Appendix G - Network Rail - Citizen Space · THE NETWORK RAIL (MANCHESTER ... Salford City and Trafford Councils Level 2 Hybrid Strategic ... by JBA Consulting, March 2010; x Manchester

THE TRANSPORT AND WORKS ACT 1992

THE NETWORK RAIL (MANCHESTER PICCADILLY AND OXFORD ROAD)ORDER

DOCUMENT 21: ENVIRONMENTAL STATEMENT

DOCUMENT 21.19: FLOOD RISK ASSESSMENT

Flood Risk Assessment for theManchester Piccadilly and Oxford Road

Capacity Scheme, Northern Hub,Manchester

Prepared by Parsons BrinckerhoffJune 2014 for Network Rail

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June 2014

FLOOD RISK ASSESSMENT FOR THE

MANCHESTER PICCADILLY AND

OXFORD ROAD CAPACITY SCHEME,

NORTHERN HUB, MANCHESTER

Network Rail

Job No 3513120DFinal

Flood Risk Assessment for theManchester Piccadilly and

Oxford Road Capacity Scheme,Northern Hub, Manchester

Prepared forNetwork RailKings Place

90 York WayLondonN1 9AG

Prepared byParsons Brinckerhoff

Queen Victoria HouseRedland Hill

BristolBS6 6US

01179339300 www.pbworld.com

http://www.pbworld.com/

Report Title : Flood Risk Assessment for the ManchesterPiccadilly and Oxford Road Capacity Scheme,Northern Hub, Manchester

PIMS Number :

Report Status : Draft

Job No : 3513120D

Date : June 2014

DOCUMENT HISTORY AND STATUS

Document control

Prepared by Elzbieta Szostak Checked by(technical) Joanna Goodwin

Approved by Jonathan Ralph Checked by(quality assurance) Jonathan Price

Revision details

Version Date Pagesaffected Comments

1.0 June 2014




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CONTENTSPage

INTRODUCTION 9

1 INTRODUCTION 111.1 Project Background 111.2 Development Proposals 111.3 Consultation 12

ASSESSMENT METHODOLOGY 13

2 ASSESSMENT METHODOLOGY 152.1 Overview 152.2 Definition of Flood Risk 162.3 Potential Sources of Flooding 172.4 Potential Effects of Climate Change 172.5 The Flood and Water Management Act 2010 182.6 Review of Relevant Planning Policy 19

SITE DESCRIPTION 21

3 SITE DESCRIPTION 233.1 Site Location 233.2 Site Description 23

EXISTING FLOOD RISK 27

4 EXISTING FLOOD RISK 294.1 Historical Flooding 294.2 Fluvial Flooding 294.3 Other Sources of Flooding 304.4 Summary of Existing Flood Risk 35

POST DEVELOPMENT FLOOD RISK 37

5 POST DEVELOPMENT FLOOD RISK 395.1 Post Development Flood Risk 395.2 Works in Proximity of River Channel 395.3 Works in Proximity to Floodplain 405.4 Management of Site Generated Surface Water Runoff 415.5 Summary of Post Development Flood Risk 41

outline surface water drainage strategy 43

6 OUTLINE SURFACE WATER DRAINAGE STRATEGY 456.1 Surface Water Management Approach 456.2 Surface Water Management Strategy 46

sequential test and exception test 49

7 sequential test and exception test 517.1 Sequential Test 51




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7.2 Exception Test 51

CONCLUSIONS 53

8 CONCLUSIONS 558.1 Introduction 558.2 Summary of the Existing Flood Risk and Flood Risk During Construction 558.3 Summary of Post Development Flood Risk 56

APPENDICES 59

PROPOSED ALTERATION/IMPROVEMENT WORKS 61

APPLICATION SITE BOUNDARY 63

EA INDICATIVE FLOOD MAP 65

LOCATION OF CONSTRUCTION SITE COMPOUNDS 67

CANAL BREACH HAZARD ZONES 69

LOCATION AND DETAILS OF FOOTBRIDGE SUPPORT STRUCTURE 71

proposed outline drainage strategy 73




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SECTION 1

INTRODUCTION




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1 INTRODUCTION

1.1 Project Background

1.1.1 Parsons Brinckerhoff Ltd (PB) has been commissioned by Network Rail (NR) toprepare a site-specific Flood Risk Assessment (FRA) to support the proposedimprovement works for the Manchester Piccadilly and Oxford Road Scheme (theScheme) in Manchester. These works forms part of the wider Northern Hubprogramme, which aims to stimulate economic growth by improving the rail network inthe North.

1.1.2 Review of indicative flood maps available from the Environment Agency (EA) websiteindicates that part of the application site is located in a medium risk Flood Zone 2 anda high risk Flood Zone 3. Therefore, a site-specific FRA is required.

1.1.3 The FRA will be conducted in accordance with National Planning Policy Framework(NPPF), providing a quantitative analysis of flood risk to support the planningapplication. The FRA will be supported by the results of hydraulic modelling of theRiver Medlock. The assessment will include the following:

Confirmation of the sources of flooding which may affect the application site;

A quantitative assessment of the risk of flooding to the site and to adjacent sitesas a result of Scheme;

Review of the availability and adequacy of existing information; and

Identification of possible measures which could reduce flood risk to acceptablelevels.

1.2 Development Proposals

1.2.1 The Scheme is divided into two areas for the purpose of this report. The proposedimprovement works for each of these areas would include:

Area 1 – Piccadilly Station area:

- Construction of two new platforms – Platform 15 and 16, such that twoplatforms can be used alternately for trains travelling in either direction;

- Construction of a new bridge providing lift, stair and escalator to all platformsand linking to the existing Platform 13/14 satellite lounge;

- Construction of a new viaduct which supports the track, platforms and bridgefor the proposed Platforms 15/16;

- Construction of a new overall canopy roof over the full extent of the newplatforms;

- Modifications to the existing satellite lounge serving Platform 13/14 to tie-inwith the new bridge, including associated access modifications to Platform12;

- Limited modifications to Platform 13/14 including the removal of a section ofcanopy; and

- Highway realignments and reconfiguration of an Electricity Northwestsubstation arising from the proposed substructure arrangement.

Area 2 – Oxford Road Station area:




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- Extension of the length of the four through platforms 1-4 to permitsimultaneous arrivals and departures in the same direction;

- Construction of a new footbridge with its support structure located within thechannel of the River Medlock;

- Construction of new canopies over approximately two-thirds of platforms 1-4;

- Construction of a new covered concourse area to extend the existing tickethall;

- Removal of sections of Grade II listed station infrastructure;

- Changes to copper alignment and regrading of platform at DeansgateStation;

- Widening of the viaduct structures over Whitworth Street West to provide anextended footprint for the new platforms and track alignment and to act assubstructure for the proposed station footbridge.

1.2.2 Drawings showing the proposed improvement works are included in Appendix A.

1.3 Consultation

1.3.1 Consultation has been undertaken with the EA in January and February 2014 todiscuss potential project constraints and appropriate mitigation measures.

1.3.2 In addition, a meeting with the EA, PB and the contractors’ representatives was heldon 3rd April 2014. This meeting discussed the potential impacts of construction of afootbridge support within the channel of River Medlock and potential mitigationmeasures.




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SECTION 2

ASSESSMENT METHODOLOGY




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2 ASSESSMENT METHODOLOGY

2.1 Overview

2.1.1 The assessment has been conducted in accordance with the NPPF. The NPPF andits supporting Technical Guidance replaced previous guidance document PlanningPolicy Statement (PPS) 25 and provides guidance on how new developments musttake into account flood risk, including making allowance for climate change impacts.

2.1.2 NPPF maintains the same principles as PPS25, encouraging decision makers to:

Steer development to lower risk locations that are appropriate to the proposeduse and ensure development is safe;

Prevent any increase in flood risk elsewhere and reduce flood risk through thelayout and form of the development and the appropriate application ofsustainable drainage systems;

Reduce flood risk by making space for water by creating flood flow paths and byidentifying, allocating and safeguarding space for flood storage;

Use regeneration to help relocate development to lower risk locations whenclimate change is expected to mean that some existing development may not besustainable in the long-term.

2.1.3 The methodology adopted in this FRA comprises:

Review of available flood data to identify existing flood risk from fluvial, tidal,groundwater, overland flow and artificial sources;

Further assessment of fluvial flood risk through hydraulic modelling of affectedwatercourses;

Consideration of existing ground conditions on-site to determine groundwaterlevels, soil permeability and contamination risks through review of previous landuse and information available from the EA, the British Geological Survey (BGS)and National Soil Resources Institute (NSRI) Soils Site Report;

Review of the development proposals in terms of flood risk vulnerability and floodzone compatibility, in accordance with the methodology defined in the NPPF;

Consideration of how the development proposals may affect flood risk to the siteand surrounding areas; and

Proposals for the appropriate management of flood risk to facilitate developmentwhilst not increasing risks elsewhere.

2.1.4 Data regarding flood risk relevant to the proposed Scheme and surrounding area hasbeen obtained from the following sources:

EA indicative flood risk maps and groundwater maps;

1D ISIS hydraulic model of the River Medlock;

Manchester City, Salford City and Trafford Councils Level 2 Hybrid StrategicFlood Risk Assessment (SFRA) Level 1 report, by JBA Consulting, March 2010;

Manchester City, Salford City and Trafford Councils Level 2 Hybrid SFRA Level 2report, by JBA Consulting, March 2011;




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Manchester City, Salford City and Trafford Councils Level 2 Hybrid SFRA UserGuide, by JBA Consulting, May 2010;

Manchester City Council Preliminary Flood Risk Assessment (PFRA), by JBAConsulting, May 2011;

River Basin Management Plan North West River Basin District, by the EA,December 2009;

BGS Geology of Britain Viewer:http://mapapps.bgs.ac.uk/geologyofbritain/home.html;

Northern Hub Programme. Part 1: Oxford Road Station and Approaches – InitialDrainage Survey and Condition, by PB, November 2013;

Northern Hub programme. Part 2: Piccadilly Station and Approaches – InitialDrainage Survey and Conditions, by PB, January 2014;

Manchester’s Local Development Framework Core Strategy Development PlanDocument, adopted 11th July 2012; and

Direct consultation with the EA as discussed in Section 1.3.

2.2 Definition of Flood Risk

2.2.1 Flood risk is the product of the likelihood or chance of a flood occurring (floodfrequency) and the consequence or impact of the flooding (flood consequence).

Flood Frequency

2.2.2 Flood frequency is identified in terms of the return period and annual probability. Forexample, a 1 in 100 year flood event has a 1% annual probability of occurring. Table1 provides a conversion between return periods and annual flood probabilities.

Table 1 – Flood Probability Conversion TableReturn Period (years) 2 5 10 20 50 100 200 1000

Annual Flood Probability (%) 50 20 10 5 2 1 0.5 0.1

2.2.3 The NPPF identifies Flood Zones in relation to flood frequency. The zones refer to theprobability of river (fluvial) and sea (tidal) flooding, whilst ignoring the presence ofdefences. Table 2 summarises the relationship between Flood Zone category and theidentified flood risk.

Table 2 – Flood ZonesFlood RiskArea

Identification Annual Probability ofFluvial Flooding

Annual Probabilityof Tidal Flooding

Zone 1 Low Probability <0.1% <0.1%

Zone 2 Medium Probability 1% – 0.1% 0.5% – 0.1%

Zone 3a High Probability >1% >0.5%

Zone 3b Function Flood Plain >5% >5%

http://mapapps.bgs.ac.uk/geologyofbritain/home.html;




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Flood Consequences

2.2.4 The consequence of a flood event describes the potential damage, danger anddisruption caused by flooding. This is dependent on the mechanism andcharacteristics of the flood event and the vulnerability of the affected land and its landuse.

2.2.5 The EA have identified five classifications of flood risk vulnerability and providerecommendations on the compatibility of each vulnerability classification with theFlood Zones, as shown in Table 3.

2.2.6 Full details of the EA Flood Zones and flood risk vulnerability classification can befound in the Technical Guidance to the NPPF.

Table 3 – Flood Risk Vulnerability and Flood Zone CompatibilityEA FloodZone

EssentialInfrastructure

WaterCompatible

HighlyVulnerable

Morevulnerable

Lessvulnerable

Zone 1

Zone 2 Exceptiontest required

Zone 3a Exception testrequired

Exceptiontest required

Zone 3b Exception testrequired

Development considered acceptable Development considered unacceptable

2.2.7 Within the site boundary, a sequential approach should be adopted that aims to steernew development to areas with the lowest probability of flooding.

2.3 Potential Sources of Flooding

2.3.1 In accordance with the NPPF, the following sources of flooding will be considered inthis assessment:

Fluvial flood risk from nearby watercourses;

Overland surface water flooding from adjacent sites;

Site generated surface water runoff;

Surcharging sewers; and

Groundwater flooding.

2.4 Potential Effects of Climate Change

2.4.1 Scientific consensus is that the global climate is changing as a result of humanactivity. While there remain uncertainties in how a changing climate will affect areasalready vulnerable to flooding, it is expected to increase risk significantly over time.For the UK, projections of future climate change indicate that more frequent short-duration high-intensity rainfall events and more frequent periods of long-durationrainfall could be expected.




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2.4.2 The Technical Guidance to the NPPF provides recommended national precautionarysensitivity ranges for possible peak rainfall intensities resulting from climate changefor the next 100 years, shown in Table 4.

Table 4 – Recommended National Precautionary Sensitivity Ranges for PeakRainfall Intensities and Peak Rive Flow

Parameter 1990 to2025

2025 to2055

2055 to2085

2085 to2115

Peak rainfall intensity +5% +10% +20% +30%

Peak river flow +10% +20%

2.4.3 In accordance with this guidance, the surface water drainage network has beenassessed for a 100 design life with peak rainfall intensities increased by 30% andpeak river flows increased by 20%.

2.5 The Flood and Water Management Act 2010

2.5.1 The Flood and Water Management Act 2010 (FWMA) introduces new responsibilitiesfor flood risk management for local authorities and sets out new requirements for themanagement of sustainable drainage.

2.5.2 The FWMA Act is still being implemented and this report will provide guidance on howits implementation will impact on the management of surface water and flood risk forthe proposed development.

Lead Local Flood Authorities

2.5.3 Under the FWMA the unitary authority or county council for an area is designated the‘Lead Local Flood Authority’ (LLFA), with responsibility for managing flood risk fromsurface water, ground water and ordinary watercourses within their area. The LLFAare also the consenting authority for works near or within ordinary watercourses.

Sustainable Drainage

2.5.4 Schedule 3 of the FWMA introduces new National Standards for SustainableDrainage Systems (SUDS) against which proposed drainage systems should comply.Under Schedule 3 of the FWMA, LLFAs will become the SUDS Approving Body(SAB) for surface water drainage systems for new development. Approval from theSAB for drainage proposals must be agreed prior to construction. For drainagesystems that serve more than one property, the SAB will have responsibility formaintenance of adopted SUDS schemes that meet SAB requirements.

2.5.5 These standards are currently in draft and their implementation has been delayed.

2.5.6 The draft standards introduce the SUDS hierarchy that states that the followingmethods of surface water disposal must be considered in order of preference:

Discharge into the ground;

Discharge to a surface water body;

Discharge to a surface water sewer;




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Discharge to a combined sewer.

2.5.7 The draft standards also promote the management of surface water runoff at source,on the surface and integrated with public open space where it is reasonablypracticable to do so.

Agreements on New Drainage Systems

2.5.8 Under Section 106 of the Water Industry Act 1991, owners of premises and sewershad the right connect to the public sewer network to discharge foul and surface flows.The sewerage undertake has the right to refuse to permit new connections to bemade if the mode of construction or condition of the connection does not satisfy thestandards reasonably required by the undertaker, or if the making of the connectionwould be prejudicial to the undertaker’s sewerage connection.

2.5.9 Section 42 of the FWMA inserts a new Section into the Water Industry Act 1991,adding two conditions to the right to connect. The first condition is that the personconstructing the connection has entered into an adoption agreement between theowner of the connection and the sewerage undertaker under Section 104 of the WaterIndustry Act 1991. The second condition is that the agreement must include provisionabout the standards to which the sewer must be constructed, and about the adoptionof the drain or sewer by the undertaker.

2.6 Review of Relevant Planning Policy

Manchester’s Local Development Framework Core Strategy Development PlanDocument (adopted 11th July 2012)

2.6.2 Manchester’s Core Strategy includes policies related to flood risk and climate change:

Policy EN8 Adaptation to Climate Change – All new development will beexpected to be adaptable to climate change in terms of the design, layout, sitingand function of both buildings and associated external spaces. In achievingdevelopments which are adaptable to climate change developers should haveregard to the following, although this is not an exhaustive list:

- Minimisation of flood risk by appropriate siting, drainage, and treatment ofsurface areas to ensure rain water permeability;

- Reduction in urban heat island effect through the use of Green Infrastructuresuch as green roofs, green walls, increased tree cover and waterways;

- The need to control overheating of building through passive design;

- The opportunity to provide linked and diverse green space to enhancenatural habitats which will assist species adaptation.

Policy EN14 Flood Risk:

- In line with the risk-based sequential approach contained within the NPPF,development should be directed away from sites at the greatest risk offlooding, and towards sites with little or no risk of flooding; this should takeaccount of all sources of flooding identified in the Manchester – Salford-Trafford SFRA;

- In addition to the requirements for a site-specific FRAs set out in the NPPF,an appropriate FRA will also be required for all development proposals,including changes of use, on sites greater than 0.5ha within Critical DrainageAreas (CDAs) and Canal Hazard Zones identified in the SFRA;




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- All new developments should minimise surface water runoff, includingthrough SUDS and the appropriate use of Green Infrastructure. Developersshould have regard to the surface water runoff rates in the SFRA UserGuide. In CDAs, evidence to justify the surface water runoff approach / rateswill be required;

- The City of Manchester contains many sections of rivers which are culvertedor ‘hidden’; where these are indicated in the SFRA beneath the proposeddevelopment site, further investigation will be required and the developmentproposal should take this into account; where feasible and appropriatedevelopment should seek to open up culverted / hidden rivers to reduce theassociated flood risk and danger of collapse, taking advantage ofopportunities to enhance biodiversity and Green infrastructure.

Manchester City, Salford City and Trafford Council Level 2 Hybrid SFRA User Guide

2.6.3 The User Guide provides information on allowable surface water discharge rates forCDAs and other areas:

Development should aim to deliver Greenfield runoff on Greenfield sites up to a 1in 100 year storm event, considering climate change;

Development should aim for a minimum reduction in surface water runoff rates of50% for Brownfield sites, with an aim of reducing runoff to greenfield rates up toa 1 in 100 year storm event, considering climate change;

Development should be designed so that there is no flooding to the developmentin a 1 in 30 year event and so that there is no property flooding in a 1 in 100year plus climate change event.

2.6.4 Reduction in surface water runoff rates should be achieved through theimplementation of SUDS.




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SECTION 3

SITE DESCRIPTION




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3 SITE DESCRIPTION

3.1 Site Location

3.1.1 The Scheme site is located in central Manchester - Oxford Road Station is located atNational Grid Reference (NGR) 384027, 397492 and Piccadilly Station is located atNGR 384842, 397864. The approximate Scheme site boundary is shown in Figure 1.A more detailed illustration of the exact Scheme site boundary is show in Appendix B.

Figure 1 – Approximate Application Site Boundary

3.2 Site Description

3.2.1 The Scheme site consists of areas of Oxford Road Station and Piccadilly Station, theexisting railway viaduct and two existing car park areas located to the west of AlbionStreet.

3.2.2 The site is located in the centre of Manchester in a heavily urbanised area. The vastmajority of the application site is currently hard surfaced. The railway lines are raisedon viaducts and bridges.

Hydrology and Water Features

3.2.3 The River Medlock is designated a ‘main river’ under EA management and passesthrough the Scheme site. It flows in close proximity to Oxford Road Station andadjacent to the improvement works proposed for this area. The river also flowsapproximately 150m to the south of Piccadilly Station. The lower reach of the RiverMedlock that crosses the application site has been extensively modified and is

RiverIrwell

RochdaleCanal

RiverMedlock

OxfordRoadStation

PiccadillyStation

OxfordRoad

GloucesterStreet

WhitworthStreet

FairfieldStreet

BridgewaterCanal

CulvertedRiver Tib

AlbionStreet




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partially culverted between the City of Manchester Stadium and Deansgate/ChesterRoad area. Its location is shown in Figure 1.

3.2.4 From Oxford Road Station, the River Medlock flows west beneath the BridgewaterCanal to discharge to the River Irwell approximately 1.3km to the west of Oxford RoadStation. Under normal flow conditions the level of the river is lower than the waterlevel in the Bridgewater Canal and the river is carried in a tunnel under the Castlefieldcanal basin, reappearing at Potato Wharf where it is supplemented by excess canalwater draining into a circular weir. When the river is at high flow the tunnel cannotcope and river water enters the canal, flows across the basin, and exits via the weirand manually operated gates. Location of the Bridgewater Canal is shown in Figure 1.

3.2.5 Rochdale Canal is located approximately 35m to the north of Oxford Road Stationand approximately 210m to the north of Manchester Piccadilly Station. The RochdaleCanal connects the Ashton Canal to the Bridgewater Canal. It is designated as an‘ordinary watercourse’ and is under the management of the Canal & River Trust.Location of the Rochdale Canal is shown in Figure 1.

3.2.6 The River Tib is a minor tributary of the River Medlock. It has been culverted along itsentire length since circa1820. Its source is in Miles Platting from where it flowsunderneath Oldham Road and Tib Street to reach the city centre. After flowingunderneath West Mosley Street, the river crosses Princess Street to flow underneaththe Manchester Town Hall, the Central Library, Whitworth Street and First Streetdevelopment area before joining the River Medlock at Gaythorn, close to DeansgateStation. The River Tib flows underneath the MSJ&AR viaduct approximately 60m tothe east of Albion Street. It is planned that the river will be diverted as part of ongoingworks at First Street Development. The approximate location of the River Tib isshown in Figure 1.

3.2.7 The River Irwell is located approximately 1.3km to the west of Oxford Road Station.This part of the river is designated as ‘ordinary watercourse’ under the managementof Manchester City Council (MCC) and Salford City Council (SCC). Location of theRiver Irwell is shown in Figure 1.

Geology and Hydrogeology

3.2.8 Examination of the BGS map indicates that the entire Scheme site is underlain bybedrock identified as Chester Pebble Beds Formation – Sandstone. Superficialdeposits in the form of Till, Devensian – Diamicton are identified throughout themajority of the site. Superficial deposits in the form of Glaciofluvial Sheet Deposits,Devensian – Sand and Gravel were identified in the area to the west of the OxfordRoad Station.

3.2.9 The EA Groundwater Maps identify bedrock within the Scheme site boundary asbeing predominantly a Principal Aquifer. Superficial deposits within the area of OxfordRoad Station and on land to the west of the station are classified as a Secondary AAquifer.

Soil Infiltration

3.2.10 To date, no intrusive ground investigation has been undertaken on the site to informthe preparation of the FRA or supporting environmental studies. Therefore, theunderlying soil infiltration rates are currently unknown.




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3.2.11 The proposed works consist of alterations to existing structures located in a heavilyurbanised area. The vast majority of the Scheme site is already hard surfaced. Theunderlying soil within the vicinity of the railway stations has the potential to becontaminated from drips and accidental spillages from trains.

3.2.12 Considering these facts, infiltration techniques for the management of surface waterrunoff from the proposed works are unlikely to be feasible as part of surface waterdrainage design. However, it is recommended that soil infiltration tests are undertakenin any grassed areas adjacent to the proposed Scheme works to investigate thepotential for infiltration techniques.

Existing Drainage

3.2.13 The affected length of the existing tracks in the area of the proposed alterations issupported predominantly by brick masonry arch viaducts, with occasional steel andconcrete flat spans. It is assumed that the track bed drains through the ballast sub-grade onto the bridge deck waterproofing, and then water drains internally through thestructures to downpipes inlaid into the supporting brickwork of the piers. Downstreamof the piers, the downpipes either outfall to adjacent surfaces to be collected by thehighway drainage, are connected to an underground drainage system, or soak awayinto the underlying soils.

3.2.14 The existing drainage of the University of Manchester Institute of Science andTechnology (UMIST), especially adjacent to the railway arches in Altrincham Street,receives some flow either directly or indirectly from the existing railway structures.Their condition is not known.

3.2.15 No information on the internal drainage of the railway viaduct structures or of the pierswas available at the time of completing the assessment. It is recommended thatfurther site investigation is completed to improve understanding of the existingdrainage network throughout the area of proposed Scheme and the Station itself.

3.2.16 A highways drainage system is located in the vicinity of the proposed Scheme. It isnot known whether Network Rail has any existing connections to this system or ifthere is capacity in this system to receive additional flow.

3.2.17 It is not known whether Network Rail has any existing discharge permits to dischargesurface water runoff into the River Medlock.

3.2.18 There are a number of public sewers located in the vicinity of the proposed Scheme.The majority of these sewers are identified as combined and receive both surfacewater and foul water flow. Information on their condition and whether the existingrailway structures are connected to them was not available at the time of theassessment. A number of chambers surrounding Piccadilly Station are identifiedwithin the existing combined sewer system as having combined sewer overflows.

3.2.19 Piccadilly Station is drained by the combined drainage system and outfalls towardsLondon Road. Oxford Road Station and its approaches are also drained by thecombined drainage system. Platform drainage comprises a number of drainagechannels set into the platforms. The drainage channels also receive flow from the roofdownpipes. It is assumed that the drainage channels then connect to an outfall intothe platform/track drainage systems within the voids of the supporting structures.




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SECTION 4

EXISTING FLOOD RISK




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4 EXISTING FLOOD RISK

4.1 Historical Flooding

4.1.1 The Manchester PFRA shows that there are no records of historical flooding withinthe Scheme site boundary or its close vicinity.

4.2 Fluvial Flooding

4.2.1 The EA Indicative Floodplain Map indicates that areas in the vicinity of River Medlockare located in a medium risk Flood Zone 2 and a high risk Flood Zone 3. However, allproposed alterations to the existing railway tracks and stations as listed in Section 1.2are located in Flood Zone 1.

4.2.2 An extract from the EA Indicative Floodplain Map is shown in Figure 2. A larger scalemap is shown in Appendix C.

Key

Figure 2 – EA Indicative Floodplain Map (March 2014)

Construction Site Compounds

4.2.3 Four temporary construction site compounds are proposed for the construction phaseof the Scheme. Their approximate locations are shown in Figure 2 and their exactlocations and extents are shown in Appendix D.

River Irwell

RiverMedlock

RochdaleCanal

PiccadillyStation

Oxford RoadStation

Compound DCompound B

Compound A

Compound C




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Construction Site Compound No A

4.2.4 The compound will be located to the south of Piccadilly Station and it is locatedentirely in a low risk Flood Zone 1.

Construction Site Compound No B

4.2.5 The compound will be located on the existing car park bounded by the River Medlockto the north and bounded by the existing railway line to the south. It is located entirelyin a high risk Flood Zone 3.

Construction Site Compound No C

4.2.6 The compound will be located in the section of Great Marlborough Street underneathOxford Road Station. The site is entirely located in a low risk Flood Zone 1.

Construction Site Compound No D

4.2.7 The compound will be located in the area of the existing car park located to the westof Medlock Street (A5103). The River Medlock bounds the site to the south. The siteis located entirely in a medium risk Flood Zone 2.

4.3 Other Sources of Flooding

Groundwater Flood Risk

4.3.2 Groundwater flooding occurs when water stored below ground reaches the ground’ssurface. It is commonly associated with porous underlying geology, such as chalk,limestone and gravels.

4.3.3 Examination of geology of the application site indicates that it is underlain bysuperficial deposits in form of Till, Devensian – Diamicton. Bedrock geology isindicated to compromise Chester Pebble Beds Formation – Sandstone.

4.3.4 The Level 2 Hybrid SFRA indicates that the area to the south and west of OxfordRoad Station is at risk of groundwater flooding. However, there are no known historicrecords of groundwater flooding in this area.

4.3.5 The EA national dataset ‘Areas Susceptible to Groundwater Flooding’ (AStGWF)provides the basis for assessing flood risk from groundwater. It shows the proportionof each 1km grid square where geological and hydrogeological conditions suggestthat groundwater might emerge. The Manchester PFRA provides AStGWFinformation and it indicates that the entire Scheme site area is in an area where lessthan 25% of the grid square is considered susceptible to groundwater flooding.

4.3.6 In view of the above, specifically that that there is no record of groundwater flooding inthe area and the site is underlain by Till that would limit groundwater emergence, therisk of groundwater flooding is considered to be low.

Flood Risk from Surface Water

4.3.7 Surface water flooding happens when rainwater does not drain away through thenormal drainage systems or soak into the ground, but lies on or flows over the groundinstead.




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4.3.8 The SFRA Level 2 identifies that the application site lies entirely within a ConurbationCore Critical Drainage Area (CDA). CDAs are areas where there is known to be eithera high risk of localised flooding from ordinary watercourses, culverts, or othersources, or where the sewer system is operating at, or near to, full capacity and isparticularly sensitive to rainfall exceedence events and surface water runoff.Therefore, in accordance with Manchester Core Strategy Policy EN14 Flood Risk, allnew developments that have the potential to impact the CDA should minimise surfacewater runoff in order that they do not increase the risk of flooding in the area orelsewhere.

4.3.9 The EA Surface Water Flood Map indicates that the area located within the bend ofthe River Medlock to the north of the existing railway line is at low risk of surfacewater flooding. Other small pockets of surface water flood risk are identifiedthroughout the Scheme site although these are most likely associated with smalldepressions in topography and do not suggest a significant surface water flood riskissue. Therefore, the risk of flooding from surface water is considered to be low. Anextract from the EA Surface Water Flood Map is shown in Figure 3.




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Figure 3: EA Surface Water Flood Map (April 2014)

Oxford RoadStation

RiverMedlock

PiccadillyStation

RochdaleCanal

River Irwell




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Flooding from Sewers

4.3.10 For the purpose of this assessment, overland flow is considered to be associated withthe lack of appropriate drainage or insufficient capacity of drainage systems that maysurcharge and therefore pose flood risk to development and infrastructure.

4.3.11 Public Water Authorities are obliged to produce a list of flooding incidents in their areacaused by sewers. The list is known as the DG5 register. United Utilities (UU)produces such information for the Manchester area. Manchester PFRA indicatesthat there are no DG5 flood incidents in the vicinity of the Scheme site.

4.3.12 In addition for the purpose of the Manchester PFRA, UU provided two main datasetsassociated with historical flood incidents in Manchester. They are named SewerageIncident Register System (SIRS) and Wastewater Incident Register System (WIRS).These incidents include all source of flooding, including those that did not have animpact on people, property or the environment. Manchester PFRA shows a few SIRSincidents recorded between Oxford Road Station and Piccadilly Station. Details of theincidents were not provided. The Manchester PFRA states that there is insufficientdata to draw definitive conclusion of these incidents and to confirm the occurrence ofan event with significant harmful consequences.

4.3.13 The majority of the proposed alterations to the existing railway tracks and stations willbe elevated above adjacent ground levels. Therefore, the risk of flooding fromoverland flow associated with surcharging of the public sewerage network isconsidered to be very low.

4.3.14 The area of the proposed highway realignment adjacent to Piccadilly Station is servedby the existing highway drainage. Any overland flow will be intercepted andchannelled by the existing highway drainage. Therefore, the risk of overland floodingin this area is considered to be low.

Flooding from Reservoirs and Canals

4.3.15 The EA publish an indicative map showing areas that could be flooded if impoundedreservoirs were to fail and release the water they hold. This map indicates that thearea to the south and east of Oxford Road Station is at risk of flooding from a numberof reservoirs. The reservoirs are listed in Table 5. However, information provided onthe EA’s Flooding from Reservoirs map states that reservoir flooding is extremelyunlikely to happen. There has been no loss of life in the UK from reservoir floodingsince 1925. All reservoirs are regularly inspected and supervised by reservoir panelengineers and essential safety work is carried out. Each reservoir has its own warningsystem installed to inform of any breach and to allow for evacuation/ preparationagainst flooding. Therefore, the risk of flooding from reservoirs is considered to below. Local authorities are responsible for coordinating emergency plans for reservoirflooding and ensuring communities are well prepared. A map showing the maximumextent of reservoir flooding is shown in Figure 4.




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Figure 4: Maximum Extent of Flooding from Reservoirs (EA website, April 2014)

Table 5: Reservoirs that Might Affect the Application Site

Name ofReservoir

ReservoirOwner Local Authority

NGR

E N

Audenshaw No 1 United UtilitiesWater plc Tameside 391852 396483



Gorton Upper United Utilitieswater plc Manchester 389893 396254

4.3.16 In the case of reservoir failure, procedures included in the Manchester EmergencyPlan and advice given by the Police and other emergency services should be followedand the area susceptible to flooding should be evacuated. The Civil Contingenciesand Resilience Unit, which is an Association of Greater Manchester Authorities(AGMA) service, conduct emergency planning on behalf of MCC. MCC is also apartner of The Greater Manchester Resilience Forum (GMRF). This partnership ofagencies from across Greater Manchester has responsibility for coordinating andoverseeing emergency planning. Its overall purpose is to ensure an appropriate levelof preparedness for an effective multi-agency response to emergency incidents whichmay have significant impact on the communities of Greater Manchester.

4.3.17 If the city centre needs to be evacuated in the area where the proposed alterationworks are located, the following methods of communication will be utilised:

The Emergency Services directly;




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Fire alarms may be activated;

Messages to members of CityCo or the Manchester Business Continuity Forum(MBCF);

Notifications through business security channels (e.g. radio network);

Media sources such as social media public address systems e.g. those inshopping centres, bus, rail and tram stations;

Electronic display boards in use across the city centre.

4.3.18 Police Officers, along with other emergency responders, will co-ordinate anyevacuation.

4.3.19 The SFRA Level 2 identifies two indicative ‘Canal Hazard Zones’ that have beencreated for the Bridgewater, Ashton and Rochdale Canals to map areas identified tobe at risk in the event of breach. The potential breach areas were sub-divided into twoCanal Breach Zones: Canal Breach Zone A and Canal Breach Zone B. Canal BreachZone A is described as an area that will be affected by a breach of a canalembankment due to its height and width. Canal Breach Zone B is described as anarea that is less likely to be affected by breach of the canal embankment. The SFRAindicates that Oxford Road Station and its vicinity are located in Canal Breach ZoneB. The same report indicates that Piccadilly Station is not located in the area at risk offlooding from canal breach. The area to the north of Piccadilly Station is located inCanal Breach Zone A. However, this area is outside of the Scheme site boundary andit will have no impact on the Scheme. The SFRA Level 2 states that it is more likelythat this source of risk (Canal Breach Zone B) could be scoped out within any sitespecific FRA due to its little likelihood of occurrence. The probability of a breachoccurring is considered to be low, primarily due to the monitoring and maintenanceactivities of the Navigation Authorities. Extent of the Canal Breach Hazard Zones isshown in Appendix E.

4.3.20 The SFRA Level 2 indicates that the Scheme site is not located in an area at risk offlooding from overtopping of the banks of Bridgewater, Ashton and Rochdale Canals.

4.4 Summary of Existing Flood Risk

4.4.1 All areas of the proposed alterations to the existing railway tracks and stations arelocated in a low risk Flood Zone 1. However, two of the four site constructioncompounds are located in a medium risk Flood Zone 2 and a high risk Flood Zone 3.

4.4.2 The Scheme site is located entirely in a Critical Drainage Area. Parts of the Schemesite are identified to be at low risk of surface water flooding.

4.4.3 The area to the south and east of Oxford Road Station is located in an area identifiedto be at risk of groundwater flooding. However, considering the geology of theScheme site and that there is no known record of historical groundwater flooding inthis area, the risk of flooding from groundwater is considered to be low.

4.4.4 There are number of records of flooding from sewers identified between Oxford RoadStation and Piccadilly Station. However, the Manchester PFRA states that there isinsufficient data to draw definitive conclusion of these incidents and therefore theirsignificance in terms of flood risk to the works is considered to be low.

4.4.5 The EA Flooding from Reservoirs map shows that an area to the south and east ofthe Oxford Road Station is identified to be at risk of reservoir failure. However, the




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likelihood of reservoir failure is very low due to its maintenance and control regime.Therefore, the risk of such flooding is considered to be low.

4.4.6 Oxford Road Station and its surrounding area are located in an area identified asCanal Breach Zone B – the area is considered less likely to be affected by breach ofthe canal and therefore the significance in terms of flood risk to the works isconsidered to be low.




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SECTION 5

POST DEVELOPMENT FLOOD RISK




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5 POST DEVELOPMENT FLOOD RISK

5.1 Post Development Flood Risk

5.1.1 The proposed Scheme consists of construction of a footbridge and alterations to theexisting Oxford Road Station, and construction of two new platforms with associatedinfrastructure in Piccadilly Station. In accordance with the Technical Guidance to theNPPF the nature of the Scheme will come under the flood risk vulnerabilityclassification of ‘Essential Infrastructure’. The majority of the proposed works will becarried out to the existing railway infrastructure located above the ground level.

5.2 Works in Proximity of River Channel

5.2.1 A new footbridge support is proposed to be constructed within the channel of theRiver Medlock which is adjacent to the existing railway viaduct in the vicinity of OxfordRoad Station. The proposed design entails construction of a support structure withinthe river channel to provide sufficient area for the footbridge support. Construction ofthis structure would reduce the capacity of the channel, which may in turn affect riverflows and water levels within the channel and increase the risk of fluvial flooding in thearea. Therefore, appropriate mitigation measures will be required to prevent anyincreased risk.

5.2.2 Drawings showing the location and details of the proposed footbridge supportstructure are shown in Appendix F.

5.2.3 The EA stated the preferred option would be for a footbridge support structure thatdoes not require construction of a structure within the river channel. However, the EAconfirmed that if the option with a structure within the river channel is taken further,the works must cause no increase in water levels to ensure that it will not increase therisk of flooding in the area.

5.2.4 The EA also raised an issue of potential debris collection on the outside of the riverbend caused by construction of the proposed footbridge support structure within theriver channel. This subject will be investigated further during the detailed designstages of the project.

5.2.5 The EA confirmed that scour assessment of the proposed structure would not berequired.

5.2.6 Any works within 8m of the River Medlock would require consent from the EA. Thiswill be sought during the detailed design stages and prior to construction.

Preliminary Hydraulic Modelling

5.2.7 A 1D ISIS hydraulic model of the River Medlock was purchased from the EA toidentify potential impacts of construction of the proposed footbridge support on floodrisk in the area. The model was developed by Atkins in 2009 as part of a strategicassessment of flooding in Greater Manchester.

5.2.8 The model was run for the 100 year, 100 year with climate change and 1000 yearevents for the following scenarios:

Existing scenario to identify baseline information; and




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Post-development scenario (including the footbridge support structure) to identifypotential impacts.

5.2.9 Initial hydraulic modelling results showed a minor increase of up to 26mm in waterlevels when the proposed structure was introduced into the river channel. However,the EA confirmed that they expect no increase in water levels to ensure that theproposed structure will not increase the risk of flooding in the area.

5.2.10 The existing hydraulic model was developed for strategic purposes rather than localassessment. Therefore, additional cross sectional survey of the river channel in thevicinity of the proposed structure will be carried out to provide more detailedinformation on the river channel in this area. The new cross sectional survey data willbe incorporated into the existing model and further modelling exercises will beundertaken to obtain more accurate results and inform the design of mitigation.

5.2.11 Construction of the footbridge support within the river channel would reduce thechannel cross sectional area. This would require appropriate compensation measureto ensure that it will not increase the risk of flooding in the area. A widening of theriver channel in the vicinity of the proposed structure is considered as potentialmitigation. This option will be hydraulically modelled at the later stage of the project tocheck its effectiveness.

5.2.12 Construction works within the river channel are envisaged to take up to two months.The EA confirmed that temporary works will not require hydraulic modelling due to therelatively short time of duration.

5.3 Works in Proximity to Floodplain

5.3.1 Two of the four construction site compounds are located within an area identified tobe at risk of fluvial flooding:

Construction Site Compound B is entirely located in a high risk Flood Zone 3,and

Construction Site Compound D is entirely located in a medium risk Flood Zone 2.

5.3.2 Their location is shown in Appendix D.

5.3.3 It is recommended that both construction site compounds are signed up to the EA’sFloodline Warnings Direct which provides information on flood warnings updated on adaily basis. It is a free service which sends a direct message when flooding isexpected and may affect subject property. Flood warnings will give time to prepare forflooding which could save time, money and lives. The warning can be received bytelephone, mobile, email, SMS text message or fax. Registration can be made online:https://fwd.environment-agency.gov.uk/app/olr/register or by calling Floodline on 0845988 1188.

5.3.4 In addition, a Flood Evacuation Plan (FEP) should be prepared for these twoconstruction site compounds and all construction workers should be made aware ofthe local flood risk and be familiar with the FEP. The plan will apply to all sources offlooding and should include the following information, but not limited to:

Evacuation procedures or procedures for safe refuge;

People responsible for evacuation and/or safe refuge;

https://fwd.environment-agency.gov.uk/app/olr/register




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Evacuation and emergency refuge routes;

Flood warning codes; and

Local emergency services contact details.

5.3.5 When construction works are finished, it is recommended that the compound areasare reinstated to the original condition in terms of ground levels to make sure that thearea of flood extents has the same capacity to manage flood water as beforeconstruction works started.

5.4 Management of Site Generated Surface Water Runoff

5.4.1 The area of the proposed Scheme is located in a heavily urbanised area ofManchester and the vast majority is already hard surfaced. Therefore, the proposedworks will not increase the amount of impermeable area and will not increase thevolume of rate of surface water runoff generated in this area.

5.4.2 Surface water runoff from existing structures and surfaces will be drained in the samemanner it is currently, with existing drainage systems retained where possible.Surface water from new canopies and track sections will be drained using a newdrainage system, the details of which will be determined during the detailed designphase of the Scheme, in consultation with appropriate stakeholders.

5.4.3 The surface water drainage for new structures and surfaces will be designed toensure that there is no flooding up to 1 in 30 year event and that there is no risk offlooding to people or properties up to 1 in 100 year event with 30% increase in rainfallintensity to allow for climate change.

5.4.4 In accordance with the Manchester Salford Telford SFRA User Guide and CoreStrategy Policy EN14 Flood Risk, the surface water runoff generated in the area ofthe proposed Scheme will take into account the aim to achieve a 50% runoff ratereduction up to a 1 in 100 year storm event, including consideration of climatechange.

5.4.5 Details of the surface water drainage strategy are described in Section 6 of thisreport.

5.5 Summary of Post Development Flood Risk

5.5.1 Construction of the proposed footbridge support within the channel of the RiverMedlock would reduce capacity of the channel and may increase risk of flooding inthe area or elsewhere. Further hydraulic modelling of the river will be carried out toassess potential impacts and to advise on appropriate mitigation measures.

5.5.2 The area of the proposed Scheme works is located in the heavily urbanised centre ofManchester. The proposed Scheme will not increase the amount of impermeable areaas the vast majority of this area is already hard surfaced. Therefore, the proposedScheme will not increase the rate or volume of surface water runoff generated withinthe area and will therefore not increase the risk of flooding from surface water.

5.5.3 Two of the four construction site compounds are located in a medium to high riskflood zone. It is recommended that these sites are signed up to the EA’s FloodWarning Direct to receive information on flooding updated on a daily basis. Inaddition, a Flood Evacuation Plan should be prepared and all workers should beaware of flood risk.




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SECTION 6

OUTLINE SURFACE WATER DRAINAGESTRATEGY




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6 OUTLINE SURFACE WATER DRAINAGE STRATEGY

6.1 Surface Water Management Approach

6.1.1 Surface water management proposals for the Scheme have been prepared taking intoaccount the following principles:

No runoff from the Scheme from rainfall depths up to 5mm;

No increase in the volume or rate of surface water runoff from the site in the 1 in1 and 1 in 100 year rainfall events;

No increase in flooding to people and property elsewhere as a result of thedevelopment;

No surface water flooding within the proposed Scheme in all rainfall events up toand including a 1 in 30 year return period storm;

Overland flows within the site from rainfall events in exceedance of a 1 in 30 yearreturn period storm are to be managed to minimise risk to people and property,up to the 1 in 100 year return period storm;

The surface water management proposals take into account a 30% increase inrainfall intensity in the 1 in 100 year rainfall event in the next 100 years.

6.1.2 In accordance with the latest guidance, including the forthcoming National Standardsfor SuDS, the Defra / EA guidance document 'Preliminary rainfall runoff managementfor developments' (Kellagher, 2012) and the Manchester SFRA the followingapproaches were considered (in order of preference):

(a) Infiltration to ground via an adequate soakaway or soil infiltration system

Piccadilly Station and Oxford Road Station

6.1.3 The area of the proposed alterations/improvement works and its surroundings islocated in the centre of Manchester and the vast majority is hard surfaced. Belowground contamination may be present, associated with areas where trains are stoodfor periods of time, potentially leading to a small build-up of pollutants over time.Therefore, usage of infiltration systems is unlikely to be feasible. However, it isrecommended that soil infiltration tests are undertaken in grassed areas adjacent tothe proposed alteration works to investigate potential for infiltration techniques.

(b) Discharge to a watercourse

Piccadilly Station

6.1.4 There are no watercourses in the vicinity of the proposed alterations that could beused to receive surface water drainage. Currently the surface water runoff generatedin the area of Piccadilly Station is partially discharged to the existing public sewers,highway sewers and sewers owned by UMIST. Some of the existing sewers servingthis area eventually discharge to the River Medlock.

Oxford Road Station

6.1.5 The River Medlock is located adjacent to the area of the proposed Scheme. Thedesign of drainage systems from the new canopy and track sections will be developedas part of the detailed design stage.




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(c) Discharge to a sewers

Piccadilly Station and Oxford Road Station

6.1.6 The design of drainage systems from the new canopy and track sections at bothStations will be developed as part of the detailed design stage.

6.2 Surface Water Management Strategy

6.2.1 The proposed surface water drainage strategy for both stations is shown in AppendixG.

Piccadilly Station

6.2.2 Piccadilly Station and the vast majority of its surroundings are hard surfaced, withsmall isolated grassed areas adjacent to the highway and railway infrastructure. Theproposed alterations will not increase the amount of impermeable area and willtherefore not increase the volume or rate of surface water runoff generated in thisarea.

6.2.3 The proposed alteration works to Piccadilly Station include construction of thefollowing: two new platforms, bridge, a new viaduct and a new overall canopy roof forthe new platforms, highway realignment and reconfiguration of a substation. Thesurface water runoff generated on roofs of the bridge and canopy and new structuresover Fairfield Street / Temperance Street will be drained to a new surface waterdrainage system within the station area and land owned by Network Rail. Surfacewater runoff generated in the area of the proposed highway realignment will bedrained to the highway drainage as it is now.

6.2.4 Piccadilly Station and its surroundings are located in CDA. The Manchester SFRAUser Guidance in relation to surface water runoff from brownfield areas suggests thatdevelopments should reduce runoff rates by a minimum of 50%. The proposedsurface water drainage strategy allows for attenuation measures. Priority is given toinfiltration techniques. However, the surroundings of Piccadilly Station are hardsurfaced with only small areas of permeable landscaping that will limit the use ofinfiltration techniques. Attenuation measures could take the form of tanks, asinfiltration techniques are unlikely to be feasible. Nevertheless, it is recommended thatsoil infiltration tests are undertaken in the grassed areas adjacent to the proposedalterations to investigate any potential for infiltration techniques.

6.2.5 The allowable discharge rates will be agreed with UU and/or UMIST and/or EA at thedetailed design stage of the project.

6.2.6 The new surface water drainage system will be designed to take into account stormevents up to and including a 1 in 100 year with 30% climate change.

6.2.7 Drawing 109172-D-ECV- DRG-PBL-000139 provided in Appendix G shows an outlineof the proposed surface water drainage strategy including tables showing an estimateof design flow rates envisaged for each of the proposed outfalls. These rates will beconsidered in the detailed design stage of the Scheme in discussion with appropriateauthorities.

6.2.8 The detailed design of the Scheme will be undertaken after planning consent isgranted and will include the detailed design of the drainage scheme.




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Oxford Road Station

6.2.9 The existing Oxford Road Station and its surroundings are entirely hard surfaced.Therefore, the proposed alterations will not increase the amount of impermeable area,and will therefore not increase the volume or rate of surface water runoff generated inthis area.

6.2.10 The proposed alterations to Oxford Road Station include extension of the length ofthe platforms, construction of a new footbridge, construction of new canopies over theplatforms, construction of a new covered concourse area to extend the existing tickethall and widening of the viaduct structures over Whitworth Street West. The surfacewater runoff generated in these areas will be drained to a new surface water drainagesystem within the station area and land owned by Network Rail.

6.2.11 The new surface water drainage system will take into account storm events up to andincluding a 1 in 100 year with 30% climate change.

6.2.12 Oxford Road Station and its surroundings are located in a CDA. The ManchesterSFRA User Guidance, with regard to surface water runoff from brownfield areas,suggests that developments must reduce runoff rates by a minimum of 50%. Theproposed surface water drainage strategy allows for attenuation measures. Thesurroundings of the Oxford Road Station are entirely hard surfaced. Infiltration ofsurface water will occur through the ballast used as one of the Scheme materials. Theballast will naturally attenuate the rate of surface water runoff.

6.2.13 Drawing 109172-D-ECV- DRG-PBL-000179 enclosed in Appendix G shows an outlineof the proposed surface water drainage strategy including tables showing an estimateof design flow rates envisaged for each of the proposed outfalls. These rates will beconsidered in the detailed design stage of the Scheme in discussion with appropriateauthorities.

6.2.14 The detailed design of the Scheme will be undertaken after planning consent isgranted and will include the detailed design of the drainage scheme.




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SECTION 7

SEQUENTIAL TEST AND EXCEPTION TEST




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7 SEQUENTIAL TEST AND EXCEPTION TEST

7.1 Sequential Test

7.1.1 NPPF recommends that the risk-based Sequential Test should be applied by theLocal Planning Authority when considering applications for new development. Its aimis to direct new development to those areas that are at the lowest risk of flooding(Flood Zone 1). The NPPF also states that, if following application of the SequentialTest it is not possible for the development to be located in areas with a lowerprobability of flooding, the Exception Test should be applied if appropriate.

7.1.2 The proposed Scheme consists of construction of a footbridge and alterations to theexisting Oxford Road Station, and construction of two new platforms with associatedinfrastructure in Piccadilly Station. In accordance with the Technical Guidance to theNPPF the nature of the Scheme will come under the flood risk vulnerabilityclassification of ‘Essential Infrastructure’. All the proposed alterations are located in alow risk Flood Zone 1. Review of Table 3 of the Technical Guidance to the NPPF,with regards to flood risk vulnerability against Flood Zone compatibility, indicates thatthe Exception Test does not need to be applied for this type of development in FloodZone 1 and 2. Therefore, the application of the Exception Test for the proposedworks is not required.

7.1.3 Two of four proposed site construction compounds are located in a medium to highrisk Flood Zone 2 and 3. However, the construction site compounds are temporaryhence neither the Sequential Test nor the Exception Test is required.

7.2 Exception Test

7.2.1 With reference to Table 3 of the NPPF, the Exception Test does not need to beapplied for the proposed alterations.




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SECTION 8

CONCLUSIONS




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8 CONCLUSIONS

8.1 Introduction

8.1.1 The proposed Scheme and improvement works consist of construction of a footbridgeand alterations to the existing Oxford Road Station, construction of two new platformswith associated infrastructure in Piccadilly Station, and realignment of the highwayadjacent to Piccadilly Station.

8.2 Summary of the Existing Flood Risk and Flood Risk During Construction

Fluvial Flood Risk

8.2.2 The proposed alterations to the existing railway tracks and stations, as well as theexisting highway that is to be realigned, are located in a low risk Flood Zone 1.Therefore, the risk of fluvial flooding is considered to be low.

Construction Phase

8.2.3 Two of the four construction site compounds are located in a medium to high riskFlood Zone 2 and Flood Zone 3 respectively. Therefore, appropriate mitigationmeasures will be required.

8.2.4 It is recommended that the construction site compounds are signed up to the EA’sFloodline Warnings Direct, which provides information on flood warnings updated ona daily basis. In addition, a Flood Evacuation Plan should be prepared for theseareas. All contractors should be aware of potential flood risk and be familiarised withthe emergency procedures.

8.2.5 It is also recommended that when construction works are finished, the compoundareas are reinstated to the original condition in terms of ground levels, to make surethat the area of flood extents has the same capacity to manage flood water as beforeconstruction works started.

Flood Risk from Groundwater

8.2.6 The SFRA Level 2 and PFRA indicate that the application site may be at risk ofgroundwater flooding. However, there are no known historic records of groundwaterflooding and the site is underlain by Till that would limit groundwater emergence.Therefore, the risk of groundwater flooding is considered to be low.

Flood Risk from Surface Water

8.2.7 The Scheme site area is located entirely in a Critical Drainage Area. Therefore, inaccordance with Manchester Core Strategy Policy EN14 Flood Risk, all newdevelopments that have the potential to impact the CDA should minimise surfacewater runoff in order that they do not increase the risk of flooding in the area orelsewhere.

8.2.8 The EA Surface Water Flood Map indicates that the area located within the bend ofthe River Medlock to the north of the existing railway line is at low risk of surfacewater flooding as well as small areas throughout the application site. The risk offlooding from surface water is considered to be low.




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Flood Risk from Sewers including Risk of Flooding from Overland Flow

8.2.9 There are no DG5 records of sewer flooding in the vicinity of the application site.

8.2.10 A few sewer flooding incidents were recorded in the area between Oxford Roadstation and Piccadilly Station. However, the Manchester PFRA states that there isinsufficient data to draw definitive conclusion of these incidents and to confirm theoccurrence of an event with significant harmful consequences. Therefore, the risk offlooding from sewers is considered to be low.

8.2.11 The proposed alterations to the existing railway tracks and stations will be elevatedabove the adjacent ground levels. Therefore, the risk of flooding from overland flow isconsidered to be very low.

8.2.12 The area of the proposed highway realignment adjacent to Piccadilly Station is servedby the existing highway drainage. Any overland flow will be intercepted andchannelled by the existing highway drainage. Therefore, the risk of overland floodingin this area is considered to be low.

Risk of Flooding from Reservoirs

8.2.13 The area to the south and east of Oxford Road Station is identified to be at risk offlooding from reservoirs. Reservoirs are regularly checked by panel engineers andmaintenance works are carried out on a regular basis. Therefore, the risk of reservoirfailure is extremely unlikely and the risk of such flooding is considered to be low.

8.3 Summary of Post Development Flood Risk

8.3.1 Construction of the proposed footbridge support within the channel of the RiverMedlock would reduce the river’s capacity which may increase the risk of flooding inthe area. Therefore, appropriate mitigation and compensation measures will berequired.

8.3.2 A cross sectional survey of the river will be carried out to inform the existing hydraulicmodel of the River Medlock. Hydraulic modelling will be carried out for both theexisting situation and with the proposed structure in place to identify any potentialimpact on water levels for up to 1 in 100 year storm event with climate changeallowance. In addition, hydraulic modelling of the river will be carried to identifyappropriate mitigation measures to ensure that construction of the proposed structurewill not increase the risk of flooding in the area or elsewhere up to and including 1 in100 year event with climate change allowance.

8.3.3 The vast majority of the Scheme site area is hard surfaced with small grassed areasadjacent to Piccadilly Station. Construction of the proposed alterations will notincrease the amount of impermeable area and would therefore not increase risk offlooding from surface water generated on the site.

8.3.4 The application site is entirely located in a Critical Drainage Area. Therefore, inaccordance with the SFRA User Guide, the surface water drainage strategy will takeinto account the aim to reduce surface water runoff rates by a minimum of 50%.Appropriate mitigation measures will be provided to achieve the reduced rates whereappropriate.




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8.3.5 The surface water runoff generated on new roofs, canopies and track section will bedischarged through a new drainage system, the details of which will be developedduring the detailed design stage of the Scheme in consultation with appropriateconsultees.

8.3.6 The new surface water drainage system will take into account the need to managestorm events up to and including a 1 in 100 year with 30% climate change

8.3.7 In accordance with Table 2 of the NPPF the proposed alterations are classified as‘Essential Infrastructure’. All of the proposed modifications are located in a low riskFlood Zone 1. In accordance with Table 3 of the NPPF this type of development isacceptable in Flood Zone 1 and the Exception Test is not required.




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SECTION 9

APPENDICES




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APPENDIX A

PROPOSED ALTERATION/IMPROVEMENTWORKS




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APPENDIX B

APPLICATION SITE BOUNDARY




- 65 -

APPENDIX C

EA INDICATIVE FLOOD MAP




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APPENDIX D

LOCATION OF CONSTRUCTION SITECOMPOUNDS




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APPENDIX E

CANAL BREACH HAZARD ZONES




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APPENDIX F

LOCATION AND DETAILS OF FOOTBRIDGESUPPORT STRUCTURE




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APPENDIX G

PROPOSED OUTLINE DRAINAGE STRATEGY




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Documents

Appendix G - Network Rail - Citizen Space · THE NETWORK RAIL (MANCHESTER ... Salford City and Trafford Councils Level 2 Hybrid Strategic ... by JBA Consulting, March 2010; x Manchester