CARDIFF COUNCIL AGENDA ITEM: 3 CYNGOR CAERDYDD

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CARDIFF COUNCIL

AGENDA ITEM: 3

CYNGOR CAERDYDD

ENVIRONMENTAL SCRUTINY COMMITTEE: 17

th

May 2011

PRELIMINARY FLOOD RISK ASSESSMENT

Purpose of report

1. To provide Members with information of the Preliminary Flood Risk Assessment

currently being developed for Cardiff.

Background

2. A European Directive introduced the Flood Risk Regulations which came into force on

10 December 2009. These imposed strict timetables on member states for the

completion of three elements of work which will finally culminate in the publication of

Flood Risk Management Plans for River Basin districts, of which there are 11 in

England and Wales, and river catchments, which number 77 in England and Wales.

There are 9 river catchments in Wales and those that are relevant to Cardiff are the

Taff/ Ely and the Rhymney / Ebbw catchments.

3. The Regulations identify the Environment Agency and Local Authorities as lead

authorities to work with partners such as water companies to manage flood risk and to

reduce the consequences of flooding on human health, economic activity, cultural

heritage and the environment. The Regulations set out a 6 year cycle of assessment

and production of mapping and plans with the Environment Agency assigned

responsibility for main river, the sea and reservoirs and lead Local Flood Authorities (all

councils in Wales), responsible for all other sources of flooding including surface water

runoff, ground water and

ordinary watercourse flooding

.

4. The Flood Risk Regulations impose dates for the completion of 3 separate elements of

work for the management of risk associated with flooding to be completed as follows

• Preliminary Flood Risk Assessment by 22 December 2011

• Flood Risk and Flood Hazard Map by 22 December 2013

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• Flood Risk Management Plans by 22 December 2015

5. The Environment Agency Wales is tasked with collating the 22 Preliminary Flood Risk

Assessment’s covering the whole of Wales and they must submit a summary

Preliminary Flood Risk Assessment by the above deadline. In order that they have

sufficient time to meet their deadline they in turn have imposed their own deadline of

22 June 2011 for Lead Local Flood Authorities to submit reports.

6. The report on Cardiff's Preliminary Flood Risk Assessment is due for submission to the

Environment Agency by the 22 June 2011.

7. The Environment Agency has produced a guidance document which has been used by

all local authorities to draft their Preliminary Flood Risk Assessment’s. It should be

noted that the scope of the Preliminary Flood Risk Assessment covers only local flood

risk, that of tributaries, surface water run off and feeder streams and therefore excludes

flooding risk from the main rivers, the sea and large raised reservoirs. Those

watercourse risks are being assessed by the Environment Agency and a consolidated

report covering both is to be produced by the Environment Agency by the Welsh

Assembly Government prescribed deadlines.

8. The Council has engaged a consultant, Hyder Consulting Ltd, to prepare its Preliminary

Flood Risk Assessment and the draft version of this document is attached as

Appendix

1 . The document consists of:

• A text document prepared to a standard format.

• A map of the county showing the area of significant flood risk.

• A schedule of known flood events that have occurred in the past.

9. The costs of preparing the Assessment have been met from a £22,000 grant assigned

to Cardiff from the Welsh Assembly Government from which all authorities in Wales

benefited. The potential for future additional funding for further aspects of work

associated with the Flood Risk Regulations is not know at this time. Liaison with the

Welsh Assembly Government officials will continue to understand and develop the next

stage of the process.

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10. Environment Agency Wales supplied all Lead Local Flood Authorities with maps of their

areas showing Indicative Flood Risk areas based on a national methodology which has

been stipulated by the Assembly Government. To ensure a consistent and proportionate

approach Environment Agency Wales have identified 1 km squares above the flood risk

threshold using the Flood Map for Surface Water. The 1 km squares identify areas

where more than 200 people, or more than one critical service or more than 20

non-residential properties are predicted to be flooded to a depth greater than 0.3m under the

0.5% annual probability surface water event. With this as a starting point the consultant

has drawn on all available information from many sources (as set out in Appendix 2)

some internal to the Council and others external to assess whether the indicative flood

risk map is an accurate representation of the actual flood risk.

11. In undertaking a review of the maps supplied by Environment Agency Wales there has

been an analysis of all known historical flooding events both small and large and also

potential future flooding based on a 1 in 100 year event. The Preliminary Flood Risk

Assessment in Appendix 1 is the conclusion of this analysis.

12. The analysis identified three new 1km squares that should have been included but

these have not increased the area covered by the original indicative flood risk area

proposed by Environment Agency Wales. Two of the new squares cover the Whitchurch

Brook and members will be aware that European funding has already been allocated to

a project aimed to reduce the flood risk posed by the Brook. The project is currently

awaiting match funding from the Assembly before it can proceed.

13. It should also be noted that in analysing the future flood risk the consultants have

reviewed information available from Strategic Flood Consequence Assessments which

have been undertaken to support proposals contained within the Local Development

Plan. Further flood assessment work in relation to the Local Development Plan is

ongoing but is unaffected by the conclusions of the Preliminary Flood Risk Assessment.

14. The Preliminary Flood Risk Assessment report is a high-level screening exercise which

must consider flooding which has or could have a significant harmful consequence for

human health, economic activity, the environment and cultural heritage and the map

illustrating the area of flood risk will have to be refined with further study. The Plan

presents a summary of potential consequences noting; the number of people and

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critical services at risk, impacts on roads or rail infrastructure, that a number of Sites of

Special Scientific Interest, Scheduled Monuments and Listed Buildings.

15. The next stage stipulated by the Regulations will be a more detailed and comprehensive

analysis to prepare flood hazard maps and flood risk maps which will be used to

develop the Councils Flood Risk Management Plan that must be submitted to the

Environment Agency by the 22 June 2015, progress and delivery on this stage will be

the subject of a future report to the Executive.

Issues

16. Councillor Delme Bowen, Executive Member for Traffic & Transportation has been

invited to attend the meeting. At the meeting officers representing City Services will be

in attendance to deliver a presentation and answer Member questions.

Way Forward

17. Members may wish to consider whether there are any issues or comments on this item

which they would like to pass on to the Executive. Members may also wish to consider

if and when this issue should be reconsidered by the Committee.

Legal Implications

18. The Scrutiny Committee is empowered to enquire, consider, review and recommend but

not to make policy decisions. As the recommendations in this report are to consider and

review matters there are no direct legal implications. However, legal implications may

arise if and when the matters under review are implemented with or without any

modifications. Any report with recommendations for decision that goes to

Executive/Council will set out any legal implications arising from those

recommendations. All decisions taken by or on behalf the Council must (a) be within the

legal powers of the Council; (b) comply with any procedural requirement imposed by

law; (c) be within the powers of the body or person exercising powers of behalf of the

Council; (d) be undertaken in accordance with the procedural requirements imposed by

the Council e.g. Scrutiny Procedure Rules; (e) be fully and properly informed; (f) be

properly motivated; (g) be taken having regard to the Council's fiduciary duty to its

taxpayers; and (h) be reasonable and proper in all the circumstances.

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Financial Implications

19. The Scrutiny Committee is empowered to enquire, consider, review and recommend but

not to make policy decisions. As the recommendations in this report are to consider and

review matters there are no direct financial implications at this stage in relation to any of

the work programme. However, financial implications may arise if and when the matters

under review are implemented with or without any modifications. Any report with

recommendations for decision that goes to Executive/Council will set out any financial

implications arising from those recommendations.

RECOMMENDATIONS

The Committee is recommended to:

1. Take account of the information received at the meeting, and;

2. Report any comments to the Executive for their consideration.

Mike Davies

Head of Service – Scrutiny, Performance & Improvement

11

th

May 2011

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Cardiff Council

PRELIMINARY FLOOD RISK ASSESSMENT

DRAFT REPORT

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CARDIFF COUNCIL PRELIMINARY FLOOD RISK ASSESSMENT

Hyder Consulting (UK) Limited-2212959 Page 2

Hyder Consulting (UK) Limited

2212959 HCL House Fortran Road

St Mellons Business Park St Mellons Cardiff CF3 0EY United Kingdom Tel: +44 (0)29 2092 6700 Fax: +44 (0)29 20 www.hyderconsulting.com

Cardiff Council

PRELIMINARY FLOOD RISK ASSESSMENT

DRAFT REPORT

Author S Hooton Checker R Green Approver N Evans Report No 5000-UA003062-NE-R-01 Date 5 May 2011

This report has been prepared for Cardiff Council in

accordance with the terms and conditions of appointment for the Preliminary Flood Risk Assessment dated February 2011. Hyder Consulting (UK) Limited (2212959) cannot accept any responsibility for any use of or reliance on the contents of this report by any third party.

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Executive Summary

This report has been prepared by Hyder Consulting (UK) Limited on behalf of Cardiff Council to help manage local flood risk and deliver the requirements of the Flood Risk Regulations 2009 (“the Regulations”). Cardiff Council is defined as a Lead Local Flood Authority (LLFA) under the Regulations. The Preliminary Flood Risk Assessment (PFRA) which comprises this document, the supporting spreadsheets and GIS layer, meets the first stage of the requirements of the Regulations.

The PFRA process is aimed at providing a high level overview of flood risk from local flood sources, including surface water, groundwater and ordinary watercourses. As a LLFA, Cardiff Council must submit the PFRA to Environment Agency Wales (EAW) for review by the 22 June 2011. The methodology for producing the PFRA has been based on EAW guidance (EAW, 2010) and guidance provided by the Department of Environment, Food and Rural Affairs (DEFRA) and the Welsh Assembly Government (WAG) (DEFRA/WAG, 2010).

EAW has used a national methodology, which has been set out by WAG, to identify indicative Flood Risk Areas in Wales. Of the eight indicative Flood Risk Areas that have been identified nationally, one is located within the Cardiff Council boundary. Within the finalised Flood Risk Area, the Regulations require Cardiff Council to produce Flood Risk and Hazard Maps and Flood Risk Management Plans by June 2013 and June 2015 respectively.

In order to develop a clear overall understanding of the flood risk across Cardiff, flooding information and records of historical events have been collected from a range of key stakeholders, including the Council, Emergency Services, Dwr Cymru Welsh Water and Community Councils. Records relating to over 1000 flood events caused by flooding from local sources were collected and analysed.

Each historical flood record has been analysed. However, no historical flood events are judged to have met the significant harmful consequences criteria which are defined in this report as a flood event which local resources were insufficient to manage and which made national headline news and could occur again.

This PFRA has also reviewed the future flood risk to Cardiff, by analysing various local and national data sets. Based on this it is considered that there is no justification for the refinement of the EAW indicative Flood Risk Area for Cardiff.

However, the review has highlighted that the boundary of the EAW indicative Flood Risk Area for Cardiff extends into the Vale of Glamorgan Council area and an indicative Flood Risk Area for part of Rhonda Cynon Taff extends into the Cardiff Council area. It is recommended that the indicative Flood Risk Areas are refined along administrative boundary lines. Consultations with the Vale of Glamorgan and Rhonda Cynon Taff Councils are ongoing in order to gain formal agreement to these changes and agree consistency across LLFA PFRAs.

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CARDIFF COUNCIL PRELIMINARY FLOOD RISK ASSESSMENT Hyder Consulting (UK) Limited-2212959

Cardiff Council has commissioned Hyder Consulting (UK) Limited to undertake this Preliminary Flood Risk Assessment (PFRA). Under the Flood Risk Regulations 2009 (“the Regulations”), Lead Local Flood Authorities (LLFAs) are responsible for undertaking a Preliminary Flood Risk Assessment (PFRA) to provide an evidence base with which to identify areas of significant flood risk (Flood Risk Areas) from local sources such as surface runoff, groundwater and ordinary watercourses.

Under the Regulations there is a six year flood risk management planning cycle based on a four stage process of:

undertaking a PFRA;

identifying Flood Risk Areas;

preparing flood hazard and risk maps for Flood Risk Areas

preparing flood risk management plans for Flood Risk Areas. This PFRA report and annexes form the first two stages of the process.

The scope of the PFRA only covers local flood risk and therefore excludes flooding from main rivers, the sea and large raised reservoirs. This study therefore only considers flooding from surface runoff, groundwater and ordinary watercourses and any interaction these have with drainage systems and other sources of flooding including sewers, the sea and main rivers. A definition of these sources of flooding is as follows:

Surface runoff – rainwater (including snow and other precipitation) which is on the surface of the ground and has not entered a watercourse, drainage system or public sewer.

Groundwater – water which is below the surface of the ground and in direct contact with the ground or subsoil.

Ordinary Watercourses – stream, brook, ditch or non-public sewer which is not a main river.

1.2 Aims and Objectives

The PFRA is a high level screening exercise which aims to identify areas where there is a significant flood risk. The PFRA involves:

Collecting information from relevant organisations regarding past and potential future floods within the study area;

Assembling the information into the PFRA report;

Reviewing and amending, if necessary, the existing EAW Flood Risk Areas.

The PFRA also aims to inform and support the local flood risk management strategy which is required to be produced under the Flood and Water Management Act 2010.

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1.3 Study Area

The study area, shown in Figure 1-1, is the administrative boundary of Cardiff Council which is an area of approximately 158 km2 and contains a population of around 336,200. The information collated for this PFRA is for areas located within the Cardiff study area.

Cardiff falls within the Ely, Taff and Rhymney main river catchments. Two Catchment Flood Management Plans (CFMPs) cover the Cardiff area: the Taff and Ely CFMP (EAW, 2009) and the Eastern Valleys CFMP (EAW, 2009), which includes the River Rhymney.

In Cardiff there are estimated to be 148,109 residential properties, 8,011 non-residential properties and 1,341 critical services (hospitals, nursing/care/retirement homes, electricity sub stations, schools, Police, Fire and Ambulance Stations, prisons and sewerage treatment works). This information has been obtained from the EAW National Receptor Database (NRD), a

dataset which contains a number of GIS layers categorised into themes of information.

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2 LLFA Responsibilities

2.1 Introduction

The preparation of a PFRA is just one of several responsibilities of LLFAs under the new legislation. This section provides a brief overview of the responsibilities Cardiff Council are obliged to fulfil under their role as a LLFA.

2.2 LLFA Responsibilities

During the review of the summer 2007 flooding, Sir Michael Pitt stated that “the role of local authorities should be enhanced so that they take on responsibility for leading the coordination of flood risk management in their areas”. As the designated LLFA, Cardiff Council is therefore responsible for leading local flood risk management across Cardiff.

2.3 Stakeholder Engagement

Meetings have been held with representatives attending from Strategic Planning, Emergency Management and Drainage Management departments within Cardiff Council along with WAG, DCWW and IDB. The importance of working together is reflected in Regulation 35 of the Regulations and Section 13 of the Flood and Water Management Act. Table 2-1 lists the key stakeholders that were contacted during the preparation of the PFRA:

Table 2-1 Key Stakeholders

Stakeholder

1 EAW

2 British Waterways

3 Network Rail

4 Dwr Cymru Welsh Water

5 Caldicot and Wentlooge Levels Internal Drainage Board

6 South Wales Fire Service

7 South Wales Police

8 Tongwynlais Community Council

9 St Mellons Community Council

10 Radyr and Morganstown Community Council

11 Pentyrch Community Council

12 Lisvane Community Council

13 Welsh Assembly Government

2.4 Public Engagement

Local public knowledge is also considered valuable and information has been documented by Cardiff Council and community councils. Public meetings attended by Cardiff Council have been held following local flood events and the Council has provided Hyder Consulting with

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relevant information (such as meeting minutes and plans) for use in the preparation of the PFRA.

2.5 Further Responsibilities

Aside from forming partnerships and coordinating and leading on local flood management, there are a number of other key responsibilities that have arisen for LLFAs from the Flood & Water Management Act and the Flood Risk Regulations. These responsibilities include:

Investigating flood incidents – LLFAs have a duty to investigate and record details of significant flood events within their area. This duty includes identifying which authorities have flood risk management functions and what they have done or intend to do with respect to the incident, notifying risk management authorities where necessary and publishing the results of any investigations carried out.

Asset Register – LLFAs also have a duty to maintain a register of structures or features which are considered to have an effect on flood risk, including details on ownership and condition as a minimum. The register must be available for inspection and the Secretary of State will be able to make regulations about the content of the register and records.

SuDS Approving Body – LLFAs are designated the SuDS Approving Body (SAB) for any new drainage system, and therefore must approve, adopt and maintain any new sustainable drainage systems (SuDS) within their area.

Local Strategy for Flood Risk Management – LLFAs are required to develop, maintain, apply and monitor a local strategy for flood risk management in its area. The local

strategy will build upon information such as national risk assessments and will use consistent risk based approaches across different local authority areas and catchments. This PFRA will be a key resource when developing the Local Flood Risk Management Strategy for Cardiff.

Works powers – LLFAs have powers to undertake works to manage flood risk from surface runoff and groundwater, consistent with the local flood risk management strategy for the area.

Designation powers – LLFAs, as well as district councils and the EA have powers to designate structures and features that affect flooding or coastal erosion in order to safeguard assets that are relied upon for flood or coastal erosion risk management.

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3 Methodology and Data Review

3.1 Overview

The PFRA is based on existing and readily derivable data. Table 3-1 shows the key stages of the PFRA process.

Table 3-1 Timeline for PFRA Completion

Activity Indicative Completion Date

1 Set up governance & develop partnerships February 2011

2 Determine appropriate data systems February 2011

3 Collate information on past & future floods and their consequences

March - April 2011

4 Determine locally agreed surface water information April 2011

5 Complete preliminary assessment report document May 2011

6 Record information on past & future floods with significant consequences in spreadsheet

May 2011

7 Illustrate information on past and future floods May 2011

8 Review indicative Flood Risk Areas May 2011

9 Identify Flood Risk Areas May 2011

10 Record information including rationale May 2011

3.2 Data Collection Process

The key stakeholders listed in Table 2-1 were consulted to obtain any relevant data that they hold.

Figure 3-1 shows a sample of the pro forma spreadsheet that was issued to the Community Councils, Network Rail, Fire Service and the Police to assist in the collection of historic data.

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Figure 3-1 Data Collection Pro forma

3.3 Data Collected

A brief summary of the historic flooding data received from the various organisations is shown in Table 3-2. Any gaps in this data have also been summarised in this table. The data sets were compared with each other and where several organisations had recorded the same event duplications were removed to ensure that double counting did not occur.

Table 3-2 Summary of Historic Data Received

Organisation Summary of Data Provided Type of flooding Gaps in data

DCWW 814 records of internal and external

sewer flooding in Cardiff.

Sewer flooding as a result of hydraulic overload of the system. This includes 466 internal (DG5) flooding records and 348 external flooding records.

Flooding details limited to just “internal” or “external” flooding. No information on flood duration.

Cardiff Council 26 flooding records for properties

affected in Rhiwbina in June 2009.

Fluvial from an ordinary watercourse.

Limited information on flood extent and total number of properties affected.

Historical flooding record for Whitchurch Brook (between 1990 and 2009) .10 known events.

Fluvial from an ordinary watercourse.

Flooding record is relatively recent. No detailed information on the duration, extent and number of properties affected.

145 historical flooding locations/events. Surface water and fluvial from an ordinary watercourse.

No information on duration, cause and number of properties affected. Relatively recent and frequent events.

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WAG 26 flooding records for historic sewer

flooding. 604 properties and 3 schools affected.

Sewer. No information on duration or date

of event. No details of cause.

13 flooding records for historic surface water flooding. 267 properties affected.

Surface Water No information on duration or date

of event. No details of cause.

Fire Service 107 records. Records have been

screened and, where needed, removed due to some records relating to domestic burst pipes etc. Significant events appear to have occurred on 1 September 2008 and 6 June 2009.

Groundwater, surface water, fluvial and sewer.

Limited record only going back to August 2005. No information has been provided on the duration or details of number of people affected.

Police Service No data received.

Network Rail No data received.

British Waterways No data received.

IDB No historical flooding records within the

Council boundary. Tongwynlais

Community Council

3 commercial properties flooded. Fluvial from an ordinary

watercourse.

Limited number of events and events recorded are relatively recent. Mainly minor road and nuisance flooding. Limited information on the dates of the events.

St Mellons

Community Council

5 locations of regular flooding identified. Surface water.

Radyr and Morganstown Community Council

4 locations of regular flooding identified. 2 properties flooded.

Surface water and fluvial from an ordinary watercourse. Pentyrch Community

Council

1 property flooded. Surface water.

Lisvane Community Council

3 locations of regular flooding identified. Surface water, sewerage and fluvial from an ordinary watercourse.

Along with the historic data detailed in Table 3-2 additional information, as outlined in Table 3-3, was provided by Cardiff Council and EAW.

Table 3-3 Additional Data from Stakeholders

Information Source

1 Cardiff Strategic Flood Consequences

Assessment (SFCA) Cardiff Council

2 National Receptor Dataset EAW

3 Indicative Flood Risk Areas EAW

4 Areas Susceptible to Surface Water

Flooding (AStSWF) EAW

5 Flood Map for Surface Water (FMfSW) EAW

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7 Areas Susceptible to Groundwater Flooding EAW

8 Cluster Boundaries EAW

9 Flood Zone 3 Map EAW

10 Taff and Ely Catchment Flood Management

Plan (CFMP) EAW

11 Eastern Valleys CFMP EAW

12 Severn Estuary Flood Risk Management

Strategy EAW

3.4 Data Limitations

The PFRA is limited to a certain extent by the quality of the data that has been received. In general the historical flooding information is only for relatively recent events and there is significant variation in the quality, accuracy and detail of the data from the different organisations. Some key gaps in the data sets have been highlighted in Table 3-2. A large proportion of the data was not available in a geo-referenced format, this data was subsequently geo-referenced relying on location descriptions and postcodes to try and accurately allocate the National Grid Reference.

Cardiff Council do not currently have a formal database for documenting flood records. It is understood that records from some past events may have been lost or destroyed and held with individuals rather than in formal datasets.

In the future it is proposed to develop a GIS system which will record all flooding and drainage geo-referenced data collected as part of the PFRA. This GIS system will enable the LLFA to access and interrogate existing information on past and future floods as well as create new flooding records.

3.5 Licensing and Restrictions

The use of some of the data provided by EAW and DCWW is restricted to Cardiff Council in the preparation of the PFRA.

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4 Past Flood Risk

4.1 Overview

The flood information received from the various stakeholders, detailed in Table 3-2, resulted in over 1000 historic flood records within the study area. The data was reviewed and a master spreadsheet of the appropriate information was compiled. This master data set was then loaded into GIS software to enable the historic flood event data to be viewed in its graphical location along with the National Receptor Database. Analysing the information in its GIS format enabled a logical assessment of the overall flood risk.

This section summarises the findings of the review of the historical flooding records in order to extract relevant information on past events with significant harmful consequences.

4.2 Description of Past Historical Floods

4.2.1 General

A summary map showing the locations of known historical flooding is provided in Figure 4-1 and Table 4-1 provides an overview of the historical flooding records by receptor type.

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Table 4-1 Summary of Historical Flooding Records

Receptor Type Number of recorded events

Residential Properties 341

Critical Services (schools) 9

Non- Residential Properties 156

Open areas (gardens, parks, roads etc) 583

4.2.2 Surface Water Flooding

Surface water flooding can occur when heavy rainfall overwhelms the drainage capacity of local areas. The historic records show that localised surface water flooding is widely distributed throughout Cardiff, which is consistent with the general topography of the area.

4.2.3 Ordinary Watercourses

Flooding from ordinary watercourses occurs when a channel cannot cope with the water draining into it from the surrounding land. This can happen, for example, when heavy rain falls on an already waterlogged catchment.

A key historic flooding event occurred in June 2009 when 29 residential properties, 5 non-residential properties and 1 critical service (school) were inundated across Cardiff. In addition to the reported property flooding there were 71 records of flooding of open areas. In this event the flooding was predominantly in the area of the Whitchurch Brook located in the northern area of the city. The flooding that occurred in this event was shown to be caused by the flow capacity of this ordinary watercourse being exceeded as a result of a rainfall event with an annual probability of between 3.33% and 5%.

4.2.4 Groundwater Flooding

Groundwater flooding occurs when water levels in the ground rise above surface levels. It is most likely to occur in areas underlain by permeable rocks, called aquifers. These can be extensive, regional aquifers, such as chalk or sandstone, or may be more local sand or river gravels in valley bottoms underlain by less permeable rocks. There is no information on historic groundwater flooding which suggests that the risk of groundwater flooding is low in Cardiff.

4.2.5 Sewer Flooding

Sewers can become overwhelmed by heavy rainfall which can cause flooding. The likelihood of flooding depends on the capacity of the local sewerage system. Land and property can be flooded with water contaminated with raw sewage as a result. Rivers can also become polluted by sewer overflows.

A key sewer flooding event occurred in July 2001 with 230 residential properties, 129

non-residential properties and 3 critical services (schools) inundated across Cardiff. The records for this event were received from DCWW’s DG5 register but, due to lack of information dating back to 2001, no other details, apart from summary information in the Cardiff Strategic Flood Consequences Assessment (SFCA) (Atkins, 2009), were available for this event. In addition to the reported property flooding there were 177 records of flooding of open areas. The flooding

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that occurred in this event was shown to be caused by hydraulic overload of the sewers as a result of a 1.67% annual probability rainfall event which exceeded the design capacity of the sewers (generally designed to a 3.33% annual probability standard).

Once a property has been identified on DCWW’s DG5 register, it typically means that the water company can put funding in place to take it off the DG5 register and, as such, a recurrence of a similar flood event is unlikely.

4.3 Significant Harmful Consequences

National guidance issued by WAG sets thresholds for defining Flood Risk Areas where the risk of flooding is deemed to be significant. No guidance has been issued for defining locally significant harmful consequences as it is up to each LLFA to set its own definition.

As agreed with Cardiff Council in this PFRA significant harmful consequences have been defined as the consequences of a flood event which local resources were insufficient to manage and which made national headline news and could occur again.

For the localised surface water flooding and both the July 2001 and June 2009 flood events, Cardiff Council has confirmed that local resources were able to cope with the flooding

experienced. Therefore, in line with the definition above, the PFRA has confirmed that there are no known past floods which are considered to have had significant harmful consequences. Therefore, no events with significant harmful consequences have been recorded in Annex 1.

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5 Future Flood Risk

This section summarises all relevant information on future floods. Table 5-1 outlines the relevant information on future flooding that has been reviewed as part of the PFRA.

Table 5-1 Summary of Information on future floods that has been reviewed

No Information Source Use in Study

1 Flood Map for

Surface Water (FMfSW)

EAW Assess future flood risk associated with surface water

flooding

2 Flood Zone 3 Map

(excluding main river extents)

EAW Assess future flood risk associated with flooding from

ordinary watercourses

3 Areas Susceptible to

Groundwater Flooding

EAW Assess future flood risk associated with groundwater

flooding

4 Cardiff Strategic

Flood Consequences Assessment (SFCA)

LLFA In the SFCA simplistic assessments have been

undertaken to assess the flood risk from surface water and from ordinary watercourses. These assessments are mainly related to future developments. The Flood Map for Surface Water is considered to be more accurate for defining the future flood risk associated with surface water flooding and therefore the SFRA predictions on future flooding have only been used to provide background information.

5 Extracts of the

Whitchurch Brook Project Appraisal Report (PAR)

LLFA Only summary extracts of the findings of the PAR

have been obtained. No detailed information to quantify the future flood risk associated with the Whitchurch Brook has been provided.

5.1 Locally Agreed Surface Water Information

No strategic studies have been undertaken to specifically assess the flood risk from surface water in Cardiff. In the Cardiff SFCA (Atkins, 2009) reference has been made to known past surface water flooding locations, however no surface water flood maps have been produced. EAW has produced a national assessment of surface water flood risk in the form of two national mapping datasets. The first generation national mapping, Areas Susceptible to Surface Water Flooding (AStSWF) contains three susceptibility thresholds for a rainfall event that has a 0.5% annual probability of occurrence. The national methodology has since been updated to produce the Flood Map for Surface Water (FMfSW), a revised model with two flood events (3.33% and 0.5% annual probabilities) and two depth thresholds (greater than 0.1m and greater than 0.3m deep). The 0.5% event and 0.3m deep threshold has been used by the EA to produce indicative Flood Risk Areas and adopted by the LLFA to identify properties and critical services at future risk of surface water flooding.

As no local information has been produced the FMfSW national dataset forms the locally agreed surface water information. The AStSWF dataset was not adopted as it was viewed to be less

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accurate, as the estimates of surface water flows did not consider infiltration and the effects of sewers. In addition the FMfSW dataset takes into account buildings which were not represented in the AStSWF dataset. The locally agreed surface water information is shown in Figure 5-1 and illustrates areas that are predicted to flood to a depth greater than 300mm associated with a 0.5% annual probability rainfall event.

Figure 5-1 Locally agreed surface water information (FMfSW)

5.2 Ordinary Watercourses

There are four key ordinary watercourses in Cardiff: the Whitchurch Brook, Fairwater Stream, Roath Brook and Nant Glandulas. Although designated as ordinary watercourses the EAW Flood Map covers these watercourses from the point at which their catchment areas exceed 3km². As these four watercourses are an important source of flooding in Cardiff the main river sections from the flood map have been removed in order to derive information about flooding from ordinary watercourses (see Section 5.6).

A number of other ordinary watercourses are present in the area, many of which are partly culverted under the densely developed areas of the city. The Dock Feeder runs from an offtake from the River Taff at Blackweir to Bute Dock though sections of open canalised channels and culverts. It is understood that no flood studies have been undertaken for this watercourse. The Wentlooge Levels within the Cardiff Council boundary extends from the Rhymney River in the west to St Mellons Business Park in the East. The Wentlooge Levels comprise an area of reclaimed land. As part of the reclamation and subsequent management, an extensive system of ditches (reens) exists to drain the low lying land. A high level study was undertaken as part of the Cardiff SFCA (Atkins, 2009) to indicatively assess the risk of flooding from the reen system. This assessment only predicted significant flooding of low lying areas outside the Cardiff Council boundary. Therefore, in addition to the active management and regular maintenance of the reen system by the IDB, it is considered that there is no significant risk of flooding from the reens within the Cardiff Council boundary.

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5.3 Groundwater

It is understood through consultations with key stakeholders that there is no local information on future groundwater flooding for Cardiff. The risk of groundwater flooding is considered to be low, and this is confirmed by the Taff and Ely CFMP (EAW, 2009) which states that groundwater flooding is not considered to be a significant issue within the catchment.

The EAW map showing Areas Susceptible to Groundwater Flooding has been used in conjunction with the future Surface Water Flood Map (as this identifies potential areas of ponding due to topographical depressions) to assess the consequences of future groundwater flooding. The results of these are outlined in Section 5.6.

5.4 Other Sources of Flooding

No local information on other sources of future flooding has been obtained for the Cardiff area.

5.5 Local Drainage Capacity

Cardiff has both separate and combined foul and surface drainage systems. No specific information has been obtained on the capacity of highway drainage within the Cardiff area. In addition, although DCWW historical flood records are given a risk category based on a prescribed methodology (a combination of frequency of flooding and storm return periods), no specific information has been obtained on the capacity of sewer systems within the Cardiff area In line with national design standards and information on past floods in Cardiff, the capacity (surcharged conditions) of highway drainage networks and sewers is likely to be exceeded in rainfall events with an annual probability in the order of 3.33%.

5.6 Consequences of Future Floods

Detailed records of future floods and their possible consequences are provided in Annex 2.

5.6.1 Human Health

Table 5-2 summarises the consequences of flooding on human health using the indicators of the number of people and critical services affected.

Table 5-2 Summary of the consequences of flooding on human health

Criteria Surface Runoff Ordinary

Watercourses Groundwater Number of People 4,287 2,665 796 Number of Critical Services 20 5 1

The number of people at risk of flooding has been calculated by multiplying the number of properties at risk by 2.34. There are different methods for calculating the number of properties and in this study the address point data rather than the Flood Map for Surface Water Property

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Count Method has been used. In the early stages of the project the use of the Flood Map for Surface Water Property Count Method was not feasible due to the combination of the large amount of reformatting of the OS building layer and the study deadline. It is likely that the use of the address point data will slightly under predict the number of people and critical services affected. However, given the high level screening nature of the PFRA and the high level of uncertainty associated with the flood data sets the use of the address point data is considered to be acceptable.

5.6.2 Economic Activity

Table 5-3 summarises the consequences of flooding on economic activity in Cardiff. The predicted consequences of flooding of road infrastructure, although included in Table 5-3, is not considered to be adverse as alternative routes are available due to the dense road network throughout Cardiff. In addition the surface water flood maps are believed to over predict the flood risk to this infrastructure.

Table 5-3 Summary of the consequences of flooding on economic activity

Watercourses

Groundwater

Number of

non-residential properties 35 60 16

Infrastructure network (e.g. length of roads and rail flooded) M4 - 0.9km A48 – 1.3km A4232 – 0.2km A470 – 0.5km No adverse consequences identified No adverse consequences identified

5.6.3 Environment

Table 5-4 summarises the consequences of flooding on the environment in Cardiff. The information has been obtained by interrogating NRD data against the associated flood extent. The consequences of the predicted flooding of environmental assets is not considered to be adverse.

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Table 5-4 Summary of the consequences of flooding on environmental criteria

Watercourses Groundwater Pollution Prevention and Control (PPC) sites 0 0 0 Control of Major Accident Hazard

(COMAH) sites No Data Provided

Special Areas of Conservation (SAC) 2 0 0 Special Protection Areas (SPA) 0 0 0 Ramsar Sites ₀ ₀ ₀ Sites of Special Scientific Interest (SSSI) 7 1 0

World Heritage Sites ₀ ₀ ₀

Scheduled

Monuments 3 0 1

Listed Buildings ₂₇ ₁₇ ₁₁

Registered parks and

gardens 1 0 0

5.7 Climate Change and Long Term Developments

5.7.1 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.

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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%.

5.7.2 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.

5.7.3 Implications for Flood Risk

Climate changes 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.

5.7.4 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.

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5.7.5 Long Term 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 Wales, Technical Advice Note 15 (TAN15) on development and flood risk sets out a

precautionary framework to guide planning decisions. The overarching aim of the precautionary framework is "to direct new development away from those areas which are at high risk of flooding."

Adherence to Government 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).

Consultation with Cardiff Strategic Planning department has confirmed that there are no new or proposed major developments which may increase local flood risk within Cardiff.

5.7.6 Local Information Concerning Climate Change Impacts on

Flood Risk

No local information has been made available regarding climate change impacts on future flood risk.

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6 Review of Indicative Flood Risk Areas

6.1 Overview

To ensure a consistent and proportionate approach DEFRA and WAG have identified significance criteria and thresholds for defining Flood Risk Areas. EAW has applied these criteria and thresholds to produce indicative Flood Risk Areas. These areas are only based on certain nationally available data.

The indicative Flood Risk Areas have been produced as a starting point for LLFAs. They are based on available national datasets and therefore they need to be reviewed using local information as part of the PFRA. Hyder Consulting has, where possible, used the Council’s own data sets such as GIS layers to check the national data. This combined with the past and future flooding information collected as part of this PFRA, has enabled the review of the EAW

indicative Flood Risk Areas for Cardiff.

6.2 EAW Identified Blue Squares

To ensure a consistent and proportionate approach EAW have identified 1 km squares above the flood risk threshold (informally referred to as “blue squares”), using the Flood Map for Surface Water. The 1 km blue squares identify areas where more than 200 people, or more than one critical service or more than 20 non-residential properties are predicted to be flooded to a depth greater than 0.3m under the 0.5% annual probability surface water event. Table 6-1 provides an overview of 37 identified 1km blue square areas in Cardiff. An additional 2 blue squares are located within the EAW indicative Flood Risk Area but these have been excluded from Table 6-1 as they fall outside the Cardiff administrative boundary. Figure 6-1 shows the location of the blue squares.

Table 6-1 Summary of flood risk in blue squares

Criteria Predictions

Number of People 10,115

Number of Critical Services 29

Number of non-residential properties 776

The EAW blue square flood risk predictions outlined in Table 6-1 are greater than the consequences of future floods for the whole of Cardiff in this PFRA, which have been summarised in Section 5.6. This variation is a result of the different property count methods used. Information on the different property count methods is provided in 5.6.1.

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Figure 6-1 1km squares where the flood risk has been assessed to be above the threshold.

6.3 Review of Blue Squares

The locally agreed surface water information (Flood Map for Surface Water (FMfSW)) and Flood Zone 3 Map, for which the main river extents have been excluded, have been used to review the flood risk across Cardiff. GIS queries have been run to confirm and identify any potential new 1km squares that are above the flood risk threshold. Figure 6-2 shows the 1km squares for which the GIS queries have been run and the three additional 1km squares that are above the flood risk threshold. Details for the three additional blue squares are provided in Table 6-2. In Section 4.3 it has been confirmed that there are no known past floods which are considered to have had significant harmful consequences. Therefore, the review of the information on past flooding has not resulted in a need to modify the indicative Flood Risk Area.

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Figure 6-2 Proposed additional 1km squares that are above the flood risk threshold

Table 6-2 Details for the three additional 1km squares

GRIDSQ Reason for inclusion

X315Y178 As outlined in Section 5.2 the EAW Flood Map covers the Whitchurch Brook as its

catchment is greater than 3km². In this 1km square 830 people have been estimated to be located within the flood extent associated with the Whitchurch Brook.

X316Y178 As above, in this 1km square 590 people have been estimated to be located within the

flood extent associated with the Whitchurch Brook.

X320Y179 Two critical services (Gas regulating infrastructure and an electricity sub-station) were found to be located within the Surface Water Flood Map extent.

The resulting combined 1km squares that are above the flood risk threshold are shown in Figure 6-3 along with the indicative Flood Risk Area. The Figures shows that the inclusion of the additional three 1km squares will not result in a change to the indicative Flood Risk Area identified by EAW.

X315Y178

X316Y178 X320Y179

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Figure 6-3 Proposed 1km squares that are above the flood risk threshold

6.4 Consultations with adjacent LLFAs

Consultations with key adjacent LLFAs, such as the Vale of Glamorgan and Rhonda Cynon Taff Councils, are ongoing in order to share information and understand the findings of their reviews of the EAW indicative Flood Risk Areas. This will ensure consistency across LLFA PFRAs (see also Section 7). New 1km square X315Y178 New 1km square X316Y178 New 1km square X320Y179

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7 Identification of Flood Risk Areas

As shown in Figure 7-1 the indicative Flood Risk Area crosses the Cardiff administrative boundary in two locations, one to the north and one to the west of Cardiff.

Figure 7-1 EAW indicative Flood Risk Area

The identified indicative Flood Risk Area, which predominantly covers the Rhonda Cynon Taff administrative area, slightly extends into the northern area of Cardiff. Figure 7-2 shows that the extension of the identified indicative Flood Risk Area for Rhonda Cynon Taff is caused by the touching blue squares (greater than four) identified by EAW which are located immediately north of the Cardiff boundary. In this area it is proposed to amend the indicative Flood Risk Area to follow the Cardiff administrative boundary.

Rhonda Cynon Taff indicative Flood Risk Area extends slightly into the Cardiff administrative area

Cardiff indicative Flood Risk Area extends slightly into the Vale of Glamorgan administrative area

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Figure 7-2 EAW indicative Flood Risk Area with blue squares

On the west side of Cardiff the indicative Flood Risk Area extends beyond the Cardiff administrative boundary into the Vale of Glamorgan administrative area. In this area it is proposed to amend the indicative Flood Risk Area to follow the Cardiff administrative boundary. Consultations with the Vale of Glamorgan and Rhonda Cynon Taff Councils are ongoing in order to gain formal agreement to these changes and agree consistency across LLFA PFRAs. The proposed changes will result in the removal of the Flood Risk Area from the within the Vale of Glamorgan administrative area.

The proposed updated Flood Risk Area for Cardiff is shown in Figure 7-3. Rhonda Cynon Taff

indicative Flood Risk Area extends slightly into the Cardiff administrative area as a result of the blue squares located to the north.

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Figure 7-3 Proposed Flood Risk Area

A review of the local information on past and future flooding has shown that there is no justification for making further amendments to the indicative flood risk area identified by EAW. Detailed records of the Flood Risk Area are provided in the spreadsheet in Annex 3.

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8 Next Steps

It is important to ensure that information is maintained and kept up to date for future use and to support other flood risk assessments. This is key in supporting future local flood risk

management strategies which LLFAs are required to develop and implement under the Flood and Water Management Act 2010.

A GIS system has been proposed which will record all flooding and drainage geo-referenced data collected as part of the PFRA. This GIS system will enable the LLFA to access existing information on past and future floods as well as create new flooding records. This will support the review of the PFRA every six years.

The GIS system will collect information on past flooding which was optional for this first flood risk management planning cycle. The information that will be required on past flooding includes the identification of:

Flood Date

Flood Duration

Flood Probability

Main source of flooding

Main mechanism of flooding

Main characteristic of flooding

As a Flood Risk Area has been identified for Cardiff there is a requirement in line with the Regulations to produce flood hazard and risk maps as well as to develop a flood risk management plan for the area.

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9 References

Atkins (2009) Cardiff Strategic Flood Consequences Assessment

DEFRA/WAG (2010) Selecting and reviewing Flood Risk Areas for local sources of flooding – Guidance to LLFA

Edenvale Young Associates (2010) Whitchurch Brook Project Appraisal Report

Environment Agency Wales (2009) Eastern Valleys Catchment Flood Management Plan Environment Agency Wales (2009) Taff and Ely Catchment Flood Management Plan Environment Agency Wales (2010) Preliminary Flood Risk Assessment Final Guidance Environment Agency Wales (2011) Severn Estuary Flood Risk Management Strategy The Pitt Review (2008) Learning Lessons from the 2007 floods

Welsh Assembly Government (2004) Technical Advice Note (TAN) 15: Development and Flood Risk

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Annex 1

Records of past floods and their significant

consequences

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Annex 2

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Annex 3

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Annex 4

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Annex 5

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Appendix 2 The table lists the key stakeholders that were contacted during the

preparation of the PFRA:

Key Stakeholders

Stakeholder 1 EAW

2 British Waterways

3 Network Rail

4 Dwr Cymru Welsh Water

5 Caldicot and Wentlooge Levels Internal Drainage Board 6 South Wales Fire Service

7 South Wales Police

8 Tongwynlais Community Council 9 St Mellons Community Council

10 Radyr and Morganstown Community Council

11 Pentyrch Community Council

12 Lisvane Community Council 13 Welsh Assembly Government