DESIGN PACKAGE C122 - BORED...

Crossrail Plumstead Sidings Level 2 Flood Risk Assessment

C122-OVE-T3-RGN-CR148-50004 Submission Ref. GRE/2/9

Document uncontrolled once printed. All controlled documents are saved on the CRL Document System

© Crossrail Limited UNCLASSIFIED

DESIGN PACKAGE C122 - BORED TUNNELS

CROSSRAIL PLUMSTEAD SIDINGS

LEVEL 2 FLOOD RISK ASSESSMENT

Submission GRE/2/9

Document Number: C122-OVE-T3-RGN-CR148-50004

Revision: Date: Prepared by: Checked by: Approved by: Reason for Issue:

2.0 15/10/2013 Jayne Lamont Paul White Rob McCrae TWAO Application





Contents

Abbreviations ................................................................................................................. 4

Executive Summary ...................................................................................................... 5

1. Introduction ............................................................................................................... 7

1.1 Background ................................................................................................................ 7

1.2 Development Proposals ............................................................................................ 8

1.3 Proposed Construction Works and Programme ..................................................... 9

1.4 Scope ....................................................................................................................... 10

1.5 Previous Assessment .............................................................................................. 11

2. Policy Context ......................................................................................................... 12

2.1 Flood Zone Classification ....................................................................................... 12

2.2 Sequential Test ......................................................................................................... 13

2.3 Exception Test .......................................................................................................... 13

3. Assessment of Flood Risk...................................................................................... 14

3.1 Overview ................................................................................................................... 14

3.2 Historical Incidents of Flooding ............................................................................. 14

3.3 Fluvial Flood Risk .................................................................................................... 15

3.4 Tidal Flood Risk ....................................................................................................... 15

3.5 Surface Water Flood Risk ........................................................................................ 17

3.6 Groundwater Flood Risk ......................................................................................... 18

3.7 Other Sources of Flood Risk ................................................................................... 18

3.8 Climate Change ........................................................................................................ 18

4. Mitigation of All Sources of Flood Risk ................................................................. 20

4.1 Tidal ....................................................................................................................... 20

4.2 Surface Water ........................................................................................................... 20

4.3 Groundwater ............................................................................................................. 22

5. Conclusions and Recommendations .................................................................... 23

5.1 Conclusions .............................................................................................................. 23

5.2 Recommendations ................................................................................................... 24

References ................................................................................................................... 25





Appendices

Appendix A.1 Proposed Development Site Boundary

Appendix A.2 Baseline Site Layout Plan Following Temporary Development

Appendix A.3 Drainage Plans

Appendix A.4 Environment Agency Flood Maps and Flood Risk Data

Appendix B NPPF Policy Tables

Appendix C SFRA Developer Guidance

Appendix D Strategic Flood Risk Assessment (SFRA) Maps



of 25 Document uncontrolled once printed. All controlled documents are saved on the CRL Document System © Crossrail Limited UNCLASSIFIED

Abbreviations

AEP Annual Exceedence Probability

FRA Flood Risk Assessment

mAOD metres Above Ordnance Datum

mATD metres Above Tunnel Datum

NPPF National Planning Policy Framework

PPS25 Planning Policy Statement 25: Development and Flood Risk

SFRA Strategic Flood Risk Assessment

SuDs Sustainable Drainage System

SWMP Surface Water Management Plan

WCS Water Cycle Study

Annual Exceedence Probability (AEP)

The severities of the events discussed in this report are defined mainly as Annual Exceedence

Probabilities (AEP). The AEP is the probability that there will be an event exceeding a particular severity

in any one year.

Annual Exceedence Probability Probability (chance in any given year)

50% 1 in 2

10% 1 in 10

4% 1 in 25

3.3% 1 in 30

2% 1 in 50

1.33% 1 in 75

1% 1 in 100

0.5% 1 in 200

0.4% 1 in 250

0.1% 1 in 1000




Executive Summary

C122 (Arup and Atkins Joint Venture) has been commissioned by Crossrail Ltd to carry out a

Level 2 Flood Risk Assessment (FRA) for the development of the Plumstead Crossrail Sidings.

This site is located at the White Hart Triangle area of Plumstead, within the Royal Borough of

Greenwich (RBG). This Flood Risk Assessment will be used to support a Transport and Works

Act Order (“TWAO”) application for the Crossrail Plumstead Sidings. The site is well

documented both at a strategic level through assessments made by Crossrail (Crossrail, 2008)

and also by RB Greenwich, through the SFRA for Greenwich (Strategic Flood Risk Assessment,

2011).

It is proposed to use the Plumstead Crossrail Sidings, which will be located adjacent to the

Crossrail Plumstead tunnel portal, as an infrastructure maintenance facility for Crossrail’s

tunnelled central section and the passenger train stabling location for Crossrail’s south eastern

spur. The site currently has planning permission for use as a temporary railhead (herein also

referred to as the “Temporary Development”) to support the fit out of Crossrail under RBG

planning permission 13/0300/F. The Temporary Development is proposed to be constructed

from late 2013 and operate until late 2018.

The Plumstead Crossrail Sidings (“the Permanent Development”) will utilise some permanent

elements of the Temporary Development. These comprise earthworks (including drainage,

retaining wall and slope stabilisation), an electricity substation, two vehicle access points, hard

standing, rail tracks (including stabling and reception siding, a headshunt and associated

trackwork), and perimeter fencing.

The Permanent Development site lies predominately within Tidal Flood Zone 3a (high

probability of flooding) and within an ‘Area Benefitting from Defences. The National Planning

Policy Framework (NPPF) and associated Technical Guidance (both published by the

Department for Communities and Local Government (“DCLG”) in March 2012), and the PPS25

Development and Flood Risk Practice Guide (published in June 2008), require a site-specific

flood risk assessment to be carried out for all proposals for new development in Flood Zones 2

and 3. Given the nature of the permanent development and its location within an area of flood

risk level 3 it is necessary to complete a Level 2 FRA in order to provide a qualitative appraisal

of flood risk to the development, changes in flood risk elsewhere as a result of the development,

now and taking climate change into account, and the scope of any mitigation measures that




may be appropriate. The site itself is documented at strategic level and this FRA makes use of

information provided by the Environment Agency, Crossrail Ltd and the Royal Borough of

Greenwich (RBG) Strategic Flood Risk Assessment (SFRA, 2011).

The nature of the development (rail sidings and infrastructure maintenance facility) is such that

it falls within the category of ‘Less Vulnerable’ development (general industry) for the purposes

of flood risk assessment (in accordance with the definitions in Table 2 (flood risk vulnerability

classification) of the DCLG Technical Guidance.

The Southern Outfall Sewer (SOS) to the north of the site acts as a barrier in the unlikely event

of a breaching or overtopping scenario (tidal flooding) occurring from the tidal River Thames.

The SFRA shows that, without mitigation, the Plumstead Portal (situated on the south eastern

edge of the site) could convey flood flows and inundate the site in the event of breaching or

overtopping, causing flooding to the site. However, the ground elevations surrounding the

Plumstead Portal are being raised as part of the Crossrail works to ensure that it cannot act as

conveyance for flood flows should tidal or surface water flooding occur.

The existing surface water flood risk shows that the site is subject to surface water flooding of

over one metre (see Map 10 of the SFRA) during a 0.1% AEP with climate change.

The site is classed as a brownfield site and the SFRA developer guidance states that the

surface water drainage should improve the drainage of the site as part of the development. By

discharging surface water runoff rates down to greenfield rates the Proposed Development will

provide betterment for the site in terms of surface water flood risk.

The risk of groundwater flooding is low, however a previous FRA (Scott Wilson, 2007) for the

adjacent site suggests that a pumping system exists that maintains ground water at levels of

0mAOD. This system will be investigated further prior to the Temporary Development to ensure

that development on the site will not alter its operation and can be maintained both during the

construction and operation of the Proposed Development.

The assessment concludes that the flood risk to the permanent development is low, providing

the appropriate mitigation measures are implemented.




1. Introduction

1.1 Background

C122 (Arup and Atkins Joint Venture) has been commissioned by Crossrail to carry out a Level

2 Flood Risk Assessment (FRA) for the development of the Plumstead Crossrail Sidings. This

site is located at the White Hart Triangle (WHT) area of Plumstead, in Thamesmead, south east

London within the Royal Borough of Greenwich (RBG). The site is currently vacant however,

between mid 2014 and late 2018 it will be used as a temporary railhead facility (“the Temporary

Development”) to support the fit out of the Crossrail tunnels during construction. RBG granted

planning permission for the Temporary Development under the Town and Country Planning Act

1990 on 11 September 2013 under planning application no. 13/0300/F.

In total the site extends to approximately 5.5ha in area. The Proposed Development site

boundary is shown in Appendix Error! Reference source not found.. It is rectangular in shape

(approximately 85m wide by 390m long) and orientated approximately north east to south west.

The secondary (southern) part of the site is a 550m long west-east strip of land, varying in width

between 10m and 40m running parallel with the North Kent railway line to a point just west of

the White Hart Road bridge (incorporating the rail lines into the existing Network Rail sidings). A

triangle of land located immediately to the west of the former bowling green connects the main

part of the site with the southern part of the site and a vegetated embankment, which is within

the Proposed Development site boundary, separates the site from the adjacent allotments and

Seven Acres playing fields (which lie approximately 1m lower) to the south east.

The site occupies a low lying position within the wider townscape. To the south, Shooters Hill

rises to form a ridge line at Wins Common and to the north the townscape remains relatively flat

with the prominent built element being Belmarsh Prison. Prior to implementation of the

Temporary Development, the site mostly comprises open, vacant land, covered in grassland

and scrub vegetation throughout its central section with scrub and occasional birch trees in the

southern section and is generally flat except at its eastern end, where previously tipped material

has created an uneven surface and there are raised mounds, ranging in level from 2.6m to 7.6m

above tunnel datum (ATD), i.e. at a level up to 5m higher than that of White Hart Avenue to the

north west. In advance of the Temporary Development, a small area of the site has been

occupied by CRL office and welfare buildings and a temporary hard surfaced car park which

serves the construction site for the adjacent Plumstead portal.




This FRA has been completed in accordance with the NPPF and associated technical guidance,

which replaced Planning Policy Statement 25: Development and Flood Risk (PPS25) in March

2012.

The site lies within an area identified by RB Greenwich as an area for development (under the

Local Development Plan). The Unitary Development Plan (UDP) reference is DIA3. However

the proposed site does not cover the whole of site DIA3, which is 18.9ha.

Under the developer guidance (see Appendix C), taken from the SFRA the site is designated for

employment and a waste treatment facility. This type of development has a flood risk

vulnerability classification of ‘Less Vulnerable’ as per NPPF, Table 2 (Appendix B).

1.2 Development Proposals

Crossrail are proposing to construct a passenger train stabling and infrastructure maintenance

facility. The facility, known as Plumstead Crossrail Sidings (“the Proposed Development”) will

provide the functional elements described below:

Passenger Train Stabling:

Eight electrified sidings, each able to accommodate a passenger train up to

240m long and associated signalling equipment facilities;

Facilities for cleaning stabled trains including covered storage facilities with a

waste compactor; and

Accommodation and messing facility for infrastructure maintenance staff and

train crew. Facilities will include: offices, briefing, changing, shower and locker

accommodation and booking-on point.

Infrastructure Maintenance Facility:

Three non-electrified sidings for the stabling, formation, loading and unloading

of dedicated infrastructure maintenance rail vehicles;

Refuelling facilities for the infrastructure maintenance rail vehicles;

Facilities for maintaining the infrastructure maintenance rail vehicles;

Lay down space for the storage of infrastructure maintenance components

when they are not installed on a rail vehicle;

A facility for the manual jet washing of the infrastructure maintenance rail

vehicles;




Storage facilities for infrastructure maintenance equipment and consumables;

Parking for approximately 20 maintenance vans and trucks; and

Parking for approximately 100 staff vehicles.

Associated Trackwork:

The construction of trackwork for a headshunt and reception siding by which all

trains (maintenance rail vehicles and passenger trains) will egress the site and

gain access to the Crossrail lines.

1.3 Proposed Construction Works and Programme

Construction of the Proposed Development is programmed to be undertaken between mid 2017

and early 2019 and is expected to include the following works:

Reconfiguring hardstanding areas and roads retained from the Temporary Development;

Construction of support buildings:

- Accommodation building;

- Maintenance building;

- - Signalling equipment facilities; and

- Manual train wash.

Replacement of tracks for passenger stabling and maintenance trains; and

Replacement of the trackwork for the headshunt and reception siding.

No bulk earthworks for the Proposed Development will be required as this will be undertaken as

part of the Temporary Development.

Unless otherwise agreed with the relevant local authority through the Section 61 consent

process (under the Control of Pollution Act 1974), construction activities will be undertaken in

accordance with the Crossrail Environmental Minimum Requirements (EMR) i.e. during core

working hours (08:00-18:00 Monday to Friday and 08:00 – 13:00 on Saturday) and utilising a

start-up and close-down hour before and after these periods.

The operational phase of the Plumstead Crossrail Sidings will commence from early 2019. The

functional requirements of the facility are such that the site will be required to operate on a 24

hour / 7 days a week basis.




A Thames Water sewer, known as the ‘Marmadon sewer’, understood (from information

provided by Thames Water) to be a 1,280mm deep by 800mm wide egg / oval shaped Victorian

brick structure, runs beneath the site from Marmadon Road on a north eastern alignment

towards White Hart Avenue. The sewer, known to be in poor condition, is being diverted and

reconstructed as part of the Crossrail portal works prior to commencement of the Proposed

Development and these works will result in a permanent access shaft, four manholes and

pumping station being located within the site. The new sewer will consist of a 1.2m internal

diameter concrete pipe and will be connected to the combined Southern Outfall Sewer.

1.4 Scope

A Level 2 FRA is a scoping study which confirms the flood risk to the site and confirms if there is

likely to be an increase in flood risk as a result of the development. The FRA carried out for the

Plumstead temporary railhead (June 2012) forms the basis of this Level 2 FRA.

The Temporary Development comprises a temporary railhead and associated (permanent) civil

engineering works. It includes the construction of temporary rail sidings: buildings for

engineering train maintenance, inspection and cleaning and for staff welfare; storage facilities;

road vehicle access points, parking and circulation routes. At commencement of the Proposed

Development, the site baseline conditions will include an operational railhead including the

following permanent features, which will be retained from the Temporary Development:

Earthworks including drainage, retaining wall and slope stabilisation;

Electricity substation;

Two vehicle access points;

Hardstanding;

Rail tracks (including stabling and reception siding, headshunt and associated

trackwork); and

Perimeter fencing.

The site layout plan in Appendix A.2 shows the location and layout of these retained elements

which are assume to form part of the baseline conditions for this FRA.

The scoping study will also recommend potential measures that could be implemented to

reduce the risk to an acceptable level if applicable. Until further guidance in relation to the

requirements of a Level 2 FRA in line with the NPPF is made available, as best practice, the

scope of this FRA has been completed in line with the NPPF, the associated Technical

Guidance and PPS25 Guidance “Development and Flood Risk Practice Guide” (published by




DCLG in June 2008). Hence this Level 2 FRA includes the following, taking climate change into

account:

A qualitative appraisal of the flood risk posed to the site, and any potential impacts of the

development on flood risk elsewhere;

An appraisal of the possible mitigation measures to reduce flood risk to acceptable levels;

and

Demonstration of a risk based approach to the location of development by applying the

Sequential and if appropriate the Exception test.

In line with NPPF this FRA makes use of readily available information in the form of Fluvial

Modelling studies from Crossrail (Crossrail, 2008) and the Strategic Flood Risk Assessment for

the Royal Borough of Greenwich (Greenwich Council, 2011) and information provided by the

Environment Agency for the temporary railhead development (see Appendix A.4). This FRA

addresses the flood risk posed to both the construction and operational phases of the

Plumstead Crossrail Sidings.

1.5 Previous Assessment

The site is well documented both at a strategic level through assessments made by Crossrail

(Crossrail, 2008) and also by Greenwich Council, through the SFRA for Greenwich (Greenwich

Council, 2011). The SFRA provides a developer guidance summary and set of

recommendations for the site identified by the Local Development Plan (LDP). The LDP

identifies the site at Plumstead for development by Crossrail. The SFRA developer guidance for

this site can be found in Appendix C. A Level 2 FRA was also undertaken for the site as part of

the Temporary Development in 2012 (Appendix C1 of the ES for the Temporary Development

(C122-OVE-T1-XST-CR148-50002)).




2. Policy Context

In March 2012, the National Planning Policy Framework (NPPF) was published which revoked

PPS25, although the principles remain the same. This FRA has been completed in line with the

NPPF and the associated guidance. The aim of NPPF is to avoid inappropriate development in

areas at risk from flooding, but where development is necessary, making it safe without

increasing flood risk elsewhere, as per paragraphs 100 to 104 of the NPPF. In accordance with

NPPF proposed development in areas at risk from flooding, (i.e. located in Flood Zone 2 or 3)

require the submission of a FRA with the planning application. The Proposed Development is

located partially within Flood Zone 2 and 3 and thus this FRA is required in line with current

policy and as outlined in the Scoping Report for the Proposed Development (Document

reference C122-OVE-T1-RGN-CR148-50006).

2.1 Flood Zone Classification

NPPF guidance outlines four Flood Zone classifications of which three have been utilised by the

Environment Agency in the creation of their Flood Map. These Flood Zones should be used in

determining the appropriateness of Proposed Development uses when considering flood risk

through the application of the Sequential Test. They represent flooding without flood defences

in place.

The Flood Zones are defined as:

Flood Zone 1 – Areas with a ‘Low Probability’ of flooding and where the annual

probability of flooding is lower than 0.1% for either fluvial or sea flooding. NPPF impose

no constraints upon the type of development within Flood Zone 1.

Flood Zone 2 – Areas with a ‘Medium Probability’ of flooding and where the annual

probability of flooding is between 0.1 and 1.0% for fluvial flooding or between 0.5 and

0.1% for sea flooding. NPPF recommend that Flood Zone 2 is suitable for most types of

development with the exception of ‘Highly Vulnerable’ (see Appendix B) land uses which

require a passed Exception Test.

Flood Zone 3 – Areas with a ‘High Probability’ of flooding and where the annual

probability of flooding is 1.0% or greater for fluvial flooding or 0.5% or greater for sea

flooding. NPPF recommend that appropriate development is based upon a further

classification of Flood Zone 3 into 3a High Probability and 3b, functional floodplain,

(where water has to flow or be stored in times of flood).




According to NPPF the Proposed Development is classed as ‘Less Vulnerable’ (see bold text in

Appendix B, table B.1). This classification is based on Table 2: Flood Risk Vulnerability

Classification, within the NPPF and is included within this FRA in Appendix B.

Table B.2 in Appendix B has been taken from Table 3 (Flood risk vulnerability and flood zone

compatibility) in the NPPF and demonstrates where development, based on the vulnerability

classification is suitable, unsuitable and when the Exception Test is required. In line with these

tables, the temporary railhead development classed as Less Vulnerable and is therefore

suitable for development within Flood Zone 1, 2 and 3a.

2.2 Sequential Test

NPPF states that the Sequential Test should be carried out when allocating land for

development to demonstrate that there are no sites available for development in areas that are

at a lower risk from flooding. When an area is at risk from either fluvial or coastal flooding then

development should be allocated outside Flood Zones 2 and 3 where possible. However if there

are no reasonable sites for development within Flood Zone 1 then depending upon flood

vulnerability, proposed development sites could be allocated in Flood Zones 2 or 3. The

Sequential Test should be based on flood risk maps provided in a SFRA in preference to the

Environment Agency Flood Zone mapping in line with NPPF.

The proposed site for the Crossrail Plumstead Sidings has been allocated in the Unitary

Development Plan (UDP) reference (DIA3) for development under the LDP and recognised in

the SFRA as a site for development, therefore it can be concluded that this site has passed the

Sequential test. Appendix C provides the site Developer Guidance from the SFRA.

2.3 Exception Test

The SFRA, states that 52% of the identified site (DIA3) lies within Flood Zone 3a and is

appropriate for ‘Less Vulnerable’ developments (see Appendix C), 17% in Flood Zone 2 and

31% within Flood Zone 1. As per Table 3 in the NPPF, the site will not require an Exception

Test.




3. Assessment of Flood Risk

3.1 Overview

It is outlined within the accompanying technical guidance of NPPF (paragraph 9) that flood risk

from all sources must be addressed within the FRA to ensure that potential flood risk has been

considered during the development design and proposed works. Therefore this section outlines

all the potential sources of flood risk to the site and the implications these risks have on

development. It is also necessary to outline any records of previous flooding events as these

may identify areas vulnerable to flooding.

The topographical levels resulting from the Temporary Development will remain unaltered.

Based on these topographical levels the existing ground (as per the temporary railhead) will

vary between 3.7 metres above Ordnance Datum (mAOD) and 5.6mAOD. The ground level to

the north east of the site is higher than the ground to the south of the site. The site lies within an

area of general flat topography although it appears to have several raised or mounded areas.

Recent development in the vicinity of the site has altered ground levels in the area, for example

the current Crossrail Plumstead Portal construction work at the south west end of the site,

where the ground levels vary between 4mOD and 6mOD (Crossrail - C122-OVE, May 2012).

3.2 Historical Incidents of Flooding

Both the Environment Agency and the SFRA state that the site experienced tidal flooding in

1953. Appendix A.4 shows the historic flood extent for this event. As highlighted in the SFRA

and on Map 5 of the SFRA (Appendix D), Plumstead has previously had one incident of

groundwater flooding, in February 2001. The flooding did not occur on the site of the Proposed

Development. In addition, localised flooding of the Seven Acre Sports Club pitches and the

adjoining allotments occurred from mid 2012 until early 2013. Independent studies

commissioned by Crossrail, the Environment Agency and Thames Water were inconclusive as

to the source of the flooding. Surface water flooding also occurs on the Marmadon Road which

lies adjacent to the southern boundary of the site. The SFRA and the Environment Agency do

not refer to any further flooding from any source either on the site of Proposed Development or

adjacent to it.




3.3 Fluvial Flood Risk

There are no fluvial flood sources on the site of the Proposed Development. Therefore risk from

fluvial flooding is negligible.

3.4 Tidal Flood Risk

The site is located within an area benefitting from defences and within Flood Zone 3. The site is

at risk of tidal flooding from the River Thames. However the River Thames is very heavily

defended and the Environment Agency inspects the flood defences twice yearly. Whilst the

Thames flood defences can be maintained, the residual risk of overtopping or a breach of the

defence cannot be eliminated entirely. However, appropriate warning and mitigation can be

developed.

The Environment Agency has provided hydraulically modelled river levels for various scenarios

as part of this assessment (see Appendix A.4). The 1% AEP modelled present day level for the

modelled node closest to the site is 5.97mAOD and 6.63mAOD for the 0.1% AEP. The site has

a range in level from 3.7mAOD to 5.6mAOD. The Thames Flood Defences in relation to this site

provide a standard of protection for the 0.1% AEP and are maintained to a crest level of

7.20mAOD. This remains valid until the year 2070, at which point the standard of protection will

begin to decrease, the Thames Estuary 2100 project has studied options to manage flood risk in

the Thames Estuary up to the year of 2100 (Environment Agency, May 2012).

The SFRA and the Tunnel Flood Protection Strategy (Crossrail, 2008) have developed various

breaching and overtopping scenarios for both the site and the wider area through 2d hydraulic

modelling. Both the SFRA and Crossrail breach models have been developed in consultation

with the Environment Agency.

Flood Inundation Mapping

The same breach points have been used to develop breaching and overtopping scenarios in

both the Tunnel Flood Protection Strategy (Crossrail, 2008) and the SFRA. It is assumed that as

both models were carried out in consultation with the Environment Agency, that the breach

locations are deemed as fit for overtopping and breach modelling purposes by the Environment

Agency. The mapped output provides a good indication of flood inundation mapping for the site

of the Proposed Development (see maps 13 and 14 of the SFRA) (Appendix D).




For the purposes of the 2d hydraulic modelling the site lies within the East Greenwich

Embayment, also known as Thamesmead (Crossrail, 2008). This document will refer to the area

of 2d hydraulic modelling as the East Greenwich Embayment.

The East Greenwich Embayment has a major division across the embayment site due to the

embanked Southern Outfall Sewer (SOS). The SOS embankments mean that there are only

two flow routes from which water can flow from a north to south direction, one of these flow

connections is located at Plumstead Station and is known as the Plumstead Portal and the

other is from the South Mere culvert located to the east of the temporary railhead site.

The South Mere culvert flood conveyance does not affect the Plumstead Crossrail Sidings site

due to the dismantled railway (which lies to the eastern edge of the site) acting as an

embankment stopping flood conveyance flows from reaching the site.

It is at the Plumstead Portal that there is highest risk of inundation in the absence of mitigation.

The Plumstead Portal lies on the edge of the site proposed for development. Map 14 from the

SFRA (Appendix D) shows that the Plumstead Portal has a maximum flood depth of 3.5mAOD

following a breach. Further detailed hydraulic modelling of a breach scenario for the Plumstead

Portal (Crossrail, 2008) located on the site, states that maximum water level of 3.29mAOD

causes flooding. This scenario is the existing situation for a 0.1% AEP and includes the

Thames Barrier and existing defences. As expected, the Plumstead Portal is also shown to

flood under future climate change conditions.

Flood Hazard Mapping

The SFRA developer guidance summary for DIA3 (Appendix C), states that the 33% of the site

lies within a high residual risk category1, 6% lies in a medium and 13% in a low residual risk

category and 48% of the site is unaffected by residual risks. However the site area that

Crossrail wish to develop upon is approximately half the size which is designated for

1 Flood Risk to People – Phase 2 FD2321/TR2 Guidance Document, DEFRA, March 2006.




development by the LDP. The site boundary suggests that a majority of the site lies outside of

the area of high residual risk.

Assessment of Tidal Flood Risk

Whilst the Environment Agency are responsible for maintaining the Thames flood defences and

the probability that a breach or overtopping scenario is low, it is still recognised by Crossrail that

appropriate steps towards mitigation and appropriate warning should be carried out. These

steps taken by Crossrail will ensure that the Crossrail network can remain safe during a breach

or overtopping scenario.

Crossrail receive flood warnings from the Environment Agency for the whole Crossrail network

and have carried out site specific assessments of flooding for various sites including the

Plumstead Portal. As part of their assessments at Plumstead Portal, the ground elevation will be

raised at the entrance to the tunnel and therefore water will be prevented (from surface and

breach / overtopping flooding) from entering the tunnel (Crossrail, 2008). The Plumstead Portal

modification has been designed to resist a flood level of 104.553mATD (=4.553mAOD) (0.5%

AEP with climate change).

Following this assessment of tidal flood risk, it can be deemed that the risk of flooding from

overtopping or breaching of the site is low and can be mitigated.

3.5 Surface Water Flood Risk

As part of the SFRA, an assessment of surface water flooding has been undertaken. The high

level maps (Maps 9 and 10 of the SFRA) (Appendix D), show that parts of the site are subject to

a greater than one metre of surface water flooding under both the 0.1% AEP and the 0.1% AEP

with climate change. The site is shown to have greatest surface water flood risk in the area of

the Plumstead Portal.

Marmadon Road, which lies adjacent to, and along the southern boundary of the site, has had

occurrences of surface water flooding. Although the details of the flooding are not known, the

assessment carried out in the SFRA corroborates this.

The existing site currently drains to ground, and there are no existing drainage plans available

for the site, as it is a derelict/vacant Brownfield site.




Appropriate mitigation methods will be adopted (see section 4.2) to ensure that surface water

flooding does impact upon the Proposed Development, as per the SFRA developer guidance

(see Appendix C).

3.6 Groundwater Flood Risk

The site lies on a minor aquifer. There is a pumping system for the canal and lake network in

the area that maintains water levels below 0mAOD (Scott Wilson, 2007). Within the vicinity of

the site, one known incident of groundwater flooding occurred in Plumstead in February 2001,

see map 5 of the SFRA (Appendix D), however there are no further details. From the

information available it can be deemed that the risk of groundwater flooding to the site is low.

3.7 Other Sources of Flood Risk

There is a major sewer that runs across the northern boundary of the site, known as the

Southern Outfall Sewer (SOS). The sewer embankment buries the pipes of the Southern Outfall

Sewer on their way to the Crossness Sewage Treatment Works. This covered sewer is owned

and maintained by Thames Water and runs from Plumstead to Crossness. The sewer is

embanked and it has not been known to breach since it was constructed (Greenwich Council,

2011). The height of the sewer is 6.5mAOD (Crossrail - C122-OVE, May 2012). The

information available shows that the risk of flooding from other sources (such as reservoir flood

risk) is low.

3.8 Climate Change

As a result of climate change, flood risk to the site is likely to increase. Table 4 of the NPPF

accompanying technical guidance, shows the predicted changes in peak intensity and sea level

rise as outlined within NPPF. These values should be considered during a detailed assessment

for the lifetime of the development. However the UK Climate Projections (UKCP09) has been

published since PPS25 and reflects predictions in relation to climate change with updated

methodologies. NPPF makes use of the same changes as outlined within NPPF and hence the

values provided in Table B.1 and B.2 of NPPF is considered appropriate for this assessment.

The Environment Agency has provided river levels for the River Thames under two climate

change scenarios; 2055 and 2107. The 0.1% AEP levels for the year 2055 are modelled as

6.94mAOD and 7.48mAOD for the year 2070. The 1% AEP for the year 2055 is modelled as

6.29mAOD and 6.81mAOD for the year 2070.




After 2070 intervention would be required to maintain the minimum standard of protection.

However the Environment Agency is working on options to manage climate change within the

Thames Estuary. The Environment Agency project to manage climate change in the Thames

estuary is known as the ‘Thames Estuary 2100’ project and has studied options to manage

flood risk in the Thames estuary up to the year 2100.




4. Mitigation of All Sources of Flood Risk

4.1 Tidal

As the site lies within an area benefitting from defences, the actual flood risk to the site is low.

Residual risks of flooding present themselves as overtopping or breaching, and whilst this is

unlikely, previous assessment from Crossrail (2008, 2009) and the SFRA has been carried out

to determine the residual risks. Rates of inundation and maximum flood depths have been

determined both at the site (Crossrail, 2009)(Crossrail, 2008) and as part of a larger study

(Greenwich Council, 2011). It is recognised that forms of overtopping and breaching cannot be

completely eliminated and steps are being taken to ensure that the site is safe.

Steps are being taken to ensure that in the event of a breach or overtopping scenario, water

cannot reach the site of the Plumstead Crossrail Sidings. One of the flow routes to the site in

such an event is the Plumstead Portal. Raised ground levels at the Plumstead Portal are

designed to stop water from entering the running tunnels and conveying water from north to

south. The SOS embankment will also act as a barrier in an overtopping or breach scenario.

The layout of the Proposed Development will retain some elements from the temporary railhead

development (see Appendix A.2). These include earthworks (including drainage, retaining wall

and slope stabilisation), meaning that the site will have a proposed mean surface level of

5.1mATD. This will provide the relatively flat land required for the development of both the

temporary railhead and permanent development of the Plumstead Crossrail Sidings. Crossrail

have put into place a set of Emergency Procedures that determine actions to be taken at

various levels of warnings from the Environment Agency (Greenwich Council, 2011). It is

recommended that the Plumstead Crossrail Sidings development receives flood warnings from

the Environment Agency during both the construction phase and operation phase of the

Proposed Development.

4.2 Surface Water

The site is classed as a brownfield site (Greenwich Council, 2011). However the proposed

drainage has been designed to meet greenfield runoff rates, therefore providing a drainage

system which offers betterment to the existing situation. The storage capacity of the proposed

drainage has been designed to ensure capacity up to a 1% AEP flood event and will be

contained within the site. It is proposed that the site will have approximately 80% hardstanding

impermeable area, an increase of over 60% impermeability. By ensuring that runoff is mitigated




down to the greenfield runoff rate, the drainage system will provide betterment and hence

ensure that surface water flood risk is decreased and managed on-site. Therefore the Proposed

Development will not increase the flood risk elsewhere (see the site specific SFRA developer

guidance (see Appendix C)).

The installation of the surface water drainage system will have been undertaken as part of the

Temporary Development in accordance with Condition 14 of the planning permission granted by

RB Greenwich (13/0300/F) which states that:

‘No development shall take place until a surface water drainage scheme for the site,

based on sustainable drainage principles and an assessment of the hydrological and

hydrogeological context of the development, has been submitted to and approved in

writing by the local planning authority. The drainage strategy should demonstrate the off-

site surface water run-off generated up to and including the 1 in 100-year plus climate

change critical storm will not exceed 30 litres per second. The scheme shall

subsequently be implemented in accordance with the approved details before the

development is completed. The scheme shall also include details of: how the scheme

shall be maintained and managed after completion; any infiltration features’.

In addition, Condition 15 of the same planning permission states that:

‘No infiltration or surface water drainage into the ground is permitted other than with the

express written consent of the Local Planning Authority, which may be given for those

parts of the site where it has been demonstrated that there is no resultant unacceptable

risk to controlled waters.’

All infiltration methods have been discounted due to the risk of ground contamination. Following

implementation of the Temporary Development, the runoff generated on site will be collected

and conveyed into the site below the ground surface water drainage network and will discharge

off site to an external receiver. Porous paving will be utilised on the proposed site car parks, and

underground attenuation tanks constructed as part of the Temporary Development will store

water that cannot be discharged under normal greenfield runoff rates.

Proposed Site Drainage Plans are detailed in Appendix A.3. The proposed site drainage plans

show that a retaining wall will be built around the site as part of the temporary railhead

development, however as the discharge will be to greenfield runoff rates, there should not be

any impact upon surface water flood risk both on site and off site as a result of the retaining




wall, as the proposed surface water drainage will provide betterment (Chapter 4, Section 4.2,

Plumstead Temporary Railhead Level 2 Flood Risk Assessment, June 2012) (Appendix L of the

Plumstead Crossrail Sidings EIA Scoping Report reproduced in Appendix 04 of the ES for the

Proposed Development (C122-OVE-T1-XST-CR148-50004)).

4.3 Groundwater

The below ground development (attenuation storage tanks and the construction of inspection

pits forming part of the Temporary Development) will need to be maintained to ensure that the

risk of groundwater flooding is not increased. Appropriate measures will also be taken to ensure

that the groundwater flood risk does not increase during the construction phase of the

Permanent Development when below ground works are being carried out.




5. Conclusions and Recommendations

5.1 Conclusions

There are a number of conclusions that can be made from this assessment, these are as

follows:

1. The Proposed Development is classed as less vulnerable in line with NPPF;

2. The site is currently located within the Environment Agency and SFRA Flood Zones 1, 2 and

3 and within an area benefitting from defences;

3. The SOS embankment acts as barrier against water conveyance should a breaching or

overtopping scenario from the tidal River Thames occur;

4. The ground elevation around the Plumstead Portal is being raised to ensure that water

cannot be conveyed to the site in the event of flooding;

5. The retaining walls and ground levels as part of the temporary railhead proposal will remain

in situ. The retaining walls ensure that no risk from surface water will be transferred to areas

adjacent to the site. Surface water flood risk will be mitigated by discharge to 25.4l/s;

6. The fluvial flood risk to the site is negligible; and

7. Groundwater flood risk is low and currently maintained via a pumping system to ensure

groundwater does not reach 0mAOD.

Paragraph 103 of the NPPF provides guidance on developments in areas at risk of flooding. It

states that:

‘When determining planning applications, local planning authorities should ensure flood risk is

not increased elsewhere and only consider development appropriate in areas at risk of flooding

where, informed by a site-specific flood risk assessment following the Sequential Test, and if

required the Exception Test, it can be demonstrated that:

within the site, the most vulnerable development is located in areas of lowest flood risk

unless there are overriding reasons to prefer a different location; and

development is appropriately flood resilient and resistant, including safe access and

escape routes where required, and that any residual risk can be safely managed,

including by emergency planning; and it gives priority to the use of sustainable drainage

systems’.




The Proposed Development meets the criteria set out in paragraph 103 in the following

respects:

The levels across the site will be re-graded as part of the Temporary Development and

these levels will remain for the Proposed Development. The more vulnerable elements

of the development (offices) will be located on those parts of the site at a higher level in

the area at lowest risk of flooding;

Crossrail will implement their emergency procedures in response to flood warnings from

the Environment Agency to ensure that safe evacuation of the site can be carried out in

the event of flooding to the site; and

The temporary railhead development will create the necessary drainage to support its

development and this drainage system will remain in place for the permanent

development. As such this will provide betterment to the existing situation of no drainage

on the site and lower the risk of flooding from surface water both to the site and to

adjacent areas, as surface water run-off is reduced.

5.2 Recommendations

It is recommended that Crossrail receive flood warnings from the Environment Agency for this

site for both the construction and operation phase of the Proposed Development.




References

Communities and Local Government. (2012). Technical Guidance to the National Planning Policy

Framework.

Crossrail. (2012). Plumstead Temporary Railhead and Associated Permanent Works Environmental

Impact Assessment (C122-OVE-T1-XST-CR148-50004)

Crossrail - C122-OVE. (May 2012). Geotechnical Report - Desktop Study.

Crossrail. (2009). Flood Protection Strategy Report (CR-EG-CTS-CE-RT-00023).

Crossrail. (2008). Tunnel Flood Protection Strategy - Fluvial Modelling (CR-DV-PRW-X-SR-00020).

Department for Communities and Local Government. (2010). Planning Policy Statement 25: Development

and Flood Risk.

Environment Agency. (May 2012). KSL120417KR66_P4 Response.

Greenwich Council. (2011). Strategic Flood Risk Assessment.

Scott Wilson. (2007). Flood Risk Assessment - Project Harry, Thamesmead, Lodon.





Appendices





Appendix A.1 Proposed Development Site Boundary

RE

ST

RIC

TE

D

TWAO Order Boundary

Plumstead Crossrail Depot

TWAO Application GRE/2/9

1:1250

Ove Arup & Partners Limited

Woolwich to Abbey Wood

C122-OVE-T-DDA-CR148_Z-82102

HD

S4

Bored Tunnels (Alignment and Track)

---

-

0 50m25m25m 75m 100m 125m

1:1250

TWAO Order Boundary

TWAO Application

N

' Crown copyright and database rights 2012 Ordnance Survey 100035971

H.DADE

P01

P01

K.MULLINS

KM11/10/2013

B.STRAW

BS

Fit for auth

orisation

www.crossrail.co.uk

Rev :

E14 5LQ

London

Canary Wharf

25 Canada Square

Crossrail Limited

Notes

Originator :

Location :

Scale : Drawing and CAD file No :

Title :

Suitability :

DateRev. Description By Chkd App

' Crossrail

Co

py

Ap

pr

ove

d f

or

Desi

gn -

Create

d:

12-

OC

T-

20

13

By :

Auth :

Contract :

@ A1

Chk :

App :

Auth

182

1.2mCHURCH MANOR WAY

216

180

150

142

162

172

180

Posts

El Sub Sta

65.4

Sienna

Mast

1.4m

CH

UR

CH M

AN

OR W

AY

CR

Ward B

dy

1.2m

El Sub Sta

188

CHURCH MANOR WAY

1.7m

232

118

Sports Ground

242

128

St Thomas A Becket Primary School

250

136

1.6m

St Paul’s AcademyAllotment Gardens

13

117

127

133

14

MO

TTIS

FO

NT R

OA

D

13

115

105

BIRKDALE ROAD

101

25

99

26

93 97

91

185

232

238

Pavilion

139

193

CH

UR

CH M

AN

OR

WA

Y

66

2.2m

3.2m

Letter Box

80

82

88

Foot Bridge

1

100

2

110

116

1

131

135

129

2719

2125

64

214

26

Ps

1

65

Ps

Sienna

5

Ps

3

Ps

Posts

202

2.1m

175

214

Sub Sta

El

Tennis Courts

226 228

183

120

1.9m

101115

132

MARMADON ROAD

127

El Sub Sta

142

2.0m

139

Dis

mantle

d Railw

ay

154

Bowling Green

Shelter

Pool

Paddling

Playground

Tennis Court

153

WHIT

E H

ART

AVEN

UE

PCs

166

2.1m

155

Plumstead Gardens

178

165

190

Pond

Sports Ground

FB

Shelter

Pond

67 to 70

El Sub Sta

CB

Tanks

Ps

65

7

Ridgew

ayWorksPPa

th

8

Ward B

dy

Southern O

utfall S

ewers

(high and lo

w lev

el)

Works

10

6

6 KELLNER

ROAD

108

37

4 9

1

WorksTank

55

Und

El S

ub Sta

55

126b

119 to 121

1

Works 55Works

Works12

6

7

77

77a

79

79a

81

81a

83

83a

85

85a

87

87a

89

89a

91

91a

93 95c

93a

95

95a

97

97a

99

99a

95b

SL

MP 10.5

WHITE HART AVENUE

El Sub Sta

Centre

Community

Trac

k

Path

HY

LT

ON S

TR

EE

T

20

56

14

13

BA

LG

OW

AN S

TR

EE

T

13

68

30

23

26

21

Sub Sta

El

82 3

5

40110

40

2.3m

71

71a

73a

75

75a73

97

105

115

75

63

65

2

117

70

133

1

82

49

92

104

MARMADON

ROAD

59 63

77

77a

79

79a

81

BA

NN

OC

KB

UR

N R

OA

D

81a

83

83a

85

85a

87

87a

89

BARTH MEWS

69125

69a

6

El Sub Sta

SL

El Sub Sta

WB

Builder’s Yard

Depot

Tanks

NORTH ROAD

Timber Yard

Timber Yard

FactoryPath

UndRi

dgew

ay

El Sub StaCB

South

ern O

utfall Sew

ers(hi

gh an

d low le

vel)

El Sub Sta

Trac

k

Ward B

dy

Path

Ridgew

ay

CBNATHAN

WAY

67 to 69

Works

Sub Sta

El

14

92

78

123

149

137

127

125a

WHIT

E H

AR

T R

OA

D

21

31

(SA)

Memorial Hall

50

Gordon

26

36

45

55

41

37

44

49

35

4

95

43

29

85

31

67

36

67a 69

1a

Cottages

Rose

46

13

1

BA

TES

ON S

TR

EE

T

81

4

28

1

56

REIDHAVEN ROAD

El Sub Sta

93

GUNNING STREET

66

21

7

101

92a

76

111

20

14

12

BO

UG

HT

ON R

OA

D

Crown Industrial Park

2

75 to 9

9

101

103

109

LB

115

El Sub Sta

MP 10.25

Ward Bd

y

Path

Ridgew

ay

Works





Appendix A.2 Baseline Site Layout Plan Following Temporary Development

www.crossrail.co.uk

Rev :

E14 5LQ

London

Canary Wharf

25 Canada Square

Crossrail Limited

Notes

Originator :

Location :


Title :

Suitability :


' Crossrail

Co

py

Ap

pr

ove

d f

or

Desi

gn -

Create

d:

02-

MA

Y-

20

13

By :

Auth :

Contract :

@ A1

Chk :

App :

Auth

226 228

183

129

131

MARMADON ROAD

61

142

2.0m

73

154

Shelter

Pool

Paddling

Playground

PCs

166

85

Plumstead Gardens

178

97

190

Pond

FB

Shelter

Pond

202

109

214

119

3945

2 4929

21

2a

11

9

2b

2c

1

2

HY

LT

ON S

TR

EE

T

1

20

14

13

BA

LG

OW

AN S

TR

EE

T

13

30

23

26

21

Sub Sta

El

35

40

40 120

132

2.3m

1.9m

77

77a

79

79a

81

81a

83

83a

85

85a

87

87a

89

89a

91

5

Ps

3

Ps

Posts

67 to 70

El Sub Sta

Ps

Ps

65

7

PSienna

Ps

1

65

91a

93 95c

93a

95

95a

2.1m101

97

97a

99

99a

95b 115127 2.1m

139153

155

175

165

SL

MP 10.5Sub Sta

El

Tennis Court

Tennis Courts

Bowling Green

El Sub Sta Dis

mantle

d Railw

ay

Sports Ground

El Sub Sta

WHIT

E H

ART

AVEN

UE

6

El Sub Sta

SL

El Sub Sta

WB

Builder’s Yard

Depot

Tanks

NORTH ROAD

WHITE HART AVENUE

Timber Yard

Timber Yard

FactoryPath

UndRi

dgew

ay

El Sub StaCB

South

ern O

utfall Sew

ers(hi

gh an

d low le

vel)

El Sub Sta

CentreTrac

kCommunity

Ward B

dy

Path

Ridgew

ay

CBNATHAN

WAY

67 to 69

Trac

k

SL

MP 10.25

Southern O

utfall S

ewers(High and Low Level)

Ward Bd

yCF

Path

NATHAN W

AY Ridgew

ay

Works

Works

Works

117

133

1

82

49

92

104

MARMADON

ROAD

59 63

77

77a

79

79a

81

81a

83

83a

85

69

85a

87

87a

89

69a

71

71a

68

73

73a

75

82

75a

Richard NeveHouse

49

47

51

14

28

21

31

67

36

67a 69

1a

Cottages

Rose

46

13

1

81

4

1

56

REIDHAVEN ROAD

El Sub Sta

93

66

7

101

92a

76

111

92

78

123

149

137

127

125a

125

31

(SA)

Memorial Hall

50

Gordon

36

45

41

37

44

35

4

95

85

97

BARTH MEWS

105

115

75

65

2

58

59

ABERY STREET

63a

201

TCB

8

1

2a

2 7

BA

TES

ON S

TR

EE

T

21

11

28

GUNNING STREET

HE

VE

RH

AM R

OA

D

21

7

49

27

13

43

29

47

BA

RT

H R

OA

D63

Posts

68

70

BROOKDENE ROAD

Hall

BA

NN

OC

KB

UR

N R

OA

D

42

44

56

2

1

15

14

3.8m

42

161

WHIT

E H

AR

T R

OA

D

2

21

14

26

HARTVILLE ROAD

15

1

26

55

3.3m

28

Letter Box

66

1

238

80

2322

CH

UR

CH M

AN

OR

WA

Y

2.2m

193

82

1185

881

39

Foot Bridge3.2m

100

50

1

2.0m

64

2

Posts

65.4

Sienna

110

116

Pavilion

1.7m

118

Sports Ground

128

1.6m

Allotment Gardens

95.0

100.0

105.0

110.0

115.0

95.0

100.0

105.0

110.0

115.0

RE

ST

RIC

TE

D

1:1250



C122-OVE-T-DDA-CR148_Z-81134

S4


---

-

-

0 50m25m25m 75m 100m 125m

1:1250

Sub-station access road

Plumstead Portal

Scale 1 : 500

Scale 1 : 500

Elevation 1- Reinforced Earth Retaining Wall

Proposed site level

Existing site level at boundary

Reinforced earth retaining wall

Proposed site levelReinforced earth retaining wall

Retaining wall

of wall.

fencing, 2.4m tall above top

High security welded mesh

wall.

mesh infill, 2m tall above top of

Pedestrian parapet with welded

welded mesh fencing.

2.4m tall, high security

C122-OVE-T-DDA-CR148_Z-88103

(for details refer to

Transformer Building

welded mesh fencing.

2.4m tall, high security

entrance/exit

Main vehicular

mesh fencing.

aperture welded

2m tall, large

Retaining Wall

future development.

The site will be cleared of all buildings and materials, and fully secured pending3.

all other internal vehicular circulation areas will be disused.

The vehicular access road to the Transformer Building will remain operational,2.

fencing and vehicular entrances and exits to remain in-situ.

All earthtworks, retaining walls, surface water drainage, utilities, perimeter security 1.

Existing site level at boundary

1

-

2

-

remain.

Headshunt to

SD01/05/2013 Environmental Scoping Appendix

(subject to design)

vehicular access

Secondary

Application boundary

Legend

Crossrail Plumstead Depot

Gabion retaining wall

Elevation 2 - Gabion and Reinforced Retaining Wall

Temporary Railhead Use

Baseline Site Layout Plan Following

sidings to remain.

Formation for stabling

to remain

Reception road

P01

P01

K.MULLINS

KM

S.DENHAM

B.STRAW

BS

Fit for auth

orisation





Appendix A.3 Drainage Plans

www.crossrail.co.uk

Rev :

E14 5LQ

London

Canary Wharf

25 Canada Square

Crossrail Limited

Notes

Originator :

Location :


Title :

Suitability :


' Crossrail

Co

py

Ap

pr

ove

d f

or

Desi

gn -

Create

d:

01-

OC

T-

20

12

By :

Auth :

Contract :

@ A1

Chk :

App :

Auth

Ps

Ps

Dismantled Railway

WHITE HART AVENUE

P

23+000

23+050

23+100

23+150

23+200

23+050

23+200

23+150

23+000

23+000

23+050

23+100

23+150

23+200

RG

RG

RG

RG

RG

RG

RG

TG

TG

Ø225

Ø150

Ø 150

Ø 150

89a

83a

87a

85a

85

89

87

MP 10.5

2.3m

WHITE HART AVENUE

Dismantled Railway

6.5m x 3m

A

LV Room

4.3m x 5m

A

Transformer

4.5m x 5m

A

HV Room

4.7m x 3m

Store

Comms/

4.5m x 5m

B

HV Room

6.5m x 3m

B

LV Room

4.3m x 5m

B

Transformer

9m2Office

Manager’s

M1.02

2.5m2W.C

M1.05

5m2Corr.

M1.03

48m2Store

M1.07 48m2Store

M1.08

13.5m2Store

M1.13

m2700 Shed

Maintenance

M1.01

m24

PointM1.04Tea

m211

PlantM1.09 6.5m2

RoomCommsM1.10

7.5m2RoomFMLV M1.11

6.5m2RoomLV

M1.12

9m2Store

M1.15

17m2Stair Ext.

M1.14

m246.5

WorkshopM1.06

RG

RG

RG

RG

RG

RG

RGR

G

RG

RG

RG

Ø450

Ø 300

Ø450

Ø 450

Ø300

Ø 225

Ø225

Ø 450

Ø 450

Ø 250

Ø 225

Ø 225

Ø 250

Ø 450

Ø 250

Ø 150

Ø 450

Ø 225

Ø 250

Ø 300

Ø 250

Ø 250

Ø 150

Ø250

Ø 250

Ø300

Ø 300

Ø 150

Ø 300

Ø150

Ø300

Ø 300

Ø 300

Ø 300

Ø 300

Ø 300

Ø 300

Ø 150

Ø 300

Ø750

Ø450

Ø150

Ø750Ø750

Ø225

Ø150

Ø 225

Ø 225

Ø750

Ø225

Ø225

Ø 750

Ø150

RG

RG

RG

RG

RGRG

RG

RG

RG

RG

RG

RG

RG

RG

RG

RG

RG

RE

RE

RE

RE

Ø450

Ø150

RE

Ø300

Ø300

Ø300

Ø 150

Ø 150

Ø 150

Ø 150

Ø 150

Ø 150

Ø 150

Ø 150

Ø 150

Ø 300

Ø225

Ø150

Ø150

Ø 150

Ø 150

Ø250

Ø225

Ø300

Ø 150

Ø 150

Ø 150

Ø 150

Ø225

Ø 150

Ø 225

RG

RG

RG

RG

RG

RG

RG

RE

RE

RE

RE

RE

RE

RE

RE

RE

Ø 150

TG

TG

TG

TG

TG

TG

TG

TG

TG

TG

TG

TG

TG

TG

TG

TG

DP

DP

Ø225

Ø 225

Ø 225

Ø 225

Ø 225

Ø150

Ø150 Ø150

Ø150 Ø150

Ø150Ø 150

Ø225

Ø225

RE

ST

RIC

TE

D



C122-OVE-T-DDA-CR148_Z-82104

S4


---

-

-

N

Legend

Plumstead Temporary Railhead

TCPA Planning Submission GRE/2/8

Drainage Plan

Red line site boundary

Foul water

Surface water

discharge to be agreed with Thames Water.

1. Level of flow control and attenuation of surface water

N

into Thames Water Sewer

Foul Water discharge

Interceptor tank

Interceptor tank

Interceptor tank

into Thames Water Sewer

Foul Water discharge

Rainwater Harvesting Tank

into Thames Water sewer

Surface water discharge

For continuation see a

bove

For c

ontin

uatio

n see b

elo

w

RMNDMCFirst Issue04/07/2012P01

---

P02

1:5000Scale 1:500

10m 10m 20m 30m 40m 50mSD28/09/2012

S.DENHAM

P02

P02

D.WILSON

DW

R.MCCRAE

RM

Fit for auth

orisation





Appendix A.4 Environment Agency Flood Maps and Flood Risk Data

Our ref: KSL120417KR66Date: 20 April 2012

Please note:

http://www.environment-agency.gov.uk/research/planning/33580.aspx

Ordnance Survey 1: 25 000 colour raster base mapping;Flood Zone 2 and Flood Zone 3;Relevant model node locations and unique identifiers (for cross referencing to the water levels, depths and flows table);

A table showing:

Model(s) extents;FRA site boundary (where a suitable GIS layer is supplied);Flood defence locations (where available/relevant) and unique identifiers; (supplied separately)

iv) local flood history data (where available/relevant).

This letter is not a Flood Risk Assessment. The information supplied can be used to form part of your Flood Risk Assessment. Further advice and guidance regarding Flood Risk Assessments can be found on our website at

Product 4 is designed for developers where Flood Risk Standing Advice FRA (Flood Risk Assessment) Guidance Note 3 i) "all applications in Flood Zone 3, other than non-domestic extensions less than 250 sq metres; and all domestic extensions", and

If you would like advice from us regarding your development proposals you can complete our pre application enquiry form which can be found at

Flood Map areas benefiting from defences (where available/relevant);

http://www.environment-agency.gov.uk/research/planning/82584.aspx

ii) Flood defence locations unique identifiers and attributes; (supplied separately)iii) Historic flood events outlines unique identifiers and attributes; and

Statutory (Sealed) Main River (where available within map extents);

Plumstead Railway Sidings, SE28

i) model node X/Y coordinate locations, unique identifiers, levels, flows and JFLOW depths;

This information is based on that currently available as of the date of this letter. You may feel it is appropriate to contact our office at regular intervals, to check whether any amendments/ improvements have been made. Should you re-contact us after a period of time, please quote the above reference in order to help us deal with your query.

If you will be carrying out computer modelling as part of your Flood Risk Assessment, please read the enclosed guidance which sets out our requirements and best practice for computer river modelling.

This information is provided subject to the enclosed notice which you should read.

ii) "all applications with a site area greater than 1 ha" in Flood Zone 2.

Product 4 (Detailed Flood Risk) for

Product 4 includes the following information:

Flood Map flood storage areas (where available/relevant);Historic flood events outlines (where available/relevant, not the Historic Flood Map) and unique identifiers;

Thames Barrier, Eastmoor Street, Charlton, London, SE7 8LXCustomer services line: 03708 506 506Email: [email protected] www.environment-agency.gov.uk

Modelled in-channel levels KSL120417KR66

Year10% 5% 2% 1% 0.5% 0.2% 0.1%

2005 5.35 5.55 5.82 6.04 6.26 6.53 6.732055 5.77 5.96 6.19 6.38 6.58 6.84 7.042107 6.39 6.54 6.75 6.92 7.11 7.39 7.60

Year10% 5% 2% 1% 0.5% 0.2% 0.1%

2005 5.32 5.51 5.76 5.97 6.17 6.43 6.632055 5.71 5.88 6.11 6.29 6.48 6.74 6.942107 6.30 6.45 6.65 6.81 6.99 7.27 7.48

Year10% 5% 2% 1% 0.5% 0.2% 0.1%

2005 5.31 5.50 5.75 5.95 6.15 6.41 6.612055 5.70 5.87 6.09 6.26 6.45 6.71 6.912107 6.28 6.42 6.63 6.79 6.98 7.25 7.46

Modelled water levels in the Thames for locations close to your site are shown in the tables below. All levels are provided in metres above Ordnance Datum Newlyn (mAODN). In modelling the levels, three main factors were considered; the astronomical tide, the surge tide and the flow coming from the non-tidal Thames. The location, or node, closest to your site is 3.04.

Annual Probability of Occurrence

Grid ref: TQ 41634 79577Location node 3.01



Modelled River Levels (mAODN)

Grid ref: TQ 44419 80001Location node 3.04

Modelled River Levels (mAODN)Location node 3.05Grid ref: TQ 45694 81290

Modelled River Levels (mAODN)


Model notes KSL120417KR66

Model: Tidal Thames Joint Probability Extreme Water Levels 2008Date of creation: 12 May 2008

Notes: Our water levels are created from a 2-D joint-probability computer hydraulic model. As this is a joint-probability model the confluence of different factors such as astronomical tides, tide surge and river flows have been taken into account. In summary, the calculation of extreme water levels involves two main stages: 1) Estimating a matrix of water levels at various locations (or model nodes) along the estuary 2) Calculating the statistical frequency (return period) with which a particular water level might be expected to occur at each of the model nodes.

Climate change allowances:

This study modelled water levels to various annual probabilities (10%, 5%, 2%, 1%, 0.5%, 0.2% and 0.1%). Each of these probabilities have been modelled for present day (2005) and future years (2055 and 2107) taking into account DEFRA's climate change allowances as set out in the Planning Policy Statement 25 (PPS25).

Some of the levels are lower for the more extreme probabilities when including climate change because the hydraulic model used to produce these levels takes into account the Thames Barrier closure rule (circumstances/conditions of closure) and assumes that it remains unchanged up to 2107. Increased sea levels and fresh water flows mean that the Thames Barrier closure rule will be met more often. This means that a smaller number of tides will be allowed to flow up into central London each year. The highest tides experienced upstream of the Thames Barrier occur when the circumstances are within a fine margin of meeting the closure rule, and the decision is taken not to close (a near closure event). As there will be fewer tides per year upstream of the Barrier, and the ratio of near closure levels to regular tidal levels within this smaller number of tides remains constant, the number of near closure events will decrease, and therefore so do the modelled levels.


Historic flood data KSL120417KR66Our records show that the area of your site has been affected by tidal flooding. Information on floods that have affected areas near your site is provided in the table below, and is shown on the attached map:

Historic Flood Events Unique ID Flood Event Code Flood Event Name Start Date End Date Source of Flooding Cause of Flooding

EA0619530300005 EA061953 TTD_FEO_1953 31/01/1953 01/02/1953 Tidal River Thames Overtopping and Breach of defence

Extra historic flood information:

Our records show that the area of your site has been affected by tidal flooding.

The site was subject to tidal flooding, due to a storm surge in the North Sea, on the night of the 31st January into the morning of 1st February 1953. An approximate level in the Thames at the time was 5.16 m AODN.

Please note the Environment Agency maps flooding to land not individual properties. Floodplain extents are an indication of the geographical extent of a historic flood. They do not provide information regarding levels of individual properties, nor do they imply that a property has flooded internally.


Flood Defences KSL120417KR66General description:

The river Thames defences along this section of the river provide a standard of protection of 1 in 1000. This means that the defences protect against a tidal flooding event that has a 0.1% annual probability of occurring. This remains true up to the year 2070. After 2070 the standard of protection will decrease over time. However the Thames Estuary 2100 project has studied options to manage flood risk in the Thames estuary up to the year 2100. Public consultation of this study has finished, but you can access all the information here: http://www.environment-agency.gov.uk/research/library/consultations/106100.aspx

The defences along the tidal Thames in this area are all raised, man-made and privately owned. We inspect them twice a year to ensure that they remain fit for purpose. They must be maintained by their owners to a crest level of 7.10 m AODN downriver of Broadwater Dock and 7.20 m AODN upriver of Broadwater Dock (the Flood Defence Level in this reach of the Thames). The overall condition grade for defences in the area is 2 (good), on a scale of 1 (very good) to 5 (very poor).

Standard of protection provided by the tidal defences

Additional Notes



C122-OVE-T3-RGN-CR148-50004 Rev 2.0. Submission Ref. GRE/2/9



Appendix B NPPF – Policy Tables





NPPF – Policy Tables

Flood Risk Vulnerability Classification

Land Use Vulnerability Type of Development

Essential Infrastructure Essential transport infrastructure (including mass evacuation routes) which has to cross the area at risk

Essential utility infrastructure, which has to be located in a flood risk area for operational reasons, including electricity generating power stations and grid and primary substations; and water treatment works that need to remain operational in times of flood.

Wind turbines.

Highly Vulnerable Police Stations, Ambulance Stations and Fire stations, Command Centres and telecommunications installations required to be operational during flooding.

Emergency dispersal points.

Basement dwellings.

Caravans, mobile homes and park homes intended for permanent residential use.

Installations requiring hazardous substances consent.

More Vulnerable Hospitals.

Residential institutions such as care homes, children’s homes, social services homes, prisons and hostels.

Buildings used for: dwelling houses; student halls of residence; drinking establishments; nightclubs and hotels.

Non-residential uses for health services, nurseries and educational establishments.

Landfill and sites used for waste management facilities for hazardous waste.

Sites used for holiday or short let caravans and camping, subject to specific warning and evacuation plans.





Land Use Vulnerability Type of Development

Less Vulnerable Police Stations, Ambulance Stations and Fire stations which are not required to be operational during flooding.

Buildings used for: shops, financial, professional and other services; restaurants and cafes, hot food takeaways; offices; general industry; storage and distribution; non-residential institutions not included in ‘more vulnerable’; and assembly and leisure.

Land and buildings used for agriculture and forestry.

Waste treatment (except for landfill and hazardous waste facilities).

Minerals working and processing (except for sand and gravel working).

Water treatment plants which do not need to remain operational during times of flood.

Sewage treatment plants (if adequate pollution control measures in place).

Water Compatible Development

Flood control infrastructure.

Water transmission infrastructure and pumping stations.

Sewage transmission infrastructure and pumping stations.

Sand and Gravel workings.

Docks, Marinas and Wharves.

Navigation facilities.

MOD installations.

Shipbuilding, repairing and dismantling, dockside fish processing and refrigeration and compatible activities requiring a waterside location.

Water based recreation (excluding sleeping accommodation).

Lifeguard and coastguard operations.

Amenity open space, nature conservation and biodiversity, outdoor sports and recreation and essential facilities such as changing rooms.

Essential ancillary sleeping or residential accommodation for staff required by uses in this category, subject to specific warning and evacuation plans.





Appropriate Development for each Flood Zone

Flood Risk Vulnerability

Classification (see Table D2 of PPS25)

Essential Infrastructure

Water Compatible

Highly Vulnerable

More Vulnerable

Less Vulnerable

Flo

od Z

one

(see

Tab

le D

1 of

PP

S25

)

Zone1

Low Probability

Zone2

Medium Probability

Exception Test required

Zone 3a

High Probability


x Exception Test required

Zone 3b ‘Functional Floodplain’


x x x

Development is appropriate

x Development should not be permitted

Climate Change

Recommended contingency allowances for net sea level (Table from NPPF (Communities and Local Government, 2012)

Net sea level rise (mm per year) relative to 1990

1990 to 2025 2025 to 2055 2055 to 2085 2085 to 2115

East of England, east midlands, London, south-east England (south of Flamborough Head)

4.0 8.5 12.0 15.0

Recommends national precautionary sensitivity ranges for peak rainfall intensities and peak river flows (Table 5 from NPPF (Communities and Local Government, 2012)

Parameter 1990 to 2025 2025 to 2055 2055 to 2085 2085 to 2115

Peak Rainfall Intensity

+5% +10% +20% +30%

Peak River Flow +10% +20%





Appendix C SFRA Developer Guidance

London Borough of Greenwich: site summary and recommendations

Site Details

Site Name UPD

Reference

Site Location (OS NGR) 18.9

Proposed use

Flood risk vulnerability

classification

Less

Vulnerable

Comments

Brown/Greenfield Brownfield

Flood Risk

Flood Zone (Fluvial & Tidal)

Flood Type

3b 3a 2 1

0% 0% 0% 100%

3b 3a 2 1

0% 52% 17% 31%

Comments

Residual risk:

Defended?Yes

Maintainer:Private

Standard of

Protection:1000 years

Comments

Residual Risk Yes Comments

if yes:

High Medium Low None

33% 6% 13% 48%

Other sources of flood risk:

Susceptibility to surface water

floodingLess - More

Comments

Risk of groundwater floodingYes

Bedrock

geologySand

AquiferMinor

Comments

Effect of climate change:

Is a site specific Flood Risk Assessment required?

FRA required?

Yes

Comments

Exception test required for

proposed use?

No

Comments

Recommendations for Development

Plumstead DIA3

TQ 456 790 Site Area (ha)

Employment, Waste Treatment Facility

Based on definitions stated in PPS25 Table D2

Tidal

Percentage of site in each Fluvial

Flood Zone

Percentage of site in each Tidal

Flood Zone

Based on the Environment Agency's Flood Zones map, March 2009

Based on NFCDD data

Assessment of residual risk conducted by JBA Consulting

Percentage of site in each

Residual Risk category

Susceptibility to surface water flooding for 0.1% AEP event with

climate change is measured in three categories; less (water 0.3 -

0.6m in depth), intermediate (water 0.6 - 1m in depth) and more

(water >1m in depth).

Groundwater poses a potential threat of flooding if the site is underlain by a chalk, sand or sand

and gravel bedrock, which forms a minor or major aquifer.

Defra guidance suggests a 980mm increase of tidal peak levels over the next 100 years due to climate change. This will increase the

residual risk at this site.

A FRA is required to assess tidal flood risk and flood risk from

other sources, including surface water and groundwater.

PPS25 guidance states less vulnerable development is

appropriate in all flood zones accept Flood Zone 3b.

The proposed usage of this development is for Less Vulnerable uses. This is an appropriate usage at this location, and therefore meets

the requirements of PPS25. As the development is behind existing defences there is a high residual risk, therefore plans for this site

should consider this residual risk and ensure the development remains safe, the development should require an emergency plan be put

in place in case of a breach in the defences. Part of the site is susceptible to surface water flooding. The development should improve

the drainage infrastructure to reduce flood risk on site (see report chapter 9.8.1).





Appendix D Strategic Flood Risk Assessment (SFRA) Maps

DESIGN PACKAGE C122 - BORED...

Documents

Transcript of DESIGN PACKAGE C122 - BORED...