Bristol City Council Preliminary Flood Risk Assessment
Preliminary Assessment Report
June 2011
Bristol City Council Brunel House St. George's Road Bristol BS1 5UY
JBA Office
JBA Consulting Nelson House Langstone Park Priory Drive Newport South Wales NP18 2LH
JBA Project Manager
Peter May Revision History
Revision Ref / Date Issued Amendments Issued to Draft v1 10/06/2011 Steven Sodek Draft v2 16/06/2011 Steven Sodek Final 22/06/2011 Steven Sodek Contract
This report describes work commissioned by Steven Sodek, on behalf of Bristol City Council. JBA‟s representative for the contract was Peter May. Peter May, Beth Jones and George Baker of JBA Consulting carried out this work. Prepared by ...... Beth Jones Analyst
Reviewed by ...... Peter May Technical Director Purpose
This document has been prepared as a draft report for Bristol City Council. JBA Consulting accepts no responsibility or liability for any use that is made of this document other than by the Client for the purposes for which it was originally commissioned and prepared. JBA Consulting has no liability regarding the use of this report except to Bristol City Council.
2011s4891 BCC PFRA final.doc
References
Defra and WAG guidance on Flood Risk Areas 2010; Environment Agency (2010 and later amendments) Preliminary Flood Risk Assessment (PFRA) Final guidance and annexes and guidance notes associated with Environment Agency data as dated. Standard text on climate change and development in Sections 5.4 and 5.5 © Environment Agency
Carbon Footprint
874g
A printed copy of the main text in this document will result in a carbon footprint of 874g if 100% post-consumer recycled paper is used and 1113g if primary-source paper is used. These figures assume the report is printed in black and white on A4 paper and in duplex. JBA is a carbon neutral company and the carbon emissions from our activities are offset.
2011s4891 BCC PFRA final.doc
Executive Summary
This Preliminary Assessment Report for Bristol City Council has been prepared as part of the duties established under the Flood Risk Regulations 2009. It is due for submission to the Environment Agency (EA) by 22nd June 2011. The Regulations transpose and implement the requirements of the European Floods Directive, which aims to provide a consistent approach to managing flood risk across Europe. The first stage of the process is to undertake a Preliminary Flood Risk Assessment (PFRA). This involves the review of past floods and the potential for future floods, as well as determining and reviewing the presence of any "areas of significant flood risk", the so called Flood Risk Areas. Where such Flood Risk Areas have been determined, on the basis of national guidance issued by Defra and Welsh Assembly Government (WAG), Lead Local Flood Authorities (LLFAs) are required to review, and if necessary propose amendments to, the indicative areas using locally held information. One such indicative Flood Risk Area has been proposed for the Greater Bristol area, one of ten such areas in England. This is centred on the administrative area of Bristol City Council, although also extends a short way into three neighbouring LLFA areas. Bristol City Council, as a LLFA, has a responsibility under both the Flood Risk Regulations 2009 and the Flood & Water Management Act 2010 for managing local flood risk within its area. To meet this duty, the council has completed the PFRA and assessed the risk of flooding from surface water, groundwater and ordinary watercourses, together with any interaction with drainage systems, sewers and other sources. The EA is responsible for assessing the risk of flooding from main river, the sea and large reservoirs. The assessment of local flood risk has involved the collection and review of readily available information held by Bristol City Council and partners on past floods across the area. This has been considered in light of national datasets provided by the EA and informed by discussions with the local multi-agency partnership group involving other risk management authorities, including the EA, Wessex Water, the Lower Severn IDB and neighbouring LLFAs. This review has then been informed by the ongoing Surface Water Management Plan (SWMP) work and supplemented by a detailed and objective assessment of the potential risks of future flooding across the area. The PFRA has been undertaken using JBA Consulting's bespoke analytical GIS "Flood Risk Metrics" software (JFrism). This powerful graphical analysis has allowed a comprehensive study of the flood risk facing people, properties and critical infrastructure across Bristol. The exposure of these and other vulnerable receptors to a range of local flood sources has been assessed on a 1km grid square basis across the entire area. This has allowed the completion of the PFRA and provided the means to analyse and clearly display the risk from different flood sources on a Parish, Ward or entire authority basis. Details of the critical infrastructure and properties at risk will also help inform the multi- agency Emergency Flood Plan and assist in emergency planning. The PFRA has shown there are approximately 68,300 people, 29,200 residential properties, 5,000 non-residential properties and 200 critical infrastructure sites at risk from surface water flooding across Bristol City Council's administrative area. These figures form the bulk of the wider indicative Flood Risk Area that extends across into the three neighbouring LLFA areas. Within the wider Flood Risk Area, there are approximately 73,900 people, 31,600 residential properties, 5,700 non-residential properties and 200 critical infrastructure sites at risk from surface water flooding. These figures have been derived from the locally agreed Surface Water Management Plan data, in conjunction with the Flood Map for Surface Water Flooding (FMfSWF).
2011s4891 BCC PFRA final.doc
The indicative Flood Risk Area has been further reviewed in light of the locally available information, in particular that obtained and produced as part of the SWMP. This analysis has confirmed there are no proposals to suggest any amendments to the area, or to propose any new Flood Risk Areas. Consequently Bristol City Council and neighbouring partners will have further obligations to prepare Flood Hazard and Risk Maps in 2013 and Flood Risk Management Plans in 2015 as required under the Regulations. The PFRA process has helped strengthen and underline the importance of partnership working and the need for sharing data and information through the Partnership Group. A comprehensive archive of past floods has been compiled and a database structure exists to record the mandatory information necessary for documenting all future floods. This will greatly ease the PFRA review process in 6 years time. Understanding and communicating local flood risk in this way will provide the foundations for developing and delivering Bristol City Council's Local Flood Risk Management Strategy. This will be developed over the next year as part of the duties under the Flood & Water Management Act 2010. The Local Flood Risk Management Strategy will define how flood risk is to be assessed and managed across Bristol in future years. The PFRA analysis has provided the opportunity to inform how this future strategy will be taken forward.
2011s4891 BCC PFRA final.doc
Contents
Executive Summary ...... 3 1. Introduction ...... 9 1.1 Scope of the Report ...... 9 1.2 Objectives and Approach...... 9 1.3 Study Area ...... 11 2. Lead Local Flood Authority Responsibilities ...... 14 2.1 Governance and Partnership ...... 14 2.2 Communication ...... 15 3. Methodology and Data Review ...... 16 3.1 Information from EA ...... 16 3.2 Data Review ...... 18 3.3 Data Availability and Limitations ...... 19 3.4 Data Management Systems ...... 20 4. Past Flood Risk ...... 22 4.1 Introduction ...... 22 4.2 Significant Harmful Consequences ...... 22 4.3 Past Flood Events ...... 23 5. Future Flood Risk ...... 26 5.1 Introduction ...... 26 5.2 Locally Agreed Surface Water Information ...... 27 5.3 Future Floods and Consequences ...... 29 5.4 The Impacts of Climate Change ...... 36 5.5 Significant Local Developments ...... 37 6. Identification of Flood Risk Areas ...... 38 6.1 Indicative Flood Risk Areas ...... 38 6.2 New Flood Risk Areas ...... 44 7. Next Steps ...... 46 7.1 Review ...... 46 7.2 Local Flood Risk Management Strategy ...... 46 Appendices...... 48 A.1 Records of past floods and their significant consequences (preliminary assessment report spreadsheet) ...... 48 A.2 Records of future floods and their consequences (preliminary assessment report spreadsheet) ...... 49 A.3 Records of Flood Risk Areas and their rationale (preliminary assessment report spreadsheet) ...... 50 A.4 Review checklist ...... 51 A.5 GIS layer of flood risk area ...... 52
2011s4891 BCC PFRA final.doc
List of Figures
Figure 1.1 Bristol City PFRA Area ...... 11 Figure 1.2 Location Plan Showing Indicative Flood Risk Area and Severn River Basin District Boundary...... 12 Figure 2.1 Flood Risk Partnership Data Sharing Model ...... 14 Figure 3.1 Places above Local Flood Risk Threshold ...... 17 Figure 3.2 City of Bristol Initial Flood Incident Report Data ...... 20 Figure 3.3 City of Bristol Flood Incident Pro-forma and Accompanying Letter ...... 21 Figure 4.1 Location of Past Flood Events ...... 25 Figure 5.1 Hotspot Locations within Bristol ...... 26 Figure 5.2 Clustered Locations above Thresholds ...... 27 Figure 5.3 Residential Properties at Risk of Surface Water Flooding ...... 32 Figure 5.4 Non Residential Properties at Risk of Surface Water Flooding ...... 33 Figure 5.5 Critical Infrastructure at Risk of Surface Water Flooding ...... 34 Figure 5.6 Residential properties at Risk of Surface Water Flooding by Ward ...... 35 Figure 6.1 Surface Water Management Extent ...... 39 Figure 6.2 Residential Properties at Risk of Surface Water Flooding - IFRA ...... 41 Figure 6.3 Non Residential Properties at Risk of Surface Water Flooding - IFRA ...... 42 Figure 6.4 Critical Infrastructure at Risk of Surface Water Flooding - IFRA ...... 43 Figure 6.5 FMfSW v SWMP Hotspot Locations...... 45
List of Tables
Table 3-1 Information and Data Review ...... 18 Table 4-1 Summary of Past Flood Events and their Consequences ...... 24 Table 5-1 Predicted Residential Property Counts using SWMP and ...... 28 FMfSW results for the City of Bristol ...... 28 Table 5-2 Assessment of Key Flood Risk Indicators for Bristol City Council Area ...... 30 Table 5-3 Categories of Flood Risk for Local Assessment ...... 31 Table 6-1 Predicted Residential Property Counts using FMfSW and the ...... 38 locally agreed SWMP/FMfSW results for the Bristol IFRA ...... 38 Table 6-2 Assessment of Key Flood Risk Indicators for Bristol IFRA ...... 39 Table 6-3 Additional LLFA Critical Infrastructure Analysis ...... 40
2011s4891 BCC PFRA final.doc
Abbreviations & Glossary
Term or Abbreviation Definition AONB Area of Outstanding Natural Beauty Assets Structures, or a system of structures used to manage flood risk AStGWF Areas Susceptible to Groundwater Flooding AStSWF Areas Susceptible to Surface Water Flooding
Catchments An area that serves a river with rainwater. Every part of land where the rainfall drains to a single watercourse is in the same catchment CFMP Catchment Flood Management Plan Cultural heritage Buildings, structures and landscape features that have an historic value. These are also known as heritage assets
Defences A structure that is used to reduce the probability of floodwater or coastal erosion affecting a particular area (for example a raised embankment or sea wall) Defra Department for Environment, Food and Rural Affairs EC European Commission EC Inspire Directive Implemented by the 'Inspire Regulations 2009'. The main aim being to improve the quality, consistency and accessibility of spatial data sets and services for environmental data
FCERM Flood and coastal erosion risk management Flood The temporary covering by water of land not normally covered with water
FMfSW Flood Map for Surface Water Flood Risk Area An area determined as having a significant risk of flooding in accordance with guidance published by Defra and WAG
FRIS Flood Reconnaissance Information System FWMA Flood and Water Management Act GHG Greenhouse Gasses GIS Geographic Information Systems Groundwater Water which is below the surface of the ground and in direct contact with the ground or subsoil HSWGW Historic Surface Water and Groundwater IDB Internal Drainage Board Indicative Flood Risk Areas Areas determined by the Environment Agency as indicatively having a significant flood risk, based on guidance published by Defra and WAG and the use of certain national datasets. These indicative areas are intended to provide a starting point for the determination of Flood Risk Areas by LLFAs Jfrism JBA Consulting's bespoke 'Flood Risk Metrics' GIS tool LLFA Lead Local Flood Authority
2011s4891 BCC PFRA final.doc
Local flood risk Flood risk from sources other than main rivers, the sea and reservoirs, principally meaning surface runoff, groundwater and ordinary watercourses Main River A watercourse shown as such on the Main River Map, and for which the Environment Agency has responsibilities and powers
MFP City of Bristol Multi-Agency Flood Plan
NRD National Receptor Dataset – a collection of risk receptors produced by the Environment Agency
Ordinary Watercourses All watercourses that are not designated Main River, and which are the responsibility of Local Authorities or, where they exist, IDBs Preliminary Assessment A high level summary of significant flood risk, based on available and Report readily derivable information, describing both the probability and harmful consequences of past and future flooding Preliminary Assessment Reporting spreadsheet which LLFAs need to complete. The spreadsheet Spreadsheet will form the basis of the Environment Agency‟s reporting to the European Commission
PFRA Preliminary Flood Risk Assessment
PPS25 Planning Policy Statement 25 Receptor Something that may be harmed by flooding
Regulations The Flood Risk Regulations 2009 Resilience The ability of the community, services, area or infrastructure to withstand the consequences of an incident Risk Measures the significance of a potential event in terms of likelihood and impact River basin district There are 11 river basin districts in England and Wales, each comprising a number of contiguous river basins or catchments. The Environment Agency is responsible for collating LLFA reports at a river basin district level SACs Special Area of Conservation SFRA Strategic Flood Risk Assessment Source The origin of a hazard (e.g. heavy rainfall, strong winds, surge etc)
SPAs Special Protection areas SSSIs Sites of Special Scientific Interest Surface runoff Rainwater (including snow and other precipitation) which is on the surface of the ground (whether or not it is moving), and has not entered a watercourse, drainage system or public sewer SWMP Surface Water Management Plan UKIP09 UK Climate Change Projections 2009 WAG Welsh Assembly Government
2011s4891 BCC PFRA final.doc
1. Introduction
1.1 Scope of the Report Bristol City Council has new duties as a Lead Local Flood Authority (LLFA) to manage local flood risk across its area. The focus of this new role is to assess the flood risk from local sources such as surface water, groundwater and ordinary watercourses. The Environment Agency (EA) is responsible for assessing the risk of flooding from main rivers (such as the River Avon and Frome), the sea and from large reservoirs. One of the first duties is to complete a Preliminary Flood Risk Assessment (PFRA). This is required as part of the obligations under the Flood Risk Regulations 2009, which transposes and implements the requirements of the European Floods Directive. This aims to manage and reduce the risks that floods pose to human health, the environment, economic activity and cultural heritage, by providing a consistent approach to managing flood risk across Europe. This Preliminary Assessment Report presents the findings of an assessment of local flood risk and the past and potential future impacts of flooding across Bristol. It has to be provided to the EA by 22nd June 2011 as part of a national submission to be reviewed and then published and sent to the European Commission in December 2011. The Flood Risk Regulations 2009 establish a flood risk management framework consisting of four stages that will be reviewed on a 6-yearly basis, namely: To prepare a Preliminary Assessment Report on past floods and potential future floods To identify Flood Risk Areas (FRAs) where flood risk is deemed nationally significant To produce appropriate Flood Hazard and Flood Risk Maps for FRAs To prepare Flood Risk Management Plans for FRAs
This Preliminary Assessment Report presents the outcomes of the first two stages that together make up the PFRA process, namely the assessment of local flood risk and the identification of any Flood Risk Areas, where the risk of flooding is considered nationally significant. The Defra and Welsh Assembly Government guidance sets out the criteria and thresholds for assessing whether a risk of flooding is of national significance. This confirms that the Bristol area has been defined as one of the 10 indicative FRAs that have been identified in England, based upon nationally available information. The area straddles across three neighbouring LLFA areas - South Gloucestershire; Bath & North East Somerset; and North Somerset - as well as covering the bulk of Bristol City Council's area. This report therefore includes a review of this indicative FRA in respect of locally held information, in particular the data and modelling that relates to the ongoing Bristol Surface Water Management Plan. For those FRAs that are agreed with the EA and published by December 2011 as areas of significant flood risk, these will be subject to the further stages outlined above, namely the preparation of Flood Hazard and Risk Maps by 2013 and the production of Flood Risk Management Plans by 2015.
1.2 Objectives and Approach The overall aim and objective of the PFRA process is to carry out a high level exercise designed to make use of all existing and readily available data, in order to review past floods and the potential for future floods across Bristol.
2011s4891 BCC PFRA final.doc 9
The key objectives are to: Identify partner organisations involved in local flood risk management and engage in the PFRA process through ongoing collaboration Establish agreed systems for future data management, sharing and storage Describe the agreed systems and data standards for recording future flood incidents Describe the adopted approach to the PFRA Undertake an assessment of past floods across Bristol from local sources of flooding and summarise the consequences and impacts of these events Assess the potential adverse consequences of future flood events within the area Review and update the system to enable the recording of all relevant information for future floods Review the provisional national assessment of indicative Flood Risk Areas provided by the EA and provide explanation and justification for any amendments
The assessment of local flood risk has involved the collection and review of readily available information held by Bristol City Council and partners on past floods across the Bristol area. This has been considered in light of national datasets provided by the EA and further informed by discussions with the local multi-agency partnership group involving other Risk Management Authorities, including the EA, Wessex Water, the Lower Severn Internal Drainage Board (LSIDB) and neighbouring LLFAs. Previous and current flood risk management studies relevant to the study area that have been reviewed for the purpose of producing this PFRA include the following: The Shoreline Management Plan Bristol Avon Catchment Flood Management Plan BCC Strategic Flood Risk Assessment level 1 BCC Strategic Flood Risk Assessment level 2, including Avonmouth and Severnside BCC Surface Water Management Plan (ongoing at time of writing) BCC Central Area Flood Risk Assessment (ongoing at time of writing) Dundry Hills Flood Risk Assessment (ongoing at time of writing)
This review has then been supplemented by a detailed and objective assessment of the potential risks of future flooding across the area. This has been undertaken using JBA Consulting's bespoke GIS analytical "Flood Risk Metrics" ("JFrism") software, which allows a detailed assessment of the risk from local flood sources to a wide range of receptors and at differing threshold levels. This has helped with the consideration of significant flood risk and the identification of any Flood Risk Areas. It has also provided Bristol City Council with a powerful graphical tool that helps understand and communicate a range of flood risks across the area, capable of being presented at a Parish, Ward or LLFA-wide basis. The decision was taken to invest in and use these GIS tools in order to not only ensure the analysis delivered both the PFRA that is required now, but to also gain efficiencies and avoid duplication of efforts in the preparation of future flood management strategies across the council area. Understanding and communicating local flood risk in this way will provide the foundations for developing and delivering Bristol City Council's Local Flood Risk Management Strategy. This will be developed later this year as part of the duties under the Flood & Water Management Act 2010. The Local Flood Risk Management Strategy will define how flood risk is to be assessed and managed across Bristol in future years. The PFRA analysis has therefore been used as an opportunity to inform how this future strategy will be taken forward. The PFRA process is also an opportunity to review, strengthen and promote local partnership and information sharing arrangements between the local Risk Management Authorities. It
2011s4891 BCC PFRA final.doc 10
represents one of the first activities to be performed in accordance with the new requirements established under the Flood & Water Management Act 2010. Roles and responsibilities of operating authorities have now been clarified, as has the need for partner organisations to cooperate and share data and information in a spirit of partnership. This delivers on two of the central recommendations of the Pitt Review into the Summer 2007 floods. A further objective and outcome of this work is to establish or describe existing agreed data management standards and systems that will be used by Bristol City Council for recording all the critical information relating to all future floods that occur across the area. Records of past floods held by the council and others have been reviewed and consolidated into the spreadsheet contained in Annex 1. This includes a number of mandatory fields that are required as part of the EC reporting duties and provide the template for the new system, such that all flood events are thoroughly recorded in the future. This will ensure that comprehensive records are collected and recorded in the correct format, simplifying the future revision of the PFRA and updating of "past floods" which will be required in 6 years time.
1.3 Study Area Bristol City has a population of approximately 410,500 within the unitary authority boundary. The population increases to approximately 522,784 (1991 Census) when the Greater Bristol conurbation is considered, including areas such as Hanham, Kingswood, Downend, Frenchay, and Filton. It is important to consider these areas as they drain into Bristol City Council‟s area of responsibility. Bristol has been identified as „strategically significant‟ within the Draft Regional Spatial Strategy and is projected to see significant amounts of growth in the period to 2026. The study area is defined by Bristol City Council's area of responsibility, and covers an area of 110km2 (see Figure 1.1).
Figure 1.1 Bristol City PFRA Area
2011s4891 BCC PFRA final.doc 11
The Bristol indicative Flood Risk Area (IFRA) extends beyond the Bristol City Council boundary and into three neighbouring LLFA areas. This is shown in Figure 1.2, which identifies the position of each IFRA across England and Wales, as well as the setting of the study area with regards to the relevant EC Severn River Basin District boundary.
Figure 1.2 Location Plan Showing Indicative Flood Risk Area and Severn River Basin District Boundary.
Economically, the recent history of the Bristol urban area, including adjacent areas of South Gloucestershire, has been heavily influenced by the decline of the defence industry which has lead to a reduction in manufacturing employment. This has largely been replaced by service industries. Major sectors include banking, financial and legal services with major employers such as Lloyds TSB and Sun Life Assurance present; Bristol being the largest financial centre in the UK outside of London. The Bristol urban area is also a hub for environmental and aerospace industries (BAE Systems, Airbus) with strong economic contributions also coming from media (Orange, British Telecom) and information technology (Hewlett Packard) firms. Furthermore, there are a number of business parks and trading estates (for example at Filton/Parkway) across the urban area accommodating a wide range of smaller businesses. Unemployment is below the national average and some areas are among the least deprived in the country, although these lie adjacent to some of the most deprived in the country. Bristol City is characterised by a great richness in its historic environment encompassing both areas such as the medieval centre, historic dockland and individual structures such as the Clifton Suspension Bridge. Its urban areas contain nearly 4500 listed buildings and over 30 conservation areas. This, along with Bristol‟s heritage in the arts, culture and education has been credited with being a major factor in the attraction of inward investment. There has been a growing consensus around the need to protect Bristol‟s open spaces, and to balance the value of wildlife and nature conservation against the need for development.
2011s4891 BCC PFRA final.doc 12
Understanding and managing flood risk is therefore an essential requirement to help protect and minimise any damage and disruption to the social, cultural, economic and environmental assets of the city. This PFRA helps define these risks and plan for their long-term management.
2011s4891 BCC PFRA final.doc 13
2. Lead Local Flood Authority Responsibilities
2.1 Governance and Partnership The Flood & Water Management Act 2010 has established an enhanced role for local authorities so that they take on the responsibility for leading the co-ordination of flood risk management in their area. Bristol City Council, as one such Lead Local Flood Authority (LLFA), is responsible for all local flood risk management within its administrative area. This includes flooding which primarily originates from ordinary watercourses, surface water and groundwater sources, as well as any interactions between all sources of flooding, such as from main rivers or the sea, where these could impact upon local sources. These new duties also define the EA as the responsible body for the management of flood risk from main rivers, large reservoirs and the sea. The EA is also responsible for providing a strategic overview on all flood risk matters and for producing a national strategy for Flood and Coastal Erosion Risk Management (FCERM) for England. It is evident therefore that close partnership working between all the risk management authorities has been recognised as essential and of the upmost importance for effective flood risk management. Duties to co-operate and share information are now included in the Act and the Regulations. The Flood & Water Management Act also places a responsibility on LLFAs to take the lead and co-ordinate partners in the management of FCERM duties. These responsibilities now form a central principal in the delivery of the PFRA and the future development of Bristol City Council's Local Flood Risk Management Strategy. It is recognised that it is essential for all stakeholders - such as neighbouring authorities, the EA, Internal Drainage Boards (IDBs), and Water Companies - to be fully engaged and working together to fully understand any flood risk issues that may impact upon the area. Bristol City Council has engaged with the EA, Wessex Water and the Lower Severn Internal Drainage Board (LSIDB) to form a partnership that is led by Bristol City Council. The partnership model for sharing data and maintaining a central Bristol City Council database is shown in Figure 2.1 below.
Figure 2.1 Flood Risk Partnership Data Sharing Model
2011s4891 BCC PFRA final.doc 14
The partnership was established as part of the ongoing Bristol Surface Water Management Plan, in order to improve communication; to develop a shared understanding of surface water flooding issues; and to work together to share data and understanding of key asset ownership and maintenance obligations. It operates under a Memorandum of Understanding which remains in place and has helped the effective management of the PFRA process, proving particularly useful for the sharing of information. The partnership group will play a crucial role in the future delivery of local flood risk management services. Such partnership working helps facilitate more effective communications with residents at flood risk, as well as provide more co-ordinated emergency response plans and longer term management strategies. It provides the integrated approach as originally recommended by the Pitt Review, helping to deliver the SWMP and PFRA now and to prepare the foundations to the Local Flood Risk Management Strategy required in the future.
2.2 Communication Communication with partners takes place in the form of regular flood partnership group meetings, providing the forum for regular liaison with and communication between the local risk management authorities. These meetings are chaired and co-ordinated by Bristol City Council, helping to clarify roles and responsibilities as well as to plan for the effective future management of local flood risk. They provide an opportunity for partners to share data, information and knowledge and to agree a co-ordinated plan of flood management and response. This partnership approach helps to optimise locally available resources and experience, as well as to identify funding opportunities and agree local flood risk management priorities This forum provides the opportunity to communicate this shared understanding and the agreed management actions across the Council and between partner organisations. It also enables the vital link to be made with local communities and members of the public directly affected and at flood risk. Communication with the public is also achieved primarily through the Bristol City Council website. The flood risk section has recently been revised to provide a comprehensive source of local flood risk information and references to further related material. There is an intention to utilise the Neighbourhood Initiative to increase dialogue with the public, following recent success in gathering historical flooding information from members of the public through a flood event survey. This will help gather information from members of the public about either a very recent flood or perhaps capturing knowledge and experience of past floods.
2011s4891 BCC PFRA final.doc 15
3. Methodology and Data Review
3.1 Information from EA The methodology for undertaking this PFRA is based upon the national guidance prepared by the EA and the Ministerial Guidance produced by Defra and WAG. The latter provides the thresholds and criteria used for determining Flood Risk Areas where the risk of flooding is identified as significant. The EA guidance has explained the technical detail behind the PFRA, the form of the report and how to apply the Defra/WAG guidance on significant risk. The EA has also provided CDs containing supporting information and made available national datasets distributed via DataShare. This information has included: Maps, spreadsheets and GIS layers of all places above local flood risk thresholds (Figure 3.1 - the "blue squares" map) and the clusters then created in determining Flood Risk Areas Details on the consequences of flooding to cultural, environmental and historic assets and Pollution, Prevention & Control (PPC) sites Two national datasets showing surface water flooding extents have been made available by the EA to LLFAs, namely: Areas Susceptible to Surface Water Flooding map (AStSWF) - derived from one rainfall event with three susceptibility bandings: less, intermediate and more. Flood Map for Surface Water (FMfSW) - derived from two rainfall events dividing into two depth bandings: 1:200 rainfall and 1:200 rainfall deep, as well as 1:30 rainfall and 1:30 rainfall deep. There are also four national datasets on groundwater flooding detailed in the EA guidance, including the Areas Susceptible to Groundwater Flooding broad-scale map. In addition, there are details on DataShare of information on past floods, including the Historic Flood Map and Flood Event Outlines, although primarily focussing on flooding from main river and the sea. The Historic Surface Water and Groundwater (HSWGW) Geodatabase has not been available, although it is known that this contains some records originally submitted by local authorities. Whilst the information above relates to differing flood sources and records of past events, another key dataset provided by the EA and used in the PFRA is the National Receptor Dataset (NRD. This relates to receptor vulnerability to flooding and provides details of social, economic, environmental and cultural receptors including residential properties, hospitals, schools, electricity sub-stations and critical transport infrastructure. It can be seen from Figure 3.1 that the places where the national thresholds for residential, non-residential and critical infrastructure are exceeded include much of the City of Bristol, areas such as Clifton, Cabot, Ashley Ward; Redland, Cotham and Southville Wards together with other local hotspots.
2011s4891 BCC PFRA final.doc 16
± PFRA Analysis City of Bristol Places Above Flood Risk Threshold
Based on the Flood Map for Surface Water (200 year Deep) which indicates the chance of land flooding to a depth greater than 0.3m during a 1 in 200 year rainfall event.
Legend Hotspots City of Bristol Boundary Bristol Indicative Flood Risk Area (IFRA) Hotspots are1km grid squares where at least one of the following flood risk indicators is above the threshold given below (using NRD v1.0):
1. Number of People > 200 2. Critical Services > 1 3. Number of Non-Residential Properties > 20
Indicators calculated using the EnvironmentAgency's detailed method of counting (based on property outlines).
Local Authority Boundaries City of Bristol Boundary
Drawn by: Bethlyn Jones Date: 22/06/2011 Status: Draft Drawing Number:Figure 3.1 OS Licence: This map is reproduced from Ordnance Survey material with the permission of Ordnance Survey on behalf of the Controller of Her Majesty’s Stationary Office © Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution of civil proceedings. Bristol City Council. 100023406. 2011. 0 1.25 2.5 5 KM
3.2 Data Review Locally available information and studies have been reviewed in conjunction with the nationally provided data. Table 3-1 shows the main sources of information gathered or reviewed that have been used in the production of this Preliminary Assessment Report.
Data Name Source Description Historic Flood Map EA A merged, un-attributed flood extent for records of flooding from rivers, sea and groundwater only. Flood Event Outline EA Attributed spatial flood extent data for records of flooding from all sources FRIS Incidents EA Flood Reconnaissance and Information System, attributed point data for records of flooding from all sources FRIS Properties EA Flood Reconnaissance and Information System, attributed point data for records of flooding of properties from all sources Fire Service Flood Fire Service Attributed point data for records of fire service responses to Records flood incidents BCC Flood Incidents BCC Attributed spatial flood extent data for records of flooding from all sources Bristol SWMP BCC Uses detailed modelling to assess the hazard of surface water flooding in Bristol Paper records Various A qualitative description of past flood events collated from past reports and media entries BHS Hydrological Events Dundee Contains information on hydrological events that University complement existing instrumental records of rainfall, runoff and snow etc. Flood Map for Surface EA Surface water flood outlines for 0.5% and 3.33% AEP Water rainfall events National Receptor EA Spatial dataset containing various GIS layers of risk Database receptors categorised in to themes including buildings, utilities, environment, heritage and transport The Shoreline BCC Provides strategic policy for coastal management now and Management Plan in the future Bristol Avon Catchment EA Looks at current and future flood risk and identifies Flood Management Plan catchment level policies and actions BCC Strategic Flood Risk BCC Considers strategic planning issues related to flood risk in Assessment level 1 Bristol BCC Strategic Flood Risk BCC Examines several flood risk areas in more detail in order to Assessment level 2, assess suitability for development including Avonmouth and Severnside BCC Central Area Flood BCC Assesses the probability and consequences of combined Risk Assessment tidal and fluvial events in Bristol (ongoing at time of writing) Dundry Hills Flood Risk BCC Identifies necessary actions required for improved flood Assessment (ongoing at risk management in the area time of writing)
Table 3-1 Information and Data Review
2011s4891 BCC PFRA final.doc 18
Locally held data and information on past flooding has been collected over the years and has been consolidated into an archive of past flood records. The most comprehensive source of information is contained within Bristol City Councils' database of past flood events, drawn from records held by the Council's Highways Department, as well as reports received from members of the public. This main source of flood event information has been supplemented where possible with records and information from Wessex Water, the EA and the LSIDB. In addition, some records held by the Fire Service have also been incorporated into the database. The Water Company also hold records of historic sewer flooding incidents in the area on their DG5 Registers although these have not been used in the production of this PFRA. They will however provide additional useful information for the partnership group to consider for the future preparation of the Local Flood Risk Management Plan. The Bristol City Council database has provided the primary resource for the PFRA. However these records had some limitations and were often incomplete so they have been further refined and consolidated into the revised spreadsheet that is contained within Annex 1 to this report.
3.3 Data Availability and Limitations The data referenced above were readily available, the majority having already been collated for previous and ongoing studies, as well as for day-to-day flood risk management responsibilities. Quality assurance checks were carried out on the flood records, in order to identify and exclude inaccurate or incomplete records. This has improved the quality and reliability of information on past floods, helping to better inform the response to future floods. The review identified that there were limitations in the value of much of these data, as described further below: The Historic Flood Map contained spatial extents of flooding caused by main rivers only. The data were therefore not helpful for the analysis of historic flood events from local sources of flooding from surface water, ordinary watercourses and groundwater. The Flood Event Outlines data, although attributed, also contained spatial extents of flooding caused predominantly by main rivers only. This dataset therefore was also not helpful for the analysis of historic flood events from local sources. The FRIS incidents data proved most useful in identifying significant past flood events. The only limitation was that it is unknown how complete this dataset is and therefore some historical events may have been overlooked. The FRIS properties dataset was useful in verifying the locations of past events, however because incident dates were not recorded it was not possible to group incidents by date to determine significant events. The Fire Service flood records data contained data on incident date, however showed a limited number of records occurring on or around the same date and so contributed little in determining significant events. The Bristol City Council flood incidents data is a new dataset that records known and reported instances of flooding from 2009 onwards. There were no significant events identified from this data source during this short period of time. Paper records offered valuable information on significant past events. Exact property numbers were not recorded, however significant events were identified on the basis of the number of reported flooding incidents. The BHS hydrological events information lacked information on the source and extent of flooding therefore no significant events were identified from this data source.
Restricted data are stored in a secure drive location with limited access to approved Council personnel only. Data licensing requirements were considered and addressed at each stage of the assessment when viewing, storing and sharing information.
2011s4891 BCC PFRA final.doc 19
3.4 Data Management Systems Through the process of collecting and consolidating information and records on past floods, the existing flood event and data storage system has been updated by the Council. This ensures that future records contain all the necessary data fields and information consistent with the PFRA reporting template set out by the EA in Annex 1. Mandatory fields within the PFRA reporting template are included as well as some of the additional fields that are likely to be required in the future. All spatial data used in this assessment are captured by the City of Bristol Council in Arc GIS format in order to readily store and view information. It is the intention to continue with this format in to the future. Procedures for recording all future flood incidents going forward are in the process of being put in to place. This system will be shared both right across the various council departments and with the Multi-Agency Partnership Group, enabling interchange of data and the recording of all flood events regardless of responsibility or source. Members of the public who observe flood events are encouraged to contact the Council and report the incident, regardless of the type of flooding encountered and the organisation ultimately responsible for assessing this type of flood risk. Relevant details are taken from the caller and entered into the Council database, to be stored and used to inform future strategies (see example screen shot of report in Figure 3.2). Details can also be passed onto the relevant organisation at this point, i.e. reports of Main River flooding sent through to the Environment Agency. Assistance and advice as to the best form of action can then be issued to the caller once the situation is fully understood.
Figure 3.2 City of Bristol Initial Flood Incident Report Data
Following the flood event, the caller, as well as other residents and property owners in the surrounding area who may be potentially affected, are sent a Flood Incident Pro-forma which has also been developed by the City of Bristol Council (Figure 3.3).
2011s4891 BCC PFRA final.doc 20
Figure 3.3 City of Bristol Flood Incident Pro-forma and Accompanying Letter
These processes will ensure that all required information on flood events is captured in the future, recorded in the correct format for direct input to future PFRA reviews. It will ensure all local flood events are captured and assessed, providing invaluable records for developing and delivering the Local Flood Risk Management Strategy. It will also serve to simplify the process going forward and make for a more efficient means of submitting the required information on past floods. The Memorandum of Understanding between local risk management operating authorities addresses the principals of data sharing, co-operation and partnership. At its heart is the agreement for sharing data and information and recording flood event information in a consistent and complete manner, providing an invaluable archive of quality assured flood records.
2011s4891 BCC PFRA final.doc 21
4. Past Flood Risk
4.1 Introduction This section summarises the relevant information collected and analysed on past floods within the Bristol City Council area from local flood sources. This has been derived from the records described in Section 3 above and is presented in the required format in Annex 1 of this report. The Flood Risk Regulations refer to past floods which had "significant harmful consequences". However, while the meaning of "significant" has been defined in terms of national risk used to identify Flood Risk Areas, there is no such definition in terms of past floods from local sources. The guidance leaves this for individual LLFAs to determine as circumstances and approaches vary.
4.2 Significant Harmful Consequences The information provided by the EA shows there are numerous locations across the Bristol area where flood risk from surface water in any 1km2 grid square exceeds the nationally defined thresholds (see the "Blue Squares" map in Figure 3.1). The subsequent clustering process described in the Defra/WAG Guidance highlights the extent of potential flood risk across the area. Records of past floods illustrate how there are many areas where local flood risk has been an issue in the past and remains a risk in the future. The PFRA analysis has therefore been carried out focussing on all these areas, utilising the JBA Consulting JFrism GIS tools to replicate the national analysis and to consider remaining areas across the area. In considering thresholds for local flood risk across Bristol, emphasis has been placed upon ensuring the PFRA process is used to also inform and provide a consistent basis and foundation for the forthcoming Local Flood Risk Management Strategy. There are efficiencies to be gained from dovetailing the two processes and ensuring one consistent approach. This will also avoid any unnecessary duplication of effort. For the purposes of collating information on past floods for this assessment, the following indicators were used to identify past floods with significant harmful consequences: 5 or more residential properties 1 or more critical services 2 or more non-residential properties These indicators were chosen to reflect the availability of historical flooding data, in order to identify a suitable number of past flood events with significant harmful consequences. In addition, it should be stressed that the only events included in the identification of past floods are those where the main source of flooding was from a source other than main rivers or the sea. Numerous tidal and fluvial flooding events have therefore been excluded from this report.
2011s4891 BCC PFRA final.doc 22
4.3 Past Flood Events The following methodology was used in determining significant past flood events. Point data sources were analysed by date in order to group individual incidents into an event. For instances where 5 or more residential properties were flooded; 2 or more non-residential properties flooded; or incidents where one or more critical infrastructure sites were flooded, these have been recorded as distinct flood events and identified as of local significance. Paper records of past flooding incidents and events were also reviewed and professional judgment was applied to determine significant events. Spatial extent outlines of past flood events were not used to determine significant events due to data limitations described in the data review section. The list of past flood events and details of associated consequences is presented in Annex 1. It is important to realise that this record is based on available data only. It is therefore likely to overlook a number of past floods for which historical data are incomplete, unreliable or simply not available. Unreliable or incomplete records have been omitted to ensure the archive contains the best available information, to provide increased confidence in the record of past floods. The process of analysing historical flood event data and records has emphasised the importance of improving future flood event recording. This is being addressed by Bristol City Council such that all the relevant and necessary information for future flood events will be collected and archived for future reference. From the many individual entries contained in the original database, an archive of 11 distinct flood events has been prepared, dating back to 1937. Various other instances of flooding are also noted. For each event, details have been provided of the source, location and extent of the flooding. For each event, the human health, economic, environmental and cultural heritage impacts and consequences are detailed where known. These events record flooding that, for the most part, was caused by natural exceedance from either excessive surface water runoff, or from ordinary watercourse flooding, often in combination with flooding from main rivers and tidal effects. The events were generally short lived (around one day) as is characteristic with surface water flooding, although periods of river flooding lasted longer. By far the most severe event on record were the "Great Floods of 1968", when over 800 properties were flooded from surface runoff and the River Chew, as a result of an extreme rainfall event over Chew Stoke. Further details of these and other past floods and their consequences are summarised in Table 4-1 below and reproduced in Annex 1 in full. The general locations of past floods, where known, are show in Figure 4.1.
2011s4891 BCC PFRA final.doc 23
Date Flood Details Consequences 15/07/1937 5 reported incidents around the centre of the city 1 residential property and 2 non-residential properties affected
18/12/1965 10 reported incidents of flooding around Stapleton, thought to be from 2 residential properties the Frome main river. Exact source unknown and 2 non-residential properties affected
10/07/1968 “The great floods of 1968”. Major flooding caused by the river Chew and 805 residential surface water run-off from Dundry Hills. 175mm rainfall in 18 hours properties flooded. falling on Chew Stoke
30/05/1979 40mm rainfall at Horfield between 9am and 4pm. Emergency services Number of properties called to approx. 150 incidents, with major flooding of premises in flooded not known, Whitchurch, Knowle, Redland, Frenchay and Westbury-on-Trym. internal flooding of more than 5 properties confirmed
09/12/1979 From midnight 8th/9th to the following midnight 32mm of rainfall Number of properties recorded at Hartcliffe, 28mm at Horfield. 70 reports of flooding relating to flooded not known, 33 separate incidents. internal flooding of more than 5 properties confirmed 29/07/1980 5 reported incidents in North / West of city 5 residential properties and 2 non-residential properties affected
06/03/1982 9 reported incidents, concentrated around Bishopsworth 7 residential properties affected
06/08/1982 12 reported incidents across Bristol, 18mm of rainfall recorded in 1hr 9 residential properties affected
02/08/1984 86mm of rainfall recorded in 24hrs at Horfield, highest since 1968. Number of properties Majority of the rainfall occurred between 1200 and 1800hrs (80mm). flooded not known, Extensive surface water and foul sewage flooding across the city. extensive surface water flooding across the City confirmed 08/01/1995 72 reported incidents of flooding causing flooding to property, land, and 19 residential transport routes properties and 3 non- residential properties affected
19/01/1999 Several residential and non-residential properties across Bristol 3 residential and 2 non-residential properties affected
Various 40 reported instances of flooding to property in Station Road and Nibley Number of properties Road, Shirehampton. Main source of flooding recorded as tidal but flooded not known, interaction with drainage and surface water known to be a key issue internal flooding of more than 5 properties confirmed
Table 4-1 Summary of Past Flood Events and their Consequences
2011s4891 BCC PFRA final.doc 24
± PFRA Analysis City of Bristol Recorded Locations of Surface Water Flooding
Based on information collated by Bristol City Council, where more detailed location information has been provided.
All recorded locations of flood events have been plotted. However a number of additional flood events could not be plotted due to incomplete records.
Legend # # # Location of Past Flooding # City of Bristol Boundary ## # #
#
City of Bristol Boundary # Local Authority Boundaries
# Drawn by: Bethlyn Jones # Date: 22/06/2011 # Status: Draft Drawing Number: Figure 4.1 OS Licence: This map is reproduced from Ordnance Survey material with the permission of Ordnance Survey on behalf of the Controller of Her Majesty’s Stationary Office © Crown Copyright. Unauthorised reproduction infringes Crown # Copyright and may lead to prosecution of civil proceedings. 0 1.5 3 6 KM Bristol City Council. 100023406. 2011.
5. Future Flood Risk
5.1 Introduction This section of the report summarises all relevant information on future floods and provides an essential foundation for informing future flood risk strategies across the area. The national guidance issued by Defra and WAG sets out the criteria used for defining significant flood risk and the indicative Flood Risk Areas. In developing the methodology for assessing flood risk, threshold levels were defined for the key Flood Risk Indicators as follows: Number of People > 200 Non-Residential Properties > 20 Critical Infrastructure > 1 Maps of 'Hotspots' or "places above the thresholds" have been produced, defined where 1 km grid squares meet the significance level set for at least one of the key Flood Risk Indicators shown above. The national data that were provided (shown in Figure 3.1) have been reassessed using the revised NRD (v1.1) provided to LLFAs, resulting in slightly higher property counts. In addition, pumping stations, electricity sub-stations and water supply sites have been included as critical infrastructure sites. This process has resulted in a revised "Hotspots" map which is shown in Figure 5-1.
Figure 5.1 Hotspot Locations within Bristol
Where 5 or more "hotspots" are touching within a 3km2 roving grid, they are deemed to form a cluster. Those for Bristol are shown in Figure 5.2.
2011s4891 BCC PFRA final.doc 26
Figure 5.2 Clustered Locations above Thresholds
The Guidance states that indicative Flood Risk Areas are defined where the number of people at risk within a cluster is greater than 30,000 in England. The total number of people at risk of flooding within the Greater Bristol area was originally identified from the national data as 36,682, hence the designation as an indicative FRA. Ten such indicative FRAs have been so defined in England and eight in Wales (see Figure 1.2). The criteria in Wales are set at lower levels of 5000 people within clusters formed where 4 or more blue squares touch. This reflects the extensive rural nature and lower population density in Wales. This section of the report summarises the analysis of all relevant information on future floods and is presented in Annex 2. The review and assessment of the FRA is presented in Section 6.
5.2 Locally Agreed Surface Water Information In order to determine the 'locally agreed surface water information', known areas of surface water flooding and local knowledge have been considered and comparisons made with the surface water flood maps available. Both nationally consistent surface water flood maps have been assessed and metrics calculated for each. However there are other surface water data available that have also been considered, in particular that from the SWMP. The opportunity has therefore been taken to consider and compare the information and modelling output from the Bristol SWMP study. Although this is ongoing, a significant amount of work and detailed analysis has already been completed. Importantly the SWMP modelling
2011s4891 BCC PFRA final.doc 27
has taken into account the sub-surface drainage infrastructure in Bristol, a substantial improvement to nationally produced modelling. As a result, further work has been undertaken as part of the PFRA project, to determine whether this locally available dataset advances the understanding of surface water flooding, such that this now forms the "locally agreed surface water information". The surface water flooding results from the detailed SWMP modelling were obtained and incorporated into a format for reprocessing by the PFRA JFrism analytical tool. This required considerable reprocessing as the SWMP hydraulic modelling of Bristol represents buildings as solid features. This representation of buildings was done to improve the depiction of urban flow paths and is common practice. However, as a consequence modelled rainfall drains quickly off the buildings within the model thereby reporting very shallow flood depth across all building footprints. As a result no surface water flooding is reported for buildings, a fundamental requirement of property counts. To overcome this problem, the JBA ArcGIS "JPatch" tool was applied to the SWMP results, to generate depth and water level grids from the SWMP modelling. This effectively served to "correct" for the presence of buildings, by interpolating depth and water levels through the buildings. This tool treats the buildings as „holes‟ in rasters and fills them by interpolation of the values in the cells surrounding the “hole”. This method was successfully applied by JBA on the Northern Ireland PFRA. A detailed check of the patched water level and DTM grids generated by JPatch was undertaken, to verify that the tool correctly interpolated water levels over the building footprints. The depth grid generated from the patched water level and DTM grids was compared to the supplied depth grid. Typically, an increase in water depths occurs within building footprints, where water levels from either side of the building have been interpolated through the structure. An increased extent in flood outline polygons was observed in the patched data for depth outlines. This is due to the increased extent of flooding within building footprints where the depth grid was formerly shallow and has now been interpolated through the structure. A range of flood depth cut-off values and storm events (100yr and 200yr) for the SWMP data were analysed and processed with the JFrism PFRA tool to determine the predicted numbers of residential properties and people at risk from surface water flooding. The results are presented in Table 5-1 and compared to the results obtained using the Flood Map for Surface Water (FMfSW 200 year deep) which was run both nationally by the EA, and also reassessed by JBA Consulting using the updated NRD v1.1 as mentioned in the above section.
Source Residential Total Properties People
EA FMfSW 200yr Deep 11,562 27,055
JBA FMfSW 200yr Deep 12,800 29,952
200yr SWMP (0.3m) 63,414 148,388
200yr SWMP (0.5m) 33,817 79,132
100yr SWMP (0.3m) 58,500 136,890
100yr SWMP (0.5m) * 29,200 68,328
Table 5-1 Predicted Residential Property Counts using SWMP and FMfSW results for the City of Bristol * Locally Agreed Surface Water Information
2011s4891 BCC PFRA final.doc 28
Table 5-1 illustrates the range of testing and analysis which took place in order to fully assess the various types of surface water data available. It is important to note that this addresses just the Bristol City Council area, not the whole indicative FRA. The FMfSW 200yr deep data was reassessed, with the slight increase in property counts explained due to the use of the most up to date version of NRD data (v1.1 compared to that used by the Environment Agency - v1.0); considered to be more accurate and known to contain a greater amount of property points in general. The JFrism PFRA tool was then used to assess the SWMP data derived for the 200yr rainfall event for both 0.3m and 0.5m cut-off depths. Through discussions with members of the City of Bristol Council it was decided that the 0.5m cut-off depth appeared most representative of local flooding, however the rainfall event was not comparative to that of the national data provided. The FMfSW 200yr event is indicative of a 200yr rainfall scenario, resulting in approximately a 100yr flood event. The 200yr SWMP data however, represents a more "like for like" scenario, where the 200yr rainfall event equates to a 200 year flood, this scenario therefore doubling the flood return period used nationally. JFrism was again used to run the 100yr SWMP data which is comparative to that of the FMfSW 200yr event. Table 5.1 clearly shows that the 100yr SWMP data still predicts significantly higher numbers of residential properties at risk from surface water flooding than the national data. By adopting the more conservative depth cut-off figure (0.5m) still results in the SWMP information predicting over twice the numbers of properties at risk than the FMfSW. It is important to stress that all of the surface water flood maps and modelled outlines are only indicative. They are not for determining individual property risks. Following discussions between Bristol City Council, the EA, Wessex Water and the neighbouring LLFA partners, it was concluded that as it is the most accurate and up-to-date information available, the SWMP results would be adopted as the locally agreed surface water information. The SWMP modelling results provide the most detailed and informative picture of risk, however it should be noted that this work is ongoing and dependent upon a number of complex modelling assumptions. Despite this, the SWMP data is still anticipated to be the most accurate and should therefore be taken forward as the locally agreed surface water information and has been used in analysis of future flood risk that is described below. In making this decision, it is important to stress that the reported risks are potentially much higher than the national mapping suggests. It has therefore been agreed that this decision will be kept under review, with further assessment, for example, being made of surface water interactions with the sub-surface flows through the sewer system. If this work recommends that the locally agreed information be changed, Bristol City Council will re-run the analysis. This could provide important information that will have a significant bearing on the future Hazard and Risk Mapping that will be required by 2013. The AStSWF map will also be retained and considered in future flood risk assessments as well, in particular as it is deemed to provide a more accurate representation of risk in the flat, low lying areas such as the LSIDB floodplain areas.
5.3 Future Floods and Consequences Future flood risk has been assessed predominantly using NRD data (version 1.1), supplied to JBA Consulting by Bristol City Council. To replicate the national strategy, flood risk indicators have been calculated using building outlines where appropriate. To derive the number of people at risk of flooding within a given area, building outline counts were multiplied by 2.34, which is the nationally agreed average occupancy per household. Table 5-2 shows the key flood risk indicators and the counts derived for the SWMP data, both the Areas Susceptible to Surface Water Flooding (1st Generation Surface Water Map - ASTSWF) and the Flood Map for Surface Water Flooding (2nd Generation Surface Water Map), as well as the Areas Susceptible to Ground Water Flooding map (ASTGWF). In addition to this, Flood Zones 2 and 3 were also considered to try and understand any interactions that may take place despite the onus being on the Environment Agency rather than the LLFA with regard to flooding originating from main rivers and the sea.
2011s4891 BCC PFRA final.doc 29
This information has been derived using JBA Consulting's bespoke analytical GIS software (FRiSM). This powerful graphical analysis tool has allowed a comprehensive study of the risk facing people, properties and critical infrastructure across the Greater Bristol area. The exposure of these and other vulnerable receptors to a range of local flood sources has been assessed on a 1km grid square basis across the entire area, also allowing for in-depth analysis and interrogation of the data. A detailed record of future floods and their possible consequences can be found in Annex 2 but is also summarised below in Table 5-2. Flood Outline Residential No. People Critical Non Residential Properties at at Flood Infrastructure Properties at Flood Risk Risk at Flood Risk Flood Risk ASTSWF - Less 31,500 73,700 300 7,900 ASTSWF - 15,100 35,300 100 3,900 Intermediate ASTSWF - More 4,200 9,800 0 1,000 FMfSW - 30 year 12,900 31,200 100 3,000 FMfSW - 30 year Deep 3,100 7,300 0 800 FMfSW - 200 year 36,300 84,900 300 7,400
FMfSW - 200 year 12,800 30,000 100 2,500 Deep Bristol SWMP 29,200 68,300 200 5,000 ASTGWF - - - - Flood Zone 3 4,300 10,100 100 3,100 Flood Zone 2 10,300 24,100 200 5,100
Table 5-2 Assessment of Key Flood Risk Indicators for Bristol City Council Area *Locally agreed surface water information - rounded to nearest 100
As Table 5-2 illustrates, the key flood risk indicators have also been assessed in respect of the Areas Susceptible to Ground Water Flooding map (AStGWF). However this information is both very broad scale and only really addresses locations of alluvial drift. It is known that there are very few instances of groundwater flooding and that these are in general also associated with areas of surface water flooding. It is important to note that results would provide an unreliable and inaccurate picture of risk to properties. Consequently it is recommended that the groundwater information is too broadscale and should not be taken forward in any future assessment until more detailed local assessments are available. The assessment of future flood risk was also extended to include the EA main river Flood Zones 2 and 3. These were considered to help the understanding of any interactions that may take place between local flood sources of risk and main river. However the EA is responsible for main river assessments rather than the LLFA, so this has not been considered further other than to determine possible interactions. As has been stated, the PFRA stage of the Regulations has also been used to provide the basis for a flood assessment for the Local Flood Risk Management Strategy. Whilst national thresholds have been established for the key flood risk indicators to define significance (see Section 5.1 above), LLFAs are encouraged to consider the full range of local flood risk across their area in addition to any areas of "significant risk". In view of the flooding issues across the area, a further set of thresholds for residential properties - and therefore people - at risk of surface water flooding has been established. This provides additional categories of "low", "medium" and "high" risk below "significant". In this way, the scale of risk and consequence can be assessed and prioritised across the City of Bristol.
2011s4891 BCC PFRA final.doc 30
CATEGORY NUMBER OF NUMBER OF PEOPLE PROPERTIES
LOW RISK >1 – 20 people 1 - 9 properties
MEDIUM RISK 21-99 people 10 - 42 properties
HIGH RISK 100-199 people 43 - 85 properties
SIGNIFICANT RISK >200 people >85 properties
Table 5-3 Categories of Flood Risk for Local Assessment
Using these locally applied thresholds, it is possible to analyse and produce an extensive suite of maps, to illustrate a range of flood sources affecting different indicators. Furthermore, these can be presented at any scale and on a Ward or City-wide basis. This will be of value in taking the management of flood risk forward in preparing the local strategy. Figures 5.3 to 5.6 illustrate the range of maps produced as part of the PFRA process, using the City of Bristol Surface Water Management Plan data for the 100yr rainfall event, at a flood depth of 0.5m as the agreed surface water information. Figure 5.3 (Residential Properties at Risk of Surface Water Flooding), identifies that there is significant risk of surface water flooding to the majority of the City of Bristol, with the most extensive flooding identified throughout the central area. The greatest amount of properties anticipated to be at risk of surface water flooding within a single kilometre grid square are located in the Clifton area, with 1614 properties affected. This is followed by 1252 properties located in and around Montpelier (nothern Ashley Ward), and 1188 properties within Redland. Figure 5.5 shows a fairly even distribution of critical infrastructure sites at risk of surface water flooding throughout the City, with 91 of 150 grid squares containing at least 1 critical infrastructure building at risk. The grid square containing the greatest amount of risk (8 critical infrastructure buildings) is located to the south of Montpelier, located within Ashley Ward. Here there are 2 buildings of education that are thought to be at risk, along with an ambulance station (which falls within Cabot Ward), a telecommunications site and 2 electricity sub-stations. 8 critical infrastructure buildings are also at risk in Kingsdown which neighbours Ashley Ward. In total, 8 pre-school buildings and 59 buildings of education, ranging from nursery, primary to further education collages are all predicted to be at risk of surface water flooding when using the SWMP data. 3 police services buildings which are located in Bishopsworth, Southville and Cotham Wards and the aforementioned Ambulance station in Cabot Ward. 2 Fire Stations in Lawrence Hill and Brislington East Wards as well as 4 hospitals, 3 of which are located in Cabot Ward and the final one in Brislington West Ward. 93 Electrictity Sub- Stations/Electricity Generating sites, 17 Telecommunication, 4 Nursing Homes, 1 Nurses home, 1 Water Regulating site and 1 Prison located in Bishopston Ward are all predicted to be at risk of surface water flooding. On a Ward basis, Figure 5.6 shows that Cabot, Clifton, Clifton East and Ashely Wards are all deemed to be at significant risk of surface water flooding to residential properties. The analysis shows there are 2301 residential properties at flood risk within Cabot Ward, however this includes a number of house boats moored within the floating harbour. There are also in excess of 1,500 upper floor flats. These have been included within the analysis as flooding to the lower levels of apartment blocks will ultimately cause disruption to the upper levels as well. These maps and analyses provide examples of the many outputs that are possible. They show how flood risk can be assessed and illustrated across the county and the benefits this will provide in preparing the local strategy and managing the risks identified.
2011s4891 BCC PFRA final.doc 31
± PFRA Analysis City of Bristol Residential Properties At Risk Of Surface Water Flooding South Gloucestershire Based on data derived from the City of Bristol Surface Water Management Plan, indicating the chance of land flooding to a depth greater than 0.5m during a 1 in 100yr rainfall event. Legend Unitary Authority Boundaries City of Bristol Boundary Hotspots Human Health: Residential Properties None Low Risk (0.01 - 9.99) Medium Risk (10 - 42.99) High Risk (43 - 85.5) Significant(85.51 - 1614) Hotspots are1km grid squares where at least one of the following flood risk indicators is above the threshold given below:
1. Number of People > 200 2. Critical Services > 1 3. Number of Non-Residential Properties > 20
Indicators calculated using the EnvironmentAgency's detailed method of counting (based on property outlines).
North Somerset
Drawn by: Bethlyn Jones Date: 22/06/2011 Status: Draft Drawing Number: Figure 5.3 OS Licence: This map is reproduced from Ordnance Survey material Bath and North East Somerset with the permission of Ordnance Survey on behalf of the Controller of Her Majesty’s Stationary Office © Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution of civil proceedings. 0 1 2 4 KM Bristol City Council. 100023406. 2011. PFRA Analysis City of Bristol Non-residential Properties At Risk Of Surface Water Flooding South Gloucestershire Based on data derived from the City of Bristol Surface Water Management Plan, indicating the chance of land flooding to a depth greater than 0.5m during a 1 in 100yr rainfall event. Legend Unitary Authority Boundaries City of Bristol Boundary Hotspot Economic: Non-Residential Properties None Low Risk (0.01 - 9.99) Medium Risk (10 - 14.99) High Risk (15 - 19.99) Significant(20 - 410) Hotspots are1km grid squares where at least one of the following flood risk indicators is above the threshold given below:
1. Number of People > 200 2. Critical Services > 1 3. Number of Non-Residential Properties > 20
Indicators calculated using the EnvironmentAgency's detailed method of counting (based on property outlines).
North Somerset
Drawn by: Bethlyn Jones Date: 22/06/2011 Status: Draft Drawing Number:Figure 5.4 This map is reproduced from Ordnance Survey material Bath and North East Somerset OS Licence: with the permission of Ordnance Survey on behalf of the Controller of Her Majesty’s Stationary Office © Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution of civil proceedings. 0 1.25 2.5 5 KM Bristol City Council. 100023406. 2011. PFRA Analysis City of Bristol Critical Infrastructure At Risk Of Surface Water Flooding South Gloucestershire Based on data derived from the City of Bristol Surface Water Management Plan, indicating the chance of land flooding to a depth greater than 0.5m during a 1 in 100yr rainfall event. Legend Unitary Authority Boundaries City of Bristol Boundary Hotspot Human Health: Critical Infrastructure None Low Risk Medium Risk High Risk (0.01 - 0.99) Significant(1 - 9) Hotspots are1km grid squares where at least one of the following flood risk indicators is above the threshold given below:
1. Number of People > 200 2. Critical Services > 1 3. Number of Non-Residential Properties > 20
Indicators calculated using the EnvironmentAgency's detailed method of counting (based on property outlines).
North Somerset
Drawn by: Bethlyn Jones Date: 22/06/2011 Status: Draft Drawing Number:Figure 5.5 OS Licence:This map is reproduced from Ordnance Survey material with the permission of Ordnance Survey on behalf of the Bath and North East Somerset Controller of Her Majesty’s Stationary Office © Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution of civil proceedings. 0 1.25 2.5 5 KM Bristol City Council. 100023406. 2011. ± PFRA Analysis City of Bristol Residential Properties At Risk Of Surface Water Flooding South Gloucestershire Based on data derived from the City of Bristol Surface Water Management Plan, indicating the chance of land flooding to a depth greater than 0.5m during a 1 in 100yr rainfall event displayed by Ward.
35 Legend 27 Unitary Authority Boundaries 28 Ward Boundaries Human Health: 24 Residential Properties 34 None 25 Low Risk (0.01 - 499) Medium Risk (499.01 - 999) 12 26 4 High Risk (999.01 - 1499) Significant(1499.01 - 2301) 33 Indicators calculated using the EnvironmentAgency's detailed method of counting (based on property outlines). 14 22 19 ID Ward ID Ward 23 1 Southville Ward 19 Redland Ward 18 2 Brislington West Ward 20 Easton Ward 31 3 Cabot Ward 21 St. George West Ward 4 Lockleaze Ward 22 Eastville Ward 13 20 21 5 Hartcliffe Ward 23 Hillfields Ward 6 Bishopsworth Ward 24 Kingsweston Ward 30 7 Bedminster Ward 25 Westbury-on-Trym Ward 3 16 32 8 Whitchurch Park Ward 26 Henleaze Ward 9 Hengrove Ward 27 Henbury Ward 10 Filwood Ward 28 Southmead Ward 11 Stockwood Ward 29 Knowle Ward 1 12 Frome Vale Ward 30 Clifton Ward North Somerset 13 Clifton East Ward 31 Cotham Ward 15 17 14 Stoke Bishop Ward 32 St. George East Ward 7 15 Windmill Hill Ward 33 Bishopston Ward 29 16 Lawrence Hill Ward 34 Horfield Ward 2 17 Brislington East Ward 35 Avonmouth Ward 18 Ashley Ward 10
6 11 9 5 Drawn by: Bethlyn Jones Date: 22/06/2011 8 Bath and North East Somerset Status: Draft Drawing Number: Figure 5.6 This map is reproduced from Ordnance Survey material OS Licence: with the permission of Ordnance Survey on behalf of the Controller of Her Majesty’s Stationary Office © Crown Copyright. Unauthorised reproduction infringes Crown 0 1.5 3 6 KM Copyright and may lead to prosecution of civil proceedings. Bristol City Council. 100023406. 2011.
5.4 The Impacts of Climate Change
The Evidence There is clear scientific evidence that global climate change is happening now. It cannot be ignored. Over the past century around the UK we have seen sea level rise and more of our winter rain falling in intense wet spells. Seasonal rainfall is highly variable. It seems to have decreased in summer and increased in winter, although winter amounts changed little in the last 50 years. Some of the changes might reflect natural variation, however the broad trends are in line with projections from climate models. Greenhouse gas (GHG) levels in the atmosphere are likely to cause higher winter rainfall in future. Past GHG emissions mean some climate change is inevitable in the next 20-30 years. Lower emissions could reduce the amount of climate change further into the future, but changes are still projected at least as far ahead as the 2080s. We have enough confidence in large scale climate models to say that we must plan for change. There is more uncertainty at a local scale but model results can still help us plan to adapt. For example we understand rain storms may become more intense, even if we can‟t be sure about exactly where or when. By the 2080s, the latest UK climate projections (UKCP09) are that there could be around three times as many days in winter with heavy rainfall (defined as more than 25mm in a day). It is plausible that the amount of rain in extreme storms (with a 1 in 5 annual chance or rarer) could increase locally by 40%.
Key Projections for Severn River Basin District If emissions follow a medium future scenario, UKCP09 projected changes by the 2050s relative to the recent past are: Winter precipitation increases of around 12% (very likely to be between 2 and 26%) Precipitation on the wettest day in winter up by around 9% (very unlikely to be more than 22%) Relative sea level at Bristol very likely to be up between 10 and 40cm from 1990 levels (not including extra potential rises from polar ice sheet loss) Peak river flows in a typical catchment likely to increase between 9 and 18%
Increases in rain are projected to be greater at the coast and in the south of the district.
Implications for Flood Risk Climate change can affect local flood risk in several ways. Impacts will depend on local conditions and vulnerability. Wetter winters and more of this rain falling in wet spells may increase river flooding along the Severn and its tributaries. More intense rainfall causes more surface runoff, increasing localised flooding and erosion. In turn, this may increase pressure on drains, sewers and water quality. Storm intensity in summer could increase even in drier summers, so we need to be prepared for the unexpected. Drainage systems in the district have been modified to manage water levels and could help in adapting locally to some impacts of future climate on flooding, but may also need to be managed differently. Rising sea or river levels may also increase local flood risk inland or away from major rivers because of interactions with drains, sewers and smaller watercourses. Where appropriate, we need local studies to understand climate impacts in detail, including effects from other factors like land use. Sustainable development and drainage will help us adapt to climate change and manage the risk of damaging floods in future.
2011s4891 BCC PFRA final.doc 36
Adapting to Change Past emission means some climate change is inevitable. It is essential we respond by planning ahead. We can prepare by understanding our current and future vulnerability to flooding, developing plans for increased resilience and building the capacity to adapt. Regular review and adherence to these plans is key to achieving long-term, sustainable benefits. Although the broad climate change picture is clear, we have to make local decisions against deeper uncertainty. We will therefore consider a range of measures and retain flexibility to adapt. This approach, embodied within flood risk appraisal guidance, will help to ensure that we do not increase our vulnerability to flooding.
5.5 Significant Local Developments It is possible that long term developments might affect the occurrence and significance of flooding. However current planning policy aims to prevent new development from increasing flood risk. In England, Planning Policy Statement 25 (PPS25) on development and flood risk aims to "ensure that flood risk is taken into account at all stages in the planning process to avoid inappropriate development in areas at risk of flooding, and to direct development away from areas at highest risk. Where new development is, exceptionally, necessary in such areas, policy aims to make it safe without increasing flood risk elsewhere and where possible, reducing flood risk overall". In addition, the Bristol Core Strategy Policy BCS16 requires that water management measures be used to reduce surface water run-off to minimise its contribution to flood risk elsewhere. Adherence to Government and local policy ensures that new development does not increase local flood risk. However, in exceptional circumstances the Local Planning Authority may accept that flood risk can be increased contrary to Government policy, usually because of the wider benefits of a new or proposed major development. Any exceptions would not be expected to increase risk to levels which are "significant" (in terms of the Government's criteria).
2011s4891 BCC PFRA final.doc 37
6. Identification of Flood Risk Areas
6.1 Indicative Flood Risk Areas
The Bristol indicative Flood Risk Area has been assessed and identified as such by the Environment Agency through their national, strategic assessment of flood risk. This has been carried out to support LLFAs in their new role under the Flood and Water Management Act (2010), and to provide nationally consistent surface water information. The national guidance issued by Defra and WAG sets out the criteria used for defining significant flood risk and the indicative Flood Risk Areas. In developing the methodology for assessing flood risk, threshold levels were defined for the key Flood Risk Indicators as follows: Number of People > 200 Non-Residential Properties > 20 Critical Infrastructure > 1 Maps of 'Hotspots' or "places above the thresholds" were produced, defined where 1 km grid squares meet the significance level set for at least one of the key Flood Risk Indicators shown above. Where 5 or more "hotspots" were touching within a 3km2 roving grid, they were deemed to form a cluster and if the amount of people at risk of surface water flooding within this cluster exceeded 30,000 it was then classed as an indicative Flood Risk Area (IFRA). The national strategy identified 10 such IFRAs within England, with the Bristol IFRA showing that 36,681 people were at potential risk of surface water flooding, assessed by the Environment Agency using the FMfSW 200yr Deep scenario. As part of this PFRA, the national data provided by the Environment Agency have been reassessed using the revised NRD (v1.1) which was also provided to LLFAs, using the JBA JFrism PFRA tool. In addition to this, property counts were derived using the locally agreed 100yr SWMP surface water information, as detailed in section 5.2 of this report. Comparisons between the different data sets could then be made, the results of which can be seen in Table 6-1. Coverage of the SWMP data extends to the City of Bristol boundary; however it does not cover the whole of the IFRA area as this analysis was carried out solely by the City of Bristol Council. Areas of the IFRA which fall under the jurisdiction of South Gloucestershire, North Somerset or Bath and North East Somerset and are not covered by the SWMP have been assessed using the FMfSW 200yr Deep scenario (Figure 6.1).
Source Residential Total Properties People
EA FMfSW 200yr Deep 15,676 36,681
JBA FMfSW 200yr Deep 17,108 40,033
100yr SWMP (0.5m)* 31,600 73,944
Table 6-1 Predicted Residential Property Counts using FMfSW and the locally agreed SWMP/FMfSW results for the Bristol IFRA *Locally Agreed Surface Water Information
2011s4891 BCC PFRA final.doc 38
Figure 6.1 Surface Water Management Extent
Table 6-1 again identifies that by using the 100yr SWMP data, the number of properties predicted to be at risk of surface water flooding is over double that of the national data supplied by the Environment Agency. As the locally agreed surface water information, this SWMP data has been used to derive the final property counts for the Bristol IFRA. The key results of the analysis can be found in Table 6-2 below, with further detail provided in the Annex 3 spreadsheet.
Area Residential No. People Critical Non Properties at at Flood Infrastructure Residential Flood Risk Risk at Flood Risk Properties at Flood Risk Bristol FRA - total 31,600 73,944 200 5,700
City of Bristol 27,600 64,584 200 4,600
South Gloucestershire 3,900 9,126 0 1000
North Somerset 100 234 0 100
Bath & NE Somerset 100 234 0 0
Table 6-2 Assessment of Key Flood Risk Indicators for Bristol IFRA Rounded to nearest 100
2011s4891 BCC PFRA final.doc 39
Figures 6.2 to 6.4 illustrate the above results, the maps produced as part of the PFRA process, using the locally agreed surface water information (100yr SWMP 0.5m/ FMfSW combination). Figure 6.2 (Residential Properties at Risk of Surface Water Flooding), identifies that there is significant risk of surface water flooding throughout the IFRA, with the most extensive flooding identified throughout the centre of the City of Bristol. The greatest amount of properties anticipated to be at risk of surface water flooding within a single kilometre grid square are located in the Clifton area, with 1614 properties affected. This is followed by 1252 properties located in and around Montpelier (northern Ashley Ward), and 1188 properties within Redland. Figure 6.3 shows the distribution of non-residential properties predicted to be at risk from the agreed SWMP data, which again shows significant flooding throughout the IFRA. Key areas have been identified as central Bristol City, where 410 non-residential properties are at risk within a single kilometre grid square (within the Kingsdown area of the City). Outside of the City of Bristol LLFA, there is a clustering of significant risk cells located around Oldland and Stoke Gifford; both of which are found within the South Gloucestershire LLFA boundary. Figure 6.4 shows a fairly even distribution of critical infrastructure sites at risk of surface water flooding throughout the IFRA, with 101 of 219 grid squares containing at least 1 critical infrastructure building at risk. The grid square containing the greatest amount of risk (8 critical infrastructure buildings) is located to the south of Montpelier, located within Ashley Ward at the centre of Bristol City. 8 critical infrastructure buildings are also at risk in Kingsdown which neighbours Ashley Ward. A more detailed breakdown of the critical infrastructure buildings predicted to be at risk from this flood source within each LLFA can be found in Table 6-3 below. These maps and analyses provide examples of the many outputs that are possible. They show how flood risk can be assessed and illustrated across the indicative Flood Risk Area as a whole and the benefits this will provide in preparing the local strategy, ensuring a consistent approach across the IFRA and managing the risks identified in an efficient and inclusive manor.
LLFA Additional Critical Infrastructure Analysis
City of Bristol 184 Critical Infrastructure buildings including: 7 preschool and 54 buildings of education, from nursery, primary to further education collages. 3 police services located in Bishopsworth, Southville and Cotham Wards as well as 1 ambulance station in Cabot Ward. 2 fire stations in Lawrence Hill and Brislington East Wards as well as 4 hospitals, 3 of which are located in Cabot ward and the last in Brislington ward. 84 electricity sub stations/electricity generating sites, 19 telecommunication sites, 4 nursing homes, 1 nurses home, 1 water regulating site in Westbury -on-Trym and 1 prison located in Bishopston Ward. South Gloucestershire 41 Critical Infrastructure buildings affected including: 12 buildings of education, from nursery, primary to further education collages. 24 electricity sub stations, 1 gas regulating site 4 telecommunication and 1 pumping site. North Somerset 1 Critical Infrastructure building affected which is an electricity substation located in Long Ashton. Bath & NE Somerset 3 Critical Infrastructure buildings affected including: Whitchurch Primary School, 1 electricity substation and 1 telecommunication site. Table 6-3 Additional LLFA Critical Infrastructure Analysis
2011s4891 BCC PFRA final.doc 40
± PFRA Analysis Bristol Indicative Flood Risk Area Residential Properties At Risk Of Surface Water Flooding Based on data derived from the City of Bristol Surface Water Management Plan, indicating the chance of land flooding to a depth greater than 0.5m during a 1 in 100yr rainfall event. Legend Bristol IFRA Boundary South Gloucestershire Unitary Boundaries Hotspot Human Health: Residential Properties None Low Risk (0.01 - 9.99) Medium Risk (10 - 42.99) High Risk (43 - 85.5) Significant(85.51 - 1614) Hotspots are1km grid squares where at least one of the following flood risk indicators is above the threshold given below:
1. Number of People > 200 City of Bristol (B) 2. Critical Services > 1 3. Number of Non-Residential Properties > 20
Indicators calculated using the EnvironmentAgency's detailed method of counting (based on property outlines).
North Somerset
Drawn by: Bethlyn Jones Date: 22/06/2011 Status: Draft Drawing Number: Figure - 6.2 Bath and North East Somerset OS Licence:This map is reproduced from Ordnance Survey material with the permission of Ordnance Survey on behalf of the Controller of Her Majesty’s Stationary Office © Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution of civil 0 1.25 2.5 5 KM proceedings. Bristol City Council. 100023406. 2011. ± PFRA Analysis Bristol Indicative Flood Risk Area Non Residential Properties At Risk Of Surface Water Flooding Based on data derived from the City of Bristol Surface Water Management Plan, indicating the chance of land flooding to a depth greater than 0.5m during a 1 in 100yr rainfall event. Legend Bristol IFRA Boundary South Gloucestershire Unitary Authority Boundaries Hotspot Economic: Non-Residential Properties None Low Risk (0.01 - 9.99) Medium Risk (10 - 14.99) High Risk (15 - 19.99) Significant(20 - 410)
Hotspots are1km grid squares where at least one of the following flood risk indicators is above the threshold given below:
1. Number of People > 200 2. Critical Services > 1 City of Bristol 3. Number of Non-Residential Properties > 20
Indicators calculated using the EnvironmentAgency's detailed method of counting (based on property outlines).
North Somerset
Drawn by: Bethlyn Jones Date: 22/06/2011 Status: Draft Drawing Number: Figure 6.3 Bath and North East Somerset OS Licence:This map is reproduced from Ordnance Survey material with the permission of Ordnance Survey on behalf of the Controller of Her Majesty’s Stationary Office © Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution of civil 0 1.25 2.5 5 KM proceedings. Bristol City Council. 100023406. 2011. ± PFRA Analysis Bristol Indicative Flood Risk Area Critical Infrastructure At Risk Of Surface Water Flooding Based on data derived from the City of Bristol Surface Water Management Plan, indicating the chance of land flooding to a depth greater than 0.5m during a 1 in 100yr rainfall event. Legend Bristol IFRA Boundary South Gloucestershire Unitary Boundaries Hotspot Human Health: Critical Infrastructure None Low Risk Medium Risk High Risk (0.01 - 0.99) Significant(1 - 9)
Hotspots are1km grid squares where at least one of the following flood risk indicators is above the threshold given below:
City of Bristol (B) 1. Number of People > 200 2. Critical Services > 1 3. Number of Non-Residential Properties > 20
Indicators calculated using the EnvironmentAgency's detailed method of counting (based on property outlines).
North Somerset
Drawn by: Bethlyn Jones Date: 22/06/2011 Status: Draft Drawing Number: Figure 6.4 Bath and North East Somerset OS Licence:This map is reproduced from Ordnance Survey material with the permission of Ordnance Survey on behalf of the Controller of Her Majesty’s Stationary Office © Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution of civil 0 1.25 2.5 5 KM proceedings. Bristol City Council. 100023406. 2011.
6.2 New Flood Risk Areas Figure 6.5 identifies the original Environment Agency 'hotspots' produced using NRD v1.0 and the FMfSW, compared to those hotspots identified as part of this PFRA process using the agreed surface water information and NRD v1.1. It was anticipated that all EA hotspots would be reselected when the process was carried out again using the more up-to-date data however this was not necessarily the case. Some discrepancies have been identified and investigated, with confidence in the SWMP data still strong. Slight differences in flow paths are to be expected when developing different models and therefore this is not thought to be an issue. No amendments or proposed changes to the indicative Flood Risk Area boundary are recommended as a result of this PFRA analysis.
2011s4891 BCC PFRA final.doc 44
± PFRA Analysis Bristol Indicative Flood Risk Area Hotspot Locations
Based on data derived from the City of Bristol Surface Water Management Plan, indicating the chance of land flooding to a depth greater than 0.5m during a 1 in 100yr rainfall event. Legend Bristol IFRA Boundary South Gloucestershire Unitary Boundaries Hotspot EA Hotspots
Hotspots are1km grid squares where at least one of the following flood risk indicators is above the threshold given below (Using NRD v1.1):
1. Number of People > 200 2. Critical Services > 1 3. Number of Non-Residential Properties > 20
Indicators calculated using the Environment Agency's detailed method of counting (based on property outlines) but using the most recent version of the NRD (v1.1) and including the following within the critical City of Bristol (B) infrastructure buildings layer:
- Electricity Sub Station, - Sewage Filtration, - Sewage Outfall, - Sewage Pump House, - Sewage Recycling, - Sewage Storage, - Sewage Treatment.
North Somerset
Drawn by: Bethlyn Jones Date: 22/06/2011 Status: Draft Drawing Number: Figure 6.5 Bath and North East Somerset OS Licence: This map is reproduced from Ordnance Survey material with the permission of Ordnance Survey on behalf of the Controller of Her Majesty’s Stationary Office © Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution of civil proceedings. Bristol City Council. 100023406. 2011. 0 1.25 2.5 5 KM
7. Next Steps
7.1 Review This Preliminary Assessment Report forms a part of the PFRA process that addresses the requirements defined by the Flood Risk Regulations. These place a duty for LLFAs to assess both the impacts of past floods and the consequences of future floods. They are also required to identify whether flood risk is significant, by applying national guidance to define Flood Risk Areas. For these areas, there are further duties to prepare Flood Hazard and Risk Maps by 2013 which in turn inform the Flood Risk Management Plans that will be required by 2015. Bristol City Council has undertaken an internal review of the PFRA, involving Cabinet, Council staff and the Overview and Scrutiny Committee. The review agreed that the indicative assessment of flood risk in Bristol was not amended and also supported the preparation of the PFRA in accordance with the Guidance provided to all LLFAs by Defra. This PFRA has been developed with advice from members of the flood risk management partnership group, as well as from members of an internal officers working group, prior to being laid before the lead Cabinet Member for final approval ahead of the EA's deadline of 22nd June 2011. The EA is required to review, collate and publish all PFRA submissions, in time to meet the 22nd December 2011 deadline for final submission to the European Commission. LLFAs will also publish PFRAs on their websites in accordance with the requirements of the EC Inspire Directive. Under the Regulations, Bristol City Council will be required to undertake Hazard and Risk Mapping by 2013 and subsequently produce Flood Risk Management Plans for Bristol City by 2015. It is however important to remember that the PFRA will have to be reviewed and revised again in 2016 as part of the 6 yearly cycle of flood risk planning.
7.2 Local Flood Risk Management Strategy In preparing the PFRA, the opportunity has been taken to establish the foundations for preparing the City of Bristol Local Flood Risk Management Strategy. This will commence later this year under duties contained in the Flood & Water Management Act 2010. Detailed analysis of local flood risk across the City has been undertaken as part of this study and is now available to inform and communicate the issues and priorities to help prepare the future strategy. The JBA Consulting GIS software tools have allowed the completion of the PFRA and provided the means to analyse and clearly display the risk from a range of different flood sources on a Ward or entire City basis. The PFRA process has also helped strengthen and underline the importance of partnership working between the risk management authorities and the need for sharing information through the City of Bristol Partnership Group. A comprehensive archive of past floods has been compiled and a database structure now exists to record the mandatory information necessary for documenting all future flood events. This will be of benefit and greatly simplify the PFRA review process due in 6 years time. The details of critical infrastructure and properties at risk of flooding will also help inform the City of Bristol Multi-Agency Flood Plan (MFP) and assist in emergency planning and response. The Local Flood Risk Management Strategy will define how flood risk is to be assessed and managed across the City of Bristol in future years. The PFRA analysis has provided the opportunity to prepare for and inform how this future strategy will be taken forward.
2011s4891 BCC PFRA final.doc 46
Appendices
A.1 Records of past floods and their significant consequences (preliminary assessment report spreadsheet)
2011s4891 2011s4891 BCC PFRA draft pm3.docx 47
Annex 1 Past floods
ANNEX 1: Records of past floods and their significant consequences (preliminary assessment report spreadsheet) Field: Flood ID Summary description Name of Location National Grid Location Description Start date Days duration Probability Main source of Additional source(s) Confidence in main Main mechanism of Main characteristic of Significant Human health Property count Other human health Reference flooding of flooding source of flooding flooding flooding consequences to consequences - method consequences human health residential properties Mandatory / optional: Mandatory Mandatory Mandatory Mandatory Optional Optional for first cycle Optional for first cycle Optional for first cycle Optional for first cycle Optional Optional Optional for first cycle Optional for first cycle Mandatory Optional Optional Optional Format: Unique number Max 5,000 characters Max 250 characters 12 characters: 2 Max 250 characters 'yyyy' or 'yyyy-mm' or Number with two Max 25 characters Pick from drop-down Max 250 characters, Pick from drop-down Pick from drop-down Pick from drop-down Pick from drop-down Number between 1- Pick from drop-down Max 250 characters between 1-9999 letters, 10 numbers 'yyyy-mm-dd' decimal places same source terms 10,000,000 Notes: A sequential number Description of the flood and its adverse or potentially adverse consequences. Where Name of the locality National Grid A description of the The date when the The number of days The chance of the Pick the source from If flooding occurred Pick a broad level of Pick a mechanism Pick a characteristic Were there any Record the number of Where residential or If there were other starting at 1 and available, information from other fields (Start date, Days duration, Probability, Main associated with the Reference of the general location that flood commenced - (duration) of the flood - flood occuring in any which the majority of from, or interacted confidence in the Main from; 'Natural from; 'Flash flood' significant residential properties non-residential Significant incrementing by 1 for source, Main mechanism, Main characteristics, Significant consequences) should be flood, using centroid (centre point, was flooded. when land not that land not normally given year - record X flooding occurred. with, any other source of flooding exceedance' (of (rises and falls quite consequences to where the building properties have been consequences to each record. repeated here. recognised postal falls within polygon) of normally covered by covered by water was from "a 1 in X chance Refer to the PFRA sources (other than from; 'High' capacity), 'Defence rapidly with little or no human health when structure was affected counted, it is important human health, address names such the flood extent, or of water became covered by water. of occurring in any guidance for the Main source of (compelling evidence exceedance' advance warning), the flood occurred, or either internally or to record the method describe them as streets, towns, the area affected if covered by water. Values should be given year". Where definitions of sources. flooding), report the of source - about 80% (floodwater 'Natural flood' (due to would there be if it externally by the flood, of counting, to aid including information counties. If the flood there is no extent within the range 0.01 - this is difficult to source(s) here, using confident that source overtopping significant were to re-occur? or that would be so comparisons between such as the number of affected the whole information. 999.99 (permitting estimate, a range can the same source is correct), 'Medium' defences), 'Failure' (of precipitation, at a affected if the flood counts. Choose from; critical services LLFA, then record the records to the nearest be recorded. terms. (some evidence of natural or artificial slower rate than a were to re-occur. 'Detailed GIS' (using flooded. name of the LLFA. quarter of an hour, source but not defences or flash flood), 'Snow property outlines, as where appropriate). compelling - about infrastructure, or of melt flood' (due to per Environment 50% confident that pumping), 'Blockage rapid snow melt), Agency guidance), source is correct) or restriction' (natural 'Debris flow' 'Simple GIS' (using 'Low' (source or artificial blockage (conveying a high property points), assumed - about 20% or restriction of a degree of debris), or 'Estimate from map', confident that source conveyance channel 'No data'. Most UK or 'Observed number'. is correct) or or system), or 'No floods are 'Natural 'Unknown'. data'. floods'.
Example: 1 On the 14 April 1998 an intense storm system produced surface water flooding across Essex SX1234512345 Several towns and 1998-04-15 0.25 20-50 Surface runoff High Natural exceedance Natural flood Yes 23 Observed number Essex, concentrated in the west of the county. The flooding lasted about 6 hours, and 23 villages across west residential properties were recorded as suffering internal flooding, in Epping and North Essex Weald. The surface runoff exceeded the drainage capacity in several places, and so probably had a 1 in 30 to 1 in 50 chance of occuring in any given year.
Records begin here: 1 5 reported incidents around the centre of the city Centre ST5860072800 15/07/1937 Main rivers Surface runoff Medium No data No data Yes 1 Observed number 2 10 reported incidents of flooding around Stapleton thought to be from the Frome main Stapleton ST6190076100 18/12/1965 No data No data No data Yes 2 Observed number 3 "The Great Flood of 1968". Major flooding caused by the river Chew and surface water Bristol ST5860072800 10/07/1968 Main rivers Surface runoff High Natural exceedance Natural flood Yes 805 Unknown 4 40mm rainfall at Horfield between 9am and 4pm. Emergency services called to approx. Bristol ST5860072800 30/05/1979 No data No data No data Yes 5 From midnight 8th/9th to the following midnight 32mm of rainfall recorded at Hartcliffe, Bristol ST5860072800 09/12/1979 Surface runoff Medium No data No data Yes 6 5 reported incidents in North / West of city Bristol ST5300077400 29/07/1980 Artificial infrastructure Surface runoff Medium No data No data Yes 5 Observed number 7 9 reported incidents, concentrated around Bishopsworth Bishopsworth ST5770068700 06/03/1982 Surface runoff Medium No data No data Yes 7 Observed number Special needs school 8 12 reported incidents across Bristol, 18mm of rainfall recorded in 1hr Bristol ST5860072800 06/08/1982 Surface runoff Medium No data No data Yes 9 Observed number 9 86mm of rainfall recorded in 24hrs at Horfield, highest since 1968. Majority of the rainfall Bristol ST5860072800 02/08/1984 Surface runoff Medium No data No data Yes 10 72 reported incidents of flooding causing flooding to property, land, and transport routes Bristol ST5860072800 08/01/1995 Surface runoff Medium No data No data Yes 19 Observed number
11 Several residential and non-residential properties across Bristol Bristol ST5860072800 19/01/1999 Surface runoff Medium No data No data Yes 3 Observed number
12 40 reported instances of flooding to property in Station Road and Nibley Road, Shirehampton ST5270076300 Main rivers Surface runoff Medium No data No data Yes Shirehampton. Main source of flooding recorded as tidal but interaction with drainage and surface water known to be key issue Annex 1 Past floods
Significant economic Number of non- Property count Other economic Significant Environment Significant Cultural heritage Comments Data owner Area flooded Flood event outline Flood event outline Survey date Photo ID Lineage Sensitive data Protective marking European Flood Event Code consequences residential properties method consequences consequences to the consequences consequences to consequences confidence source descriptor flooded environment cultural heritage Mandatory Optional Optional Optional Mandatory Optional Mandatory Optional Optional Optional Optional Optional Optional Optional Optional Optional Optional Optional Auto-populated Pick from drop-down Number between 1- Pick from drop-down Max 250 characters Pick from drop-down Max 250 characters Pick from drop-down Max 250 characters Max 1,000 characters Max 250 characters Number with two Pick from drop-down Pick from drop-down 'yyyy' or 'yyyy-mm' or Max 50 characters Max 250 characters Pick from drop-down Max 50 characters Max 42 characters 10,000,000 decimal places 'yyyy-mm-dd' Were there any Record the number of Where residential or If there were other Were there any If there were Were there any If there were Any additional The total area of the Choose from; 'High' Provide references to Lineage is how and Has the information For use where This field will autopopulate using the LLFA significant economic non-residential non-residential Significant economic significant Significant significant Significant comments about the land flooded, in km2 (data includes one of: relevant specific what the data is made been classified under organisations apply name provided on the "Instructions" tab, and consequences when properties where the properties have been consequences, consequences to the consequences to the consequences to consequences to past flood record. Aerial video, Aerial photographs, or to a from. Has this data the Government's the Government's the Flood ID. It is an EU-wide unique the flood occurred, or building structure was counted, it is important describe them environment when the environment, describe cultural heritage when cultural heritage, photos, Professional set of relevant been created by using Protective Marking Protective Marking identifier and will be used to report the flood would there be if it affected either to record the method including information flood occurred, or them including the flood occurred, or describe them survey, Flood level photographs. It may data owned or derived Scheme? Include Scheme. information. were to re-occur? internally or externally of counting, to aid such as the area of would there be if it information such as would there be if it including information information, EA flood not be practical to from data owned by protective marking by the flood, or that comparisons between agricultural land were to re-occur? national and were to re-occur? such as the number data recording staff reference all relevant 3rd party (external) time limit where Format: UK Yes 2 Observed number No No EA data set: FRIS UKE06000023P0001 Yes 2 Observed number No No EA data set: FRIS UKE06000023P0002 Yes Yes Yes Data compiled from UKE06000023P0003 Yes No No Information compiled UKE06000023P0004 Yes No No Information compiled Yes 2 Observed number No No EA data set: FRIS UKE06000023P0006 No 0 Observed number No No EA data set: FRIS UKE06000023P0007 No 0 Observed number No No EA data set: FRIS UKE06000023P0008 Yes No No Information compiled UKE06000023P0009 Yes 3 Observed number No No EA data set: FRIS UKE06000023P0010 incidents Yes 2 Observed number No No EA data set: FRIS UKE06000023P0011 incidents No No No Data compiled from UKE06000023P0012 various data sets A.2 Records of future floods and their consequences (preliminary assessment report spreadsheet) 2011s4891 2011s4891 BCC PFRA draft pm3.docx 48 Annex 2 Future floods ANNEX 2: Records of future floods and their consequences (preliminary assessment report spreadsheet) Field: Flood ID Description of assessment method Name of Location National Grid Location Description Name Flood modelled Probability Main source of Additional source(s) of Confidence in main Main mechanism of Main characteristic of Adverse Human health Property count method Other human health Reference flooding flooding source of flooding flooding flooding consequences to consequences - consequences human health residential properties Mandatory / optional: Mandatory Mandatory Mandatory Mandatory Optional Optional Optional Mandatory Mandatory Optional Optional Mandatory Mandatory Mandatory Optional Optional Optional Format: Unique number Max 1,000 characters Max 250 characters 12 characters: 2 letters, Max 250 characters Max 250 characters Max 250 characters Max 25 characters Pick from drop-down Max 250 characters, Pick from drop-down Pick from drop-down Pick from drop-down Pick from drop-down Number between 1- Pick from drop-down Max 250 characters between 1-9999 10 numbers same source terms 10,000,000 Notes: A sequential number Description of the future flood information and how it has been produced. Cover Regulation Name of the locality National Grid A description of the Name of the model or Background, or The chance of the flood Pick the source which If the flood is generated Pick a broad level of Pick a mechanism Pick a characteristic Would there be any Record the number of Where residential or If there would be other starting at 1 and 12(6) requirements of (a) topography, (b) the location of watercourses, (c) the location of associated with the Reference of the general location that map product or project additional information occuring in any given generates the majority by, or interacts with, confidence in the Main from; 'Natural from; 'Flash flood' significant residential properties non-residential Significant incrementing by 1 for flood plains that retain flood water, (d) the characteristics of watercourses, and (e) the flood, using recognised centroid (centre point, could be flooded. which produced the on the probability of the year - record X from "a of flooding. Refer to the any other sources source of flooding exceedance' (of (rises and falls quite consequences to where the building properties have been consequences to each record. effectiveness of any works constructed for the purpose of flood risk management. Information postal address names falls within polygon) of future flood information flood modelled - such 1 in X chance of PFRA guidance for (other than the Main from; 'High' (compelling capacity), 'Defence rapidly with little or no human health if the structure would be counted, it is important human health, describe from other relevant fields (Probability, Main source, Name) should be repeated here. such as streets, towns, the flood extent, or of as whether Probability occurring in any given definitions of sources. source of flooding), evidence of source - exceedance' advance warning), future flood were to affected either to record the method of them including counties. If the flood the area affected if refers to probability of year". report the source(s) about 80% confident (floodwater overtopping 'Natural flood' (due to occur? internally or externally if counting, to aid information such as the affects the whole there is no extent rainfall or water on the here, using the same that source is correct), defences), 'Failure' (of significant precipitation, the flood were to occur. comparisons between number of critical LLFA, then record the information. If the flood ground. source terms. 'Medium' (some natural or artificial at a slower rate than a counts. Choose from; services flooded. name of the LLFA. affects the whole evidence of source but defences or flash flood), 'Snow melt 'Detailed GIS' (using LLFA, then record the not compelling - about infrastructure, or of flood' (due to rapid property outlines, as centroid of the LLFA. 50% confident that pumping), 'Blockage or snow melt), 'Debris per Environment source is correct) 'Low' restriction' (natural or flow' (conveying a high Agency guidance), (source assumed - artificial blockage or degree of debris), or 'Simple GIS' (using about 20% confident restriction of a 'No data'. Most UK property points), that source is correct) conveyance channel or floods are 'Natural 'Estimate from map', or or 'Unknown'. system), or 'No data'. floods'. 'Observed number'. Example: 1 See records below for examples of description of assessment method. Essex SX1234512345 Flood Map for Surface Probability refers to the 200 Surface runoff High Natural exceedance Natural flood Yes 12000 Detailed GIS Water - 1 in 200 deep probability of the rainfall event, in this case producing flooding of greater than 0.3m depth. Records begin here: 1 • Topography is derived from LIDAR (in larger urban areas, on 1, 2 and 3m grids; original City of Bristol ST5942072340 City of Bristol Areas Susceptible to Probability refers to the 200 Surface runoff High Natural exceedance Natural flood Yes 31500 Detailed GIS 300 Critical accuracy ± 0.15m) and Geoperspective data (original accuracy ± 1.5m), processed to Surface Water probability of the Infrastructure remove buildings and vegetation, then degraded to a composite 5m DTM. Manual edits Flooding (AStSWF) - rainfall event. This buildings. applied where flow paths clearly omitted e.g. below bridges. Less identifies areas which • Flow routes dictated by topography; no allowance made for manmade drainage. The DTM are 'less susceptible' to may miss flow paths below bridges. surface water flooding. • Areas that may flood are defined by dynamically routing a 6.5 hour duration storm with 1 in For more information 200 chance of occurring in any year, over the DTM using JBA’s JFLOW–GPU model. refer to "What are • Manning’s n of 0.1 is used throughout, to allow broad scale effects of buildings and other Areas Susceptible to obstructions to be approximated. Surface Water • No allowance made for drainage, pumping or other works constructed for the purpose of Flooding" Environment flood risk management. Agency December • The ‘less susceptible’ layer shows where modelled flooding is 0.1-0.3m deep; you must not 2010. interpret this as depth of flooding, rather as indicative of susceptibility to flooding because of modelling uncertainties. 2 • Topography is derived from LIDAR (in larger urban areas, on 1, 2 and 3m grids; original City of Bristol ST5942072340 City of Bristol Areas Susceptible to Probability refers to the 200 Surface runoff High Natural exceedance Natural flood Yes 15100 Detailed GIS 100 Critical accuracy ± 0.15m) and Geoperspective data (original accuracy ± 1.5m), processed to Surface Water probability of the Infrastructure remove buildings and vegetation, then degraded to a composite 5m DTM. Manual edits Flooding (AStSWF) - rainfall event. This buildings. applied where flow paths clearly omitted e.g. below bridges. Intermediate identifies areas with • Flow routes dictated by topography; no allowance made for manmade drainage. The DTM 'intermediate may miss flow paths below bridges. susceptibility' to surface • Areas that may flood are defined by dynamically routing a 6.5 hour duration storm with 1 in water flooding. 200 chance of occurring in any year, over the DTM using JBA’s JFLOW–GPU model. • Manning’s n of 0.1 is used throughout, to allow broad scale effects of buildings and other obstructions to be approximated. • No allowance made for drainage, pumping or other works constructed for the purpose of flood risk management. • The ‘intermediate susceptibility’ layer shows where modelled flooding is 0.3-1.0m deep; you must not interpret this as depth of flooding, rather as indicative of susceptibility to flooding because of modelling uncertainties. 3 • Topography is derived from LIDAR (in larger urban areas, on 1, 2 and 3m grids; original City of Bristol ST5942072340 City of Bristol Areas Susceptible to Probability refers to the 200 Surface runoff High Natural exceedance Natural flood Yes 4200 Detailed GIS accuracy ± 0.15m) and Geoperspective data (original accuracy ± 1.5m), processed to Surface Water probability of the remove buildings and vegetation, then degraded to a composite 5m DTM. Manual edits Flooding (AStSWF) - rainfall event. This applied where flow paths clearly omitted e.g. below bridges. More identifies areas which • Flow routes dictated by topography; no allowance made for manmade drainage. The DTM are 'more susceptible' may miss flow paths below bridges. to surface water • Areas that may flood are defined by dynamically routing a 6.5 hour duration storm with 1 in flooding. 200 chance of occurring in any year, over the DTM using JBA’s JFLOW–GPU model. • Manning’s n of 0.1 is used throughout, to allow broad scale effects of buildings and other obstructions to be approximated. • No allowance made for drainage, pumping or other works constructed for the purpose of flood risk management. • The ‘more susceptible’ layer shows where modelled flooding is >1.0m deep; you must not interpret this as depth of flooding, rather as indicative of susceptibility to flooding because of modelling uncertainties. Annex 2 Future floods Adverse economic Number of non- Property count method Other economic Adverse Environment Adverse Cultural heritage Comments Data owner Area flooded Confidence in modelled Model date Model Type Hydrology Type Lineage Sensitive data Protective marking European Flood Event Code consequences residential properties consequences consequences to the consequences consequences to consequences outline descriptor flooded environment cultural heritage Mandatory Optional Optional Optional Mandatory Optional Mandatory Optional Optional Optional Optional Optional Optional Optional Optional Optional Optional Optional Auto-populated Pick from drop-down Number between 1- Pick from drop-down Max 250 characters Pick from drop-down Max 250 characters Pick from drop-down Max 250 characters Max 1,000 characters Max 250 characters Number with two Pick from drop-down 'yyyy' or 'yyyy-mm' or Max 250 characters Max 250 characters Max 250 characters Pick from drop-down Max 50 characters Max 42 characters 10,000,000 decimal places 'yyyy-mm-dd' Would there be any Record the number of Where residential or If there would be other Would there be any If there would be Would there be any If there would be Any additional The total area of the Pick a broad level of Type of software used Type of hydrology method used to create Lineage is how and Has the information For use where This field will autopopulate using the LLFA significant economic non-residential non-residential Significant economic significant Significant significant Significant comments about the land flooded, in km2 confidence in the to create future flood future flood information. what the data is made been classified under organisations apply the name provided on the "Instructions" tab, and consequences if the properties where the properties have been consequences, consequences to the consequences to the consequences to consequences to future flood record. modelled flood outline information. from. Has this data the Government's Government's the Flood ID. It is an EU-wide unique identifier future flood were to building structure would counted, it is important describe them including environment if the environment, describe cultural heritage if the cultural heritage, from; 'High' (good been created by using Protective Marking Protective Marking and will be used to report the flood information. occur? be affected either to record the method of information such as the future flood were to them including future flood were to describe them including match to past flood data owned or derived Scheme? Include Scheme. internally or externally if counting, to aid area of agricultural land occur? information such as occur? information such as the extents - about 80% from data owned by protective marking time Format: UK No No No Epping Forest District Medium-Low 2008-08 2D-TuFlow FEH (Revised Rainfall Runoff) Ordnance Survey Unmarked Private UKE10000012F0001 Council AddressPoint; CEH 1:50k River Centreline; NextMap DTM. Yes 7900 Detailed GIS During this event it is Yes 0.44km2 of Yes 604 Listed Buildings • 122 Hotspots (81% of JBA Consulting 15.83 Low 2009-07 JFLOW-GPU Depth-duration-frequency curves derived from Protect Commercial UKE06000023F0001 estimated that 224km internationally affected by this flood Study Area). (distributed by FEH CD-ROM, from centre of each 5km of roads and 13km of designated and outline. 110 buildings • Greatest Non- Environment Agency model, with areal reduction factor applied to railways will be 0.14km2 of locally located in one 1km grid Residential (577) and under licence) convert point rainfall estimate to more affected. As the area in designated sites. 14 square in Cabot Ward, critical infrastructure representative figure. Curve then used to question is IPPC sites, 4 Active centered on the buildings (13) at risk of derive 6.5 hr, 1:200 chance rainfall depth; this predominantly urban Radio Active Sites Floating Harbour. flooding located to the is converted to hyetograph, using summer only 1.09km2 of Authorisations, 3 Active 0.34km2 of historic north of Temple rainfall profile. agricultural land will be Radio Active Sites Parks and Gardens, as Meads. flooded, including Registrations and 84 well as 0.01km2 of • Greatest number of 0.01km2 of grade 1 Waste Licence sites. Scheduled Ancient residential buildings and 0.08km2 of grade Monuments. (1596) at risk to the 2 land. west of Temple Meads. • Greatest flood extent in Avonmouth Ward (4.3km2) • Greatest percentage of ward affected in Southville Ward (30.5% or 0.8km2). Yes 3900 Detailed GIS It is estimated that Yes 0.29km2 of Yes 347 Listed Buildings • 85 Hotspots (57% of JBA Consulting 7.66 Low 2009-07 JFLOW-GPU Depth-duration-frequency curves derived from Protect Commercial UKE06000023F0002 90km of roads and internationally affected by this flood Study Area). (distributed by FEH CD-ROM, from centre of each 5km 7.5km of railways will designated and outline. 66 buildings • Greatest Non- Environment Agency model, with areal reduction factor applied to be affected. As the 0.09km2 of locally located in one 1km grid Residential (447) and under licence) convert point rainfall estimate to more area in question is designated land. 10 square in Cabot Ward, critical infrastructure representative figure. Curve then used to predominantly urban IPPC sites, 3 Active centered on the buildings (11) at risk of derive 6.5 hr, 1:200 chance rainfall depth; this only 0.35km2 of Radio Active Sites Floating Harbour, as flooding located to the is converted to hyetograph, using summer agricultural land is Authorisations, 1 Active well as 0.21km2 of north of Temple rainfall profile. anticipated to flood, Radio Active Sites historic Parks and Meads. including 0.06km2 of Registrations and 52 Gardens flooed • Greatest number of grade 2 land, no grade Waste Licence sites. throughout the City of residential buildings 1 land affected. Bristol. (1136) at risk in Easton. • Greatest flood extent in Avonmouth Ward (1.3km2) • Greatest percentage of ward affected in Southville Ward (21% or 0.6km2). Yes 1000 Detailed GIS It is estimated that Yes 0.03km2 of Yes 106 Listed Buildings • 34 Hotspots (23% of JBA Consulting 2.35 Low 2009-07 JFLOW-GPU Depth-duration-frequency curves derived from Protect Commercial UKE06000023F0003 20.7km of roads and internationally affected by this flood Study Area). (distributed by FEH CD-ROM, from centre of each 5km 2.5km of railways will designated land. 2 outline. 12 buildings • Greatest Residential Environment Agency model, with areal reduction factor applied to be affected. As the IPPC sites, however no located in one 1km grid (489) and critical under licence) convert point rainfall estimate to more area in question is Active Radio Active square which is located infrastructure buildings representative figure. Curve then used to predominantly urban Sites Authorisations or between Cabot and (4) at risk of flooding derive 6.5 hr, 1:200 chance rainfall depth; this only 0.09km2 of Active Radio Active Cliftonin Cabot Wards. located to the south of is converted to hyetograph, using summer agricultural land is Sites Registrations 0.01km2 of historic Temple Meads. rainfall profile. anticipated to flood, affected. 14 Waste Parks and Gardens • Greatest number of including 0.04km2 of Licence sites. flood throughout the Non-Residential grade 2 land, no grade City of Bristol. buildings (126) at risk 1 land affected. to the north of Temple Meads. • Greatest flood extent in Stoke Bishop Ward (0.26km2) • Greatest percentage of ward affected in Brislington East Ward (5.7% or 0.23km2). Annex 2 Future floods 4 • Topography is derived from 64.5% LIDAR (on 0.25m-2m grids; original accuracy ± 0.15m) City of Bristol ST5942072340 City of Bristol Flood Map for Surface Probability refers to the 30 Surface runoff High Natural exceedance Natural flood Yes 12900 Detailed GIS 100 Critical and 35.5% NEXTMap SAR (on 5m grid; original accuracy ± 1.0m), processed to remove Water (FMfSW) - 1 in probability of the Infrastructure buildings & vegetation, then combined on a 2m grid; buildings added with an arbitrary height 30 rainfall event, in this buildings. of 5m based on OS MasterMap 2009 building footprints, then resampled to a 5m grid DTM. case producing Manual edits applied where flow paths clearly omitted e.g. below bridges. flooding of greater than • Flow routes dictated by topography; a uniform allowance of 12mm/hr has been made for 0.1m depth. manmade drainage in urban areas. Infiltration allowance reduces runoff to 39% in rural areas and 70% in urban areas. • Areas that may flood are defined by dynamically routing a 1.1 hour duration storm with 1 in 30 chance of occurring in any year over the DTM using JBA’s JFLOW–GPU model. • Manning’s n of 0.1 in rural areas; 0.03 in urban areas, to reflect explicit modelling of buildings in urban areas. • No allowance made for local variations in drainage, pumping or other works constructed for the purpose of flood risk management. • The ‘>0.1m’ layer shows where modelled flooding is greater than 0.1m deep. 5 • Topography is derived from 64.5% LIDAR (on 0.25m-2m grids; original accuracy ± 0.15m) City of Bristol ST5942072340 City of Bristol Flood Map for Surface Probability refers to the 30 Surface runoff High Natural exceedance Natural flood Yes 3100 Detailed GIS and 35.5% NEXTMap SAR (on 5m grid; original accuracy ± 1.0m), processed to remove Water (FMfSW) - 1 in probability of the buildings & vegetation, then combined on a 2m grid; buildings added with an arbitrary height 30 deep rainfall event, in this of 5m based on OS MasterMap 2009 building footprints, then resampled to a 5m grid DTM. case producing Manual edits applied where flow paths clearly omitted e.g. below bridges. flooding of greater than • Flow routes dictated by topography; a uniform allowance of 12mm/hr has been made for 0.3m depth. manmade drainage in urban areas. Infiltration allowance reduces runoff to 39% in rural areas and 70% in urban areas. • Areas that may flood are defined by dynamically routing a 1.1 hour duration storm with 1 in 30 chance of occurring in any year over the DTM using JBA’s JFLOW–GPU model. • Manning’s n of 0.1 in rural areas; 0.03 in urban areas, to reflect explicit modelling of buildings in urban areas. • No allowance made for local variations in drainage, pumping or other works constructed for the purpose of flood risk management. • The ‘>0.3m’ layer shows where modelled flooding is greater than 0.3m deep. 6 • Topography is derived from 64.5% LIDAR (on 0.25m-2m grids; original accuracy ± 0.15m) City of Bristol ST5942072340 City of Bristol Flood Map for Surface Probability refers to the 200 Surface runoff High Natural exceedance Natural flood Yes 36300 Detailed GIS 300 Critical and 35.5% NEXTMap SAR (on 5m grid; original accuracy ± 1.0m), processed to remove Water (FMfSW) - 1 in probability of the Infrastructure buildings & vegetation, then combined on a 2m grid; buildings added with an arbitrary height 200 rainfall event, in this buildings. of 5m based on OS MasterMap 2009 building footprints, then resampled to a 5m grid DTM. case producing Manual edits applied where flow paths clearly omitted e.g. below bridges. flooding of greater than • Flow routes dictated by topography; a uniform allowance of 12mm/hr has been made for 0.1m depth. manmade drainage in urban areas. Infiltration allowance reduces runoff to 39% in rural areas and 70% in urban areas. • Areas that may flood are defined by dynamically routing a 1.1 hour duration storm with 1 in 200 chance of occurring in any year over the DTM using JBA’s JFLOW–GPU model. • Manning’s n of 0.1 in rural areas; 0.03 in urban areas, to reflect explicit modelling of buildings in urban areas. • No allowance made for local variations in drainage, pumping or other works constructed for the purpose of flood risk management. • The ‘>0.1m’ layer shows where modelled flooding is greater than 0.1m deep. 7 • Topography is derived from 64.5% LIDAR (on 0.25m-2m grids; original accuracy ± 0.15m) City of Bristol ST5942072340 City of Bristol Flood Map for Surface Probability refers to the 200 Surface runoff High Natural exceedance Natural flood Yes 12800 Detailed GIS 100 Critical and 35.5% NEXTMap SAR (on 5m grid; original accuracy ± 1.0m), processed to remove Water (FMfSW) - 1 in probability of the Infrastructure buildings & vegetation, then combined on a 2m grid; buildings added with an arbitrary height 200 deep rainfall event, in this buildings. of 5m based on OS MasterMap 2009 building footprints, then resampled to a 5m grid DTM. case producing Manual edits applied where flow paths clearly omitted e.g. below bridges. flooding of greater than • Flow routes dictated by topography; a uniform allowance of 12mm/hr has been made for 0.3m depth. manmade drainage in urban areas. Infiltration allowance reduces runoff to 39% in rural areas and 70% in urban areas. • Areas that may flood are defined by dynamically routing a 1.1 hour duration storm with 1 in 200 chance of occurring in any year over the DTM using JBA’s JFLOW–GPU model. • Manning’s n of 0.1 in rural areas; 0.03 in urban areas, to reflect explicit modelling of buildings in urban areas. • No allowance made for local variations in drainage, pumping or other works constructed for the purpose of flood risk management. • The ‘>0.3m’ layer shows where modelled flooding is greater than 0.3m deep. 8 • Areas Susceptible to Groundwater Flooding (AStGWF) is a strategic scale map showing City of Bristol ST5942072340 City of Bristol Areas Susceptible to Does not describe a Unknown Groundwater High Natural exceedance Natural flood Yes 129400 Detailed GIS 1100 Critical groundwater flood areas on a 1km square grid Groundwater Flooding probability, but shows Infrastructure buildings • This data has used the top two susceptibility bands of the British Geological Society (BGS) (AStGWF) places where 1:50,000 Groundwater Flood Susceptibility Map, which was developed on a 50m grid from: groundwater • NEXTMap 5m grid DTM. emergence more likely • National Groundwater Level data on a 50m grid to occur. • BGS 1:50 000 geological mapping, with classifications of permeability • It covers consolidated aquifers (chalk, limestone, sandstone etc.) and superficial deposits. • Flood plains are not explicitly identified; the mapping identifies where groundwater is likely to emerge, and not where the water is subsequently likely to flow or pond. • No allowance is made for engineering works, or for groundwater rebound or abstraction to prevent groundwater rebound. • Shows the proportion of each 1km grid square which is susceptible to groundwater emergence, using four area categories. Annex 2 Future floods Yes 3000 Detailed GIS It is estimated that Yes 0.03km2 of Yes 162 Listed Buildings • 100 Hotspots (67% of Environment Agency 2.83 Medium-Low 2010-11 JFLOW-GPU Depth-duration-frequency curves derived from Rainfall Hyetograph, Unmarked UKE06000023F0004 55.8km of roads and internationally affected by this flood Study Area). FEH CD-ROM, from centre of each 5km EA 2m Composite 3.41km of railways will designated sites. 5 outline. 39 buildings • 597 Residential model, with areal reduction factor applied to DTM, OSMM be affected. As the IPPC sites, 1 Active located in one 1km grid buildings at risk to the convert point rainfall estimate to more Topography area in question is Radio Active Sites square in Cabot Ward, west of Temple Meads. representative figure. Curve then used to predominantly urban Authorisations and 1 centered on the • Greatest number of derive 1.1 hr, 1:30 chance rainfall depth; this is only 0.1km2 of Active Radio Active Floating Harbour. Non-Residential converted to hyetograph, using summer rainfall agricultural land is Sites Registrations. 43 0.12km2 of historic buildings (231) at risk profile. See "Description of assessment anticipated to flood, Waste Licence sites in Parks and Gardens, located to the north of method" for allowances for infiltration and including 0.01km2 of Avonmouth Ward. but no Scheduled Temple Meads. drainage. grade 2 land, no grade Ancient Monuments • 8 Critical 1 land affected. affected. Infrastructure buildings at risk in Hengrove. • Greatest flood extent and percentage of flooding located within Hengrove Ward (0.24km2 or 6.6%). Yes 800 Detailed GIS It is estimated that Yes No internationally or Yes 53 Listed Buildings • 44 Hotspots (28% of Environment Agency 0.73 Medium-Low 2010-11 JFLOW-GPU Depth-duration-frequency curves derived from Rainfall Hyetograph, Unmarked UKE06000023F0005 11.8km of roads and nationally designated affected by this flood Study Area). FEH CD-ROM, from centre of each 5km EA 2m Composite 0.43km of railways will sites; only 0.01 km2 of outline. 9 buildings • 267 Residential model, with areal reduction factor applied to DTM, OSMM be affected. As the ancient woodland located in one 1km grid buildings and 101 Non- convert point rainfall estimate to more Topography area in question is affected. 3 IPPC sites, square in Cabot Ward, Residential buildings at representative figure. Curve then used to predominantly urban 7 Waste Licence sites centered on the risk to the north of derive 1.1 hr, 1:30 chance rainfall depth; this is only 0.02km2 of prodominantly located Floating Harbour. Temple Meads. converted to hyetograph, using summer rainfall agricultural land is in Avonmouth Ward 0.03km2 of historic • 7 Critical profile. See "Description of assessment anticipated to flood, which could cause Parks and Gardens, Infrastructure buildings method" for allowances for infiltration and however only flooding pollution if flooded. but no Scheduled at risk in Hengrove drainage. to grade 3 land occurs. Ancient Monuments • Greatest flood extent affected. and percentage of flooding located within Hengrove Ward (0.069km2 or 2%). Yes 7400 Detailed GIS During this event it is Yes 0.06km2 of Yes 425 Listed Buildings • 125 Hotspots (84% of Environment Agency 8.64 Medium-Low 2010-11 JFLOW-GPU Depth-duration-frequency curves derived from Rainfall Hyetograph, Unmarked UKE06000023F0006 estimated that 166km internationally affected by this flood Study Area). FEH CD-ROM, from centre of each 5km EA 2m Composite of roads and 8km of designated, 0.01 of outline. 88 buildings • 1328 Residential model, with areal reduction factor applied to DTM, OSMM railways will be nationally designated located in one 1km grid buildings at risk at the convert point rainfall estimate to more Topography affected. As the area in and 0.08km2 of locally square in Cabot Ward, centre of the City, representative figure. Curve then used to question is designated sites. 13 centered on the around the Floating derive 1.1 hr, 1:200 chance rainfall depth; this predominantly urban IPPC sites, 3 Active Floating Harbour. Harbour. is converted to hyetograph, using summer only 0.33km2 of Radio Active Sites 0.12km2 of historic • 448 Non-Residential rainfall profile. See "Description of agricultural land will be Authorisations, 2 Active Parks and Gardens, properties at risk in assessment method" for allowances for flooded, including Radio Active Sites but no Scheduled Newtown area. infiltration and drainage. 0.01km2 of grade 1 Registrations and 79 Ancient Monuments • 11 Critical and 0.02km2 of grade Waste Licence sites. affected. Infrastructure buildings 2 land. at risk in Lower Knowle. • Greatest flood extent located in Avonmouth Ward (0.94km2). • Greatest percentage of flooding located within Hengrove Ward (0.51km2 or 14.4%). Yes 2500 Detailed GIS During this event it is Yes 0.01km2 of Yes 155 Listed Buildings • 88 Hotspots (59% of Environment Agency 2.77 Medium-Low 2010-11 JFLOW-GPU Depth-duration-frequency curves derived from Rainfall Hyetograph, Unmarked UKE06000023F0007 estimated that 43km of internationally affected by this flood Study Area). FEH CD-ROM, from centre of each 5km EA 2m Composite roads and 3km of designated, no outline. 32 buildings • 634 Residential model, with areal reduction factor applied to DTM, OSMM railways will be nationally designated located in one 1km grid buildings at risk at the convert point rainfall estimate to more Topography affected. As the area in and 0.01km2 of locally square in Cabot Ward, centre of the City, representative figure. Curve then used to question is designated sites centered on the around the Floating derive 1.1 hr, 1:200 chance rainfall depth; this predominantly urban flooded. 6 IPPC sites, Floating Harbour. Harbour. is converted to hyetograph, using summer only 0.09km2 of 2 Active Radio Active 0.12km2 of historic • 230 Non-Residential rainfall profile. See "Description of agricultural land will be Sites Authorisations, 1 Parks and Gardens, properties at risk in assessment method" for allowances for flooded, with only Active Radio Active but no Scheduled Newtown area. infiltration and drainage. grades 3 and 4 being Sites Registrations and Ancient Monuments • 9 Critical affected. 32 Waste Licence affected. Infrastructure buildings sites. at risk in Lower Knowle. • Greatest flood extent located in Hengrove Ward (0.19km2). • Greatest percentage of flooding located within Bedminster Ward (0.15km2 or 5.9%). Yes 18,500 Detailed GIS During this event it is Yes 2.1km2 of Yes 1160 Listed Buildings Data developed Environment Agency 87.1 Low 2010-11 ArcGIS Uses data which is developed from published British Geological Unmarked UKE06000023F0008 estimated that 1014km internationally affected by this flood specifically for PFRA, BGS groundwater level contours, groundwater Society (BGS) of roads and 37km of designated, 0.4km2 of outline. 280 buildings and is unlikely to be levels in BGS WellMaster database and some DiGMapGB-50 railways will be Ancient Woodland and located in one 1km grid suitable for any other river levels. No probability is associated with [Susceptibility to affected. 4.36km2 of 0.73km2 of locally square in Cabot Ward, purposes. this data. Groundwater Flooding]. agricultural land will be designated sites centered on the • 99 Hotspots (66% of flooded, with 0.06km2 flooded. 16 IPPC Floating Harbour. Study Area) of grade 1 and 0.21 sites, 3 Active Radio 4km2 of historic Parks • If grid square poses a grade 2 land affected. Active Sites and Gardens and potential risk of Authorisations, 3 Active 0.13km2 Scheduled groundwater flooding Radio Active Sites Ancient Monuments all NRD points within Registrations and 95 affected. are calculated as being Waste Licence sites. at risk, hence the resulting high values entered in the spreadsheet. • Data provides an inaccurate account of risk posed by this flood source. Annex 2 Future floods 9 • Modelling developed from combination of national (2004) and local (generally 1998-2010) City of Bristol ST5942072340 City of Bristol Flood Map (for rivers Fluvial 1 in 100, tidal 1 100 Main rivers Sea, ordinary Medium Natural exceedance Natural flood Yes 4300 Detailed GIS 100 Critical modelling. and sea) - flood zone 3 in 200 watercourses Infrastructure buildings. • Topography derived from LIDAR (on 0.25m-2m grids; original accuracy ± 0.15m), NEXTMap SAR (on 5m grid; original accuracy ± 1.0m), processed to remove buildings & vegetation. For local modelling, topography may include ground survey. • Location of watercourses and tidal flow routes dictated by topographic survey. • Areas that may flood are defined for catchments >3km² by routing appropriate flows for that catchment through the model to ascertain water level and thus depth and extent. • Manning’s n of 0.1 used for national fluvial modelling; variable (calibrated) values for national tidal modelling; appropriate values selected for local modelling. Channel capacity assumed as QMED for national fluvial modelling; local survey methods used for local modelling. • For the purpose of flood risk management, models assume that there are no raised defences. 10 • Modelling developed from combination of national (2004) and local (generally 2004-2010) City of Bristol ST5942072340 City of Bristol Flood Map (for rivers Extreme flood outline is 1000 Main rivers Sea, ordinary Medium Natural exceedance Natural flood Yes 10300 Detailed GIS 200 Critical modelling. and sea) - flood zone 2 1 in 1000, and includes watercourses Infrastructure buildings. • Topography derived from LIDAR (on 0.25m-2m grids; original accuracy ± 0.15m), some historic where NEXTMap SAR (on 5m grid; original accuracy ± 1.0m), processed to remove buildings & judged that this gives vegetation. For local modelling, topography may include ground survey. an indication of areas • Location of watercourses and tidal flow routes dictated by topographic survey. at risk of future • Areas that may flood are defined for catchments >3km² by routing appropriate flows for that flooding. catchment through the model to ascertain water level and thus depth and extent. • Manning’s n of 0.1 used for national fluvial modelling; variable (calibrated) values for national tidal modelling; appropriate values selected for local modelling. Channel capacity assumed as QMED for national fluvial modelling; local survey methods used for local modelling. • For the purpose of flood risk management, models assume that there are no raised defences. 11 • Surface Water Management Plan Data (100yr rainfall event - 0.5m cutoff) City of Bristol ST5942072340 City of Bristol Surface Water Flood Flood modelled is 100 Surface runoff High Natural exceedance Natural flood Yes 29200 Detailed GIS 200 Critical • Modelling developed from combination of local (generally 2004-2010) models from various Map representative of the 1 Infrastructure buildings. sources including EA (River Models) and Wesex Water (sewer models). in 100 year surface • Topography derived from LIDAR (on 4m grids; original accuracy ± 0.15m), NEXTMap SAR water flood event with (on 5m grid; original accuracy ± 1.0m), processed to remove buildings & vegetation. For local threshold of 0.5m used. modelling, topography may include ground survey and MasterMap for property footprints. • Areas that may flood are defined for all catchments by routing appropriate flows for that catchment through the model to ascertain water level and thus depth and extent. • Manning’s used are variable based on depth of flow • Ancilaries modeled - pumps; CSO's; sewers greater than 450 mm dia.; water escaping manholes; gullies; watercourses; • 24h superstorm (critical storm for the whole catchment) • FSR data allowing dinamic loss model to be used and Wallingford dynamic loss model used. Annex 2 Future floods Yes 3100 Detailed GIS During this event it is Yes 1.98km2 of Yes 109 Listed Buildings Data updated quarterly. Environment Agency 19.35 Medium 2010-11 Varies but mainly National methodology described in "National NextMap SAR DTMe, Protect Commercial UKE06000023F0009 estimated that 123km internationally affected by this flood To understand the JFLOW, ISIS, HEC- Generalised Modelling for Flood Zones - UKHO Admiralty of roads and 13km of designated, no outline. 33 buildings likelihood of future RAS, TUFLOW for Fluvial & Tidal Modelling Methods - Charts, 1:50K CEH railways will be nationally designated located in one 1km grid flooding, taking account fluvial, and HYDROF Methodology, Strengths and Limitations". A River Centre Line, CEH affected. As the area in and 0.12km2 of locally square in Cabot Ward, of defences, refer to for tidal. national dataset (for England and Wales) of FEH Q(T) Grids, POL question is designated sites centered on the Areas Benefitting from fluvial flood peak estimates was derived from CSX Peak Extreme predominantly urban flooded. 15 IPPC sites, Floating Harbour. Defences and National the Flood Estimation Handbook (FEH) to Water Levels, POL only 2.48km2 of 1 Active Radio Active 0.13km2 of historic Flood Risk Assessment generate a 1 in 100 chance fluvial flood. Local CS3 Astronomical agricultural land will be Sites Authorisations, 1 Parks and Gardens (NaFRA) data. Marked fluvial modelling uses FEH methods. Peak tidal Tides, UKHO Admiralty flooded, with 0.11km2 Active Radio Active and 0.02km2 'Protect' for complete water levels from either Dixon & Tawn (DT3) Tide Time-Series of grade 2 land Sites Registrations and Scheduled Ancient national dataset only. or local data sets to derive 1 in 200 chance Calibration Locations, affected and no grade 73 Waste Licence Monuments affected. • 49 Hotspots (33% of tide levels including surge from POL CSX OS 1:10 Boundary Line 1. sites. Study Area). model. MHW • 560 Residential buildings at risk within Avonmouth Ward. • 326 Non-Residential and 18 Critical Infrastructure buildings at risk within the same square in Avonmouth Ward. • Greatest flood extent and percentage of flooding occurs within Avonmouth Ward (14.59km2 or 81%). Yes 5100 Detailed GIS During this event it is Yes 2.01km2 of Yes 279 Listed Buildings Data updated quarterly. Environment Agency 23.07 Medium 2010-11 Varies but mainly National methodology described in "National NextMap SAR DTMe, Protect Commercial UKE06000023F0010 estimated that 178km internationally affected by this flood To understand the JFLOW, ISIS, HEC- Generalised Modelling for Flood Zones - UKHO Admiralty of roads and 15km of designated, no outline. 114 buildings likelihood of future RAS, TUFLOW for Fluvial & Tidal Modelling Methods - Charts, 1:50K CEH railways will be nationally designated located in one 1km grid flooding, taking account fluvial, and HYDROF Methodology, Strengths and Limitations". A River Centre Line, CEH affected. As the area in and 0.12km2 of locally square in Cabot Ward, of defences, refer to for tidal. national dataset (for England and Wales) of FEH Q(T) Grids, POL question is designated sites centered on the National Flood Risk fluvial flood peak estimates was derived from CSX Peak Extreme predominantly urban flooded. 17 IPPC sites, Floating Harbour. Assessment (NaFRA) the Flood Estimation Handbook (FEH) to Water Levels, POL only 2.59km2 of 2 Active Radio Active 0.16km2 of historic data. Marked 'Protect' generate a 1 in 1000 chance fluvial flood. CS3 Astronomical agricultural land will be Sites Authorisations, 1 Parks and Gardens for complete national Local fluvial modelling uses FEH methods. Tides, UKHO Admiralty flooded, with 0.11km2 Active Radio Active and 0.02km2 dataset only. Peak tidal water levels from either Dixon & Tide Time-Series of grade 2 land Sites Registrations and Scheduled Ancient • 65 Hotspots (43% of Tawn (DT3) or local data sets to derive 1 in Calibration Locations, affected and no grade 78 Waste Licence Monuments affected. Study Area). 1000 chance tide levels including surge from OS 1:10 Boundary Line 1. sites. • 1198 Residential POL CSX model. MHW, Historic Flood buildings at risk within 1 Map grid square located to the east of the Floating Harbour. • 478 Non-Residential buildings at risk in Newtown. • 19 Critical Infrastructure buildings at risk within 1 grid square in Avonmouth Ward. • Greatest flood extent and percentage of flooding occurs within Avonmouth Ward (15km2 or 84%). Yes 5000 Detailed GIS During this event it is Yes 0.03km2 of Yes 540 listed buildings are 111 Hotspots (74% of City of Bristol Council 4.8 High-Medium 2011 UKE06000023F0011 estimated that 54.43km internationally, affected by this flood Study Area). of roads and 4.65km of 0.02km2 of locally and outline. 88 buildings • 2301 Residential railways will be 0.01km2 of policy located in the area of buildings at risk within affected. 0.44km2 of designated sites. 7 Kingsdown, Cabot Cabot Ward, the centre agricultural land will be IPPC sites, 3 Active Ward. 10.22km2 of of Bristol indicated as flooded, with 0.01km2 Radio Active Sites Historic Parks and being at greatest risk of of grade 2 and 0.02 of Authorisations, 2 Active Gardens and no surface water flooding. grade 1 land affected. Radio Active Sites Scheduled Ancient • 410 Non-Residential Registrations and 39 Monuments are buildings at risk in the Waste Licence sites. affected. kingsdown area of Cabot Ward. • 8 Critical Infrastructure buildings at risk within 1 grid square to the east of Kingsdown. • Greatest flood extent and percentage of flooding occurs within Southville Ward (0.31km2 or 6.32%). A.3 Records of Flood Risk Areas and their rationale (preliminary assessment report spreadsheet) 2011s4891 2011s4891 BCC PFRA draft pm3.docx 49 Annex 3 Flood Risk Areas ANNEX 3: Records of Flood Risk Areas and their rationale (preliminary assessment report spreadsheet) Field: Flood Risk Area ID Name of Flood Risk National Grid Main source of Additional source(s) Confidence in main Main mechanism of Main characteristic Significant Human health Property count method Other human health Significant economic Number of non- Area Reference flooding of flooding source of flooding flooding of flooding consequences to consequences - consequences consequences residential properties human health residential properties flooded Mandatory / optional: Mandatory Mandatory Mandatory Mandatory Optional Optional Mandatory Mandatory Mandatory Optional Optional Optional Mandatory Optional Format: Unique number Max 250 characters 12 characters: 2 Pick from drop-down Max 250 characters, Pick from drop-down Pick from drop-down Pick from drop-down Pick from drop-down Number between 1- Pick from drop-down Max 250 characters Pick from drop-down Number between 1- between 1-9999 letters, 10 numbers same source terms 10,000,000 10,000,000 Notes: A sequential number Name of the locality National Grid Pick the source from If there is also Pick a broad level of Pick a mechanism Pick a characteristic Has the Flood Risk Record the number of Where residential or If the Flood Risk Area Has the Flood Risk Record the number of starting at 1 and associated with the Reference of the which there is a significant flood risk confidence in the Main from; 'Natural from; 'Flash flood' Area been identified as residential properties non-residential has been identified as Area been identified as non-residential incrementing by 1 for Flood Risk Area; a centroid (centre point, significant flood risk. generated by another source of flooding exceedance' (of (rises and falls quite a result of significant where the building properties have been a result of other a result of significant properties where the each record. town, city, or county. falls within polygon) of Refer to the PFRA source (other than the from; 'High' capacity), 'Defence rapidly with little or no consequences to structure would be counted, it is important Significant economic building structure the Flood Risk Area. guidance for Main source of (compelling evidence exceedance' advance warning), human health? affected either to record the method consequences to consequences? would be affected definitions of sources. flooding), report the of source - about 80% (floodwater 'Natural flood' (due to internally or externally of counting, to aid human health, either internally or source(s) here, using confident that source overtopping defences), significant by the flood. comparisons between describe them (such externally by the flood. the same source is correct), 'Medium' 'Failure' (of natural or precipitation, at a counts. Choose from; as information about terms. (some evidence of artificial defences or slower rate than a 'Detailed GIS' (using the number of critical source but not infrastructure, or of flash flood), 'Snow property outlines, as services flooded). compelling - about pumping), 'Blockage or melt flood' (due to per Environment 50% confident that restriction' (natural or rapid snow melt), Agency guidance), source is correct) 'Low' artificial blockage or 'Debris flow' 'Simple GIS' (using (source assumed - restriction of a (conveying a high property points), about 20% confident conveyance channel degree of debris), or 'Estimate from map', that source is correct) or system), or 'No 'No data'. Most UK or 'Observed number'. or 'Unknown'. data'. floods are 'Natural floods'. Example: 1 London SX1234512345 Surface runoff NA High Natural exceedance Natural flood Yes 50000 Detailed GIS No Records begin here: 1 Bristol ST5942072340 Surface runoff N/A High Natural exceedance Natural flood Yes 31,600 Detailed GIS 200 Critical Yes 5,700 Infrastructure buildings Annex 3 Flood Risk Areas Property count method Other economic Significant Environment Significant Cultural heritage Origin of Flood Risk Amended Flood Risk New Flood Risk Area Rationale detail European Flood Risk Area Code consequences consequences to the consequences consequences to consequences Area Area rationale rationale environment cultural heritage Optional Optional Mandatory Optional Mandatory Optional Mandatory Mandatory Mandatory Mandatory Auto-populated Pick from drop-down Max 250 characters Pick from drop-down Max 250 characters Pick from drop-down Max 250 characters Pick from drop-down Pick from drop-down Pick from drop-down Max 1,000 characters Max 42 characters Where residential or If the Flood Risk Area Has the Flood Risk If the Flood Risk Area Has the Flood Risk If the Flood Risk Area Pick the origin from Pick the main rationale Pick the main rationale Summarise the rationale for amending an indicative Flood Risk Area, or identifying a new This field will autopopulate using the LLFA non-residential has been identified as Area been identified as has been identified as Area been identified as has been identified as either; 'Indicative' from either; from either 'Past Flood Risk Area. Refer to Defra & WAG guidance to LLFAs on "Selecting and reviewing name provided on the "Instructions" tab, and properties have been a result of other a result of significant a result of Significant a result of significant a result of Significant Flood Risk Area, 'Geography', 'Past floods', or 'Future Flood Risk Areas for local sources of flooding". If the Flood Risk Area was an indicative the Flood Risk Area ID. It is an EU-wide counted, it is important Significant economic consequences to the consequences to the consequences to consequences to 'Amended' Flood Risk floods', or 'Future floods'. Then provide Flood Risk Area and has not been amended, record "indicative Flood Risk Area". unique identifier and will be used to report the to record the method consequences, environment? environment, describe cultural heritage? cultural heritage, Area (in which case floods'. Then provide further detail in Flood Risk Area information. of counting, to aid describe them (such them (such as describe them (such Amended Flood Risk further detail in Rationale detail. This is comparisons between as information about information about as information about Area rationale is Rationale detail. This is not mandatory if the Format: UK No No Indicative NA NA indicative Flood Risk Area UKE10000012A0001 Detailed GIS It is estimated that Yes 0.03km2 of Yes 512 Listed Buildings Indicative Indicative Flood Risk Area UKE06000023A0001 71.8km of roads and internationally affected by this flood 6.05km of railways will designated, 0.06km2 outline. 0.2km2 of be affected. 1.56km2 of locally designated historic Parks and of agricultural land is and 0.24km2 of Gardens, and anticipated to flood, Ancient Woodland 0.004km2 of including 0.1km2 of sites potentially Scheduled Ancient grade 1 and 0.17km2 flooded from 2 IPPC Monuments affected. of grade 2 land. sites, 5 Active Radio Active Sites (Auths), 2 Active Radio Active Sites (Regs) and 20 Waste Licence sites. A.4 Review checklist 2011s4891 2011s4891 BCC PFRA draft pm3.docx 50 Preliminary Flood Risk Assessment Checklist LLFA Name: Environment Agency Checklist questions Notes for completion LLFA Environment Agency area review national review Step 1 Set up governance and develop partnerships Have appropriate governance and partnership Refer to section 2.3 of guidance. Governance and partnership 1.1 Yes arrangements been set up? arrangements should be to the satisfaction of the LLFA. Who in the LLFA reviewed the PFRA and when Please state the review and approval process and when approval 1.2 was it done? was gained e.g. Officer, Scrutiny Committee, Cabinet. Refer to Section 5 of the guidance. Step 2 Determine appropriate data systems Has a data management system been established See Annex 5 for information about data standards Yes 2.1 and implemented? Step 3 Collate information on past and future floods and their consequences Has information been requested from all relevant See Flood Risk Regulations Part 6 Co-operation. Yes 3.1 partners? Are there any gaps in available information? (This LLFAs - Are there gaps in certain locations, or for certain events No could include gaps which could have been filled but that you are aware of, or for certain sources of flooding (such as weren't, or gaps which couldn't be filled because groundwater). Respond with Yes/No and provide comments on any 3.2 the information wasn't available) missing information. EA Review - Has all available information has been gathered and included? Step 4 Determining locally agreed surface water information Which dataset (or combination of datasets) has LLFAs - Select from drop down. Refer to "Locally agreed surface Combination of FMfSW and other local 4.1 been determined as "locally agreed surface water water information" text box in section 3.5.1 (p.17) of guidance. informationinfo rmation information"? EA review - Has this been agreed? Has the locally agreed surface water information LLFAs - Select Yes/No from drop down list. Refer to "locally Yes 4.2 been clearly stated and presented (on a map) in the agreed surface water information" text box in section 3.5.1 (p.17) Preliminary Assessment Report? of guidance. If available, what is the total property count for If known, please enter the total number of properties at risk in the 34,200 (Res + Non Res) 4.3 locally agreed surface water information in the LLFA. LLFA? If applicable, has the method for counting Refer to text box on page 17 of guidance Yes 4.4 properties been described in the Preliminary Assessment Report? Has available information on local drainage Refer to text box on page 17 of guidance. Information provided on Yes capacity (where used to inform the determination of drainage may inform options for any future improvements to the 4.5 locally agreed surface water information) been Flood Map for Surface Water. included in the report? Preliminary Flood Risk Assessment Checklist LLFA Name: Environment Agency Checklist questions Notes for completion LLFA Environment Agency area review national review Step 5 Complete Preliminary Assessment Report Document Does the Preliminary Assessment Report cover all LLFAs - If the Preliminary Assessment Report contains all the Yes the content described in Annex 1 of the content described in Annex 2 of the PFRA guidance, respond with 5.1 Environment Agency's PFRA guidance? a 'Yes'. If there are some elements missing, please provide a brief explanation. EA Review - Include comments on any missing content. Has a summary table of flood events been Refer to section 3.4 and 3.5 of guidance Yes 5.2 produced? Has a description of past flood events been Refer to section 3.4 and 3.5 of guidance Yes 5.3 included? Has additional information been included on Refer to 3.6 of guidance. Standard text has been provided for No climate change and long term developments? Preliminary Assessment Reports which meets the minimum 5.4 requirements of the Flood Risk Regulations. Please respond with Yes or No, and if additional information has been included, please state the information source(s) Step 6 Record information on past and future floods with significant consequences in spreadsheet Are records of past flooding with significant harmful LLFAs - past flooding should be recorded on the spreadsheet and Yes consequences recorded on the Preliminary included as Annex 1 of the Preliminary Assessment Report. 6.1 Assessment Report spreadsheet (Annex 1 of EA review - Are all the mandatory fields complete? Prelminary Assessment Report) ? Are there any past floods with significant harmful LLFAs - Respond with Yes or No. If No, provide additional No consequences that have not been recorded? If so, information e.g. anecdotal information on flood, but not enough 6.2 please explain why not. evidence to include EA review - Do you agree with LLFA response and comments? Have any additional records of future flooding LLFAs - future flooding information should be recorded on the Yes (other than the national dataset information which is spreadsheet and included as Annex 2 of the Preliminary already completed) been recorded on the future Assessment Report. 6.3 flooding Preliminary Assessment Report EA review - Are all mandatory fields complete? spreadsheet (Annex 2 of Preliminary Assessment Report) Step 7 Illustrate information on past and future floods Have summary maps been produced for past and Refer to section 3.4 and 3.5 of guidance Yes 7.1 future floods? Step 8 Review indicative Flood Risk Areas Is your LLFA within an indicative Flood Risk Area? Indicative Flood Risk Areas were provided to LLFAs by the Yes 8.1 Environment Agency in December 2010. If the answer to 8.1 is yes, have you reviewed it Refer to section 4 of guidance. LLFAs should identify whether they Yes using the locally agreed surface water information, have reviewed against local information or just used the indicative 8.2 and relevant local information in the Preliminary Flood Risk Area information provided by the Environment Agency. Assessment Report? Preliminary Flood Risk Assessment Checklist LLFA Name: Environment Agency Checklist questions Notes for completion LLFA Environment Agency area review national review Step 9 Identify Flood Risk Areas Is a Flood Risk Area proposed? LLFA - select a response from the drop down list and then Yes - it is exactly the same as the indicative complete the relevant questions 9.1.1 - 9.1.5. (NB. Indicative Flood Flood Risk Area (go to question 9.1.1) 9.1 Risk Areas can be amended due to Geography, past flooding and/or future flooding.) If the proposed Flood Risk Area is exactly the same LLFA - please confirm that the boundary of the indicative Flood Yes as the indicative Flood Risk Area, please confirm. Risk Area has not been changed and no change has been made to 9.1.1 the flood risk indicators. EA review - please confirm If changes have been made to the indicative Flood Use the drop down list to identify the reasons for the change. Risk Area because of geography, please identify Options are the same as the table on page 26 of the PFRA 9.1.2 what changes have been made. guidance. EA review - please confirm evidence supports change If changes have been made to the indicative Flood LLFA - identify the scale of the changes made e.g. major/minor n/a Risk Area because of past / historic flooding, increase or decrease in size of Flood Risk Area and the source of please indicate the changes and the reasons why. information used e.g. records of historic flooding. 9.1.3 EA review - confirm scale of the changes made and provide indication of confidence in the evidence provided e.g. anecdotal evidence versus detailed report on flooding event. If changes have been made to the indicative Flood LLFA - identify the scale of the changes made e.g. major/minor n/a Risk Areas because of future flooding, please increase or decrease in size of Flood Risk Area and the source of 9.1.4 indicate the changes and the reasons why. information used e.g. detailed modelling as part of SWMP. EA review - confirm scale of the changes made and indication of confidence in the evidence If a new Flood Risk Area is being proposed, does it Criteria and thresholds are set out in the Defra/WAG guidance on N/A meet the Defra / WAG thresholds? selecting and reviewing Flood Risk Areas for local sources of 9.1.5 flooding EA review - identify the evidence provided to support this and indicate degree of confidence in the evidence. Does the proposed Flood Risk Area include LLFAs should respond with Yes or No. No 9.2 flooding from interactions with main river, reservoirs EA Review - Summarise the location and nature of interactions i.e. or the sea? river or sea. Has an indicative Flood Risk Area been deleted? LLFA - Respond with Yes/No and if an indicative Flood Risk Area No has been deleted please provide a short description why. 9.3 EA - confirm the evidence presented to support this is aligned to 'locally agreed surface water information' Step 10 Record information including rationale - ONLY COMPLETE IF ANSWER TO 9.1 IS YES If proposing Flood Risk Areas, have the mandatory LLFAs - the spreadsheet indicates mandatory columns to be Yes 10.1 fields in the spreadsheet been completed? completed. EA Review - Are all mandatory fields complete? Has a rationale and evidence for LLFAs - Refer to Table 5 on page 26 of the PFRA guidance and N/A amending/adding/deleting Flood Risk Areas been Annexes A-D of the Defra/WAG Guidance. Rationale should be included in the Preliminary Assessment Report? included in "Identification of Flood Risk Areas" section of 10.2 Preliminary Assessment Report. EA Review - Confirm that supporting evidence for any amendments/additions/deletions has been provided in the Preliminary Assessment Report and annexes A.5 GIS layer of flood risk area 2011s4891 2011s4891 BCC PFRA draft pm3.docx 51 Offices at Atherstone Doncaster Edinburgh Haywards Heath Limerick Newcastle upon Tyne Newport Northallerton Saltaire Skipton Tadcaster Wallingford Warrington Registered Office South Barn Broughton Hall SKIPTON North Yorkshire BD23 3AE t:+44(0)1756 799919 e:[email protected] Jeremy Benn Associates Ltd Registered in England 3246693 Visit our website www.jbaconsulting.co.uk