STRATEGIC FLOOD RISK ASSESSMENT Stage 1

Regeneration and Environment Department December 2008

STRATEGIC FLOOD RISK ASSESSMENT: LEVEL 1

TABLE OF CONTENTS

1 Introduction 3 2 The Study Area 4 Demography Topography Ground water vulnerability 3 An Overview Of The Sequential Flood Risk Test 5 The exception test 4 Data Collection 9 5 An Overview Of Flooding Sources 15 Watercourse Flooding Sewer Flooding Groundwater Flooding Overland Flow Infrastructure Failure The Effects of Climate Change 6 Adaptation to Climate Change and Managing Surface Water 18 Flood Risk Assessments Site Drainage Further Design Mitigation Measures 7 The Next Steps 20

Appendices 1 Flood Risk Vulnerability Classification 2 Flood Zone Definitions 3 Historic Flood Events in with 4 Rivers Blakewater and Darwen Defences – Assets in Poor Condition (graded 4) 5 Flood Risk Assessments (FRAs) 6 Flood Zones Maps (Extracts) Map 6/1Blackburn Map 6/2 Darwen Map 6/3 Moulden Bridge, Fensicowles Map 6/4 , Feniscliffe Map 6/5 Waterfall Map 6/6 Darwen Valley Parkway Map 6/7 Earcroft Map 6/8 Duckworth Street Darwen Map 6/9 Road Darwen Map 6/10 Springvale Darwen Map 6/11 Eccleshill Map 6/12 Map 6/13 Central West Blackburn Map 6/14 Blackburn Central Map 6/15 Bastwell Map 6/16 Map 6/17 Stanworth Woods 7 Glossary 8 Useful Websites

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Figures Figure 1: Application of the Sequential Test 7 Figure 2: Flood Zones 2 and 3 in Borough 10 Figure 3: Suds Techniques 18 Figure 4: Composite Strategic Flood Risk Assessment Plan 22

Tables Table 1: Flood Risk Vulnerability and Flood Zone Compatibility 8 Table 2: Watercourse in Blackburn with Darwen Borough 15

Pictures Picture 1: Flooding of Blackburn Road, Darwen 13 Picture 2: Damage caused by flooding 13

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1 INTRODUCTION

1.1 The Planning System The Planning and Compulsory Purchase Act 2004 and accompanying regulations requires regional planning bodies and local planning authorities to produce spatial plans, Regional Spatial Strategies (RSSs) and Local Development Documents (LDDs). The policies in the RSS and LDDs together form the statutory development plan against which planning applications will be assessed. Statutory development plans should reflect the Government’s policies for sustainable development. These include Planning Policy Statement 25, Development and Flood Risk, published in December 2006. It requires local planning authorities in the preparation of Local Development Documents to appraise flood risk in strategic flood risk assessments, which will then provide the background to the selection of sites for allocation and avoid placing new development in areas at risk of flooding. The Department for Communities and Local Government in February 2007 published a Practice Guide Companion to PPS25, Development and Flood Risk in the form of a consultation paper.

1.2 The objective, scope and intended users of the SFRA

1.2.1 The purpose of the SFRA is to highlight areas that may flood, taking into account known sources of flooding and the likely impacts of climate change. This enables the local planning authority to prepare policies for flood risk management of potential areas of flood risk and to make development allocations taking this constraint into account. It is advised that the SFRA should be used to inform the Sustainability Appraisals of LDDs and it will provide the basis from which to apply the Sequential Test and Exception Test which come into play when it is not possible to locate development in a zone with a lower probability of flooding, preferably Zone 1. The objective for the development plan (LDF) process is to allocate land for vulnerable uses in lower flood risk zones (PPS25 Annex D Table D.2 is set out in Appendix 1).

1.2.2 The SFRA will provide an aid to decision-making and forms part of the evidence base for the Local Development Framework on the issue of flooding.

1.2.3 To summarise, the purpose of the SFRA is: • To provide a reference document on possible flooding and flood risk management which will inform the LDF. This enables a risk-based approach to the preparation of development documents. • To ensure that Blackburn with Darwen Borough Council meets its obligations under PPS25 and raises awareness of flooding issues. • To provide information for developers, local communities and Council officers.

1.2.4 The main benefits of the SFRA are: • It identifies high risk areas for flooding, unsuitable for many types of development. • It informs the site allocation process. • It allows early input by the Environment Agency into the development plan process. • It provides constraint information for developers on flood risk.

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2 THE STUDY AREA

2.1 Demography The total population of the Borough is around 141,000 in 51,200 households (2006 mid year estimate). With 10 persons per hectare Blackburn with Darwen is the twentieth most densely populated area out of 43 local authorities in the North West Region. Bastwell ward is the most densely populated with 100 people per hectare. with has the lowest population density with 0.7 persons per hectare. 30% of the population is aged under 19, ranking the authority the second highest in for child population.

2.2 Topography The Borough covers an area of 137 sq. km. The original settlement of Blackburn was located to the north bank of the River Blakewater (from which the settlement took its name), and the town of Darwen is located within the steep narrow sided River Darwen valley; the former river flowing from the east sometimes in tunnel and culvert and the latter from the south to join the to the north west. The two rivers join at . The central parts of the town lie at a height of approximately 100 metres above sea level in the bottom of the ‘river confluence bowl’ with the suburbs encroaching on the framing hills of the Revidge ridge, Royshaw Hill and Whinny Heights. Darwen lies at approximately 220 metres above sea level and occupies the narrow valley between Darwen Moor and Grey Stone Hill, rising up the valley sides and surrounded to the west, east and south by the high .

The southern part of the Borough comes within a second river catchment, the which drains south to the Mersey Basin. The land rises to heights approaching 400 metres on Turton Moor and Causeway Height.

The rural population is largely located to the west, south and east in river valley or reservoir valleys.

2.3 Groundwater Vulnerability Groundwater collects in openings, cavities and spaces in rocks and is derived either from water rising from deep underground or from rainwater seeping down. The Environment Agency checks the quality of groundwater through a number of bore holes.

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3 AN OVERVIEW OF THE SEQUENTIAL FLOOD RISK TEST

3.1 PPS25 requires local planning authorities to prepare and implement planning strategies that help to deliver sustainable development by:

Appraising Risk in a spatial plan by: • Identifying land at risk and the degree of risk of flooding from river and other sources in their areas; and

• Preparing Strategic Flood Risk Assessments (SFRAs) as freestanding assessments that contribute to the sustainability appraisals of their plans.

Managing Risk by: • Devising policies for the location of development which avoid risk to people and property where possible and manage any residual risk;

• Only permitting development in areas of known flood risk when there are no reasonably available sites in areas of lower flood risk and the benefits of the development outweigh risks from flooding;

Reducing Risk by: • Safeguarding land from development which is required for flood management;

• Considerations put into practice in new development: safe locations, layout, design including SUDS, mitigation measures such as green infrastructure for flood storage, re-creating functional flood plain and setting back defences.

3.2 Planning Policy Statement 12 – Local Development Frameworks (ODPM, 2004) requires development plan documents to be evidence based. The SFRA will provide an evidence base on the issue of flooding and will initially inform the Core Strategy Development Plan Document.

3.3 Regional Spatial Strategy for the North West sets one of its objectives for ‘Enjoying and Managing the North West’ to “promote a more integrated approach to delivering a better environment through land and water management, including better relationships of new development to water resources, flood risk and adaptation to the impacts of climate change.

3.4 The relevant policy of the RSS, Policy EM5, on integrated water management and delivery of the EU Water Framework Directive, requires plans to have regard to river basin management plans and the regional flood risk appraisal. Local authorities and developers should aim to protect the quantity and quality of surface and ground waters, and manage flood risk. It is advised that allocations of land should comply with the sequential test in PPS25 and where development must take place in flood risk areas appropriate protection from floods must be designed into schemes and incorporate sustainable drainage systems and water conservation and efficiency measures.

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3.5 In 2004 the NW Regional Assembly supported a project which devised guidelines for carrying out a sequential flood risk test1. The report outlines a step-by-step approach to the SFRT process, highlighting potential data sources, technical issues that may need consideration and gives recommendations for outputs from the various stages.

3.6 The following flow chart outlines the Sequential Test in detail.

1 Meeting the Sequential Flood Risk Test Guidelines for the North West Region ’ , NWRA/JBA, July 2004

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Figure 1: Application of the Sequential Test

Is the site No Is there an alternative No Is the potential (proposed or potential site in Zone l allocation site in Zone allocated) in Zone Low Risk? 2 Medium Probability? l Low Probability? No

Yes Is there an alternative Yes allocation site in Zone2? Yes

No

Is the flood risk at the site likely to be affected by Yes Does the proposed No climate change? allocation lie in Zone 3b Functional Floodplain? Is the alternative allocation site less suitable because Yes of other planning issues? Yes Yes Yes

Is there an alternative Is there an alternative site not sensitive allocation site in Zone 3a to climate change? High Probability? Yes No

Consider original Consider alternative No site site No

Will the proposed development type be acceptable in this Flood Zone?

Yes Possibly No Are there other potential Yes Are parts A) and B) No allocation sites in the same of the Exception Flood Risk Zone? Test satisfied?

Consider site details and flood risk management requirements. Is the development site appropriate and No safe?

Yes No Proposed Development is likely to be Proposed Development is likely to be acceptable in flood risk terms unacceptable and should be refused

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3.6 The Exception Test

3.6.1 This test is applied only after application of the sequential test.

3.6.2 In some areas lacking low flood risk sites, further development may be essential to maintain economic viability and social vitality and the Test allows it. Three conditions must be satisfied: • The development must provide wider sustainability benefits to the community that outweigh flood risk. • The development must be on brownfield, previously developed land or, if not on brownfield land, there are no reasonably alternative sites on developable brownfield land;g • A FRA must show that the development will be safe, without increasing flood risk elsewhere, and, where possible, will reduce flood risk overall.

Table 1: Flood Risk Vulnerability and Flood Zone Compatibility Flood Risk Essential Water Highly More Less Vulnerability Infrastructure Compatible Vulnerable Vulnerable Vulnerable classification Flood Zone 1 yes yes yes yes yes

Flood Zone 2 yes yes Exception yes yes Test required Flood Zone 3a Exception yes Not Exception yes Test compatible Test required required Flood Zone 3b Exception yes Not Not Not ‘Functional Test compatible compatible compatible Floodplain’ required

See Appendix 1 for details of land uses and vulnerability to flood risk.

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4 DATA COLLECTION

General

4.1 Environment Agency

4.1.1 The EA has a supervisory duty for all matters relating to flood defences and is responsible for issuing flood warnings. The Environment Agency is responsible for identifying those areas considered to be at risk of flooding from fluvial and tidal events, and these areas are identified on a Flood Zone map which has been issued to every LPA in the country. The flood zones shown on the maps, Zones 2 and 3, also copied in Appendix 5, correspond to those defined in PPS25 Annex D Table D1. Zone 2 is the area that would be affected in case of a 1 in 1000 year fluvial flood event, ignoring the presence of defences. Zone 3 is the area that could be affected by fluvial flooding in a 1 in 100 year flood event if there were no flood defences. The maps provide an indication of some areas which are defended by existing flood defences, but the Flood Zones do not take into account of the presence of defences or other man-made structures.

4.1.2 Under Section 105 of the Water Resources Act 1991 the EA has a duty to survey matters relating to flooding and flood defences. Section 105 survey information helps to identify the extent of flood plains, washlands and other areas liable to flood.

4.1.3 A major source of information are the catchment flood management plans available on the EA website (www.environment-agency.gov.uk). The southern tip of the Borough falls in the River Irwell catchment and information is contained in the River Irwell Catchment Flood Management Plan. An action plan for this catchment was published in 2000. The River Ribble Catchment Flood Management Plan was published in draft in September 2005 and was available in its final version in June 2007.

4.1.4 There is no river basin management plan developed for the North West at present. It is a requirement of the Water Framework Directive that such a plan should be in place by December 2009. It is expected that a draft management plan will be published by December 2008.

4.1.5 Periodic surveys of the condition of assets and culverts are carried out by the Council and the Environment Agency, which provide sources of information (ref. Appendix 4). Also, non-fluvial sources of flooding may provide information such as sewer surcharges where blockages or capacity constraints may cause sewer capacity to be exceeded, groundwater resources, canal and reservoir surveys.

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Figure 2: Flood Zones 2 and 3 in Blackburn with Darwen Borough M65 M65

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Specific 4.2 River Irwell Catchment Flood Management 4.2.1 The River Irwell Catchment Flood Management Plan sets out flooding issues in the Croal/Irwell catchment. The upper reaches in the West Pennine Moors such as Turton Moor, Turton Heights, Longworth Moor and Winter Hill Flats rise to heights of 350 to 400 metres and water levels of brooks and streams may rise quickly in response to sudden rainfall events, creating a surge of water running rapidly downstream. Where storm events take place in developed areas surcharges of drainage systems such as sewers, surface water and highway drains may occur. Sewer flooding brings an increased health risk.

4.2.2 Higher animal stocking rates on the uplands contributes to run-off problems by leading to greater compaction of the soil which increases the speed of run-off from land. Measures to decrease the risk of flooding include changes to agricultural drainage to reduce flood peaks from areas of low permeability soils, harnessing economic incentives to reduce agricultural intensity, the creation of wetland ponds and afforestation. A report from Defra, a Strategy for England’s Trees, Woods and Forests, 2007, claims that woodland has a significant role in flood management because it creates a stronger barrier to water than other vegetation.

4.2.3 Mill buildings from the Industrial Revolution were often constructed adjacent to watercourses, the channels being modified by narrowing of channels and culvert construction. Channels walls, flood walls and culverts present risks because of their age and restrictions on volume of flows. Also old structures may develop cracks and faults which add to the risks of structural collapse. There are a number of culverts in the Croal northern catchment within the Borough which have no condition grade. (Catchment Flood Management Plan Pilot Study 2005 Figure 2A)

4.3 Croal/Irwell River Catchment Action Plan 4.3.1 An Action Plan for the Croal/Irwell catchments was produced by the Environment Agency in 2000. This plan was intended to set out actions over the next five years. One of the actions concerned (1824). A survey of Belmont Reservoir has established that the exact capacity of the reservoir is 2,142,000 cubic metres, with available water 1,928,000 cu. m. 10% of capacity is estimated to be ‘dead water’. The Environment Agency has started a study to establish the reliable yield of the reservoir. This is needed because of the need to balance competing demands downstream such as industrial abstractions, ecological needs and recreational use of the reservoir. The Turton and Entwistle Reservoir and the have considerable value as recreational resources. The smaller privately owned Wards Reservoir at Belmont is valued as a nature reserve and recreational resource. There are ongoing discussions about the future role of the reservoir as there are concerns about the condition of structures associated with the reservoir. A project plan is being devised which will improve habitats around the reservoir and develop new ones in line with the Biodiversity Action Plan.

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4.4 Integrated Catchment Flood Management Plan for the River Ribble 4.4.1 The Integrated Catchment Flood Management Plan for the River Ribble was published in June 2007. It sees as a main source of flooding localised surcharges of subsurface drainage systems and blockages of structures such as culverts, outfalls and bridges. Channels are heavily modified in the Darwen catchment. Sudden flooding events arise more frequently in an area in close proximity to high moorlands. Locally intense, short duration rainfall may affect the tributaries of the River Darwen, which has a steep catchment with narrow, clough, incised valleys. Water would rise rapidly in these headwaters and spill down into the major rivers. 78% of rainfall in the Darwen catchment is on average converted to surface runoff.

4.5 Canal Flooding 4.5.1 Flooding from canals has led to localised flooding incidents where raised sections of the Leeds and Liverpool Canal have been breached particularly in the course of the development of sites in close proximity to the Canal and where there have been culvert failures beneath the canal.

4.5.2 An incident occurred in the mid 1960s at Gorse Street, Blackburn when a sewer was being installed beneath the bed of the Canal. A leak developed through the bed of the Canal into the tunnel below which is reputed to have been stemmed by plugging the hole with cotton bales from a nearby mill having first cut the bindings. Subsequent standard conditions on the precautions to be taken when carrying out Canal crossings will have greatly reduced the likelihood of a similar event.

4.7 River Flooding 4.7.1 The Plan names key problem flood risk areas all of which are caused by culvert blockages restricting capacity: the River Darwen in Darwen where 550 properties are at risk of flooding (Zone 3) with a one percent chance of occurrence in any one year.

4.7.2 A further 2,519 properties are located in Flood Zone 2 and may be at risk of flooding in a serious flood. The flood warning area runs along Duckworth Street/Blackburn Road from the Ambulance Station on George Street to the Weir at Clarence Street. This area flooded in summer 2004.

4.7.3 The River Darwen through the Waterfall area of Blackburn is the subject of a flood warning plan; 117 properties are potentially affected and include those on Cartwell Road, Grange Road, Stancliffe Street, Hollin Bridge Street and Albert Street. This area flooded on 14 June 2002 after a storm.

4.7.4 The River Blakewater at The Wrangling is the subject of a flood warning plan. 114 properties in the area can potentially be affected by river flooding; previous flood events in the Wrangling include in 1936, 1964, 1989 and 2002 (Appendix 3). The streets affected include Harrison Street, Whalley Banks, Brunswick Street, Thomas Street, Canterbury Street, George Street West and Stoneyhurst Road.

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4.8 Sewer & Surface Water Flooding 4.8.1 There is a risk of flooding from sewers and surface waters, and also from restricted culverts when flow restrictions occur through fly tipping and litter dumping.

Picture 1: Flooding of Blackburn Road Darwen

Excess overland flow after a sudden summer storm in June 1980 when 67 mm of rain fell in one hour. The view is south from Hollins Grove towards Darwen Town Centre.

Picture 2: Damage caused by flooding

Excess overland flow from a watercourse in caused damage to property in a May 1989 flood.

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4.9 Some information is given in the Plan about the condition of flood defences. In Darwen there are localised areas of defences in poor condition.

Maria and Portland Streets experienced some flooding in September 2004 when an earth bund retaining mill lodges was overtopped. One short section of defences along the River Blakewater is in poor condition (Appendix 4).

4.10 It is a stated objective of the Environment Agency in the River Ribble Catchment Flood Management Plan to achieve a reduction in the proportion of properties in the floodplain exposed to a high risk of flooding.

4.11 Concerns are expressed in the Plan about low fish populations along many sections of the rivers due to the artificial nature of the channels which results in few suitable habitats for fish.

4.12 The heavily modified channels discourage the development of wetland habitats. Invasive weeds such as Japanese knotweed and Himalayan balsam have a presence in the river corridors nevertheless though attempts have been made to manage these undesirable plants.

4.13 The Council’s Emergency Planning Unit is one of the stakeholders in communicating flood warnings from the Environment Agency particularly in the three flood warning areas: Waterfall, The Wrangling and in Darwen.

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5 AN OVERVIEW OF FLOODING SOURCES

5.1 Watercourse Flooding 5.1.1 This happens when, for a variety of reasons, not all of the waterflow stays in its normal channel. The Borough is at the head of a watercourse system which includes Main Rivers , the Darwen and the Blakewater. Under Land Drainage legislation the ditches and streams which collect and convey water off the West Pennine hills surrounding the major valleys are classified as Ordinary Watercourses. The larger watercourses into which the streams flow are classified as Main Rivers. The Council has controls over Ordinary Watercourses, whilst the Environment Agency has controls over both Main Rivers and Ordinary Watercourses. The short streams feeding the three Main Rivers run at gradients rarely less than 1 in 350 in narrow valleys which has implications during periods of heavy rainfall. Historical drainage of peat moorland through the installation of small drainage channels, grips, together with heavy livestock trampling has encouraged erosion and the delivery of sediment to watercourses.

5.1.2 Flooding may occur when, after periods of heavy rainfall, water flow cannot be accommodated within culverted or heavily modified channels due to restrictions, partial blockages or inadequately sized culverts. Debris may collect at culvert entrances and cause blockages. Water can accumulate behind culvert entrances to significant depths and run overland until it can re-enter the watercourse network of find its way into other drainage facilities such as sewers.

Table 2: Watercourses in Blackburn with Darwen Borough Watercourse Status Responsibility (Some with raised defences, which may cause problems) River Darwen Main River Environment Agency River Blakewater " " " " River Irwell tributaries (incl. " " " " Longworth Clough) Arley Brook and tributary MR/Critical Ordinary BwD BC Watercourse (COW) Little Harwood Brook COW " Knuzden Brook " " " " Ewood Mill Race 1 and 2 " " " " Scotshaw Brook " " " " Bradshaw Brook Main River Environment Agency

5.2 Sewer Flooding 5.2.1 Sewer flooding occurs when the level of effluent flowing through a sewer pipe builds up through blockages to a height that causes some effluent to flow backwards out of points of access to the sewer. Properties with cellars are often susceptible to the backing up of sewage from the sewer network. Sewer flooding is caused by an obstruction in the sewer or by insufficient capacity due to the sewer not being of sufficient size.

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5.3 Groundwater Flooding 5.3.1 Groundwater is water held in aquifers or permeable underground strata. Flooding from groundwater sources involves water discharging from an aquifer to create a nuisance. The only recorded incident in this category in the Borough followed the filling up of coal workings to allow development nearby after which water was a problem at downhill properties. This happened in the course of residential development in the Pole Lane and Marsh House Lane, Darwen area. There is a possibility of this being repeated in areas of worked out coal measures.

5.4 Overland Flow 5.4.1 Overland flow is run-off that has not entered a watercourse of other drainage system but is significantly concentrated to be of concern to properties. This may happen in severe storm conditions.

5.5 Infrastructure Failure i) Canal The Leeds and Liverpool Canal passes for 7 miles through the Borough. It contains a considerable volume of water and therefore has the potential to cause severe flooding if an embankment were to fail through structural weakness. The Canal has at least two watercourses and other smaller discharges feeding into it. It will intercept overland flow and other flood water; Excess water in it is spilt from three overflows: one at Whitebirk discharges into Knuzden Brook, one at Mill hill into an unnamed watercourse that outfalls into the River Darwen and another at that discharges into an unnamed tributary of the River Darwen.

Also, problems may occur when work is taking place on culverted watercourses and sewers or other structures crossing beneath the canal.

The Leeds and Liverpool Canal Study and Strategy (2004) in its Action Plan mentions that bank stabililisation is required in various stretches: in various sections between bridges 90 (Ollerton No. 2 Bridge, Ollerton Fold) and 93B (Feniscowles Bridge, A6062) and between bridges 104B (Whitebirk Bridge) and 104C (Whitebirk Drive, A6119).

5.6 Infrastructure Failure ii) Reservoir A possible source of flooding is from reservoirs. These structures are designed to store water. Many were constructed in Victorian times. The failure of a reservoir has the potential to cause serious damage to nearby properties if structural failure takes place. Since 2004 the Environment Agency has regulated large reservoirs (containing over 25.000 cubic metres of water) which are covered by the 1975 Reservoirs Act. The Health and Safety Executive regulates reservoirs below 25,000 cubic metres where they form part of commercial activity. Statutory reservoir plans are under preparation by reservoir undertakers.

5.7 Infrastructure Failure iii) Defences

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Flood defences can protect areas from flooding. They are, however, artificial, designed for a prescribed height of flooding. The Environment Agency’s flood zone maps ignore flood defences which need to be managed and maintained to remain effective. (Appendix 4)

5.8 The Effects of Climate Change 5.8.1 It is widely accepted as a result of scientific evidence that rainfall events in the future will be more extreme and unpredictable: more frequent, short-duration rainfall will be experienced and also long-duration rainfall events. Winters over the last few decades have become wetter and milder overall. It is predicted that they will become wetter by 20% by the 2050s.

5.8.2 The recent draft Lancashire Climate Change Strategy states that a 20% decrease in rainfall has been recorded over the last century with increased high intensity rainfall since the 1960s. Seasonal rainfall during the last 30 years has varied by as much as 15% from the average and there has been increased frequency of flooding of the major rivers of the North West in the last few decades. The prospect of more frequent river floods has implications for spatial planning.

5.8.3 The Foresight Project (2004) concluded that towns will in the future be subject to localised flooding caused by sewer and drainage systems being overwhelmed by sudden, localised downpours. Winters are predicted to get wetter and summers become drier and maybe hotter than at present. Sea level rise does not directly affect the Borough. Also changes in land management and land use could increase future flood risk. For example, changes in crop types and methods of cultivation could affect the porosity and surfaces of the ground and therefore the volume, speed and direction of storm run-off.

5.8.4 It should be noted that the Environment Agency’s flood maps and flood zones do not take account of climate change impacts, but the spatial planning process is required to do so by PPS25.

5.8.5 In making an assessment of the impact of climate change on flooding from the land as part of a flood risk assessment, increases in rainfall intensity of up to 10% for a given return period to 2050 may provide an appropriate precautionary response to the uncertainty about climate change impacts on rainfall intensities; an allowance for an increase in peak flows from rivers of up to 20% giving rise to flooding from rivers may be assumed, as advised in PPS25 Annex B.

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6 ADAPTATION TO CLIMATE CHANGE AND MANAGING SURFACE WATER

6.1 Flood Risk Assessments 6.1.1 PPS25 requires that site-specific flood risk assessments be undertaken for all development sites with an area greater than one hectare to ensure that development run-off does not exacerbate any downstream flooding problems.

6.1.2 The matters covered in FRAs are given in Appendix 5.

6.2.1 Site Drainage A well-designed surface water drainage system should ensure that there is little or no residual risk of property flooding during flooding events well in excess of the return period for which a sewer system is designed. Certainly no flooding of property should occur as a result of a 1 in 100 year storm event, including an allowance for a changing climate.

6.2.2 Run-off from previously developed sites should be compared with existing rates for such sites. Developers are encouraged to reduce run-off rates from previously developed sites by techniques such as infiltration. Where infiltration techniques are not viable, discharging site run-off to watercourses is preferable to the use of sewers. Sustainable drainage systems (SUDS) are encouraged: green roofs, permeable paving, rainwater harvesting, filter strips and swales, soakaways, detention basins, ponds, reed beds and wetlands. These are likely to be most appropriate in areas of low flood risk (Zone 1) to reduce the potential for flooding in other areas, rather than the flood risk zones.

Figure 3: Suds Techniques

6.2.3 The primary purpose of SUDS is to convey water away from buildings and reduce surface flow flood peaks by controlling the quantity of run off. SUDS mimic natural drainage patterns and can attenuate surface water run-off, encourage the recharge of groundwater, provide significant amenity value and wildlife

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enhancements and, by using pollutant-trapping and degradation processes, SUDs can protect and even improve water quality. Their primary purpose, to delay and modify run-off, must prevail over their secondary function as amenity and/or wildlife habitats and there must therefore be effective maintenance of the systems. Information on SUDS can be found on www.environment- agency.gov.uk/suds and www.ciria.org/suds.

6.3 Further design mitigation measures:

6.3.1 Raising Floor Levels The most important measure that can be taken to reduce the impact of flooding is to raise the minimum floor level of a property or development above anticipated flood levels. This will avoid damage to internal walls, wiring and furnishings. The raising of electrical wiring and sockets reduces risks to health and safety. In some high risk areas it may be expedient to raise living areas to first floor level, with storage or garages at ground level. These raised floor levels will have implications for disabled access and for those with special needs such as the aged and carers with pushchairs. Public access will be required to all public buildings and facilities including shops at all times.

6.3.2 Construction Measures Flood resilience measures can be incorporated during the construction of buildings to reduce inundation should flooding occur. Flood resistant fixtures and fittings could be used; for example concrete floors rather than timber, plastic and metal rather than chipboard or MDF.

6.3.3 Landscaping and planting will increase hydraulic ‘roughness’ of the floodplain, slowing the passage of flood flows. Trees can direct or concentrate floodwaters; the effect is to delay and decrease the size of the flood peak.

6.3.4 Strengthened containment of watercourses may be an option involving hard engineering techniques. New or strengthened flood walls and embankments should be provided by developers’ Section 106 contributions and maintenance contributions included in the Agreement. Offices, industry and private car parks which do not have a high proportion of visits from the general public may not need to provide the same standard of containment as for publicly accessible buildings including residential properties. The FRA should demonstrate that the design of such buildings provides for the safety of employees and visitors during a flood. In a 2002 planning application at Cardwell Mill, Charnley Street, Mill Hill, a site in Flood Zone 3A, the height of the flood defence wall alongside the River Darwen was raised to contain the river channel in a 1 in 100 year flood flow.

6.3.5 Flood proofing measures should be considered in addition to flood protection measures. These may include the construction of barriers on ground floor windows, doors and access points and the protection of electrical services by bringing them into a building at a high level and installing sockets above possible flood levels.

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7 THE NEXT STEPS

7.1 The second stage of the SFRA will concern flood risk pressures on development sites, with emphasis on those sites identified in high and medium flood risk areas where modelling work may clarify the risks of flooding. If, following assessment, it is concluded that the potential for flood risk is increased, mitigation works should be designed.

7.2 The Council’s Core Strategy Preferred Options Report was published in October 2007 for a six week consultation period and sets out the overall framework for the Local Development Framework.

7.3 Six options for the development strategy are presented:

• A compact towns strategy concentrating development into the urban areas; there is a focus on the protection and enhancement of green infrastructure • Growth opportunities: Blackburn town centre for employment development; employment development on the M65 corridor; increased development on the urban fringe; higher market housing in the villages. • Regeneration: development focussed on inner urban areas and town centres with enhancement of green spaces and the development of green networks • Sustainable Accessibility: development focussed on public transport corridors and transport ‘hubs’ with doorstep provision of open space • Smaller settlements: development focussed on Darwen and villages • Development within environmental limits: use of brownfield sites in the urban areas and the protection of environmental assets; where major developed sites exist in the open rural area and become available for development, new built development should be minimised .

7.4 In addition to the development options selected, the Core Strategy Preferred Options suggests a major employment site opportunity in the north east of the Borough at Whitebirk, largely in Borough.

7.5 At the end of the consultation responses will be collated and in the light of views expressed an option or combination of options will go forward as the preferred Core Strategy. The SFRA Stage 1 will then provide baseline information which will influence where future development can feasibly be located and where development is not acceptable due to flood risks.

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Strategic Flood Risk Assessment Stage 1: December 2008 21

Figure 4: Composite Strategic Flood Risk Assessment Plan

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Strategic Flood Risk Assessment Stage 1: December 2008 1

Appendix 1 Flood Risk Vulnerability Classification

Use Classification Land Use Essential Infrastructure • Essential transport • Strategic utility infrastructure Highly vulnerable • Public services: police, fire, ambulance • Basement dwellings • Caravans, mobile homes • Installations needing hazardous substances consent More vulnerable • Hospitals, clinics, health centres • Residential institutions • Dwellings, halls of residence; hotels, pubs, nightclubs • Schools, colleges, nurseries • Sites for landfill and waste management • Holiday caravans, camping sites Less vulnerable • Shops, offices, services, cafes, restaurants, takeaways, industry, storage, assembly and leisure • Land and buildings used for agriculture and forestry • Waste treatment • Mineral working and processing • Water/sewage treatment plants Water-compatible development • Flood control infrastructure • Water transmission infrastructure & pumping stations • Sewage transmission infrastructure & pumping stations • Sand and gravel workings • Navigation facilities • Marinas • MOD defence installations • Water-based recreation • Amenity open space, nature conservation, outdoor sports and recreation plus associated residential accommodation for staff subject to a warning and evacuation plan Adapted from Planning Policy Statement (PPS) 25: Development and Flood Risk; Annex D; Table D.2: Flood Risk Vulnerability Classification

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Appendix 2 Flood Zone Definitions

Zone Definition Policy Aims Appropriate FRA Content Uses 1 Land having a Pay attention to All uses of land Development Low less than 1 in layout and form proposals of 1 Probability 1000 annual to reduce the hectare or > : of probability of overall level of Identify & assess Flooding river flooding in flood risk; seek the risks of all any year opportunities to forms of flooding, (<0.1%) reduce flood demonstrating how risk onsite and risks will be elsewhere managed, consider through layout, flood risk form and use of elsewhere as a SUDs result of the addition of hard surfaces. 2 Land having Reduce flood Water- All proposals: Medium between 1 in risk through compatible, less contents as above Probability 100 and 1 in layout, form and vulnerable uses of 1000 annual appropriate and essential Flooding probability of application of infrastructure; river flooding SUDs; create Highly space for vulnerable uses flooding only if Exception (pathways and Test passed storage); design mitigation measures 3a Land having a 1 Create space Water All proposals: High in 100 or for flooding compatible and contents as above Probability greater annual (pathways and less vulnerable of probability of storage); design uses: retail, Flooding river flooding mitigation financial and (>1%) measures professional services, offices, restaurants, Industry, storage, non- residential institutions, assembly and leisure 3b Land where Reduce flood Water All proposals: Functional water has to risk thro’ layout compatible uses contents as above Floodplain flow / be stored and form & essential in times of infrastructure flood; annual which passes probability 1 in Exception Test 20 (5%) or >

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Appendix 3 Historic Flood Events in Blackburn with Darwen

Year Location Event Details Cause of Flooding Several Red Lion pub, Flooding of ground floor Sewer surcharge, Whitebirk Road run off from highway, lack of escape route to brook July 1977 Harrison Street, River Blakewater overspilled A section of wall Blackburn that acted as a defence had been dismantled. 1980/1 River Darwen, Construction of major sewer Temporary Darwen works connection between the sewer and the river. May 1987 Revidge, Blackburn Flooding of the River A localised, heavy Blakewater, Little Harwood storm resulted in considerable overland flow. 24 May Stream to the south Flooding of cottage Road culvert 1989 of Pleckgate School unable to cope with flood volume same Woolridge Playing Flooding Sluice on Little Field and area east Harwood Brook of the railway, responsible Bastwell same Acrefield, Flooding of garage built over Flash flood from tributary of Arley Brook golf course June 2002 Blackburn and River Darwen, Waterfall A tree impeded the Darwen culverted river beneath Stancliffe Street; Demolition of a rear mill wall in Albert Street which had acted as a flood defence. 2002 Dominica Avenue, Flooding Scotshaw Brook Darwen flood Summer River Blakewater Flooding, George Street 2004 West, Blackburn August River Darwen Flooding of area around Damage to Albert 2004 Cross Street, Darwen Mill and the vicinity 12 Culverted Buryfold Overtopping of manhole: 17 Capacity of culvert September Brook, North of houses, 13 commercial 2004 Epworth Street to properties flooded Junction Street, Darwen

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Appendix 4 River Blakewater Defences – Assets in Poor Condition (graded 4)

Asset Type Description Length Maintenance Location (M.) Responsibility Non-flood Bridge - Private Gordon defence Street West structure Flood defence Weir - Private Bridge structure Street Maintained Channel bed and bank 142.4 Environment River channel Agency Raised Channel bed and wall 49.5 Environment Culvert to defence Agency Bridge (man-made) Street

River Darwen Defences – Assets in Poor Condition (graded 4)

Asset Type Description Length Maintenance Location (M.) Responsibility Culverted Culvert 100.8 Environment Stancliffe channel Agency Street Culverted Culvert 194.8 BwDBC Stancliffe channel Street Culverted Culvert 96.3 BwDBC Aqueduct channel Street Culverted Culvert 302.7 Private Azko Nobel channel Culvert Flood defence Culvert - BwDBC Shorey Bank structure Flood defence Culvert - Environment Hardman Way structure Agency Culverted Culvert 459.0 Environment -- channel Agency Culverted Culvert 247.6 Environment Spring Vale channel Agency Road Culverted Culvert 71.9 BwDBC Watery Lane channel Non-flood Farm bridge - Private -- defence structure Culverted Culvert 157.3 Environment Track off channel Agency Watery Lane Culverted Confined space 88.2 Environment M65 channel Agency Maintained Channel bed 322.1 Environment -- channel and flood wall Agency Raised defence Channel bed 166.9 Environment Bridge St., Mill (man-made) and flood wall Agency Hill

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Appendix 5 Flood Risk Assessments (FRAs)

The purpose of a FRA will be to show how flood risk to, and from, a development from all likely sources will be managed at the time of the planning application and taking future climate change into account. It should show that a development will be safe, will not increase flood risk elsewhere and, where possible, will reduce overall flood risk.

The FRA will be prepared by the developer.

It is required when: • the size of a development site is over 1 hectare lying in Flood Zone 1; • any development is proposed to be located in Flood Zone 2; • any development proposed is located in Flood Zone 3; • a change of use to a more vulnerable class is proposed which may be subject to other sources of flooding; • an indication has been given that there may be drainage problems, for example where there is the potential to cause flood risk from excessive surface water run off.

Contents of the FRA

1 Plans • Location plan identifying geographical features including watercourses and water bodies; • Plan showing the location of structures which may influence local hydraulics: bridges, embankments, pipes, walls, outfalls and the condition of the channel; • Plan showing the location of relevant flood events, indicating levels and depths.

2 Assessment Report • I) An indication of all potential sources of flooding and information on rainfall and / or the return period of any flood; the extent and depth of flood waters and, if appropriate, routes and speeds of flow; • 2) An assessment of flood levels, ground or road levels, both current and following the development. Information on proposed floor levels should relate to these levels; • 3) An assessment of any flood alleviation measures including consideration of structure condition and performance; • 4) An assessment of the volume and speed of run off from the development; • 5) The impact of flooding on the site including, rate or speed of surfaces water run off, the order in which parts of the site might flood, the duration of flood events and the economic, social and environmental consequences; • 6) An assessment of the likely impact of displaced water on third parties caused by ground raising, embankments, loss of flood plain storage and conveyance, increases in impermeable area.

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• 7) An assessment of the likely impact of climate change, assessing its effects over the design life of the development; • 8) An assessment of the hydraulics of any existing or proposed drains or sewers during flood events; • 9) An assessment of the potential impact of any development on fluvial morphology and the long term stability and sustainability of existing defences; • 10)An assessment of the residual risks after construction of any necessary defences.

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Appendix 6 Flood Zones Maps (Extracts)

Key:

Zone 3 (High Flood Risk) Zone 2 (Medium Risk Zone)

Map 6/1 Blackburn and

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Map 6/2 Darwen

Map 6/3 Moulden Bridge, Fensicowles

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Map 6/4 River Darwen, Feniscliffe

Map 6/5 Waterfall

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Map 6/6 Darwen Valley Parkway

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Map 6/7 Earcroft

Map 6/8 Duckworth Street Darwen

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Map 6/9 Bolton Road Darwen

Map 6/10 Springvale Darwen

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Map 6/11 Eccleshill

Map 6/12 Hoddlesden

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Map 6/13 Central West Blackburn

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Map 6/14 Blackburn Central

Map 6/15 Brookhouse, Bastwell and Little Harwood

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Map 6/16 Whitebirk

Map 6/17 Stanworth Woods

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Appendix 7 Glossary

Catchment A strategic planning tool through which the Environment Agency seeks Flood to work with key decision-makers in a river catchment to identify and Management agree policies for sustainable flood risk management. Plans

Critical A watercourse that is known to have caused flooding or is perceived to Ordinary pose a flood risk to large numbers of people and properties. (25 or Watercourse more properties at risk per kilometre in 2003).Responsibility for COWs passed to the EA.

Defended An area offering a degree of protection against flooding through the area presence of a flood defence

Exceedance A study to assess the risk of a site or area being affected by flood risk exceedance flow, and to assess the impact that any changes made to a Assessment site or area will have on the exceedance flood risk.

Exceedance Excess flow that emerges on the surface once the conveyance capacity flow of a drainage system is exceeded.

Filter strips Vegetated areas of gently sloping ground designed to drain water evenly off impermeable areas and to filter out silt and other particulates

Flood Flood defence infrastructure, such as flood walls and embankments,

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Flood effect All measures to reduce the effect of flooding on a building and its mitigation occupants including flood avoidance, flood resistance and flood resilience.

Floodplain An area if land that borders a watercourse, over which water flows in times of flood or would flow but for the presence of flood defences where they exist.

Flood Map A map produced by the Environment Agency providing an indication of the likelihood of flooding in all areas of England and Wales, assuming there are no flood defences.

Flood risk A study to assess the risk to an area or site from flooding, now and in assessment the future, and to assess the impact that any changes or development on the site or area will have on flood risk on the site and elsewhere. It may also identify at more local levels, how to manage those changes to ensure that flood risk is not increased.

Flood zone 1 Low probability; land assessed as having a less than 1 in 1000 annual probability of river or sea flooding in any year (<0.1%)

Flood zone 2 Medium probability; land assessed as having a between a 1 in 100 and 1 in 1000 annual probability of river flooding (1% - 0.1%)

Flood zone High probability; land assessed as having a 1 in 100 or greater annual 3a probability of river flooding (>1%) in any year.

Flood zone The Functional Floodplain; land where water has to flow or be stored in 3b times of flood. Land which would flood with an annual probability of 1 in 20 (5%) or greater in any year or is designed to flood in an extreme (0.1%) flood including water conveyance routes.

Green roofs Vegetated roofs that reduce the volume and rate of run-off and remove pollution.

Greenfield Land that has not been previously developed. land Main River A watercourse designated on a statutory map of Main Rivers, maintained by Defra, on which the Environment Agency has permissive powers to construct and maintain flood defences.

Major a) Where the number of dwellings to be provided is 10 or more, or the development site area is 0.5 ha. or more; or b) Non-residential development where the floorspace to be provided is 1,000 m2 or more; c) or the site area is 1 ha. or more.

Mitigation The management (reduction) of flood risk

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Ordinary All rivers, streams, ditches, drains, cuts, dykes, sluices, sewers (other watercourse than the public sewers) and passages through which water flows which do not form part of a Main River. Local authorities have similar permissive powers on ordinary watercourses as the Environment Agency has on Main Rivers.

Previously Land which is, or was, occupied by a permanent structure including the developed curtilage of the developed land and any associated fixed surface land infrastructure.

Probability The likelihood that a flood event will occur.

Resilience Constructing a building in such a way that, though flood water may enter a building, its impact is minimised and repair, drying and cleaning are facilitated.

Resistance Constructing a building in such a way to prevent flood water entering the building or damaging its fabric. This has the same meaning as flood proof.

Residual risk The risk which remains after all risk avoidance, reduction and mitigation measures have been implemented

Return The expected time between the exceedance of a particular extreme period threshold. The frequency of occurrence of an event.

Run-off The flow of water from an area caused by rainfall

Sewer Means of conveyance through pipes of effluent from buildings and the land attached to them. They may be public or private.

Standard of The return period to which properties are protected against flooding. protection Sustainable A sequence of management practices and control structures designed Drainage to drain water in a more sustainable manner than some conventional Systems techniques. Typically these are used to attenuate run-off from (SUDS) development sites.

Swales Shallow vegetated channels that conduct and retain water and may also permit infiltration; the vegetation filters particulate matter.

Washland An area of the floodplain that is allowed to flood or is deliberately flooded by a river or stream for flood management purposes.

Watercourse A watercourse is a route along which water from a natural source makes its way towards the sea. The water should follow a reasonably well-defined channel comprising bed and banks. Some watercourses have been artificially channelled, significantly diverted or filled over by culverting.

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Appendix 8 Useful Websites www.environment-agency.gov.uk www.ciria.org.uk www.pipernetworking.com www.defra.gov.uk www.odpm.gov.uk

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