Innovative Approaches to Urban Surface Water Management

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1 Innovative Approaches to Urban Surface Water Management Liveable City Conference Climate Adaptation Creating Flood Resilient Cities

2 In Brief o Flood risk challenges within London/Southwark o Future challenges - Climate change and urban development o Southwark Council s Approach o Case studies

3 Flooding Challenges Tidal Flood Risk Location within the fluvial and tidal floodplain of River Thames Dominated by flat, low-lying topography and reclaimed marshland High vulnerability due to dense population and uniquely valuable cultural and heritage assets High reliance on artificial flood defences How London might look without the Thames Barrier (Source: the Sun)

4 Flooding Challenges Surface Water

5 Flooding Challenges Sewer capacity Southwark

6 Flooding Challenges Combined 850,000 properties at risk 1 in 4 of all properties 250 billion at risk 10 of the top 25 in the country Southwark tops in London More than 50% of properties are at risk

7 Future Challenges Climate Change It could get worse! Rising sea levels More winter rainfall and increased intensity and variability of rainfall Increased tendency of flooding and interaction between flood sources Population Growth and Development Increased vulnerability 11.3 million people by 2051, impacting infrastructure capacity Increased catchment urbanisation and subterranean development

8 Flooding Challenges in Southwark Surface Water Flood Risk High levels of urbanisation and landscape change: o Altered natural processes o Increasing the volume and speed of runoff A largely combined Victorian-era sewer system Historical watercourses routed underground and incorporated in the sewer system More than 30,000 properties at risk (1:200 event)

9 Southwark s Approach Partnership (internal & external) working Working closely with communities Strategic spatial planning Development control Flood alleviation schemes Enriching the urban environment Enhancing biodiversity Providing amenity

10 Working Together Internal Flood Risk Partners Asset Management Emergency Planning and Resilience Development planning and control Parks and Open spaces Housing Data Management Capital Projects Communication Corporate Risk Regeneration & Neighbourhoods Legal External Flood Risk Partners Environment Agency Greater London Authority Neighbouring Boroughs Thames Water Local community groups and residents Framework Consultants Project specific third parties Developers

11 Case Study Herne Hill FAS The Challenge 100 year History of flooding: River Effra culverted in 1880 s 1915 first recorded incident Dulwich Sports Ground Belair Park Dulwich Park Surface water flow path

12 Herne Hill FAS 1960s/1984 / 2004 widespread (sewer + surface water) 2006 / 2007 / 2012 localised Mechanism - large open fields surrounded by higher ground Lack of capacity in sewer 2004 flooding incident

13 Herne Hill FAS The Scheme 1. Underground geocellular storage tanks 4,330 m 3 2. Detention basin 3. Earth bund 4. Play bund and improvement to play area 5. Wetland and wildflower habitat 6. Flood wall 51,000m 3 of water stored on the surface of park

14 Herne Hill FAS The Results Surface water flood protection to 200 homes and businesses Reduced risk of surface water flooding to 447 more homes and businesses Over 110 properties removed from sewer flooding risk register 0.82Ha new wetland and wildflower habitat and playground improvements Scheme has been tested (23/06/17) Model of effective partnership 3 Awards won

15 Case Study East Camberwell FAS The Challenges Highly built up urban area unlike Herne Hill Very little room for storage More than 3000 properties in the wider area ~120 properties at risk within immediate area 4 of which had experienced recent sewer flooding

16 The Original Concept Urban greening measures Permeable paving Rain gardens Linear planting Swales Focused on: Local Authority housing estates Streetscape interventions Open space

17 East Camberwell FAS Challenges Complex sewer network with an extremely large catchment area feeding into the direct study area

18 East Camberwell Challenges

19 East Camberwell Urban Greening Little local interventions can collectively have substantial impact on local flood risk in addition to increasing urban green space and improving amenity, biodiversity and liveability.

20 East Camberwell FAS The Solution Urban Greening not providing sufficient storage Not yielding enough benefit Spatially efficient underground attenuation proposed Complements urban greening Reduce discharge from 200/l/s to 10l/s Partnership project

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22 Conclusion The threat is real The challenge is complex The solution is in partnerships The concept is every little helps

23 Thank You Any Questions?