts and implemented by the service providers, currently Thiess Services, for both of these contracts. The specifications for the contracts were revised
and updated in 2009 and are current in their use of the relevant standards.
Q6 On average, how much money has been spent on flood mitigation each year over the past decade, and what are the key areas where expenditure occurs? And how has funding changed, if at all, over the past decade? The graph below shows variations in costs over the past ten years, based on established commonwealth funding programs, including the Natural Disaster Risk Management Studies Program, Natural Disaster Mitigation Program, Regional Flood Mitigation Program and Natural Disaster Resilience Grants Scheme, for flood investigations, works, flood warning system improvements, flood awareness and education. Funding for these costs includes contributions from State, Commonwealth, CMA and local government sources. The costs do not include:
Costs incurred by catchment management authorities as part of their statutory functions
Flood recovery work to waterways and assets through natural disaster relief payments
Salary or oncosts incurred by government agencies managing the funding programs. Graph: Costs of flood mitigation
Flood Mitigation Costs
$-
$500,000
$1,000,000
$1,500,000
$2,000,000
$2,500,000
$3,000,000
2010
-11
2009
-10
2008
-09
2007
-08
2006
-07
2005
-06
2004
-05
2003
-04
2002
-03
2001
-02
Flood Investigations & Studies
Mitigation Works
Flood Warning
Flood awareness
Flood Event Data Gathering
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Q4 Which CMAs and Local Governments have best addressed flood mitigation and what has given them the leading edge? There are a number of factors that give catchment management authorities and local government the leading edge. These include the:
Willingness of local government and catchment management authorities to work together. It is preferable that councils quickly incorporate the results of flood studies into planning schemes;
Financial base of the respective municipality and catchment management authority and how affordable flood mitigation projects are in relation to the many other things that must also be managed, such as other emergency risks, river health, infrastructure, drainage, etc;
Flood risk of the locality, which is not distributed uniformly across the state. Areas with a high risk feature more predominately in Melbourne because of the large established populations in the older suburbs that are subject to overland flooding without provision for adequate drainage. While outside Melbourne the high flood risk areas are the North East, Goulburn‐Broken and West Gippsland catchments;
Degree of flood awareness of communities. This is often reflected by how often areas flood, and when the last flood was; and
The priority that CMAs allocate to the implementation of floodplain management statutory functions compared to other activities they undertake.
In term of overall performance it is considered that where floods have occurred with greater frequency, catchment management authorities and local government have more capacity and experience. Communities also are likely to be more resilient. Over the last three years or so Melbourne Water has revised its approach to flood mitigation. Its current approach is contained in the Flood Management and Drainage Strategy for Port Phillip and Westernport Region, released in 2007. Rather than its traditional approach of using engineering solutions to improve flood protection in identified high risk areas, Melbourne Water’s Strategy recognises that it is not possible to make the region completely free from flooding. While Melbourne Water and metropolitan councils will continue to deploy engineering solutions to mitigate flood risks, they will also continue to use non structural measures to reduce flood risks, such as planning controls and public awareness programs. Melbourne Water’s approach is considered to be consistent with best practice. We have not however evaluated its performance. Councils and catchment management authorities are encouraged to apply for funding for flood investigations to improve the understanding of flood risk. These investigations are usually undertaken through a Commonwealth funding program which typically apportions the cost equally among the Victorian Government, Commonwealth Government, local government authorities and catchment management authorities.
Q5 Are councils required to take the advice of CMA’s regarding planning matters, including development of floodplains, or is this discretionary? The Planning and Environment Act 1987 (Vic) legislates for the minimisation of flood risk through forward planning of land use and development. Generally, this applies to the newer planning schemes,
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post 1994, so it is not a mechanism to address past mistakes or oversights, except when land is redeveloped. Section 6(e) of the Planning and Environment Act 1987 (Vic) enables planning schemes to ‘regulate or prohibit any use or development in hazardous areas, or areas likely to become hazardous’, and so provides the legislative backing for management of flood risk. Where flood overlays are in place, councils are required to take the advice of the catchment management authorities. Sections 55 and 56 of Part 4 of the Planning and Environment Act 1987 (Vic) specify that a referral authority (catchment management authority or Melbourne Water) must consider referred planning permit applications and advise the council in writing of its decision, including reasons and/or conditions that may apply. A condition specified by a referral authority can include a requirement that something is done to the satisfaction of the council, minister, public authority, or referral authority. The council must include the referral authority’s conditions on any permit that it may issue2. This power is to ensure that developments are strictly controlled in a known and mapped flood affected area. Catchment management authorities and Melbourne Water are considered to have the relevant skills and knowledge to assess the flood risk. In situations where no flood overlay is in place, councils have discretion to refer planning permit applications to the relevant catchment management authority or Melbourne Water under Section 52 of the Planning and Environment Act. In such situations, the advice provided is not binding. As indicated in our answers to Questions 9 and 23, a small number of councils have no flood controls or limited flood controls in their planning schemes. This means that development proposals in areas affected by flooding are not referred for flood advice, and development has taken place which does not consider the risk of flooding. Two examples of what can occur where the advice of the relevant catchment management authority, or a development proposal is not referred, are provided below. Example: Creek Street & Hamin Street Miners Rest near Ballarat
Existing site use: Farmland.
Development proposal: residential sub‐division.
Planning context: No flood related planning overlays in planning scheme.
Flood risk: Flood mapping showing frequent inundation.
Authority advice: No referral made.
Council response: Approved development.
Outcome: Flooding of properties occurs frequently with significant damage and demand on emergency services. The September 2010 & January 2011 events impacted on properties.
Example: Sherwood Park Estate Traralgon
Existing site use: Farmland.
Development proposal: residential sub‐division.
Planning context: Land subject to inundation overlay in planning scheme.
Flood risk: Flood mapping showing frequent inundation.
2 It should also be noted that Under the provisions of s 62 (4), planning permits must not be inconsistent with the Building Act 1993 (Vic) or its regulations or any determinations made by the Building Appeals Board
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Authority advice: Section 55 referral. Conditions placed on development footprint.
Council response: Approved development.
Outcome: Development proceeded with conditions. Flooding occurred in June 2007 with limited inundation within development. Avoided damage to properties and infrastructure.
Q8 What are the key strengths and weaknesses of current floodplain management and planning in Victoria? Are CMA’s and Councils adequately resourced and skilled to undertake this planning? The major strength of current floodplain management is that it is based on a robust strategic framework that was set up during the 1990s by the development of the Victoria Flood Strategy, the definition of powers in the Water Act 1989 (Vic), and the introduction of the Victorian Planning Provisions in 1997. The Department considers that the implementation of the Victoria Flood Strategy established the following systemic strengths:
Decentralisation of oversight of local floodplain management to catchment management authorities;
Establishment of a statewide geographic information system (GIS) database as a tool for decision making on catchment‐wide planning, local land use planning, flood mitigation and emergency response planning;
Use of the risk management approach to assess development proposals on floodplains;
Improved interagency liaison on planning/prevention, response and recovery issues;
Completion of a range of works and measures to support floodplain management, such as the development of best practices (e.g. project evaluation methods, rapid impact assessment), improvements to flood warning systems, and levee system upgrades; and
Establishment of a culture of continual assessment and improvement. Experience has also shown that it is preferable (safer and more cost effective) to use non‐structural measures, such as land use planning, flood awareness and flood warning to achieve floodplain management objectives, rather than using structural measures to try to build out floods with levees, diversion channels, retention basins, etc. Key weaknesses of floodplain management and statutory planning during the implementation of the Victoria Flood Strategy have included:
A low profile and poor understanding of floodplain management issues during the recent drought.
The removal of the tariff as a mechanism for CMAs to fund floodplain management, waterway management and rural drainage activities in 1999. This has resulted in an inadequate level of resourcing for catchment management authorities and councils to perform designated functions. It has also created an additional burden for local government to fund projects.
A failure to have the best available flood controls in planning schemes. A ten year target in the Victoria Flood Strategy 1998 was to incorporate flood maps into planning schemes. As indicated in our answer to Q9, 100% of local government authorities in Melbourne and 71% of local government authorities outside Melbourne have incorporated flood maps of a reasonable standard into planning schemes. There is an ongoing need for councils to update flood overlays when better information from flood studies is available. DSE is aware that many councils find it difficult to do because of the cost and time required to do the planning scheme amendments. The
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current process takes more than two years and requires resources that many municipal councils don’t have.
The lack of an effective institutional framework for the management of rural levees.
A failure to implement flood warning network upgrades in many parts of the State. In the 1998 strategy, responsible agencies, under the coordination of the Victorian Flood Warning Consultative Committee, were to have upgraded or implemented 29 flood warning systems on a priority basis throughout the State over the next ten years at an indicative cost of $8.7 million. Funding under the Reform Initiative was not provided for this purpose.
In terms of resourcing and skills:
Catchment management authorities are resourced to undertake their statutory functions to provide flood advice (mainly as a referral authority), but lack resources to co‐fund flood studies or undertake other floodplain management activities. The experience and skill set varies across the different catchment management authorities.
Municipal councils are also resourced to administer their planning schemes but many municipalities lack resources to co‐fund studies, implement works, or contribute to the maintenance of flood warning systems through the regional monitoring partnerships, particularly if their rate base is small. The experience and skill set also varies. For instance, most councils are capable of project managing studies and works but many do not understand the technical issues related to flooding.
Melbourne Water generally takes a lead role in floodplain management and appears to be well resourced. Melbourne Water generally contributes at least $20 million per annum for flood risk reduction projects (studies and works) and works cooperatively with municipal councils with their planning scheme amendments.
Q23 You stated in your briefing that ‘in relation to the planning system, we already realise that there are a lot of opportunities to do a lot of things perhaps better than we are doing them now’. What are the improvements that could be made regarding planning? The Review of Floodplain Management in Rural and Provincial Victoria (Water Studies Pty Ltd, 1995) identified land‐use planning as the most effective means of reducing the growth of future flood damage. Following this review, flood related zones and overlay controls were introduced into the Victoria Planning Provisions in 1997 and a program undertaken over three years to identify land liable to flooding and the higher risk floodway areas. At the time it was envisaged that all of these identified areas would be incorporated into municipal planning schemes. While most councils have incorporated some form of flood mapping into their planning schemes, a small number outside Melbourne have not introduced flood controls. As such, at times developments have taken place that do not consider the risk of flooding because they are not referred to a catchment management authority. As indicated in our answer to Q9 twenty‐one municipalities outside of the Melbourne Water (44% of municipalities) area either do not have a flood zone or flood overlay in their planning schemes, or (in the view of the relevant catchment management authority) have only limited flood mapping in their
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planning schemes. The two major reasons for this are the low reliability of the available flood maps and the low imperative to incorporate flood controls in planning schemes for sparsely settled areas. Possible solutions to improve the effectiveness of the planning system to reduce flood risk are to:
Ensure sufficient funding is available for flood studies to improve the standard of flood mapping;
Streamline the process for incorporating up to date flood information into flood overlays and zones in planning schemes. This could be achieved through Ministerial amendments rather than expensive and time consuming municipal processes;
Provide an incentive or require (within a reasonable time frame) flood overlays and zones to be incorporated into all municipal planning schemes in Victoria, based on the best available information;
Provide a requirement for flood overlays and zones to be reviewed regularly; and
Introduce a process for independent auditing.
Q7 What is the estimated Annual Average Damage in Victoria over the past ten years?
The average annual damage (AAD) is the average damage per year that would occur in a particular area from flooding over a very long period of time. In many years there may be no damage, in some years there will be minor damage (caused by small, relatively frequent flood events) and in some years there will be major damage (caused by large, rare flood events). Average annual damage (AAD) provides the basis for comparing the economic effectiveness of different management measures against floods of all sizes, i.e. their ability to reduce the AAD. In 2000 a ‘Rapid Appraisal Method’ was developed to estimate the AAD for catchments by catchment management authorities. It provides a relatively quick and consistent method for assessing the relative flood risk. The table below shows results for the nine catchment management authorities and Melbourne Water, CPI adjusted to 2010. The Melbourne Water data has been obtained from its Flood Management and Drainage Strategy, while the catchment management authority data are derived from the regional strategies. Table: Annual Average Damage for Victoria
Area AAD ($ million ‐ Dec 2010)
Melbourne Water 245
Goulburn Broken CMA 35.1
North Central CMA 27.1
West & East Gippsland CMA 14.9
Wimmera & Mallee CMA 12.6
Corangamite CMA 6.9
North East CMA 6.0
Glenelg Hopkins CMA 3.3
Total 350.9
It should be noted that the catchment management authority data does not include flood damage from urbanised stormwater flooding. This is likely to be significant for heavily urbanised communities like Geelong, Ballarat, Bendigo and Shepparton. Of the $245 million AAD for Melbourne, only $30 million is attributed to riverine flooding. The remaining $215 million is attributed to stormwater flooding.
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The table below shows estimated damages for floods since 2001, where we have been able to find information. It is indicative only, and is likely to underestimate the cost of flooding. Over this ten year period, the damage equates to $260 million per annum. This shows that, even in a dry period, Victoria still experiences significant economic loss from flooding.
Date CPI Adjusted Cost $million
Location Source Comments
Apr 2001
7.4 Geelong, Lara, Melbourne
EMA Information obtained from Emergency Management Australia database
Dec 2003
122 Melbourne EMA Information obtained from EMA database
Jan 2004
21 Melbourne Insurance Council of Australia
Insurance payouts
Nov 2004
0 Melbourne EMA No damage figure available but three peopled drowned
Feb 2005
0 Melbourne and Central Victoria
EMA No damage figure available. Melbourne Water reports widespread flooding but not much property damage.
Jun/Jul 2007
112.7 Gippsland DSE Estimated from preliminary data provided shortly after the flood.
Mar 2010
1044 Melbourne ICA Insurance payouts
Sep 2010 to Mar 2011
1293.5 Statewide except parts of Gippsland
Secretaries Flood Recovery Group, BERC bids & ICA
Preliminary damage estimates.
Total 2600.6
Q9 In a 1995 Review of Floodplain Management in Rural and Provincial Urban Victoria (Water Studies Pty Ltd), a number of key Floodplain Management Activities were identified. For LGA’s where flood problems are known or expected to exist, these are the: number of LGA’s with completed flood maps; number of LGA’s with maps started; number of LGA’s with flood studies completed or underway; number of further flood studies required by LGA; percentage of LGA’s where identified structural works have been completed; and percentage of LGA’s where flood maps and planning controls have been introduced. Could you please provide updated figures in relation to these matters? The figures are provided below are not directly comparable to the 1995 data, as the:
210 municipal councils in 1995 have been restructured to 79;
Boundaries of the Melbourne Water service area have expanded;
Victorian planning system underwent a major overhaul from 1997 to 2000; and
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Information quoted in the 1995 review was based on estimates. Important background Information In the late 1990s, the Flood Data Transfer Project converted most of the available spatial flood information (of variable accuracy and reliability) from paper maps and plans held by various government agencies into a GIS format. The information collected during the Flood Data Transfer Project was used to establish the Victoria Flood Database in 2000. The Victoria Flood Database is a series of spatial layers depicting flood information from both actual flood events and modelled flood events across Victoria. Some flood related infrastructure, such as levees, is also included. Included in this database are two layers which are available online as interactive maps in the water surfaces layer (see http://nremap‐sc.nre.vic.gov.au/MapShare.v2/imf.jsp?site=water):
Land subject to inundation, which represents the best available estimate of the one in one hundred probability flood event; and
Floodway, which represents the high hazard part of the floodplain. The Victoria Flood Database covers all Victoria except for the area managed by Melbourne Water (which encompasses the greater metropolitan area of Melbourne and most of the Port Phillip and Westernport catchment area). The Department of Sustainability and Environment’s Floodplain Management Unit is the current custodian of the Victoria Flood Database and maintains a library that contains flood studies and other records used to update the Victoria Flood Database. Since 2000, the Victoria Flood Database has been regularly updated with information from numerous local flood studies and mapping projects carried out by councils and catchment management authorities. Flood mapping has been undertaken for every municipality and included in the Victoria Flood Database. It is estimated that seven to eight per cent of Victoria is liable to flooding from a one per cent probability event. Comparing information from the Victoria Flood Database and municipal planning schemes, it is estimated that approximately:
Eighty per cent of the floodplains in Victoria have been mapped; and
Seventy per cent of the mapped areas are delineated in municipal planning schemes as land subject to inundation from a one in one hundred probability event. It is acknowledged that the information in some areas is of low reliability, reflecting the poor quality of data available.
There are 31 municipalities entirely in the Melbourne Water Drainage area, 41 entirely within the CMA areas and 7 partially in both. For the sake of the analysis below it has been assumed that there are 31 municipalities in the Melbourne area and 48 in the CMA area. Melbourne Water has mapped areas liable to riverine and overland flooding in all metropolitan areas, but some further work is required to complete mapping some parts of the seven municipalities that were incorporated into its region in late 2005. Melbourne Water has undertaken to continue to upgrade flood mapping and to incorporate relevant information into planning schemes in its Port Phillip and Westernport Region Flood Management and Drainage Strategy 2007. Melbourne Water currently spends about $3 million per annum on flood mapping and flood mitigation option development. Number of local government authorities with completed flood maps
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As indicated above, flood mapping is available (though the VFD and Melbourne Water flood maps) for all municipalities, but not all the information has been incorporated into planning schemes. Some of the information is of low reliability, reflecting the poor quality of the data available. Within the Melbourne water region all available approved flood maps are incorporated into council planning schemes and are available through “planning schemes on line” via http://www.dpcd.vic.gov.au/planning/planningschemes . Number of local government authorities with maps started Both the Department of Sustainability and Environment and Melbourne Water encourage and contribute to the funding of flood investigations that inform land use decisions, improve mapping of flood extents, and provide a good basis for emergency management activities. The Department of Sustainability and Environment generally contributes to the funding of up to ten flood studies per year. It is hoped that with additional funding provided since the recent severe and recurrent flood events, this figure may double for the next four years. However, this is dependent on the capacity of catchment management authorities and councils to manage these projects. The Department of Sustainability and Environment has reviewed projects that are currently being funded through the Natural Disaster Resilience Grants Scheme or its predecessors. These types of projects are generally funded under cost sharing arrangements that include Commonwealth, State and local contributions. Currently there are projects for 11 municipalities that the Department of Sustainability and Environment contributes funding to. Three additional studies have also been identified as high priority studies as part of the Department of Sustainability and Environment’s Floodzoom initiative (see question 10). All studies have flood mapping components. Melbourne Water has on ongoing program to review and revise existing available flood mapping. For example during 2010/11 12 packages of flooding modelling costing some $2.8 million was commenced. The 12 packages involve waterway and drainage systems in 10 municipalities. In addition to this work an additional $17 million per annum is spent on flood mitigation structural works to reduce flood risk in those catchments with an extreme flood risk. Number of local government authorities with flood studies completed or underway Since 2000, it is estimated that 80 studies have been completed across 36 municipalities using the NDRGS or its equivalent. This is in addition to the 14 flood studies that are currently underway and the projects undertaken by Melbourne Water. Number of further flood studies required by LGA The Department undertook a preliminary analysis of flood study needs outside Melbourne, during the preparation of the Floodzoom funding initiative. We estimate that at least 36 further flood studies will be required; however the number will vary when more detailed analysis is undertaken as part of Floodzoom. As indicated previously, due to the need to ensure mapping is up to data and current, Melbourne water has ongoing program of flood mapping activity currently estimated at $3 million per annum. . Percentage of local government authorities where identified structural works have been completed Since about 1980, the Department and its predecessor bodies have, or are contributing funding for structural works across 21 municipalities outside Melbourne. Of these 17 (81%) have been completed. Since 1996 Melbourne Water has invested some $101 million in 35 projects over a number of municipalities to reduce flood risk for waterways and drainage systems. The majority of these works
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has been to address flood risk associated with urban stormwater drainage systems, the major flood issue within the region. Melbourne Water is constantly updating and prioritising the requirement for identified structural works, so it is meaningless to convert this to a percentage. Percentage of local government authorities where flood maps and planning controls have been introduced The following four municipalities do not have a flood zone or flood overlay in their planning schemes:
Ararat. Limited Victoria Flood Database mapping is available for small areas in south of municipality from Streatham to Lake Bolac on Fiery Creek. The mapping is not high reliability and the area is nearly all rural, so has been a low priority for council to incorporate into their planning scheme.
Pyrenees. Only limited and poor quality Victoria Flood Database information is available and the Shire is not prepared to incorporate mapping into the planning scheme without a flood study.
Corangamite. In the Victoria Flood Database, small mapped areas are scattered across scattered across municipality, most of them around lakes rather than streams or rivers. The data is of low reliability and council lacks resources to incorporate the information into planning schemes.
Queenscliffe. There are no major watercourses in the municipality. Victoria Flood Database mapping is for potential flash flooding or coastal flooding and it has been a low priority for council to incorporate into their planning scheme.
There are also 17 other councils that, in the view of the relevant catchment management authority have only limited flood mapping in their planning schemes. They are Alpine, Ballarat, Buloke, Central Goldfields, East Gippsland, Glenelg, Greater Bendigo, Hepburn, Macedon Ranges, Mansfield, Moorabool, Mount Alexander, Moyne, North Grampians, Wellington, West Wimmera and Yarriambiack councils. It is understood that where available mapping has not been incorporated into planning schemes, the two major reasons for this are the:
Low reliability of some of the mapping information which had been captured over many decades based on available flood photography or flood information; and
Low imperative to incorporate flood controls in planning schemes for sparsely settled areas. Therefore, as indicated in the diagram below:
All 31 Melbourne municipalities and 27 non Melbourne municipalities have flood mapping of an acceptable standard incorporated into planning schemes;
17 non Melbourne municipalities have some flood mapping in planning schemes but this is incomplete or of low quality; and
4 non Melbourne municipalities do not have flood controls in planning schemes.
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Percentage of Municipalities with Flood Controls
73%
22%
5%
acceptable standard
incomplete or low quality
no controls
Melbourne Water has been more successful in incorporating areas liable to flooding into municipal planning schemes, because it has the capacity to assist councils to produce high quality flood maps and process their flood related planning scheme amendments, through the provision of funding or technical expertise. Summary See Table below
Indicator Metro area Outside Metro area
LGAs with completed flood maps (no.) Flood mapping is available for all municipalities, but not all the information has been incorporated into planning schemes
31 48
LGAs with flood studies producing flood maps underway or completed since June 2010 (no.)
201 14
Further flood studies required by LGA (no.) Ongoing2 36
LGAs where identified structural works have been completed (%.) Ongoing3 81%
LGAs where flood maps and planning controls have been introduced to a reasonable standard (%)
100% 56%
NOTE: There are 48 non‐metropolitan and 31 metropolitan municipalities. 1‐ Annual program of activity. Number represents projects undertaken during 2009/10 and 2010/11. 2 – Melbourne Water will always be required to review and update flood mapping due to changes in development, climate and improved data and standards. 3 – 35 projects completed since 1996 in various municipalities. It does not mean that all possible projects within the municipality have been undertaken.
Q10 You mentioned in your briefing that a further 25 flood studies are to be undertaken across Victoria in the next four years. Where specifically are these studies to be undertaken, and what makes them priority areas? Under the Floodzoom initiative, flood studies will be undertaken for up to 25 locations over four years. These have not been finalised and cannot all be completed at once. Currently:
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Flood studies have commenced or will shortly commence at Charlton, Creswick and Clunes. These towns were heavily affected by the recent floods and are considered to have a high flood risk.
For 2011/12 flood studies are proposed for ten locations including: o Donald, Carisbrook, Rochester (applicant was North Central Catchment Management
Authority); o Wickcliffe, Skipton and Burumbeet (applicant was Glenelg Hopkins Catchment
Management Authority); o Natimuk, Upper Wimmera ‐ Landsbourgh & Narvee (applicant was Wimmera Catchment
Management Authority); o Corop Lakes (applicant was Goulburn Broken Catchment Management Authority); and o Update of previous studies in Shepparton Mooroopna (applicant was Greater Shepparton
City Council). The 2011/12 studies are subject to an approval process that is not yet complete, and the list is therefore still preliminary. The studies have been incorporated into a Commonwealth funding program called the Natural Disaster Resilience Grants Scheme, thereby attracting funding from the Commonwealth Government. All eligible projects were assessed to the following criteria: the quality of the proposal; the risk; and the value of outputs or outcomes. Advice was also taken from the catchment management authorities as to which were the top priority studies in their areas, given that the number of studies submitted greatly exceeded the capacity for the catchment management authorities to project manage them. For future years applicants (predominately the catchment management authorities) will be encouraged to reapply for studies that cannot be supported this financial year. They include:
For the North Central Catchment Management Authority area: Bridgewater, Castlemaine, Dunolly, Kyneton, Lower Avoca, Lower Loddon, Maryborough & Woodend; and
For the Wimmera Catchment Management Authority: Mount William Creek, Horsham & South Horsham.
It is also expected that applications will be made from other parties in subsequent years.
Q11 The Department of Sustainability and Environment is to undertake a levee audit in Northern Victoria. What is the scope and key objectives of the audit? When will the project be completed, and can the Committee obtain a copy of the findings when it is completed? The audits of levees will asses both rural and urban levees. . Specifically, the assessment will:
Capture survey data of levee crests and cross‐sections;
Identify points of weakness in the levees;
Establish land tenure;
Establish general the level of protection to be provided;
Develop a priority list of works to repair weak points in order to provide the established level of protection;
Estimate the costs to carry out the works; and
Record all outputs into suitable GIS layers.
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The assessment covers approximately 600 km of levees but does not include many private levee systems constructed over the years. It is not expected that the assessment will be completed until the end of June 2012. Rural Levees The levees are located in the North Central, Goulburn Broken and North East Catchment Management Authority regions. The rural levees assessment project aims to better understand the condition of strategic levees at the following locations:
Gunbower Creek from Torrumbarry to Koondrook;
Murray River and Little Murray River from Murrabit to Vinifera;
Goulburn River from Loch Garry to Murray River;
Murray River from Cobram to Barmah; and
King, Ovens and Kiewa River valleys. The assessment will be used as a guide to decision making when considering measures to improve the existing level of protection of the levee system. Each catchment management authority is responsible for undertaking the assessment in their region. Urban Levees In addition to the rural levee assessments, urban levees constructed to protect urban townships over the past 25 years through government funding programs will also be assessed to check that they still meet the standard of protection developed at the time of construction. These are levee systems maintained by municipal councils and towns include Wangaratta, Kerang, Seaspray, Traralgon, Echuca, Bendigo, Horsham, Lara, Nathalia, Woodend and Euroa. It is also envisaged that the temporary levees constructed during the recent flood event at Warracknabeal, Pyramid Hill and Quambatook will be assessed to determine location, height and standard of construction. Once assessments have been completed for each region, copies of the report can be made available to the Committee. The report is not expected to be completed until the end of June 2012.
Q12 There are many rural levees in Victoria where ownership and maintenance is currently unclear. You stated in your initial briefing to the Committee that the Department of Sustainability and Environment has been looking at this issue for a number of years. What policy options have been considered by Department of Sustainability and Environment in addressing this issue, and what are the benefits and disadvantages of each policy option? Over the years there has been discussion of various gaps and issues in relation to the management of levees in Victoria. Levees have been in existence for well over a hundred years and their management has long been a major issue.
The comments below are confined to rural levees. Many urban areas in regional Victoria are also subject to flooding, and levee systems have been constructed to provide an agreed level of protection. Since the 1980s, most levee mitigation schemes have been implemented through an Approved Scheme under the Water Act 1989 (Vic), with a council nominated as the management authority. These levee systems were designed to an appropriate standard and built using appropriate
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construction standards at the time with a freeboard allowance. It is expected that they should offer safe protection up to the design standard, which is typically the one in one hundred year level of protection plus freeboard. Councils have accepted their responsibility for management and ongoing maintenance. However, an audit of these levees some 10 years ago found a number of design level and maintenance issues for several of these levee systems and hence councils’ levels of management are quite varied.
A number of towns in Victoria also have some ad hoc levees which were constructed at various times. These were not necessarily designed to a specified level of protection or constructed to modern standards. Some are maintained by councils whereas others are not maintained at all. It is likely that municipalities may not be receptive to taking on management of these levees. However, councils have readily accepted responsibility for urban levees in other areas.
Levee classifications Overall some 4,000 km of levees have been identified across Victoria. About 1 per cent of these are urban levees and 99 per cent are rural levees. In order to consider appropriate and workable management arrangements, rural levees have been classified as follows:
Rural levee systems that have some history of being funded or supported by government
These include the:
Former Public Works Department (PWD) levees along the Murray River from Cobram to Ulupna Island constructed about one hundred years ago;
Lower Goulburn levees downstream of Shepparton, also constructed about one hundred years ago; and the
Tyntynder Flats levee along the Murray River from Swan Hill to Nyah, first constructed in 1896 and realigned in the 1930’s.
These levees total some 520 km in length and were all constructed on a combination of crown land and private land with government funding through government programs at the time3. They are not currently being maintained.
Their original design protection levels have been lost in time and with a lack of maintenance their ability to provide a level of protection against major floods is slowly diminishing with failures at specific locations over the years.
Indicative costs for upgrading the levees to a minimum acceptable standard for rural protection are at least $25 million and in addition, indicative maintenance and depreciation funding of $500,000 per annum would be needed. If funding was extended to major re‐construction, the upgrading cost would rise to at least $150 million. The estimated damage should the three levees mentioned above fail in a major flood event is estimated at $200 million, mainly to private infrastructure. These indicative costs may need to be revised following further audits and studies.
Levee audits for the three levee systems were undertaken in 1997 and 1999. The auditors found that the levees had deteriorated from their intended level of service, which is considerable less than for levees protecting urban communities. They proposed remedial work to repair the levees.
Some work was carried out on the worst sections of the PWD levees about ten years ago by Goulburn Broken Catchment Management Authority on behalf of the Department of Sustainability and Environment.
3 In at least one case the government paid the wages of workers involved through an unemployment scheme
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In addition to the three strategic levee systems mentioned above, a number of levees exist that were built by former government agencies and other authorities such as the River Improvement Trusts, for example the levees on Pental Island, near Swan Hill. They are currently not being maintained by any authority and are also slowly deteriorating. Their length is estimated to be about 300 km.
The levees in this category are regarded as strategic in that they protect rural farm land, isolated dwellings and government infrastructure, and have provided significant reductions in flood damages to adjoining landholders and government infrastructure. In the case of river management activities, levees can also be used to control potentially undesirable river breakaways or realignments.
The issues around these levees include a:
Lack of an authority to maintain, either because no consideration was given originally to this need, or because the agency or authority originally responsible no longer exists;
Lack of funding to maintain;
The level of protection is not defined; and
There are legal impediments to allowing individuals to construct works on public land.
Private rural levees
These have been privately funded and constructed, either by an individual seeking to protect his property, or a group of landowners.
Most private levees were constructed in an era where no planning controls restricting development were in place. Consequently there are many levee systems built close to the natural banks of rivers, or along the boundary of public and private land4, including:
Murray River from Torrumbarry to Koondrook;
Murray River, Little Murray River and Loddon River upstream of Swan Hill;
King, Ovens and Kiewa River valleys; and
Murray River, near the Barmah Forest.
It is estimated that about 80 per cent of rural levees have been constructed privately by landowners and believed to be are located on private land or along the boundary of private and public land.
Where private levees link with adjoining levees, they are considered to be strategic, in that they provide some degree of protection to significant areas of land. The beneficiaries include adjoining landowners and public infrastructure (e.g. roads, channels, bridges, railway lines).
The private levees have all been constructed to varying standards and with little regard to a standard of protection. Their failure levels are generally unknown. Landowners generally do not undertake maintenance on a regular basis and as a result, the standard of protection declines over time.
Although it would be desirable for an authority such as a catchment management authority or council to have records of heights and conditions of existing private levees, the cost of obtaining this information would be prohibitive. As such, there is no scope for management to be by anybody other than the landowners themselves upon which land the levees are situated.
While the “beneficiaries pay” principle and the fact that they are private levees would appear to absolve government from a requirement to get involved, there are some significant issues, such as:
If privately constructed levee systems are located partially on public land and are strategic in nature there are difficulties in allowing individuals to maintain their section of levee;
4 Because there were no development controls landowners may have built levees on “the other side of the fence.” Title searches would be required to establish which parts of the levee systems are on private land and which parts are on public land.
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Because private levees have been around for many decades there will be an expectation from some that the government should maintain them, particularly if the levees are partially located on public land;
While landowners can maintain levees on their land they are not responsible for maintaining levees on adjoining land. This can be a problem if absentee landowners are involved;
The level of protection is not defined;
Landowners may not have the funding to maintain their levees; or
Increasing the height of levees may lead to changed flooding problems elsewhere.
Management responsibility for levees is the single most important issue when it comes to developing a policy for managing rural levees. Currently most levees do not have an authority taking responsibility and undertaking maintenance. As a result, the levees are prone to failure and their standard of protection is diminishing with time.
Planning schemes provide a basis for controlling levees on private land. Generally old levees may be strengthened but not raised, and new levees will only be permitted to protect farmhouses and outbuildings.
Planning schemes do not provide a good mechanism for maintaining levees on public land. Any authority or collective given responsibility for maintaining levees will need to have:
A mechanism for funding to bring the levee up to an agreed and acceptable standard;
A mechanism for funding regular maintenance; and
A process to resolve any liability issues should the levees fail.
From time to time there have been proposals to develop principles to guide the management of levees, such as:
A process for identifying and prioritising how levee systems can be managed (e.g. landowner responsibility, collective responsibility, an accountable authority);
Audit of their condition case by case;
Risk based assessment of estimates and options for bringing up to a reasonable standard;
Benefits and costs of these options and recommended options;
Appraisal of who the beneficiaries are; and
Cost‐sharing arrangements – how much Government will contribute (for the wider public good) vs beneficiaries pay.
However, there has not been universal support from the beneficiaries of rural levees for those principles outlined above.
Management options include:
(a) Management by catchment management authorities
As catchment management authorities have responsibility for floodplain management, they would appear to be the appropriate body to manage strategic levee systems. For example one of their functions under section 202 of the Water Act is to develop and implement plans and to take any action necessary to minimise flooding and flood damage.
However, legal advice given to the catchment management authorities indicates that once they assume responsibility, they would be required legally to maintain the assets and not allow them to deteriorate.
For catchment management authorities to manage these assets guaranteed funding for operational and capital expenses would be required to:
Bring levees up to an acceptable standard;
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Enable assets to the maintained to the agreed standard; and
Allow for eventual replacement of the asset, particularly if it can be better located (e.g. at the edge of a forest rather than along the natural bank of the river).
(b) Management by regional water corporations
Regional water corporations do not rate landowners in irrigation districts and would need to be given the power to charge rates. It is considered that they would be able to source the technical ability to undertake both capital and maintenance aspects of levee management. Assuming that they could rate benefiting landowners, their business would need to expand beyond irrigation, drainage and salinity mitigation activities. It is considered that they would be very reluctant to take on any levee management roles as these are part of floodplain management rather than their core business activities of water storage, treatment and delivery. It is likely that some legislative changes would also be necessary, if this option is pursued.
The capital funding to bring the levees up to an acceptable standard would also be an issue with Government funding the only viable option if regional water corporations are able to be adequately resourced for these additional activities.
(c) Management by local government authorities
Local government authorities currently build and maintain urban levees and therefore have suitable processes for undertaking levee upgrades, maintaining the levees through rating. However municipal councils are unlikely to accept any additional responsibilities given the potential drain in resources. They are also unlikely to afford the capital cost of upgrades and they would need to source the technical ability to upgrade levees. As indicated previously an audit of these levees some 10 years ago found a number of design level and maintenance issues for several of these levee systems and hence councils’ levels of management are quite varied.
Liability Issues The issue of legal liability has been one of the single greatest causes of concern to authorities when considering taking responsibilities for rural levee management. Although private levees can be managed through planning controls, as indicated previously, the management of privately constructed levees on public land, or levees with a history of being funded or supported by government, cannot be easily managed.
Well designed, constructed and maintained levees can only provide protection up to a design level. Once this level is exceeded, the levee can overtop and/or fail through structural weaknesses.
Responsibility may also extend to management of levees where the levee is of a low standard with unknown construction methods. For such levees the chance of failure increases, due to a lack of maintenance, use of poor quality material, deficiencies in design cross section, poor construction, etc. Structural failure through weaknesses in the bank is more likely to occur before the levee overtops.
As such, authorities are concerned that taking on management of levees on public or private land, particularly those that have not been maintained for many years, could expose them to a claim for litigation in the event of a levee failure.
Policy options have not been developed for resolving the liability issues. However possible options could be some form of legal indemnity through legislation or a legal process that enables an authority to undertake activities on behalf of government without transferring liability to that authority.
Levee liability issues were recognised by the former Department of Natural Resources and Environment (DNRE) as part of the Floodplain Management Reform Program from 1997 to 2000. A
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series of principles were developed by the then Department of Natural Resources and Environment as follows:
“Public Good” Authorities should not be exposed to high levels of potential legal damages when they are acting reasonably and responsibly in the public interest.
Managers of public levees should not be exposed to liability when flood levels exceed the standard of service (e.g. By overtopping or failure), or when ‘inherited levees’ of poor standard fail because of flooding.
Authorities must have powers to construct and maintain levees.
Authorities must have powers to control the location and standard to which public levees are built and maintained.
Authorities must have powers to control the location and height of private levees.
Individuals should have rights of redress if Authorities act unreasonably or negligently in relation to levee management.
Q13 In Victoria levees have been built by communities as part of emergency response. Who is responsible for ownership and maintenance of these levees after the emergency? What policy options are available to government in dealing with unauthorised levees, and what are the benefits and disadvantages of each policy option? Levees were constructed at a number of locations by communities as part of the emergency response. Some are still in existence and others have been removed. They were also constructed on a variety of ownership tenures but were not constructed to any design standard. Some were also constructed by communities without any authorisation by councils or emergency response agencies. As such, there are concerns on potential failure during the next flood, the possible impacts on nearby properties and the fact that there is no authority or agency responsible for ownership or maintenance. Options exist to determine the location of these levees and for councils to investigate whether such levees should be formalised. The process could involve:
A flood study to determine flood heights and levels with and without the levee
Development of a floodplain management plan with community input to determine appropriate levels of protection and impacts
Agreement of council to be responsible for construction and ongoing management
Determining funding for the project
Land acquisition to give council ownership
Rebuilding of the levee to appropriate standards including fencing, road crossings, drainage structures etc.
Consideration of an alternative to a permanent structure, such as temporary levees, together with a process to authorise its construction during emergencies and removal after the event.
While the Victorian Government does not have powers to remove unauthorised levees, councils could use powers under the Planning and Environment Act 1987 (Vic) to remove the works. However, each case would need to be treated on its merits so responses would differ for each case. As such, benefits and disadvantages would need to be assessed on a case by case basis.
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Q15 In your briefing to the Committee you mentioned that in about 10 of the 82 towns affected by flood, the capacity of the channel through the town has exercised interest and comment. Moreover, some evidence has been collected regarding the capacity of the channel at Creswick and the view that ‘a lot of these channels were choked with weeds and vegetation’. What evidence can be provided to the Committee regarding the capacity of the channel at Creswick and other towns affected by the recent floods?
The flood events that occurred between September 2010 and March 2011 affected a total of 172 towns or named localities in Victoria. Of these, 24 towns or localities were flooded more than once. Community members, in several towns, were adamant that, if the channel through the town had been cleared of vegetation and blockages before the floods, then their properties and the towns more generally, would not have been flooded. At the very least, the communities of many towns consider choked streams as a major factor in the flooding. Blocked streams were considered to be a particular concern in the towns of Creswick, Skipton, Beaufort, Clunes, Horsham, and Carisbrook. Through the last decade of drought, channels through many Victorian towns have been neglected such that they have become choked with vegetation, debris and weeds. The channel through Creswick was choked with willows and ash trees, as well as blackberries. It is understandable that people would blame a very visible issue, such as channel blockage, for the severity of flooding. However, channel capacity is likely to have had a negligible impact on the height, or extent, of major floods in Victorian rural towns. This conclusion is based on studies that are currently being reviewed and will be provided to the Environment and Natural Resources Committee in September. This conclusion is also based on hydraulic studies that have now been completed on the flooding in the town of Creswick, and this provides a typical example that should hold true for most flooded towns (refer attachment 1, Creswick Case Study below). The condition of the stream channel can have an effect on the height and extent of small, frequent floods (below the five year flood). However, the condition of the channel has a negligible effect on the height and extent of flooding in Victorian towns during major, rare floods such as those that occurred in 2010 and 2011. Hydraulic modelling of the 2010 and 2011 floods in Creswick, indicates that clearing the vegetation and blockages from the channel through the town would have reduced the height of the flood waters by about 15 cm (refer attachment 1, Creswick Case Study). This decrease in flood level would not have altered the extent of flooding (i.e. the number of houses flooded). Since February 2011, the channel through Creswick has been cleared of vegetation and physically increased in width. The hydraulic model suggests that these works will have increased the channel capacity by about 20 per cent (which is 10‐15 m3/s ‐ the previous channel capacity was 40 to 50 m3/s). This increase in capacity would have reduced overbank water levels in Creswick (between Water Street and Clunes Road) by an average of 200 mm (a maximum of 300 mm). The effect of clearing the channel would have had no appreciable effect on the lateral extent of flooding, and on the duration of flooding (that is the length of time that the flood was peaking). In large floods, the effect of channel conveyance is likely to be overwhelmed by larger hydraulic controls downstream, such as bridges and culverts. In Creswick, the major hydraulic control on flooding was the capacity of culverts under the major bridges, which were too small to pass the flood flows (refer attachment 1: Creswick Case Study).
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Thus, while maintaining clear channels through towns maybe desirable, and it will reduce the severity of smaller floods. This is particularly true for weed species. However, in some specific cases clearing of vegetation should not be seen as having a major impact on the height, velocity, or duration of major floods. Channel condition is just one part of a larger flood management plan. In addition, over zealous clearing of streams through towns can have negative effects that need to be considered. These include:
Increasing flood peaks in downstream towns;
Allowing flood debris to move more easily through the town and pile up on bridges;
Increased erosion of banks, and around structures, such as bridges;
Reduced aesthetics (bare channels are less attractive for urban communities); and
Environmental effects (including reduced fish passage, and damage to local values).
Q14 Who has responsibility for the flood mitigation aspects of waterways management in Victoria? Responsibility for flood mitigation in Victoria is shared between local government authorities and catchment management authorities (including Melbourne Water). However, whilst these organisations are empowered to manage channels for flood mitigation, they do so to the extent provided by funding and priorities. Local government authorities are accountable for street and property drainage issues under the Local Government Act 1989 (Vic). While under Part 10 of the Water Act 1989 (Vic), catchment management authorities have waterway, regional drainage and floodplain functions that are relevant to flooding. Relevant flood mitigation functions of catchment management authorities are set out in the Water Act 1989 (Vic) and include that:
With regards designated waterways, they can ‘develop and implement effectively schemes for the use, protection and enhancement of land and waterways’ at section 189(1)(b);
They are empowered to ‘provide, operate and protect drainage systems, including the drainage of water into all designated waterways and all designated land’ at section 199(1)(a); and
Under their floodplain management function they can ‘develop and implement plans and take any action necessary to minimise flooding and flood damage’ at section 202(1)(e).
Importantly, the Water Act 1989 (Vic) section 124(5) also states that ‘[a]n Authority is not obliged to perform any function conferred by the Act, unless this Act expressly provides otherwise’. This means that while a catchment management authority is empowered to carry out these functions, they are not obliged to do so. Without a consistent rating base, a catchment management authority is reliant on annual State government grants, which means that their functions depend on funding and annual priorities. Responsibility for managing urban channels for flooding The management of urban channels for flood mitigation is a subset of the process for protecting communities from floods. Therefore, the clearing of urban channels, or other actions, needs to be part of a strategic flood plan that includes land‐use planning controls, combined with strategic flood mitigation works, such as levees, floodways, and channel management. Planning, construction and maintenance of all components of this flood plan needs to be consistent. Elsewhere in this response
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the Department of Sustainability and Environment describes a proposed approach for managing urban levees, and this provides a model for managing urban stream clearing as well. Urban levees are built under a shared program between the commonwealth, the state and local government, as part of a Floodplain Management Plan (which follows a Flood Study). The plan is then approved by the Minister for Water under section 216 of the Water Act 1989 (Vic) as a Water Management Scheme. Funding cannot flow to the plan from the Victorian Government until the plan is approved. For urban levees, approval is dependent on local government taking responsibility for the on‐going maintenance of levees once they have been built with joint funding between Commonwealth, State and Local governments. The same situation should apply for channel maintenance (clearing) works – they would be completed as part of a larger plan, with subsequent maintenance falling to the local council.
The logic for local councils being responsible for the maintenance of urban stream channels for flood protection includes that the:
Local community are the sole beneficiaries (in fact flooding of a downstream town may be made worse by measures to protect a specific town);
Channels need to be managed as a component of an overall flood plan for the town, and this plan is the responsibility of the Council; and
Councils already manage stormwater and drainage systems, such as culverts, rock work, and pipes in towns. These urban stormwater drainage systems flow into urban stream channels and can contribute to local flooding worse. It is logical that these are managed as part of the plan, which includes managing the receiving channel.
In some cases the local government authority and catchment management authority have a Memorandum of Understanding describing responsibilities around channels through towns. A good example is that between the City of Wangaratta and the North East Catchment Management Authority which describes the management of One Mile Creek through Wangaratta. Other permits required for channel management works If councils, or any agency, want to clear a channel or do any works on a channel, they require some permits to do so. Under the Water Act 1989 (Vic) they are required to apply to the relevant catchment management authority for a Works on Waterways Permit. In issuing this permit the catchment management authority considers the environmental values of the channel, as well as any up or downstream impacts of the works. For example, pools in the channel might provide habitat for an endangered fish, or provide passage for a fish into the upstream reaches. Similarly, increasing flood peaks from the town could have impacts on other communities downstream, or impacts on erosion rates. During the recent floods there were complaints that local councils had not cleared channels of weeds and blockages because of delays in granting such permits. Permits are also required from the Department of Sustainability and Environment under the Fauna and Flora Guarantee Act 1988 (Vic), and as part of the Native Vegetation Framework. There is also the potential for a permit to be required from the Commonwealth under the Environment Protection and Biodiversity Conservation Act 1999 (Cth) if endangered species are involved. Roles after flood emergencies The management of urban channels after a flood emergency differs from the flood mitigation process described above, which applies prior to an emergency. During an emergency, i.e. during or immediately after a flood, the catchment management authority and local government authority, under the direction of emergency services work together to clear debris from streams, and immediately make the town safe in case there is a second, or subsequent flood peak. Asset owners
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(such as VicRoads or VicRail) will also be involved. Such emergency works might involve clearing of stream channels. For example, the channel through Creswick was cleared by the Hepburn Shire Council soon after the January 2011 floods, using money provided to the North Central CMA from the State Government. While a catchment management authority might contribute to this work during, or immediately subsequent to an emergency this does not make them responsible for their on‐going maintenance. As discussed above, such maintenance is clearly the responsibility of the relevant local government authority and needs to be supported by the beneficiaries, the rate‐payers.
Q16 You mentioned in your briefing that DSE is putting together ‘a few reviews’ regarding the revegetation of waterways and their impact on flooding. What is the scope and objective of these reviews? Who is undertaking these reviews, and when are these reviews expected to be complete? Flood Studies The most informative studies for the Environment and Natural Resources Committee to consider are the Flood Studies being undertaken by the Department of Sustainability and Environment, catchment management authorities and local government authorities across Victoria. The Victorian Government has committed to completing studies that lead to increased protection of 25 Victorian communities from flooding. Each of these studies begins with a hydraulic study that will identify the factors that caused flooding in each affected town. This includes the role of the stream channel in flood mitigation (i.e. flood levels, velocities and how long the flooding lasts). Each study will also explore various scenarios, including the relative effect of vegetated and cleared channels. These studies are expected to takes about six months each to complete. The Creswick Study is progressing well, with the hydraulic model completed (refer attachment 1, Creswick Case Study). Two further studies, for Clunes and Charlton, have also gone out to tender, with several other studies to be commissioned in coming months. It is likely that at least six of these studies will be available for the Environment and Natural Resources Committee to consider before its final report is due in May 2012. These studies will allow the Environment and Natural Resources Committee to determine if the results from the Creswick study are typical of the situation in other flood affected towns. Other Relevant Studies Three further studies have been commissioned by the Department of Sustainability and Environment and the catchment management authorities around issues of flood conveyance. These include a
1. A small study to summarise the effect of in‐stream vegetation on flooding. The study was carried out by Associate Professor Andrew Western at the University of Melbourne. This study considered the local effect of vegetation on flooding, but also the catchment scale effect (i.e. the role of vegetation in slowing down flood waves throughout whole stream systems). This report was completed and provided to ENRC.
2. A larger study reviewing the effect of channel revegetation programs on erosion and other damage to streams. This examined whether streams that have had large‐scale revegetation programs along their banks suffer less erosion, and hence less damage to infrastructure and communities. It examined historical floods, such as the 1998 flood in Gippsland, as well as the 2010 and 2011 floods. This study was completed by Alluvium Consulting.
3. A study of erosion patterns in the September 2010 floods in north‐east Victoria. This project was funded by the North East Catchment Management Authority and included consideration of the management of willows. While some communities complain that willows that choke streams have not been cleared and cause more flooding, other communities equally argue that
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where willows have been removed that stream banks are vulnerable to erosion. The report is now complete.
Q17 To what degree are community views taken into account regarding waterways clearing and maintenance? Stream channel capacity (flood conveyance) is always a component of flood studies and the resulting floodplain management plans that are produced. The community has opportunities to consider channel clearing and maintenance within the process for the development of the relevant Flood Study and Flood Management Plans through the:
1. Flood Study, which is completed by the relevant catchment management authority and local government authority;
2. Recommendations of the Flood Study, which are provided in a Floodplain Management Study. The community is heavily involved in reviewing these recommendations with:
a. Questionnaires to all affected members of the community; b. Community meetings; and c. Meetings with individual landholders.
3. Community consultations into the full range of flood options. Community views on channel capacity are provided at this time, in the context of the Flood Study’s finding as to the hydraulics of the channel provided; and finally through the
4. Recommendations of the Floodplain Management Study, which are incorporated into the final Flood Plan for the town or region.
In addition catchments management authorities prepare Waterway Action Plans that describe the detailed plan for managing specific stream reaches. The community is heavily involved in developing these plans, with the clearing of streams considered and discussed with communities. Up to the mid‐1980s, stream managers in Victoria (predominantly River Improvement Trusts) would clear fallen timber from streams across the state in a practice known as desnagging. This practice fell out of favour as evidence mounted of the:
Critical importance of large wood in the biology of Australian streams:
Modest flood benefits produced for the large cost: and
Increased erosion caused by the increased local flow velocities. Some members of the community remember the stream clearing (desnagging) work of the River Improvement Trusts up to the 1980s, and expect government to continue to clear wood from streams. Thus, every year here are a small, but consistent, number of calls to catchment management authorities to clear stream channels for flood conveyance purposes. Where the requests relate to situations where bridges, or willows, are blocking streams, the catchment management authority will usually respond positively. Such requests do not mean that the catchment management authority will actually pay for such works, as this depends on its priorities at the time and place. However, the catchment management authority would typically provide a works on waterway permit to allow the relevant Councils or individual landholders to manage the problem locally. In some cases landholders will simply not accept the catchment management authority view that large wood has only a modest impact on flood levels. The Loddon River provides an example of this debate. During the drought the channel of the Loddon River dried out and many thousands of river red gum seedlings germinated in the bed of the channel, and began to grow, and choke the channel. Over 80 kilometres of the channel was affected.
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Landholders along the river complained to the North Central Catchment Management Authority (NCCMA) that these blockages would cause flooding, and could cause the river channel to jump into a new course (a process known as ‘break‐aways’). The NCCMA did not remove these saplings as the effect on flooding was assessed to be modest. While the debate was still continuing, the 2010 and 2011 floods occurred. The result was that the blockages had little or no effect on flooding, no break‐aways occurred, and no mention has been made of the issue since.
Q18 Early in the briefing to the Committee you mentioned that ‘they [floods] are predictable over human life spans to a much greater extent that other disasters’, and ‘we can predict the frequency, the level and the extent of flooding often to within millimetres’. Yet later in the briefing you mention that ‘it is actually really hard to predict for a particular town…the size of the flood that is coming, where it is going to get to…what houses are going to be flooded to what depths’. How difficult is it to predict when and where floods will occur? What technology is currently used to assist flood prediction and what can new technology do to improve predictions about flooding in Victoria? The ability to predict when and where flooding occurs varies with the lead time before a flood. This ability reflects the certainty surrounding the prediction of significant rainfall events. As the lead time shortens before a rainfall event, the intensity and location of the predicted rainfall improves. In turn the ability to identify the likelihood and location of significant flooding is refined. The following flood advisory and warning products are currently in use:
Seasonal weather forecasts are prepared and issued by the Bureau of Meteorology on a quarterly basis. These forecasts provide an indication of the likelihood of above or below rainfall, and streamflows for some river basins. These seasonal forecasts provide useful information on the medium term flood likelihood at the state and regional basis.
Severe weather outlooks are prepared and issued by the Bureau of Meteorology on a weekly basis. These outlooks identify severe weather events (i.e. heavy rainfall, high winds etc) at a regional level. The likelihood of flash and riverine flooding is assessed as minor, moderate or major.
A flood watch for a region can be issued by the Bureau of Meteorology, if the predicted rainfall is sufficient to result in flooding. Generally flood watches may be issued 2‐3 days before a significant rainfall event. A flood watch provides general information about likely flooding. The intent of the flood watch is to raise community awareness.
A flood warning for river basin and location is issued by the Bureau of Meteorology once significant rainfall occurs and stream level rises commence, and there is strong likelihood that the river heights at locations will exceed flood warning class levels. The flood warning class levels, minor, moderate and major, reflect flooding consequences at locations or river reaches. The flood warnings include a forecast of the peak flood height and the time of the peak height. During a flood event, the flood warnings are generally updated to reflect the movement of the flood down a river.
The seasonal forecasts, severe weather weekly outlooks, and flood watches use an array of weather prediction computer models. These weather prediction computer models are operated and maintained by the Bureau of Meteorology. The flood warnings use real time streamflow and rainfall data, and computer models to simulate the catchment runoff and flood travel times along rivers.
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At some locations, detailed flood mapping based on hydraulic models has been undertaken by catchment management authorities and local councils, with funding made available through DSE. This flood mapping enables the flood extent, depth and likely consequences for a forecasted peak flood height to be determined. On 2 May 2011, the Minster for Water announced funding for the Floodzoom initiative. Under the Floodzoom initiative, funding has been provided for improvements in real time stream flow and rainfall data collection. These improvements will upgrade the capacity to transmit rainfall and streamflow data via the mobile phone network, satellite, and radio. Also, additional rainfall and streamflow gauges will be installed. Combined together, these improvements will enhance the ability to monitor and predict riverine flooding. The initiative will fund flood mapping studies to increase understanding of flood behaviour and likely consequences. This will add to the number of locations with detailed flood mapping. These flood mapping studies will use computer modelling to simulate the flow of floodwaters. A flood intelligence platform will be developed as part of Floodzoom. The platform will draw together flood predictions and flood mapping to assess community impacts (i.e. properties affected, roads closed, infrastructure inundated etc). The platform will include a web based mapping interface.
Q19 What is the role, condition, location and performance of Victoria’s river gauges? Water monitoring data is collected from the majority of Victoria’s regional river gauges under the Regional Water Monitoring Partnerships for a range of purposes, including flood warning, water allocation and resource assessment. The location of river gauges for flood monitoring under the Regional Water Monitoring Partnerships is decided by the relevant partners requiring the data. A list of the current partnership sites is provided in the appendix to this document. The Bureau of Meteorology is strongly involved in decisions on changes in current river gauge instrumentation and infrastructure to ensure that monitoring information collected for flood warning purposes can be used effectively and efficiently. Monitoring for flood warning across all of Victoria is overseen by the Bureau of Meteorology and is conducted at a total of 585 surface water sites. Some additional sites are used to provide flash flooding information and are operated by other organisations, e.g. City of Greater Geelong, Melbourne Water and Goulburn Murray Water. Of the 585 flood monitoring sites, 283 sites are part of the Regional Water Monitoring Partnerships and are located in regional Victoria. While in metropolitan Melbourne Metropolitan sites are monitored by Melbourne Water outside of the Partnership arrangements. Under Partnership processes the condition of the stream gauges are inspected on a regular basis, currently monthly, by the service providers, to ensure that they continue to provide the requirements specified by the partners. In addition, the Service Provider reports on the work program at quarterly partnership committee meetings, as specified in the Regional Water Monitoring Partnership Agreements.
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During and after the floods many of the gauge stations were damaged and destroyed. This is not unexpected as they need to be located close to or in the river to monitor flows. The January floods in particular severely impacted on Victoria’s flood warning network. Given the unprecedented river levels reached in many of the catchments around 87 surface water monitoring sites sustained some damage, with at least 14 sites requiring full reconstruction. Debris accumulation and erosion at the sites was also severe. Funding has been obtained through the Victorian Government to repair the damage.
Q21 What does the South Eastern Australian Climate Initiative say about the future likelihood and size of flooding in Victoria? Can we please have a copy of their reports that address flooding? The South Eastern Australian Climate Initiative (SEACI) is a partnership between the SCIRO Water for a Healthy Country Flagship, the Bureau of Meteorology, the Murray‐Darling Basin Authority, the Victorian Government’s Department of Sustainability and Environment and the Australian Government’s Department of Climate Change and Energy Efficiency. Phase 1 of SEACI was undertaken in 2006‐2009 with a primary focus on investigating the causes and impacts of climate variability and change across south‐eastern Australia to understand the causes of the recent dry period from 1997 through till 2009 to improve forecasts and projections of climate and water availability. Research under SEACI is now in its second phase, which will conclude in 2012.
Major findings from Phase 1 of SEACI are contained in its report, Climate variability and change in south‐eastern Australia: A synthesis of finding from Phase 1 of the south Eastern Australian Climate Initiative. However, the major findings are focussed on seasonal, interannual, and multi‐decadal timeframes rather than two hour to three day rain events associated with floods.
Nevertheless the report does note that in extreme rainfall events ‘research suggests that short‐duration events may become more intense across the (south‐eastern Australian) region in the future, especially the inland plains’.5 SEACI further notes that ‘although the average rainfall and streamflow in south‐eastern Australia are projected to decline, extreme rainfall events are likely to be more intense because warmer temperatures will provide stronger convection and increased capacity for moisture to be held in the air. These higher‐intensity storms will increase flood risks, cause greater storm and sewer runoff in urban areas, and increase erosion and nutrient delivery to water ways, particularly during high‐runoff events’6.
5 Climate variability and change in south-eastern Australia: A synthesis of finding from Phase 1 of the south Eastern Australian Climate Initiative (CSIRO, 2010), 25. 6 Factsheet 1: The South Eastern Australian Climate Initiative (CSIRO, July 2011), 8.
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Attachment 1: Creswick Case Study ‐ the effect of channel conveyance on flooding in Creswick Creek 2010 and 2011 (Note: the following is information provided to ENRC in August 2011. The study has now been complete and is available on request.) The following analysis of the floods in Creswick has been synthesised from material provided by Water Technology consultants. Water Technology is completing a flood study of the town for the North Central Catchment Management Authority with preliminary results from the hydraulic models presented below. Creswick Creek is the main watercourse flowing through Creswick. It crosses beneath Water Street and then Midland Highway and North Parade before heading north‐west towards Clunes. The catchment area above Creswick is approximately 85 km2. Slaty Creek, Sawpit Gully (also called Spring Gully) and Nuggetty Gully are major tributaries of Creswick Creek. The two dams upstream of Creswick along Creswick Creek are Cosgrave Reservoir and St Georges Lake. Creswick was flooded four times between late 2010 and early 2011, as follows:
September 2010 (Large flood event);
November 2010 (Minor flood event);
January 2011 (Large flood event); and
February 2011 (Moderate flood event – highly localised). The September 2010 and January 2011flood events were significantly larger than the November 2010 and February 2011 events. Both major flood events were a result of heavy rainfall in the upstream catchment, whilst the November and February flood events were due to heavy localised rainfall across the upper reaches of the gullies near town.
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Figure 1: Streams in and around Creswick. With regards the two largest floods in Creswick Creek the:
September 2010 flood had a peak discharge of 93.8 m3/s, which is estimated to have a recurrence interval of 35 years (ARI 1:35); and
January 2011 flood was slightly larger, with a discharge of 100.2 m3/s, with a recurrence interval of 45 years.
In comparison, the 100 year ARI flow in Creswick Creek is estimated to be 355 m3/s. The size of the floods through Creswick was a product of intense rainfall. However, the exact depth and extent of flooding through the town was influenced, to some extent, by factors that affected hydraulics through the town including that the:
Culverts under the Castlemaine and Clunes Road bridges which have a flow capacity through the main bridge structures of approximately 80 m3/s. This capacity was exceeded by the September 2010 and January 2011 floods. The result was that the water level immediately above the bridge was some 0.3m higher than without the bridges;
Creswick Creek, through Creswick, had already been ‘channelised’ (widened and straightened) at sometime in the past, so that it is not a natural channel; and
Channel capacity of Creswick Creek through the town varies, but through the main section of Creswick Creek between Water Street and Clunes Road, the capacity is between 40‐50 m3/s. This means that this artificial channel carried up to half of the flood peak (which is considerably higher proportion than for a natural channel).
The effect of channel condition on flooding in Creswick Two scenarios were run through the hydraulic model to assess the effect of modifying the channel on the larger January flood flows. Variations to assumption in these scenarios included in:
Model 1 – All vegetation removed from the channel between Water Street to D/S of Clunes Road, i.e. through the main section of town. The clearing of vegetation was modelled by reducing Mannings ‘n’ value from 0.05 to 0.03 to account for the removal of bushes/shrubs; and
Model 2 ‐ Channel widened and minor vegetation removed (cross‐section of the creek enlarged, and Manning’s value reduced to 0.035 in the creek) between Water Street to D/S Clunes Road. These changes represent the works that were undertaken in Feb 2011 (i.e. the present state of the channel through Creswick).
The two runs were compared against the January 2011 flood extent and depths (Figure 2), and the results shown as difference plots (Figure 3 and 4). Negative values in the difference plots show decreases in water levels when compared against the January 2011 flood depths. The results show that:
Completely clearing the creek has increased the channel capacity by 10‐15m3/s which would have reduced overbank water levels in Creswick (between Water Street and Clunes Road) by an average of 150mm (a maximum of 300mm);
This decrease in water depth would have had no significant effect on the flood extent (that is the number of properties flooded);
The effect of clearing the channel would have had no appreciable effect on the duration of flooding (that is the length of time that the flood was peaking); and
Both widening the channel, as well as removing most vegetation, (Model 2) has a slightly greater impact on channel capacities than clearing all vegetation, reducing the water levels by approximately 200mm.
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In summary water depths for the recent flood events were not significantly influenced by the vegetation and debris in Creswick Creek. The channel only carries a small portion of the flow in higher events (for the 100 year event it would be just over 10 per cent of the flood). Therefore, clearing the creek will have a minor benefit for flood levels, but the local community should not imagine that clearing the channel will eliminate flooding in Creswick. Management of the channel needs to be one part of an integrated flood management and mitigation strategy.
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Figure 2: Creswick, January 2011 Flood Extent
Span of clearing and alignment works in Creswick
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Figure 3: Difference Plot ‐ Effect of Creek Clearing (Vegetation Removed minus Jan 2011) (Difference shows the reduction in flood depth with all vegetation cleared).
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Figure 4: Difference Plot ‐ Effect of channel widening and clearing (Channel Works minus Jan 2011) (Difference shows the decrease in flood depth produced by the widening and clearing of the channel carried out in February 2011).