APPENDIX 1 Floodplain Management Strategies & Guidelines

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1 APPENDIX 1 Floodplain Management Strategies & Guidelines A. Port Phillip Flood Management Plan (2012) B. Draft Flood Management Strategy Port Phillip and Westernport (2015) C. Revised Draft Victorian Floodplain Management Strategy (2015) D. Principles for Provision of Waterway and Drainage Services for Urban Growth (2007)

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3 Flood Management Plan For City of Port Phillip and Melbourne Water March 2012

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5 Table of contents Approval 1 1 Executive Summary 2 2 Background 4 3 Purpose 5 4 Objectives 6 5 Scope 7 6 The Municipalities Waterways and Drainage System The City of Port Phillip Waterways and Drainage Networks Flood History and Issues Flood Data, Information and Intelligence The Existing Knowledge Base 13 7 Flood Risk The Tolerability of Existing Flood Risk Existing Flood Risks within the Municipality Future Flood Risks Medium to Long-Term Pressures on the Drainage System 17 8 Flood Management and Mitigation Drainage Strategy Flood Modelling and Mapping completing the knowledge base Asset Management Planning Controls Capital Works Flood Emergency Response Planning Community Education and Awareness Flood Warning System Flood Proofing Drainage studies and guidelines 31 9 Roles and Responsibilities Improvement Plan Monitoring and Review How this document was developed Acknowledgements 51 ABBREVIATIONS & ACRONYMS 52 REFERENCES 53 APPENDIX A ROLES AND RESPONSIBILITIES 55 APPENDIX B - FLOOD RISK ASSESSMENT 58 APPENDIX C DATA, DRAINAGE SYSTEM UPGRADES & STUDIES 62 APPENDIX D FLOOD HOT SPOTS LIST AND MAP 73 Flood Management Plan for City of Port Phillip & Melbourne Water i

6 Approval This plan has been developed by the City of Port Phillip and Melbourne Water in consultation with the Victoria State Emergency Service. The plan will continually evolve as improved information becomes available to help manage flood risks across the Port Phillip municipality. As lead stakeholders for managing flood risks across the region, Melbourne Water and City of Port Phillip will endeavour to implement the recommendations made in this plan and also to review and update it as required on annual basis. Flood Management Plan for City of Port Phillip and Melbourne Water 1

7 1 Executive Summary The Flood Management Plan (FMP) has been developed in partnership between the City of Port Phillip and Melbourne Water as part of a joint focus on managing existing, residual and future flood risks within the City of Port Phillip. The genesis for that focus is provided in Melbourne Water s Port Phillip and Westernport Region Flood Management and Drainage Strategy (2007). Approximately 35% of the City of Port Phillip is three metres or less above sea level and the terrain is relatively flat. Flooding issues that have occurred within the City of Port Phillip include floods caused by high tides, floods due to pipe blockages and floods associated with intense rainfall events. The Flood Management Plan details the flood risks within the City of Port Phillip, particularly identifying any areas previously flood mapped, known hot spot or problem areas. Within its 20 km 2 municipality, Council has calculated that its flood zone affects 300 properties over an area of 38 Ha and the Special Building Overlay (SBO) impacts on 1,583 properties over 690 Ha. Additionally, modelling undertaken by Melbourne Water has identified approximately 9,052 properties within the City of Port Phillip that are affected by flooding from the catchment. Of these properties, 7,588 are considered to be at extreme risk; 636 are high risk; and 828 are medium risk. Areas and known hot spots of most concern within the municipality are the Elwood Canal (including Elster Creek extending to Koornang, Caulfield and Moorabbin) and Shakespeare Grove Main Drain. The Flood Management Plan details the potential impacts on flood risk from climate change within the City of Port Phillip. The predicted change in rainfall patterns within the Port Phillip and Westernport area is likely to lead to more frequent flash flooding and overland flow events associated with localised storm activity. At the same time, sea levels are expected to rise resulting in additional flooding pressures within the City of Port Phillip. Even a smaller sea level rise of 10 to 20 cm, which may occur over the medium term (i.e to 2045), is likely to impact on the drainage system within the City of Port Philip. The Flood Management Plan outlines roles and responsibilities and describes, at a high level, Council s and Melbourne Water s key flood management planning and management activities. There are a number of flood issues and knowledge gaps that have been identified in the Flood Management Plan that need to be addressed within the City of Port Phillip in order to effectively manage flood risks. These include a need for additional drainage asset information, flood modelling and mapping that does not take into account climate change impacts, need for more information to be made available to the community on flood risks and preparedness, need for major flood and emergency planning and flood management responses to climate change. An Improvement Plan has been developed which identifies the actions required to address the key issues and knowledge gaps identified in the Flood Management Plan. Actions include:

8 Development of a high level flood management framework or policy to communicate how the flood and climate change related Plans fit together Improvements to drainage asset management planning and information Ongoing communication networks to better share knowledge Investigate opportunities to mitigate extreme flood risks A more holistic approach to flood modelling and mapping Continue to understand climate change impacts on flood risk and effective drainage, with consideration of urban consolidation, sea level changes, tide levels, and potential changes to rainfall intensities Update and maintain planning scheme overlays to help prevent inappropriate development in flood prone areas Management of underground car parks Flood community education Flood emergency planning The Improvement Plan is detailed in Section 10 (page 35). The City of Port Phillip, Melbourne Water, VICSES and other flood management stakeholders have recognised the need for an integrated and sustainable approach where responsibility for activities is assigned on the capability of the agency to deliver. While key agencies can demonstrate the provision of specialised flood management skills in the planning for, response to and recovery from flooding there are opportunities to strengthen regional flood management arrangements through greater collaboration and more efficient use of resources. The Plan was developed by City of Port Phillip and Melbourne Water staff who worked in collaboration, with input from other agencies (particularly VICSES) through a series of interviews, file reviews, meetings, site visits and workshops, to gather the background information, identify flood risk management and mitigation activities, and arrangements, undertake a gap analysis and develop an improvement plan. This document was developed by the people listed in Section 12 (page 47), which includes workshop attendees and other contributors. The collaborative development of this Flood Management Plan and the Flood Response Plan for Port Phillip provides a basis for improved coordination and collaboration involving both technical and financial contribution in the future. Flood Management Plan for City of Port Phillip and Melbourne Water 3

9 2 Background This Flood Management Plan has been prepared in partnership between the City of Port Phillip and Melbourne Water as part of a joint focus on managing existing, residual and future flood risks within the City of Port Phillip. The genesis for that focus is provided in Melbourne Water s Port Phillip and Westernport Region Flood Management and Drainage Strategy (2007). The Port Phillip and Westernport Region Flood Management and Drainage Strategy (Melbourne Water, 2007), prepared by Melbourne Water in consultation with government departments, councils, emergency service organisations and other agencies, recognises that no single organisation and no single approach can deliver an effective response to flood management issues. A coordinated and collaborative approach by flood managers and communities is required. The five key objectives of the Strategy are: Objective 1: Completing the knowledge base (flood mapping and understanding social impacts) Objective 2: Potential long term future pressures on existing drainage systems (development in established areas and climate change) Objective 3: An agreed approach to managing existing regional flood problems (understanding intolerable flood risks) Objective 4: Enhanced community education, flood awareness and preparation Objective 5: Agreed responsibilities and improved collaboration between flood management agencies (integrated framework and flood management plans) One of the key outcomes from the strategy is the commitment from Melbourne Water to work with each Municipality within the region to produce a detailed local Flood Management Plan. This document represents the delivery on that commitment for the City of Port Phillip. 4 Flood Management Plan for City of Port Phillip and Melbourne Water

10 3 Purpose The Purpose of the Plan is to: Assist the City of Port Phillip and Melbourne Water to undertake their flood management responsibilities and ensure that suitable measures have been (or are being) implemented where possible to manage the existing and future risks associated with flooding. Ensure the objectives of the Port Phillip and Westernport Region Flood Management and Drainage Strategy can be effectively implemented in the City of Port Phillip in a coordinated and effective manner at a local level, within an integrated flood management framework. Assist the City of Port Phillip address their climate change concerns and commitments to future flood management and drainage effectiveness through linkage with the City of Port Phillip s Climate Adaptation Plan - Climate Adept City. Fostering preparedness for flood events and enhancing the ability to respond to floods in an informed and appropriate manner within the City of Port Phillip and its communities. While the Plan has due regard for current flood related legislation and supporting policies and strategies, it recognises that no single organisation and no single approach can deliver an effective response to flood management issues. It also recognises that it is not possible to make the City of Port Phillip completely free from flooding. A residual flood risk will remain that needs to be managed. Flood Management Plan for City of Port Phillip and Melbourne Water 5

11 4 Objectives The objectives in developing and maintaining this Flood Management Plan are to: Ensure that drainage and flood management matters within the Municipality are effectively managed and coordinated through flood management agency collaboration and partnership; Facilitate coordination and cooperation in the implementation of the five key objectives outlined by Melbourne Water (2007) with particular attention to existing flood risks; Promote improved collaboration between councils, Melbourne Water and SES Victoria; Understand flood risks and identify extreme/intolerable flood risks and hot spot areas; Identify gaps and improvement actions that are needed to address these risks and better prepare for and manage floods; Clarify the roles and responsibilities of stakeholders in addressing existing flood risks; and Continuously review drainage design and effectiveness needs with regard to future projected flooding impacts from a changing climate (including coastal inundation). 6 Flood Management Plan for City of Port Phillip and Melbourne Water

12 5 Scope While management of and preparedness for floods arising from waterways and drainage systems involves many different agencies, this plan is largely aimed at outlining the key activities, roles and responsibilities for Melbourne Water, the City of Port Phillip and the Victorian SES within a total system framework that recognises their joint responsibility for the management and ownership of the drainage system. Flood Management Plan for City of Port Phillip and Melbourne Water 7

13 6 The Municipalities Waterways and Drainage System 6.1 The City of Port Phillip The City of Port Phillip lies on the northern edge of Port Phillip Bay, to the south of the Melbourne central business district. It is approximately 20 km 2 in area with 11 km of foreshore and it has a population of 85,000. Approximately 35% of the Municipality is three metres or less above sea level and the terrain is relatively flat. The following figure shows the extents of the City of Port Phillip and the suburbs in the Municipality. The City of Port Phillip is bordered by the Cities of Glen Eira, Melbourne, Stonnington and Bayside. Figure City of Port Phillip Municipality The predominant land use is residential with a high proportion of flats and high rise accommodation. However, there are significant pockets of light and medium industry, notably in South Melbourne and Port Melbourne. The area has been extensively developed which reflects its location as an inner suburb of Melbourne. There are also areas of commercial offices, particularly along St Kilda Road and Queens Road. Albert Park Lake and the surrounding park land is also located in the municipality. 8 Flood Management Plan for City of Port Phillip and Melbourne Water

14 6.2 Waterways and Drainage Networks The City of Port Phillip drainage infrastructure was largely installed in the late 1800 s to the mid 1900 s, to standards and requirements applicable at the time. Since the installation of the drainage system the City of Port Phillip has seen intense development and in many situations the existing drainage does not cater for the requirements of today or meet today s design standards. The residential, industrial and commercial areas mainly consist of a piped drainage network (250 km) or concrete channel (2km) that conveys the stormwater to Port Phillip Bay or the Yarra River. The location and details of each drain and associated infrastructure are available on Geographic Information Systems (GIS) at the City of Port Phillip or at Melbourne Water. Melbourne Water is responsible for the installation and maintenance of drainage systems, including drain capacity and flood mitigation works, for catchments greater than 60ha 1. There are numerous pits and pipes along arterial roads and highways that are the responsibility of VicRoads. The Code of Practice for Operational Responsibility for Public Roads outlines how these drains are identified. On the next page is a map of the City of Port Phillip showing the main drains and the 100 year Average Recurrence Interval (ARI) (i.e. 1% Annual Exceedence Probability) flood extent for rivers and underground drains 2. The City of Port Phillip has surveyed and mapped all of its drains in three separate projects between 1998 and This survey information was input to Council s GIS system. These drainage maps contain some errors and omissions and ongoing work is required to improve their accuracy. 1 Melbourne Water is also responsible for managing Melbourne s waterways. 2 Map shows flood extent for Melbourne Water assets only. Flood extent does not reflect council owned drains or assets. Flood Management Plan for City of Port Phillip and Melbourne Water 9

15 Figure 6-2 Map of the City of Port Phillip showing the main drains and the 100 year ARI flood extent for rivers and underground drains 10 Flood Management Plan for City of Port Phillip and Melbourne Water

16 6.3 Flood History and Issues There have been three different types of flood issues that have occurred in the catchment that the City of Port Phillip and Melbourne Water have needed to manage: A. Flooding caused by high tides reducing the capacity of the stormwater drains to discharge runoff into Port Phillip Bay (for examples see Figure 6.3). B. Flooding due to pipe blockages from tree roots, sand, seaweed, tidal sand movement, debris on grates, runoff unable to get into pipes, broken pipes, etc (for examples see Figure 6.4). C. Flooding associated with intense rainfall events, which creates runoff greater than the capacity of the existing drain network (for examples see Figure 6.4). The frequency and consequences of these types of flooding has and will continue to vary. Typically the more severe flooding has occurred less often, but has had greater consequences, including causing flood damage and creating hazards. More frequent events have also caused damage and created hazards. However, more often more frequent events have resulted in nuisances such as water in streets. The recent flood history in the City of Port Phillip has been documented in two ways: 1. The City of Port Phillip maintains a customer service register which includes information reported to Council regarding drainage and flooding problems. The City of Port Phillip has produced maps showing the reported locations of drainage problems and flooding for the year s 2003 to 2010 inclusive (see Appendix D). 2. Council has a contractor that has maintained their drainage infrastructure since the year 2000 and responds to drainage issues and reported flooding with actions including traffic management and clearing of drain blockages, as well as regular maintenance. The locations where drainage / flooding problems are known to occur have been documented for this project as Flood Hot Spots. See Appendix D for a table and map of the flooding and drainage hotspots that have developed from opinions expressed at a workshop (Workshop #1, 17th May 2010) and a meeting held with the City of Port Phillip maintenance crew (4th June 2010). Flood Management Plan for City of Port Phillip and Melbourne Water 11

17 Marine Parade outfall submerged Barkly Meredith East Elwood Canal at Marine Parade Marine Parade (pit full) Elwood Canal at Marine Parade Elwood foreshore Figure 6.3 Flooding caused by high tides reducing the capacity of the stormwater drains to discharge runoff into Port Phillip Bay Main Drain Lynott Street east Wright Street north-side between Page & Richardson Streets Victoria Street on corner with Richardson Street Page Street at Kerferd Road north-west corner inlet McGregor Street between Canterbury & Richardson Streets Blessington Street Outfall B Figure 6.4 Flooding due to pipe blockages and flooding associated with intense rainfall events, which creates runoff greater than the capacity of the existing drain network 12 Flood Management Plan for City of Port Phillip and Melbourne Water

18 6.4 Flood Data, Information and Intelligence The Existing Knowledge Base Overview A summary of the flood related information for the City of Port Phillip catchment has been collated from studies/reports completed by the City of Port Phillip, Melbourne Water and DSE between 1998 and the present. The studies/reports detail hydraulic/hydrology modelling, monitoring data, records of floods, records of drainage/flood complaints, GIS information/plans, planning scheme overlays, council s MEMP (Municipal Emergency Management Plan), survey, cost estimates for implementing of recommendations, prioritised work programs and asset information. From this analysis a table has been developed detailing each report and its available information. The Flood Study Overview table (Appendix C) details the following information: The name of the study completed, the date it was completed and which company completed the works and initiated the works. The purpose and aim of the study. The methodology. The data collated and used. The main assumptions. The area covered. Outcomes and recommendations. A list of project deliverables. Maps available. Missing information. The City of Port Phillip has an extensive record of GIS information. A summary of this information is provided below. See Appendix C for a detailed list of the available data. Council drains and other drainage assets 100 year Average Recurrence Interval (ARI) flood extents for some Council drains. Municipal boundary. Suburbs/town names. Major and minor roads. Contours and digital terrain data Flood Management Plan for City of Port Phillip and Melbourne Water 13

19 Planning scheme maps Aerial photographs Property maps and details Melbourne Water also has a set of data for the City of Port Phillip area which includes: Catchment boundaries. 100 year Average Recurrence Interval (ARI) flood extents for Melbourne Water main drains and waterways Melbourne Water Main Drains and other main drain assets Contours and digital terrain data Waterways. The City of Port Phillip and Melbourne Water share this information with each other for the purposes of understanding drainage and flooding in the municipality and fulfilling their roles in managing drainage, waterways and flooding. Data and Knowledge Gaps There are aspects of the existing data/knowledge that is either not fully up to date, or where gaps in the data have been identified. These include: Asset Management: There is a need for improvement in the quality of information about drainage assets (particularly larger drains in the network (i.e. >600mm) to reflect what is on the ground and plan for asset renewal and form assessments of flood risks. There are some gaps in Council drainage asset information and Council is working on eliminating these gaps. Flood Modelling: Flood mapping was done ten years ago and does not include climate change scenarios. Flood mapping was undertaken using one dimensional hydraulic modelling techniques. Current two dimensional modelling techniques are expected to be better suited to representing flooding patterns in the City of Port Phillip (draft results are being developed for Melbourne Water for the Elwood Canal, Byron Street Main Drain and Shakespeare Grove Main Drain that use two dimensional flood modelling techniques). The Australian Rainfall and Runoff published in 1987 is currently under review, once completed the updated data will be used as required. 14 Flood Management Plan for City of Port Phillip and Melbourne Water

20 Climate change impacts on flood risk including sea level changes and potential changes to rainfall intensities have not been assessed (draft results are being developed for Melbourne Water for the Elwood Canal, Byron Street Main Drain and Shakespeare Grove Main Drain that include consideration of climate change effects). Historic mapping studies would not have considered a full range of ARI events or various tide levels nor urban consolidation. As a result analysis of depth and velocity is not currently possible for a range of ARI events. Planning: There is a need for future planning for flood damages prevention and response to climate change. There is a lack of clear direction within council on what is required in the design of underground car parks to protect them from floods. Community Education: There is a lack of information on flood risks and advice on how to prepare for and respond to floods. This may affect community awareness of the risk and preparedness for flooding. Emergency Planning: Lack of coordination and awareness of flood information will hinder flood mitigation and reduce efficiency of responses. These are described in the Improvement Plan (see Section 10), which describes known gaps and actions to address these gaps. Flood Management Plan for City of Port Phillip and Melbourne Water 15

21 7 Flood Risk 7.1 The Tolerability of Existing Flood Risk Melbourne Water uses a Flood Risk Assessment Framework (Melbourne Water, 2009) to identify and assess flood risks, based on a triple bottom line assessment, considering economic, social and safety factors. The Framework was developed in consultation with metropolitan councils and other stakeholders to provide a more transparent process to help people understand the decision making and flood mitigation prioritisation process. The Flood Risk Assessment Framework classifies flood risks, by catchment, as low, medium, high or extreme. Extreme flood risks are those considered to be intolerable. While flooding is a natural occurrence, in some cases the risks from flooding may be considered intolerable that is, so high that measures should be put in place to reduce the risks. For intolerable risk flooding a range of control measures will be considered with the aim of reducing the risk to a more tolerable level. Measures to be considered will include both engineering works and non-structural approaches. In most cases the risk will be reduced but not removed; a residual risk will remain. The City of Port Phillip has two catchments within its municipality that are identified as having extreme flood risk - Elwood Canal (including Elster Creek extending to Koornang, Caulfield and Moorabbin) and Shakespeare Grove Main Drain. Since catchments and Municipal boundaries do not necessarily coincide, it is possible that matters giving rise to or contributing to flood risk may be outside the Municipal boundary. Under such circumstances, Melbourne Water will ensure that the issue will be recognised and considered within the flood risk prioritisation; particularly in cases where the risk is assessed as being intolerable. 7.2 Existing Flood Risks within the Municipality Modelling undertaken by Melbourne Water to date has identified 9,052 properties within the City of Port Phillip that are affected by flooding from the catchment. Of these properties, 7,588 are considered to be at extreme risk; 636 are high risk; and 828 are medium risk. Within its 20 km 2 municipality, Council has calculated that its flood zone affects 300 properties over an area of 38 Ha and the SBO impacts on 1,583 properties over 690 Ha. The current list of Melbourne Water flood risks, by catchment, within the City of Port Phillip is provided at Appendix B. A map of the flood risk by catchment area, colour-coded by risk level is also shown in Appendix B. 16 Flood Management Plan for City of Port Phillip and Melbourne Water

22 The riverine and/or flash flood risk within the municipality has been assessed as High in the Port Phillip Municipal Emergency Management Plan (MEMP); based on the likely damage to property and environment, and number of people displaced. The MEMP may require review to update the risk assessment, and the identified treatment plans. The development of this Plan has involved identification of flood hot spots or a known flood problem area. A flood hot spot is an area of known flood problems, with a history of repeated flooding of a road crossing or property, often highlighted through anecdotal information or customer complaints. Identified flood hot spots for City of Port Phillip are identified in Appendix D. Typically the Flood Hot Spots relate to locations where flooding occurs on a frequent basis and tend to be localised flooding relating to blockages rather than riverine flash flooding. 7.3 Future Flood Risks Medium to Long-Term Pressures on the Drainage System This section considers the medium to long term pressures on the drainage system from urban development and climate change. Greenfields Development and Urban Expansion The City of Port Phillip is predominantly residential with a high proportion of flats and high rise accommodation. There are also significant pockets of light to medium industry. The area is already densely developed and has practically a zero rate of green fields development and urban expansion. Urban Consolidation and Infill Development Typically urban consolidation increases runoff and can either create drainage problems or exacerbate existing problems. The City of Port Phillip is already densely developed and existing sites have increased in height but not necessarily increased in ground cover. The height of the building adds no further impact to the existing drainage system as the impervious area stays approximately the same. It should be noted there is an increase in the number of under ground car parks in the area. If the underground car parks are constructed in areas with existing street flooding there is potential that overland flow will be directed into the underground car park and cause flooding if the construction does not account for the existing flood risk. This could exacerbate the flood damage and increase flood hazards. Melbourne Water has investigated redevelopment services schemes for Elwood Canal and Shakespeare Grove Catchments. These investigations recommended mitigation options that would be unfeasible or extremely difficult to implement and therefore these schemes have not been implemented by Melbourne Water. Consultation and ongoing discussion with the Flood Management Plan for City of Port Phillip and Melbourne Water 17

23 Council on flood awareness and preparedness, and having flood management plans were thought to be more appropriate and achievable. There are no specific drainage redevelopment schemes in the City of Port Phillip. Council s development engineer reviews specific project proposals and make decisions on drainage requirements on a project by project basis. The City of Port Phillip does have the C13 Port Melbourne development contribution scheme. However, it is not tied to any drainage projects. Climate Change Climate change has the potential to increase flood risk within the Port Phillip and Westernport region and hence the Port Phillip municipality. While the latest predictions are for a long-term reduction in catchment yield (i.e. a reduction in runoff volumes) it is likely that the intensity of extreme rainfall events will increase. The change in rainfall patterns is likely to lead more frequent flash flooding and overland flow events associated with localised storm activity. At the same time, sea levels are expected to rise resulting in additional flooding pressures within the City of Port Phillip. Even a smaller sea level rise, which may occur over the medium (i.e to 2045) term, is likely to impact on the drainage system within the City of Port Philip. For the City of Port Phillip, potential impacts of climate change have been detailed in the City of Port Phillip s Climate Adaptation Plan - Climate Adept City. A summary of the potential impacts to increase flooding are listed below: 1. Sea level rise, storm surge & storm tide Sea level rises are currently tracking at the upper end of all projections, with a rise of 10 to 20 cm by 2025, 40 to 55 cm by 2050 and 80 to 120 cm by However, there remains considerable uncertainty related to these projections. The observed projected rises in sea level for the City of Port Phillip are largely consistent with global projections. Middle Park, St Kilda and Elwood Beaches are particularly susceptible to potential loss. Higher water levels in Port Phillip Bay, result in reduced outlet capacity for the drainage system, increased siltation and sand build up in drains, infrastructure instability, reduced water quality and higher stormwater contamination, beach erosion and loss of beaches, loss of some coastal properties assets, impacts on the City of Port Phillip s coastal recreational spaces, trails and paths, higher maintenance costs, deposition of debris on beaches. 18 Flood Management Plan for City of Port Phillip and Melbourne Water

24 2. Intense Rainfall A changing climate will increase the magnitude (intensity and duration) of rainfall, wind, surge and storm events. The current estimates of potential changes in rainfall intensity due to climate change have large ranges. The City of Port Phillip is likely to experience a 1 in 5 year or 1 in 100 year storm event more regularly. For example, if rainfall intensity increases by 5% then a 100 year ARI storm under current climate would have an Average Recurrence Interval of 80 years in the future. However, if rainfall intensity were to increase by 20% under climate change then a 100 year ARI storm under current climate would have an Average Recurrence Interval of 30 years in the future. In terms of pipe capacity a drain that currently has its capacity exceeded on average once every 5 years would be exceeded on average every 4 years if rainfall intensity increased by 5% and on average once every 2.5 years if rainfall intensity increased by 20%. Strong winds often increase the magnitude of accompanying stormwater surges and intense rainfall. More intense rainfall events may result in more flooding, beach erosion or loss of beaches, more storm damage to buildings, roads, powerlines and recreational spaces, higher maintenance and insurance costs, more blackouts and lack of road access from extreme weather and reduce water quality in Port Phillip Bay and waterways. Climate risks for the City of Port Phillip were assessed by using the NATCLIM s assessment of local climate risks and impacts (Planning for Climate Change 2007 NATCLIM) as well as data from the CISRO and the Intergovernmental Panel on Climate Change to develop climate and greenhouse emissions scenarios (See Climate Change in the City of Port Phillip An Initial Perspective). The local assessment data was then updated to reflect the most recent climate assessments (Fourth IPCC Assessment Report 2007, Copenhagen Diagnosis 2009, CSIRO 2009). The update demonstrates higher climate risks than previously anticipated, with all risk tracking at the upper end or projections. Given the location and characteristics of the municipality and proximity to the coast, the expected impacts of climate change may be very significant in the City of Port Phillip. The most significant impact may well be increases in sea level rise. The Victorian Planning Provisions include a requirement to consider a potential sea level increase of 0.8 metres by the year A sea level increase of 0.8 metres would have a significant impact on flooding in the City of Port Phillip, because as suggested previously, even a smaller sea level rise of 10 to 20 cm that may occur in the medium term (i.e. 2025) is likely to impact on the drainage system. A map (Figure 7-1) has been produced of the City of Port Phillip showing 1.6 m and 2.4 m AHD contours that correspond to ground levels compared to water levels under current and future frequency of tidal inundation (please note that this map doesn t include any adaptation or flood defence actions, nor does it consider potential beach or coastal erosion). According to the National Coastal Vulnerability Study (February 2006), the City of Port Phillip has over 9,000 Flood Management Plan for City of Port Phillip and Melbourne Water 19

25 addresses within 3km of the coastline and below 4m in elevation, and it is these properties that will be most at risk from beach erosion and subsequent flooding. The table below indicates that should sea level rise of 0.8 metres occur, then the high tides we currently observe on average to be once every 100 years will occur approximately every 1 to 2 years. However, even a smaller change in sea level rise of 0.1 to 0.2 metres is likely to affect the capacity of drainage within the City of Port Phillip. The potential impacts associated with these higher water levels in Port Phillip Bay are described above. In addition, the future flooding risks include frequent inundation of some parts of the municipality that have high density and heritage value. Over time, this will substantially alter the fabric and characteristics of the current building stock. Progressively higher AHD levels and redrafted Flooding Overlay SBOs will also mean dramatic infrastructure upgrade challenges for the City of Port Phillip. Key tide levels include: Average Interval Recurrence Current estimated tide levels (Melbourne Water) Future estimated tide levels with 0.8 m sea level rise 1 year 0.7 m AHD 1.5 m AHD 10 year 1.1 m AHD 1.9 m AHD 100 year 1.6 m AHD 2.4 m AHD There are many challenges and uncertainties of additional pressures on drainage and flood management resulting from coastal inundation, especially as the data and design solutions are still being determined. Currently there remains a need to determine the extent of the inundation and to identify vulnerable areas along the coastline of the City of Port Phillip. In addition, flood modelling needs to be updated and drainage networks need to be analysed to determined reduced drainage capacity in the medium (i.e. 2025, 2045) and long term (i.e. 2070, 2100) with climate change. Future flood risks will increase due to the combined impacts of coastal inundation and intense rainfall. Over the coming years, continued modeling of climate change impacts on flooding from both waterways and coastal inundation will be needed to gain a more comprehensive picture of the total future flooding risks to the City of Port Phillip. In early 2007, the City of Port Philip published a report Climate Change in the City of Port Phillip An Initial Perspective. The report showed that the city faces significant climate change impacts in coming decades that will need to be managed. Since then the City of Port Phillip has develop a Climate Change Adaptation Plan, which outlines five key actions for council to begin to climate proof the city. One of the five actions relates directly to flood management. Six key sub actions related to flood management have been identified: 20 Flood Management Plan for City of Port Phillip and Melbourne Water

26 Complete updated flood modelling to determine new drainage design parameters. This includes obtaining data from neighbouring cities to understand this city s total drainage needs; Conduct drainage network analysis and map reduced capacity under medium term (2025, 2045) and long term climate risk projection (2070, 2100) to determine total drainage capacity required; Introduce and pilot innovative drainage design in priority areas, with capacity to monitor and evaluate performance during flooding events; Develop a Master Plan that ensures integration between drainage strategies and the following three areas coastal protection actions, water conservation and reuse actions in council s Water Sensitive City and Open Space Water Management Plans, and maintaining and building local roads; Increase the use of flood calming devices to reduce flood events water sensitive urban design applications, retention basis and systems; and Reduce pressures on the drainage network by introducing new development and building requirements to reduce/prevent future flooding in properties. Likely requirements include increasing absorbent surfaces, stormwater storage and treatment and water sensitive urban design applications. In addition, many of the other sub actions within the Climate Change Adaptation Plan are highly relevant to flood management, planning and response, particularly a number of actions that address coastal inundation flooding pressures. The Climate Change Adaptation Plan has been carefully considered in the development of the Improvement Plan (see Section 10). The City of Port Phillip along with nine other councils formed the Association of Bayside Municipalities (ABM) which represents the councils that have frontage to Port Phillip Bay and also represents a population of greater then one million. The ABM is committed to enhancing local government s effectiveness in the sustainable management of the Port Phillip Bay environment. One of the projects the ABM has recently been involved in is working with DSE to acquire a Digital Elevation Model (DEM) of Victoria s entire coast, which involved data collection of sea depths and land coordinate points. The DEM shows the lie of the land 10 metres above and 10m below sea level. The data for the DEM as gathered using LiDAR technology, which is an airborne laser system. Flood Management Plan for City of Port Phillip and Melbourne Water 21

27 Figure 7-1 Map of the City of Port Phillip showing predicted current and future frequency of flood levels to sea level rise 22 Flood Management Plan for City of Port Phillip and Melbourne Water

28 8 Flood Management and Mitigation This section captures what has been done within the Municipality to understand, identify and treat flood risks as well as what is planned to further improve the management of existing, future and residual flood risks. Flood control measures can be structural or non structural. 8.1 Drainage Strategy A number of drainage studies have been completed over the past 10 years as detailed in Section 6.5, although no specific drainage strategy for the entire municipality has been created. There are relevant reports that inform the way City of Port Philip manages its drainage including this plan, the 2009 Stormwater Action Plan, the Melbourne Water Flood Management Strategy and the Climate Adaptation Plan Climate Adept City and these have been considered in the development of the Improvement Plan (see Section 10). 8.2 Flood Modelling and Mapping completing the knowledge base Introduction Accurate survey and modelling of floodplains and overland flow paths is required to determine flood depths and delineate areas subject to inundation on floodplains and along overland flow paths. This information is aimed at improving community safety through informed planning (ensuring that new development is designed to take into account floodplain and overland flow paths and associated flow depths) and emergency response. The mapped information is therefore required not only by Melbourne Water as the floodplain management authority, but also by municipal planning departments, emergency response organisations, other infrastructure providers, land developers, prospective land purchasers and existing land owners and occupiers. The City of Port Phillip in conjunction with Melbourne Water is initiating a flood mapping project aimed at mapping the overland flow paths for nominated storm intervals for all main drain catchments within the Municipality. Some pilot studies are underway using two dimensional flood modelling and considering climate change impacts on flood models. This is a critical first stage in achieving a safer community. The City of Port Phillip, in conjunction with other regional stakeholders and Melbourne Water, plans to initiate further coastal inundation modelling and mapping to determine risks to the City of Port Phillip associated with inundation from Port Phillip Bay as well as from stormwater. Catchment and coastal inundation data under various climate change scenarios will be brought together to understand total future flooding risks and drainage Flood Management Plan for City of Port Phillip and Melbourne Water 23

29 needs for the municipality. The flood information developed by the project will be used to give flood advice on properties affected by overland flow and / or flood inundation along Melbourne Water and City of Port Phillip drains, and to enable Melbourne Water and the City of Port Phillip to set capital works programs by identifying relative flood risks. The information will also be used to assist in determining land development requirements. In addition, the 100 year ARI flood extents determined through the project will be incorporated as a Special Building Overlay, Land Subject to Inundation Overlay, Floodway Overlay or Urban Floodway Zone as appropriate, in the Port Phillip Planning Scheme under the Victorian Planning Provisions. Mapping Program In the late 1990 s and early 2000, flood mapping studies were undertaken in the City of Port Phillip catchment area as detailed in Section 6.5 (refer to Appendix B for detail on each study). The studies produced scaled plans showing the extent of flood inundation for a 100 year ARI flood event, the flood mapping was primarily based on hydrologic modelling (RORB) and one dimensional hydraulic modelling only. To date, flood mapping for various tide levels, that includes a full range of ARI events and that includes ranges of depths and velocities to represent varying hazards across the flood prone areas has not been done. Also climate change impacts on flood risk including sea level changes and potential changes to rainfall intensities have not been assessed. Melbourne Water is undertaking flood mapping in for the Elwood Canal, Byron Street Main Drain and Shakespeare Grove Main Drain that use two dimensional flood modelling techniques. The mapping currently being done includes the consideration of climate change effects. The City of Port Phillip has engaged URS to carry out mapping for a range of ARI s for 5 year, 20 year, 50 year, 100 year and PMF. Council is also proposing to initiate coastal hazards vulnerability assessment (CHVA) with other stakeholders including Melbourne Water in order to determine impacts from coastal inundation. 8.3 Asset Management It is important that the existing drainage infrastructure within the City of Port Phillip operates as intended. This is especially important in the City of Port Phillip due to the density of development, flat terrain, drains located below sea level, risks of sand blockage for beach outlets and the age of the drainage infrastructure. Drainage and flood mitigation assets are maintained to a fit for purpose state to ensure they work as designed during a flood. All Melbourne Water drainage assets and waterways have an ongoing inspection and maintenance program. 24 Flood Management Plan for City of Port Phillip and Melbourne Water

30 Melbourne Water has significant drainage assets that require maintenance and renewal. Melbourne Water drainage assets are managed in accordance with the Asset Management Guidelines and Strategic Asset Management Plans, e.g. with the level of service of no failure/collapse of significant drain. Melbourne Water main drain conditions are assessed and reported annually in the State of the Assets Report. In the last few years Melbourne Water has undertaken work on the Shakespeare Main Drain outlet to reduce the risk of sand blockage and drainage and other problems. Work has also been completed on the Cowderoy Street Main Drain to assess corrosion and to undertake structural repairs. Melbourne Water waterways have ongoing programs to remove flow restrictions such as dumped rubbish, shopping trolleys and willow trees. The City of Port Phillip has an active road and pit cleaning service, but pipes are only cleaned on a reactive basis. Leaf blockage is a major problem in the municipality and it is thought that blockages and maintenance issues are the main reason for flooding rather than the actual level of service of the assets. There are continual silt and litter blockages, along with illegal connections. Given the relatively low lying and flat nature of much of the city the normal flows in the drains are often not sufficient to flush silt, leaves and litter out of the drainage pipe system. The City of Port Phillip has put in considerable effort into maintaining the performance of its drainage infrastructure over the last ten years or so, including: Reviewing the capacity of all of their drains in 1998 to 2000 and then upgrading high priority drains to provide a 5 year ARI level of service in the drain capacity Contracting the drain maintenance and repairs since the year 2000 with defined tasks and performance for regular inspection and clearing of drains. The current Council spending on these activities is approximately $440k drainage maintenance and $600k renewal It is expected that this expenditure will need to grow in the future to include more asset renewal as well as more maintenance and other operating expenses. Council has identified a need for further investment in asset management to improve its response to flooding issues within the municipality and has been responded to within the Improvement Plan (see Section 10). This includes additional and new costs for developing new drainage design solutions and gaining a drainage network that is deemed to capably provide effective drainage for future flooding risks from a changing climate. 8.4 Planning Controls Melbourne Water Melbourne Water is the Regional Floodplain and Drainage Authority for the Port Phillip and Westernport region. Thus all applications for subdivision and developments on flood prone land are referred by Council to Melbourne Water, Flood Management Plan for City of Port Phillip and Melbourne Water 25

31 as the authority responsible for the administration of the Planning Scheme, under Section 55 of the Planning and Environment Act, This includes consideration of flooding and projected rises in mean sea levels. However, this does not extend to factors contributing to coastal physical vulnerability such as storm surge and erosion. Melbourne Water has developed interim guidelines to assist in assessing development proposals affected by tidal inundation and flooding associated with sea level rise (Melbourne Water 2010). New flood levels for areas affected by predicted sea level rise to be applied for planning purposes are an increase on existing year flood levels of 200mm by 2040 and 800mm by These new flood levels should be used in accordance with the principles and core requirements contained in Melbourne Water s Guidelines for Development in Flood-Prone Areas. The Melbourne Water Guidelines link directly with the Department of Sustainability and Environment Draft Guidelines that direct/assist authorities assessing development in coastal flood risk areas such as within the City of Port Phillip (DSE 2010). Council The City of Port Phillip Planning Scheme contains a Special Building Overlay (SBO) which applies to land liable to overland flows from urban piped drainage systems (see Figure 8.1). Figure 8.1 also shows the 100 ARI flood extent. The 100 year ARI flood extents determined through the flood mapping project initiated by the City of Port Phillip in conjunction with Melbourne Water (see Section 8.2) will be incorporated as additional Special Building Overlays, Land Subject to Inundation Overlays, Floodway Overlays or Urban Floodway Zones as appropriate, in the Port Phillip Planning Schemes under the Victorian Planning Provisions. In addition, Council intends to update their Special Building Overlay controls in response to climate change and informed by flood/inundation mapping that will incorporate climate change scenarios (see Improvement Plan Section 10). In addition, to the update of the Special Building Overlay, there is the possibility that new flood information may also be incorporated into the development of a new climate change overlay. New formal arrangements and interagency coordination would be required to develop and support the development of a new overlay such as this. The State Government will be responsible for appropriate planning controls on climate change affected areas which will provide direction to Melbourne Water and the City of Port Phillip. The City of Port Phillip has no specific drainage redevelopment schemes in place at this time. They have the C13 Port Melbourne development contribution scheme but it is not tied to drainage projects. The development engineer considers specific projects if referred to him and makes decisions on drainage requirements as needed. 26 Flood Management Plan for City of Port Phillip and Melbourne Water