London Resilience Partnership. Strategic Flood Response Framework

Transcription

1 London Resilience Partnership Strategic Flood Response Framework Version 3 June 2015

2 Ownership and document control This framework (version 3) replaces the London Strategic Flood Framework version 2 (April 2012), it has been updated by the Flooding Task and Finish group and was signed off by the London LRF on Monday 8 June Record of amendments Date Version Author Changes September- October 2012 January 2012 March 2012 March April 2012 V1.2 Joe Cuthbertson Significant amendments from previous flood framework, incorporating updates to flood warning codes, weather products and references to plans and organisations. V1.3 Joe Cuthbertson V1.4 Joe Cuthbertson Incorporation of comments from across the Partnership (virtual flooding task & finish group) who supplied comments between October and December Final series of amendments following further consultation in February and March 2012 for approval by LRPB. V1.5 Joe Cuthbertson Final minor amendments to produce version for LLRF sign-off. V2 Joe Cuthbertson Version number changed to reflect LLRF sign- off on 16 April February 2015 V2.1 Hayley Deakin Draft revision following lessons learnt from Winter 2014 floods. Incorporation of comments from the LRP flooding sub group. Amendments include a comprehensive triggers and actions section, SCG considerations and improved flood risk contextualisation section. 14 May 2015 V2.2 Hayley Deakin Incorporated feedback following London Resilience Partnership consultation period. Version for LRBP approval. 21 May 2015 V2.3 Hayley Deakin Incorporated minor feedback following LRPB. Final version for London LRF sign off. 10 June 2015 V3 Hayley Deakin Version number changed to reflect London LRF sign- off on 8 June London Resilience Partnership Strategic Flood Response Framework Version 3 (June 2015) Principal Author: Hayley Deakin Strategic Flood Response Framework Version: 3 Page 2 of 56

3 For information, please contact: London Resilience Team London Fire and Emergency Planning Authority 169 Union Street London SE1 0LL Critical Information Who is the national lead? Who initiates the London Strategic Flood Response Framework? Department for the Environment, Food and Rural Affairs The decision on whether to invoke this Framework is made through tripartite discussion between the raising agency, LRT and the Metropolitan Police Service. Who notifies partners within London of a flood event? Partners will be notified by the Environment Agency and Met Office when flooding is forecast or possible. Actual flooding on the ground can be reported by any organisation or members of the public once it has happened. What communication methods will be used to alert partners? Environment Agency and Met Office will issue warnings and notifications to the Partnership through usual channels. Consideration of plan activation will take place through tripartite discussion and information cascaded to Partnership by LRT. When will the London Strategic Flood Response Framework be reviewed? Who will coordinate the media? Delivery of London-wide measures In line with LRF processes or as required depending on outcomes of flooding incidents and exercises. Coordinated through the London Resilience Gold Communications Group (LRGCG) If an incident is likely to require strategic input an SCG will be convened Strategic Flood Response Framework Version: 3 Page 3 of 56

4 Table of Contents 1 Aim and Objectives... 5 Scope... 5 Aim... 5 Objectives... 5 Related and interdependent plans Triggers for Activation and Levels of Response... 7 LEVEL 0: Flood Mitigation and Climate Change Adaptation... 8 LEVEL 1: Horizon Scanning... 8 LEVEL 2: Flood Preparation - Triggers and Actions... 9 LEVEL 3: Flood Response - Triggers and Actions LEVEL 4: London Strategic Flood Response - Triggers and Actions Expectations of SCG attendees Roles & Responsibilities Properties Flooded Data Specific SCG Considerations APPENDIX A: Flood Risk in London A.1 Surface Water Flooding A.2 Groundwater Flooding A.3 Fluvial (river) Flooding A.4 Tidal Flooding A.5 Reservoir Flooding A.6 Sewer Flooding A.7 Water Mains Flooding A.8 Artificial Canal/Waterways flooding APPENDIX B: Reservoirs in London falling under the Reservoirs Act APPENDIX C: Flood Information and Warning Products C.1 Flood Guidance Statements (FGS) C.2 Met Office Hazard Manager C.3 Floodline Warnings Direct (FWD) C.4 Live Flood Warning Map and GaugeMap C.5 Water Situation Reports Glossary Strategic Flood Response Framework Version: 3 Page 4 of 56

5 1 Aim and Objectives Scope 1.1 This framework relates to flooding, of any kind, causing or with the potential to cause London-wide impacts. This includes flooding from rivers, the sea (tidal), surface water, groundwater, reservoirs, sewers, canals and artificial waterways. This may be severe flooding in one or more locations requiring a London-wide response, or a greater number of less severe flooding in multiple locations within London. 1.2 The framework also covers the pre-flooding phase. It can therefore be activated prior to impacts being observed in preparation for potential flooding. Aim 1.3 This plan aims to provide strategic direction to London responders, before, during and after a significant flooding incident in London. Objectives 1.4 The objectives of the London Strategic Flood Response Framework are to: Identify triggers and mechanisms for invoking a London-wide strategic response Provide responders with some context around the impacts of each type of flood risk Confirm the actions responders should take at each stage of a flooding incident Provide the necessary links to existing plans and procedures Related and interdependent plans 1.5 The table below illustrates different levels of flood emergency planning and response. Strategic Flood Response Framework Version: 3 Page 5 of 56

6 1.6 Flooding will usually stretch across administrative boundaries. Therefore it is important the LRF shares plans and maintains good relationships with its other neighbouring areas Essex, Hertfordshire, Thames Valley, Surrey and Kent. 1.7 The River Thames Scheme Maidenhead to Teddington emergency response plan outlines the arrangements for Thames Valley, Surrey and relevant s (Richmond and Kingston) to respond to flooding together for one of the largest, most developed, undefended flood plains in England. 1.8 The below diagram shows plans referenced within this document. They should be used in conjunction with the London Strategic Flood Response Framework. These plans all sit on the same level of response (strategic pan-london). The plans are linked to Resilience Direct where they are saved. London Mass Evacuation London Mass Shelter LESLP Major Incident Procedure Manual London Strategic Coordination Protocol Emergency Response and Recovery LONDON STRATEGIC FLOOD RESPONSE FRAMEWORK London Recovery Management Protocol London Humanitarian Assistance Plan London Local Flood Warning Plan London Communicating with the Public Framework 1.9 The London Flood Response Framework sits below the National Flood Emergency Framework for England written by DEFRA (December 2014). This plan is saved on gov.uk at this link here. Strategic Flood Response Framework Version: 3 Page 6 of 56

7 2 Triggers for Activation and Levels of Response 2.1 In the event that the flooding is impacting, or has the potential to impact a number of Boroughs within London, a decision should be made to consider implementation of the strategic multi-agency response (level 4). 2.2 Within this plan there are 4 levels of response that have been identified. These can aid decision making in the event of a flood. These are similar to those triggers identified in local borough Multi-agency Flood Plans. 2.3 Escalation through the levels may not always be sequential. The diagram below illustrates this with past flood event examples. Ruislip 2014 event During July minutes of intense rainfall fell in Hillingdon, Ruislip. Level 3 local flood response was triggered. As this was a local incident, Level 4 strategic flood response was not triggered. Impacts included: A day closure of the A40 and 19 other roads flooded Metropolitan and Piccadilly tube lines affected South Ruislip train station closed 15 properties flooded Gloucestershire 2007 event During the summer of 2007 Gloucestershire experienced very heavy rainfall. Gloucestershire being part of Thames Valley LRF activated a strategic flood response. Similar to level 4 strategic flood response outlined within this document. Impacts included: Approximately 5,000 properties flooded and 2,000 people evacuated 48,000 homes without electricity for 2 days 40 million bottles of drinking water distributed 10,000 people stranded on county roads (many remained overnight) Strategic Flood Response Framework Version: 3 Page 7 of 56

8 LEVEL 0: Flood Mitigation and Climate Change Adaptation 2.4 There is no trigger to activate level 0. During peacetime, organisations such as Local Authorities and the Environment Agency work to mitigate flooding. This includes improving flood modelling, designing flood alleviation schemes, implementing sustainable urban drainage techniques, consenting on building works in flood zone to name only a few. 2.5 Emergency planning peacetime activities should include flood training, exercising and promotion of flood risk. Climate change and adaptation A.9.1 There is clear evidence to show that climate change is happening. Measurements show that the average temperature at the Earth s surface has risen by about 0.8 C over the last century. 13 of the 14 warmest years on record have occurred in the 21st century and in the last 30 years each decade has been hotter than the previous one. A.9.2 Along with warming at the Earth s surface, many other changes in the climate are occurring: more extreme weather events (including flooding and drought) warming oceans melting polar ice and glaciers rising sea levels A.9.3 A.9.4 The National Adaptation Programme (NAP) sets out what government, businesses and society are doing to adapt better to a changing climate. Further information on climate change can be found on the GOV.UK pages here LEVEL 1: Horizon Scanning 2.4 There is no trigger to activate level 1. Ongoing risk assessment and horizon scanning is integrated into category 1 and 2 responder s normal arrangements and included in the London Common Operating Picture (COP) circulated to the Resilience Partnership. 2.5 This includes keeping a watching brief over forecasts, Met Office weather warnings, Environment Agency flood alerts and warnings and the Flood Forecasting Centres Flood Guidance Statements. Cross-boundary flooding 2.8 If fluvial (river) flooding is occurring in neighbouring areas around London, such as the Thames in Surrey or Lee Valley in Hertfordshire, the Environment Agency will provide a further assessment on the possible impacts for London. 2.9 The assessment will also include whether London will not be impacted from fluvial (river) flooding that is happening just outside its boundaries. This is to ensure responders aren t preparing unnecessarily and are more informed when supplying mutual aid to neighbouring areas. Strategic Flood Response Framework Version: 3 Page 8 of 56

9 LEVEL 2: Flood Preparation - Triggers and Actions TRIGGERS FOR FLOOD PREPARATION: London is coloured yellow, amber or red on the Flood Guidance Statement (1 or 2 day lead time) The Met Office Advisor (Civil Contingencies) issues a specific update for London confirming the likelihood of disruption Environment Agency issues Flood Alerts for multiple locations within London Problems have been identified with a reservoir which has not yet failed, with potential to impact on London Problems have been identified with a flood defence with potential to impact on London, which has not yet failed Credible reports in the media are focused on potential widespread flooding in London Disruption to utilities with possibility of a secondary consequence of flooding WHEN ONE OR MORE OF THE TRIGGERS HAVE BEEN MET SEE ACTIONS BELOW ACTIONS TO CONSIDER FOR FLOOD PREPARATION: All Organisations should: Report any observations of properties or infrastructure flooding to the relevant London Borough, Environment Agency or LLACC (if open). See section 5 of this plan for further guidance. All organisations consider: Assess the severity and decide whether an SCG is needed to manage the strategic response. London Strategic Coordination Protocol provides information for SCG initiation. Manage staff to deal with a potential incident. This may involve placing staff on standby, assessing availability for the next 3-5 days and briefing key operatives internally. Prepare to implement operational response plans. Borough MAFPs should identify critical assets that may need protecting or assets that require inspection or regular monitoring. Check your organisation s control centre is fully prepared to be opened if necessary. LFB-EP and local authorities to consider whether the LLACC is likely to be required, and activate early in preparation if necessary. Prepare for potential media interest. Consider issuing proactive press releases providing advice to the public on how to prepare for flooding. Check your BCM plans to ensure your organisation s critical business activities can still be met, if flooding were to occur. Keep a watching brief on the situation and up-to-date with the latest flood forecasts. Strategic Flood Response Framework Version: 3 Page 9 of 56

10 Escalating from LEVEL 2 Flood Preparation to LEVEL 3 Flood Response: 2.10 There may be a period of inactivity between the preparation phase and the response phase. This could range from hours to days depending on the detail and confidence of the weather/flood forecasts There will be occasions when the preparation phase (level 2) is activated but response phase (level 3) is not necessary. Activating the preparation phase ensures responders stay ahead of the incident, instead of trying to catch up during the response phase All organisations should aim to inform the relevant, Environment Agency and/or LLACC (if open) of any flooding to property or infrastructure. Strategic Flood Response Framework Version: 3 Page 10 of 56

11 LEVEL 3: Flood Response - Triggers and Actions TRIGGERS FOR FLOOD RESPONSE: London is coloured amber or red (medium or high likelihood) on the Flood Guidance Statement (less than 1 day lead time) The Environment Agency issues or plans to issue flood warnings for multiple locations in London or/and a Severe Flood Warning for any location in London Any organisation becomes aware of widespread disruption to transport or other infrastructure due to flooding from any source Reports of properties flooding internally in multiple locations (Boroughs) across London A reservoir which has the potential to impact on London is failing A flood defence structure has been breached or has failed with significant impact for London Disruption to utilities which is causing secondary flooding impacts Cabinet Office Briefing Room (COBR) is opening due to flooding in London or flooding has the potential to affect London Credible reports in the media are reporting flooding in London WHEN ONE OR MORE OF THE TRIGGERS HAVE BEEN MET SEE ACTIONS BELOW ACTIONS TO CONSIDER FOR FLOOD RESPONSE: All Organisations to consider: Assess the severity and decide whether an SCG is needed to manage the strategic response. The full arrangements for activating strategic response in London are contained in the London Strategic Coordination Protocol. Activate emergency response plans and/or BCM plans where appropriate. Scale up Open control centres / incident rooms where appropriate to provide coordination for your organisation and a central point of contact Check the status of key sites and infrastructure that are known to be in flood risk areas. Media messages need to be agreed and circulated on a regular basis. A flooding situation can change rapidly. Log all details of any reports of flooding and pass them to the Environment Agency, relevant or LLACC (if open) on a regular basis. The Environment Agency will try, when possible, to consult with the SCG before issuing a Severe Flood Warning. This will allow all responders to prepare for increased media and public interest. Escalating from Level 3 Flooding Response to Level 4 Strategic Flooding Responses: 2.13 There will be occasions when level 3 local flooding response phase is activated but strategic response phase (level 4) is not necessary. Strategic Flood Response Framework Version: 3 Page 11 of 56

12 LEVEL 4: London Strategic Flood Response - Triggers and Actions TRIGGER FOR STRATEGIC RESPONSE: Decision has been made to escalate the response strategically following a tripartite discussion. London Resilience Team will inform all partners that a Strategic Coordinating Group for London is being held at the SCC. The full arrangements for activating strategic response in London are contained in the London Strategic Coordination Protocol. AIM FOR STRATEGIC COORDINATION GROUP: The London Strategic Coordination Protocol outlines the initial and generic strategy for partnership response as: 1. Protect life 2. Provide conditions for a safe and secure London 3. Promote public confidence through communication and engagement 4. Minimise disruption to London s infrastructure and people 5. Manage resourcing to meet Partner s planning assumptions Further SCG considerations specifically relevant to flooding are detailed in the next section. De-escalating from Level 4 Strategic Flood Response: 2.14 Following level 4, before returning back to level 1 there will be a period of recovery and deescalation. It is possible that following a de-escalation from level 4 to level 2/3, there could be further escalations dependant on the forecast/conditions. Strategic Flood Response Framework Version: 3 Page 12 of 56

13 3 Expectations of SCG attendees 3.1 In some circumstances strategic decisions will have to be made based on a forecast alone. This might be before any rain has started to fall, and before we know which areas within London are likely to be worst impacted. An example of this would be the July 2007 rainfall falling on London rather than Oxfordshire and Gloucestershire. This would look like the below mocked up Flood Guidance Statement. For further information about the Flood Guidance Statement product please see appendix C. In Area A, there is a high likelihood of severe impacts from surface water flooding in London and Greater London. Typical impacts could include flooding of whole communities, widespread disruption to infrastructure and travel, danger to life and large scale evacuations. In Area B, there is a medium likelihood of significant impacts from surface water flooding. Typical impacts could include flooding of multiple properties, possible danger to life and some disruption to infrastructure and travel. B In Area C, there is a very low likelihood of significant surface water flooding. Impacts could include multiple properties, possible danger to life and some disruption to infrastructure and travel. C A 3.2 In a situation such as this as shown above, SCG attendees may be required to make the following types of decisions quickly and without complete information. A high confidence high impact rainfall event forecast might only provide responders with 24 hours notice. In this circumstance the following will have to be considered by strategic leaders in London: Proactive evacuation of vulnerable locations Protection of infrastructure to mitigate secondary consequences Develop a coordinated media strategy prior to impacts being observed Provide information on the likely level of disruption to travel and other services Identify mutual aid to help with rest centres, evacuation, erecting temporary defences, managing traffic disruption, dealing with injuries and rescue etc See section 6 for further SCG considerations. Strategic Flood Response Framework Version: 3 Page 13 of 56

14 4 Roles & Responsibilities 4.1 LESLP describes the generic roles and responsibilities of its members within London. The Cabinet Office Emergency Response and Recovery guidance describes specific responsibilities across the full range of Category 1 and 2 responders and other response organisations. The National Flood Emergency Framework for England describes the specific roles of lead government departments, the Environment Agency, Flood Forecasting Centre and other national organisations in the response to flooding. Lead agency throughout a flood event 4.2 The lead agency during a flood depends upon the level of the flood event, impacts, flood type and response actions. 4.3 During a smaller scale flood event (level 3) the Local Authority or Police may lead dependant on the impacts and which organisation has the primary response actions to manage the impacts. 4.4 The response phase of a widespread pan-london flood event (level 4) would be the Police. Recovery stage is led by the Local Authority. Strategic Flood Response Framework Version: 3 Page 14 of 56

15 Managing flood risk: Who is responsible? The Environment Agency has a strategic overview of all types of flood risk and works closely with Lead Local Flood Authorities and other organisations in order to manage the risk. The below table shows which organisations manages flood risk day to day, this is not to be confused with which organisation might lead during the response and recovery phases, which is outlined in the previous page. Flooding is a complex hazard and so it is worth bearing in mind that different sources of flooding often happen together and impact one another. For example highway flooding caused by a blocked sewer is not the responsibility of the Highways Authority. Reservoir responsibility is explained in appendix A.5. Organisation Flood Risk Type Main rivers (large rivers) Ordinary watercourses (small rivers) Surface water Ground water Sewer flooding Road drainage Canals and artificial waterways Environment Agency x s (Lead Local Flood Authorities and Highways Authorities) x x x X (Non M or TLRN roads) Highways England Transport for London (TfL) X (M Roads) X (Red route roads TLRN) Utility companies x Canal and Rivers Trust x Strategic Flood Response Framework Version: 3 Page 15 of 56

16 5 Properties Flooded Data 5.1 During a widespread flood event the need for real time properties flooded data is key for reporting, allocating resources, evacuating communities, mobilising flood rescue efforts and planning recovery to name a few. 5.2 Although collating properties flooded data is an operational and tactical responsibility, it features within this plan for two reasons. To ensure that across London we have a consistent way to define and record property flooding. And to put in place a mechanism for sharing this information and reporting it centrally during a pan London flood event. 5.3 As per the Flood and Water Management Act it is the responsibility of the LLFA to collate properties flooded information for their. The Environment Agency will also pull together properties flooded data and information during a flood event to assist with flood warning work and defence operation. 5.4 s and the Environment Agency need to work together jointly to share this information with one another during the response and recovery phase. 5.5 During a widespread flood event across London there will be a need for this information to be pulled together to provide a pan London picture. When this is necessary the LLACC will ask s to start filtering in properties flooded information to them so it can be collated centrally. 5.6 When recording properties flooded it is important to capture: 1. The address 2. Flooding type: fluvial (river), surface water, groundwater, tidal, reservoir, sewers, canals, highways drainage etc. 3. Flooding extent: Internal Basement Garage (attached or not attached onto main building) Occupied caravans Park homes Gardens Driveways Outhouses and sheds These can then separated out into the following categories: Internal property flooding: water has entered the property. This includes basements and below ground level floors. Garages are included if attached onto the main building. Occupied caravan and park homes are also included. External property flooding: where water has entered gardens, driveways, outhouses, garages (that are separate from the main building) and sheds. (National Flood Emergency Framework, DEFRA, 2015) It is important to capture as much information as possible when recording and reporting properties flooded data. Strategic Flood Response Framework Version: 3 Page 16 of 56

17 6 Specific SCG Considerations Infrastructure National Infrastructure ISSUE This is defined as: those facilities, systems, sites and networks necessary for the functioning of the country and the delivery of the essential services upon which daily life in the UK depends. Critical National Infrastructure There are certain critical elements of national infrastructure that if lost would lead to severe economic or social consequences or to loss of life in the UK. These critical elements make up the critical national infrastructure (CNI). Evacuation & shelter Evacuation may not always be the safest option for those potentially at risk. At times it may be safer for residents to seek refuge in the upper storey of a building rather than run the risk of being overcome by flood water. The decision to evacuate an affected area will be the responsibility of the police. CONSIDERATIONS Identify which CNI has been impacted or is at risk. Assess the direct and indirect impacts on: o Energy o Food o Water o Waste o Transportation o Communications o Emergency services capability o Health care o Financial services / Government Consider the scale and duration of loss. Prioritise CNI sites. Identify mitigation measures and alternative supplies. Consider the knock-on consequences and how these will be managed. Assess resource requirement and whether military aid is needed. Evacuation arrangements are detailed in the London Mass Evacuation Plan and London Mass Shelter Plan and will apply to evacuation due to flooding. Consider basement dwellings. Prioritise areas for evacuation. Assess impact on receiving areas. Provide guidance on funding for accommodation. Agree on the ground evacuation communications and circulate this operationally i.e. what to advise people upon a refusal to evacuate. Assess resource requirement and whether military aid is needed. Consider the need to re-provide displaced services i.e. local heath care and social services. Strategic Flood Response Framework Version: 3 Page 17 of 56

18 ISSUE Vulnerable people and areas Vulnerable people may be less able to help themselves in an emergency than self-reliant people. Those who are vulnerable will vary depending on the nature of the emergency. In general those with mobility or mental health difficulties and dependants that receive medical care in their own homes or children may be especially vulnerable in a flood. Waste removal Expect to see a major increase in the amount of waste that needs to be disposed of as a result of severe flooding. Normal waste collection and disposal arrangements will probably be disrupted. Sewerage network disruption Flood water ingress into the sewerage network may cause sewerage flooding. Therefore sewerage disposal might be disrupted during a flood event. Loss of the Thames navigation Consecutive Thames Barrier closures or severe flooding of the Tidal Thames will impact the use of the river CONSIDERATIONS Identify vulnerable areas based upon building service e.g. schools, nursing home, hospitals, prisons, basement dwellings etc. Consider: o Issuing specific communications. o Prioritising vulnerable areas. o Mitigating the impact accordingly e.g. temporary defences, evacuation. o Safety and ability to evacuate. o Those that re A strategy to manage increased waste removal such as: o Contaminated and hazardous materials. o Sandbags. o Environmental e.g. dead animals. o Household waste (residential). o Building recovery e.g. flood damaged items. o Commercial businesses. Communicate waste disposal advice to the public. Consider: o Other methods such as portaloos (950 portaloos were deployed during 2007 summer floods). o Minimise sewer flooding by tankering or pumping. o The need for evacuation. Keep the community continually informed. Consider: o Who uses the Thames to transport waste. o Will any critical activities be disrupted. o What will the impact be for construction projects such as crossrail and Thames Tideway tunnel. Strategic Flood Response Framework Version: 3 Page 18 of 56

19 Health advice ISSUE Risks include: drowning, electrocution, carbon monoxide poisoning, physical trauma, chemical contamination, fire, infectious diseases from contaminated water etc. Recovery A longer-term activity of rebuilding, restoring and rehabilitating the community. Public messages It is important public communications from all organisations are coordinated to ensure there is no contradicting information issued. Mutual Aid Successful response to emergencies in the UK has demonstrated that joint working and support can resolve very difficult problems that fall across organisational boundaries. Political and Government Liaison Incidents in London attract national and international attention CONSIDERATIONS Consider: o Health risks related to flooding (see health advice box opposite). o Remedial or mitigation solutions for contamination or pollution. o Long-term recovery needs including surveillance, screening and mental health well-being. Brief: o General public on risks associated with flooding. o Responders on the ground around health and safety requirements. Consider the long-term recovery needs of communities affected by flooding. London s recovery arrangements are detailed in the London Recovery Management Protocol and will apply to recovery from a flooding incident. Develop a media strategy. Disseminate: o Take action messages. o Public advice. o Service updates. o Joined-up messaging between responding agencies through the SCG media cell. Assess mutual aid requirement for: o Evacuation o Rest centres o Protecting assets o Inputting mitigation measures o Managing major traffic disruption o Dealing with injuries o Flood rescue o Managing the media Concise and timely information on scale and duration of impact Managing media and political scrutiny Cost recovery Strategic Flood Response Framework Version: 3 Page 19 of 56

20 APPENDIX A: Flood Risk in London This section provides a summary of the types of flooding, risk and possible impacts in London. A.1 Surface Water Flooding Hazard description A.1.1 A.1.2 A.1.3 A.1.4 Surface water flooding occurs where rainfall exceeds natural and highway drainage capacity and therefore lies or flows over the ground instead. Surface water flooding can occur very quickly with little or no warning. This will often result from intense downpours over small localised areas and also from more prolonged rainfall over a wide area where the ground becomes saturated. Road networks are affected most frequently from seemingly small amounts of rainfall and properties are affected in the more severe events. London s built-up land surface does not allow rainwater to soak away into the ground. Therefore there is an increased risk that severe rain will lead rapidly to flooding. A major surface water flood would cause great property damage, with a high chance of loss of life, especially in basement dwellings. Warning lead times A.1.5 A.1.6 In very intense storms, typical in summer months, localised flooding can occur within minutes of the rain starting. More widespread flooding could happen within a few hours. In general to implement any operational response to reduce impacts (for example erecting temporary barriers) would need to be carried out on the basis of a forecast. Multi Agency Flood Plans should have identified critical or vulnerable areas that would merit protection. It is important to note that a heavy rainfall weather forecast is unlikely to be able to pinpoint specific areas in London that might be worst affected. Often forecasts of this nature cover all of London. Further information A.1.7 Impacts, risks, warning mechanisms and confidence of forecasting are outlined in the following tables and mapping. Strategic Flood Response Framework Version: 3 Page 20 of 56

21 Flood Risk Type Likelihood Consequence / Impact Typical Impacts SURFACE WATER Lead Authority s HIGH 1 in 30 year (3.3%) MEDIUM between 1 in 100 year (1%) and 1 in 30 year (3.3%) LOW between 1 in 100 year (1%) and 1 in 1000 year (0.1%) VERY LOW 1 in 1000 year (0.1%) Low to Medium Impacts High Impact Very High Impacts Very High Impacts Low lying areas flooded including low spots in roads. Underpasses flooded for at least a day causing localised but potentially significant disruption to transport and utilities. Clusters of properties (10s to low 100s) flooded with the need for some evacuation. Some risk to life particularly in areas of London where there are basement dwellings. Very fast flowing water passing along streets and pavements. Hundreds of properties flooded. Disruption to road, underground and over-ground rail services. Widespread evacuation. People trapped or stranded with loss of life (trapped in basements or from fast flowing water). Thousands of properties flooded with widespread evacuation. Significant disruption to transport and utilities. Many iconic locations flooded creating an international news story. Warning methods Confidence and understanding of the impacts from FGS 5 days out Confidence and understanding of the impacts from FGS 2 days out Ability to reduce impacts through strategic operational response Flood Guidance Statements Met Office Severe Weather Warnings (See appendix C for explanation of warning products) There would be very low confidence in forecasting surface water flooding five days before an event. There would be low confidence of the precise impacts (location and scale) for a major surface water flood. In the Summer of 2007 there was reasonable confidence that there was going to be a major flood somewhere in central southern England 24 hours beforehand. Surface water flooding would happen very quickly following intense rainfall significant effects could be seen within 30 minutes. For high impact events, evacuation or erection of temporary defences (for example around the entrance to tube stations or sub-stations) would need to be done before the onset of rainfall. Risk Register ID number: L19 (for reference only) Strategic Flood Response Framework Version: 3 Page 21 of 56

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23 A.2 Groundwater Flooding Hazard description A2.1 Flooding from groundwater can happen when the level of water within the rock or soil that makes up the land surface (known as the water table) rises and reaches ground level. The level of the water table changes with the seasons due to variations in long term rainfall and water abstraction. A2.2 There are some key features of flooding from groundwater: Flooding will usually occur days or even weeks after heavy or prolonged rainfall. Flooding may occur for a long time, often lasting several weeks. The water doesn t always appear where you would expect it to (i.e. valley bottoms). It may also emerge on hillsides. Water may rise up through floors rather than coming in through doors. Flooding from groundwater is most common in areas where the underlying bed rock is chalk (see London geology diagram on following pages). Groundwater flooding causes an increased risk to sewer flooding. Warning lead times A2.3 There is generally a long lead time for the conditions where groundwater flooding can occur - several days or longer. It is however, difficult to predict precisely where the location of flooding will happen. Further information A.2.4 Impacts, risks, warning mechanisms and confidence of forecasting are outlined in the following tables and mapping. Strategic Flood Response Framework Version: 3 Page 23 of 56

24 Flood Risk Type Likelihood Consequence / Impact Typical Impacts GROUND WATER Lead Authority s HIGH 1 in 30 year (3.3%) MEDIUM between 1 in 100 year (1%) and 1 in 30 year (3.3%) LOW between 1 in 100 year (1%) and 1 in 1000 year (0.1%) VERY LOW 1 in 1000 year (0.1%) Low to Medium Impacts High Impact Very High Impacts Very High Impacts Localised flooding of roads, utilities and clusters of properties primarily in South London. Localised flooding of roads, utilities and clusters of properties in South London. Risks to public water supply. 100s of properties impacted. Transport and utilities severely disrupted. Main impacts in South London. Warning methods Flood Guidance Statements Water Situation Reports (Environment Agency) (See appendix C for explanation of warning products) Confidence and understanding of the impacts from FGS 5 days out Confidence and understanding of the impacts from FGS 2 days out Ability to reduce impacts through strategic operational response High confidence with an improving understanding of impacts. However it will be difficult to predict precisely where the location of flooding will happen. High confidence with an improving understanding of impacts. However it will be difficult to predict precisely where the location of flooding will happen. In some areas it might be possible to protect key assets using temporary defences and storing or routing water to areas where the impacts are less significant. Risk register ID number: L19 (for reference only) Strategic Flood Response Framework Version: 3 Page 24 of 56

25 Flooding from groundwater is most likely to happen where the underlying geology is chalk Strategic Flood Response Framework Version: 3 Page 25 of 56

26 A.3 Fluvial (river) Flooding Hazard description A.3.1 Fluvial flooding happens when a river cannot cope with the amount of water draining into it from the surrounding land. The result is often water overtopping or breaching of a river bank or defence. River flooding can also occur from a blockage in the channel. A.3.2 Rivers respond to rainfall at different rates according to several factors such as land use, catchment size and topography. In some areas of London, fluvial flooding can occur within 30 minutes following the onset of rain. Some other larger rivers can take several days to reach their highest level following a rainfall event. Warning lead times A.3.3 The Environment Agency aims to provide a two hour warning of property flooding (flood warning). However, there are some rivers in London that can react very quickly to heavy rainfall; particularly smaller tributaries. Further information A3.4 Impacts, risks, warning mechanisms and confidence of forecasting are outlined in the following tables and mapping. Strategic Flood Response Framework Version: 3 Page 26 of 56

27 Flood Risk Type Likelihood Consequence / Impact Typical Impacts Fluvial (Main Rivers) Lead Authority Environment Agency HIGH 1 in 30 year (3.3%) MEDIUM between 1 in 100 year (1%) and 1 in 30 year (3.3%) LOW between 1 in 100 year (1%) and 1 in 1000 year (0.1%) VERY LOW 1 in 1000 year (0.1%) Low to Medium Impacts High Impact Very High Impacts Very High Impacts Risk of flooding to low lying properties situated close to the river. Some low lying roads and other infrastructure may also be affected. Potentially several hundred of properties flooded. Evacuation of some properties would be likely. Disruption to transport and utilities. Likely to be regional disruption around London. Thousands of properties flooded and major disruption to transport. Potentially several thousand homes evacuated with impacts on public water supply, transport and utilities. Thousands of properties flooded and major disruption to transport. Potentially several thousand homes evacuated with significant impacts on public water supply, transport and utilities. Warning methods Floodline Warnings Direct (Environment Agency warnings) Flood Guidance Statements Flood Advisory Service (initiated upon an amber FGS) Met Office Severe Weather Warnings (See appendix C for explanation of warning products) Confidence and understanding of the impacts from FGS 5 days out Confidence and understanding of the impacts from FGS 2 days out Ability to reduce impacts through strategic operational response There would be low certainty on any forecast of major river flooding five days before an event. For flooding in the winter (usually from frontal rainfall) there would be reasonable confidence of fluvial flooding 1 to 2 days before an event, though the precise impacts may not be clear. There would be less confidence from summer thunderstorms and convective rainfall. Flooding could happen quickly in London. Decisions relating to evacuation and the protection of key assets would need to be made very early on in an event, before widespread flooding took place or even before rain started to fall. Risk register ID number: HL19 (for reference only). Fluvial and tidal maps and statistics located on following pages in A.4. Strategic Flood Response Framework Version: 3 Page 27 of 56

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29 A.4 Tidal Flooding Hazard description A.4.1 Tidal flooding results from an incoming tide coming from the sea, raising river levels above the level of defences or from a breach in defences. The river Thames in London is tidal. Warning lead times A4.2 There is a generally a few days warning of tidal flooding. The scale of any impacts will be refined closer to the actual event. London is protected from tidal flooding by the Thames Barrier but on tides that are high (but not high enough to trigger a closure of the Barrier) some riverside locations in West London are prone to local flooding. In these circumstances timely Flood Alerts are issued to the places impacted. Further information A4.3 Impacts, risks, warning mechanisms and confidence of forecasting are outlined in the following tables and mapping. Thames Barrier A.4.4 A.4.5 A.4.6 A.4.7 A.4.8 A.4.9 The Thames Barrier and its associated gates are operated and maintained by the Environment Agency. It is used to protect London from large incoming tides. It is one of the largest movable flood barriers in the world, spanning 520 metres across the Thames near Woolwich and protecting 125 square km of central London. The Thames Barrier and its downstream defences have a 0.1% annual exceedance probability (AEP). This is equivalent to providing protection against a 1 in 1000 year surge event or smaller. The upstream walls and embankments are lower to allow greater use and enjoyment of the river. Thames Barrier is closed when surge conditions threaten to overtop these defences, increasing central London s level of protection to that of the downstream defences. The Thames Barrier may also be closed during periods of high flow over Teddington Weir to reduce the risk of river flooding in some areas of South West London including Richmond and Twickenham. The barrier has no individual trigger level for closure. The closing process is partly guided by a mathematical matrix that considers these 3 major factors: the height of the tide (usually a spring tide) measured at the Thames Estuary the height of the tidal surge, which naturally accompanies each tide the river flow entering the tidal Thames, measured as it passes over Teddington Weir When required, the Thames Barrier is closed on an incoming tide to hold back any surge activity. The nearer to low tide the Thames Barrier is closed, the lower the upstream river levels remain and the greater capacity there is to cope with high fluvial flows. The Thames Barrier will remain closed over high water until the water level downstream of the barrier has reduced to the upstream level. The Thames Barrier is then opened, allowing the water upstream to flow out to sea with the outward-bound tide. The Environment Agency has closed the Thames Barrier 174 times since it became operational in 1982 (correct as of Feb 2015). Of these closures, 87 were to protect against Strategic Flood Response Framework Version: 3 Page 29 of 56

30 tidal flooding and 87 were to alleviate river flooding. The frequency of closures has increased over recent decades. A.4.10 The Thames Barrier is designed with numerous back-up systems and undergoes a rigorous maintenance programme. However, London s tidal flood risk cannot be completely removed and, although very unlikely, inundation could still occur as a result of extremely high surge activity, a breach in the walls and embankments or barrier and gate failure. A.4.11 The last major tidal flooding to affect central London was in 1928, when large sections of the Thames embankment were overtopped and the majority of riverside s were flooded to varying extents. 15 people died during the flood, of which many were drowned in basements. Strategic Flood Response Framework Version: 3 Page 30 of 56

31 Flood Risk Type Tidal Lead Authority Environment Agency Likelihood Consequence / Impact Typical Impacts HIGH 1 in 30 year (3.3%) MEDIUM between 1 in 100 year (1%) and 1 in 30 year (3.3%) LOW between 1 in 100 year (1%) and 1 in 1000 year (0.1%) Low Low Low in London but impacts in Kent and Essex Localised flood alerts for the tidal Thames, mainly in South West London. Minor flooding to some low lying unprotected riverside areas in the South West of London. Localised flood alerts for the tidal Thames, from the Thames Barrier to South West London. Minor flooding to some low lying unprotected riverside areas in the South West of London. Impacts in Kent and Essex may require resources from London and disrupt transport. Minor flooding to some low lying unprotected riverside areas in the South West of London. VERY LOW 1 in 1000 year (0.1%) Low to Medium in London but major impacts in Kent and Essex There would be major impacts in Kent and Essex that could impact transport into London and require aid from within London. Minor flooding to some low lying unprotected riverside areas in the South West of London. Warning methods Floodline Warnings Direct (Environment Agency) Flood Guidance Statements (Flood Forecasting Centre) (See appendix C for explanation of warning products) Confidence and understanding of the impacts from FGS 5 days out Confidence and understanding of the impacts from FGS 2 days out Ability to reduce impacts through strategic operational response In December 2013, five days before the tidal flooding on the East Coast, there was an indication of a high impact surge which could impact the east coast but with low confidence. There would be reasonable confidence of a tidal surge two days before it is forecast. The precise impacts would be difficult to predict as they would depend upon interaction of tides, pressure and wind. Extremely high surge activity that the Thames Barrier could not protect against would be forecast with a couple of days lead time. Evacuation and protection of key assets would need to be made early on, before flooding happens. However a gate failure or breach in the tidal embankments could present a no notice flood event. Risk register ID number: HL17 (for reference only). Strategic Flood Response Framework Version: 3 Page 31 of 56

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33 Strategic Flood Response Framework Version: 3 Page 33 of 56 Note: these figures are not cumulative

34 1 in 5yr (defended) FLUVIAL 1 in 20yr (defended) 1 in 100yr (defended) TIDAL THAMES ONLY 1 in 200yr (undefended) (Tidal boroughs only) FLUVIAL AND TIDAL 1 in 1000yr (undefended) Barking and Dagenham Barnet N/A 3469 Bexley Brent N/A 3434 Bromley N/A 8970 Camden N/A N/A N/A N/A N/A City of London N/A N/A N/A Croydon N/A N/A N/A N/A 4639 Ealing Enfield N/A 9550 Greenwich Hackney N/A 3628 Hammersmith and Fulham N/A N/A N/A Haringey N/A 5685 Harrow N/A 2845 Havering Hillingdon N/A 5262 Hounslow Islington N/A N/A N/A N/A N/A Kensington and Chelsea N/A N/A N/A Kingston upon Thames N/A 6648 Lambeth N/A Lewisham Merton N/A N/A 5526 Newham Redbridge Richmond upon Thames Southwark Sutton 8 50 N/A N/A 2139 Tower Hamlets Waltham Forest N/A 4877 Wandsworth N/A Westminster N/A N/A N/A Strategic Flood Response Framework Version: 3 Page 34 of 56

35 Environment Agency data. Correct as of current date of plan. Where N/A is indicated this means either the data is not applicable as the doesn t have any tidal or fluvial influences or where data is not available. Frequency Probability Explanation 1: % 1: % 1:100 1% 1:20 5% 1:5 20% 1 in 1000 year (0.1%) chance of this flood extent to occur. This assumes an undefended worst case scenario, in which there are no flood defences. Takes into account both tidal and fluvial flood modelling. 1 in 200 year (0.5%) chance of this flood extent to occur. This assumes an undefended worst case scenario, in which there are no flood defences. This modelling extent is only present for those boroughs with a tidal influence. Takes into account tidal flood modelling only. 1 in 100 year (1%) chance of this flood extent to occur. This assumes current flood defences are in place. For fluvial boroughs only. 1 in 20 year (5%) chance of this flood extent to occur. This assumes current flood defences are in place. For fluvial boroughs only. 1 in 5 year (20%) chance of this flood extent to occur. This assumes current flood defences are in place. For fluvial boroughs only. Strategic Flood Response Framework Version: 3 Page 35 of 56