DRAINAGE STATEMENT - BXS Positive Dialogue · Figure 3 - Landscape Architecture plan of Plot 12 layout and adjacent private streetscape corridors . BXS Limited Partnership Brent Cross

H O W LO N D O N S H O U L D G R O W

INFORMATION PACK

Plot 12, Phase 1B (South)Reserved Matters Application

Brent Cross South Limited Partnership

October 2017

DRAINAGE STATEMENT

Contacts

Brent Cross South Limited Partnership 4 Stable Street London N1C 4AB www.brentcrosssouth.co.uk www.argentrelated.co.uk @argentrelated

ARUP Ove Arup & Partners Ltd.13 Fitzroy Street London W1T 4BQ www.arup.com

AKT IIWhite Collar Factory1 Old Street YardLondonEC1Y 8AF

www.akt-uk.com

BXS Limited Partnership

Brent Cross South

Plot 12 RMA Drainage Statement

BXS-ARP-1BS-XX-RP-CD-0001

Rev B | 24 October 2017

This report takes into account the particular

instructions and requirements of our client.

It is not intended for and should not be relied

upon by any third party and no responsibility

is undertaken to any third party.

Job number 245526

Ove Arup & Partners Ltd

13 Fitzroy Street

London

W1T 4BQ

United Kingdom

www.arup.com

BXS-ARP-1BS-XX-RP-CD-0001 | Rev B | 24 October 2017

\\GLOBAL.ARUP.COM\LONDON\ILG\JOBS\245000\245526-00 BRENT CROSS SOUTH\INTERNAL (WIP)\CD_CIVILDRAINAGE\RP_REPORT\PHASE 1BS\BXS-ARP-1BS-XX-RP-CD-0001_PLOT 12 RMA DRAINAGE

STATEMENT_ISSUE3.DOCX

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Statement - DRAFT 02.docx Description Second draft


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CD-0001_PLOT 12 RMA DRAINAGE STATEMENT_ISSUE3.DOCX

Contents Page

1 Introduction 1

2 Project 2

3 Existing Site 2

4 Proposed Scheme 3

5 Policy and Planning Conditions 4

6 Design Criteria 5

7 Flood Risk 6

8 Proposed Surface Water Drainage Design 7

8.1 Introduction 7

8.2 Allowable Discharge Rates 8

8.3 Public Realm Design (Arup) 8

8.4 Building Plot Design (AKTII) 11

8.5 Operation and Maintenance 11

9 Foul Water Drainage 11

10 Consultation 12

11 Conclusions 12

Appendix A

Relevant Policy and Legislation

Appendix B

Public Realm Drainage Design

Appendix C

Pre-Planning Application Consultation

Appendix D

Plot 12 Flood Risk

Appendix E

Building Drainage Design (AKTII)






Page 1

1 Introduction

This Drainage Statement has been prepared by Arup and outlines the proposed

drainage strategy for the Reserved Matters Application (RMA) pursuant to

Condition 1.2.2 and part discharge of Condition 13.1, for Plot 12 and adjacent

streets and public realm (which form part of Phase 1B (South)) of the S73

Permission, on behalf of the Brent Cross South Limited Partnership (BXS LP).

Figure 1 below shows the planning application boundary.

Arup has been commissioned by BXS LP to provide infrastructure design services

for site wide infrastructure for the Brent Cross South (BXS) development,

including flood risk and drainage. AKTII have been commissioned to provide

engineering design services for the Plot 12 building, which includes drainage

design. Arup are the authors of this Drainage Statement, while AKTII have

provided input with relevant designs for the Plot 12 building.

Figure 1 - Plot 12 and adjacent streets and public realm RMA boundary






Page 2

2 Project

The Plot 12 and adjacent streets and public realm RMA is part of the wider Brent

Cross Cricklewood (BXC) regeneration, for which Section 73 planning

permission was granted on 23 July 2014 (Reference F/04687/13, the S73

Permission). Key documents that have been used as the basis for the drainage

design include the following:

S73 Permission Drainage Strategy (BXC15);

S73 Permission Flood Risk Assessment (BXC16);

Thames Water Utilities Limited Hydraulic Impact Studies. Latest X4503-722 SMG 1540 March 2017;

Previous consultation and agreements between London Borough of Barnet, The Environment Agency and Thames Water.

3 Existing Site

The Plot 12 and adjacent streets and public realm RMA site is 0.77 ha in area and

is located to the south of the existing A406 North Circular and north of Claremont

Park (also referred to as the Claremont Way Open Space). The north half of the

site consists of the existing Clarefield Park and the southern section

predominately includes existing buildings which are accessed from Claremont

Way, which joins the existing Claremont Road to the south, see Figure 2. The

Brent Terrace and Claremont industrial estate is located within and to the west of

the RMA boundary. There are existing utilities and drainage pipes within the plot

boundary which will be removed or diverted.

Figure 2 - Aerial view of the existing site with RMA boundary for Plot 12 and adjacent

streets and public realm RMA






Page 3

4 Proposed Scheme

Figure 3 shows the proposed design layout for Plot 12. The proposals are for

principally residential use with mixed uses at ground floor level including a

packet park and courtyard. The extent of the site also includes tertiary routes

running approximately north-south on both the east and west sides of the

buildings.

Figure 3 - Landscape Architecture plan of Plot 12 layout and adjacent private streetscape

corridors






Page 4

5 Policy and Planning Conditions

The proposed design addresses, and where relevant, complies with the S73

Permission conditions below, and complies with the Revised Development

Specification & Framework (S73 Permission Volume BXC01), specifically

paragraph 2.75 which is also reproduced below.

S73 Permission Conditions (relevant to Flood Risk and Drainage for Plot 12

Brent Cross South)

44.5. Any Sustainable Urban Drainage System to be submitted for approval in

accordance with Condition 1.27 in relation to each Phase or Sub-Phase shall be

integral to the site and ensures a commitment to a minimum 25% reduction in

surface runoff of current 1 in 100 year flow plus 30% for climate change through

incorporation of SUDS features, such as Green and Brown Roofs, detention

basins, gravelled areas, swales, permeable paving and pipe storage. It must be

demonstrated that SuDS have been maximised across the site, with justification

provided if targets set in the London Plan cannot be met. The system must treat

water pollution in line with Section C of Defras National Standards for

Sustainable Drainage Systems with regard to specific hazards and receptors.

44.9. No infiltration of surface water drainage into the ground related to new

development is permitted other than with the express written consent of the LPA ,

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.

45.2. All finished floor levels (excluding car parks, service yards, customer

collection areas, goods handling and ancillary basement activities) shall be set no

lower than 300mm above the 1 in 100 year (+ climate change) flood level. In

addition the threshold levels into the car parks service yards, customer collection

areas, goods handling and ancillary basement activities hereby permitted shall be

set no lower than 300mm above the 1 in 100 year (+ climate change) flood level

or located outside of the floodplain. Any application to deviate from these

standards shall be submitted and approved by the LPA in consultation with the

Environment Agency.

S73 Permission Volume BXC01 Revised Development Specification &

Framework (paragraphs relevant to Flood Risk and Drainage for Plot 12

Brent Cross South)

2.75. Surface water and foul water drainage will utilise existing infrastructure

where possible, thus minimising disruption. It is intended that all surface water

drainage provision will operate under gravity where achievable, avoiding the

need for a pumped system. New surface water pipe-work will connect to existing

public drainage at the most convenient locations, and will generally follow the

alignment of the proposed internal road network. The development will reduce

surface water run off to approximately 75% of the current 1:100 year return flow

plus 30% for climate change. This will be achieved through the careful selection

of Sustainable Urban Drainage (SUDS) features which will be agreed with the

LPA at a detailed design stage, but which are likely to include green/brown roofs

and storage cells with filtration. The existing baseline run-off for the site is






Page 5

estimated at 8,810 l/second as explained in the Drainage Strategy and

Supplementary Strategy. Prior to each stage of the development commencing,

details will be provided to demonstrate that the development will be self-sufficient

in terms of providing adequate levels of attenuation to reduce surface water run-

off toward the site wide calculated level.

Relevant national and regional policies and legislation which relate to flood risk

and drainage are outlined in Appendix A for reference.

6 Design Criteria

The design of the drainage will be conform to the S73 Permission requirements

and the following standards and guidance:

WRc Sewers for Adoption 7th Edition;

Building Regulations 2010 Approved Document H Drainage and Waste Disposal (2015 edition);

CIRIA SuDS Manual 2015.






Page 6

7 Flood Risk

During the consultation process with the London Borough of Barnet it has been

agreed that a site-specific Flood Risk Assessment (FRA) is not required as part of

the Plot 12 Reserved Matters Application. This is because an FRA was

undertaken as part of the S73 submission. There are conditions attached to the S73

Permission relating to Flood Risk accordingly (see Condition 45). During pre-

application discussions with LBB planning officers it was agreed that a further

FRA would not need to be undertaken to support this RMA. LBB officers did,

however, confirm that the RMA submission should demonstrate compliance with

Condition 45.2 accordingly.

The Environment Agencys flood maps show the site is located in Flood Zone 1.

This is regarded has having a low risk of flooding, i.e. a probability of less than

1% per annum.

Planning Condition 45.2 requires finished floor levels (FFLs) to be 300mm above

the 1 in 100 year + climate change (CC) flood level. As the site is in Flood Zone

1, the nearest flood level of the River Brent for a 100 year + CC event should be

used for the Plot 12 site. As the River Brent will be realigned as part of the Brent

Cross Cricklewood development and before the completion of Plot 12, the

resulting flood water levels from the realigned hydraulic modelling exercise

should be used, instead of Product 41 information from the Environment Agency

which would provide existing flood modelling data.

These hydraulic model outputs are included in the BXC Flood Risk Assessment

(S73 Permission Volume BXC16). Node BRpr_SK657, which is located close to

the existing Templehof Bridge, provides a 100 year + CC flood water level of

39.4 mAOD (metres above Ordnance Datum). This can therefore be used as the

relevant flood level for Plot 12, see Appendix D for annotated plans. All FFLs and

basement levels are above this level (by minimum 300 mm) which therefore

ensures compliance with Planning Condition 45.2.

1 Product 4: Detailed Flood Risk Assessment Map, including flood zones, defences and storage

areas, areas benefiting from defences, statutory main river designations, historic flood event

outlines and more detailed information from our computer river models (including model extent,

information on one or more specific points, flood levels, flood flows).






Page 7

8 Proposed Surface Water Drainage Design

8.1 Introduction

The surface water drainage design for Plot 12 has been split in two sections which

correspond to separate areas and separate consultant scopes. The first section

considers the drainage design for the Tertiary Routes and has been designed by

Arup. The second section then assesses the drainage design for the two buildings,

pocket park and courtyard, which has been designed by AKTII, see Figure 4. This

section will explicitly address the requirements of all the aforementioned planning

conditions.

Figure 4 - Plot 12 surface water drainage catchments and split in consultant scope

(blue/green catchments designed by Arup, purple catchment designed by AKTII)






Page 8

8.2 Allowable Discharge Rates

The allowable discharge rates for these catchments have been derived to align

with the S73 Permission Volume BXC15 Drainage Strategy. The allowable

discharge rates for Plot 12 are a proportion of the allowable discharge rate for the

site wide catchment, based on the Plot 12 areas.

The maximum allowable discharge rate for the site wide catchment is calculated

as 75% of the existing maximum 100 year return period runoff rate, this complies

with S73 Permission Condition 44.5. The current 10 ha site wide catchment has a

maximum allowable discharge rate of 751 l/s. This value may change if the

catchment area changes, but this should not impact on the value for the Plot 12

site as the value is prorated relative to its contribution to the site wide catchment.

Table 1 includes the catchment areas and associated maximum allowable

discharge rates.

Table 1 - Catchment size and maximum allowable discharge rates

Catchment

Total

Catchment

Area (ha)

Maximum

allowable

discharge rate

(l/s)

30- year

Attenuation

vol. (m3)

100 year

Attenuation

vol. (incl. 30%

CC) (m3)

Plot 12/13 public

realm corridor 0.17 14 33 67

Plot 11/12 public

realm corridor 0.18 14 33 67

Plot 12 building plot 0.61 45 Refer to AKTII Plot 12 report

(Appendix E)

8.3 Public Realm Design (Arup)

8.3.1 Catchments and Connection Location

The two Tertiary Routes adjacent Plot 12 form the public realm catchments for

the site. The intention is to keep each catchment separate to avoid unnecessary

pipes connections through the building plot (the majority of which includes a

basement).

Drawing BXS-ARP-1BS-XX-DR-CD-1200 in Appendix B includes the proposed

design for these catchments. Due to the location of Plot 12 in relation to other

areas of the Plot 12 site both corridors will include adoptable surface water carrier

pipes to pick up plot and highway drainage. These carrier pipes fall from south to

north and will then connect into the proposed surface water drainage network in

the High Street, and eventually into the existing Thames Water network in Tilling

Road, which runs parallel to the south edge of the A406.






Page 9

8.3.2 Attenuation Volumes

Each public realm catchment is approximately 85% impermeable. Using the

Micro Drainage Quick Storage Estimate a maximum of 25 m3 of attenuation

volume is predicted to be required for each catchment in a 1 in 30 year storm

event, and 55 m3 for a 1 in 100 year + CC storm event. The actual amount of

attenuation required will be calculated at the detailed design stage.

8.3.3 SUDS Features

Drawing BXS-ARP-1BS-XX-DR-CD-2200 in Appendix B illustrates the drainage

design for the public realm areas including the proposed SUDS features. This

design includes planters and rain gardens to collect runoff from roads and public

realm areas. Water will then slowly make its way through perforated pipes at the

base of the planters into below ground cellular attenuation tanks, which will

provide the majority of the attenuation storage.

The planters will help improve the water quality of the runoff whilst also

providing significant amenity and bio-diversity value to the wider area. These are

key aims of the SUDS approach set out in the London Plan and CIRIA SuDS

Manual. Appropriate soils and plant types will be selected by the landscape

architect to ensure the plants flourish in wet and dry periods.

8.3.4 Water Quality

The proposed strategy conforms to the relevant guidance on water quality.

Pollution hazard levels from CIRIA SuDS Manual Table 26.2 are defined as the

following:

Residential roofs Very Low;

Low Traffic Roads Low;

Main Site Roads Medium.

The Tertiary Routes can be classed as low traffic roads and therefore only require

one form of treatment before discharge into a water course. The planters and rain

gardens therefore provide this level of treatment.






Page 10

Figure 5 - SUDS planter to drain public realm areas (source: Townshend Landscape

Architects)

Figure 6 - SUDS planter to drain public realm areas (source: Townshend Landscape

Architects)

Figure 7 - Typical below ground geo-cellular crate storage (source: Polypipe Permavoid).

Surface finish can be either soft or hard landscaping.






Page 11

8.4 Building Plot Design (AKTII)

Refer to the AKTII Plot 12 report (Appendix E) for the building plot drainage

design. This includes a surface water drainage design which is spilt into two

catchments:

The northern catchment discharges to the site wide network via a shallow attenuation tank above the basement podium slab, flowing by gravity;

The southern catchment discharges into two attenuation tanks located within the basement, which then discharge by gravity via a flow control into the site

wide network in Claremont Park Road.

These connections are shown indicatively on drawing BXS-ARP-1BS-XX-DR-

CD-2200, included in Appendix B.

The rainwater discharge from the building is restricted to 45.0 l/s, which is

equivalent to a 25% reduction from the current 1 in 100 year design storm on the

existing site. The calculations also include an allowance for increase in rainfall

intensity due to climate change of 30%, as defined by S73 Permission condition

44.5 and Volume BXC01 Revised Development Specification & Framework

paragraph 2.75.

The current building design also includes a target for rainwater harvesting; refer to

the Sweco Plot 12 report for more information.

The proposals for building drainage are compliant with the relevant S73

Permission conditions and Volume BXC01 Revised Development Specification &

Framework.

8.5 Operation and Maintenance

Provided the soil and plants are correctly selected, only minimal maintenance is

expected for the SUDS features, which will consist of removing silt from

chambers, jet washing and removal of debris and rubbish from planters.

The site wide carrier pipes will be adopted and maintained by Thames Water

Utilities Limited as they will receive flows from properties as well as public realm

and highway areas.

9 Foul Water Drainage

The foul water drainage for the plots will be designed to Sewers for Adoption 7th

Edition and offered up for adoption by Thames Water Utilities Limited.

The foul water drainage peak discharge rate shall be agreed with Thames Water

Utilities Limited. The calculations which Thames Water have previously carried

out will be revised due to alterations to the area schedules consultation is

ongoing.






Page 12

10 Consultation

The London Borough of Barnets planners and drainage engineers have been

consulted prior to this planning application. A record of the meeting minutes is

included in Appendix C.

11 Conclusions

This Drainage Statement responds to the S73 Permission conditions and

Development Specification & Framework relevant to Plot 12 and the adjacent

streets and public realm, and demonstrates compliance with those conditions as

summarised below.

S73 Permission Condition 44.5

Surface water discharge from Plot 12 and the adjacent streets and public realm is limited to 75% of the existing runoff from a 1:100 year design storm event;

The calculations of proposed surface water runoff include a 30% allowance for increase in rainfall intensity due to climate change;

SUDS features such as rain gardens and buried cellular attenuation storage have been incorporated.


No infiltration of surface water runoff has been incorporated into the proposed design.


All finished floor levels (FFLs) and threshold levels are set a minimum of 300 mm above the 1:100 year design flood level (including an allowance for

climate change), as provided in the S73 Permission Volume BXC16 Flood

Risk Assessment.

S73 Permission Volume BXC01 Revised Development Specification &

Framework Paragraph 2.75

All surface water drainage operates under gravity;

Surface water discharge from Plot 12 and the adjacent streets and public realm is limited to 75% of the existing runoff from a 1:100 year design storm event;

The calculations of proposed surface water runoff include a 30% allowance for increase in rainfall intensity due to climate change;

SUDS features such as cellular storage within the building and public realm, and rain gardens and buried cellular attenuation storage within the adjacent

streets have been incorporated.

Appendix A

Relevant Policy and Legislation

A1 Legislation

A1.1 Floods Directive (2007/60/EC)

The aim of the Directive2 is to provide a consistent approach across the European Union to

reducing and managing the risks posed by flooding to human health, the environment,

cultural heritage and economic activity. The Floods Directive is to be delivered in

conjunction with the objectives of the Water Framework Directive (2000/60/EC) to deliver a

better water environment through river basin management.

In the UK the Floods Directive is transposed into law via the Flood Risk Regulations (2009)

by setting out the duties of local government in assessing flood risk to their area.

A1.2 Flood Risk Regulations (2009)

The Flood Risk Regulations3 transpose the Floods Directive (2007/60/EC) into law in

England and Wales.

The Regulations required the Lead Local Flood Authority (LLFA), in this case LBTH, to

produce:

a Preliminary Flood Risk Assessment (PFRA) by December 2011;

flood hazard and flood risk maps by December 2013; and

a Local Flood Risk Management Strategy by December 2015.

A1.3 The Flood and Water Management Act (2010)

The Flood and Water Management Act 2010 (FWMA)4, which received Royal Assent on 8th

April 2010, takes forward some of the proposals in three previous documents published by

the UK Government:

Future Water;

Making Space for Water; and

The Governments Response to the Sir Michael Pitts Review of the summer 2007 Floods.

The Act gives the EA a strategic overview of the management of flood and coastal erosion

risk in England. In accordance with the Governments Response to the Pitt Review, it also

gives upper tier local authorities in England responsibility for preparing and putting in place

strategies for managing flood risk from groundwater, surface water and ordinary

watercourses in their areas.

2 European Parliament and Council, October 2007. Directive 2007/60/EC of the European Parliament and of the

Council of 23 October 2007 on the assessment and management of flood risks. 3 UK Parliament, November 2009. The Flood Risk Regulations 2009, 2009 No. 3042. 4 UK Parliament, April 2010. The Flood and Water Management Act 2010, 2010 c. 29.

A1.4 The Water Resources Act (1991) and Water Act (2003, 2014)

The Water Resources Act 19915 provides legislation for the control of the pollution of water

resources. Under this Act, offences of polluting controlled waters occur if a person

knowingly permits any poisonous, noxious or polluting matter or any solid waste matter to

enter any controlled waters. The Water Resources Act also provides an all-embracing system

for the licensing of the abstraction of water for use, which is administered by the EA. The

Water Acts (20036, 20147) modernise water legislation and amend the Water Resources Act

1991 to improve long-term water resource management.

A1.5 Land Drainage Acts (1991, 1994)

The water quality and flood risk management of controlled waters including rivers and

aquifers is protected by legislation under the Land Drainage Acts (19918, 19949).

A1.6 Land Drainage Byelaws (1981)

This law was made by the Thames Water Authority under Section 34 of Land Drainage Act

1976. The Thames Water Authority Land Drainage Byelaws 198110 are in force in the

Thames Region of the EA. They are now enforced by the EA by virtue of the Water

Resources Act and the Environment Act. These Byelaws have effect within the area of the

Thames Regional Flood Defence Committee of the National Rivers Authority for the

purposes of their functions relating to land drainage and flood risk management.

A2 National Policy and Guidance

A2.1 National Planning Policy Framework (March 2012)

The NPPF11 includes policies on flood risk and minimising the impact of flooding under 10.

Meeting the challenge of climate change, flooding and coastal change (Paragraphs 100

104). The NPPF supersedes Planning Policy Statement 25 (PPS25). PPS25 set out UK

planning policy on development in relation to flood risk.

The NPPF states that:

Local Plans should be supported by a Strategic Flood Risk Assessment [(SFRA)] and develop policies to manage flood risk from all sources, taking account of advice from the

EA and other relevant flood risk management bodies, such as LLFAs and internal

drainage boards.

5 UK Parliament, November 2009. Water Resources Act 1991, 1991 c. 57. 6 UK Parliament, November 2003. Water Act 2003, 2014 c. 37. 7 UK Parliament, May 2014. Water Act 2014, 2014 c. 21. 8 UK Parliament, July 1991. Land Drainage Act 1991, 1991 c. 59. 9 UK Parliament, July 1994. Land Drainage Act 1994, 1994 c. 25. 10 Environment Agency, April 2014. Thames water authority: land drainage byelaws, Thames Region: Land

Drainage Byelaws. 11 Department for Communities and Local Government, March 2012. National Planning Policy Framework.

Local Plans should apply a sequential, risk-based approach to the location of development to avoid where possible flood risk to people and property and manage any

residual risk, taking account of the impacts of climate change.

When determining planning applications, [Local Planning Authorities (LPAs)] 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 Urban

Drainage Systems (SuDS)].

A2.2 National Planning Practice Guidance (November 2016)

The NPPG12, comprising a web-based resource, has been issued to ensure the effective

implementation of the NPPF and contains a section covering Flood Risk and Coastal Change.

With regard to planning for flood risk, the Guidance retains key elements of the

aforementioned PPS25 (now withdrawn) and assesses the suitability of the development type

with respect to the flood risk zone in which it lies.

The PPG also provides an overview of the expected effect of climate change and

recommends contingency allowances for sensitivity ranges for peak rainfall intensities.

Advice regarding allowance for climate change was updated in February 2016.

A2.3 Sewers for Adoption (2012)

An adopted drainage network needs to meet the criteria outlined in Sewers for Adoption13. A

piped drainage system is required to not flood the ground in a 1 in 30 year flood, or surcharge

for a 1 in 2 year event, using a design storm with the critical duration relevant to the site (i.e.

the worst-case for a given return period). Private drainage systems also tend to use these

criteria as a basis for design. Adoption of new sewers or abandonment of old sewers should

take place in accordance with the Water Industry Act 1991, Sections 104 and 116

respectively.

A2.4 National Encroachment Policy for Tidal Rivers and Estuaries (2005)

The EAs National Encroachment Policy for Tidal Rivers and Estuaries has been approved by

the Regional Flood Defence Committees of England and Wales. The

EA is generally opposed to works on tidal rivers and estuaries that cause encroachment, but

treat developments on a case by case basis.

12 Department for Communities and Local Government, November 2016. Planning practice guidance. 13 Water UK/WRc plc, August 2012. Sewers for Adoption (7th Edition): A design and construction guide for

developers.

A3 Regional Policy and Guidance

A3.1 The London Plan: The Spatial Development Strategy for London Consolidated with Alterations Since 2011 (March

2016)

The document in its current state is The London Plan (2011) consolidated with Revised Early

Minor Alteration to The London Plan (2013), Further Alterations to The London Plan

(2015), Housing Standards Minor Alterations to The London Plan (March 2016) and Parking

Standards Minor Alterations to The London Plan (March 2016)14.

The London Plan is the overall strategic plan for London setting out an integrated economic,

environmental, transport and social framework for the development of London; it recognises

the need to address the increasing effects of climate change as predictions show there are

more people likely to be living and working on the floodplain.

Relevant policies from the Plan are outlined below:

Policy 5.12: Flood risk management

The policy states:

Development proposals must comply with the flood risk assessment and management requirements set out in the NPPF on flood risk over the lifetime of the development and

have regard to measures proposed in Thames Estuary 2100 and Catchment Flood

Management Plans.

Developments which are required to pass the Exceptions Test set out in the NPPF will need to address flood resilient design and emergency planning by demonstrating that:

a) The development will remain safe and operational under flood conditions; b) A strategy of either safe evacuation and/or safely remaining in the building is

followed under flood conditions;

c) Key services including electricity, water etc. will continue to be provided under flood conditions; and

d) Buildings are designed for quick recovery following a flood.

Development adjacent to flood defences will be required to protect the integrity of existing flood defences and wherever possible should aim to be set back from the banks of

watercourses and those defences to allow their management, maintenance and upgrading

to be undertaken in a sustainable and cost effective way.

Policy 5.13: Sustainable drainage

The policy states:

Development should utilise Sustainable Urban Drainage Systems (SuDS) unless there are practical reasons for not doing so, and should aim to achieve Greenfield runoff rates and

ensure that surface water runoff is managed as close to its source as possible in line with

the following drainage hierarchy:

14 Greater London Authority, March 2016. The London Plan: The Spatial Development Strategy for London

consolidated with alterations since 2011.

1. Store rainwater for later use;

2. Use infiltration techniques, such as porous surfaces in non-clay areas;

3. Attenuate rainwater in ponds or open water features for gradual release;

4. Attenuate rainwater by storing in tanks or sealed water features for gradual release;

5. Discharge rainwater direct to a watercourse;

6. Discharge rainwater to a surface water sewer/drain;

7. Discharge rainwater to the combined sewer.

Drainage should be designed and implemented in ways that deliver other policy objectives of this plan, including water use efficiency and quality, biodiversity, amenity

and recreation.

Policy 7.13: Safety, security and resilience to emergency

The policy states that developments should maintain a safe, secure environment and minimise

potential physical risks, including those arising from flooding and related hazards.

A3.2 The London Plan: Supplementary Planning Guidance - Sustainable Design and Construction (April 2014)

The Supplementary Planning Guidance (SPG)15 sets out the Mayors priorities with regard to

flooding as follows:

Through their Local Flood Risk Management Strategies boroughs should identify areas where there are particular surface water management issues and develop policies and

actions to address these risks.

Developers should maximise all opportunities to achieve greenfield runoff rates in their developments.

When designing their schemes developers should follow the drainage hierarchy set out in London Plan policy 5.13.

Developers should design Sustainable Drainage Systems (SuDS) into their schemes that incorporate attenuation for surface water runoff as well as habitat, water quality and

amenity benefits.

Development in areas at risk from any form of flooding should include flood resistance and resilience measures in line with industry best practice.

Developments are designed to be flexible and capable of being adapted to and mitigating the potential increase in flood risk as a result of climate change.

Developments incorporate the recommendation of the TE2100 plan for the future tidal flood risk management in the Thames Estuary.

Where development is permitted in a flood risk zone, appropriate residual risk management measures are to be incorporated into the design to ensure resilience and the

safety of occupiers.

15 Greater London Authority, April 2016. Sustainable Design and Construction Supplementary Planning

Guidance.

Appendix B

Public Realm Drainage Design

B1 Micro Drainage Quick Storage Estimates

1 in 30 year storm event

1 in 100 year + climate change storm event

B2 Drawings

SLOW

Plot 13 Plot 11Plot 12/13

Public Realm

Corridor

Area = 0.17ha

Plot 12

Area = 0.61ha

Plot 11/12

Public Realm

Corridor

Area = 0.18ha

Plot 12 RMA to

discharge into surface water

drainage in High Street (directed

to TWUL sewer in Tilling Road)

P

L

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1

2

A

4

0

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Draft Stage 3 Developed Design

TMDHTGP22/08/17P01

Notes :

1. Design shown indicative only.

2. The allowable discharge rates for these catchments

aligns with the site wide drainage strategy. The

allowable discharge rates for Plot 12 RMA are a

proportion of the allowable discharge rate for the

site wide catchment, based on the Plot 12 RMA

areas. The maximum allowable discharge rate for

the site wide catchment is calculated as 75% of the

existing maximum 100 year return period run off

rate, this complies with the Section 73 Planning

Condition 44.5.

A1 A B C D E F G H I J K L M N

1

2

3

4

5

6

7

8

9

10

11

Do not scale

Role

Arup Job No

Suitability

Name

Rev

Project Title

Client

Arup

Rev Date By Chkd Appd

Scale at A1

Drawing Title

BXS-ARP-1BS-XX-DR-CD-1200

P03

As Shown

S2 - Suitable for Information

Civil Drainage

245526

PLOT 12 RMA

Public Realm

Surface Water Drainage

Catchment Areas

BXS LP

Brent Cross South

13 Fitzroy Street

London W1T 4BQ

Tel +44(0)20 7636 1531 Fax +44(0)20 7580 3924

www.arup.com

5 10 Metres0

Scale 1:250

Legend :

Planning Boundary

Indicative Site Wide Surface Water

Network

Catchment

Plot 12/13

Public Realm

Area (ha) Allowable Discharge

Rate (l/s)

Plot 11/12

Public Realm

0.17 14

0.18 14

0.61 45

Plot 12

Building

P02 05/10/17 TB HT TMD

For Information

P03 13/10/17 TB HT TMD

For Plot 12 RMA

N

40

50

100 Metres200

10

Scale 1:2500

30

N

Location Plan

Refer to drawing AKTII drawing

for building plot drainage

Solid pipe beneath road surface

Rain gardens to drain road,

footpath and car parking

spaces - Perforated pipe

beneath soil medium

Surface water drainage carrier

pipe for site wide network

1.2m Geo-cellular below

ground attenuation tank

Catchpit with flow control to

limit flow into adoptable site

wide drainage network

Solid pipe beneath

road surface

Rain gardens to drain road,

footpath and car parking

spaces - Perforated pipe

beneath soil medium

1.2m Geo-cellular below

ground attenuation tank




Building storm water

drainage connection point











Plot 12 RMA Site Area to

discharge into surface water

drainage in High Street (directed

to TWUL sewer in Tilling Road)

P

L

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Draft Stage 3 Developed Design

TMDHTGP22/08/17P01

Notes :


2. Attenuation volumes storage require is indicative

only.

3. SUDS adoption requirements are still to be

confirmed and may impact final drainage layout.

4. Building connection locations not shown but are

expected into the surface water carrier drain.

5. Attenuation volumes provided are designed for 1

in 100 year + 30% return period storm events.


1

2

3

4

5

6

7

8

9

10

11

Do not scale

Role

Arup Job No

Suitability

Name

Rev

Project Title

Client

Arup


Scale at A1

Drawing Title

BXS-ARP-1BS-XX-DR-CD-2200

P03

As Shown

S2 - Suitable for Information

Civil Drainage

245526

PLOT 12 RMA

Public Realm

Surface Water Drainage

Layout

BXS LP

Brent Cross South

13 Fitzroy Street

London W1T 4BQ

Tel +44(0)20 7636 1531 Fax +44(0)20 7580 3924

www.arup.com

Legend :

Geocellular Attenuation Tanks

1.2m deep

Recessed tree pit/rain garden

with filter drain beneath

Site Wide Surface Water Carried Train

(Proposed to be adopted by TWUL)

Catchment Boundary

Manhole

Indicative Site Wide Surface Water

Network outside plot boundary

Private plot connection pipes

N

5 10 Metres0

Scale 1:250

P02 05/10/17 TB HT TMD

For Information

P03 13/10/17 TB HT TMD

For Plot 12 RMA

40

50

100 Metres200

10

Scale 1:2500

30

N

Location Plan

Notes :


2. Attenuation volumes storage require is indicative

only.

3. SUDS adoption requirements are still to be

confirmed and may impact final drainage layout.

4. Building connection locations not shown but are

expected into the surface water carrier drain.

5. Attenuation volumes provided are designed for 1

in 100 year + 30% return period storm events.


1

2

3

4

5

6

7

8

9

10

11

Do not scale

Role

Arup Job No

Suitability

Name

Rev

Project Title

Client


Scale at A1

Drawing Title

BXS-ARP-1BS-XX-DR-CU-2000

00

1:500

For Information

Civil

245526

Phase 1BS

Existing Utilities

Layout

Argent Related

Brent Cross South

13 Fitzroy Street

London W1T 4BQ

Tel +44(0)20 7636 1531 Fax +44(0)20 7580 3924

www.arup.com

10 20 Metres50

Scale 1:500

Key :

Site Boundary

EX HV EX HV

EX LV EX LV

EX W EX W EX W

EX BT EX BT EX BT

EX CATV EX CATV

EX GAS EX GAS

EX MPG EX MPG

EX IPG EX IPG

EX SW EX SW

EX FW EX FW

Existing High Voltage

Existing Low Voltage

Existing Potable water

Existing BT Comms

Existing Virgin Media

Existing Gas

Existing Medium Pressure Gas

Existing Intermediate Pressure Gas

Existing Surface Water Sewer

Existing Foul Water Sewer

EX SW EX SW

Existing Thames Water

Surface Water Sewer

PLOT 12 RMA

Appendix C

Pre-Planning Application

Consultation

Meeting Minutes

Prepared by Will Dunford Date of circulation

J:\245000\245526-00 BRENT CROSS SOUTH\INTERNAL (WIP)\CX\MI_MINUTESAGENDAS\BXS-ARP-01-XX-MM-CD-0001-LBB DRAINAGE MEETING 01 - MINUTES.DOCX

Page 1 of 3Arup | F0.6

Project title Brent Cross South Job number 245526

Meeting name and number Drainage pre-application meeting with

LBB

File reference

BXS-ARP-01-XX-MM-CD-

0001 Location Arup offices Time and date

11.00 3 July 2017 Purpose of meeting Introduction of BXS drainage strategy prior to planning submissions

Attendance Jorge, Tiago ;

'Leppard, David (Capita)' ;

Tristan McDonnell ;

Benoit Dufour ([email protected]);

Jay Rao ;

Freeman, Jude

Agenda

Project title Job number Date of Meeting

Brent Cross South 245526 3 July 2017



Action

flow rate as defined in Planning Condition 44.5 DL agreed with this

approach.

Arup explain that the allowable discharge for each plot has been

prorated based on its area, relative to the entire catchment and

therefore is not necessarily specific to the existing discharge rate for

that specific plot. DL accepted this approach.

Arup explained that the downstream TWUL network does not

appear to have capacity to accept the catchments flows, however

this has not been confirmed by TWUL and has not been modelled

hydraulically. Arup suggested utilising the proposed LBB drainage

network under the A406 to provide extra capacity for the network,

particularly as this run eventually discharges into the River Brent.

LBB planners did not see a technical reason why this option could

not be used but would be dependent on adoption requirements.

Arup to follow up with LBB highways team to understand if this

strategy is a possibility and then speak to HSL regarding

significance on design changes and construction programme

constraints. It should be noted that LBB as a partner of the BXS JV

should considered the context of this option for the development as

a whole. TWUL will also need to be consulted to understand their

own adoption requirements for such a strategy.

The BXN team need to be kept up to date with current proposals for

BXS that will affect the infrastructure they are responsible for. This

is to ensure the designs are coordinated technically and any

agreements BXN have with stakeholders including the Environment

Agency and TWUL are still complied with.

5. Foul Drainage

Arup explained that the Hendon Trunk combined sewer is at

capacity and therefore any opportunity to reduce surface water

flows into it should be addressed.

6. Phase 1BS RMA Deliverables

All parties agreed that the drainage deliverable for Phase 1BS

should be limited to the extent of the Plot 12 and side streets only,

to avoid having to change RMA information later when the street

layout changes. The RMA submission should include maximum

allowable discharge rates, attenuation volumes and the SUDS types

proposed. Hydraulic model outputs or detailed information on

invert levels is not required at this stage.

All parties also agreed that the drainage statement will include a

statement such as surface water drainage from this plot extent is

Arup

Arup/Argent

Agenda


Brent Cross South 245526 3 July 2017



Action

limited to X l/s and will then discharge into surface water drains in

the High Street.

LBB confirm that no FRA is required as part of the RMA for plot

12 provided the requirements in Planning Condition 45.2 are met.

Minutes

Prepared by Will Dunford Date of circulation 24/07/2017 Date of next meeting 01/08/2017

J:\245000\245526-00 BRENT CROSS SOUTH\INTERNAL (WIP)\CX\MI_MINUTESAGENDAS\THAMES WATER MEETING MINUTES 03 - 17072017 - DRAFT.DOCX


Project title Brent Cross South Job number 245526-00

Meeting name and number Thames Water Meeting 03 File reference BXS-ARP-TW-XX-MM-

CD-0003 Location Argent Offices Time and date

17 July 2017 Purpose of meeting Update on current BXS drainage strategies and impact on current BXN

and TWUL work done to date Present Mahmoud Hejabizadeha (TWUL), Lenny Aristodemou (Schofield

Lothian), Paul Battersby (Aecom), Benoit Dufour (Argent Related), Jay

Rao (Argent Related), Matthew Parker (Gattica Associates) Tristan

McDonnell (Arup), Will Dunford (Arup), Apologies Circulation Those present + Mike Turland (Schofield Lothian) Godfried Nyamekyeh

(Thames Water).

1. BXS application submitted, but confusion regarding this application together

with existing BXN application MH to check internally how to progress.

Argent have paid application fee and provided money for meetings and

consultation. Argent application number IRef: 1014888914 DS6031409

PDEV NW2 1LL, Brent Cross South.

2. Arup presented surface water drainage strategy for the site, which aligns with approved planning Section 73 Drainage Strategy document BXC 15.

3. Arup indicated that current TWUL Impact assessment X4503-722 commissioned by HSL included inputs for Phase 1 and Full Development

scenarios but did not actually involve modelling for all the surface water

connections. This has been confirmed by the modelling company MWH. The

reports justification is as follows, The un-modelled parts of the network are

typically small diameter pipes discharging to local outfalls into the River

Brent. It is the Developers responsibility to ensure that these parts of the

network have sufficient capacity to accept the proposed flows from the

redeveloped plots that are to be connected into them.

4. The discharge location of the existing TWUL 600mm surface water pipe in Tilling Road is unknown. It expected that it discharges into the

Action

MH

AR

Minutes


Brent Cross South 245526-00 17 July 2017



Clitterhouse Stream but this has not been confirmed by survey

information. MH requested that AR/HSL need to conduct a survey to

confirm this. MH reaffirmed the point that if the 600mm pipe connects

into the Hendon Trunk Sewer then no additional flow will be

acceptable.

5. MH stated that any discharge into the Clitterhouse Stream requires an Environment Agencys consent. Arup asked if TWUL knew of any

existing consents. MH said he would check, but that it is possible that

no existing consent exists.

Post Meeting Note: BXN confirmed the Clitterhouse Stream culvert

beneath the A406 is a TfL asset and therefore permission to discharge

into this will be required from TfL.

6. The proposed LBB highway drainage beneath the A406 was discussed. The current design includes highway run off from LBBs adopted

roads on the south side of the A406 only. This then discharges into the

River Brent via a 1200mm pipe jack beneath the A406. The current

design includes an allowance for an additional 1.3ha of highway run-

off from the BXS site. Any increase above the 1.3ha will likely require

design changes to the network.

7. The option of discharging TWUL surface water plot and non-adopted highway drainage into the proposed LBB drain beneath the A406 was

discussed. MH agreed with this in principal provided a suitable

agreement between LBB and TWUL was provided.

8. Arup presented the proposed strategy where there is a need for a TWUL surface water drain in an adoptable highway to drain plots and

public realm areas, that this could also be used to drain the adoptable

highway above. MH agreed with this approach provided the gullies

and gully leads were adopted by the highway authority. MH to consult

TWUL adoption team further.

9. Arup presented minor update to foul drainage strategy. Arup confirmed no increase in overall flows into the Hendon Trunk Main

but that some plots discharge into different connection manholes. Arup

asked whether additional modelling is required for minor changes. MH

asked that changes be formally submitted to TWUL. MH to chase

status of Argent application to agree process to submitting updates.

10. Abandonment of existing TWUL assets discussed. MH stated that

assets should be CCTV surveyed prior to abandonment to ensure no

MH

MH MH Arup/AR

Minutes


Brent Cross South 245526-00 17 July 2017



unknown connections are mistakenly cut off. Arup informed MH that

CPOs have been granted for large sections of the site and therefore

full CCTV will not be required for all areas of the site. Arup and AR to

develop abandonment plan to align with CPO and demolition

sequencing and propose extent of CCTV surveys.

Action Action Date

Appendix D

Plot 12 Flood Risk

Documents

DRAINAGE STATEMENT - BXS Positive Dialogue · Figure 3 - Landscape Architecture plan of Plot 12 layout and adjacent private streetscape corridors . BXS Limited Partnership Brent Cross