Flooding and Planning: Planning for the impacts. Carrie Dearnley & Neil Collins 4 September 2018

Transcription

1 Flooding and Planning: Planning for the impacts Carrie Dearnley & Neil Collins 4 September 2018

2 Presentation Overview Background Flood models Flood risk and risk management Flood resilience Floodable cities Floodable spaces Flood resilient architecture Flood resilient communities Floodproof cities Dutch solution The Australian Situation Considerations for implementation

3 Background

4 Information you can get from a flood model Extent / location Depth / level Velocity (speed of water and direction) Flow rate Hazard (combination of velocity and depth) Peak information (e.g. maximum water levels) Dynamic information (every calculation step from a flood model, can be animated) Time to X (inundation, reaching a critical velocity, hazard) Timing related to road closures, inundation of properties etc Pipe capacity identification / mapping Understanding of range of flood behaviour across all likelihoods (frequent to extreme / probable maximum flood)

5 Quick refresher: what is flood risk? (flood hazard and likelihood) (community attributes) (land use type)

6 Flood risk management essentials Three key approaches to managing risk to existing development: Reduce risk at community scale with structural works Levees, flood gates, detention basins etc Reduce risk at property scale with mitigation works House raising, flood proofing buildings etc Treat residual risk at the community scale Flood warning, emergency response plans, community education etc Seeks to exclude flooding from developed areas Seeks to adapt to / live with floods Key approach to managing risk to future development: Reduce risk at property scale with land use planning responses

7 Why not develop out of the floodplain? Brisbane PMF example Milton CBD New Farm South BNE West End Woolloongabba St Lucia

8 What does flood resilience mean? Ability to withstand disturbances, shocks, stressors to the system Traditionally, focus on bounce back, returning to original state Now, bounce back better adaptive, learn from experiences. What does this mean for flooding? Consideration of design flood levels and worse Equipping residents to respond and recover from any event, not just what they ve seen before, or a flood of a particular size / nature How can planning help? Floodable spaces Flood resilient architecture Flood resilient communities

9 Floodable spaces

10 Floodable spaces Already used extensively in QLD many parks and recreation spaces exist because of flood risk. Cheers for flooding! Increasingly being recognised elsewhere, e.g. Room for the River project, Netherlands Flood function understanding areas of conveyance and storage and using this to inform design Implementation options / ideas: Maintain as open space in greenfield areas Daylight rivers Property buybacks / repurpose land

11 Mapping and investigations to understand behaviour/risk Flood extents vs risk Frequent event + DFE + PMF VS Hydraulic risk

12 Daylighting Rivers Cheonggyecheon example Provide more capacity, re-establish floodplains or connections to floodplains Makes waterways more visible, highlights to community they are living in a floodplain, near a waterway Create recreational spaces, restore ecological function, regulate temperatures

13 Buyback / repurposing Northey Street City Farm Residential development built onsite in 1880s Devastated in 1974 floods Resumed by BCC; vacant parkland City farm established 1994 State Library of QLD

14 Northey Street City Farm

15 Flood resilient architecture

16 Adaptive housing in Mekong Delta, Vietnam Dry season: community space and shelter

17 Adaptive housing in Mekong Delta, Vietnam Wet season: floodable space > 2 m

18 Adaptive housing in Mekong Delta, Vietnam Wet season monkey bridge

19 Adaptive living in Mekong Delta, Vietnam Floatable pig pen

20 Adaptive living Too extreme?

21 Adaptive living Venice Also: floodable materials, raised floor levels, waterproofing buildings

22 Adaptive living Singapore s HDB void decks Getty images We accommodate the practices and the beliefs and the customs of different races and religions. We share our void decks for Malay weddings, Chinese funerals, other ceremonies, there is a spirit of give and take, mutual accommodation PM Lee Hsien Loong Maintains floodplain storage Provides community space Permanent furniture, floodable materials

23 Adaptive living Queenslanders

24 Adaptive living Mecca Café, Lismore When the Gray family moved the business to the present site in 1932, they made it somewhat flood proof: The art deco booths can be dismantled Valuable photographs are on a hinged, false wall that the hinged pictures can be swung up into, safe and dry

25 Thought experiment Rockhampton & Mekong Delta The Australian Elevated infrastructure Slow onset, low velocity flooding Resilient residents What if we planned for it? What would that look like?

26 Flood resilient communities

27 Community flood resilience Awareness measures increase knowledge of a particular hazard Resilience measures strengthen and empower communities to withstand and recover from any shock or stressor

28 Community building How does it contribute to flood resilience? Many studies have found that social networks are important to resilience outcomes and can contribute to better mental health outcomes (mental health is a significant, ongoing impact of flooding) People triangulate information, seeking confirmation from multiple sources People who only rely on tight networks (like family) generally stay put during disasters, whereas people with broader networks (from work, community etc) are more likely to evacuate and follow evacuation orders

29 Community building In practice Participatory planning: involving the community in developing local resilience plans, increasing community ownership (might include community champion programs etc) Provision of public meeting spaces and social infrastructure Design of public spaces to encourage convenient access and use by all including mixed use, universal design, aged friendly, child friendly etc. Dwelling mix that encourages social diversity Design of buildings that provide (privacy and) spaces for interaction Active / public transport that gets people out of cars

30 Floodproof cities

31 Dutch Approach Without dikes, the Netherlands would be flooded to this extent The Netherlands Today

32 Dutch Approach (Continued) 33 % of the country is below sea level 60% of Dutch people live in these areas 65% of the Netherlands GDP is produced in these areas 4 million people are flood affected Lowest point 6.7m below sea level The Dutch have learned to manage river flood and storm tide inundation over 1000 years

33 Dutch Approach Protection involves: Levees, barriers and gates

34 Dutch Approach Waterproofing of buildings

35 Dutch Approach Building over water

36 Dutch Approach Dry Period Wet Period Pumped drainage Storm tide barrier Leveed rivers and canals Saline intrusion management

37 Dutch Approach Storm tide barriers and levees

38 Dutch Approach Storm tide barriers

39 Dutch Approach Archimedes Screw Pumped Drainage

40 Dutch Approach

41 The Australian Situation Potential Flooding on the Gold Coast

42 The Australian Situation Mackay CBD Inundation Current

43 The Australian Situation Cairns Storm Tide Inundation (with Climate Change)

44 The Australian Situation Many of our cities are flood affected and the situation is worsening with climate change. Current planning schemes require any new development to : Balance floodplain storage Build to year 2100 climate change levels No adverse flood impact on adjacent properties Ensure that in a flood situation suitable evacuation routes and emergency flood management for the year 2100 flooding is in place Generally set design levels based on the 1 in 100 AEP event This effectively precludes redevelopment of many existing high density and high economic value areas, particularly in the lower estuarine / storm tide affected areas. Forces sterilisation of valuable land and ultimately abandonment. Flood planning in Australia is currently not widely assessing the benefit of a targeted Dutch approach protection and flood proofing system.

45 The Australian Situation Area specific cost / benefits analysis is required Some areas too sparsely populated or of insufficient value to warrant the investment. However, in many places (e.g. Cairns foreshore, Sandgate, Gold Coast foreshore), simple levee and pumped drainage systems are feasible without the need for expensive tidal barriers. A co-ordinated State Government and Local Authority approach is required. Funding mechanism for capital works and ongoing operating costs need to be assessed: Special rates Area specific special levies Headworks charges for developer contributions

46 The Australian Situation Pumped Drainage and Levee

47 Considerations for implementation

48 Where to start Understand full range of flood behaviour and risk Consider relative risk: how much worse can it get Have the hard discussion: What locations / assets should be prioritised and protected What land should be repurposed What structures are suitable for retrofit etc Be prepared to mix and match solutions Avoid single line approach; match development to risk

49 Where to start Use a graduated response: avoid / prevent flooding to a point, use flood proof materials for rarer likelihood, ensure communities are resilient and able to adapt to any size flood Tolerance and nature of the community. Think about: Communities already living in the current floodplain Future communities who ll be established in the current floodplain Current and future communities who ll be living in the future floodplain (climate change!) Cost to implement vs cost not to Ongoing costs to operate and maintain, committed funding

50 Questions?

51 Daylighting Rivers Western Creek Rosalie / Milton? Oxley s chain of ponds

52 Community building: PIA policy what is good planning? 1. Stronger communities and choices available for where and how people live and work such as, shorter travel times to work; safe and walkable neighbourhoods; a range of choices and opportunities of places to live; and better education, healthcare and recreation opportunities that are respectful of cultural diversity 3. Places of inherent value and opportunities for current and future generations, such as a reduction of health-related illnesses and providing interesting streets and places to visit; 5. Resilient communities able to mitigate and adapt to the impact of climate change and natural hazards, including reduced recovery and reconstruction costs, and reduced loss of life, property and essential infrastructure.

53 Cheonggyecheon flood considerations

54 Brisbane City Council Resilient homes program Being piloted from June 2018 to June 2019 in areas with 50% chance of flooding from overland flow every year 1. In-home assessment of property s flood resilience 2. Tailored report with flood resilience info / recommendations 3. Financial assistance for modification (if eligible) State Gov doing similar with household resilience program for cyclone risk in NQ