Haweswater Aqueduct Resilience Programme - Proposed Haslingden and Walmersley Section

Environmental Statement

Volume 4

Appendix 8.1: Flood Risk Assessment

May 2021

Floo d Risk Assessment - Hasling den & Walmersley Secti on United U tilities

Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment

Haweswater Aqueduct Resilience Programme – Proposed Haslingden and Walmersley Section

Project No: B27070CT Document Title: Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Document Ref.: HBC_RBC_BMBC-HW-TA-008-001 Revision: 0 Date: May 2021 Client Name: United Utilities Water Ltd

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i Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment

Contents 1. Introduction ...... 1 1.1 Purpose ...... 1 1.2 Proposed Programme of Works Overview ...... 1 2. Scope and Methodology ...... 5 2.1 Introduction ...... 5 2.2 Assessing Flood Risk ...... 5 2.3 Scoping Phase Assessment ...... 6 2.4 Main Phase Assessment ...... 10 3. Enabling and Construction Phase ...... 13 3.1 Introduction ...... 13 3.2 Fluvial Flood Risk ...... 13 3.3 Surface Water Flood Risk ...... 20 3.4 Groundwater Flood Risk ...... 22 3.5 Reservoir Flood Risk ...... 25 3.6 Mitigation ...... 26 4. Commissioning Phase ...... 28 4.1 Introduction ...... 28 4.2 Groundwater Flood Risk ...... 28 4.3 Mitigation ...... 28 5. Operational Phase ...... 29 5.1 Introduction ...... 29 5.2 Fluvial Flood Risk ...... 29 5.3 Surface Water Flood Risk ...... 29 5.4 Groundwater Flood Risks ...... 30 5.5 Mitigation ...... 30 6. Decommissioning Phase ...... 31 6.1 Introduction ...... 31 6.2 Fluvial Flood Risk ...... 31 6.3 Groundwater Flood Risks ...... 31 6.4 Mitigation ...... 32 7. Summary and Conclusion ...... 33 7.1 Summary ...... 33 7.2 Cumulative Impacts ...... 35 7.3 Conclusion ...... 35 Annexe A: Flood Risk Assessment Tables ...... 36 Annexe B: EIA Assessment Criteria ...... 37 Annexe C: Figures...... 40 Annexe D: Drainage Assessment ...... 41

ii Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment

1. Introduction

1.1 Purpose 1) This Flood Risk Assessment (FRA) has been prepared to support the planning applications for the Proposed Haslingden and Walmersley Section of the Haweswater Aqueduct Resilience Programme (HARP). The assessment of Flood Risk has been carried out in combination with the Proposed Haslingden and Walmersley Section design development through the Environmental Impact Assessment (EIA) process and informs Chapter 8 (Flood Risk) of the Environmental Statement (ES).

1.1.1 Scope and structure 2) This FRA has been carried out in accordance with the National Planning Policy Framework (NPPF)1 and the Planning Practice Guidance (PPG)2. Complying with planning policy would promote a Scheme that would be appropriate given the level of local flood risks, would be safe during the construction and operational phases of its lifetime, and would not increase flood risk both on site and elsewhere. 3) This FRA will provide the evidence to demonstrate that the Proposed Haslingden and Walmersley Section complies with the above requirements. The structure of the FRA is outlined below:

▪ Section 2 describes the methodology adopted to define the scope of this assessment and details the methodology of the main assessment along with key datasets, assumptions and limitations

▪ The assessment of flood risk has been used to: - Define the level of flood risk to the Proposed Haslingden and Walmersley Section - Determines the potential impacts of the Proposed Haslingden and Walmersley Section on flood risk elsewhere - Outlines any proposed measures required to mitigate the risk and impacts identified

▪ The assessment is reported across four phases, linked to key phases of the design life of the Proposed Haslingden and Walmersley Section, as detailed below: - Enabling and construction phase (Section 3) - Commissioning phase (Section 4) - Operational phase (Section 5) - Decommissioning of the existing aqueduct (Section 6)

▪ Section 7 summarises the key flood risk issues and any additional mitigation measures identified

▪ Annexe A provides further detail of the results of the FRA against each source of flooding identified.

1.2 Proposed Programme of Works Overview 4) The existing 110 km Haweswater Aqueduct takes raw water from Haweswater Reservoir in the Lake District National Park along a 16 km section of the aqueduct to a Treatment Works (WTW) near Kendal for treatment. From this WTW, the aqueduct conveys treated water to customers in Greater Manchester, Cumbria and Lancashire. 5) The aqueduct comprises six existing tunnel sections replaced with five proposed tunnels(generally 2.6 m internal diameter). The flow of water along the entire length of the aqueduct is achieved by gravity, with no energy-consuming pumps involved in supplying the water from north to south. Out of the total 110 km length of the aqueduct, the Proposed Programme of Works on the single line sections accounts for just under half this distance, about 53 km.

1 Department for Communities and Local Government (2018) National Planning Policy Framework. [Online] Available from: https://www.gov.uk/government/publications/national-planning-policy-framework--2. [Accessed: 22/05/20]. 2 Department for Communities and Local Governments (2019) Planning Practice Guidance. [Online] Available from: https://www.gov.uk/government/collections/planning-practice-guidance. [Accessed: 22/05/20].

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1.2.1 Proposed Haslingden and Walmersley Section 6) Towards the southern extent of the aqueduct is the Proposed Haslingden and Walmersley Section, extending from Huncoat, approximately 1.7 km east of Accrington to Woodgate Hill Water Treatment Works (WTW). The location and alignment of the Proposed Haslingden and Walmersley Section is presented in Figure 1. 7) The existing aqueduct between Huncoat and Woodgate Hill would be replaced with a single tunnel, identified as the proposed Haslingden and Walmersley Section. It would be constructed by tunnel boring below ground level with short open-cut surface trenching sections at each end making connections back to the existing aqueduct. 8) The new tunnel would be bored in two directions (north and south) from a compound at Haslingden, with reception shafts at Huncoat and Woodgate Hill. Further details on the tunnel boring and associated works are provided within Chapter 3: Design Evolution and Development Description of the ES. 9) The ES for the Proposed Haslingden and Walmersley Section, has defined four distinct project phases linked to the design life of the scheme:

▪ Enabling works and construction

▪ Commissioning

▪ Operation

▪ Decommissioning. 10) An overview of the key activities and infrastructure components of each of these phases is presented below. Drawings showing the layout of the enabling and construction works is presented on drawings within Annexe C. A further description of the Proposed Haslingden and Walmersley Section is provided in Chapter 3: Design Evolution and Development Description of the ES. 11) Subject to planning permission, the proposed Programme of Works could start in 2023, with enabling works. The works would ultimately reach completion and commissioning in 2028.

1.2.2 Enabling works 12) Enabling works would include fencing off working areas and preparing sites ready for construction and would include:

▪ Five compound sites at both ends and at the middle of the proposed tunnel to provide areas for plant, machinery, equipment, welfare, offices and vehicle movements - The Bolton Avenue Compound is located at the northern end of the Proposed Haslingden and Walmersley Section and comprises a Tunnel Boring Machine (TBM) Reception Site Compound adjacent to Bolton Avenue - The Haslingden Road Compound is a double drive shaft serving the Bolton Avenue Compound to the north and Woodgate Hill WTW Compound to the south. It is located between Haslingden Road, Manchester Road (A680), the A56 the A682 - The New Hall Hey Compound is proposed to receive the TBM from the Haslingden Road Compound and re-launch it beneath the River Irwell for a connection to an existing United Utilities facility (the Townsend Fold WTW) at the proposed Townsend Fold WTW Compound via a new shaft. It is located at north (right) bank of River Irwell - The Townsend Fold Water Treatment Works (WTW) Compound is proposed to receive the TBM from the New Hall Hey Compound in a temporary shaft adjacent to the River Irwell from where a trenched connection to the existing Townsend Fold WTW would be made. It is located at the south (left) bank of River Irwell - The Woodgate Hill WTW Compound is located at the south of the Proposed Haslingden and Walmersley Section and comprises a reception shaft receiving the south TBM from the Haslingden Road Compound in a 15 m diameter shaft.

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▪ Surface water drainage systems serving compound sites

▪ Construction access tracks and associated drainage linking compounds to the public road network

▪ Mine stabilisation works to minimise future mine collapse and to stabilise the workings at the tunnel horizon. This requires drilling boreholes through the soils and into bedrock and introducing a liquid grout into them. To protect the topsoil, these works are normally carried out within prepared stock fenced working areas comprising: topsoil storage mounds; geotextile/stone access road (where required); treatment area, stoned where required, and surrounded by surface water catch ditches and sumps. Three areas have been identified to facilitate the safe construction of the Proposed Haslingden and Walmersley Section: - Plantation Road mine grouting area - White Carr Lane mine grouting area - Woodgate Hill mine grouting area.

1.2.3 Construction 13) Construction works would take place within construction compounds, within tunnels and on public highways and access routes and would include:

▪ Tunnel boring construction - The Proposed Haslingden and Walmersley Section would be constructed using a slurry TBM - The new tunnel would be driven (launched) from the double Drive shaft at Haslingden Road Compound (middle section) to the reception shaft at Bolton Avenue Compound (north end) and to the reception shaft at Woodgate Hill WTW Compound (south end). The tunnel between Bolton Avenue and Haslingden, (the Haslingden tunnel) would have an internal diameter of approximately 3.5 m and would be 8.8 km in length. The maximum depth of the tunnel would be approximately 200 m below ground level. The tunnel between Haslingden and Woodgate Hill, (the Walmersley tunnel) would have an internal diameter of approximately 3.5 m and would be 10.4 km in length. The maximum depth of the tunnel would be approximately 165 m below ground level - The twin drive shafts would be approximately 15 m in diameter, located immediately adjacent to each other and would be approximately 55 m deep - Arisings from tunnel construction would be brought to the surface at the Haslingden Road Compound and would be treated and stored temporarily before being taken off site to licenced facilities or appropriate reuse - Temporary surface water drainage and de-watering of groundwater from deep excavations and tunnels would be stored and treated before discharge into the receiving watercourse

▪ Open-cut trenches would be excavated to enable the construction of multi-line siphons to join the existing aqueduct to the new tunnel at both the north and south of the Proposed Haslingden and Walmersley Section. A second shorter tunnel section via open-cut trench would also connect the new tunnel to the Greater Manchester Supply Network

▪ The construction of permanent infrastructure, including above ground installations such as new valve house buildings to control flow within the aqueduct and air valves along the multi-line siphon

▪ Restoration of the enabling works to their pre-construction condition.

1.2.4 Commissioning 14) Following the construction phase, a commissioning process is required during which the proposed sections of tunnel would be flushed through with potable water to wash away any debris from the construction phase. The commissioning flow would be discharged to Heaton Park Reservoir. Water would then be managed in accordance with the normal practices of the works and discharged from the

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reservoir through the current discharge agreement for the works at the current rates. The commissioning process would take approximately four to six weeks.

1.2.5 Operational 15) For most of the length of the replacement aqueduct there would be no permanent above-ground structures with much of the new sections of aqueduct being located deep below ground level. 16) Operational phase activities and features of relevance to the FRA, would therefore be limited to operation of the proposed valve house buildings and air valves which would be accessed via existing, permanent access tracks.

1.2.6 Decommissioning 17) Following completion and commissioning of the new replacement section, the old tunnel sections of the existing aqueduct would be taken out of service. A future maintenance and usage strategy for the redundant sections of aqueduct is being prepared; however, was not available at the time of preparing this FRA and has therefore not be considered. 18) The existing overflow structure would however remain in operation and would link both the decommissioned aqueduct and the Proposed Haslingden and Walmersley Section to the River Roch via an overflow weir at the Roch north well in the Woodgate Hill WTW site. This overflow would protect the siphon sections of the new aqueduct from excessive pressure and provide a discharge location for groundwater ingress from the decommissioned aqueduct.

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2. Scope and Methodology

2.1 Introduction 19) The assessment of flood risk has been undertaken over two stages. This includes a scoping and a main phase in line with the development of the EIA and the Proposed Haslingden and Walmersley Section design. This FRA only documents the findings of the main phase in support of the Proposed Haslingden and Walmersley Section design as outlined in the planning applications. However, a summary of the scoping process and its results are presented in the following sections along with key datasets, assumptions and limitations.

2.2 Assessing Flood Risk

2.2.1 Source-pathway-receptor 20) Flood risk is conceptualised using the source-pathway-receptor model. For a flood risk to be present each of the three elements is required:

▪ A source of flood water such as a river or groundwater body

▪ A pathway that enables the flow of flood water from a ‘source’ to a ‘receptor’. This could include low lying land within a floodplain or permeable strata that enable groundwater to seep to the surface, or construction activities such a tunnelling

▪ A receptor such as a person, property or habitat that may be impacted by a flood event. 21) Flood risk is therefore dependent on all elements being present and is assessed in terms of the probability (likelihood) of an event occurring and the consequence of the flood.

2.2.2 Probability 22) The probability of flooding in this report is defined using Annual Exceedance Probability (AEP). This is the preferred approach in comparison to the annual maximum return period (e.g. 1 in 100-year event). This is due to the potential misconception that return periods are associated with a regular occurrence rather than an average recurrence interval. For example, it is sometimes assumed that the 1 in 100-year event flood will occur once every 100-years. However, events with a magnitude of the 1 in 100-year event have a 1 % chance of being exceeded in any one year. Table 1 provides a comparison of AEP to return periods to aid the understanding of flood frequency. Table 1: Equivalent annual exceedance probabilities and return periods AEP 10 % 3.33 % 2 % 1.33 % 1 % 0.1 % Return Period 1 in 10-year 1 in 30-year 1 in 50-year 1 in 75-year 1 in 100-year 1 in 1000-year

2.2.3 Consequence 23) The consequence of flooding is dependent on two factors:

▪ Exposure – For example, the number of people or properties potentially affected

▪ Vulnerability – The potential for people or property to be harmed or damaged. 24) Floods impact both individuals and communities, and have social, economic, and environmental consequences. These can be both negative and positive and can include direct and indirect loss. 25) With regards to development and flood risk, vulnerability is largely driven by the type of development proposed or affected. Different classes of vulnerability are defined in in Table 2 of PPG Flood Risk and Coastal Change3. In accordance with this table, the Proposed Haslingden and Walmersley Section is

3 Department for Communities and Local Governments (2019) Planning Practice Guidance. [Online] Available from: https://www.gov.uk/guidance/flood-risk-and-coastal-change#Table-2-Flood-Risk-Vulnerability-Classification. [Accessed: 22/05/20].

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classified as ‘water transmission infrastructure’ and is listed as ‘Water-Compatible Development’. The construction of water compatible development is permitted within all Flood Zones defined by the Flood Map for Planning.

2.2.4 Impacts 26) The assessment of the flood risk impacts as a result of the Proposed Haslingden and Walmersley Section and the magnitude of the change in flood risk, considers the potential effects on all elements of flood risk including: flood frequency, extent, depth, velocity and combinations of these components. 27) The duration of changes to flooding is also considered when assessing flood risk impacts, where a distinction is made between permanent changes and temporary changes where the effect would cease to be felt after a period. Temporary changes can be long-term or short term in nature. 28) Embedded mitigation measures are also considered when determining potential impacts on flood risk. These measures form part of an optimised design used to reduce the significance of flood risk effects, for example:

▪ Following the sequential approach to avoid placing assets, features and activities within areas at high flood risk where possible

▪ Discharge surface water run-off from construction compounds as high up the drainage hierarchy and implementing sustainable drainage systems (SuDS) where possible, to avoid or reduce impacts on receiving watercourses

▪ The management of groundwater discharges within the surface water drainage system. 29) It is assumed that good practice mitigation measures would be applied where the design has not been fully developed. Details of good practice are provided within the Construction Code of Practice (CCoP) is Appendix 3.3 of the Environmental Statement.

2.2.5 Links to the Environmental Statement 30) The EIA process adopts a slightly different assessment model to flood risk (sensitivity x magnitude of change = significance), where:

▪ The sensitivity of a feature or resource is typically determined by, among other things, its level of designation or protection (e.g. importance, value or rarity), its susceptibility to or ability to accommodate change. Within the context of this FRA, sensitivity is a function of the likelihood of flooding and the potential consequences (i.e. baseline flood risk)

▪ The magnitude of change is a measure of the scale or extent of the change in the baseline condition, irrespective of the value of the feature or resource(s) affected (i.e. impact on flood risk)

▪ The significance of the overall flood risk is a product of the sensitivity of the resource or feature and the magnitude of the impacts. 31) Whilst the flood risk assessment model (probability x consequence = risk) will be used within this FRA, technical evidence provided in this FRA will be used to inform Chapter 9 (Flood Risk) of the Proposed Haslingden and Walmersley Section ES. Annexe A therefore provides a set of assessment criteria used within the ES to define sensitivity, magnitude of change and significance.

2.3 Scoping Phase Assessment 32) During the scoping phase of the EIA, a high-level assessment of flood risk was undertaken to identify which sources of flood risk were present within the Proposed Haslingden and Walmersley Section and to identify those flood sources or high risk or high impact elements of the Proposed Haslingden and Walmersley Section that would require further detailed assessment during the main phase of the EIA.

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2.3.1 Sources of information and data 33) The scoping assessment was a high-level qualitative assessment based on the following readily available sources of development and flood risk information and datasets, including:

▪ Conceptual designs for the construction and operation of the Proposed Haslingden and Walmersley Section provided by United Utilities

▪ Environment Agency Flood Map for Planning4

▪ Environment Agency Risk of Flooding from Surface Water Mapping5

▪ Environment Agency Reservoir Flood Mapping5

▪ British Geological Survey (BGS) mapping6

▪ British Geological Survey (BGS) groundwater flooding susceptibility maps7

▪ Ordnance Survey Datasets including 1:25,000 scale mapping

▪ The Hyndburn8, Rossendale9 and Bury10 Strategic Flood Risk assessments

▪ United Utilities asset data

▪ A web search of historical flood incidents

▪ Draft GI data package (for the groundwater flood risk assessment).

2.3.2 Scoping Assessment Summary 34) Table 2 provides a summary of the findings of the scoping FRA and identifies those sources of flood risk or Proposed Haslingden and Walmersley Section design features “scoped in” for consideration during the main phase flood risk assessment (this report). Table 2: Scoping phase assessment, Haslingden and Walmersley Section

Flood Source / Assessment Assessment Scope Summary Conclusion Element Assessment Area The FRA does not have a fixed assessment area. The Assessment This defines the area used to assessment focuses on the area within the planning area varies identify sources of flood risk application boundary, and specifically on the extents of according to and the extents of potential surface and shallow works. As the design developed, the source impacts. assessment was extended to include areas downstream of the planning application boundary and areas of deep tunnelling where appropriate, due to the sensitivity of receptors and magnitude of potential impacts. Coastal Flood Risk The Proposed Haslingden and Walmersley Section is Scoped out Flooding originating from the approximately 35 km from the River Ribble Estuary and is at a sea where water levels exceed minimum elevation of approximately 100 m above ordnance the normal tidal range and datum (AOD).

4 Environment Agency (2020) Flood Map for Planning. [Online] Available from: https://flood-map-for-planning.service.gov.uk/. [Accessed: June 2020]. 5 Environment Agency (2020) Risk of Flooding from Surface Water Mapping. [Online] Available from: https://flood-warning- information.service.gov.uk/long-term-flood-risk/map. [Accessed: June 2020]. 6 British Geological Survey (2020) Geology of Britain viewer (classic). [Online] Available from: https://mapapps.bgs.ac.uk/geologyofbritain/home.html. [Accessed: June 2020]. 7 BGS (2020) BGS Groundwater Flooding Susceptibility Dataset [Accessed in 2020] 8 Hyndburn Borough Council (2010) STRATEGIC FLOOD RISK ASSESSMENT (Level 1). [Online] Available from: [https://www.hyndburnbc.gov.uk/download-package/strategic-flood-risk-assessment-level-1/. [Accessed: May 2020]. 9 Rossendale Borough Council (2016) Rossendale Hybrid Level 1 and Level 2 Strategic Flood Risk Assessment. [Online] Available from: [https://www.rossendale.gov.uk/downloads/file/13624/strategic_flood_risk_assessment_2016. [Accessed: May 2020]. 10 JBA (2009) BURY ROCHDALE AND OLDHAM STRATEGIC FLOOD RISK ASSESSMENT – Volume III Level 2 SFRA. [Online] Available from: [https://www.bury.gov.uk/CHttpHandler.ashx?id=5498&p=0. [Accessed: May 2020].

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Flood Source / Assessment Assessment Scope Summary Conclusion Element flood onto the low-lying areas Therefore, no risk from this source has been identified and no that define the coastline. further assessment is necessary. Fluvial Flood Risk (Main Environment Agency Flood Zone definitions are set out in the Scoped in Rivers) National Planning Policy Guidance (2014) these range from 1 Flooding originating from to 3, with Flood Zone 1 having the lowest flood risk. The Main Rivers, including the Proposed Haslingden and Walmersley Section is located River Irwell and the River entirely within Flood Zone 1 except a small area of Flood Zone Roch. 2 and 3 area adjacent to River Irwell. No temporary or permanent above ground crossings of Main Rivers are proposed. Construction phase and operational discharges (such as groundwater ingress into the decommissioned section of the Haweswater Aqueduct) into the catchments of the River Irwell and River Roch have the potential to increase flow and increase downstream flood risk, and therefore need to be considered in further detail. Fluvial Flood Risk (Ordinary During the enabling, construction and operational phases, Scoped in Watercourses) features such as temporary construction access tracks and Flooding originating from crossings, construction compounds and valve houses would be minor watercourses, with constructed near or over Ordinary Watercourses. The scoping localised or less significant assessment identified that enabling and construction phase flood risk issues. impacts were likely to be short-term in duration, and could be mitigated effectively through the application of good design and construction practices. Long-term impacts to ordinary watercourses would be limited to small changes to surface water runoff rates from new valve houses and associated infrastructure which could also be mitigated through the application of good practice. The need for further detailed assessment of fluvial flooding from Ordinary Watercourses would be considered on a case- by-case basis once additional design information is available. Surface Water (Pluvial) During the enabling and construction phase of the Proposed Scoped in Urban or rural flooding Haslingden and Walmersley Section, temporary construction resulting from high intensity access tracks and construction compounds would be rainfall, with runoff travelling constructed near or over surface water flow paths. These overland and ponding in local features also have the potential to increase runoff and flood topographic depressions risk downstream if not managed appropriately. before the runoff enters any Surface water flooding would need to be assessed in further watercourse, drainage detail on a case-by-case basis once additional design systems or sewer. information is available to determine if detailed assessment or mitigation beyond good practice would be required. Groundwater Earthworks associated with the construction of shafts, Scoped in Flooding due to a significant attenuation ponds, working platforms, sections of rise in the water table, construction access tracks and open-cut trenches have the normally as a result of potential to encounter groundwater and, in some instances, prolonged and heavy rainfall release localised artesian groundwater pressures. These works over a sustained period. therefore have the potential to allow groundwater to flood excavation areas and reach the surface.

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Flood Source / Assessment Assessment Scope Summary Conclusion Element The grouting of historical mine working also has the potential to displace groundwater resulting in short term, temporary flooding. It also has the potential to form a barrier to groundwater flow resulting in long term or permanent impacts on flood risk. Failure of Water Retaining Environment Agency mapping indicates that flooding from Reservoir Infrastructure the reservoirs in the Upper Irwell Catchment would flow in the flood risk direction the Proposed Haslingden and Walmersley Section scoped in for Flooding due to the collapse along the course of the River Irwell. Flooding from the closed construction and/or failure of man-made Woodgate Hill Reservoir would flow in the direction of the phase only water retaining features such residential area of Fern Grove downstream. as hydro-dams, water supply reservoirs, canals, flood No canals or flood defences have been identified within the defences structures, vicinity of the Proposed Haslingden and Walmersley Section. underground conduits, and Therefore, the assessment will focus on reservoir flood risk. water treatment tanks or pumping stations. Failure of the existing The risk of flooding from the aqueduct itself will not be Scoped out Haweswater Aqueduct assessed in the EIA, as this is an existing risk and the Proposed Haslingden and Walmersley Section would reduce the likelihood of failure. Sewer and Water Mains Whilst United Utilities has identified that sewer flooding has Scoped out Flooding due to surcharging occurred in the vicinity of the proposed Bolton Avenue of man-made drainage Compound, this is downstream of the proposed compound systems. and no other areas of risk have been identified in close proximity to the Proposed Haslingden and Walmersley Section. No discharges to the sewer network are proposed. Failure of water mains are a potential source of flooding but are unlikely to impact this type of development. Therefore, no further assessment of these sources is required. Land Drainage and Artificial No data are available on the location of local land drainage Scoped out Drainage assets. Where these features are identified on site and Failure of land drainage affected, they would be replaced, if necessary, with assets that infrastructure such as drains, have the same performance. channels and outflow pipes, Therefore, the risk of flooding is unlikely to change, and no which is most commonly the further assessment is required. result of obstructions, poor maintenance and/or blockages. Climate Change The enabling and construction phase of the Proposed Scoped in Climate change and the Haslingden and Walmersley Section would be approximately impacts associated with six years in duration, starting in 2023. The effects of climate wetter winters and more change would not be discernible over this period. intense storm events have the Operational phase infrastructure is predominantly below potential to increase flood ground. The impact of climate change on flood risk to risks. permanent above ground features would be undertaken on a case-by-case basis to determine if detailed assessments would be required.

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Flood Source / Assessment Assessment Scope Summary Conclusion Element Existing Infrastructure Existing structures and associated operational activities have Scoped out Existing components of the been excluded from the scope of assessment. This includes: Haweswater Aqueduct and ▪ Operation of existing washouts to drain the aqueduct for associated operational routine maintenance activities. ▪ Existing overflows that enable discharge from the aqueduct into local watercourses in the event of a downstream blockage or collapse ▪ Existing tracks leading to valve houses that would be utilised by the Proposed Haslingden and Walmersley Section. These structures would continue to operate as they do currently and would therefore not be affected by the Proposed Haslingden and Walmersley Section.

2.3.3 Limitations and assumptions 35) The scoping flood risk assessment was undertaken with the following limitations and assumptions:

▪ The assessment was based upon early conceptual design information that included generalised route corridors and wide areas for potential temporary works. Several key design decisions had not yet been made, such as - The aqueduct construction technique (tunnelling) - The location of enabling works including construction access tracks and construction compounds - The requirement for any stabilisation works at mine grouting areas - The location of (operational phase) surface water and groundwater discharge outfalls - The strategy to decommission the section of the Haweswater Aqueduct to be replaced by the Proposed Haslingden and Walmersley Section.

▪ The assessment was based on a qualitative review of national datasets and publicly available data only.

2.4 Main Phase Assessment 36) Given the limited potential to impact on flood risk identified during the scoping phase assessment, it was agreed with the Environment Agency, Lancashire County Council and Bury Metropolitan Borough Council (LLFAs) that the main phase assessment would be focused on the key flood risks and potential impacts that have been confirmed to be present within the assessment area (“scoped in”) linked to:

▪ Fluvial flooding

▪ Surface water flooding

▪ Groundwater flooding

▪ Reservoir flooding. 37) The Proposed Haslingden and Walmersley Section design has also developed since the scoping phase, and further design information is now available. Therefore, the assessment has also focussed on the following key high risk or high impact activities or features associated with the construction, operation and decommissioning of the Proposed Haslingden and Walmersley Section including:

▪ Temporary construction compounds, associated features, construction access tracks and surface water drainage

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▪ Grouting of historical mine workings

▪ Management of groundwater dewatered during tunnel boring construction

▪ Commissioning of the tunnel by flushing water through the completed tunnel

▪ The operation of permanent above ground infrastructure (valve house buildings and air valves)

▪ Permanent discharge of groundwater from the decommissioned aqueduct. 38) Like the scoping phase assessment, the main phase has also been based upon readily available national flood risk datasets (Section 2.3.1), supplemented with hydrological and hydrogeological assessment, design information provided by United Utilities and from site walkover surveys undertaken by Jacobs during spring 2020. Where the design of assets and features of the Proposed Haslingden and Walmersley Section are not as well developed by the time of undertaking this assessment, a key assumption regarding flood mitigation will be made (see Section 2.4.2). 39) No detailed hydraulic river modelling or other quantitative assessment has been undertaken. Therefore, the assessment of risk and potential scheme impacts has been determined based on a conceptual understanding of changes to flooding mechanisms. Where there is uncertainty, a precautionary approach would be taken.

2.4.1 Assessment area 40) The definition of the assessment area for the FRA varies depending upon the source of flooding. For fluvial and surface water flooding, a 50 m buffer from the planning application boundary associated with the above ground elements of the Proposed Haslingden and Walmersley Section was adopted. This has been extended along watercourses or identified flow routes if there is potential for impacts further downstream. However, any features bounding the construction footprint such as roads were taken into account. The assessment area for fluvial and surface water flooding would not include the route of the tunnel where there would be limited potential with interaction with flooding at the surface. 41) For groundwater flooding, the area of the construction footprint was assessed with no buffer zone applied. Given the horizontal boring method proposed, the assessment area for the assessment of groundwater flood risk does not include the route of the tunnel due to the short term, temporary and insignificant impact to groundwater levels from the construction method for the tunnel itself (refer to Chapter 3: (Design Evolution and Development Description of the ES for further details). The assessment area includes all other construction activities within the red line boundary. The assessment also includes the decommissioning of the existing aqueduct due to potentially long duration impacts on groundwater flows.

2.4.2 Limitations and assumptions 42) As is the case with many infrastructure projects of this type/scale, planning permission is sought as the basis for informing the award of a contract for undertaking detailed design and build activities. A key implication of this is that the design is limited to that sufficient to inform the EIA process and design details will come forward at the detailed design stage. To enable the level of design to be developed in sufficient detail to inform the EIA several assumptions have been made in advance of detailed design by a design and build contractor. 43) As details have emerged from the ongoing ground investigation and discussions with landowners and stakeholders some design iterations have been required to accommodate changes to these assumptions. In some areas, it will be necessary to resolve aspects of the design post determination through application of conditions requiring the contractor (who will carry out detailed design and construction activity) to provide details for agreement with the Local Planning Authority. It is intended that such details would be within the parameters assessed in the ES. 44) The main phase flood risk assessment has been undertaken with the following limitations and assumptions:

11 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment

▪ The assessment is based on the design details that were available at the time of writing. Whilst the location of most infrastructure components has been confirmed, full details of vertical alignments and detailed designs were not available

▪ The Draft Factual Ground Investigation (GI) Report available at the time of writing is not a finalised and fully checked set of data. The assessment is reliant on the accuracy of the information reported by the GI contractor at the time of writing

▪ Limited consultation was undertaken with Lancashire County Council and Bury Metropolitan Borough Council as LLFA due to the limited availability of council officers during the COVID-19 pandemic, and therefore no flood history data was provided 45) It is assumed that in addition to embedded mitigation measures the elements of the Proposed Haslingden and Walmersley Section that have yet to be designed in detail would be designed and constructed using appropriate flood design standards and good practice to help mitigate the flood risks and potential scheme impacts. The Construction Code of Practice (CCoP) is Appendix 3.3 and has been developed for the Haslingden and Walmersley Section to provide an overview of appropriate flood design principles, standards and good practice to be considered at later stages of the design process.

12 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment

3. Enabling and Construction Phase

3.1 Introduction 46) This section of the FRA focuses on both the flood risk to the Proposed Haslingden and Walmersley Section and potential impacts on flood risk as a result of the Proposed Haslingden and Walmersley Section during the enabling and construction phases only. In line with Section 2.4, this focuses on fluvial, surface water, groundwater and reservoir flooding associated with temporary construction compound sites, associated features, construction access tracks, surface water drainage and mine grouting activities. 47) A location specific assessment of flood risk associated with the Proposed Haslingden and Walmersley Section is presented in Annexe A. This includes details of the baseline flood risk, the potential effects and the likely magnitude of impacts. The section therefore provides an overview of the key findings.

3.2 Fluvial Flood Risk 48) Fluvial flooding refers to flooding from rivers, streams and other inland watercourses. Fluvial flooding is usually caused by prolonged or intense rainfall, generating high rates of runoff which overwhelm the capacity of the channel. When this occurs, excess water spills onto low-lying areas of land adjacent to the channel. 49) Fluvial flood risk can be divided between risk from Main Rivers and risk from Ordinary Watercourses. Main Rivers are usually larger rivers and streams where the Environment Agency carries out maintenance, improvement or construction work to manage flood risk. Ordinary Watercourses are any other watercourses not designated as Main Rivers. LLFAs are responsible for managing flood risk from Ordinary Watercourses.

3.2.1 Fluvial flood sources 50) The northern section of the Proposed Haslingden and Walmersley Section is located within the River Calder (Lancashire) catchment, which is part of the wider River Ribble catchment, whilst the central and southern sections are within the catchments of River Irwell and River Roch, all of which are Main Rivers. The Environment Agency Flood Map for Planning (FMfP) as illustrated in Figure 2 shows the extents of Flood Zone 3 and 2. The Strategic Flood Risk Assessments (SFRA) for Hyndburn11, Rossendale12 and Bury13 do not identify any areas of Functional Floodplain (Flood Zone 3b) associated with these Main Rivers within the development envelope of the Proposed Haslingden and Walmersley Section. 51) The River Irwell flows between the New Hall Hey Compound, which is located on the northern bank and the Townsend Fold WTW Compound on the southern river bank. The Proposed Haslingden and Walmersley Section itself is located within Flood Zone 1 with the exception of the Townsend Fold WTW Compound which is located within Flood Zone 2 and partially within Flood Zone 3. The River Roch is approximately 1 km to the south from the southern end of the Proposed Haslingden and Walmersley Section whilst the River Calder is approximately 3 km to the north. 52) Several Ordinary Watercourses are present within and adjacent to the Proposed Haslingden and Walmersley Section. These Ordinary Watercourses are generally small, first or second order streams with small catchments that are tributaries of either the River Irwell or River Roch. Some of these Ordinary Watercourses become Main Rivers a short distance downstream of the Proposed Haslingden and Walmersley Section including the River Hyndburn and Pigs Lee Brook. Existing land use is a combination of urban areas, undeveloped and agricultural areas; and transport infrastructure including the M66, A56, A682 and A680 roads.

11 Hyndburn Borough Council (2010) STRATEGIC FLOOD RISK ASSESSMENT (Level 1). [Online] Available from: https://www.hyndburnbc.gov.uk/download-package/strategic-flood-risk-assessment-level-1/. [Accessed: May 2020]. 12 Rossendale Borough Council (2016) Rossendale Hybrid Level 1 and Level 2 Strategic Flood Risk Assessment. [Online] Available from: https://www.rossendale.gov.uk/downloads/file/13624/strategic_flood_risk_assessment_2016. [Accessed: May 2020]. 13 JBA (2009) BURY ROCHDALE AND OLDHAM STRATEGIC FLOOD RISK ASSESSMENT – Volume III Level 2 SFRA. [Online] Available from: https://www.bury.gov.uk/CHttpHandler.ashx?id=5498&p=0. [Accessed: May 2020].

13 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment

53) These Ordinary Watercourses are not included in the Environment Agency fluvial flood mapping at the point where they pass the Proposed Haslingden and Walmersley Section and do not have any fluvial Flood Zones defined. Therefore, the probability of flooding along these watercourses has been inferred from the Environment Agency’s Risk of Flooding from Surface Water Mapping, which is presented in Figure 3. This mapping shows that flooding from these Ordinary Watercourses is generally restricted to narrow floodplains with an overall low probability of flooding (between the 1 % and 0.1 % AEP). Although the probability of flooding is low, a combination of steep upland catchments or small urban catchments indicate that they are likely to have flashy flow regimes that can rise and fall very quickly, giving little warning of flooding.

3.2.2 Fluvial flood risk to enabling and construction activities 54) As noted in Table 2, fluvial flooding is not assessed along the route of the proposed tunnel as this element of the Proposed Haslingden and Walmersley Section would be entirely below ground with no interaction with fluvial sources.

Fluvial flood risk to construction compounds 55) As shown on Figure 2, all enabling work and construction activities would be located within Flood Zone 1 except for the Townsend Fold WTW Construction compound. This would be located within the floodplain of the River Irwell and would be entirely within Flood Zone 2 and partially within Flood Zone 3. Townsend Fold WTW Compound would therefore have a high risk of flooding. 56) Townsend Fold WTW Compound and it’s access track is located on the left (south) bank of the River Irwell. The River Irwell’s banks rise steeply in this location and result in a narrow and well-defined floodplain. The width of Flood Zone 3 is approximately 40 m in this location and peak water levels during the 1 % AEP flood event are inferred to be approximately 157.5 mAOD based on a comparison of flood zone extents with site levels. Away from the steep banks, the compound site is relatively flat with levels generally around 158 mAOD. Therefore, flood events in excess of 1 % AEP would spill across a wider area, with Flood Zone 2 being approximately 160 m wide. The Environment Agency’s Historical Flood Outline and Recorded Flood Extent mapping does not indicate any historical flooding within the application boundary in the Townsend Fold location. 57) The TBM reception shaft is proposed to be located adjacent to the top of bank to avoid constraints associated with the existing WTW. To create a working area around the shaft, it is proposed to install a temporary retaining wall using sheet piles along the south bank of the River Irwell. This would encroach approximately 10 m into the area of steep bank to the north of the compound which comprises Flood Zone 3. The area behind this retaining wall (on the landward side) would then be built up to match the wider site levels and create a level working platform for the duration of the construction phase in this location. 58) As a result of the proposed raising of site levels within the north of the compound, the construction compound would not be at risk during the 1 % AEP flood event. However, there would be a moderate risk of flooding during events of greater magnitude. 59) The contractor would prepare a Flood Response Plan as identified within the CCoP for the Proposed Haslingden and Walmersley Section. This identifies the areas that are likely to flood and the actions that should be taken to ensure onsite safety. The contractor would subscribe to the Environment Agency’s Flood Warning service for the River Irwell at Rawtenstall Flood Warning Area. Water levels and weather forecasts would also be monitored. Proactive measures would be implemented if required, including removing workers and equipment from the floodplain prior to a flood event occurring. During operation of the compound, these measures would help to manage the risk of fluvial flooding. In the event that the compound site flooded, any flood consequences likely to be limited to short- term (hours to days) construction programme delays. If floodwaters enter the tunnel, this would be removed using pumping equipment that would be in place to dewater groundwater. 60) The contractor should also be aware of the potential for floodwater to enter the tunnel during extreme fluvial events (>1 % AEP) and should develop their detailed construction methodologies with this risk in mind.

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61) The Bolton Avenue, Haslingden Road, and Woodgate Hill construction compounds have an anticipated operational life of up to six years, whilst the Townsend Fold WTW and New Hall Hey compounds would have an anticipated life of only one year. Therefore, the impact of climate change on existing flood risks is not considered. 62) All construction compounds would also be located within areas with a low probability of flooding from Ordinary Watercourses as construction activities are remote from watercourses, as illustrated by Figure 2. The fluvial flood risk from Ordinary Watercourses to construction and enabling activities is detailed within Annexe A. 63) The proposed Bolton Avenue Compound would be located above a culverted section of Unnamed Watercourse 466. The location of this watercourse corresponds to a surface water flow path identified on the Environment Agency’s flood map for surface water. Detailed assessment of the condition and hydraulic performance of this culvert did not form part of the scope of this FRA and it is assumed that EA surface water mapping represents the extent and depth of flooding that would occur in the event that this culvert became blocked or surcharged. Therefore, the risk is assessed in Section 3.3. 64) The proposed Bolton Avenue Compound would be accessed from Oakfield Avenue, which is unsurfaced, Haslingden Road would be accessed from a new access from the A680 and Woodgate Hill would be accessed from a new access road from Castle Hill Road. Townsend Fold WTW and Newhall Hey Compounds would be accessed via existing access roads. No watercourses would be crossed by the proposed compound access tracks; however, the construction access track linking the Townsend Fold WTW Compound site to the Holme Road is approximately 35 m from Balladen Brook. The Environment Agency’s Risk of Flooding from Surface Water Mapping has been used to infer fluvial flood risks due to lack of fluvial hydraulic model data along Balladen Brook. This mapping indicates that during the 1 % AEP flood event, flooding from this watercourse would spill onto the adjacent Holme Road resulting in flood depths of less than 300 mm. If flooded, this would cause potential disruption to access to the compound site. With an upstream catchment of approximately 1.7 km2 any disruption caused by flooding from Balladen Brook is likely to be short-term and limited to a period of hours rather than days.

Fluvial flood risk to mine grouting works 65) All mine grouting areas would be located within Flood Zone 1 and would have a low risk of flooding from Main Rivers. 66) Areas of sensitive environmental receptors e.g. close to watercourses, mature trees, third party property, public footpaths or where significant obstacles e.g. steep valleys exist, angled drilling would be undertaken rather than vertical drilling. This embedded mitigation would enable the grouting works to be located remote to areas of fluvial flood risk along Ordinary Watercourses. 67) The Environment Agency’s Risk of Flooding from Surface Water Mapping has been used to infer fluvial flood risks from these watercourses due to lack of fluvial hydraulic model data in this area. This mapping indicates that the crossing of Unnamed Watercourse 1692 would not be at risk of flooding during the 1 % AEP flood event whilst the crossing of the River Hyndburn and Unnamed Watercourse 1970 would be at risk of flooding up to a depth of up to 900 mm during a 1 % AEP flood event. In both cases, flood extents are predicted to be narrow. 68) The actual level of flood risk to the construction access tracks at these locations would be dependent on upstream channel capacity and the capacity of the existing crossing, which are not accurately represented in the Environment Agency’s Risk of Flooding from Surface Water Mapping. 69) No alterations to the existing crossing are proposed. There would remain a residual risk of flooding to the construction access tracks during flood events that exceed the capacity of the existing culverts. As the tracks in this location run across the slope of the hillside, flood flows surcharging from the culverts would likely back up and spill across the road before re-entering the watercourse downstream resulting in relatively shallow flood depths (less than the 900 mm indicated on the Risk of Flooding from Surface Water Mapping) and continue downstream along the watercourse. 70) The third mine grouting area at Woodgate Hill and its access road follows the route of a tributary of Gypsy Brook. This is a headwater stream with an upstream catchment of approximately 0.2 km2 and

15 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment

poorly defined channels. The Environment Agency’s Risk of Flooding from Surface Water Mapping indicates that flow along the ephemeral channel would pond upstream of Castle Hill Road resulting in flooding of the grouting area in this location to a depth of up to 900 mm during the 3.33 % AEP flood event. Smaller areas of out of bank flooding up to 900 mm in depth are also predicted to affect the mine grounding areas during the 3.33 % AEP flood event downstream of Castle Hill Road as shown on Figure 3 although depths are typically shallow (less than 300 mm). During higher magnitude flood events, flood flows over top Castle Hill Road resulting in wider flood extents across the mine grouting area although even in the 0.1 % AEP flood event, depths are predicted to generally remain shallow (below 300 mm). 71) Due to the localised areas of high risk along the Woodgate Hill mine grouting area and the potential risk of flooding at the existing crossing locations at the Plantation Road and White Carr Lane mine grouting areas, good practice mitigation outlined in the CCoP would be required to minimise the risk to these works. 72) Measures would include: timing the works to avoid periods of high flow, keeping works within the floodplain to a minimum, monitoring of water levels, closure of roads during periods of flooding and emergency procedures to respond to a flood event. With these measures in place, the direct risk of flooding from Ordinary Watercourses to the mine grouting works would be low and would be limited short-term (hours to days) disruptions to access. 73) It is recognised that the Environment Agency’s Risk of Flooding from Surface Water Mapping is a national scale data set that would not consider local features including drains and walls and that the actual risk may be greater, or less than that indicated. Therefore, the detailed design of these temporary works would need to consider local conditions and features.

Fluvial flood risk to open cut trenches 74) All open cut trenches that connect the Proposed Haslingden and Walmersley Section to the existing aqueduct are located within Flood Zone 1 and therefore have a low risk of flooding from Main Rivers. These construction elements are also remote from Ordinary Watercourses except for the section of trench which crosses Unnamed Watercourse 608 (required to connect the Proposed Haslingden and Walmersley Section to the Greater Manchester Supply Network). 75) Unnamed Watercourse 608 first rises to the south of the Woodgate Hill WTW and has a small catchment of approximately 0.5 km2. The Environment Agency’s Risk of Flooding from Surface Water Mapping indicates that during the 0.1 % AEP flood event, flooding would be limited to a narrow area either side of the channel with flood depths less than 300 mm. 76) During construction, the watercourse would be conveyed over the trench via a temporary flume or over- pumping, which will be designed in accordance with CIRIA C78614. There would however remain a residual risk that these flumes could be exceeded during flood flows impacting the works and open cut trenches. Further good practice mitigation would therefore be required as detailed within the CCoP, which would include the monitoring of flow, and emergency response plans would result that this residual risk to the construction phase works would be low. 77) In addition to the open cut trenches, a new construction access track to provide access to the open cut trenches and works area, would run parallel to the trench and would cross Unnamed Watercourse 608 requiring a new culvert. 78) The actual level of flood risk to the construction access road at these locations would be dependent on upstream channel capacity and the capacity of the existing or proposed culvert crossing, which are not accurately represented in the Environment Agency’s Risk of Flooding from Surface Water Mapping. As part of the construction of the access road at these locations, new culverts would be required (see Section 3.2.3), which would also influence the level of flood risk.

14 CIRIA (2019) Culvert, screen and outfall manual (C786F) [Online] Available from: https://www.ciria.org/ItemDetail?iProductCode=C786F&Category=FREEPUBS. [Accessed: June 2020].

16 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment

79) Following construction of the construction access track and culvert, there would remain a residual risk of flooding to the road during flood events that exceed the capacity of the existing channel and new culvert. As the track in the crossing location would run across the slope of the hillside upstream of the trench, flood flows surcharging from the culvert would back up and spill across the road before flowing into the trench. As flooding of the trench would have the potential to cause significant disruption to construction, measures detailed within the CCoP including the monitoring of water levels and closure of roads during periods of flooding and the provision of emergency pumping would be implemented to help manage these residual risks and impacts upon the works. 80) With these measures in place, the direct risk of flooding from Ordinary Watercourses would be low and would be limited short-term disruptions to access.

3.2.3 Fluvial flood risk impacts from enabling and construction activities 81) This section assesses the impacts that the Proposed Haslingden and Walmersley section would have on flood risk elsewhere. Embedded mitigation has been incorporated into the design of the Proposed Haslingden and Walmersley section to avoid or reduce the potential for the following enabling phase effects on flood risk:

▪ Restriction in flood flows or the loss of floodplain storage associated with the construction of the Townsend Fold WTW Compound within the floodplain of the River Irwell

▪ Restriction in flood flows or the loss of floodplain storage associated with temporary watercourse crossings

▪ Temporary increase in runoff rates entering watercourses due to an increase in hard standing associated with compound sites, temporary buildings and construction access tracks

▪ Temporary discharges of groundwater entering watercourses from excavations and tunnelling activities.

Impact on fluvial flood risk from construction compounds 82) Whilst four of the five construction compounds would be located within Flood Zone 1 and remote from Ordinary Watercourses, the Townsend Fold WTW Compound would be located within the floodplain of the River Irwell and entirely within Flood Zone 2 and partially within Flood Zone 3 as shown on Figure 2. 83) Based on the plans that are available, the construction of the Townsend Fold WTW Compound would involve the installation of sheet pile retaining wall along the south bank of the River Irwell to enable a level working platform to be built up behind it. The raising of levels within Flood Zone 3 would result in a loss of approximately 190 m3 from the volume of the River Irwell floodplain. Whilst the retaining wall would be parallel to the river channel except for where it ties into the banks at each end, it would have the potential to, impact flow within the floodplain. The loss of floodplain storage and impact on floodplain flows both have potential to result in an increase in flood risk upstream and downstream which may impact nearby residential properties on Holme Lane that are partially within Flood Zone 3. 84) Whilst the loss of floodplain is minimal, without access to the results of detailed hydraulic modelling, it is not possible to determine the potential adverse impacts occurring including the magnitude of the changes to flood onset, extent or depth. Therefore, it is assumed that magnitude of change would be large and that additional mitigation would be required. Details of the recommended mitigation is provided in Section 3.6.

Impact on fluvial flood risk from temporary watercourse crossings 85) All the proposed construction compounds would be accessible from the existing road network without the need for any new watercourse crossings. This includes tracks to the mine grouting areas which would use existing crossings without any modifications. 86) Temporary watercourse crossings would be limited to the section of open cut trench across Unnamed Watercourse 608 that would enable the Proposed Haslingden and Walmersley Section to join into the Greater Manchester Supply Network. As discussed in Section 3.2.2, the design of the crossing has not

17 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment

yet been developed. At this stage, it is assumed that a construction access track would run parallel to the trench that would require a culvert crossing, whilst the watercourse would be conveyed over the trench via a temporary flume or over-pumping. 87) Watercourse crossings have the potential to reduce floodplain volume and constrict fluvial flood flows, which could increase the risk of fluvial flooding to agricultural land upstream and residential properties further downstream. 88) The use of an appropriately sized culverts and flumes designed in accordance with CIRIA C78615 together with a track surface at, or close to existing ground levels would result in a negligible loss of floodplain volume and minimal constriction of flood flows. 89) During flood events that exceed the design capacity of the culvert, there would be potential for flood depths upstream to increase, especially if the track would be raised above existing ground levels. However, upstream agricultural land has a low vulnerability to flooding and given the low probability of impacts during the construction period and the limited consequences, the impact on flood risk would be low. 90) As the trench and a construction access track would run across the catchment of the watercourse, there is potential to divert flows across catchment boundaries. This would increase the risk of fluvial flooding in the receiving watercourse and potentially to downstream residential properties. 91) The development of a drainage strategy to allow runoff from the track to be drained to permeable ground either side of the proposed track with appropriate drainage would prevent any transfer of flow between catchments. At the detailed design stage, additional measures would be considered including appropriate use of cross drainage, water bars, or changes in the track level to maintain existing drainage divides. It is therefore assumed that impacts to fluvial flood risk would be negligible.

Impact on fluvial flood risk from temporary surface water discharges 92) The TBM drive and reception compounds would discharge runoff to nearby watercourses that could result in an impact on fluvial flooding within receiving watercourses and to downstream receptors. 93) In line with NPPF surface water management strategies have been developed for the TBM drive and reception site compounds. These are presented in Annexe C (site layout drawings) and Annexe D (Drainage assessment). 94) In line with this strategy, the drainage system serving the shaft compounds would discharge surface water to nearby Ordinary Watercourses or Main Rivers including Unnamed Watercourses 466 and 2054, River Irwell and Gypsy Brook. In all cases, surface water would be routed to storage lagoons with discharge controlled at agreed rates. 95) Table 3 provides a summary of the discharges of surface water to watercourses. It is noted than the maximum discharge rates at all compound areas would be at the greenfield runoff rate or a maximum of 5 l/s which is the lowest rate that can be practically achieved without a high risk of blockage. This rate of discharge also represents a negligible contribution to flood flows within the receiving watercourses. The drainage design at the Townsend Fold and New Hall Hey Compounds have not been fully developed at the time of writing this assessment. However, surface water management in these locations would follow the same principles stated within the CCoP and applied for the other compounds with flow attenuated prior to discharge to ground, or watercourse if possible. 96) Drainage strategies have not been developed for the mine grouting areas. However, strategies to manage surface water runoff would be developed in line with good practice outlined within the CCoP during the detailed design stage to ensure that there would be no increase in surface water runoff rate.

15 CIRIA (2019) Culvert, screen and outfall manual (C786F) [Online] Available from: https://www.ciria.org/ItemDetail?iProductCode=C786F&Category=FREEPUBS. [Accessed: June 2020].

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Table 3: Summary of drainage design parameters used within the Surface Water Drainage Strategy Average Maximum Receiving Compound Attenuation Discharge from Compound Qbar** Discharge Watercourse Area Volume Tunnelling Rate Activities* Unnamed Bolton Avenue Watercourse 0.5 ha 4.45 l/s 284 m3 2.5 l/s 5 l/s Compound 466 Unnamed Watercourse Haslingden Road 2054 Dual Drive 1.7 ha 23.19 l/s 1055 m3 6 l/s 23 l/s Compound (also known as Langwood Brook) Unnamed Watercourse Haslingden Road 2054 Office/welfare and 0.7 ha 9.55 l/s 435 m3 None 9.5 l/s (also known parking Compound as Langwood Brook)

New Hall Hey To be confirmed at permitting stage, flow would be attenuated to River Irwell Compound greenfield rates or 5 l/s

Townsend Fold To be confirmed at permitting stage, flow would be attenuated to River Irwell WTW Compound greenfield rates or 5 l/s

Woodgate Hill WTW Gypsy Brook 0.5 ha 5.46 l/s 264 m3 2.5 l/s 5.5 l/s Compound

Notes * Discharge at greenfield runoff rate from tunnelling activities assumed within surface water drainage strategy includes all generated flows including groundwater ingress and estimated use of potable water brought to site. ** Qbar is defined the mean annual flood flow.

Impact on fluvial flood risk from groundwater discharges 97) Groundwater would likely be intercepted during construction activities associated with excavations, including:

▪ Construction of new tunnel (launch and reception) shafts

▪ Tunnel boring

▪ Sections of open cut trenches that are required to join the existing aqueduct to the proposed new tunnel. 98) Groundwater dewatered from the excavations would be managed in accordance with the surface water management strategies Annexe C (site layout drawings) and Annexe D (Drainage assessment). with any groundwater intercepted and attenuated by lagoons and water treatment plants before being discharged into the watercourses detailed in Table 3. 99) As shown in Table 3, the maximum rate of discharge from all tunnelling activities has been estimated by United Utilities to be 2.5 l/s at the TBM Reception Site Compounds and 6 l/s at the TBM Dual Drive Site Compound. However, a more detailed analysis has also been undertaken as part of the groundwater

19 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment

impact assessment, which is presented in Chapter 7: Water Environment of the ES. This more detailed assessment uses the Sichardt method as described by Preene (2000)16 to estimate the dewatering zone of influence around each of the shafts at Bolton Avenue Compound, Haslingden Road Compound and Woodgate Hill WTW Compound. This assessment concluded the rate of dewatering at Bolton Avenue Compound would be less than 1 l/s, at Haslingden Road Compound would be less than 3 l/s, and at Woodgate Hill WTW Compound would be less than 1.5 l/s. Therefore, the discharge rates from tunnelling activities assumed within the drainage strategy are conservative. 100) Groundwater dewatered from the Townsend Fold and Newhall Hey shafts would also be discharged to watercourses. Whilst a detailed strategy to manage these discharges would be developed as part of the detailed design, the application of good practice to control the discharges would ensure that the impact on the River Irwell would be negligible. 101) The predicted rate of groundwater flow that would need to be discharged during the construction phase would be low, typically representing less than half of the Qbar runoff from the compound area. Therefore, it would be unlikely to have an adverse impact on peak flow in receiving watercourses. In addition, the management of groundwater discharges through attenuation lagoons would ensure that the impact on flow within the receiving watercourses and on downstream flood risk would be negligible.

3.3 Surface Water Flood Risk 102) Surface water runoff is defined as water flowing over the ground that has not yet entered a drainage channel or similar. It usually occurs as a result of an intense period of rainfall, which exceeds the infiltration capacity of the ground or sewer system.

3.3.1 Surface water flood sources 103) Areas at risk of surface water flooding have been identified from the Environment Agency’s Risk of Flooding from Surface Water Mapping as presented on Figure 3. The mapping suggests that the risk of surface water flooding is generally low across the Proposed Haslingden and Walmersley Section (less than 0.1 % AEP). 104) Areas of high surface water flood risk identified by the mapping are usually associated with Ordinary Watercourses as assessed in Section 3.2. There are however, localised areas at higher risk of surface water flooding. These are detailed in Section 3.3.2.

3.3.2 Surface water flood risk to enabling and construction activities 105) As shown on Figure 3, the majority of enabling and construction activities would be located within areas at low risk of surface water flooding, with a probability of flooding of less than 0.1 % AEP although areas of higher risk have been identified. It is noted that the Environment Agency’s surface water flood mapping is a national scale dataset that does not consider local features such as highway drainage and kerbs and walls that may influence the direction of surface water flow paths shown in Figure 3 and surface volumes and peak flows. It is also noted that surface water mapping also identifies flow along watercourses. Flooding from watercourses is assessed in Section 3.2. 106) The locations of highest risk from surface water are summarised below and detailed in Annexe A:

▪ The Bolton Avenue Compound is at high risk from surface water flooding. As shown on Figure 3, a localised area (approximately 50 m wide) within the proposed location for the attenuation pond and valve house building is at risk of surface water ponding over 900 mm deep during the 3.33 % AEP flood event. A flow path along the existing track to the north of the compound is not predicted to pose a risk to the compound itself. However, during the 1 % AEP flood event, a surface water flow path less than 300 mm deep is predicted to run through the shaft location. - Given the limitations of the surface water flood mapping, the actual level of flood risk at this site may differ from that shown on the map. Any works proposed at this location should therefore

16 Preen (2000) Assessment of settlements caused by groundwater control. Proceedings of the Institution of Civil Engineers - Geotechnical Engineering Volume 143 Issue 4, October 2000, pp. 177-190.

20 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment

take a precautionary approach and consider the potential for large volumes of surface water flows running adjacent to and through the site.

▪ A flow path through the Plantation Road mine grouting area which would be less than 300 mm deep during the 0.1 % AEP rainfall event

▪ An area immediately south of the Haslingden Road Compound to the north of the A56 that would be no more than 900 mm deep during the 1 % AEP rainfall event

▪ An area along the access corridor to the New Hall Hey Compound that would be flooded to a depth of up to 900 mm during the 1 % AEP rainfall event

▪ At Townsend Fold WTW Compound and area approximately 70 m wide along an existing access road is at risk of flooding over 900 mm during the 1 % AEP

▪ Two areas at Woodgate Hill WTW Compound approximately 30 m diameter that is at risk of flooding up to 900 mm during the 1 % AEP. 107) To manage normal surface water run-off and areas of higher flood risk, drainage strategies have been prepared that would manage surface water flood risk to the construction compounds. Details of these strategies are presented in Annexe D and include compound perimeter drainage that would capture runoff from areas up-gradient and route it to infiltration trenches; or to an attenuation lagoon prior to discharge to a watercourse. These strategies would be developed further as part of the permitting process to characterise local conditions and account for any additional risks. With this mitigation embedded into the Proposed Haslingden and Walmersley Section design, the compounds are considered to have a low risk from surface water flooding. 108) Other temporary works including the open cut trenches and stabilisation works at mine grouting areas would have temporary drainage installed that would divert flows around working areas. Designs for this temporary drainage has not been fully developed at the time of writing but the principles that would be followed are incorporated into the CCoP. There would remain a residual risk that drainage infrastructure would be overwhelmed by rainfall events that exceeds its design standard. However, adoption of these measures would result in a low residual risk from surface water flooding to temporary works.

3.3.3 Impact on surface water flood risk from enabling and construction activities 109) The proposed locations for the five construction compound sites currently comprise areas of open space including some woodland. The development of the construction compound sites and associated features are likely to increase the area of impermeable surfaces and therefore increase the rate of surface water runoff. Uncontrolled, any increase in runoff could increase the risk of surface water flooding downstream through the surface water catchment or to the discharge location. 110) There is a potential indirect flood risk associated with surface water drainage into watercourses becoming limited by high water levels within the watercourse. This has potential to result in an increased risk of surface water flooding within the compounds. The detailed design of the temporary outfalls from the surface water drainage system into Unnamed Watercourse 466, Unnamed Watercourse 2054 and Gypsy Brook has not yet been completed. However, it is assumed that this design will be undertaken at the permitting stage and would result in an outfall that can operate effectively during the design flood event without causing the system to surcharge. With this mitigation embedded into the design of the Proposed Haslingden and Walmersley Section, the risk to the surface water drainage system from fluvial flooding is considered to be low. 111) In line with NPPF surface water management strategies have been developed for each compound site and construction access track. These are presented in Annexe C (site layout drawings) and Annexe D (Drainage assessment). 112) The proposed drainage strategies include:

▪ The placement of stockpiles of materials outside of areas of surface water flood risk

▪ A system serving the compounds that captures runoff and drain to attenuation lagoons prior to discharge into Unnamed Watercourses 466, 2054, the River Irwell or Gypsy Brook

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▪ Water recycling within each tunnelling shaft site to be used for washdown activities, which would significantly reduce the demand for potable water and would also reduce the flow rate of generated water that has to be discharged to a watercourse. 113) The proposed surface water drainage strategy would manage any increase in surface water runoff rates as a result of the Proposed Haslingden and Walmersley Section through interception and attenuation before being discharged and surface water flood risk would be negligible.

3.4 Groundwater Flood Risk 114) Groundwater flood risk refers to either a rise in the water table or lowering of the ground level leading to an increased likelihood of flooding at the ground surface. The magnitude of the change in groundwater levels relative to the ground surface and spatial extent affected is considered for this assessment of groundwater flood risk impacts.

3.4.1 Groundwater flood sources 115) Groundwater is stored in the superficial aquifers, typically of Glacial Till, and underlying bedrock aquifers which is discussed in the Water Environment section of the main ES report (Chapter 7). However, at Woodgate Hill WTW Compound, no superficial deposits are mapped as being present for the most part within the northern half of the compound. 116) Bedrock aquifers along the Proposed Haslingden and Walmersley Section comprise the Pennine Lower Coal Measures Formation, the Marsden Formation and the Rossendale Formation, the latter two formations being part of the Millstone Grit Group. 117) The groundwater-bearing Glacial Till is designated as a Secondary Undifferentiated aquifer and each bedrock formation designated as a Secondary A aquifer. This means that each of the aquifers have the potential to store and yield limited amounts of groundwater with the bedrock aquifers potentially important to river baseflow and abstractions at a local scale only. 118) Information from a borehole near the Bolton Avenue shaft indicates slight artesian groundwater levels in the bedrock, artesian or semi-confined conditions are therefore possible across the site. 119) Generally, works are proposed in areas of low value agricultural land, heath or grassland or open grassy recreation areas, often bounded by higher value motorways, A-roads or access chambers associated with the existing aqueduct.

3.4.2 Groundwater flood risk to enabling and construction activities 120) A set of GI data was available at the time of writing. Analysis of groundwater levels is discussed in the Water Environment section of the ES report (Chapter 7). Two boreholes are located within the construction envelope of the Bolton Avenue Compound some 190 m and 42 m from the shaft. Groundwater levels at these locations range from less than 1 to 8.5 metres below ground level (mbgl). 121) The closest boreholes to the shafts at Haslingden Road Compound, situated approximately 650 m south of the Haslingden Road double launch shaft, are considered too far away to represent conditions at the shafts. This is also applicable to New Hall Hey Compound shaft and Townsend Fold shaft. No boreholes with available groundwater information are situated in the vicinity of the Woodgate Hill WTW Compound shafts. In light of this, groundwater levels are conservatively assumed to be shallow at both Haslingden Road and Woodgate Hill WTW Compounds. 122) The susceptibility for groundwater flooding at the site of the Proposed Haslingden and Walmersley Section recorded by the BGS, ranges from very Low to Very High 17 , with the majority of the site categorised as Very Low to Low as shown in Figure 4. Several small, localised areas categorised as Very High susceptibility to groundwater flooding exist along the length of the route including to a partial extent at each of the three compounds (Bolton Avenue, Haslingden Road and Woodgate Hill WTW). These localised areas indicate there is potential for the emergence of groundwater at the surface.

17 BGS (2020) BGS Susceptibility Dataset [Accessed in 2020]

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123) Below ground elements of the construction and enabling works would be designed to manage groundwater ingress and so would not be vulnerable to flooding whilst embedded mitigation such as perimeter drainage would ensure that the compounds and access roads also have a low vulnerability to any groundwater emerging at ground level. 124) In summary, based on the available GI data and BGS flooding susceptibility maps the embedded mitigation incorporated into the design of the Proposed Haslingden and Walmersley Section would ensure that the groundwater flood risk to enabling and construction activities is low and that no additional mitigation is required. However, groundwater flood risk is expected to be increased for construction activities at the Woodgate Hill WTW Compound due to grouting activities that would take place before construction activities begin in the enabling phase. Assessment of impacts on groundwater flooding is presented in Section 3.4.3.

3.4.3 Impact on groundwater flood risk from enabling and construction activities 125) Enabling and construction activities would result in impacts on groundwater flooding through:

▪ Dewatering of excavations including shafts and tunnels

▪ Grouting of historic mine workings

Impact on groundwater flood risk from dewatering of excavations 126) Given the proposed excavation depths of the three deepest shaft excavations to 53.5 mbgl (Haslingden Road Compound launch shaft) and 26.5 mbgl (Woodgate Hill WTW main shaft) and other shaft excavations (Bolton Avenue Compound shaft, New Hall Hey Compound shaft, Townsend Fold WTW Compound reception shaft and secondary shaft at Woodgate Hill WTW) to 14 mbgl, 17 mbgl, 16 mbgl and 10 mbgl respectively, an emergence of groundwater would be expected inside the open excavation during construction. Appropriate drainage strategies embedded into the design would be implemented to mitigate for flooding within the excavation which would also be expected to adequately cope with any additional rise of groundwater level at the Woodgate Hill WTW Compound following grouting works. During the construction of the shafts, groundwater drawdown would occur down to the base of the excavation, lowering the water table potentially by 52.5 m, 52.5 m, 25.5 m, 13 m, 16 m, 15 m and 9 m respectively for each shaft. 127) Similarly, a drainage strategy to control groundwater ingress would apply to the following shallower excavations:

▪ Open-cut trenches required for pipe connections to 5 mbgl

▪ New meter chamber and new valve house buildings to 5 mbgl

▪ Attenuations ponds to 2 mbgl

▪ The south western section of the shaft platform at Woodgate Hill WTW Compound to 4 mbgl. 128) As shown in Annexe A, the majority of impacts from proposed construction activities are assessed as negligible. Given that the water volumes abstracted during the shaft construction are anticipated to be more significant and some would require a licence, the construction of the three shafts (Bolton Avenue shaft, Haslingden Road double launch shafts and Woodgate Hill WTW Main shaft) is expected to have a minor beneficial impact on groundwater flood risk during construction. 129) In terms of impacts to surface water, Unnamed Watercourse 466 lies in proximity to the Bolton Avenue Connection and new meter chamber. At the Haslingden Road Compound, Unnamed Watercourses 1805 and 2054 are in proximity to the double launch shafts and the River Irwell lies close to the small reception shaft at Townsend Fold WTW Compound. The only watercourse in proximity to the Woodgate Hill WTW Compound is Unnamed Watercourse 608, potentially impacted by the Secondary shaft and Mains Connection excavation. The contribution of baseflow to these watercourses could be locally and temporarily slightly reduced due to dewatering. This is considered likely to have a negligible impact on fluvial flood risk..

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Impact on groundwater flood risk as a result of grouting works 130) Sections of the tunnel that form part of the Proposed Haslingden and Walmersley Section route would be constructed within the Pennine Lower Coal Measures Formation. The Pennine Lower Coal Measures Formation has been subject to significant historical coal mining and this is expected to have left a network of below ground open features, including abandoned and collapsed tunnels and adits. These features are likely to have left the formation relatively unstable. In order to enhance stability and limit losses of drilling fluids and displacement of groundwater during tunnelling, grouting activities would target specific horizons within the Pennine Lower Coal Measures Formation for grout injection aimed at infilling any voids. Grouting would be performed through boreholes drilled in a grid pattern from the surface at three separate grouting areas: Plantation Road mine grouting area, White Carr Lane mine grouting area and Woodgate Hill mine grouting area. 131) Mine grouting has the potential to have short-term and long-term impacts on groundwater flooding.

Short-term impact on groundwater flows as a result of grouting works 132) The targeted voids are expected to be fully saturated. The grouting activity, typically undertaken under pressure, has the potential to displace volumes of groundwater via former mine networks which have not collapsed and generate rapid rise of groundwater levels where vertical pathways may be available (such as former non-backfilled shafts and/or faults) or create/enhance existing surface discharges. This would result in a short-term disruption of groundwater levels and would be limited to the duration of the pressurised grouting.

133) The Outline Mine Grouting Proposal 18 (Appendix 3.2) suggests low risks of significant increases to underground pressures during grouting. However, grouting details and requirements are still to be confirmed. In addition, the Preliminary Mining Risk Assessment19 (Appendix 11.1 and 11.2 of the ES) has indicated the presence of various potential vertical pathways within the assessment area. These could be in connection with the former mine networks proposed to be grouted. As a result, potential horizontal and vertical displacements of groundwater which could reach the surface / sub-surface, whilst unlikely, cannot be ruled out and would result in a short-term potential minor increase in groundwater flooding. This could result in a localised minor negative impact on groundwater flooding. Sensitive receptors could be affected by these localised impacts and as a result, flood risk would be moderate and additional mitigation would be required as detailed within Section 3.6.

Long-term impact on groundwater flows as a result of grouting works 134) It is envisaged that the grouting boreholes would be spaced in accordance with a 4.2 m square grid pattern, with a percentage of additional boreholes installed as “check” boreholes. The proposed extent of grouting either side of the centreline of the tunnel would be 9 m. On this basis, boreholes would be drilled within an 18 m wide corridor for the length of the grouting areas, which is contained within a wider grouting envelope to accommodate working areas. 135) The grouting areas at the three separate sections would be likely to create an impediment to groundwater flow, especially these grouted areas are expected to be perpendicular to the groundwater flow. The shortest section of grouting works is the White Carr section at 200 m long with the Plantation Road section 825 m long and the Woodgate Hill section is 1.3 km long. Each section runs perpendicular to the slope of the ground surface and the expected groundwater flow direction. The horizons targeted by the grouting activities would currently be preferential flow pathways for groundwater and when infilled the grout would create an impediment to groundwater flow at depth. A further impediment to flow would be expected as a result of the grouting boreholes being backfilled with impermeable material on completion of grout injection. 136) Whilst it is likely that groundwater would find alternative flow pathways around the grouted areas (including grouted boreholes) the blockage of preferential flow paths by grouting is likely to result in an increase in groundwater levels upstream of the grouting works, with a decrease in groundwater levels

18 Outline Mine Grouting Proposal, Wardell Armstrong, 2020 19 Preliminary Mining Risk Assessment, Wardell Armstrong, 2020

24 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment

expected on the downgradient side. Following completion of the works, the grout would remain in-situ and therefore, any impacts would be long term in nature. 137) The Plantation Road mine grouting area is relatively long in length but dominated with baseline Low groundwater flooding susceptibility. The White Carr Lane mine grouting area is significantly shorter in length, but the groundwater flooding susceptibility dominates as Very High. Finally, the Woodgate Hill mine grouting area is both long in length and covers variable groundwater conditions including areas where groundwater flooding susceptibility is High. As a result, at all mine grouting areas, this could cause a local change in groundwater levels and flows. This would potentially result in localised minor negative groundwater flooding impacts upgradient of the grouted areas and localised minor beneficial impacts downgradient of the grouted areas. The presence of these vulnerable receptors is accounted for during the assessment of the significance of flood risk as shown in Annexe A. Sensitive receptors could be affected, therefore flood risk would be moderate and additional mitigation measures would be needed, as discussed in Section 3.6.

3.5 Reservoir Flood Risk 138) Reservoir failure can be a particularly dangerous form of flooding as it results in the sudden release of large volumes of water that can travel at high velocity. This can result in deep and widespread flooding, potentially resulting in significant damage. The likelihood of reservoir flooding occurring is however extremely low given that all large reservoirs (over 25,000 m3) are managed in accordance with the Reservoirs Act 1975.

3.5.1 Reservoir flood sources 139) There are several large reservoirs located upstream of the above ground elements of the Proposed Haslingden and Walmersley Section including several within the catchment of the Upper Irwell and the Woodgate Hill Service Reservoirs. No smaller reservoirs that would fall outside of the Reservoirs Act of 1975 have been identified. 140) The Environment Agency’s online reservoir flood mapping (Figure 5) illustrates the maximum flood extents from reservoir failures along the route of the Proposed Haslingden and Walmersley Section.

3.5.2 Reservoir flood risk to enabling and construction activities 141) Reservoirs within the Upper Irwell catchment are upstream of the New Hall Hey and the Townsend Fold WTW Compounds. The Townsend Fold WTW Compound is located entirely within the maximum extent of potential reservoir flooding and would be subject to flood depths of between 0.3 and 2 m; and velocities of between 0.5 and 2 m/s. However, failure of any reservoir in this location is highly unlikely during the enabling and construction phase of the Proposed Haslingden and Walmersley Section. Therefore, the risk to these works is considered to be low. Embedded mitigation including the subscription to Environment Agency Flood Warnings would minimise this risk further. 142) The Woodgate Hill Service Reservoirs are located upstream of proposed connection to the Greater Manchester Supply Network. Again, failure of these reservoirs are highly unlikely during the enabling and construction phase of the Proposed Haslingden and Walmersley Section. Drawdown of these reservoirs is achieved through a combination of discharges into the River Roch via the overflow structure that is shared with the existing Haweswater Aqueduct; discharges into the sewer network; and through the management of flows within the Greater Manchester Supply Network. Therefore, there would be no discharges to any watercourses adjacent to the construction works and the risk to these works from both the routine operation of the reservoir or its failure is considered to be low.

3.5.3 Impact on reservoir flood risk from enabling and construction activities 143) The Proposed Haslingden and Walmersley Section is remote from all the large reservoirs identified within the Upper Irwell. Therefore, no mechanism has been identified by which the Proposed Haslingden and Walmersley Section would increase the likelihood of reservoir failure to these remote reservoirs.

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144) The works within the vicinity of the Woodgate Hill Service Reservoirs include mine grouting that would be approximately 30 m from the reservoir at its closest point whilst the tunnelling activities would be more than 50 m away. Whilst the stabilisation of historic mine workings close to the reservoir should improve reservoir safety by reducing the risk of future ground movement, there is potential that intrusive ground works in such close proximity could impact the reservoir. As such, it would be requirement of the construction contract that the contractor would consult with the Qualified Civil Engineer for the reservoir with regard to all designs and construction method statements. 145) Full details of construction methods are not yet available. However, it is considered that this process of review and supervision of the works by the appointed Panel Engineer for the reservoir would be sufficient and the resulting impact of the enabling and construction phase activities on Woodgate Hill Service Reservoir and the potential impact on reservoir flooding would be negligible.

3.6 Mitigation

3.6.1 Mitigation of impacts on fluvial flooding 146) The assessment has concluded that the risk of flooding to the Townsend Fold WTW Compound would be adequately mitigated through embedded mitigation and good practice detailed within the CCoP. However, the proposed works would result in the loss of floodplain volume and the constriction of flood flows within the River Irwell floodplain, which (without detailed modelling) is assumed to potentially result in large impacts. As a result of these potential impacts, additional mitigation would be required. 147) Due to the absence of detailed flood risk information considered at this stage, the proposed mitigation would initially include a detailed assessment of the fluvial flood risk along the River Irwell at the Townsend Fold WTW Compound location. This would likely be through the analysis of the existing hydraulic model for the River Irwell followed by the modification of this model to include a representation of the Proposed Townsend Fold WTW Compound to enable the impacts to be accurately quantified. Following the outcome of this process, it is likely that a short list of mitigation measures would need to be considered. The focus would be on design developments to avoid development within the floodplain or to reduce the extent of construction in this area. 148) Assuming that one or a combination of the mitigation measures identified were found to be effective and were successfully incorporated into the design of the Proposed Haslingden and Walmersley Section, the impact on flood risk would be negligible.

3.6.2 Mitigation of impacts on groundwater flooding 149) The assessment has demonstrated both short and long-term potential increase in localised groundwater flooding risk as a result of grouting works. 150) The grouting requirements would be refined during the detailed design stage, and a detailed groundwater risk assessment to assess potential impacts on the groundwater environment would be carried out in general accordance with ‘Stabilising Mine Workings With PFA Grouts Environmental Code of Practice’ (BRE BR505, 2009 20 ). This risk assessment would consider both potential impacts on groundwater flow and quality, including potential indirect impacts on receptors such as buildings, existing groundwater abstractions, Groundwater Dependent Ecosystems (GWDTEs) and surface water features. The groundwater risk assessment would consider both short-term and long-term impacts. Where required, the risk assessment would identify additional mitigation measures. Such mitigation measures for short-term impacts could include (but may not be limited to) implementing a Grouting, Groundwater and Surface Monitoring Plan, triggering grouting pressures to be reduced or interrupted to allow groundwater levels to stabilise. 151) Mitigation measures for long-term impacts, if required, could include (but may not be limited to) continuing with groundwater and surface water monitoring and/or introducing groundwater drainage

20 BRE. 2009. Stabilising Mine Workings with PFA Grouts Environmental Code of Practice. BR505

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management which would be embedded into the detailed design phase. This groundwater risk assessment would require approval by the Environment Agency before starting the works. 152) Assuming these mitigation measures identified for grouting were successfully incorporated into the working methods and the design of the Proposed Haslingden and Walmersley Section, the impacts would be negligible.

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4. Commissioning Phase

4.1 Introduction 153) This section of the FRA focuses on both the flood risk to the Proposed Haslingden and Walmersley Section and potential impacts on flood risk as a result of the Proposed Haslingden and Walmersley Section during the commissioning phase. 154) The commissioning flow would be discharged to Heaton Park Reservoir. Water levels prior to and following the commissioning process would be managed in accordance with the normal practices and discharged from the reservoir through the current discharge agreement for the reservoir. This would involve a controlled drawdown of the reservoir by discharging water into the watercourse that runs through Heaton Park and into the Boating Lake before joining the River Irk. The commissioning process would take approximately four to six weeks. 155) As no new infrastructure would be required as part of the commissioning activities and the existing infrastructure would operate in accordance with current arrangements and permits, there would be no new flood risk to the Proposed Haslingden and Walmersley Section from any of the sources of flooding identified. Flood risk impacts associated with the commissioning phase would be negligible for all of the identified flood sources. The commissioning process would be planned and undertaken in consultation with the supervising engineer for the reservoir.

4.2 Groundwater Flood Risk 156) None of the commissioning activities would require any excavations or below ground structures which would intercept groundwater. None of the commissioning activities involve a discharge to ground. Therefore, no mechanism by which groundwater flooding would be altered has been identified.

4.3 Mitigation 157) With Commissioning flows managed using existing infrastructure and in accordance with agreed procedures and discharge limits, no adverse impacts have been identified and no additional mitigation requirements are considered to be necessary.

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5. Operational Phase

5.1 Introduction 158) This section of the FRA focuses on both the flood risk to the Proposed Haslingden and Walmersley Section and potential impacts on flood risk as a result of the Proposed Haslingden and Walmersley Section during the operational phase. In line with Section 2.4, this focuses on fluvial, surface water and groundwater flooding associated with permanent above ground infrastructure, which comprises new valve house buildings with associated hardstanding, kiosk and air valves. The operational phase of the Proposed Haslingden and Walmersley Section is not predicted to have any impact on reservoir flooding and is not considered further.

5.2 Fluvial Flood Risk

5.2.1 Fluvial flood risk to operational activities 159) All permanent infrastructure, including above ground installations, associated with the operational activities would be located within Flood Zone 1. Therefore, the risk of flooding from Main Rivers to operational activities is low. All permanent above ground infrastructure are also located in areas that are at low risk of fluvial flooding from any Ordinary Watercourses, as inferred from the Risk of Flooding from Surface Water Mapping.

5.2.2 Impact on fluvial flood risk from operational activities 160) Without mitigation, operational phase activities assessed could potentially result in fluvial flood risk impacts associated with permanent increase in runoff rates entering watercourses due to an increase in hard standing associated with new valve house buildings. 161) The new valve house buildings would result in an increase in impermeable area. The existing valve house buildings would be retained at each location. An additional small access building may be required at the Haslingden Road Compound to provide secure access to valves located in the construction shafts. Operational access to these buildings would be via access roads. There are currently no proposals to discharge runoff from these features into a watercourse. Therefore, the impacts on surface water runoff from these features is assessed in Section 5.3.

5.3 Surface Water Flood Risk

5.3.1 Surface water flood risk to operational activities 162) Whilst the valve house buildings at the Woodgate hill would be located within an area with a probability of flooding of less than 0.1 % AEP, the valve house building at Bolton Avenue would be located within an area that is predicted to flood to depths of up to 900 mm during the 3.33 % AEP surface water flood event. Good practice measures to mitigate this risk would be embedded into the detailed design of the valve house building and associated surface water drainage systems. Therefore, although the baseline flood risk within the Bolton Avenue area is high, the residual risk to the valve house building at Bolton Avenue would be low.

5.3.2 Impact on surface water flood risk from operational activities 163) The proposed locations for the new valve house buildings are existing greenfield sites currently comprising grassland. Each of the permanent valve house buildings would increase the area of impermeable surfaces by approximately 200m2 and therefore increase the rate of surface water runoff. Uncontrolled, any increase in runoff could increase the risk of surface water flooding downstream through the surface water catchment or to the discharge location. 164) At the time of preparing this FRA, no surface water management strategies have been prepared for the permanent valve house buildings. It is however assumed, that surface water management strategies would be developed post planning and would follow the same principles as those outlined in Annexe D,

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where surface water would be discharged to the ground as a first preference. This drainage system would be designed to take account of the high level of surface water risk identified at this location. 165) As these are permanent features, it would be expected that the drainage design would incorporate the impacts of climate change and as a result the impacts would be negligible over the design life of the Proposed Haslingden and Walmersley Section.

5.4 Groundwater Flood Risks

5.4.1 Groundwater flood risk to operational activities 166) As shown on Figure 4, although the valve house buildings at the Woodgate Hill WTW would be within an area with a Low susceptibility to groundwater flooding, the valve house building at Bolton Avenue would be located within an area with a Very High susceptibility to groundwater flooding with potential for groundwater to emerge at the ground surface. In both locations additional ground and groundwater site characterisation would be obtained. Following detailed site characterisation, any mitigation associated with controlling groundwater conditions, if required, would be embedded into the design of these buildings to ensure that it would be safe from flooding for the life of the Proposed Haslingden and Walmersley Section. 167) Therefore, whilst the baseline risk to the valve house building at Bolton Avenue is high based on BGS data, it is assumed that the risk to the valve house building with its embedded mitigation would be low and no additional mitigation is required.

5.4.2 Impacts on groundwater flood risk arising from operational activities 168) Grouted areas (as explained in more details in Section 3.4.3) and excavation backfill, could locally disturb groundwater flows. The impact associated with grouted areas would remain the same as the long-term impacts described during the construction phase. The mitigation would be the same as for the construction phase and is detailed in Section 3.6. 169) Backfilled trenches with gravel materials have the potential to act as a localised drain for groundwater and locally lower groundwater levels. 170) The excavation required to level the ground for the construction of the shaft platform at Woodgate Hill WTW may not be backfilled following construction, once the platform structure has been removed. This could lead to increased infiltration to ground or localised accumulation of water should the conditions be saturated. This would result in a very localised change that has no impact at wider scale. 171) Impacts for the majority of the operational impacts are assessed as negligible as shown in Annexe A, which includes shafts creating barriers to groundwater flow, backfilled trenches and the reinstated attenuation pond acting as localised drains for groundwater and the side slope excavation required for the Woodgate Hill WTW shaft Platform.

5.5 Mitigation 172) The mitigation described in Section 3.6 addressing groundwater flooding impacts due to grouting covers long-term impacts and therefore remains applicable during the operational phase. Assuming that the design of the valve house building at Bolton Avenue takes into account the risk of surface water and groundwater flooding, no additional mitigation would be required.

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6. Decommissioning Phase

6.1 Introduction 173) This section of the FRA focuses on the potential impacts on flood risk as a result of the decommissioning of the existing aqueduct in the Proposed Haslingden and Walmersley Section and the ongoing discharge of groundwater ingress into River Roch. This section focuses on fluvial and groundwater flood risk impacts only as no surface water flood sources would be affected.

6.2 Fluvial Flood Risk

6.2.1 Impact on fluvial flood risk from decommissioning activities 174) As part of the Proposed Haslingden and Walmersley Section, the existing section of aqueduct would be decommissioned. This section of the Haweswater Aqueduct showed signs of groundwater ingress occurring during condition assessments carried out in 2016. The proposed strategy to manage this ingress of groundwater would be to allow it to flow into River Roch via the existing overflow structure. 175) Using observed data and a Monte Carlo analysis, United Utilities have estimated the rate of groundwater ingress into the decommissioned aqueduct up to the year 2055, as presented in Table 4. Future uncertainties have limited the ability to provide a realistic forecast beyond 2055. United Utilities would continue to monitor the tunnel condition. 176) To assess the potential impact of these groundwater discharges from the decommissioned Haweswater Aqueduct into River Roch, a comparison has been made to QMED21 and Q1022 predicted flow rates at the discharge location within River Roch, as presented in Table 4. Table 4: Comparison of groundwater discharge and peak flows within the River Roch

River Roch Peak Flow Groundwater Discharge Estimate for Percentage Increase in Peak Flow 2055

Mean Maximum Mean Maximum

Q10 9.65 m3/s 0.061 m3/s 0.132 m3/s +0.64 % +1.37 % QMED 52.5 m3/s 0.061 m3/s 0.132 m3/s +0.12 % +0.25 %

177) Table 4 shows that even the maximum estimated discharge from the decommissioned aqueduct would be a negligible contribution to the QMED flow in River Roch (less than 1 % of QMED flows). The additional contribution of flow would also not be enough to increase the Q10 flow to the point where it could be considered a flood flow. 178) Given the negligible contribution that discharges from the decommissioned aqueduct would make to fluvial flood flows, the impact on flood risk downstream of the Proposed Haslingden and Walmersley Section is also considered to be negligible.

6.3 Groundwater Flood Risks

6.3.1 Impacts on groundwater flood risk arising from decommissioning activities 179) Once the new aqueduct is operational, the existing aqueduct would be decommissioned but remain in place. Ingress of groundwater into the existing aqueduct could occur over time representing a small

21 QMED is the median of the annual maximum flow series which is equivalent to the 50 % Annual Exceedance Probability event and is used as an approximation of bank full flow. 22 Q10 is the 90-percentile flow or the flow equalled or exceeded for 10 % of the flow record.

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dewatering rate, as described in Chapter 7: Water Environment of the ES. This would be expected to generate a small, long-term groundwater drawdown over the length of the aqueduct. 180) Decommissioning of the existing aqueduct has the potential to generate a minor beneficial impact to groundwater flooding due to the relatively small rate of inflow to the tunnel and associated drawdown at the aquifer scale as shown in Annexe A. Although no significant groundwater flood risk has been identified in this area, several high value receptors are located in proximity to the existing aqueduct including residential dwellings and a sewage treatment site.

6.4 Mitigation 181) Due to the negligible magnitude of impacts associated with the decommissioning of the existing aqueduct, no additional mitigation requirements have been identified.

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7. Summary and Conclusion

7.1 Summary 182) This FRA has been prepared to support the planning applications for the Haslingden and Walmersley Section of the Haweswater Aqueduct Resilience Programme (the Proposed Haslingden and Walmersley Section), which is located towards the southern extent of the aqueduct. This extends from Huncoat, east of Accrington in the north to Woodgate Hill Water Treatment Works (WTW). 183) This FRA has been carried out in accordance with the NPPF and its PPG. Complying with planning policy will promote a Scheme that would be appropriate given the level of local flood risks, would be safe during the construction and operational phases of its lifetime, and would not increase flood risk both on site and elsewhere. It has been carried out in combination with the Proposed Haslingden and Walmersley Section design development through the EIA process and informs Chapter 9: Flood Risk of the ES. 184) The Proposed Haslingden and Walmersley Section is classified as ‘water transmission infrastructure’ and is therefore considered within the NPPF to be a ‘water compatible development’ that is suitable in all areas of flood risk providing that it is safe, can operate in times of flood and does not increase flood risk elsewhere. 185) Given the generally low levels of flood risk identified during the scoping phase assessment, this FRA focuses on the key flood risks and potential impacts that have been confirmed to be present within the assessment area: fluvial, surface water, groundwater and reservoir flooding. 186) For most of the length of the replacement aqueduct, there would be no permanent above-ground structures with much of the new sections of aqueduct being located deep below ground level. The assessment therefore focuses on the following key high risk or high impact activities or features associated with the construction and operation of the Proposed Haslingden and Walmersley Section in addition to the decommissioning of the existing aqueduct including:

▪ Temporary compound sites, associated features, construction access tracks and surface water drainage associated with the enabling and construction phase

▪ Stabilisation works at mine grouting areas

▪ Management of groundwater intercepted during excavation works including construction of the shafts, tunnelling and the open cut trenches to connect the new tunnel to the existing aqueduct

▪ The commissioning of the proposed tunnel by flushing the section through with potable water that would be discharged to the Heaton Park Reservoir

▪ The operation of permanent above ground infrastructure (valve house buildings and air valves)

▪ Permanent discharge of groundwater from the decommissioned aqueduct. 187) Using readily available national flood risk datasets, the FRA concludes that the level of flood risk to the Proposed Haslingden and Walmersley Section is low from all sources of flooding with the exception of the Townsend Fold WTW Compound and the Bolton Avenue Compound and valve house building. Proposed assets and activities are generally located away from areas of high flood risk, in Flood Zone 1 or in areas with a low probability of flooding from other sources. However, the Townsend Fold WTW Compound would be located within Flood Zone 3 and additional mitigation would be required to ensure that it would be safe from flooding by the River Irwell. The Bolton Avenue valve house building is also located in an area with high risk from groundwater and surface water and would also require additional mitigation embedded within its design. 188) The main impact on flood risk would be associated with the construction of the Townsend Fold WTW Compound which has the potential to displace floodplain storage and constrict floodplain flows. Additional mitigation relating to the impact of this element of the development would focus on optimisation of the design to avoid or reduce impacts on the floodplain. If the works could not be moved a detailed assessment based on hydraulic modelling would be undertaken. However, it is assumed that

33 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment

effective mitigation of risks and impacts would be possible. Table 5 provides a summary of flood risk assessment. 189) As a result of the groundwater flooding assessment, the only significant adverse groundwater flooding impacts expected would be from mine grouting works during the enabling phase. For each grouting area, the short term impact on groundwater flood risk during the enabling phase would be minor adverse due to the displacement of groundwater potentially discharging at the surface from the injection of grout. In the long term, the rise in groundwater levels upgradient of the structure could impact works resulting in a minor adverse impact during the construction and operational phases. 190) In terms of beneficial impacts to groundwater flood risk, a minor beneficial potential impact is assessed for three shafts (Bolton Avenue Compound shaft, Haslingden Road Compound double launch shafts and Woodgate Hill WTW Compound main shaft) during the construction phase due to dewatering. A lowering of the water table is also expected downgradient of the grouting areas resulting in a minor beneficial impact on groundwater flood risk in the long-term. The decommissioning of the existing aqueduct is assessed as a minor beneficial impact due to a relatively small rate of water ingress lowering the water table potentially reducing the groundwater flood risk to highly vulnerable receptors. Table 5: Flood risk assessment summary Phase Flood Assessment Fluvial Surface Water Groundwater Reservoirs Flood Risks High Low Low Low Enabling and Flood Risk Impacts Large Negligible Moderate Negligible Construction (adverse) Additional Mitigation Yes No Yes No Flood Risks Low Low Not Low applicable Flood Risk Impacts Negligible Negligible Not Negligible Commissioning applicable Additional Mitigation No No Not No applicable Flood Risks Low Low Low Low Flood Risk Impacts Negligible Negligible Moderate Negligible Operation (adverse) Additional Mitigation No No Yes No Not Minor Not Flood Risk Impacts Negligible applicable (beneficial) applicable Decommissioning Not Not Additional Mitigation No No applicable applicable

191) A key assumption of this assessment is that in addition to embedded mitigation measures the elements of the Proposed Haslingden and Walmersley Section that have not yet been designed in detail, would be designed using appropriate flood design standards and good practice to help mitigate the flood risks and potential Proposed Haslingden and Walmersley Section impacts. The CCoP has been produced to provide an overview of appropriate flood design principles, standards and good practice to be considered at later stages of the design process. With embedded mitigation and good practice applied within the design of these assets and activities it is assumed that they would remain safe from flooding and would not impact flood risk elsewhere. 192) As part of this good practice mitigation, and specific to the Haslingden and Walmersley Section of the HARP, it is recommended that all designs and construction method statements associated with the mine grouting areas within the vicinity of Woodgate Hill Service Reservoirs would need to be reviewed by the

34 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment

appointed Panel Engineer and that the use of Heaton Park Reservoir during the commissioning phase would also be undertaken in accordance with the supervising engineer for this reservoir.

7.2 Cumulative Impacts 193) As identified in Section 1.2, the Proposed Haslingden and Walmersley Section is part of a wider project to replace the tunnelled sections of the Haweswater Aqueduct. Therefore, consideration has been given to the potential for multiple project sections to have a cumulative impact on flood risk. The north of the Proposed Haslingden and Walmersley Section is located within the River Ribble catchment as are the Bowland and Marl Hill sections of the wider Haweswater Aqueduct Resilience Programme. 194) Discharges into the Ribble catchment from the Proposed Haslingden and Walmersley Section would be limited to construction phase discharges from the Bolton Avenue Compound and potential operational discharges of surface water runoff from the proposed valve house building at this location. This FRA has concluded that the attenuation of all surface water and groundwater discharges into the Ribble catchment would result in a negligible impact on runoff rates within the receiving watercourses. Impacts on the River Ribble further downstream would therefore, also be negligible and therefore no potential adverse cumulative effects with the other sections of the Proposed Programme of Works have been identified within this catchment. 195) No other sections of the Proposed Programme of Works discharge to the River Irwell or River Roch catchments. Therefore, this is no potential for cumulative impacts within these rivers. 196) Two developments within 5 km of the Proposed Haslingden and Walmersley Section have been identified as having the potential to change groundwater levels or flows. Scout Moor Quarry, an Inert Landfill development is located up groundwater gradient, approximately 0.7 km from the Proposed Haslingden and Walmersley Tunnel route and Whinney Hill Landfill, a Non-Hazardous Landfill is located approximately 0.7 km to the north-west of the Proposed Bolton Avenue Compound. No adverse impacts to groundwater flooding from the Proposed Haslingden and Walmersley Section are predicted within the vicinity of these developments. Therefore, cumulative impacts on groundwater levels and flows from these developments would be unlikely resulting in no cumulative effects for the groundwater flood risk.

7.3 Conclusion 197) In conclusion, based on the assumption that embedded mitigation is effectively designed and implemented and that good practice is applied to the design and construction of scheme components not yet designed, the Proposed Haslingden and Walmersley Section has been assessed to be generally safe from flooding throughout its operational life and would generally not increase the risk of flooding elsewhere. However, additional mitigation measures would be required including:

▪ Design optimisation of the Townsend Fold WTW compound to avoid the floodplain of the River Irwell or a detailed assessment undertaken to inform the design of measures to mitigate any impact on flood risk associated with the River Irwell

▪ Detailed assessment of the temporary and permanent impacts of mine grouting on groundwater flood risk. If adverse impacts are predicted, this assessment would be used to design measures to mitigate the predicted impacts. 198) With this additional mitigation in place, the Proposed Haslingden and Walmersley Section would comply with the requirements of the NPPF and with the requirements of local planning policies and guidance.

35 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment

Annexe A: Flood Risk Assessment Tables

36

fhar d

Haweswater Aqueduct Resilience Programme - Proposed Haslingden and Walmersley Section

Environmental Statement

Volume 4

Appendix 8.1: Flood Risk Assessment

Annexe A: Flood Risk Assessment Tables

May 2021

Floo d Risk Assessment - Hasling den & Walmersley Secti on

United U tilities

Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Haweswater Aqueduct Resilience Programme - Proposed Haslingden and Walmersley Section

Project No: B27070CT Document Title: Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables Document Ref.: HBC_RBC_BMBC-HW-TA-008-001 Revision: 0 Date: May 2021 Client Name: United Utilities Water Ltd

Jacobs U.K. Limited

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© Copyright 2021 Jacobs U.K. Limited. The concepts and information contained in this document are the property of Jacobs. Use or copying of this document in whole or in part without the written permission of Jacobs constitutes an infringement of copyright.

Limitation: This document has been prepared on behalf of, and for the exclusive use of Jacobs’ client, and is subject to, and issued in accordance with, the provisions of the contract between Jacobs and the client. Jacobs accepts no liability or responsibility whatsoever for, or in respect of, any use of, or reliance upon, this document by any third party.

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Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Contents

1. Fluvial flood risk – Enabling and Construction Phase Haslingden and Walmersley Section ...... 1 2. Other sources of flood risk – Enabling and Construction Phase Haslingden and Walmersley Section ...... 12 3. Groundwater flood risk - Enabling and Construction Phase Haslingden and Walmersley Section 16 4. Fluvial flood risk – Commissioning Phase Haslingden and Walmersley Section ...... 54 5. Other sources of flood risk – Commissioning Phase Haslingden and Walmersley Section ...... 55 6. Groundwater flood risk – Commissioning Phase Haslingden and Walmersley Section ...... 56 7. Fluvial flood risk – Operational Phase Haslingden and Walmersley Section ...... 56 8. Other sources of flood risk – Operational Phase Haslingden and Walmersley Section ...... 57 9. Groundwater flood risk – Operational Phase Haslingden and Walmersley Section ...... 58 10. Fluvial flood risk – Decommissioning Phase Haslingden and Walmersley Section ...... 81 11. Groundwater flood risk – Decommissioning Phase Haslingden and Walmersley Section...... 82

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Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

1. Fluvial flood risk – Enabling and Construction Phase Haslingden and Walmersley Section

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score

Unnamed The Bolton Avenue High The proposed Bolton Avenue TBM Reception Compound and the associated Neutral Watercourse 466 TBM Reception Flood Zone 1. access track is at low risk of fluvial flooding and does not cross any above ground Compound area and watercourses although a culverted watercourse is present underneath the Ordinary Fluvial flood risk is inferred temporary access compound location. Therefore, the main potential impact would be from changes Watercourse from the Flood Map for road. The shaft is in surface water runoff and discharges of groundwater from excavations Surface Water and approximately 125 m increasing flow within the watercourse. indicates that the to the south-west of probability of flooding Construction compound sites have the potential to increase surface water runoff the watercourse and from this watercourse is due to an increase in impermeable surfaces and the potential to alter flood flow the surface water greater than or equal to routes as the result of temporary buildings and/or the installation of drainage attenuation lagoon is 3.33% AEP. systems. These activities have the potential to increase runoff rates entering located around 30 m Unnamed Watercourse 466. to the south-west of The surrounding land is Surface water runoff from the proposed TBM Reception Compound would this watercourse. woodland but approximately 150 m however be captured and attenuated within a storage lagoon prior to discharge A culverted downstream (north) of the into the Unnamed Watercourse 466 at a maximum rate of 5 l/s. The attenuation watercourse is proposed compound, the of runoff would ensure that there would be a small increase in peak flows in this present below the watercourse is culverted watercourse 466 and that the magnitude of effects would be negligible. proposed compound beneath the Preston to location Deep excavations during the construction phase in this area include the TBM Neutral Colne railway. reception shaft and an open cut trench to connect the new tunnel to the existing infrastructure. Groundwater intercepted during construction would be discharged into Unnamed Watercourse 466 via the storage lagoon and treatment plant used to manage surface water runoff. Groundwater flows are predicted to be less than 1 l/s and the attenuation of these flows through the storage lagoon would ensure that the impact on fluvial flood risk downstream of the discharge location would be negligible. Unnamed The potential access Low The mine grouting works would be located outside of the areas of fluvial flood Neutral Watercourse 1692 road to the Plantation Flood Zone 1. risk as indicated by surface water flood risk mapping. The access road to these Road mine grouting mine grouting works follows an existing track and would cross this watercourse at

1 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score Ordinary area intersects this Fluvial flood risk is inferred an existing crossing. It is assumed that no change would be needed to the existing Watercourse watercourse. from the Flood Map for crossing. Therefore, the impact on fluvial flood risk downstream would be Surface Water and negligible. indicates that the probability of flooding from this watercourse is greater than 0.1% AEP. Land use adjacent to the access road is agricultural. River Hyndburn Plantation Road mine Very High The mine grouting works would be located outside of the areas of fluvial flood Neutral Ordinary grouting area and its Flood Zone 1. risk as indicated by surface water flood risk mapping. The grouting of mine access road intersects workings beneath this watercourse would be undertaken using angled, rather Watercourse Fluvial flood risk is inferred this watercourse. than vertical drilling techniques to ensure that works would be located outside of (becomes Main from the Flood Map for the floodplain. The access road to these mine grouting works follows an existing River around 600 m Surface Water and road and would cross this river. It is assumed that no change would be needed to downstream from indicates that the the existing crossing on the unnamed road to Plantation Road. the mining probability of flooding stabilisation area) from this watercourse is The stripping of topsoil and compaction of soils along the corridor within which greater than or equal to the mine grouting works would take place would reduce infiltration rates and 3.33% AEP. have the potential to increase runoff rates into the River Hyndburn. These potential increases in flow would increase risk to downstream residential Land use adjacent to the properties. However, development of temporary drainage strategies in line with stabilisation works is the principles detailed within the Construction Code of Practice (CCoP) in woodland but residential Appendix 3.3 including maintaining existing flow paths and attenuating any properties are present increase in runoff rate would ensure that the magnitude of any short-term effects downstream. would be negligible. Unnamed Plantation Road mine Very High The mine grouting works would be located outside of the areas of fluvial flood Neutral Watercourse 1970 grouting area and its Flood Zone 1. risk as indicated by surface water flood risk mapping. The grouting of mine including tributaries access road intersects workings beneath this watercourse would be undertaken using angled, rather Fluvial flood risk is inferred Unnamed this watercourse and than vertical drilling techniques to ensure that works would be located outside of from the Flood Map for the two tributaries. the floodplain. The access road to these mine grouting works follows an existing Surface Water and

2 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score Watercourses 1690 indicates that the track and would cross this watercourse 1970 but it is assumed that no change and 481 probability of flooding would be needed to the existing crossing. Ordinary from this watercourse is The stripping of topsoil and compaction of soils along the corridor within which Watercourse greater than or equal to the mine grouting works would take place would reduce infiltration rates and 3.33% AEP. have the potential to increase runoff rates into this watercourse. These potential Land use adjacent to the increases in flow would increase risk to downstream residential properties. stabilisation works is However, development of temporary drainage strategies in line with the woodland but residential principles detailed within the CCoP including maintaining existing flow paths and properties are present attenuating any increase in runoff rate would ensure that the magnitude of any downstream. short-term effects would be negligible. Unnamed This watercourse High The proposed Haslingden Road TBM double drive Compound including the Neutral Watercourse 2054 emerges from a Flood Zone 1. office, welfare and parking facilities to the south of the watercourse; and the shaft (also known as culvert and flows and material storage areas to the south of the watercourse are at low risk of Fluvial flood risk is inferred Langwood Brook) through the fluvial flooding. There is potential for increases in surface water runoff and from the Flood Map for Haslingden Road discharges of groundwater from excavations increasing flow within the Ordinary Surface Water and Compound area watercourse. Watercourse indicates that the before entering probability of flooding Construction compound sites have the potential to increase surface water runoff another culvert from this watercourse is due to an increase in impermeable surfaces and the potential to alter flood flow beneath the A682. greater than or equal to routes as the result of temporary buildings and/or the installation of drainage The surface water 3.33% AEP. The floodplain systems. These activities have the potential to increase runoff rates entering drainage serving the however appears to be watercourse 2054, which would increase flood risk downstream to residential compound includes very narrow and not much properties along Holme Lane. two attenuation wider than the channel Surface water runoff from the proposed Haslingden Road Compound would lagoons (around itself. however be captured and attenuated by a surface water drainage system that 12 m to the east and would discharge runoff from the access road, offices, welfare and car parking area west of this This watercourse to this watercourse. The discharge would be at greenfield runoff rates (maximum watercourse) that discharges into the River rate of 23 l/s) via a storage lagoon and from the tunnelling site compound and would discharge into Irwell around 300 m to the access road via the attenuation tanks. The attenuation of runoff would ensure that this watercourse via east of the Proposed there would be no increase in peak flows in this watercourse and the magnitude two separate outfalls. of the effects would be negligible.

3 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score

Haslingden and Deep excavations in this area during the construction phase include the TBM Neutral Walmersley Section. double drive shafts and a new tunnel to connect to an existing United Utilities The land surrounding the facility. Groundwater intercepted (predicted to be between 2 and 3 l/s) during watercourse is scrubland construction would be discharged into this watercourse. The management of or rough grazing. these flows through the attenuation tanks would ensure that the impact on fluvial The A56 road passes flood risk downstream of the discharge location would be negligible. above the upstream culvert and the A682 road passes above the downstream culvert around 20 m to the east. Unnamed The Haslingden Road Low The proposed Haslingden Road TBM double drive Compound is at low risk of Neutral Watercourse 1805 Compound area with Flood Zone 1. fluvial flooding from this watercourse, which is the tributary of watercourse 2054. Ordinary temporary site access The Proposed Haslingden and Walmersley Section is remote from this Fluvial flood risk is inferred Watercourse road. The shafts are watercourse and no effects are predicted. The magnitude of flood risk effects is from the Flood Map for around 125 m to the therefore considered to be negligible. Surface Water and south-west and indicates that the 250 m to the east probability of flooding from the confluence from this watercourse is of this watercourse less than 0.1% AEP. This and watercourse watercourse and flows 2054. adjacent to All Saints Roman Catholic Language School from the north and then flows through woodland adjacent to the school before it discharges into watercourse 2054.

4 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score

River Irwell This Main River flows Very High The proposed New Hall Hey Compound TBM drive and reception Compound Very Large Main River in between the New Flood Zone 3. (north bank) is located within Flood Zone 1. However, the proposed Townsend Hall Hey Compound Fold WTW TBM reception Compound (south bank compound) is located entirely The River Irwell floodplain on the northern bank within Flood Zone 2 and partially within Flood Zone 3. A sheet pile wall would be is well defined in this reach and the Townsend constructed to facilitate the establishment of a level working platform around the of the river with an area Fold WTW Compound compound. This sheet pile wall would encroach into Flood Zone 3 along the approximately 40 m wide on the southern river southern (left) bank of the River Irwell. at a greater than or equal bank. to the 1% AEP flood event. Due to the confined nature of the floodplain of the River Irwell in this location, the This flood plain would sheet pile wall within the Flood Zone 3 would have the potential to act as a extend approximately restriction to floodplain flow and would reduce the volume of floodplain storage 3 150 m between the 0.1% by approximately 190 m . Whilst the impact of these effects has not been and 1% AEP flood event. quantified through hydraulic modelling, it is likely to result in an increase in flood depths upstream with potential impacts on the flood extents and the frequency of The land surrounding the flooding. It is noted that any potential impacts would be temporary and limited to watercourse is urban the duration of the construction phase, after which the site would be restored to including non-residential its baseline condition. However, without further detailed assessment, it is properties immediately assumed that the impact would be major and that further mitigation would be downstream of the required. Proposed Haslingden and Walmersley Section with As part of the environmental permitting process, a detailed assessment of flood residential properties risk in this area based on hydraulic modelling would need to be undertaken in located further consultation with the EA to confirm the level of risk to the Proposed Haslingden downstream. and Walmersley Section and the flood risk impacts. It is likely that mitigation measures would need to be considered. These would focus on the optimisation of the compound design to avoid any adverse impacts.

5 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score

Construction compounds have the potential to increase surface water runoff due Neutral to an increase in impermeable surfaces and the potential to alter flood flow routes as the result of temporary buildings and/or the installation of drainage systems. It is assumed that surface water runoff from the proposed Townsend Fold WTW TBM reception Compound would however be attenuated at greenfield run off rate and discharge to the ground or to the River Irwell. The attenuation of runoff would ensure that there would be no increase in peak flows in this watercourse and the impact on fluvial flood risk to receptors downstream would be negligible. Deep excavations in this area during the construction phase include the TBM drive Neutral and reception shafts and an open cut trench to connect to an existing United Utilities facility. Groundwater intercepted (predicted to be between 2 and 3 l/s) during these excavations would be discharged into this watercourse. The management of these flows through the attenuation tanks would ensure that the impact on fluvial flood risk downstream of the discharge location would be negligible. Balladen Brook This watercourse is High Construction compounds have the potential to increase surface water runoff due Neutral Ordinary around 70 m to the Flood Zone 3 (associated to an increase in impermeable surfaces and the potential to alter flood flow Watercourse south of the with the River Irwell). routes as the result of temporary buildings and/or the installation of drainage Townsend Fold WTW systems. These activities have the potential to increase runoff rates entering The River Irwell Flood Compound TBM Balladen Brook, which would increase flood risk to non-residential properties Zone 3 floodplain is well reception shaft. along Holme Lane. defined and approximately 40 m wide during the 1% The existing access road to the compound area in this location would be at risk of AEP flood event upstream fluvial flooding. However, it is assumed that suitable mitigation would be in place to the Balladen Brook to limit impacts on flood risk to constriction of the watercourse due to increased confluence and 30 m surface water runoff rates into the watercourse. downstream of it. At the It is assumed that surface water runoff from the proposed TBM reception confluence the floodplain Compound would however be attenuated to greenfield run off rate prior to extends upstream along discharge to the ground or to a watercourse. The attenuation of runoff would Balladen Brook to create

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Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score an area of floodplain ensure that there would be no increase in peak flows in this watercourse and the approximately 110 m impact on fluvial flood risk to receptors downstream would be negligible. wide. Fluvial flood risk is also inferred from the Flood Map for Surface Water upstream of the confluence and indicates that the probability of flooding from this watercourse is greater than or equal to 3.33% AEP. This flooding would impact Holme Lane. The land surrounding the watercourse is urban including non-residential properties in the close proximity of the Proposed Haslingden and Walmersley Section. Unnamed The potential access High The mine grouting works would be located outside of the areas of fluvial flood Neutral Watercourse 582 road to the White Carr Flood Zone 1. risk as indicated by surface water flood risk mapping. The access road to these Lane mine grouting mine grouting works follows an existing track and would cross this watercourse at Ordinary Fluvial flood risk is inferred area intersects this an existing crossing. No change would be needed to the existing crossing. Watercourse from the Flood Map for watercourse. Therefore, the impact on fluvial flood risk downstream would be negligible. Surface Water and indicates that the probability of flooding from this watercourse is

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Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score greater than or equal to 3.33% AEP. Land use adjacent to the access road is agricultural. Pigs Lee Brook White Carr Lane mine Very High The mine grouting works would be located outside of the areas of fluvial flood Neutral Ordinary grouting area is to the Flood Zone 1. risk as indicated by surface water flood risk mapping. The access road to these south of the mine grouting works follows White Carr Lane and would cross this river but no Watercourse Fluvial flood risk is inferred watercourse but the change would be needed to the existing crossing. including the from the Flood Map for potential access road tributary Unnamed Surface Water and The stripping of topsoil and compaction of soils along the corridor within which to the White Carr Watercourses 995 indicates that the the mine grouting works would take place would reduce infiltration rates and Lane mine grouting and 587 probability of flooding have the potential to increase runoff rates into the brook. These potential area intersects this from this watercourse is increases in flow would increase risk to downstream residential properties. watercourse. greater than or equal to However, development of temporary drainage strategies in line with the 3.33% AEP. principles detailed within the CCoP including maintaining existing flow paths and attenuating any increase in runoff rate would ensure that the magnitude of any Land use adjacent to the short-term effects would be negligible. stabilisation works is agricultural but the M66 is located downstream. Unnamed White Carr Lane mine Very High The mine grouting works would be located outside of the areas of fluvial flood Neutral Watercourse 589 grouting area is to the Flood Zone 1. risk as indicated by surface water flood risk mapping. north of the Ordinary Fluvial flood risk is inferred The stripping of topsoil and compaction of soils along the corridor within which watercourse. Watercourse from the Flood Map for the mine grouting works would take place would limit infiltration rates and have Surface Water and the potential to increase runoff rates into the brook. These potential increases in indicates that the flow would increase risk to downstream residential properties in Walmersley. probability of flooding However, development of temporary drainage strategies in line with the from this watercourse is principles detailed within the CCoP including maintaining existing flow paths and less than 1% AEP. attenuating any increase in runoff rate would ensure that the magnitude of any short-term effects would be negligible. Land use adjacent to the stabilisation works

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Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score comprises a golf course and the M66 downstream. Gipsy Brook The Woodgate Hill Very High The proposed Woodgate Hill WTW TBM Reception Compound is at low risk of Neutral Ordinary WTW Compound area. Flood Zone 1. fluvial flooding from this watercourse. Therefore, the main impact would be from The shaft is around changes in surface water runoff and discharges of groundwater from excavations Watercourse Fluvial flood risk is inferred 320 m to the south- increasing flow within the receiving watercourse. including the from the Flood Map for east from this tributary Unnamed Surface Water and Construction compounds have the potential to increase surface water runoff due watercourse. Watercourses 602 indicates that the to an increase in impermeable surfaces and the potential to alter flood flow and 605 Woodgate Hill mine probability of flooding routes as the result of temporary buildings and/or the installation of drainage grouting area and its from this watercourse is systems. access road intersects greater than or equal to Surface water runoff from the proposed TBM Reception Compound would this watercourse and the 3.33% AEP. however be captured and attenuated by a surface water drainage system that Unnamed The land surrounding the would discharge runoff to this watercourse at a maximum rate of 5.5 l/s. The Watercourse 602. watercourse is woodland attenuation of runoff would ensure that there would be a negligible increase in and agricultural land in the peak flows in this watercourse and that any increase to fluvial flood risk to close proximity of the receptors downstream including the M66 would be negligible. Proposed Haslingden and Deep excavations in this area include the TBM Reception shaft and the tunnel Neutral Walmersley Section. itself. Groundwater from these excavations would be discharged into Gipsy Brook The M66 is approximately via the treatment plant used to manage surface water runoff. Groundwater flows 30 m to downstream from from each of the excavations are predicted to be around 1.38 l/s and the the proposed surface management of these flows through the storage lagoon would ensure that the water drainage outfall to impact on fluvial flood risk downstream of the discharge location would be Gipsy Brook. negligible. The mine grouting works themselves including its access road (without crossing Neutral Gipsy Brook) would be located within areas of fluvial flood risk as indicated by the Flood Map for Surface Water. Therefore, embedded mitigation outlined in the CCoP including the use of angled drilling, timing the works to avoid periods of high flow, keeping works within the floodplain to a minimum and emergency procedures to respond to a flood event would be required to ensure that the risk

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Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score to the works would be low. These works would be subject to land drainage consents from Bury Council. The stripping of topsoil and compaction of soils along the corridor within which the mine grouting works would take place would reduce infiltration rates and have the potential to increase runoff rates into the watercourse. These potential increases in flow would increase risk to downstream residential properties. However, development of temporary drainage strategies in line with the principles detailed within the CCoP including maintaining existing flow paths and attenuating any increase in runoff rate would ensure that the magnitude of any short-term effects would be negligible. Unnamed The Greater Very High The proposed Greater Manchester Supply Network Tunnel reception is at low risk Neutral Watercourses 608 Manchester Supply Flood Zone 1. of fluvial flooding from these watercourses. Therefore, the main impact would be and 607 converge Network Tunnel from changes in surface water runoff increasing flow within the watercourses, or Fluvial flood risk is inferred the south-west from reception shaft is through impacts associated with works required to undertake open cut trench from the Flood Map for the construction around 25 m to the crossing of the watercourse. Surface Water and compound area west from indicates that the The design of the temporary works associated with the open cut trench crossing boundary watercourse 608. probability of flooding has not yet been finalised. However, embedded mitigation set out in the CCoP Ordinary A section of open cut from these watercourses is including the appropriate sizing of flumes or diversion channels would ensure Watercourses trench would then less than 1% AEP. that any increase in upstream flood risk due to constriction of flows would be cross this watercourse negligible. The land at the proposed to enable the trench crossing is Construction compounds have the potential to increase surface water runoff due Neutral connection of the undeveloped but to an increase in impermeable surfaces and the potential to alter flood flow tunnel into the residential property is routes as the result of temporary buildings and/or the installation of drainage existing Greater located downstream. systems. Manchester Supply network. A temporary Surface water runoff from the proposed TBM Reception Compound would track would run however be captured and attenuated by a surface water drainage system that alongside the trench would discharge runoff to Gipsy Brook greenfield runoff rate or at a maximum to facilitate its rate of 5 l/s via the water treatment plant. The attenuation of runoff would ensure construction and this that there would be a negligible increase in peak flows in this watercourse and

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Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score track would cross the that the effect on fluvial flood risk to receptors downstream would also be watercourse negligible. Woodgate Hill mine grouting area runs across this watercourse 608.

The mine grouting works would be located outside of the areas of flood risk as Neutral indicated by surface water flood risk mapping. The grouting of mine workings beneath this watercourse would be undertaken using angled, rather than vertical drilling techniques to ensure that works would be located outside of the floodplain. The mine grouting works would be located outside of the areas of flood risk as indicated by surface water flood risk mapping. The grouting of mine workings beneath this watercourse would be undertaken using angled, rather than vertical drilling techniques to ensure that works would be located outside of the floodplain. Therefore, the main impact would be changes to runoff rates into the watercourse. The stripping of topsoil and compaction of soils along the corridor within which the mine grouting works would take place would limit infiltration rates and have the potential to increase runoff rates into this watercourse. These potential increases in flow would increase risk to downstream residential properties. However, development of temporary drainage strategies in line with the principles detailed within the CCoP including maintaining existing flow paths and attenuating any increase in runoff rate would ensure that the magnitude of any short-term effects would be negligible.

11 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

2. Other sources of flood risk – Enabling and Construction Phase Haslingden and Walmersley Section

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score

Surface water The Bolton Avenue High According to the Flood Map for Surface Water, the proposed compound Neutral flooding – Bolton TBM Reception The Flood Map for Surface Water area would be at high risk of surface water flooding. Avenue Compound Compound and indicates a high risk of surface Due to an increase in impermeable surfaces, the proposed construction area associated works water flooding. site has the potential to increase surface water runoff during an extreme including valve house During the 3.33% AEP surface rainfall event, and therefore increasing the risk of flooding downstream building and water flood event, a flow path less through the surface water catchment. attenuation lagoons. than 300 mm deep would form Surface water runoff from the proposed compounds would however be along the existing track running captured and attenuated by a surface water drainage system. The from Bolton Avenue towards the drainage system serving the access road would discharge to ground and Unnamed Watercourse 466. A the system serving the TBM Reception Compound would discharge at a deeper area of flooding (over controlled rate to Unnamed Watercourse 466 via a storage lagoon, 900 mm) would form during this pumping station and packaged water treatment plant. event in the proposed location of The impact on local surface water flood risk would therefore be the connection of the Proposed negligible. Haslingden and Walmersley The management of surface water flows through a drainage system that Section to the existing has been designed to cope with the anticipated flows from off site would infrastructure. Existing land use is also ensure that the risk to the Proposed Haslingden and Walmersley amenity grassland. Section would be low. Surface water Plantation Road mine Low The mine stabilisation works themselves would be almost entirely located Neutral grouting area. flooding – the area The Flood Map for Surface Water outside of the areas of flood risk as indicated by surface water flood risk between the River indicates that the risk of surface mapping. However, some shallow surface water flow paths are indicated Hyndburn and water flooding would be less than along the north and south end of the access road. Therefore, the main Unnamed 0.1% except for a few narrow areas impact would be on changes to surface water runoff rates and patterns. Watercourse 1970 of shallow (less than 300 mm The stripping of topsoil along the corridor within which the mining adjacent to Spire deep) flooding. One of these flow stabilisation works would take place would have the potential to increase Farm paths would flow into Unnamed surface water runoff rates into the brook. These potential increases in flow Watercourse 1970 during events would increase risk to downstream residential property. However, with a probability greater than 1% embedded mitigation detailed within the CCoP including temporary

12 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score AEP and would flow along the end drainage that maintained existing flow paths and attenuated any increase of the proposed access road for in runoff rate would ensure that the magnitude of any short-term effects approximately 300 m. The other would be negligible. flow path would flow along the start of the proposed access road for approximately 60 m where it crosses the A56 during the 3.33% AEP surface water flood event. Existing land use is agricultural land. Surface water The Haslingden Road High According to the Flood Map for Surface Water, the proposed Haslingden Neutral flooding – Compound area and The Flood Map for Surface Water Road TBM double drive compound area is generally at low risk of surface Haslingden Road temporary site access indicates that a small area to the water flooding except for around 50 m length before watercourse 2054 Compound area road from north of the A680 slip road would culvert where it is at high risk of surface water flooding to the proposed Manchester Road. flood to a depth of between 300 temporary access road. and 600 mm during the 3.33% Due to an increase in impermeable surfaces, the proposed construction AEP surface water flood event. sites have the potential to increase surface water runoff during an Existing land use is agricultural. extreme rainfall event, and therefore increasing the risk of flooding downstream through the surface water catchment. Surface water runoff from the proposed compound would however be captured and attenuated by a surface water drainage system. The system serving the TBM double drive compound area would discharge at a controlled rate to watercourse 2054 via attenuated drainage systems. The impact on local surface water flood risk would therefore be negligible. Surface water The New Hall Hey Low According to the Flood Map for Surface Water, the proposed New Hall Neutral flooding - New Hall Compound area and The Flood Map for Surface Water Hey Compound TBM drive and reception compound area is at low risk of Hey Compound area temporary site access indicates a low risk of surface water surface water flooding. road from the A682. flooding. A localised area of

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Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score (north bank of the surface water flooding between Due to an increase in impermeable surfaces, the proposed construction River Irwell) 300 mm and 900 mm deep is sites have the potential to increase surface water runoff during an predicted during the 0.1% AEP extreme rainfall event, and therefore increasing the risk of flooding event along the proposed access downstream through the surface water catchment. road to New Hall Hey. Existing land Surface water runoff from the proposed compound would however be use is undeveloped grassland. captured and attenuated by a surface water drainage system. The system serving the TBM drive and reception compound area would discharge at a controlled rate to the River Irwell. The impact on local surface water flood risk would therefore be negligible. Surface water The Townsend Fold High According to the Flood Map for Surface Water, the proposed Townsend Neutral flooding – WTW Compound area The Flood Map for Surface Water Fold WTW TBM reception compound area is at high risk of surface water Townsend Fold and temporary site indicates that an area in the south- flooding, including the access track to the compound area. WTW Compound access road from east of the compound would be at Due to an increase in impermeable surfaces, the proposed construction area (south bank of Holme Lane. risk during the 3.33% AEP surface sites have the potential to increase surface water runoff during an the River Irwell) water flood event with flood extreme rainfall event, and therefore increasing the risk of flooding depths of over 900 mm predicted. downstream through the surface water catchment. Site is an existing water treatment Surface water runoff from the proposed compound would however be works. captured and attenuated by a surface water drainage system. The system serving the TBM reception compound area would discharge at a controlled rate to the River Irwell. The impact on local surface water flood risk would therefore be negligible. The management of surface water flows through a drainage system that has been designed to cope with the anticipated flows from off site would also ensure that the risk to the Proposed Haslingden and Walmersley Section would be low. Surface water The Woodgate Hill High According to the Flood Map for Surface Water, the proposed Woodgate Neutral flooding – WTW Compound area Hill WTW TBM Reception Compound area is generally at low risk of

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Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score Woodgate Hill WTW and temporary site The Flood Map for Surface Water surface water flooding although small areas of high risk have been Compound area access road from indicates that whilst the probability identified. Castle Hill Road. of surface water flooding is Due to an increase in impermeable surfaces, the proposed construction generally low, there are small sites have the potential to increase surface water runoff during an areas which would flood up to a extreme rainfall event, and therefore increasing the risk of flooding maximum depth of 900 mm downstream to some residential properties between Meadowbrook Close during a 3.33% AEP surface water and Woodgate Hill Road through the surface water catchment. flood event. Existing land use is Surface water runoff from the proposed compounds would however be grassed areas within the WTW. captured and attenuated by a surface water drainage system. The system serving the TBM Reception compound area would discharge at a controlled rate to Gipsy Brook via a storage lagoon. The impact on local surface water flood risk would therefore be negligible. The management of surface water flows through a drainage system that has been designed to cope with the anticipated flows from off site would also ensure that the risk to the Proposed Haslingden and Walmersley Section would be low. Reservoir flooding New Hall Hey Low The Proposed Haslingden and Walmersley Section is remote from any of Neutral from reservoirs in Compound on the EA reservoir flood mapping the reservoirs and does not include any works that would affect the the Upper Irwell northern bank of the indicated that the failure of probability of flooding from these reservoirs. Therefore, no potential Catchment River Irwell and the reservoirs located in the upper effects on reservoir safety have been identified in this area and the Townsend Fold WTW Irwell catchment would pose a risk magnitude of effects would be negligible. Compound on the to construction compounds southern bank. located adjacent to the River Irwell. The likelihood of a reservoir flood during the construction phase of the Proposed Haslingden and Walmersley Section is very low.

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Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score

Reservoir flooding The Woodgate Hill Low The Proposed Haslingden and Walmersley Section includes construction Neutral from Woodgate Hill WTW Compound area EA reservoir flood mapping and enabling activities in close proximity to the Woodgate Hill Service Service Reservoirs and temporary site indicated that the failure of the Reservoirs with the mine grouting works approximately 30 m away at its access road from Woodgate Hill Reservoirs would closest point. Whilst the stabilisation of historic mine workings close to Castle Hill Road. not pose a risk to the Proposed the reservoir should improve reservoir safety by reducing the risk of Woodgate Hill mine Haslingden and Walmersley future ground movement, there is potential that intrusive ground works in grouting area. Section but would pose a risk to such close proximity could impact the reservoirs. As such it is residential areas downstream. The recommended that all designs and construction method statements are likelihood of a reservoir flood reviewed by the Panel Engineer appointed to inspect this reservoir. With during the construction phase of suitable mitigation measures embedded into the design of the works, the the Proposed Haslingden and magnitude of any effects on reservoir safety would be negligible. Walmersley Section is very low.

3. Groundwater flood risk - Enabling and Construction Phase Haslingden and Walmersley Section

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score

Secondary Bolton Avenue Shaft Medium Given the proposed depths of the shaft excavation to 14 mbgl, an Slight Undifferentiated For the majority of the site, there is emergence of groundwater would be expected inside the open excavation (beneficial) Superficial Aquifer a Very Low to Low potential risk of during construction. Appropriate drainage strategies embedded into the (Glacial Till) as groundwater emergence (limited design would be implemented to mitigate for flooding within the indicated by nearby potential for groundwater flooding excavation. Groundwater drawdown would occur down to the base of the GI borehole data to occur) (BGS, 2020) (low excavation, lowering the water table potentially by 13 m. sensitivity). An exception lies in the At these depths, artesian pressures may be encountered which could west of the shaft where the potentially lead to upwellings of groundwater at the surface. Specified susceptibility of groundwater embedded mitigation measures such as sump drainage, is expected to flooding is classified as Moderate adequately cope with artesian release.

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Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score to High (potential for flooding of The magnitude of change to groundwater flood risk would therefore be below ground properties) (medium minor (beneficial). sensitivity). Land use: Bracken, heath or rough grassland, and non-coniferous trees (Water Compatible Development, low sensitivity) The most conservative sensitivity for this element is medium. Bolton Avenue Very High Given the proposed depths of the excavation to 5 mbgl and groundwater Neutral Connection - open For roughly half of the site to the levels at this location, an emergence of groundwater would be expected cut section north east, there is a Very High inside the open excavation during construction. However, the rate of connecting the potential risk of groundwater inflow would be small as the excavation is considered to lie within glacial existing pipeline to emergence (potential for till which is of low permeability. If dewatering were required, it would the Proposed groundwater flooding to occur at have a marginal beneficial effect on groundwater flood risk. Haslingden and surface level) (BGS, 2020) (high Any dewatering would have a betterment effect on fluvial flood risk due Walmersley Tunnel sensitivity). In the southwest of the to a reduction of baseflow, although the size of the impact would depend site, there is a Very Low to Low on the abstraction rate and amount of baseflow which is unknown. As potential risk of groundwater such, the impacts to Unnamed Watercourse 466 due northeast have not emergence (limited potential for been assessed as no increase to the contribution to baseflow would be groundwater flooding to occur) expected. (low sensitivity). The magnitude of change to groundwater flood risk would therefore be Land use includes amenity negligible. grassland, bracken and electricity substation. The most conservative sensitivity for this element is very high. Bolton Avenue New High The depth of construction is assumed to be the same as the connection Neutral Meter Chamber excavations at 5mbgl. Given the assumed excavation depth and

17 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score There is a Very High potential risk groundwater levels at this location, an emergence of groundwater would of groundwater emergence be expected inside the open excavation during construction. However, the (potential for groundwater rate of inflow would be small as the excavation is considered to lie within flooding to occur at surface level) glacial till which is low permeability. If dewatering were required, it would (BGS, 2020) (high sensitivity). have a marginal beneficial effect on groundwater flood risk. Land use: Bracken, heath or rough Any dewatering would have a betterment effect on fluvial flood risk due grassland (Water Compatible to a reduction of baseflow, although the size of the impact would depend Development, low sensitivity) on the abstraction rate and amount of baseflow which is unknown. As The most conservative sensitivity such, the impacts to Unnamed Watercourse 466 due northeast have not for this element is high. been assessed as no increase to the contribution to baseflow would be expected. The magnitude of change to groundwater flood risk would therefore be negligible. Bolton Avenue Very High No changes to groundwater levels would be anticipated as no dewatering Neutral Compound - enabling For the majority of the site, there is would be required for construction of the compound. works (e.g. top soil a Very Low to Low potential risk of The magnitude of change to groundwater flood risk would therefore be stripping) groundwater emergence (limited negligible. potential for groundwater flooding to occur) (BGS, 2020) (low sensitivity). Exceptions lie in the north and northwest of the compound where the susceptibility of groundwater flooding is classified as Very High in the north (potential for groundwater flooding to occur at surface level) (high sensitivity) and for a small area northwest of the compound, there is a Moderate to High potential risk of groundwater

18 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score emergence (potential for flooding of below ground properties) (medium sensitivity). Land use: includes amenity grassland, bracken and electricity substation. The most conservative sensitivity for this element is very high. Secondary Haslingden Road Low Given the proposed depths of the shaft excavation to 53.5 mbgl, an Neutral Undifferentiated Double Drive shafts There is a Very Low to Low emergence of groundwater would be expected inside the open excavation Superficial Aquifer potential risk of groundwater during construction. Appropriate drainage strategies embedded into the (Glacial Till) (BGS, emergence (limited potential for design would be implemented to mitigate for flooding within the 2020) groundwater flooding to occur) excavation. Groundwater drawdown would occur down to the base of the (BGS, 2020) (low sensitivity). excavation, lowering the water table potentially by 52.5 m. Land use: Bracken, heath or rough At these depths, artesian pressures may be encountered which could grassland (Water Compatible potentially lead to upwellings of groundwater at the surface. Specified Development, low sensitivity). embedded mitigation measures such as sump drainage, is expected to adequately cope with artesian release. The most conservative sensitivity for this element is low. Any dewatering would have a betterment effect on fluvial flood risk due to a reduction of baseflow, although the size of the impact would depend on the abstraction rate and amount of baseflow which is unknown. As such, baseflow contribution to Unnamed Watercourse 1805 and Unnamed Watercourse 2054 due northeast is expected to marginally reduce flood risk during the construction of the shaft. The magnitude of change to groundwater flood risk would therefore be minor (beneficial). New Hall Hey Medium Given the proposed depths of the shaft excavation to 17 mbgl, an Neutral Compound There is a Moderate to High emergence of groundwater would be expected inside the open excavation potential risk of groundwater during construction. Appropriate drainage strategies embedded into the

19 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score emergence (potential for flooding design would be implemented to mitigate for flooding within the of below ground properties) (BGS, excavation. Groundwater drawdown would occur down to the base of the 2020) (medium sensitivity). excavation, lowering the water table potentially by 16 m. Land use: Open grassland (Water The magnitude of change to groundwater flood risk would therefore be Compatible Development, low negligible. sensitivity). The most conservative sensitivity for this element is medium. Haslingden Road Low Given the proposed depths of the excavation to 2 mbgl and groundwater Neutral Attenuation Pond There is a Very Low to Low levels at this location, no significant amount of groundwater would be potential risk of groundwater expected to drain into the open excavation during construction. If emergence (limited potential for dewatering were required, it would have a marginal beneficial effect on groundwater flooding to occur) groundwater flood risk. (BGS, 2020) (low sensitivity). The magnitude of change to groundwater flood risk would therefore be Land use: Bracken, heath or rough negligible. grassland (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is low. Haslingden Road High No changes to groundwater levels would be anticipated as no dewatering Neutral Compound Flooding susceptibility data would be required and any change to recharge would be negligible. temporary site access coverage is only available for the The magnitude of change to groundwater flood risk would therefore be road western half of the access track. negligible. For the majority of the site coverage, there is a Moderate to High potential risk of groundwater emergence (potential for flooding of below ground properties) (BGS, 2020) (medium sensitivity).

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Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score Exceptions lie for two small areas in the west and middle of the access track where there is a Very High potential risk of groundwater emergence (potential for groundwater flooding to occur at surface level) (high sensitivity). Land use: Bracken, heath or rough grassland (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is high. Haslingden Road Very High No changes to groundwater levels would be anticipated as no dewatering Neutral Compound - enabling For approximately half of the site, would be required for construction of the compound. works (e.g. top soil there is a Very Low to Low The magnitude of change to groundwater flood risk would therefore be stripping) potential risk of groundwater negligible. emergence (limited potential for groundwater flooding to occur) (BGS, 2020) (low sensitivity). Exceptions exist to the north and west of the site where the susceptibility of groundwater flooding is classified as a Moderate to High (potential for flooding of below ground properties) (medium sensitivity) and Very High (potential for groundwater flooding to occur at surface level) (high sensitivity).

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Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score Land use includes Bracken, the A682 and an electricity substation The most conservative sensitivity for this element is very high. Secondary Shaft at Medium Given the proposed depths of the shaft excavation to 10 mbgl, an Neutral Woodgate Hill WTW There is a Moderate to High emergence of groundwater would be expected inside the open excavation (connection to potential risk of groundwater during construction. Appropriate drainage strategies embedded into the Greater Manchester emergence (potential for flooding design would be implemented to mitigate for flooding within the Supply Network) of below ground properties) (BGS, excavation. Groundwater drawdown would occur potentially down to the 2020) (medium sensitivity). base of the excavation. Land use: Open grassland (Water Any dewatering would have a betterment effect on fluvial flood risk due Compatible Development, low to a reduction of baseflow, although the size of the impact would depend sensitivity). on the abstraction rate and amount of baseflow which is unknown. As such, baseflow contribution to Unnamed Watercourse 608 due southeast The most conservative sensitivity is expected to marginally reduce flood risk during the construction of the for this element is medium. shaft. The magnitude of change to groundwater flood risk would therefore be negligible. Woodgate Hill WTW High Given the construction method proposed, no changes to groundwater Neutral tunnel (connection to For approximately half of the levels would be anticipated as no dewatering would be required for the Greater Manchester length of the tunnel in the north, construction of the proposed tunnel. Supply Network) - there is a Very Low to Low The magnitude of change to groundwater flood risk would therefore be constructed using potential risk of groundwater negligible. horizontal boring emergence (limited potential for method, running groundwater flooding to occur) from the main shaft (BGS, 2020) (low sensitivity). In to the mains to the south the susceptibility of Manchester groundwater flooding is classified as a Moderate to High (potential for flooding of below ground

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Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score properties) (medium sensitivity) with a small area classified as Very High (potential for groundwater flooding to occur at surface level) (high sensitivity). Land use brackens includes the WTW and a farm. The most conservative sensitivity for this element is high. Woodgate Hill WTW High Given the proposed depths of the excavation to 5 mbgl, an emergence of Neutral Mains Connection - For the majority of the site, there is groundwater would be expected inside the open excavation during open-cut section to a Moderate to High potential risk construction. Appropriate drainage strategies embedded into the design allow for connection of groundwater emergence would be implemented to mitigate for flooding in the excavation. from smaller (potential for flooding of below Groundwater drawdown would occur down to the base of the excavation, diameter tunnel to ground properties) (BGS, 2020) lowering the water table potentially by 4 m. existing Greater (medium sensitivity). An exception Any dewatering would have a betterment effect on fluvial flood risk due Manchester Supply lies in the southeast of the to a reduction of baseflow, although the size of the impact would depend Network excavation where the susceptibility on the abstraction rate and amount of baseflow which is unknown. As of groundwater flooding is such, baseflow contribution to Unnamed Watercourse 608 crossing the classified as Very High (potential excavation is expected to marginally reduce flood risk during the for groundwater flooding to occur construction of the shaft. at surface level) (high sensitivity). The magnitude of change to groundwater flood risk would therefore be Land use: Open grassland (Water negligible. Compatible Development, low sensitivity), bracken, heath or rough grassland (Water Compatible Development, low sensitivity) and an access road (medium sensitivity).

23 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score The most conservative sensitivity for this element is high. Woodgate Hill WTW High No changes to groundwater levels would be anticipated as no dewatering Neutral Compound (main For the majority of the site, there is would be required for construction of the compound. shaft) a Very Low to Low potential risk of The magnitude of change to groundwater flood risk would therefore be groundwater emergence (limited negligible. potential for groundwater flooding to occur) (BGS, 2020) (low sensitivity). Exceptions predominantly lie in the north of the compound where the susceptibility of groundwater flooding is classified as Moderate to High (potential for flooding of below ground properties) (medium sensitivity) and Very High (potential for groundwater flooding to occur at surface level) (high sensitivity). Small areas in the southwest and southeast are classified as Moderate to High (potential for flooding of below ground properties) (medium sensitivity). Land use: includes the WTW and a farm The most conservative sensitivity for this element is high. Woodgate Hill WTW Very High No changes to groundwater levels would be anticipated as no dewatering Neutral Compound (Greater would be required for construction of the compound.

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Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score Manchester Supply For approximately half of the site The magnitude of change to groundwater flood risk would therefore be Network) in the northeast, there is a Very negligible. Low to Low potential risk of groundwater emergence (limited potential for groundwater flooding to occur) (BGS, 2020) (low sensitivity). For the southwestern section of the compound, there is a combination of Moderate to High and High to Very High potential risk of groundwater emergence (potential for flooding of below ground properties and potential for groundwater flooding to occur at surface level) (high sensitivity). Land use: Bracken, heath or rough grassland, and non-coniferous trees (Water Compatible Development, low sensitivity), access tracks (medium sensitivity), construction yards (medium sensitivity) and bounded by dwellings (More Vulnerable, very high sensitivity). The most conservative sensitivity for this element is very high. Plantation Road mine High Sections of the route are to be constructed within the Pennine Lower Coal Moderate grouting area For the majority of the site, there is Measures Formation. The Pennine Lower Coal Measures Formation has (adverse) a Very Low to Low potential risk of been subject to significant historical coal mining and this is expected to groundwater emergence (limited have left a network of open features, including abandoned and collapsed tunnels and adits, and have left the formation relatively unstable. In order

25 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score potential for groundwater flooding to enhance stability and limit losses of drilling fluids and displacement of to occur) (BGS, 2020) (low groundwater during tunnelling, grouting activities would target specific sensitivity). An exception lies in the horizons within the formation for grout injection aimed at infilling any north of the grout section where voids. Grouting would be performed through boreholes drilled in a grid the susceptibility of groundwater pattern from the surface. flooding is classified as Very High to High (potential for groundwater Short term impact flooding to occur at surface level) (high sensitivity). The targeted voids are expected to be fully saturated. The grouting activity, typically undertaken under pressure, has the potential to displace Land use: Agricultural land (rough volumes of groundwater via former mine networks which have not grazing etc) (Less Vulnerable, low collapsed and generate rapid rise of groundwater levels where vertical sensitivity), the area crosses the pathways may be available (such as former non-backfilled shafts and/or A56 highway (high sensitivity) and faults) or create / enhance existing surface discharges. This would be a unclassified roads (medium short-term impact. The outline mine grouting proposal (Wardell sensitivity) and bounds an Armstrong, 2020) suggests low risks of significant increases to agricultural building (Less underground pressures during grouting. However, grouting details and Vulnerable, high sensitivity). requirements are still to be confirmed. In addition, the preliminary mining The most conservative sensitivity risk assessment (Wardell Armstrong, 2020) has indicated the presence of for this element is high. various potential vertical pathways within the study area; these could be in connection with the former mine networks proposed to be grouted. As a result, potential horizontal and vertical displacements of groundwater which could reach the surface / sub-surface cannot be ruled out. The magnitude of change to groundwater flood risk would therefore be minor (adverse). Long term impact Moderate The horizons targeted by the grouting activities would currently be (adverse) for preferential flow pathways for groundwater and when infilled the grout up-gradient would create an impediment to groundwater flow at depth. A further effects and impediment to flow would be expected as a result of the grouting Moderate boreholes being backfilled with impermeable material on completion of (beneficial)

26 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score grout injection. The groundwater would tend to find alternative flow for down- pathways around the grouted areas (including grouted boreholes). gradient Generally, the impediment would likely increase the groundwater effects pressure head on the upstream side and within the grouted areas, and would likely lower the pressure head on the downstream side and may locally redirect groundwater flows. This is a long-term impact potentially affecting construction activities carried out during the construction phase and beyond. Several surface watercourses would potentially be affected by changes in groundwater levels around the proposed grouting areas. Reduced groundwater levels on the down-gradient side of the grouting area could lead to potential reduced groundwater baseflow contribution to Unnamed Watercourses 498, 1694, 1690 and 482. Increased groundwater levels on the up-gradient side of the grouting area could lead to potential increased baseflow contributions to Unnamed Watercourse 1690. The magnitude of change to groundwater flood risk would therefore be minor (adverse) for up-gradient effects and minor (beneficial) for down- gradient effects. White Carr Lane mine High Sections of the route are to be constructed within the Pennine Lower Coal Moderate grouting area For the majority of the site, there is Measures Formation. The Pennine Lower Coal Measures Formation has (adverse) a Very High to High potential risk been subject to significant historical coal mining and this is expected to of groundwater emergence have left a network of open features, including abandoned and collapsed (potential for groundwater tunnels and adits, and have left the formation relatively unstable. In order flooding to occur at surface level) to enhance stability and limit losses of drilling fluids and displacement of (BGS, 2020) (high sensitivity). groundwater during tunnelling, grouting activities would target specific Exceptions exist for small areas in horizons within the formation for grout injection aimed at infilling any the southwest and the coal seam voids. Grouting would be performed through boreholes drilled in a grid arm in the west of the grouted pattern from the surface. section where the susceptibility of

27 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score groundwater flooding is classified Short term impact as Very Low to Low (limited The targeted voids are expected to be fully saturated. The grouting potential for groundwater flooding activity, typically undertaken under pressure, has the potential to displace to occur) (low sensitivity). A small volumes of groundwater via former mine networks which have not area in the northwest of the collapsed and generate rapid rise of groundwater levels where vertical grouted section is classified as pathways may be available (such as former non-backfilled shafts and/or Moderate to High (potential for faults) or create / enhance existing surface discharges. This would be a flooding of below ground short-term impact. The outline mine grouting proposal (Wardell properties) (medium sensitivity). Armstrong, 2020) suggests low risks of significant increases to Land use: Agricultural land (high underground pressures during grouting. However, grouting details and quality productive wheat fields) requirements are still to be confirmed. In addition, the preliminary mining (medium sensitivity), existing risk assessment (Wardell Armstrong, 2020) has indicated the presence of access track (medium sensitivity). various potential vertical pathways within the study area; these could be The most conservative sensitivity in connection with the former mine networks proposed to be grouted. As for this element is high. a result, potential horizontal and vertical displacements of groundwater which could reach the surface / sub-surface cannot be ruled out. The magnitude of change to groundwater flood risk would therefore be minor (adverse). Long term impact Moderate The horizons targeted by the grouting activities would currently be (adverse) for preferential flow pathways for groundwater and when infilled the grout up-gradient would create an impediment to groundwater flow at depth. A further effects and impediment to flow would be expected as a result of the grouting Moderate boreholes being backfilled with impermeable material on completion of (beneficial) grout injection. The groundwater would tend to find alternative flow for down- pathways around the grouted areas (including grouted boreholes). gradient Generally, the impediment would likely increase the groundwater effects pressure head on the upstream side and within the grouted areas, and would likely lower the pressure head on the downstream side and may locally redirect groundwater flows. This is a long-term impact potentially

28 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score affecting construction activities carried out during the construction phase and beyond. Several surface watercourses would potentially be affected by changes in groundwater levels around the proposed grouting areas. Reduced groundwater levels on the down-gradient side of the grouting area could lead to potential reduced groundwater baseflow contribution to Pigs Lee Brook and Unnamed Watercourses 995, 588, 589. The magnitude of change to groundwater flood risk would therefore be minor (adverse) for up-gradient effects and minor (beneficial) for down- gradient effects. Woodgate Hill mine High Sections of the route are to be constructed within the Pennine Lower Coal Moderate grouting area For approximately half of the Measures Formation. The Pennine Lower Coal Measures Formation has (adverse) proposed grouting area, there is been subject to significant historical coal mining and this is expected to predominantly a Very Low to Low have left a network of open features, including abandoned and collapsed potential risk of groundwater tunnels and adits, and have left the formation relatively unstable. In order emergence (limited potential for to enhance stability and limit losses of drilling fluids and displacement of groundwater flooding to occur) groundwater during tunnelling, grouting activities would target specific (BGS, 2020) (low sensitivity). For horizons within the formation for grout injection aimed at infilling any other sections there is a Moderate voids. Grouting would be performed through boreholes drilled in a grid to High potential risk of pattern from the surface. groundwater emergence (potential for flooding of below ground Short term impact properties) (medium sensitivity) The targeted voids are expected to be fully saturated. The grouting and a High to Very High potential activity, typically undertaken under pressure, has the potential to displace risk of groundwater emergence volumes of groundwater via former mine networks which have not (potential for groundwater collapsed and generate rapid rise of groundwater levels where vertical flooding to occur at surface level) pathways may be available (such as former non-backfilled shafts and/or (high sensitivity). faults) or create / enhance existing surface discharges. This would be a Land use: Agricultural land (rough short-term impact. The outline mine grouting proposal (Wardell grazing etc), bracken, heath or Armstrong, 2020) suggests low risks of significant increases to

29 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score rough grassland, and non- underground pressures during grouting. However, grouting details and coniferous trees (Water requirements are still to be confirmed. In addition, the preliminary mining Compatible Development, low risk assessment (Wardell Armstrong, 2020) has indicated the presence of sensitivity), existing access track various potential vertical pathways within the study area; these could be (medium sensitivity), unclassified in connection with the former mine networks proposed to be grouted. As roads (medium sensitivity) and a a result, potential horizontal and vertical displacements of groundwater construction yard (medium which could reach the surface / sub-surface cannot be ruled out. sensitivity). The magnitude of change to groundwater flood risk would therefore be The most conservative sensitivity minor (adverse). for this element is high. Long term impact Moderate The horizons targeted by the grouting activities would currently be (adverse) for preferential flow pathways for groundwater and when infilled the grout up-gradient would create an impediment to groundwater flow at depth. A further effects and impediment to flow would be expected as a result of the grouting Moderate boreholes being backfilled with impermeable material on completion of (beneficial) grout injection. The groundwater would tend to find alternative flow for down- pathways around the grouted areas (including grouted boreholes). gradient Generally, the impediment would likely increase the groundwater effects pressure head on the upstream side and within the grouted areas, and would likely lower the pressure head on the downstream side and may locally redirect groundwater flows. This is a long-term impact potentially affecting construction activities carried out during the construction phase and beyond. Several surface watercourses would potentially be affected by changes in groundwater levels around the proposed grouting areas. Reduced groundwater levels on the down-gradient side of the grouting area could lead to potential reduced groundwater baseflow contribution to Gipsy Brook and Unnamed Watercourses 602 (upstream Gipsy Brook), 605 (upstream Gipsy Brook), 608, 603, 604 and 607. Increased groundwater

30 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score levels on the up-gradient side of the grouting area could lead to potential increased baseflow contributions to Unnamed Watercourses 602 (upstream Gipsy Brook), 605 (upstream Gipsy Brook) and 608. The magnitude of change to groundwater flood risk would therefore be minor (adverse) for up-gradient effects and minor (beneficial) for down- gradient effects. Secondary A Townsend Fold WTW High Given the proposed depths of the shaft excavation to 16 mbgl, an Neutral Superficial Aquifer Compound There is a Very High potential risk emergence of groundwater would be expected inside the open excavation (Alluvium) (BGS, of groundwater emergence during construction. Appropriate drainage strategies embedded into the 2020) (potential for groundwater design would be implemented to mitigate for flooding within the flooding to occur at surface level) excavation. Groundwater drawdown would occur down to the base of the (BGS, 2020) (high sensitivity). excavation, lowering the water table potentially by 15 m. Land use: Non coniferous trees Any dewatering would have a betterment effect on fluvial flood risk due (Water Compatible Development, to a reduction of baseflow, although the size of the impact would depend low sensitivity). on the abstraction rate and amount of baseflow which is unknown. As such, baseflow contribution to the River Irwell due northwest is expected The most conservative sensitivity to marginally reduce flood risk during the construction of the shaft. for this element is high. The magnitude of change to groundwater flood risk would therefore be negligible. Haslingden Road High No changes to groundwater levels would be anticipated as no dewatering Neutral Compound Flooding susceptibility data would be required and any change to recharge would be negligible. temporary access coverage is only available for the The magnitude of change to groundwater flood risk would therefore be road western half of the access track. negligible. For the majority of the site coverage, there is a Moderate to High potential risk of groundwater emergence (potential for flooding of below ground properties) (BGS, 2020) (medium sensitivity). Exceptions lie for two small areas

31 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score in the west and middle of the access track where there is a Very High potential risk of groundwater emergence (potential for groundwater flooding to occur at surface level) (high sensitivity). Land use: Bracken, heath or rough grassland (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is high. Townsend Fold WTW High Given the proposed depths of the excavation to 5 mbgl, an emergence of Neutral Connection - open There is a Very High potential risk groundwater would be expected inside the open excavation during cut section of groundwater emergence construction. Appropriate drainage strategies embedded into the design connecting the (potential for groundwater would be implemented to mitigate for flooding in the excavation. existing supply flooding to occur at surface level) Groundwater drawdown would occur down to the base of the excavation, network to the (BGS, 2020) (high sensitivity). lowering the water table potentially by 4 m. Proposed Haslingden Land uses include Existing access The magnitude of change to groundwater flood risk would therefore be and Walmersley road and water treatment works negligible. Tunnel The most conservative sensitivity for this element is high. Haslingden Road Very High No changes to groundwater levels would be anticipated as no dewatering Neutral Compound - enabling For approximately half of the site, would be required for construction of the compound. works (e.g. top soil there is a Very Low to Low The magnitude of change to groundwater flood risk would therefore be stripping) potential risk of groundwater negligible. emergence (limited potential for groundwater flooding to occur) (BGS, 2020) (low sensitivity). Exceptions exist to the north and

32 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score west of the site where the susceptibility of groundwater flooding is classified as a Moderate to High (potential for flooding of below ground properties) (medium sensitivity) and Very High (potential for groundwater flooding to occur at surface level) (high sensitivity). Land use includes Bracken, the A682 and an electricity substation The most conservative sensitivity for this element is very high. No superficial Woodgate Hill WTW Low Given the proposed depths of the shaft excavation to 26.5 mbgl, an Neutral deposits are Main Shaft There is a Very Low to Low emergence of groundwater would be expected inside the open excavation identified on BGS potential risk of groundwater during construction. Appropriate drainage strategies embedded into the mapping (BGS, emergence (limited potential for design would be implemented to mitigate for flooding within the 2020) groundwater flooding to occur) excavation. Groundwater drawdown would occur down to the base of the (BGS, 2020) (low sensitivity). excavation, lowering the water table potentially by 25.5 m. Land use: Bracken, heath or rough At these depths, artesian pressures may be encountered which could grassland (Water Compatible potentially lead to upwellings of groundwater at the surface. Specified Development, low sensitivity). embedded mitigation measures such as sump drainage, is expected to adequately cope with artesian release. The most conservative sensitivity for this element is low. The magnitude of change to groundwater flood risk would therefore be minor (beneficial). Woodgate Hill WTW Low Given the proposed depths of the excavation to 4 mbgl at the south west Neutral Shaft Platform (for There is a Very Low to Low corner of the proposed shaft platform, an emergence of groundwater the Main Shaft) - built potential risk of groundwater would be expected inside the open excavation during construction. into the side slope emergence (limited potential for Appropriate drainage strategies embedded into the design would be implemented to mitigate for flooding in the excavation. Groundwater

33 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score groundwater flooding to occur) drawdown would occur down to the base of the excavation, lowering the (BGS, 2020) (low sensitivity). water table potentially by 3 m. Land use: Bracken, heath or rough The magnitude of change to groundwater flood risk would therefore be grassland (Water Compatible negligible. Development, low sensitivity). The most conservative sensitivity for this element is low. Woodgate Hill WTW Medium No changes to groundwater levels would be anticipated as no dewatering Neutral Access Road (from There is a Very Low to Low would be required and any change to recharge would be negligible. Castle Hill Road to potential risk of groundwater The magnitude of change to groundwater flood risk would therefore be the main shaft) (only emergence (limited potential for negligible. the section of the groundwater flooding to occur) proposed access track (BGS, 2020) (low sensitivity). that does not follow Land use: rough grazing farmland an existing road or (low sensitivity), the proposed road access track has been joins with an existing unclassified assessed) road (Castle Hill Road) (medium sensitivity). The most conservative sensitivity for this element is medium. Woodgate Hill WTW Medium Given the proposed depths of the excavation to 5 mbgl, an emergence of Neutral Compound There is a Very Low to Low groundwater would be expected inside the open excavation during Connection (East) - potential risk of groundwater construction. Appropriate drainage strategies embedded into the design open-cut section to emergence (limited potential for would be implemented to mitigate for flooding in the excavation. allow for connection groundwater flooding to occur) Groundwater drawdown would occur down to the base of the excavation, from main shaft to (BGS, 2020) (low sensitivity). lowering the water table potentially by 4 m. existing Reservoir Land use: The excavation crosses The magnitude of change to groundwater flood risk would therefore be Valve House an access track (medium negligible. sensitivity) and areas of bracken,

34 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score heath or rough grassland (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is medium. Woodgate Hill WTW High Given the proposed depths of the excavation to 5 mbgl, an emergence of Neutral Compound There is a Very Low to Low groundwater would be expected inside the open excavation during Connection (West) - potential risk of groundwater construction. Appropriate drainage strategies embedded into the design open-cut section to emergence (limited potential for would be implemented to mitigate for flooding in the excavation. allow for connection groundwater flooding to occur) Groundwater drawdown would occur down to the base of the excavation, from main shaft to (BGS, 2020) (low sensitivity). lowering the water table potentially by 4 m. existing Reservoir Land use: The excavation crosses a The magnitude of change to groundwater flood risk would therefore be Valve House warehouse yard premises (Less negligible. Vulnerable, high sensitivity), open grassland (Water Compatible Development, low sensitivity) and an access road (medium sensitivity). The most conservative sensitivity for this element is high. Woodgate Hill WTW Low The depth of construction is assumed to be the same as the connection Neutral New Valve House There is a Very Low to Low excavations at 5mbgl. Given the assumed excavation depth and potential risk of groundwater groundwater levels at this location, an emergence of groundwater would emergence (limited potential for be expected inside the open excavation during construction. However, the groundwater flooding to occur) rate of inflow would be small as the excavation is considered to lie within (BGS, 2020) (low sensitivity). glacial till which is low permeability. If dewatering were required, it would have a marginal beneficial effect on groundwater flood risk. Land use: heath or rough grassland (Water Compatible Development, The magnitude of change to groundwater flood risk would therefore be low sensitivity). negligible.

35 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score The most conservative sensitivity for this element is low. Secondary A Bolton Avenue Shaft Medium Given the proposed depths of the shaft excavation to 14 mbgl, an Slight Bedrock Aquifer For the majority of the site, there is emergence of groundwater would be expected inside the open excavation (beneficial) (Pennine Lower Coal a Very Low to Low potential risk of during construction. Appropriate drainage strategies embedded into the Measures groundwater emergence (limited design would be implemented to mitigate for flooding within the Formation) potential for groundwater flooding excavation. Groundwater drawdown would occur down to the base of the to occur) (BGS, 2020) (low excavation, lowering the water table potentially by 13 m. sensitivity). An exception lies in the At these depths, artesian pressures may be encountered which could west of the shaft where the potentially lead to upwellings of groundwater at the surface. Specified susceptibility of groundwater embedded mitigation measures such as sump drainage, is expected to flooding is classified as Moderate adequately cope with artesian release. to High (potential for flooding of The magnitude of change to groundwater flood risk would therefore be below ground properties) (medium minor (beneficial). sensitivity).

Land use: Bracken, heath or rough grassland, and non-coniferous trees (Water Compatible Development, low sensitivity) The most conservative sensitivity for this element is medium. Bolton Avenue Very High Given the proposed depths of the excavation to 5 mbgl and groundwater Neutral Connection - open For roughly half of the site to the levels at this location, an emergence of groundwater would be expected cut section north east, there is a Very High inside the open excavation during construction. However, the rate of connecting the potential risk of groundwater inflow would be small as the excavation is considered to lie within glacial existing pipeline to emergence (potential for till which is of low permeability. If dewatering were required, it would the Proposed groundwater flooding to occur at have a marginal beneficial effect on groundwater flood risk. Haslingden and surface level) (BGS, 2020) (high Any dewatering would have a betterment effect on fluvial flood risk due Walmersley Tunnel sensitivity). In the southwest of the to a reduction of baseflow, although the size of the impact would depend site, there is a Very Low to Low on the abstraction rate and amount of baseflow which is unknown. As

36 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score potential risk of groundwater such, the impacts to Unnamed Watercourse 466 due northeast have not emergence (limited potential for been assessed as no increase to the contribution to baseflow would be groundwater flooding to occur) expected. (low sensitivity). The magnitude of change to groundwater flood risk would therefore be Land use includes amenity negligible. grassland, bracken and electricity substation. The most conservative sensitivity for this element is very high. Bolton Avenue New High The depth of construction is assumed to be the same as the connection Neutral Meter Chamber There is a Very High potential risk excavations at 5mbgl. Given the assumed excavation depth and of groundwater emergence groundwater levels at this location, an emergence of groundwater would (potential for groundwater be expected inside the open excavation during construction. However, the flooding to occur at surface level) rate of inflow would be small as the excavation is considered to lie within (BGS, 2020) (high sensitivity). glacial till which is low permeability. If dewatering were required, it would have a marginal beneficial effect on groundwater flood risk. Land use: Bracken, heath or rough grassland (Water Compatible Any dewatering would have a betterment effect on fluvial flood risk due Development, low sensitivity) to a reduction of baseflow, although the size of the impact would depend on the abstraction rate and amount of baseflow which is unknown. As The most conservative sensitivity such, the impacts to Unnamed Watercourse 466 due northeast have not for this element is high. been assessed as no increase to the contribution to baseflow would be expected. The magnitude of change to groundwater flood risk would therefore be negligible. Bolton Avenue Very High No changes to groundwater levels would be anticipated as no dewatering Neutral Compound - enabling For the majority of the site, there is would be required for construction of the compound. works (e.g. top soil a Very Low to Low potential risk of The magnitude of change to groundwater flood risk would therefore be stripping) groundwater emergence (limited negligible. potential for groundwater flooding

37 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score to occur) (BGS, 2020) (low sensitivity). Exceptions lie in the north and northwest of the compound where the susceptibility of groundwater flooding is classified as Very High in the north (potential for groundwater flooding to occur at surface level) (high sensitivity) and for a small area northwest of the compound, there is a Moderate to High potential risk of groundwater emergence (potential for flooding of below ground properties) (medium sensitivity). Land use includes amenity grassland, bracken and electricity substation. The most conservative sensitivity for this element is very high. Woodgate Hill WTW Low Given the proposed depths of the shaft excavation to 26.5 mbgl, an Neutral Main Shaft There is a Very Low to Low emergence of groundwater would be expected inside the open excavation potential risk of groundwater during construction. Appropriate drainage strategies embedded into the emergence (limited potential for design would be implemented to mitigate for flooding within the groundwater flooding to occur) excavation. Groundwater drawdown would occur down to the base of the (BGS, 2020) (low sensitivity). excavation, lowering the water table potentially by 25.5 m. Land use: Bracken, heath or rough At these depths, artesian pressures may be encountered which could grassland (Water Compatible potentially lead to upwellings of groundwater at the surface. Specified Development, low sensitivity). embedded mitigation measures such as sump drainage, is expected to adequately cope with artesian release.

38 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score The most conservative sensitivity The magnitude of change to groundwater flood risk would therefore be for this element is low. minor (beneficial). Woodgate Hill WTW Low Given the proposed depths of the excavation to 4 mbgl at the south west Neutral Shaft Platform (for There is a Very Low to Low corner of the proposed shaft platform, an emergence of groundwater the Main Shaft) - built potential risk of groundwater would be expected inside the open excavation during construction. into the side slope emergence (limited potential for Appropriate drainage strategies embedded into the design would be groundwater flooding to occur) implemented to mitigate for flooding in the excavation. Groundwater (BGS, 2020) (low sensitivity). drawdown would occur down to the base of the excavation, lowering the water table potentially by 3 m. Land use: Bracken, heath or rough grassland (Water Compatible The magnitude of change to groundwater flood risk would therefore be Development, low sensitivity). negligible. The most conservative sensitivity for this element is low. Secondary Shaft at Medium Given the proposed depths of the shaft excavation to 10 mbgl, an Neutral Woodgate Hill WTW There is a Moderate to High emergence of groundwater would be expected inside the open excavation (connection to potential risk of groundwater during construction. Appropriate drainage strategies embedded into the Greater Manchester emergence (potential for flooding design would be implemented to mitigate for flooding within the Supply Network) of below ground properties) (BGS, excavation. Groundwater drawdown would occur down to the base of the 2020) (medium sensitivity). excavation, lowering the water table potentially by 9 m. Land use: Open grassland (Water Any dewatering would have a betterment effect on fluvial flood risk due Compatible Development, low to a reduction of baseflow, although the size of the impact would depend sensitivity). on the abstraction rate and amount of baseflow which is unknown. As such, baseflow contribution to Unnamed Watercourse 608 due southeast The most conservative sensitivity is expected to marginally reduce flood risk during the construction of the for this element is medium. shaft. The magnitude of change to groundwater flood risk would therefore be negligible.

39 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score

Woodgate Hill WTW High Given the construction method proposed, no changes to groundwater Neutral tunnel (connection to For approximately half of the levels would be anticipated as no dewatering would be required for the Greater Manchester length of the tunnel in the north, construction of the proposed tunnel. Supply Network) - there is a Very Low to Low The magnitude of change to groundwater flood risk would therefore be constructed using potential risk of groundwater negligible. horizontal boring emergence (limited potential for method, running groundwater flooding to occur) from the main shaft (BGS, 2020) (low sensitivity). In to the mains to the south the susceptibility of Manchester groundwater flooding is classified as a Moderate to High (potential for flooding of below ground properties) (medium sensitivity) with a small area classified as Very High (potential for groundwater flooding to occur at surface level) (high sensitivity). Land use includes the WTW and a farm. The most conservative sensitivity for this element is high. Woodgate Hill WTW Medium No changes to groundwater levels would be anticipated as no dewatering Neutral Access Road (from There is a Very Low to Low would be required and any change to recharge would be negligible. Castle Hill Road to potential risk of groundwater The magnitude of change to groundwater flood risk would therefore be the main shaft) (only emergence (limited potential for negligible. the section of the groundwater flooding to occur) proposed access track (BGS, 2020) (low sensitivity). that does not follow Land use: rough grazing farmland an existing road or (low sensitivity), the proposed road joins with an existing unclassified

40 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score access track has been road (Castle Hill Road) (medium assessed) sensitivity). The most conservative sensitivity for this element is medium. Woodgate Hill WTW Medium Given the proposed depths of the excavation to 5 mbgl, an emergence of Neutral Compound There is a Very Low to Low groundwater would be expected inside the open excavation during Connection (East) - potential risk of groundwater construction. Appropriate drainage strategies embedded into the design open-cut section to emergence (limited potential for would be implemented to mitigate for flooding in the excavation. allow for connection groundwater flooding to occur) Groundwater drawdown would occur down to the base of the excavation, from main shaft to (BGS, 2020) (low sensitivity). lowering the water table potentially by 4 m. existing Reservoir Land use: The excavation crosses The magnitude of change to groundwater flood risk would therefore be Valve House an access track (medium negligible. sensitivity) and areas of bracken, heath or rough grassland (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is medium. Woodgate Hill WTW High Given the proposed depths of the excavation to 5 mbgl, an emergence of Neutral Compound There is a Very Low to Low groundwater would be expected inside the open excavation during Connection (West) - potential risk of groundwater construction. Appropriate drainage strategies embedded into the design open-cut section to emergence (limited potential for would be implemented to mitigate for flooding in the excavation. allow for connection groundwater flooding to occur) Groundwater drawdown would occur down to the base of the excavation, from main shaft to (BGS, 2020) (low sensitivity). lowering the water table potentially by 4 m. existing Reservoir Land use: The excavation crosses a The magnitude of change to groundwater flood risk would therefore be Valve House warehouse yard premises (Less negligible. Vulnerable, high sensitivity), open grassland (Water Compatible Development, low sensitivity) and

41 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score an access road (medium sensitivity). The most conservative sensitivity for this element is high. Woodgate Hill WTW High Given the proposed depths of the excavation to 5 mbgl, an emergence of Neutral Mains Connection - For the majority of the site, there is groundwater would be expected inside the open excavation during open-cut section to a Moderate to High potential risk construction. Appropriate drainage strategies embedded into the design allow for connection of groundwater emergence would be implemented to mitigate for flooding in the excavation. from smaller (potential for flooding of below Groundwater drawdown would occur down to the base of the excavation, diameter tunnel to ground properties) (BGS, 2020) lowering the water table potentially by 4 m. existing Greater (medium sensitivity). An exception Any dewatering would have a betterment effect on fluvial flood risk due Manchester Supply lies in the southeast of the to a reduction of baseflow, although the size of the impact would depend Network excavation where the susceptibility on the abstraction rate and amount of baseflow which is unknown. As of groundwater flooding is such, baseflow contribution to Unnamed Watercourse 608 crossing the classified as Very High (potential excavation is expected to marginally reduce flood risk during the for groundwater flooding to occur construction of the shaft. at surface level) (high sensitivity). The magnitude of change to groundwater flood risk would therefore be Land use: Open grassland (Water negligible. Compatible Development, low sensitivity), bracken, heath or rough grassland (Water Compatible Development, low sensitivity) and an access road (medium sensitivity). The most conservative sensitivity for this element is high. Woodgate Hill WTW Low The depth of construction is assumed to be the same as the connection Neutral New Valve House There is a Very Low to Low excavations at 5mbgl. Given the assumed excavation depth and potential risk of groundwater groundwater levels at this location, an emergence of groundwater would be expected inside the open excavation during construction. However, the

42 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score emergence (limited potential for rate of inflow would be small as the excavation is considered to lie within groundwater flooding to occur) glacial till which is low permeability. If dewatering were required, it would (BGS, 2020) (low sensitivity). have a marginal beneficial effect on groundwater flood risk. Land use: heath or rough grassland The magnitude of change to groundwater flood risk would therefore be (Water Compatible Development, negligible. low sensitivity). The most conservative sensitivity for this element is low. Woodgate Hill WTW High No changes to groundwater levels would be anticipated as no dewatering Neutral Compound (main For the majority of the site, there is would be required for construction of the compound. shaft) a Very Low to Low potential risk of The magnitude of change to groundwater flood risk would therefore be groundwater emergence (limited negligible. potential for groundwater flooding to occur) (BGS, 2020) (low sensitivity). Exceptions predominantly lie in the north of the compound where the susceptibility of groundwater flooding is classified as Moderate to High (potential for flooding of below ground properties) (medium sensitivity) and Very High (potential for groundwater flooding to occur at surface level) (high sensitivity). Small areas in the southwest and southeast are classified as Moderate to High (potential for flooding of below ground properties) (medium sensitivity).

43 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score Land use: Bracken, heath or rough grassland, and non-coniferous trees (Water Compatible Development, low sensitivity), access roads or tracks (medium sensitivity), telecommunications mast (high sensitivity), warehouse premises (Less Vulnerable, high sensitivity). The most conservative sensitivity for this element is high. Woodgate Hill WTW Very High No changes to groundwater levels would be anticipated as no dewatering Neutral Compound (Greater For approximately half of the site would be required for construction of the compound. Manchester Supply in the northeast, there is a Very The magnitude of change to groundwater flood risk would therefore be Network) Low to Low potential risk of negligible. groundwater emergence (limited potential for groundwater flooding to occur) (BGS, 2020) (low sensitivity). For the southwestern section of the compound, there is a combination of Moderate to High and High to Very High potential risk of groundwater emergence (potential for flooding of below ground properties and potential for groundwater flooding to occur at surface level) (high sensitivity). Land use: Bracken, heath or rough grassland, and non-coniferous trees (Water Compatible

44 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score Development, low sensitivity), access tracks (medium sensitivity), construction yards (medium sensitivity) and bounded by dwellings (More Vulnerable, very high sensitivity). The most conservative sensitivity for this element is very high. Plantation Road mine High Sections of the route are to be constructed within the Pennine Lower Coal Moderate grouting area For the majority of the site, there is Measures Formation. The Pennine Lower Coal Measures Formation has (adverse) a Very Low to Low potential risk of been subject to significant historical coal mining and this is expected to groundwater emergence (limited have left a network of open features, including abandoned and collapsed potential for groundwater flooding tunnels and adits, and have left the formation relatively unstable. In order to occur) (BGS, 2020) (low to enhance stability and limit losses of drilling fluids and displacement of sensitivity). An exception lies in the groundwater during tunnelling, grouting activities would target specific north of the grout section where horizons within the formation for grout injection aimed at infilling any the susceptibility of groundwater voids. Grouting would be performed through boreholes drilled in a grid flooding is classified as Very High pattern from the surface. to High (potential for groundwater flooding to occur at surface level) Short term impact (high sensitivity). The targeted voids are expected to be fully saturated. The grouting Land use: Agricultural land (rough activity, typically undertaken under pressure, has the potential to displace grazing etc) (Less Vulnerable, low volumes of groundwater via former mine networks which have not sensitivity), the area crosses the collapsed and generate rapid rise of groundwater levels where vertical A56 highway (high sensitivity) and pathways may be available (such as former non-backfilled shafts and/or unclassified roads (medium faults) or create / enhance existing surface discharges. This would be a sensitivity) and bounds an short-term impact. The outline mine grouting proposal (Wardell agricultural building (Less Armstrong, 2020) suggests low risks of significant increases to Vulnerable, high sensitivity). underground pressures during grouting. However, grouting details and requirements are still to be confirmed. In addition, the preliminary mining

45 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score The most conservative sensitivity risk assessment (Wardell Armstrong, 2020) has indicated the presence of for this element is high. various potential vertical pathways within the study area; these could be in connection with the former mine networks proposed to be grouted. As a result, potential horizontal and vertical displacements of groundwater which could reach the surface / sub-surface cannot be ruled out. The magnitude of change to groundwater flood risk would therefore be minor (adverse). Long term impact Moderate The horizons targeted by the grouting activities would currently be (adverse) for preferential flow pathways for groundwater and when infilled the grout up-gradient would create an impediment to groundwater flow at depth. A further effects and impediment to flow would be expected as a result of the grouting Moderate boreholes being backfilled with impermeable material on completion of (beneficial) grout injection. The groundwater would tend to find alternative flow for down- pathways around the grouted areas (including grouted boreholes). gradient Generally, the impediment would likely increase the groundwater effects pressure head on the upstream side and within the grouted areas, and would likely lower the pressure head on the downstream side and may locally redirect groundwater flows. This is a long-term impact potentially affecting construction activities carried out during the construction phase and beyond. Several surface watercourses would potentially be affected by changes in groundwater levels around the proposed grouting areas. Reduced groundwater levels on the down-gradient side of the grouting area could lead to potential reduced groundwater baseflow contribution to Unnamed Watercourses 498, 1694, 1690 and 482. Increased groundwater levels on the up-gradient side of the grouting area could lead to potential increased baseflow contributions to Unnamed Watercourse 1690.

46 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score The magnitude of change to groundwater flood risk would therefore be minor (adverse) for up-gradient effects and minor (beneficial) for down- gradient effects. White Carr Lane mine High Sections of the route are to be constructed within the Pennine Lower Coal Moderate grouting area For the majority of the site, there is Measures Formation. The Pennine Lower Coal Measures Formation has (adverse) a Very High to High potential risk been subject to significant historical coal mining and this is expected to of groundwater emergence have left a network of open features, including abandoned and collapsed (potential for groundwater tunnels and adits, and have left the formation relatively unstable. In order flooding to occur at surface level) to enhance stability and limit losses of drilling fluids and displacement of (BGS, 2020) (high sensitivity). groundwater during tunnelling, grouting activities would target specific Exceptions exist for small areas in horizons within the formation for grout injection aimed at infilling any the southwest and the coal seam voids. Grouting would be performed through boreholes drilled in a grid arm in the west of the grouted pattern from the surface. section where the susceptibility of groundwater flooding is classified Short term impact as Very Low to Low (limited The targeted voids are expected to be fully saturated. The grouting potential for groundwater flooding activity, typically undertaken under pressure, has the potential to displace to occur) (low sensitivity). A small volumes of groundwater via former mine networks which have not area in the northwest of the collapsed and generate rapid rise of groundwater levels where vertical grouted section is classified as pathways may be available (such as former non-backfilled shafts and/or Moderate to High (potential for faults) or create / enhance existing surface discharges. This would be a flooding of below ground short-term impact. The outline mine grouting proposal (Wardell properties) (medium sensitivity). Armstrong, 2020) suggests low risks of significant increases to Land use: Agricultural land (high underground pressures during grouting. However, grouting details and quality productive wheat fields) requirements are still to be confirmed. In addition, the preliminary mining (medium sensitivity), existing risk assessment (Wardell Armstrong, 2020) has indicated the presence of access track (medium sensitivity). various potential vertical pathways within the study area; these could be The most conservative sensitivity in connection with the former mine networks proposed to be grouted. As for this element is high. a result, potential horizontal and vertical displacements of groundwater which could reach the surface / sub-surface cannot be ruled out.

47 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score The magnitude of change to groundwater flood risk would therefore be minor (adverse). Long term impact Moderate The horizons targeted by the grouting activities would currently be (adverse) for preferential flow pathways for groundwater and when infilled the grout up-gradient would create an impediment to groundwater flow at depth. A further effects and impediment to flow would be expected as a result of the grouting Moderate boreholes being backfilled with impermeable material on completion of (beneficial) grout injection. The groundwater would tend to find alternative flow for down- pathways around the grouted areas (including grouted boreholes). gradient Generally, the impediment would likely increase the groundwater effects pressure head on the upstream side and within the grouted areas, and would likely lower the pressure head on the downstream side and may locally redirect groundwater flows. This is a long-term impact potentially affecting construction activities carried out during the construction phase and beyond. Several surface watercourses would potentially be affected by changes in groundwater levels around the proposed grouting areas. Reduced groundwater levels on the down-gradient side of the grouting area could lead to potential reduced groundwater baseflow contribution to Pigs Lee Brook and Unnamed Watercourses 995, 588, 589. The magnitude of change to groundwater flood risk would therefore be minor (adverse) for up-gradient effects and minor (beneficial) for down- gradient effects. Woodgate Hill mine High Sections of the route are to be constructed within the Pennine Lower Coal Moderate grouting area For approximately half of the Measures Formation. The Pennine Lower Coal Measures Formation has (adverse) proposed grouting aera, there is been subject to significant historical coal mining and this is expected to predominantly a Very Low to Low have left a network of open features, including abandoned and collapsed potential risk of groundwater tunnels and adits, and have left the formation relatively unstable. In order to enhance stability and limit losses of drilling fluids and displacement of

48 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score emergence (limited potential for groundwater during tunnelling, grouting activities would target specific groundwater flooding to occur) horizons within the formation for grout injection aimed at infilling any (BGS, 2020) (low sensitivity). For voids. Grouting would be performed through boreholes drilled in a grid other sections there is a Moderate pattern from the surface. to High potential risk of groundwater emergence (potential Short term impact for flooding of below ground properties) (medium sensitivity) The targeted voids are expected to be fully saturated. The grouting and a High to Very High potential activity, typically undertaken under pressure, has the potential to displace risk of groundwater emergence volumes of groundwater via former mine networks which have not (potential for groundwater collapsed and generate rapid rise of groundwater levels where vertical flooding to occur at surface level) pathways may be available (such as former non-backfilled shafts and/or (high sensitivity). faults) or create / enhance existing surface discharges. This would be a short-term impact. The outline mine grouting proposal (Wardell Land use: Agricultural land (rough Armstrong, 2020) suggests low risks of significant increases to grazing etc), bracken, heath or underground pressures during grouting. However, grouting details and rough grassland, and non- requirements are still to be confirmed. In addition, the preliminary mining coniferous trees (Water risk assessment (Wardell Armstrong, 2020) has indicated the presence of Compatible Development, low various potential vertical pathways within the study area; these could be sensitivity), existing access track in connection with the former mine networks proposed to be grouted. As (medium sensitivity), unclassified a result, potential horizontal and vertical displacements of groundwater roads (medium sensitivity) and a which could reach the surface / sub-surface cannot be ruled out. construction yard (medium sensitivity). The magnitude of change to groundwater flood risk would therefore be minor (adverse). The most conservative sensitivity for this element is high. Long term impact Moderate The horizons targeted by the grouting activities would currently be (adverse) for preferential flow pathways for groundwater and when infilled the grout up-gradient would create an impediment to groundwater flow at depth. A further effects and impediment to flow would be expected as a result of the grouting Moderate boreholes being backfilled with impermeable material on completion of (beneficial) grout injection. The groundwater would tend to find alternative flow for down-

49 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score pathways around the grouted areas (including grouted boreholes). gradient Generally, the impediment would likely increase the groundwater effects pressure head on the upstream side and within the grouted areas, and would likely lower the pressure head on the downstream side and may locally redirect groundwater flows. This is a long-term impact potentially affecting construction activities carried out during the construction phase and beyond. Several surface watercourses would potentially be affected by changes in groundwater levels around the proposed grouting areas. Reduced groundwater levels on the down-gradient side of the grouting area could lead to potential reduced groundwater baseflow contribution to Gipsy Brook and Unnamed Watercourses 602 (upstream Gipsy Brook), 605 (upstream Gipsy Brook), 608, 603, 604 and 607. Increased groundwater levels on the up-gradient side of the grouting area could lead to potential increased baseflow contributions to Unnamed Watercourses 602 (upstream Gipsy Brook), 605 (upstream Gipsy Brook) and 608. The magnitude of change to groundwater flood risk would therefore be minor (adverse) for up-gradient effects and minor (beneficial) for down- gradient effects. Secondary A Haslingden Road Low Given the proposed depths of the shaft excavation to 53.5 mbgl, an Neutral Bedrock Aquifer Double Drive There is a Very Low to Low emergence of groundwater would be expected inside the open excavation (Marsden potential risk of groundwater during construction. Appropriate drainage strategies embedded into the Formation, emergence (limited potential for design would be implemented to mitigate for flooding within the Millstone Grit groundwater flooding to occur) excavation. Groundwater drawdown would occur down to the base of the Group) (BGS, 2020) (BGS, 2020) (low sensitivity). excavation, lowering the water table potentially by 52.5 m. Land use: Bracken, heath or rough At these depths, artesian pressures may be encountered which could grassland (Water Compatible potentially lead to upwellings of groundwater at the surface. Specified Development, low sensitivity). embedded mitigation measures such as sump drainage, is expected to adequately cope with artesian release. The most conservative sensitivity for this element is low.

50 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score Any dewatering would have a betterment effect on fluvial flood risk due to a reduction of baseflow, although the size of the impact would depend on the abstraction rate and amount of baseflow which is unknown. As such, baseflow contribution to Unnamed Watercourse 1805 and Unnamed Watercourse 2054 due northeast is expected to marginally reduce flood risk during the construction of the shaft. The magnitude of change to groundwater flood risk would therefore be minor (beneficial). New Hall Hey Medium Given the proposed depths of the shaft excavation to 17 mbgl, an Neutral Compound There is a Moderate to High emergence of groundwater would be expected inside the open excavation potential risk of groundwater during construction. Appropriate drainage strategies embedded into the emergence (potential for flooding design would be implemented to mitigate for flooding within the of below ground properties) (BGS, excavation. Groundwater drawdown would occur down to the base of the 2020) (medium sensitivity). excavation, lowering the water table potentially by 16 m. Land use: Open grassland (Water The magnitude of change to groundwater flood risk would therefore be Compatible Development, low negligible. sensitivity). The most conservative sensitivity for this element is medium. Townsend Fold WTW High Given the proposed depths of the shaft excavation to 16 mbgl, an Neutral Compound There is a Very High potential risk emergence of groundwater would be expected inside the open excavation of groundwater emergence during construction. Appropriate drainage strategies embedded into the (potential for groundwater design would be implemented to mitigate for flooding within the flooding to occur at surface level) excavation. Groundwater drawdown would occur down to the base of the (BGS, 2020) (high sensitivity). excavation, lowering the water table potentially by 15 m. Land use: Non coniferous trees Any dewatering would have a betterment effect on fluvial flood risk due (Water Compatible Development, to a reduction of baseflow, although the size of the impact would depend low sensitivity). on the abstraction rate and amount of baseflow which is unknown. As

51 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score The most conservative sensitivity such, baseflow contribution to the River Irwell due northwest is expected for this element is high. to marginally reduce flood risk during the construction of the shaft. The magnitude of change to groundwater flood risk would therefore be negligible. Haslingden Road Low Given the proposed depths of the excavation to 2 mbgl and groundwater Neutral Attenuation Pond There is a Very Low to Low levels at this location, no significant amount of groundwater would be potential risk of groundwater expected to drain into the open excavation during construction. If emergence (limited potential for dewatering were required, it would have a marginal beneficial effect on groundwater flooding to occur) groundwater flood risk. (BGS, 2020) (low sensitivity). The magnitude of change to groundwater flood risk would therefore be Land use: Bracken, heath or rough negligible. grassland (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is low. Haslingden Road High No changes to groundwater levels would be anticipated as no dewatering Neutral Temporary Access Flooding susceptibility data would be required and any change to recharge would be negligible. Track coverage is only available for the The magnitude of change to groundwater flood risk would therefore be western half of the access track. negligible. For the majority of the site coverage, there is a Moderate to High potential risk of groundwater emergence (potential for flooding of below ground properties) (BGS, 2020) (medium sensitivity). Exceptions lie for two small areas in the west and middle of the access track where there is a Very High potential risk of groundwater

52 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score emergence (potential for groundwater flooding to occur at surface level) (high sensitivity). Land use: Bracken, heath or rough grassland (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is high. Townsend Fold WTW High Given the proposed depths of the excavation to 5 mbgl, an emergence of Neutral Connection - open There is a Very High potential risk groundwater would be expected inside the open excavation during cut section of groundwater emergence construction. Appropriate drainage strategies embedded into the design connecting the (potential for groundwater would be implemented to mitigate for flooding in the excavation. existing pipeline to flooding to occur at surface level) Groundwater drawdown would occur down to the base of the excavation, the Proposed (BGS, 2020) (high sensitivity). lowering the water table potentially by 4 m. Haslingden and Land use: Existing access road The magnitude of change to groundwater flood risk would therefore be Walmersley Tunnel (medium sensitivity), sewage negligible. treatment works (Less Vulnerable, high sensitivity) and non- coniferous trees (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is high. Secondary A Haslingden Road Very High No changes to groundwater levels would be anticipated as no dewatering Neutral Bedrock Aquifers Compound - enabling For approximately half of the site, would be required for construction of the compound. (Marsden Formation works (e.g. top soil there is a Very Low to Low The magnitude of change to groundwater flood risk would therefore be and Rossendale stripping) potential risk of groundwater negligible. Formations, both emergence (limited potential for part of the Millstone groundwater flooding to occur)

53 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score Grit Group) (BGS, (BGS, 2020) (low sensitivity). 2020) Exceptions exist to the north and west of the site where the susceptibility of groundwater flooding is classified as a Moderate to High (potential for flooding of below ground properties) (medium sensitivity) and Very High (potential for groundwater flooding to occur at surface level) (high sensitivity). Land use includes Bracken, the A682 and an electricity substation The most conservative sensitivity for this element is very high.

4. Fluvial flood risk – Commissioning Phase Haslingden and Walmersley Section

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score

Fluvial Flood Risk The Woodgate Hill Low No new structures are proposed as part of the commissioning phase of the Neutral WTW Compound and Proposed Haslingden and Walmersley Section with all the flows managed Flood Zone 1. pipework connecting using existing infrastructure. Therefore, there would be no risk to any new commissioning flow Fluvial flood risk is inferred structures. to the reservoirs at from the Flood Map for The commissioning phase of the Proposed Haslingden and Walmersley Heaton Park. Surface Water and indicates that the probability of Section would involve the discharge of water to reservoirs at Heaton Park. As flooding from these

54 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score watercourses is less than 1% the discharge from Heaton Park would be in accordance with existing, agreed AEP. discharge rates the impact on flood risk downstream would be negligible. The land at the proposed trench crossing is undeveloped but residential property is located downstream.

5. Other sources of flood risk – Commissioning Phase Haslingden and Walmersley Section

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score

Surface Water flood The Woodgate Hill High No new structures would be required as part of the commissioning phase, there Neutral risk - Woodgate Hill would be no additional flood risks to this phase of the Proposed Haslingden WTW Compound and The Flood Map for Surface WTW Compound and Walmersley Section. pipework connecting Water indicates that whilst the commissioning flow probability of surface water As there would be no new structures required as part of the commissioning to the reservoirs at flooding is generally low, phase of the Proposed Haslingden and Walmersley Section, no impacts on Heaton Park. there are small areas which surface water flooding have been identified and the magnitude of change is would flood up to a maximum considered to be negligible. depth of 900 mm during a 3.33% AEP surface water flood event. Existing land use is grassed areas within the WTW.

55 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

6. Groundwater flood risk – Commissioning Phase Haslingden and Walmersley Section

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score

No impacts identified

7. Fluvial flood risk – Operational Phase Haslingden and Walmersley Section

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score

Unnamed A new permanent High The proposed new permanent valve house building Bolton Avenue TBM Neutral Watercourse 466 valve house building Flood Zone 1. Reception Compound would be at very low risk of fluvial flooding. within Bolton Avenue Ordinary Fluvial flood risk is inferred All surface water runoff would be captured and attenuated using sustainable TBM Reception Watercourse from the Flood Map for drainage techniques and either discharge to the watercourse at greenfield Compound area in Surface Water and indicates runoff rates or discharged to the ground. Therefore, the impact on fluvial flood the vicinity of the that the probability of risk downstream would be negligible. connection manifold flooding from this housing isolation watercourse is greater than or valves. equal to 3.33% AEP. The surrounding land is woodland but approximately 150 m downstream (north) of the proposed compound the watercourse is culverted beneath a railway. Gipsy Brook A new permanent Very High The proposed new permanent valve house building within Woodgate Hill WTW Neutral Ordinary building within Flood Zone 1. TBM Reception Compound the next to Castle Hill Road would be at very low Woodgate Hill WTW risk of fluvial flooding. Watercourse Fluvial flood risk is inferred Compound Site next from the Flood Map for

56 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score to Castle Hill Road to Surface Water and indicates All surface water runoff would be captured and attenuated using sustainable the west with around that the probability of drainage techniques and either discharge to the watercourse at greenfield 35 m. The building is flooding at the permanent runoff rates or discharged to the ground. Therefore, the impact on fluvial flood around 800 m to the building is less than 0.1% risk downstream would be negligible. south-east of Gipsy AEP. The land surrounding Brook. the watercourse is woodland in the close proximity of the Proposed Haslingden and Walmersley Section but the M66 is located downstream.

8. Other sources of flood risk – Operational Phase Haslingden and Walmersley Section

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score

Surface water flow A new permanent Low The operational infrastructure in this area has a low risk of surface water Neutral path close to valve house building The Flood Map for Surface Water flooding. Oakfield Avenue in the vicinity of the generally indicates a low risk of Surface water runoff from the proposed elements would be captured and connection manifold surface water flooding at the attenuated by a surface water drainage system., which would discharge to housing isolation proposed location of the ground. The impact on local surface water flood risk would therefore be valves. permanent valve house with negligible. flood depths below 300 mm is predicted during the 0.1% AEP event. Surface water flow A permanent valve Low The operational infrastructure in this area has a low risk of surface water Neutral path on Castle Hill house building would The Flood Map for Surface Water flooding. Road be next to Castle Hill generally indicates a low risk of Surface water runoff from the proposed elements would be captured and Road (approximately surface water flooding along attenuated by a surface water drainage system, which would discharge to

57 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score 30 m to the west Castle Hill Road with flood ground. The impact on local surface water flood risk would therefore be from the road). depths below 300 mm is negligible. predicted during the 0.1% AEP event.

9. Groundwater flood risk – Operational Phase Haslingden and Walmersley Section

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score

Secondary Bolton Avenue Shaft Medium The proposed shaft, 15 m in diameter and 14 m deep, could act as a very Neutral Undifferentiated For the majority of the shaft, there localised barrier to groundwater flow potentially leading to a localised rise Superficial Aquifer is a Very Low to Low potential risk of the water table up hydraulic gradient of the structure. (Glacial Till) as of groundwater emergence The magnitude of change to groundwater flood risk would therefore be indicated by (limited potential for groundwater negligible. nearby GI flooding to occur) (BGS, 2020) borehole data (low sensitivity). An exception lies in the west of the shaft where the susceptibility of groundwater flooding is classified as Moderate to High (potential for flooding of below ground properties) (medium sensitivity). Land use: Bracken, heath or rough grassland, and non-coniferous trees (Water Compatible Development, low sensitivity)

58 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score The most conservative sensitivity for this element is medium. Bolton Avenue Very High The open-cut construction method proposed for the Bolton Avenue Neutral Connection - open cut For approximately half of the site Connection, means that the trench would need to be backfilled with section connecting to the north east, there is a Very arisings or a granular bedding material. This could create a preferential the existing pipeline High potential risk of groundwater groundwater flow path and a local groundwater drawdown. to the Proposed emergence (potential for The magnitude of change to groundwater flood risk would therefore be Haslingden and groundwater flooding to occur at negligible. Walmersley Tunnel surface level) (BGS, 2020) (high sensitivity). In the southwest of the site, there is a Very Low to Low potential risk of groundwater emergence (limited potential for groundwater flooding to occur) (low sensitivity). Land use includes amenity grassland, bracken and electricity substation. The most conservative sensitivity for this element is very high. Bolton Avenue New High The open-cut construction method proposed for the Bolton Avenue New Neutral Meter Chamber There is a Very High potential risk Meter Chamber, means that the excavation would need to be backfilled of groundwater emergence with arisings and/or concrete for the foundations. This could create a (potential for groundwater localised barrier to groundwater flow potentially leading to a localised rise flooding to occur at surface level) of the water table up hydraulic gradient of the structure. (BGS, 2020) (high sensitivity). The magnitude of change to groundwater flood risk would therefore be Land use: Bracken, heath, or rough negligible. grassland (Water Compatible Development, low sensitivity)

59 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score The most conservative sensitivity for this element is high. Secondary Haslingden Road Low The proposed shaft, 15 m in diameter and 53.5 m deep, could act as a very Neutral Undifferentiated Double Drive There is a Very Low to Low localised barrier to groundwater flow potentially leading to a localised rise Superficial Aquifer potential risk of groundwater of the water table up hydraulic gradient of the structure. (Glacial Till) (BGS, emergence (limited potential for The magnitude of change to groundwater flood risk would therefore be 2020) groundwater flooding to occur) negligible. (BGS, 2020) (low sensitivity). Land use: Bracken, heath, or rough grassland (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is low. New Hall Hey Medium The proposed shaft , 9 m in diameter and 17 m deep, could act as a very Neutral Compound There is a Moderate to High localised barrier to groundwater flow potentially leading to a localised rise potential risk of groundwater of the water table up hydraulic gradient of the structure. emergence (potential for flooding The magnitude of change to groundwater flood risk would therefore be of below ground properties) (BGS, negligible. 2020) (medium sensitivity). Land use: Open grassland (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is medium. Reinstated Low The attenuation ponds are assumed to be reinstated to ground level. The Neutral Haslingden Road There is a Very Low to Low associated backfilling of the excavation could lead to permanent localised Attenuation Pond potential risk of groundwater alterations in groundwater flows and levels at the site, depending on the emergence (limited potential for use of arisings / granular bedding material. However, due to the relatively

60 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score groundwater flooding to occur) shallow depth of the excavation it is not considered deep enough to (BGS, 2020) (low sensitivity). significantly affect groundwater flow. Land use: Bracken, heath or rough The magnitude of change to groundwater flood risk would therefore be grassland (Water Compatible negligible. Development, low sensitivity). The most conservative sensitivity for this element is low. Secondary Shaft at Medium The proposed shaft, 9 m in diameter and 10 m deep, could act as a very Neutral Woodgate Hill WTW There is a Moderate to High localised barrier to groundwater flow potentially leading to a localised rise (connection to potential risk of groundwater of the water table up hydraulic gradient of the structure. Greater Manchester emergence (potential for flooding The magnitude of change to groundwater flood risk would therefore be Supply Network) of below ground properties) (BGS, negligible. 2020) (medium sensitivity). Land use: Open grassland (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is medium. Woodgate Hill WTW High No significant change to groundwater levels would be expected in the long Neutral Tunnel (connection to For roughly half of the length of term. Greater Manchester the tunnel in the north, there is a The magnitude of change to groundwater flood risk would therefore be Supply Network) - Very Low to Low potential risk of negligible. constructed using groundwater emergence (limited horizontal boring potential for groundwater flooding method, running from to occur) (BGS, 2020) (low the main shaft to the sensitivity). Exceptions exist in the mains to Manchester south, where the susceptibility of groundwater flooding is classified as a Moderate to High (potential

61 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score for flooding of below ground properties) (medium sensitivity) with a small area classified as Very High (potential for groundwater flooding to occur at surface level) (high sensitivity). Land use includes the WTW and a farm. The most conservative sensitivity for this element is high. Woodgate Hill WTW High The open-cut construction method proposed for the connection Neutral Mains Connection - For the majority of the site, there is excavation, means that the trench would need to be backfilled with arisings open-cut section to a Moderate to High potential risk or a granular bedding material. This could create a preferential allow for connection of groundwater emergence groundwater flow path and a local groundwater drawdown. from smaller (potential for flooding of below The magnitude of change to groundwater flood risk would therefore be diameter tunnel to ground properties) (BGS, 2020) negligible. existing Greater (medium sensitivity). An exception Manchester Supply lies in the southeast of the Network excavation where the susceptibility of groundwater flooding is classified as Very High (potential for groundwater flooding to occur at surface level) (high sensitivity). Land use: Open grassland (Water Compatible Development, low sensitivity), bracken, heath or rough grassland (Water Compatible Development, low sensitivity) and an access road (medium sensitivity).

62 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score The most conservative sensitivity for this element is high. Plantation Road mine High Sections of the route are to be constructed within the Pennine Lower Coal Moderate grouting area For the majority of the site, there is Measures Formation. The Pennine Lower Coal Measures Formation has (adverse) for a Very Low to Low potential risk of been subject to significant historical coal mining and this is expected to up-gradient groundwater emergence (limited have left a network of open features, including abandoned and collapsed effects and potential for groundwater flooding tunnels and adits, and have left the formation relatively unstable. In order Moderate to occur) (BGS, 2020) (low to enhance stability and limit losses of drilling fluids and displacement of (beneficial) sensitivity). An exception lies in the groundwater during tunnelling, grouting activities would target specific for down- north of the grout section where horizons within the formation for grout injection aimed at infilling any gradient the susceptibility of groundwater voids. It is assumed that the grouting boreholes would be backfilled with effects flooding is classified as Very High impermeable material on completion of grout injection, which is likely to to High (potential for groundwater create a semi-permeable zone, both in superficial deposits and bedrock. flooding to occur at surface level) Long term impact (high sensitivity). The horizons targeted by the grouting activities would currently be Land use: Agricultural land (rough preferential flow pathways for groundwater and when infilled the grout grazing etc) (Less Vulnerable, low would create an impediment to groundwater flow at depth. A further sensitivity), the area crosses the impediment to flow would be expected as a result of the grouting A56 highway (high sensitivity) and boreholes being backfilled with impermeable material on completion of unclassified roads (medium grout injection. The groundwater would tend to find alternative flow sensitivity) and bounds an pathways around the grouted areas (including grouted boreholes). agricultural building (Less Generally, the impediment would likely increase the groundwater pressure Vulnerable, high sensitivity). head on the upstream side and within the grouted areas, and would likely The most conservative sensitivity lower the pressure head on the downstream side and may locally redirect for this element is high. groundwater flows. This is a long-term impact potentially affecting construction activities carried out during the construction phase and beyond. Several surface watercourses would potentially be affected by changes in groundwater levels around the proposed grouting areas. Reduced groundwater levels on the down-gradient side of the grouting area could

63 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score lead to potential reduced groundwater baseflow contribution to Unnamed Watercourses 498, 1694, 1690 and 482. Increased groundwater levels on the up-gradient side of the grouting area could lead to potential increased baseflow contributions to Unnamed Watercourse 1690. The magnitude of change to groundwater flood risk would therefore be minor (adverse) for up-gradient effects and minor (beneficial) for down- gradient effects. White Carr Lane mine High Sections of the route are to be constructed within the Pennine Lower Coal Moderate grouting area For the majority of the site, there is Measures Formation. The Pennine Lower Coal Measures Formation has (adverse) for a Very High to High potential risk been subject to significant historical coal mining and this is expected to up-gradient of groundwater emergence have left a network of open features, including abandoned and collapsed effects and (potential for groundwater tunnels and adits, and have left the formation relatively unstable. In order Moderate flooding to occur at surface level) to enhance stability and limit losses of drilling fluids and displacement of (beneficial) (BGS, 2020) (high sensitivity). groundwater during tunnelling, grouting activities would target specific for down- Exceptions exist for small areas in horizons within the formation for grout injection aimed at infilling any gradient the southwest and the coal seam voids. It is assumed that the grouting boreholes would be backfilled with effects arm in the west of the grouted impermeable material on completion of grout injection, which is likely to section where the susceptibility of create a semi-permeable zone, both in superficial deposits and bedrock. groundwater flooding is classified Long term impact as Very Low to Low (limited The horizons targeted by the grouting activities would currently be potential for groundwater flooding preferential flow pathways for groundwater and when infilled the grout to occur) (low sensitivity). A small would create an impediment to groundwater flow at depth. A further area in the northwest of the impediment to flow would be expected as a result of the grouting grouted section is classified as boreholes being backfilled with impermeable material on completion of Moderate to High (potential for grout injection. The groundwater would tend to find alternative flow flooding of below ground pathways around the grouted areas (including grouted boreholes). properties) (medium sensitivity). Generally, the impediment would likely increase the groundwater pressure Land use: Agricultural land (high head on the upstream side and within the grouted areas, and would likely quality productive wheat fields) lower the pressure head on the downstream side and may locally redirect groundwater flows. This is a long-term impact potentially affecting

64 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score (medium sensitivity), existing construction activities carried out during the construction phase and access track (medium sensitivity). beyond. The most conservative sensitivity Several surface watercourses would potentially be affected by changes in for this element is high. groundwater levels around the proposed grouting areas. Reduced groundwater levels on the down-gradient side of the grouting area could lead to potential reduced groundwater baseflow contribution to Pigs Lee Brook and Unnamed Watercourses 995, 588, 589. The magnitude of change to groundwater flood risk would therefore be minor (adverse) for up-gradient effects and minor (beneficial) for down- gradient effects. Woodgate Hill mine High Sections of the route are to be constructed within the Pennine Lower Coal Moderate grouting area For the southern half of the site, Measures Formation. The Pennine Lower Coal Measures Formation has (adverse) for there is predominantly a Very Low been subject to significant historical coal mining and this is expected to up-gradient to Low potential risk of have left a network of open features, including abandoned and collapsed effects and groundwater emergence (limited tunnels and adits, and have left the formation relatively unstable. In order Moderate potential for groundwater flooding to enhance stability and limit losses of drilling fluids and displacement of (beneficial) to occur) (BGS, 2020) (low groundwater during tunnelling, grouting activities would target specific for down- sensitivity). For the northern half horizons within the formation for grout injection aimed at infilling any gradient of the site, there is predominantly voids. It is assumed that the grouting boreholes would be backfilled with effects a Moderate to High potential risk impermeable material on completion of grout injection, which is likely to of groundwater emergence create a semi-permeable zone, both in superficial deposits and bedrock. (potential for flooding of below Long term impact ground properties) (medium The horizons targeted by the grouting activities would currently be sensitivity) with a large section in preferential flow pathways for groundwater and when infilled the grout the centre that is classified as High would create an impediment to groundwater flow at depth. A further to Very High (potential for impediment to flow would be expected as a result of the grouting groundwater flooding to occur at boreholes being backfilled with impermeable material on completion of surface level) (high sensitivity). grout injection. The groundwater would tend to find alternative flow Land use: Agricultural land (rough pathways around the grouted areas (including grouted boreholes). grazing etc), bracken, heath or Generally, the impediment would likely increase the groundwater pressure

65 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score rough grassland, and non- head on the upstream side and within the grouted areas, and would likely coniferous trees (Water lower the pressure head on the downstream side and may locally redirect Compatible Development, low groundwater flows. This is a long-term impact potentially affecting sensitivity), existing access track construction activities carried out during the construction phase and (medium sensitivity), unclassified beyond. roads (medium sensitivity) and a Several surface watercourses would potentially be affected by changes in construction yard (medium groundwater levels around the proposed grouting areas. Reduced sensitivity). groundwater levels on the down-gradient side of the grouting area could The most conservative sensitivity lead to potential reduced groundwater baseflow contribution to Gipsy for this element is high. Brook and Unnamed Watercourses 602 (upstream Gipsy Brook), 605 (upstream Gipsy Brook), 608, 603, 604 and 607. Increased groundwater levels on the up-gradient side of the grouting area could lead to potential increased baseflow contributions to Unnamed Watercourses 602 (upstream Gipsy Brook), 605 (upstream Gipsy Brook) and 608. The magnitude of change to groundwater flood risk would therefore be minor (adverse) for up-gradient effects and minor (beneficial) for down- gradient effects. Secondary A Townsend Fold WTW High The proposed shaft, 9 m in diameter and 16 m deep, could act as a very Neutral Superficial Aquifer Compound There is a Very High potential risk localised barrier to groundwater flow potentially leading to a localised rise (Alluvium) (BGS, of groundwater emergence of the water table up hydraulic gradient of the structure. 2020) (potential for groundwater The magnitude of change to groundwater flood risk would therefore be flooding to occur at surface level) negligible. (BGS, 2020) (high sensitivity). Land use: Non coniferous trees (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is high.

66 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score

Townsend Fold WTW High The open-cut construction method proposed for the Haslingden Road Neutral Connection - open cut There is a Very High potential risk Connection, means that the trench would need to be backfilled with section connecting of groundwater emergence arisings or a granular bedding material. This could create a preferential the existing pipeline (potential for groundwater groundwater flow path and a local groundwater drawdown. to the Proposed flooding to occur at surface level) The magnitude of change to groundwater flood risk would therefore be Haslingden and (BGS, 2020) (high sensitivity). negligible. Walmersley Tunnel Land use: Existing access road (medium sensitivity), sewage treatment works (Less Vulnerable, high sensitivity) and non- coniferous trees (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is high. No superficial Woodgate Hill WTW Low The proposed shaft, 15 m in diameter and 26.5 m deep, could act as a very Neutral deposits are Main Shaft There is a Very Low to Low localised barrier to groundwater flow potentially leading to a localised rise identified on BGS potential risk of groundwater of the water table up hydraulic gradient of the structure. mapping (BGS, emergence (limited potential for The magnitude of change to groundwater flood risk would therefore be 2020) groundwater flooding to occur) negligible. (BGS, 2020) (low sensitivity). Land use: Bracken, heath or rough grassland (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is low. Woodgate Hill WTW Low The open cut excavation into the side slope is not assumed to be backfilled Neutral Shaft Platform (for There is a Very Low to Low post construction. Given that the excavation would be left open and the Main Shaft) - built potential risk of groundwater unfilled after the platform is removed, seepage of groundwater into the

67 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score into the side slope to emergence (limited potential for excavation would be expected. This would result in minor, localised provide a level groundwater flooding to occur) flooding at the ground surface. ground surface with (BGS, 2020) (low sensitivity). The magnitude of change to groundwater flood risk would therefore be an excavation at the Land use: Bracken, heath or rough negligible. south west corner grassland (Water Compatible excavated down to 4 Development, low sensitivity). mbgl The most conservative sensitivity for this element is low. Woodgate Hill WTW Medium The open-cut construction method proposed for the connection Neutral Compound There is a Very Low to Low excavation, means that the trench would need to be backfilled with arisings Connection (East) - potential risk of groundwater or a granular bedding material. This could create a preferential open-cut section to emergence (limited potential for groundwater flow path and a local groundwater drawdown. allow for connection groundwater flooding to occur) The magnitude of change to groundwater flood risk would therefore be from main shaft to (BGS, 2020) (low sensitivity). negligible. existing Reservoir Land use: The excavation crosses Valve House an access track (medium sensitivity) and areas of bracken, heath or rough grassland (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is medium. Woodgate Hill WTW High The excavated platform may not be backfilled with arisings or a granular Neutral Compound There is a Very Low to Low bedding material. This could lead to increased infiltration to ground or Connection (West) - potential risk of groundwater localised accumulation of water should the conditions be saturated. This open-cut section to emergence (limited potential for would result in a very localised change that has no impact at wider scale. allow for connection groundwater flooding to occur) The magnitude of change to groundwater flood risk would therefore be from main shaft to (BGS, 2020) (low sensitivity). negligible.

68 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score existing Reservoir Land use: The excavation crosses a Valve House warehouse yard premises (Less Vulnerable, high sensitivity), open grassland (Water Compatible Development, low sensitivity) and an access road (medium sensitivity). The most conservative sensitivity for this element is high. Woodgate Hill WTW Low The open-cut construction method proposed for the Woodgate Hill WTW Neutral New Valve House There is a Very Low to Low New Valve House, means that the excavation would need to be backfilled potential risk of groundwater with arisings or concrete for the foundations. This could create a localised emergence (limited potential for barrier to groundwater flow potentially leading to a localised rise of the groundwater flooding to occur) water table up hydraulic gradient of the structure. (BGS, 2020) (low sensitivity). The magnitude of change to groundwater flood risk would therefore be Land use: heath or rough negligible. grassland (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is low. Secondary A Bolton Avenue Shaft Medium The proposed shaft, 15 m in diameter and 14 m deep, could act as a very Neutral Bedrock Aquifer For the majority of the shaft, there localised barrier to groundwater flow potentially leading to a localised rise (Pennine Lower is a Very Low to Low potential risk of the water table up hydraulic gradient of the structure. Coal Measures of groundwater emergence The magnitude of change to groundwater flood risk would therefore be Formation) (limited potential for groundwater negligible. flooding to occur) (BGS, 2020) (low sensitivity). An exception lies in the west of the shaft where the susceptibility of groundwater

69 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score flooding is classified as Moderate to High (potential for flooding of below ground properties) (medium sensitivity). Land use: Bracken, heath or rough grassland, and non-coniferous trees (Water Compatible Development, low sensitivity) The most conservative sensitivity for this element is medium. Bolton Avenue Very High The open-cut construction method proposed for the Bolton Avenue Neutral Connection - open cut For approximately half of the site Connection, means that the trench would need to be backfilled with section connecting to the north east, there is a Very arisings or a granular bedding material. This could create a preferential the existing pipeline High potential risk of groundwater groundwater flow path and a local groundwater drawdown. to the Proposed emergence (potential for The magnitude of change to groundwater flood risk would therefore be Haslingden and groundwater flooding to occur at negligible. Walmersley Tunnel surface level) (BGS, 2020) (high sensitivity). In the southwest of the site, there is a Very Low to Low potential risk of groundwater emergence (limited potential for groundwater flooding to occur) (low sensitivity). Land use includes amenity grassland, bracken and electricity substation. The most conservative sensitivity for this element is very high.

70 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score

Bolton Avenue New High The open-cut construction method proposed for the Bolton Avenue New Neutral Meter Chamber There is a Very High potential risk Meter Chamber, means that the excavation would need to be backfilled of groundwater emergence with arisings and/or concrete for the foundations. This could create a (potential for groundwater localised barrier to groundwater flow potentially leading to a localised rise flooding to occur at surface level) of the water table up hydraulic gradient of the structure. (BGS, 2020) (high sensitivity). The magnitude of change to groundwater flood risk would therefore be Land use: Bracken, heath or rough negligible. grassland (Water Compatible Development, low sensitivity) The most conservative sensitivity for this element is high. Woodgate Hill WTW Low The proposed shaft, 15 m in diameter and 26.5 m deep, could act as a very Neutral Main Shaft There is a Very Low to Low localised barrier to groundwater flow potentially leading to a localised rise potential risk of groundwater of the water table up hydraulic gradient of the structure. emergence (limited potential for The magnitude of change to groundwater flood risk would therefore be groundwater flooding to occur) negligible. (BGS, 2020) (low sensitivity). Land use: Bracken, heath or rough grassland (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is low. Woodgate Hill WTW Low The open cut excavation into the side slope is not assumed to be backfilled Neutral Shaft Platform (for There is a Very Low to Low post construction. Given that the excavation would be left open and the Main Shaft) - built potential risk of groundwater unfilled after the platform is removed, seepage of groundwater into the into the side slope to emergence (limited potential for excavation would be expected. This would result in minor, localised provide a level groundwater flooding to occur) flooding at the ground surface. ground surface with (BGS, 2020) (low sensitivity). the south west corner

71 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score excavated down to 4 Land use: Bracken, heath or rough The magnitude of change to groundwater flood risk would therefore be mbgl grassland (Water Compatible negligible. Development, low sensitivity). The most conservative sensitivity for this element is low. Secondary Shaft at Medium The proposed shaft, 9 m in diameter and 10 m deep, could act as a very Neutral Woodgate Hill WTW There is a Moderate to High localised barrier to groundwater flow potentially leading to a localised rise (connection to potential risk of groundwater of the water table up hydraulic gradient of the structure. Greater Manchester emergence (potential for flooding The magnitude of change to groundwater flood risk would therefore be Supply Network) of below ground properties) (BGS, negligible. 2020) (medium sensitivity). Land use: Open grassland (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is medium. Woodgate Hill WTW High No significant change to groundwater levels would be expected in the long Neutral Tunnel (connection to For roughly half of the length of term. Greater Manchester the tunnel in the north, there is a The magnitude of change to groundwater flood risk would therefore be Supply Network) - Very Low to Low potential risk of negligible. constructed using groundwater emergence (limited horizontal boring potential for groundwater flooding method, running from to occur) (BGS, 2020) (low the main shaft to the sensitivity). Exceptions exist in the mains to Manchester south, where the susceptibility of groundwater flooding is classified as a Moderate to High (potential for flooding of below ground properties) (medium sensitivity)

72 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score with a small area classified as Very High (potential for groundwater flooding to occur at surface level) (high sensitivity). Land use includes the WTW and a farm. The most conservative sensitivity for this element is high. Woodgate Hill WTW Medium The open-cut construction method proposed for the connection Neutral Compound There is a Very Low to Low excavation, means that the trench would need to be backfilled with arisings Connection (East) - potential risk of groundwater or a granular bedding material. This could create a preferential open-cut section to emergence (limited potential for groundwater flow path and a local groundwater drawdown. allow for connection groundwater flooding to occur) The magnitude of change to groundwater flood risk would therefore be from main shaft to (BGS, 2020) (low sensitivity). negligible. existing Reservoir Land use: The excavation crosses Valve House an access track (medium sensitivity) and areas of bracken, heath or rough grassland (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is medium. Woodgate Hill WTW High The excavated platform may not be backfilled with arisings or a granular Neutral Compound There is a Very Low to Low bedding material. This could lead to increased infiltration to ground or Connection (West) - potential risk of groundwater localised accumulation of water should the conditions be saturated. This open-cut section to emergence (limited potential for would result in a very localised change that has no impact at wider scale. allow for connection groundwater flooding to occur) The magnitude of change to groundwater flood risk would therefore be from main shaft to (BGS, 2020) (low sensitivity). negligible.

73 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score existing Reservoir Land use: The excavation crosses a Valve House warehouse yard premises (Less Vulnerable, high sensitivity), open grassland (Water Compatible Development, low sensitivity) and an access road (medium sensitivity). The most conservative sensitivity for this element is high. Woodgate Hill WTW High The open-cut construction method proposed for the connection Neutral Mains Connection - For the majority of the site, there is excavation, means that the trench would need to be backfilled with arisings open-cut section to a Moderate to High potential risk or a granular bedding material. This could create a preferential allow for connection of groundwater emergence groundwater flow path and a local groundwater drawdown. from smaller (potential for flooding of below The magnitude of change to groundwater flood risk would therefore be diameter tunnel to ground properties) (BGS, 2020) negligible. existing Greater (medium sensitivity). An exception Manchester Supply lies in the southeast of the Network excavation where the susceptibility of groundwater flooding is classified as Very High (potential for groundwater flooding to occur at surface level) (high sensitivity). Land use: Open grassland (Water Compatible Development, low sensitivity), bracken, heath or rough grassland (Water Compatible Development, low sensitivity) and an access road (medium sensitivity).

74 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score The most conservative sensitivity for this element is high. Woodgate Hill WTW Low The open-cut construction method proposed for the Woodgate Hill WTW Neutral New Valve House There is a Very Low to Low New Valve House, means that the excavation would need to be backfilled potential risk of groundwater with arisings or concrete for the foundations. This could create a localised emergence (limited potential for barrier to groundwater flow potentially leading to a localised rise of the groundwater flooding to occur) water table up hydraulic gradient of the structure. (BGS, 2020) (low sensitivity). The magnitude of change to groundwater flood risk would therefore be Land use: heath or rough negligible. grassland (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is low. Plantation Road mine High Sections of the route are to be constructed within the Pennine Lower Coal Moderate grouting area For the majority of the site, there is Measures Formation. The Pennine Lower Coal Measures Formation has (adverse) for a Very Low to Low potential risk of been subject to significant historical coal mining and this is expected to up-gradient groundwater emergence (limited have left a network of open features, including abandoned and collapsed effects and potential for groundwater flooding tunnels and adits, and have left the formation relatively unstable. In order Moderate to occur) (BGS, 2020) (low to enhance stability and limit losses of drilling fluids and displacement of (beneficial) sensitivity). An exception lies in the groundwater during tunnelling, grouting activities would target specific for down- north of the grout section where horizons within the formation for grout injection aimed at infilling any gradient the susceptibility of groundwater voids. It is assumed that the grouting boreholes would be backfilled with effects flooding is classified as Very High impermeable material on completion of grout injection, which is likely to to High (potential for groundwater create a semi-permeable zone, both in superficial deposits and bedrock. flooding to occur at surface level) Long term impact (high sensitivity). The horizons targeted by the grouting activities would currently be Land use: Agricultural land (rough preferential flow pathways for groundwater and when infilled the grout grazing etc) (Less Vulnerable, low would create an impediment to groundwater flow at depth. A further sensitivity), the area crosses the impediment to flow would be expected as a result of the grouting

75 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score A56 highway (high sensitivity) and boreholes being backfilled with impermeable material on completion of unclassified roads (medium grout injection. The groundwater would tend to find alternative flow sensitivity) and bounds an pathways around the grouted areas (including grouted boreholes). agricultural building (Less Generally, the impediment would likely increase the groundwater pressure Vulnerable, high sensitivity). head on the upstream side and within the grouted areas, and would likely The most conservative sensitivity lower the pressure head on the downstream side and may locally redirect for this element is high. groundwater flows. This is a long-term impact potentially affecting construction activities carried out during the construction phase and beyond. Several surface watercourses would potentially be affected by changes in groundwater levels around the proposed grouting areas. Reduced groundwater levels on the down-gradient side of the grouting area could lead to potential reduced groundwater baseflow contribution to Unnamed Watercourses 498, 1694, 1690 and 482. Increased groundwater levels on the up-gradient side of the grouting area could lead to potential increased baseflow contributions to Unnamed Watercourse 1690. The magnitude of change to groundwater flood risk would therefore be minor (adverse) for up-gradient effects and minor (beneficial) for down- gradient effects. White Carr Lane mine High Sections of the route are to be constructed within the Pennine Lower Coal Moderate grouting area For the majority of the site, there is Measures Formation. The Pennine Lower Coal Measures Formation has (adverse) for a Very High to High potential risk been subject to significant historical coal mining and this is expected to up-gradient of groundwater emergence have left a network of open features, including abandoned and collapsed effects and (potential for groundwater tunnels and adits, and have left the formation relatively unstable. In order Moderate flooding to occur at surface level) to enhance stability and limit losses of drilling fluids and displacement of (beneficial) (BGS, 2020) (high sensitivity). groundwater during tunnelling, grouting activities would target specific for down- Exceptions exist for small areas in horizons within the formation for grout injection aimed at infilling any gradient the southwest and the coal seam voids. It is assumed that the grouting boreholes would be backfilled with effects arm in the west of the grouted impermeable material on completion of grout injection, which is likely to section where the susceptibility of create a semi-permeable zone, both in superficial deposits and bedrock.

76 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score groundwater flooding is classified Long term impact as Very Low to Low (limited The horizons targeted by the grouting activities would currently be potential for groundwater flooding preferential flow pathways for groundwater and when infilled the grout to occur) (low sensitivity). A small would create an impediment to groundwater flow at depth. A further area in the northwest of the impediment to flow would be expected as a result of the grouting grouted section is classified as boreholes being backfilled with impermeable material on completion of Moderate to High (potential for grout injection. The groundwater would tend to find alternative flow flooding of below ground pathways around the grouted areas (including grouted boreholes). properties) (medium sensitivity). Generally, the impediment would likely increase the groundwater pressure Land use: Agricultural land (high head on the upstream side and within the grouted areas, and would likely quality productive wheat fields) lower the pressure head on the downstream side and may locally redirect (medium sensitivity), existing groundwater flows. This is a long-term impact potentially affecting access track (medium sensitivity). construction activities carried out during the construction phase and The most conservative sensitivity beyond. for this element is high. Several surface watercourses would potentially be affected by changes in groundwater levels around the proposed grouting areas. Reduced groundwater levels on the down-gradient side of the grouting area could lead to potential reduced groundwater baseflow contribution to Pigs Lee Brook and Unnamed Watercourses 995, 588, 589. The magnitude of change to groundwater flood risk would therefore be minor (adverse) for up-gradient effects and minor (beneficial) for down- gradient effects. Woodgate Hill mine High Sections of the route are to be constructed within the Pennine Lower Coal Moderate grouting area For the southern half of the site, Measures Formation. The Pennine Lower Coal Measures Formation has (adverse) for there is predominantly a Very Low been subject to significant historical coal mining and this is expected to up-gradient to Low potential risk of have left a network of open features, including abandoned and collapsed effects and groundwater emergence (limited tunnels and adits, and have left the formation relatively unstable. In order Moderate potential for groundwater flooding to enhance stability and limit losses of drilling fluids and displacement of (beneficial) to occur) (BGS, 2020) (low groundwater during tunnelling, grouting activities would target specific for down- sensitivity). For the northern half horizons within the formation for grout injection aimed at infilling any

77 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score of the site, there is predominantly voids. It is assumed that the grouting boreholes would be backfilled with gradient a Moderate to High potential risk impermeable material on completion of grout injection, which is likely to effects of groundwater emergence create a semi-permeable zone, both in superficial deposits and bedrock. (potential for flooding of below Long term impact ground properties) (medium The horizons targeted by the grouting activities would currently be sensitivity) with a large section in preferential flow pathways for groundwater and when infilled the grout the centre that is classified as High would create an impediment to groundwater flow at depth. A further to Very High (potential for impediment to flow would be expected as a result of the grouting groundwater flooding to occur at boreholes being backfilled with impermeable material on completion of surface level) (high sensitivity). grout injection. The groundwater would tend to find alternative flow Land use: Agricultural land (rough pathways around the grouted areas (including grouted boreholes). grazing etc), bracken, heath or Generally, the impediment would likely increase the groundwater pressure rough grassland, and non- head on the upstream side and within the grouted areas, and would likely coniferous trees (Water lower the pressure head on the downstream side and may locally redirect Compatible Development, low groundwater flows. This is a long-term impact potentially affecting sensitivity), existing access track construction activities carried out during the construction phase and (medium sensitivity), unclassified beyond. roads (medium sensitivity) and a Several surface watercourses would potentially be affected by changes in construction yard (medium groundwater levels around the proposed grouting areas. Reduced sensitivity). groundwater levels on the down-gradient side of the grouting area could The most conservative sensitivity lead to potential reduced groundwater baseflow contribution to Gipsy for this element is high. Brook and Unnamed Watercourses 602 (upstream Gipsy Brook), 605 (upstream Gipsy Brook), 608, 603, 604 and 607. Increased groundwater levels on the up-gradient side of the grouting area could lead to potential increased baseflow contributions to Unnamed Watercourses 602 (upstream Gipsy Brook), 605 (upstream Gipsy Brook) and 608. The magnitude of change to groundwater flood risk would therefore be minor (adverse) for up-gradient effects and minor (beneficial) for down- gradient effects.

78 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score

Secondary A Haslingden Road Low The proposed shaft, 15 m in diameter and 53.5 m deep, could act as a very Neutral Bedrock Aquifer Double Drive There is a Very Low to Low localised barrier to groundwater flow potentially leading to a localised rise (Marsden potential risk of groundwater of the water table up hydraulic gradient of the structure. Formation, emergence (limited potential for The magnitude of change to groundwater flood risk would therefore be Millstone Grit groundwater flooding to occur) negligible. Group) (BGS, (BGS, 2020) (low sensitivity). 2020) Land use: Bracken, heath or rough grassland (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is low. New Hall Hey Medium The proposed shaft, 9 m in diameter and 17 m deep, could act as a very Neutral Compound There is a Moderate to High localised barrier to groundwater flow potentially leading to a localised rise potential risk of groundwater of the water table up hydraulic gradient of the structure. emergence (potential for flooding The magnitude of change to groundwater flood risk would therefore be of below ground properties) (BGS, negligible. 2020) (medium sensitivity). Land use: Open grassland (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is medium. Townsend Fold WTW High The proposed shaft, 9 m in diameter and 16 m deep, could act as a very Neutral Compound There is a Very High potential risk localised barrier to groundwater flow potentially leading to a localised rise of groundwater emergence of the water table up hydraulic gradient of the structure. (potential for groundwater The magnitude of change to groundwater flood risk would therefore be flooding to occur at surface level) negligible. (BGS, 2020) (high sensitivity).

79 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score Land use: Non coniferous trees (Water Compatible Development, low sensitivity). The most conservative sensitivity for this element is high. Reinstated Low The attenuation ponds are assumed to be reinstated to ground level. The Neutral Haslingden Road There is a Very Low to Low associated backfilling of the excavation could lead to permanent localised Attenuation Pond potential risk of groundwater alterations in groundwater flows and levels at the site, depending on the emergence (limited potential for use of arisings / granular bedding material. However, due to the relatively groundwater flooding to occur) shallow depth of the excavation it is not considered deep enough to (BGS, 2020) (low sensitivity). significantly affect groundwater flow. Land use: Bracken, heath or rough The magnitude of change to groundwater flood risk would therefore be grassland (Water Compatible negligible. Development, low sensitivity). The most conservative sensitivity for this element is low. Townsend Fold WTW High The open-cut construction method proposed for the Townsend Fold Neutral Connection - open cut There is a Very High potential risk Connection, means that the trench would need to be backfilled with section connecting of groundwater emergence arisings or a granular bedding material. This could create a preferential the existing pipeline (potential for groundwater groundwater flow path and a local groundwater drawdown. to the Proposed flooding to occur at surface level) The magnitude of change to groundwater flood risk would therefore be Haslingden and (BGS, 2020) (high sensitivity). negligible. Walmersley Tunnel Land use: Existing access road (medium sensitivity), sewage treatment works (Less Vulnerable, high sensitivity) and non- coniferous trees (Water Compatible Development, low sensitivity).

80 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score The most conservative sensitivity for this element is high.

10. Fluvial flood risk – Decommissioning Phase Haslingden and Walmersley Section

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score

River Roch Existing overflow Very High The existing overflow structure remains in situ. However, the operation of the Neutral Main River structure remains in Flood Zone 2 and 3 indicating overflow would change as a result of the Proposed Haslingden and Walmersley situ to this river. a risk of fluvial flooding Section, which would now use the overflow to permanently discharge greater than or equal to 1% groundwater ingress from the existing section of aqueduct to be AEP. decommissioned into the River Roch. The continuous discharge of groundwater has the potential to increase flood risk downstream of the The Flood Map for Planning discharge location. identifies that the River Roch poses a risk to the M66 and A comparison of anticipated groundwater discharge flows from the downstream urban area decommissioned section of aqueduct with estimated QMED flood flows within including non-residential the River Roch has been undertaken. This indicates that the discharge from the properties at the end of overflow would be less than 1% of the QMED flow within the beck. Therefore, it Bridge Hall Lane. is considered that the impact on flood risk along the River Roch to downstream receptors would be negligible.

81 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

11. Groundwater flood risk – Decommissioning Phase Haslingden and Walmersley Section

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score

Secondary A Existing aqueduct Very high Once the new aqueduct is operational, the existing aqueduct will be Moderate Superficial Aquifer running between For the majority of the length decommissioned but remain in place. Ingress of groundwater into the existing (beneficial) (Alluvium, Bolton Avenue and of the existing aqueduct, aqueduct would be likely to occur over time representing a small dewatering Glaciofluvial sheet Woodgate Hill WTW susceptibility to groundwater rate (estimated at up to 61.4 l/s). This would be expected to generate a long- deposits) (BGS, Compounds flooding at the existing term groundwater drawdown over the length of the existing aqueduct at the 2020) aqueduct ranges from no Proposed Haslingden and Walmersley Section. Secondary B significant risk to a Low risk The magnitude of change to groundwater flood risk would therefore be minor Superficial Aquifer (BGS, 2020) (low sensitivity). (beneficial). (Head) (BGS, Small areas of High to Very 2020) High potential risk generally lie in the north and south of Secondary the route (potential for Undifferentiated groundwater flooding to Superficial Aquifer occur at surface level) (high (Glacial Till) (BGS, sensitivity). 2020) Land use: rough grazing Unproductive farmland (low sensitivity), Strata (Peat, productive land agriculture Glaciolacustrine (e.g. wheat) (medium deposits) (BGS, sensitivity), unclassified roads 2020) (medium sensitivity), residential dwellings (More Secondary A Vulnerable, very high Bedrock Aquifers sensitivity) and large areas of (Millstone Grit bracken, heath or rough Group, Rossendale grassland (Water Compatible Formation Development, low sensitivity), (Millstone Grit A56 highway (high Group), Marsden sensitivity), scrap yard

82 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment Annexe A: Flood Risk Assessment Tables

Flood Source Proposed Haslingden Likelihood / Importance Magnitude of Change Significance and Walmersley Name Type Section Element Score Justification Score Justification Score Formation (medium sensitivity) and (Millstone Grit sewage treatment works Group) (BGS, (Essential Infrastructure, very 2020) high sensitivity). The most conservative sensitivity for this element is very high.

83 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment

Annexe B: EIA Assessment Criteria

B.1 Baseline Sensitivity 199) The baseline sensitivity for flood sources considers:

▪ Probability (likelihood) of flooding from the flood source considered e.g. main rivers, ordinary watercourses, groundwater etc. (the primary receptor) using probability values used by the Environment Agency on flood zone data; and

▪ Consequences of flooding as indicated by the vulnerability of receptors at risk (property, infrastructure, agricultural land etc.) using vulnerability classifications within NPPF. Table B-1: Baseline sensitivity criteria Sensitivity Criteria Importance Low ▪ Fluvial - Land having a less than 0.1 % AEP of river flooding (Flood Zone 1) ▪ Surface water - Land having between 1 % and 0.1 % AEP of flooding from surface water ▪ Groundwater - areas with limited potential for groundwater flooding to occur ▪ Artificial infrastructure - Areas at risk of flooding from failures of water infrastructure; or ▪ Land use that is defined within the NPPF as water compatible. Medium ▪ Fluvial- Land having between 1 % and 0.1 % AEP of river flooding (Flood Zone 2) ▪ Surface water - Land having between a 1 % and 3.3 % AEP of flooding from surface water ▪ Groundwater - Areas with potential for groundwater flooding to receptors situated below ground level; or ▪ Land use including productive farmland or unclassified roads. High ▪ Fluvial - Land having a greater than 1 % AEP of river flooding (Flood Zone 3) ▪ Surface water - Land having a greater than 3.3 % AEP of flooding from surface water ▪ Groundwater - Areas with potential for groundwater flooding to occur at surface level or ▪ Land uses classified as Less Vulnerable within the NPPF or local transport networks and infrastructure. Very High ▪ Fluvial – Land where water has to flow or be stored in times of flood, referred to as Functional Floodplain (Flood Zone 3b) ▪ Land uses classified as Essential Infrastructure; More Vulnerable; or Highly Vulnerable; or where the increase in flood risk would result in a risk to life (i.e. a flood hazard that is dangerous for all).

B.1 Magnitude of Change Criteria 200) The magnitude of change is a measure of the scale or extent of the change in the baseline condition, irrespective of the value of the resource(s) affected. However, flood risk can be influenced by several factors, including:

▪ Potential changes associated with the source of flooding linked to a change (or combination in changes) in run-off/higher discharge, flood storage volume, conveyance, flood frequency, depth/extent, velocity and/or peak flow

37 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment

▪ Temporal changes to flooding such as permanent or temporary changes such as those that would be limited in duration to the construction period and those that would remain for the full duration of the operational life of the Proposed Haslingden and Walmersley Section

▪ “Embedded” mitigation measures that form part of an optimised design used to manage the likely significant flood risk effects. 201) The magnitude of change has been determined based on the factors above, the data available for flood sources and the criteria set within Table B-2 The term “Magnitude” of effects has been used to describe the severity of impacts within both the FRA and the Environmental Statement. 202) The overall baseline sensitivity was determined by the availability of data to determine probability for all flood sources and the potential for multiple receptors to be at risk. Where there was uncertainty regarding whether a receptor would be at risk, a precautionary approach was taken. Table B-2: Magnitude of change criteria Magnitude Criteria

Major A large adverse or beneficial change in flood depth, flood extent, velocity, or peak flow, that may have an impact some distance upstream or downstream. Potential to significantly change flood frequency. Potential change in risk to life. A large adverse or beneficial change in groundwater levels and flows which would affect groundwater flooding susceptibility over catchment scale. Moderate A moderate adverse or beneficial change in flood depth, flood extent or peak flow that may have limited impact some distance upstream or downstream. Potential for some change in flood frequency. Minor changes in floodplain flow pathways that increase velocity or extent of flooding but does not lead to new areas being inundated or new flow pathways forming. A moderate adverse or beneficial change in groundwater levels and flows which would affect groundwater flooding susceptibility over catchment scale or a large adverse or beneficial change in groundwater levels and flows which would affect groundwater flooding susceptibility over local scale. Minor A small or very localised adverse or beneficial change in flood depth, extent or peak flow with no perceptible impact upstream or downstream or in the floodplain. Small changes in flood frequency. A small adverse or beneficial change in groundwater levels and flows which would affect groundwater flooding susceptibility over catchment scale or a moderate adverse or beneficial change in groundwater levels and flows which would affect groundwater flooding susceptibility over local scale. Negligible Very limited potential for change. No change in flood frequency.

B.3 Significance of Impacts 203) The Significance of the overall flood risk is a product of the likelihood (sensitivity/value) and the magnitude of the impacts. Should the overall significance of flood risk be classified as moderate, large or very large, then additional mitigation would be required. Any effects that cannot be mitigated would be recorded as residual effects. 204) The overall risk of flooding during the construction and operational phases is a product of the likelihood of occurrence and the severity of impact as indicated in Table -3.

38 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment

Table B-3: Significance of flood risk Impacts

Magnitude of Impact

Negligible Minor Moderate Major

Low Neutral Neutral Slight Moderate/Large

Medium Neutral Slight Moderate Large

High Neutral Slight/Moderate Moderate/Large Large/Very Large

Very High Neutral Moderate/Large Large/Very Large Very Large Baseline Flood Risk Flood Baseline

39 Proposed Haslingden and Walmersley Section ES, Volume 4 Appendix 8.1: Flood Risk Assessment

Annexe C: Figures

Figure 1 – Proposed Haslingden and Walmersley Section Layout

Figure 2 – The Flood Map for Planning

Figure 3 – The Risk of Flooding from Surface Water Mapping

Figure 4 – Areas Susceptible to Groundwater

Figure 5 – Reservoir Flood Map

Refer to Planning Application drawings for further details on drainage.

▪ Proposed Haslingden and Walmersley Section - Construction Phase Drawing

▪ Proposed Haslingden and Walmersley Section - Connection Phase Drawing

40 / FIGURE 1

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The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. FIGURE 2 UNNAMED / WATERCOURSE 1901

UNNAMED WATERCOURSE 465

UNNAMED WATERCOURSE 466

Legend Planning Application Boundary UNNAMED WATERCOURSE Environment Agency Main Rivers 477 UNNAMED WATERCOURSE 1698 Watercourses

Flood Zone 3 UNNAMED WATERCOURSE 479 Flood Zone 2

UNNAMED WATERCOURSE 1695 UNNAMED UNNAMED WATERCOURSE 478 WATERCOURSE 475 UNNAMED UNNAMED WATERCOURSE 474 WATERCOURSE 1946 UNNAMED WATERCOURSE 476 UNNAMED UNNAMED WATERCOURSE 1694 WATERCOURSE 1693 UNNAMED WATERCOURSE 471 UNNAMED WATERCOURSE 480 RIVER HYNDBURN UNNAMED RIVER WATERCOURSE 1692 UNNAMED HYNDBURN WATERCOURSE 473

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UNNAMED UNNAMED WATERCOURSE 472 WATERCOURSE 498

UNNAMED WATERCOURSE 1970 UNITED UTILITIES WATER LIMITED UNNAMED HAWESWATER AQUEDUCT RESILIENCE PROGRAMME WATERCOURSE 1690 FLUVIAL FLOOD RISK PAGE 1 OF 8 UNNAMED SCALE SHEET SIZE WATERCOURSE 482 UNNAMED WATERCOURSE 481 UNNAMED 1:10,000 A3 0 0.25 0.5 1 WATERCOURSE 497 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-002 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right. © Crown copyright and database rights 2019 Ordnance Survey 100024198. Some features of this map are based on digital spatial data from the Centre for Ecology & Hydrology, © NERC (CEH). © Crown copyright and database rights 2018 Ordnance Survey 100024198 / FIGURE 2 UNNAMED WATERCOURSE 1970

UNNAMED WATERCOURSE 1690

UNNAMED UNNAMED WATERCOURSE 482 WATERCOURSE 481 UNNAMED WATERCOURSE 497

UNNAMED WARMDEN WATERCOURSE 1689 BROOK

Legend Planning Application Boundary

Environment Agency Main Rivers

Watercourses

Flood Zone 3

Flood Zone 2

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-002 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right. © Crown copyright and database rights 2019 Ordnance Survey 100024198. Some features of this map are based on digital spatial data from the Centre for Ecology & Hydrology, © NERC (CEH). © Crown copyright and database rights 2018 Ordnance Survey 100024198 / FIGURE 2

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Environment Agency Main Rivers

Watercourses

Flood Zone 3

Flood Zone 2

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-002 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right. © Crown copyright and database rights 2019 Ordnance Survey 100024198. Some features of this map are based on digital spatial data from the Centre for Ecology & Hydrology, © NERC (CEH). © Crown copyright and database rights 2018 Ordnance Survey 100024198 / FIGURE 2

UNNAMED UNNAMED WATERCOURSE 1809 WATERCOURSE 1808 UNNAMED UNNAMED WATERCOURSE WATERCOURSE 1810 1805 UNNAMED WATERCOURSE 1804 Legend UNNAMED Planning Application Boundary WATERCOURSE 2054 Environment Agency Main Rivers

Watercourses UNNAMED WATERCOURSE Flood Zone 3 1807 Flood Zone 2

UNNAMED WATERCOURSE BALLADEN 1802 BROOK

UNNAMED WATERCOURSE 1657 UNNAMED WATERCOURSE 1654

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RIVER IRWELL

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-002 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right. © Crown copyright and database rights 2019 Ordnance Survey 100024198. Some features of this map are based on digital spatial data from the Centre for Ecology & Hydrology, © NERC (CEH). © Crown copyright and database rights 2018 Ordnance Survey 100024198 RIVER IRWELL / FIGURE 2

Legend Planning Application Boundary

Environment Agency Main Rivers

Watercourses

Flood Zone 3

Flood Zone 2

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-002 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right. © Crown copyright and database rights 2019 Ordnance Survey 100024198. Some features of this map are based on digital spatial data from the Centre for Ecology & Hydrology, © NERC (CEH). © Crown copyright and database rights 2018 Ordnance Survey 100024198 / FIGURE 2

Legend Planning Application Boundary

Environment Agency Main Rivers

Watercourses

Flood Zone 3

Flood Zone 2

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-002 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right. © Crown copyright and database rights 2019 Ordnance Survey 100024198. Some features of this map are based on digital spatial data from the Centre for Ecology & Hydrology, © NERC (CEH). © Crown copyright and database rights 2018 Ordnance Survey 100024198 / FIGURE 2

UNNAMED WATERCOURSE 580

Legend Planning Application Boundary UNNAMED WATERCOURSE 1638 Environment Agency Main Rivers

UNNAMED Watercourses WATERCOURSE 582 PIGS LEE BROOK Flood Zone 3 Flood Zone 2

UNNAMED WATERCOURSE 995

UNNAMED WATERCOURSE 587

PIGS LEE BROOK

UNNAMED WATERCOURSE 589

UNNAMED UNNAMED WATERCOURSE 588 WATERCOURSE 600 0 SP CD CI Initial Issue 25/03/2021

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UNNAMED WATERCOURSE 1955

UNNAMED WATERCOURSE 601

UNNAMED WATERCOURSE 1988 UNITED UTILITIES WATER LIMITED HAWESWATER AQUEDUCT RESILIENCE PROGRAMME UNNAMED FLUVIAL FLOOD RISK WATERCOURSE 1639 PAGE 7 OF 8 UNNAMED WATERCOURSE SCALE SHEET SIZE 1900 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-002 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right. © Crown copyright and database rights 2019 Ordnance Survey 100024198. Some features of this map are based on digital spatial data from the Centre for Ecology & Hydrology, © NERC (CEH). © Crown copyright and database rights 2018 Ordnance Survey 100024198 UNNAMED FIGURE 2 / WATERCOURSE 1955 UNNAMED WATERCOURSE 601

UNNAMED WATERCOURSE 1988

UNNAMED WATERCOURSE 1639 UNNAMED WATERCOURSE 1900

UNNAMED WATERCOURSE 1640

UNNAMED WATERCOURSE UNNAMED 603 WATERCOURSE 602

UNNAMED WATERCOURSE 605

GYPSY Legend BROOK Planning Application Boundary

Environment Agency Main Rivers UNNAMED WATERCOURSE 604 Watercourses Flood Zone 3

Flood Zone 2

UNNAMED WATERCOURSE 603

UNNAMED WATERCOURSE 608

UNNAMED WATERCOURSE 607

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-002 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right. © Crown copyright and database rights 2019 Ordnance Survey 100024198. Some features of this map are based on digital spatial data from the Centre for Ecology & Hydrology, © NERC (CEH). © Crown copyright and database rights 2018 Ordnance Survey 100024198 / FIGURE 3

Legend Planning Application Boundary Risk of Flooding from Surface Water Surface Water Flood Extent 3.33% AEP

Surface Water Flood Extent 1% AEP

Surface Water Flood Extent 0.1% AEP

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-003 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right 2015. All rights reserved. / FIGURE 3

Legend Planning Application Boundary Risk of Flooding from Surface Water Surface Water Flood Extent 3.33% AEP

Surface Water Flood Extent 1% AEP

Surface Water Flood Extent 0.1% AEP

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-003 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right 2015. All rights reserved. / FIGURE 3

Legend Planning Application Boundary Risk of Flooding from Surface Water Surface Water Flood Extent 3.33% AEP

Surface Water Flood Extent 1% AEP

Surface Water Flood Extent 0.1% AEP

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-003 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right 2015. All rights reserved. / FIGURE 3

Legend Planning Application Boundary Risk of Flooding from Surface Water Surface Water Flood Extent 3.33% AEP

Surface Water Flood Extent 1% AEP

Surface Water Flood Extent 0.1% AEP

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-003 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right 2015. All rights reserved. / FIGURE 3

Legend Planning Application Boundary Risk of Flooding from Surface Water Surface Water Flood Extent 3.33% AEP

Surface Water Flood Extent 1% AEP

Surface Water Flood Extent 0.1% AEP

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-003 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right 2015. All rights reserved. / FIGURE 3

Legend Planning Application Boundary Risk of Flooding from Surface Water Surface Water Flood Extent 3.33% AEP

Surface Water Flood Extent 1% AEP

Surface Water Flood Extent 0.1% AEP

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-003 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right 2015. All rights reserved. / FIGURE 3

Legend Planning Application Boundary Risk of Flooding from Surface Water Surface Water Flood Extent 3.33% AEP

Surface Water Flood Extent 1% AEP

Surface Water Flood Extent 0.1% AEP

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-003 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right 2015. All rights reserved. / FIGURE 3

Legend Planning Application Boundary Risk of Flooding from Surface Water Surface Water Flood Extent 3.33% AEP

Surface Water Flood Extent 1% AEP

Surface Water Flood Extent 0.1% AEP

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-003 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right 2015. All rights reserved. / FIGURE 4

Legend Planning Application Boundary Groundwater Flooding Susceptibility Areas Very Low - Low

Moderate - High

Very High

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-004 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right. © Crown copyright and database rights 2019 Ordnance Survey 100024198. Some features of this map are based on digital spatial data from the Centre for Ecology & Hydrology, © NERC (CEH). © Crown copyright and database rights 2018 Ordnance Survey 100024198 / FIGURE 4

Legend Planning Application Boundary Groundwater Flooding Susceptibility Areas Very Low - Low

Moderate - High

Very High

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-004 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right. © Crown copyright and database rights 2019 Ordnance Survey 100024198. Some features of this map are based on digital spatial data from the Centre for Ecology & Hydrology, © NERC (CEH). © Crown copyright and database rights 2018 Ordnance Survey 100024198 / FIGURE 4

Legend Planning Application Boundary Groundwater Flooding Susceptibility Areas Very Low - Low

Moderate - High

Very High

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-004 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right. © Crown copyright and database rights 2019 Ordnance Survey 100024198. Some features of this map are based on digital spatial data from the Centre for Ecology & Hydrology, © NERC (CEH). © Crown copyright and database rights 2018 Ordnance Survey 100024198 / FIGURE 4

Legend Planning Application Boundary Groundwater Flooding Susceptibility Areas Very Low - Low

Moderate - High

Very High

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-004 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right. © Crown copyright and database rights 2019 Ordnance Survey 100024198. Some features of this map are based on digital spatial data from the Centre for Ecology & Hydrology, © NERC (CEH). © Crown copyright and database rights 2018 Ordnance Survey 100024198 / FIGURE 4

Legend Planning Application Boundary Groundwater Flooding Susceptibility Areas Very Low - Low

Moderate - High

Very High

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-004 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right. © Crown copyright and database rights 2019 Ordnance Survey 100024198. Some features of this map are based on digital spatial data from the Centre for Ecology & Hydrology, © NERC (CEH). © Crown copyright and database rights 2018 Ordnance Survey 100024198 / FIGURE 4

Legend Planning Application Boundary Groundwater Flooding Susceptibility Areas Very Low - Low

Moderate - High

Very High

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-004 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right. © Crown copyright and database rights 2019 Ordnance Survey 100024198. Some features of this map are based on digital spatial data from the Centre for Ecology & Hydrology, © NERC (CEH). © Crown copyright and database rights 2018 Ordnance Survey 100024198 / FIGURE 4

Legend Planning Application Boundary Groundwater Flooding Susceptibility Areas Very Low - Low

Moderate - High

Very High

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-004 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right. © Crown copyright and database rights 2019 Ordnance Survey 100024198. Some features of this map are based on digital spatial data from the Centre for Ecology & Hydrology, © NERC (CEH). © Crown copyright and database rights 2018 Ordnance Survey 100024198 / FIGURE 4

Legend Planning Application Boundary Groundwater Flooding Susceptibility Areas Very Low - Low

Moderate - High

Very High

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SCALE SHEET SIZE 1:10,000 A3 0 0.25 0.5 1 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-004 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. © Environment Agency copyright and/or database right. © Crown copyright and database rights 2019 Ordnance Survey 100024198. Some features of this map are based on digital spatial data from the Centre for Ecology & Hydrology, © NERC (CEH). © Crown copyright and database rights 2018 Ordnance Survey 100024198 / FIGURE 5

Legend Planning Application Boundary

500m Assessment Area Risk of Flooding from Reservoirs Maximum Extent of Flooding

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SCALE SHEET SIZE 1:25,000 A3 0 0.5 1 2 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-005 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. Contains public sector information licensed under the Open Government Licence v3.0. / FIGURE 5

Legend Planning Application Boundary

500m Assessment Area Risk of Flooding from Reservoirs Maximum Extent of Flooding

0 SP CD CI Initial Issue 25/03/2021

VERSION AUTH CHKD REVD REASON FOR ISSUE DATE

UNITED UTILITIES WATER LIMITED HAWESWATER AQUEDUCT RESILIENCE PROGRAMME RESERVOIR FLOOD MAP PAGE 2 OF 3

SCALE SHEET SIZE 1:25,000 A3 0 0.5 1 2 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-005 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. Contains public sector information licensed under the Open Government Licence v3.0. / FIGURE 5

Legend Planning Application Boundary

500m Assessment Area Risk of Flooding from Reservoirs Maximum Extent of Flooding

0 SP CD CI Initial Issue 25/03/2021

VERSION AUTH CHKD REVD REASON FOR ISSUE DATE

UNITED UTILITIES WATER LIMITED HAWESWATER AQUEDUCT RESILIENCE PROGRAMME RESERVOIR FLOOD MAP PAGE 3 OF 3

SCALE SHEET SIZE 1:25,000 A3 0 0.5 1 2 DRAWING NUMBER REVISION kilometres HBC_RBC_BMBC-HW-FIG-FRA-005 0 The copyright of this document, which contains information of a proprietary nature, is vested in United Utilities Water Limited. The content of this document may not be used for purposes other than that for which it has been supplied and may not be reproduced, either wholly or in part, in any way whatsoever. It may not be used by, or its contents divulged to any other person whatsoever without the prior written permission of United Utilities Water Limited. Copyright Acknowledgement: Use of Ordnance Survey map data sanctioned by the controller of H.M. Stationery Office. OS Licence Number 100019326.Contains OS data © Crown copyright and database right 2020.© Crown copyright and database rights 2020 Ordnance Survey 0100031673. Contains public sector information licensed under the Open Government Licence v3.0.