DRAINAGE AND SUDS DESIGN STATEMENTconsultation-online.co.uk/UserFiles/harlow/Drainage and SUDS Design... · DRAINAGE AND SUDS DESIGN STATEMENT Gilden Way Harlow 04/09/2014 Client

DRAINAGE AND SUDS DESIGN STATEMENT Gilden Way Harlow 04/09/2014

Project number: 50600547 Dated: 04/09/2014 2 Revised:

Quality Management

Issue/revision Issue 1 Revision 1 Revision 2 Revision 3

Remarks DRAFT FINAL

Date June 2014 September 2014

Prepared by James Dyason James Dyason

Signature

Checked by Martin Stillion Martin Stillion

Signature

Authorised by Jim Hutchins Jim Hutchins

Signature

Project number 50600547 50600547

File reference SW and SUD statement draft.doc

SW and SUD statement final.doc

3

DRAINAGE AND SUDS DESIGN STATEMENT Gilden Way Harlow

04/09/2014

Client Taylor Wimpey, Persimmon, Barratt

Consultant WSP UK Unit 9, The Chase Hertford SG13 7NN UK

Registered Address WSP UK Limited 01383511 WSP House, 70 Chancery Lane, London, WC2A 1AF

WSP Contacts James Dyason


Table of Contents

1 Introduction .................................................................................. 5 2 Proposed Development ................................................................ 6 3 Surface Water and SuDS Strategy ............................................... 7 4 Foul Water Strategy ................................................................... 16 5 Conclusion ................................................................................. 17 Appendices Appendix A – Site Location Plan Appendix B – Topographical Survey Appendix C – Existing Drainage Catchment Plan Appendix D – Illustrative Scheme Layout Appendix E – Planning Appeal Decision Appendix F – Landscape Parameter Plan Appendix G – Ditch / Watercourse Location Plan Appendix H – ECC Ditch Submission and Response Appendix I – WSP Hydraulic Modelling Report Extracts Appendix J – Thames Water Correspondence Appendix K – Proposed Development Platform Levels Appendix L – Proposed Drainage Catchment Plan Appendix M – JCM Hydraulic Calculations Appendix N – Proposed Surface Water Drainage Strategy Appendix O – FEH Greenfield Runoff Analysis Appendix P – Volumetric Calculations and Mitigation Appendix Q – Outline SuDS Maintenance Regime Appendix R – Proposed Foul Water Peak Flow Estimates Appendix S – Proposed Foul Water Strategy Appendix T – Foul Water Hydraulic Calculations

5

1 Introduction

1.1 Background 1.1.1 WSP have been commissioned by Taylor Wimpey, Persimmon and Barratt to prepare a Drainage

and SUDS Design Statement in order to demonstrate a robust strategy in the disposal of foul and surface water for the Proposed Development and support the discharge of planning conditions 9, 31, 32, that accompanied the 2012 outline consent (Planning reference number HW/PL/11/0005 and appeal decision number APP/N1540/A/11/2167480).

1.1.2 The refined foul and surface water strategy contained within this report builds upon the principles set out within the 2011 WSP Flood Risk Assessment that accompanied the consented scheme and has also involved discussions with Thames Water (TWUL), Environment Agency (EA) and Essex Country Council (ECC) under their role as Lead Local Flood Authority (LLFA) and emerging Sustainable Drainage System (SuDS) Approving Body (SAB).

1.2 Site Location and Description 1.2.1 The Site is located to the north of Gilden Way (B183) in Harlow. The site is approximately centred on

National Grid Reference TL 481 121 and comprises approximately 58 hectares of arable farmland. A site location plan can be viewed within Appendix A.

1.3 Natural Drainage Catchment 1.3.1 Due to local topography there are two main natural drainage catchments on site that relate to the

area of proposed built development:

A small area to the north east of the Site of approximately 1.1ha, generally falls in a north easterly direction off site towards the Pinceys Brook (an EA designated Main River). Levels range from approximately 61.8m AOD in the west to 61.2m AOD in the east.

The remaining area of the Site can be broken down into four existing sub-catchments, however all sub-catchments fall in a westerly direction towards the Harlowbury Brook (an EA designated Main River). The combined area of this catchment is approximately 31.5ha and levels range from approximately 61.8m AOD in east to 48.5m AOD in the west.

1.3.2 There is no known formal sewerage arrangement associated with the Site. Runoff generated from the north east catchment is thought to drain directly to the Princeys Brook via overland flow routes whilst the remaining catchment drains to the Harlowbury Brook either directly via overland flow routes or indirectly via the existing onsite open ditch network and ordinary watercourses. Both the Harlowbury Brook and Pinceys Brook are tributaries of the River Stort which is located north of the Site.

1.3.3 Refer to Site Topographical Survey and Existing Drainage Catchment Plan within Appendices B and C respectively for further details.


2 Proposed Development

2.1.1 The outline planning consent is for up to 1,100 residential dwellings; site for a primary school (2.16 ha); community buildings (0.06 ha); retail/business/live work units (0.18 ha); together with associated uses comprising allotments, sport pitches and public open space.

2.1.2 The proposed development masterplan can be viewed within Appendix D. It should be noted that the internal arrangement of the development parcels are still subject to confirmation and therefore not shown at this stage.

2.2 Planning Status 2.2.1 The Site was granted outline planning consent under an appeal for non-determination to the

Secretary of State in November 2012 (Planning reference number HW/PL/11/0005 and appeal decision number APP/N1540/A/11/2167480). A copy of the appeal decision and associated conditions can be viewed within Appendix E.

2.3 Proposed Drainage Arrangements Surface Water

2.3.1 The surface water drainage strategy will be split into two catchments to take into consideration localised topography. Both catchments will utilise a traditional drainage network, as per the earlier strategy, supplemented by various SuDS devices to provide water quality treatment and bio diversity enhancement. Flows will drain into proposed detention basins whereby surface waters are attenuated before discharging into the Harlowbury Brook via an onsite ordinary watercourse. Further details of the surface water drainage strategy are set out within Section 3 of this Report.

Foul Water

2.3.2 The foul water drainage strategy will comprise a single gravity drainage network that will connect into the existing TWUL 300mm diameter foul sewer located along the eastern bank of the Harlowbury Brook.

2.3.3 Further details of the foul water drainage strategy are set out within Section 3 of this Report.

7

3 Surface Water and SuDS Strategy

3.1 Design Considerations

GROUND CONDITIONS AND HYDROGEOLOGY 3.1.1 A geotechnical Site Investigation for this Site was undertaken by WSP in August 2005, and a

supplementary investigation in 2006. The general underlying geology is quite variable, and consists of Made Ground, Head and Glacial deposits and Boulder Clay. London Clay, Lambeth Beds and ultimately Upper Chalk are anticipated at depth.

3.1.2 Groundwater was encountered during the investigation within a clayey gravelly sand layer and within a stiff sandy gravelly clay layer. During subsequent monitoring visits groundwater levels between 2.49m bgl and 9.17m bgl were observed. Within the clayey sand layer, a groundwater level of about 4.40m bgl was recorded.

3.1.3 Some minor strikes of groundwater were found, but these are probably the result of perched water tables over the relatively impermeable boulder clay. It is therefore considered that there is little risk of groundwater flooding at this site or detrimentally affecting the performance of the proposed development drainage system – especially after development.

3.1.4 It is considered that the relatively impermeable upper soil layer will make the widespread use of infiltration systems impracticable. The focus of the proposed surface water drainage arrangement will therefore be to provide attenuation and surface water balancing to ensure that runoff from the site will not exceed the pre-development greenfield runoff rates, and thereby mitigate the impact of development on the existing flood regime.

EXISTING TREES AND HEDGEROWS 3.1.5 The consented Landscape Parameter Plan (included within Appendix F) that accompanied the

outline application identified trees for retention, both in the hedgerow and the woodland block within the western section of the Site. Section 13.3 of the consented Design and Access Statement (DAS) states that all hedges will be retained subject only to the creation of gaps for access.

3.1.6 The above has been taken into consideration when assessing the positioning of the proposed detention basins within the Proposed Development.

EXISTING DRAINAGE DITCHES 3.1.7 There is a number of existing drainage ditches within the Site. These ditches serve the Site

exclusively and convey into the onsite ordinary watercourse located within the west of the site. Although they will remain as part of the Proposed Development due to integral hedgerows and trees, there is no realistic prospect of incorporating the existing ditches into the proposed surface water strategy because of the channel depth constraints and future maintenance issues if they were to carry substantial flows. For a ditch/watercourse location plan refer to Appendix G.

3.1.8 In order to accommodate the school site it is proposed to provide boundary fencing within 3m from the top of bank associated with the affected ditches. The potential flows within the affected ditches are limited and current flows will be largely eliminated when the comprehensive drainage network is constructed. In conjunction with future maintenance being widely available along the other side of


the banks it is deemed that the positioning of the boundary fencing will not have a detrimental impact on the ditches. This has been subsequently presented to ECC who have agreed with the conclusions and proposed approach Refer to Appendix H for details.

3.1.9 New crossings over the ditches will be subject to Flood Defence Consent with ECC.

ORDINARY WATERCOURSE

3.1.10 The ordinary watercourse onsite runs in a northerly direction within the western area of the Site and outfalls into the Harlowbury Brook via a 1000mm diameter culvert. This watercourse predominantly caters for the Site with the exception of a small upstream catchment that discharges into the watercourse onsite via a 300mm culvert. Refer to watercourse/ditch location plan in Appendix G for details.

3.1.11 Along the reach of the watercourse onsite there are two existing culverts; the first is a 225mm diameter culvert that conveys flow underneath existing residential gardens associated with The Oxleys, the second is a 1350mm x 900mm brick built culvert that provides vehicular access from the arable fields to the Harlowbury Brook and meadow.

3.1.12 Due to physical and topographical constraints the proposed foul and surface water drainage arrangements require two crossings over this watercourse:

The existing brick culvert will be replaced with a 1500mm x 1200mm pre cast concrete item to accommodate the drainage arrangement and will ensure minimal cross sectional area is main-tained. Crossing over the watercourse with the drainage has resulted in marginal widening of the culverted section of the ordinary watercourse.

A new culvert is proposed further upstream of the brick built culvert for foul water sewer routing and pedestrian access purposes. The proposed culvert is pre cast concrete and 1500mm x 1200mm in size in order not to inhibit flow over and above the downstream culvert arrangement.

3.1.13 An element of hedgerow removal is required to accommodate the culverts and access arrangements however this is in line the Design and Access Statement approach in respect to creating new access through existing hedgerows. No existing tree loss is proposed to accommodate the arrangement. The new culvert arrangement has been included within the updated WSP fluvial hydraulic model. Typical details of the new crossing can be viewed within Appendix N.

3.1.14 The new crossings associated with the ordinary watercourse will be subject to Flood Defence Consent from ECC.

EXISTING FLOOD PLAIN AND FLOOD MITIGATION MEASURES

Baseline

3.1.15 Due to spatial constraints imposed by the hedgerow and woodland within the western area of the Site, it has become necessary to position surface water storage in the form of a detention basin within the existing identified floodplain associated with the Harlowbury Brook. The flood plain extents were originally modelled by WSP as part of the outline planning application and were subsequently approved by the Environment Agency.

9

3.1.16 The original 1D hydraulic model has been updated by WSP and a 2D hydrodynamic model produced to assess and refine the existing baseline model and subsequent flood extents. In summary the baseline model demonstrates that;

Within the area in question, the Harlowbury Brook overtops its banks for the critical 1 in 100 year plus 20% allowance for climate change fluvial event, subsequently resulting in flood waters con-veying across the existing meadow to a maximum depth of approximately 600mm. These flood waters in part, drain into the existing on site ordinary watercourse. This watercourse discharges into the Harlowbury Brook approximately 100m downstream via an existing 1000mm diameter culvert;

The 225mm diameter sewer associated with the ordinary watercourse is undersized and creates flooding across residential areas within The Oxleys to a maximum depth of approximately 150mm for the critical 1 in 100 year plus 20% allowance for climate change fluvial event. This flood water conveys in a northerly direction into the site and combines with flood water associat-ed with the Harlowbury Brook.

Post Development Mitigation Measures

3.1.17 The positioning of the northern pond will detrimentally affect the flood plain due to restriction of conveyance therefore to mitigate following mitigation measures have been proposed:

Three 2100mm by 600mm culverts have been proposed adjacent to the watercourse to divert flood water into the onsite meadow land to the north and into the aforementioned ordinary water-course;

Due to topography and spatial constraints level for level compensation is not achievable, howev-er an additional 3,700m3 of flood storage has been created on site by lowering the existing open space to the north and an area of land immediately west of the proposed northern detention ba-sin; and

A 600mm diameter flood relief sewer is proposed to reduce flooding within The Oxleys and sub-sequently the site.

Results

3.1.18 The results of the post mitigation fluvial modelling are as follows:

The flooding to The Oxleys has been removed, as it is been accommodated in the channel with the extra capacity from the relief culvert;

Due to the volumetric mitigation proposed results indicate no impact on flooding downstream of the project site. With no impacts on the overall hydrograph at the railway bridge; and

A small area of existing flooding within the Scheduled Ancient Monument site has also been re-moved as part of the development fluvial flood risk mitigation proposals

3.1.19 For further details please refer to extracts of the WSP hydraulic modelling report within Appendix I

SUDS ADOPTION 3.1.20 The Proposed Development has been granted outline consent. Current indications from DEFRA are

that for outline consents in place upon implementation of Schedule 3 of the Flood and Water Management Act 2010, all reserved matters relating to that consent will have to be discharged within a year to avoid the requirements of the Act. Once that year has expired the National SuDS Standards will apply to all works which are not exempt and a new SuDS/Drainage application will have to be


made to the SAB. At the time of writing this report implementation of Schedule 3 has been further delayed within no known proposed timetable for its implementation.

3.1.21 Although Schedule 3 has been delayed, WSP consulted in November 2013 the emerging ECC SAB, who is currently providing informal comments on new SuDS schemes on sites over 1ha, to discuss the prospective adoption/maintenance options for surface water drainage. It was concluded that due to the development already being granted outline consent, the SAB not being empowered, uncertainly on financial and adoption mechanisms and in the absence of an interim ECC SAB Voluntary Adoption Policy, that the surface water drainage disposal will follow the principles set out within the outline consent with additional SuDS being implemented, where practicable, within the housing development parcels as they are brought forward. The planning conditions for the development require that applications for approval for reserved matters must be made within 3 years from the date of consent –i.e. by 15th November 2015. This will limit the opportunity to introduce additional SuDs features after implementation of Schedule 3 that could eligible for adoption by the ECC SAB. Where additional SuDS within the development parcels are proposed prior to enactment they will be adopted by a third party management and maintenance company. Refer to paragraph 3.1.22 below.

3.1.22 Due to Section 106 obligations the public open space within the development will be adopted by a management company that will be setup by the Consortium. In light of the current position of SuDS adoption this management company will also manage all SuDS within the Proposed Development including potential SuDS provision within the development housing parcels

3.1.23 The proposed sewer arrangement will be offered for adoption to Thames Water, who have stated in principle that this approach is acceptable for the pipework. Refer to Appendix J for details.

GROUND RAISING 3.1.24 In order to ensure effective foul and surface water drainage systems that can outfall via gravity the

existing topography was assessed and where applicable areas identified for ground raising.

3.1.25 Ground raising is also required to accommodate the surface water storage within the detention basins whilst ensuring the outfalls from the basins can still be drained via gravity. Details of the detention basins can be viewed within Appendix N.

3.1.26 The drainage ground raising requirements were subsequently incorporated into the Proposed Development earthworks strategy. For details on initial development platform levels refer to Appendix K.

GENERAL PRINCIPLES 3.1.27 A 10% allowance for urban creep has been applied to the impermeable areas associated with the

proposed residential development.

3.1.28 The proposed drainage strategy has been designed not to exacerbate any existing flood risk associated with third parties situated upstream, or downstream, of the Site in accordance with principles set out within the NPPF and consented Flood Risk Assessment.

3.2 The SuDS Management Train 3.2.1 To mimic the natural catchment processes as closely as possible, where practicable, SuDS are

proposed to incrementally reduce pollution, flow rates and volumes.

11

3.2.2 Taking into account the above design considerations and consented Flood Risk Assessment, a hierarchy has been considered in applying the use of SuDS into the Proposed Development to help provide; prevention in terms of runoff and pollution, source control and Site control. Refer to summary Table 3.1 for details.

3.2.3 For further details of the surface water strategy refer to Appendix N for details.

Table 3.1 – Proposed on-site SuDS features within Western and Eastern Neighbourhoods

SuDS Technique

Can they be feasibly incorporated into the

Site?

Reason

Green Roofs X Green roofs are not proposed on site due to house type roof pitches

Basins and Ponds

Two detentions basins are proposed to manage surface water storage on site. They will incorporate a rill in the base of each basin as well as a sediment forebay to provide two stages of treatment of surface water during low flow conditions.

Filter Strips and Swales

Conveyance swales are not proposed due to spatial constraints and for reasons set out within paragraph 3.1.16 however shallow dished dry swales and cut off drains will be utilised within areas on Site for exceedance drainage. These devices will also provide a degree of passive treatment to exceedance surface waters.

Infiltration techniques X Due to the underlying geology infiltration techniques will not be utilised onsite

Permeable surfaces and filter drains

Permeable paving can be provided within communal parking areas within the development parcels to provide source control and water quality enhancement. The quantum of which will be confirmed during the detailed design stages for each plot sub phase.

Rainwater Harvesting

Rainwater butts will be considered further as part of the detailed design and would provide an element of rain water harvesting.

During the detailed design rainwater/greywater harvesting will be considered for the school to provide possible source control and water efficiency benefits whilst also providing irrigation for localised landscaping. This will be discussed further with the Educational Authority during the later stage of design.

Tanked Systems X

No geo-cellular or tanked storage is proposed as part of the development surface water drainage strategy

3.3 Source Control Measures 3.3.1 Permeable paving within the development parcels will provide an element of source control for

surface waters. The permeable paving will help provide initial attenuation at source as well as providing water quality benefits prior to discharging surface waters into the proposed traditional drainage network. For the management/maintenance of these devices refer to Appendix R.


3.4 Drainage Catchments and Water Quality Treatment 3.4.1 It is the intention that the proposed surface water drainage strategy will be split into two catchments

that will drain into the ordinary watercourse onsite (Northern and Southern catchments). Refer to the proposed drainage catchment plan in Appendix L for details.

3.4.2 Within each catchment the permeable paving will focus on water quality from car parking areas prior to discharging surface waters into the traditional drainage arrangement.

3.4.3 The proposed traditional surface water sewer arrangement will incorporate, where appropriate, (for instance up stream of the surface water outfalls), suitable pollution control measures such as trapped gullies, catchpit manholes and class1 petrol interceptors to help manage sediment control and water quality.

3.4.4 The exceedance SuDS features will also provide a degree of passive treatment prior to conveying the waters into the catchment storage controls. Refer to surface water conveyance techniques below for further details.

3.4.5 The catchment control detention basin proposed within each catchment will incorporate a rill in the base of the basin as well as a sediment forebay, (sized in accordance with CIRIA C697), to provide two stages of treatment of surface water during low flow conditions.

3.4.6 The number of water quality treatment stages of surface waters prior to offsite disposal is deemed to be in accordance with CIRIA C697 SuDS Design manual and/or the emerging National SuDS Standards.

3.5 Surface Water Conveyance Techniques 3.5.1 During low flow/design storm conditions surface water will drain into the proposed adoptable surface

water sewer network via the proposed permeable paving and where appropriate private drainage networks.

3.5.2 The quantum of permeable paving within the development parcels cannot be readily quantified at this stage, therefore for the purposes of the surface water sewer hydraulic modelling, a cautious and robust approach has been applied whereby no upstream permeable paving is included within the assessment.

3.5.3 The surface water sewer arrangements have been sized to ensure that no surcharging occurs for the 1 in 2 year design storm rainfall event and no flooding for the 1 in 30 year event in accordance with Sewers for Adoption 7th Edition. Refer to the INFOWORKS ICM hydraulic calculations in Appendix N for further details. It should be noted that the sewer locations are approximate only at this stage. Final details of the sewer arrangements including finalised line and levels will be confirmed during the detailed design stages of the housing areas.

3.5.4 In an exceedance event such as the 1 in 100 year plus 30% allowance for climate change rainfall event, flows from the development parcels will be directed away from properties and the school via overland flow routes towards proposed exceedance SuDS features. These SuDS features will include dished dry swales and filter drains within the built development/green Infrastructure. These devices will help manage exceedance flows close to source as possible whilst also providing a degree of attenuation prior to discharging into the catchment storage controls. The SuDS will convey into the proposed catchment detention basins and will also provide a degree of passive treatment to the waters. The surface water exceedance strategy is included within Appendix N.

13

3.6 Surface Water Runoff Rates and Volumes 3.6.1 The existing Site is currently undeveloped farm land, therefore a Greenfield runoff assessment has

been carried out for the Site using an FEH runoff assessment in accordance with BS 8585:2013. . Refer to Appendix O for FEH calculations.

3.6.2 The existing site area is approximately 58 hectares, while the contributing area for the Proposed Development is approximately 34.8 hectares. This area was broken down to reflect the two proposed drainage catchments and these areas were used for the Greenfield runoff assessment. Refer to the table below for the Greenfield runoff rates.

Table 3.2 – Existing Greenfield Runoff Rates

Greenfield Runoff Rate (l/s)

Area (ha.) 2 year 30 year 100 year QBAR

Northern Catchment 22.4 71 155 219 69

Southern Catchment 12.4 40 86 122 38

Total 34.8 111 241 341 107

3.6.3 Although the Proposed Development will largely mimic the natural drainage catchment it will increase the volume of runoff by approximately 3580m3. Refer to WSP volumetric calculations within Appendix P for details. To mitigate for this it is therefore proposed to incorporate the estimated 100 year 6 hour long term storage volume within the proposed northern catchment detention basin and restrict the southern catchment discharge to QBAR.

3.6.4 This approach to volumetric excess mitigation is in line with the DEFRA document W5-074 Preliminary Rainfall Runoff Management for Developments criteria, BS8582:2013 and mandatory guidance provided by the Code for Sustainable Homes.

3.6.5 The northern catchment will therefore incorporate two outfalls; a control arrangement to accommodate the volumetric excess mitigation and the other to control the contributing catchment to greenfield rates. The southern catchment will restrict all storms the existing greenfield QBAR runoff rate. For details of the proposed surface water discharge rates refer to subheading 3.7 below.

3.7 Final Site Runoff Arrangements 3.7.1 Final runoff from the two proposed drainage catchments will be controlled via detention basins

located within the public open spaces to the west of the built development.


3.7.2 Proposed discharge rates associated with each basin outfall are as follows:

Table 3.3 – Proposed Development Discharges Rates

Proposed Discharge Rates (l/s)

2 year 30 year 100 year 100yr+30%

Northern Catchment (variable control)

0 45 257 257

Northern Catchment (Long Term

Storage control

lmitied to 2l/s/ha)

45 45 45 45

Southern Catchment 38 38 38 38

Total 80 128 340 340

3.7.3 All the catchment control arrangements have been sized to accommodate the critical 1 in 100 year plus 30% allowance for climate change rainfall event based up the runoff rates set out above with inclusion of Long Term Storage within the northern catchment basin. It should be noted that the combined northern and southern catchment discharge rates are no greater than existing greenfield rates. This approach accords with the consented Flood Risk Assessment in order not to exacerbate off site flood risk. Refer to hydraulic calculations in Appendix N for details. The storage sizes per catchment have been summarised below:

Table 3.4 – Storage Required by Catchment

Catchment Required Storage (m3)

Northern Catchment 9,855

Southern Catchment 7,535

3.8 Health and Safety Assessment 3.8.1 The proposed layout of the SuDS features has been designed in accordance with CIRIA C697 to

ensure that they are effective from not only a hydraulic but also from a safety of operatives’ and the wider publics’ perspective during construction, operation and maintenance and takes into consideration (for the northern basin) the proposed footway link between the existing and proposed school sites.

3.8.2 Health and Safety Risk Assessments will be produced for the scheme in terms of surface water drainage during the detailed design stages. The assessments will set out the risks and how these will be managed to an acceptable level.

15

3.9 Adoption and Maintenance of SuDS features 3.9.1 It is proposed that all SuDS and exceedance features within communal areas and green

Infrastructure will be maintained by the management company set up by the developers to maintain the SuDS devices throughout the lifetime of the development. Refer to paragraph 3.1.22 for details.

3.9.2 An outline plan of the maintenance regime of the SuDS elements is included within Appendix Q.


4 Foul Water Strategy 4.1.1 It is proposed that the foul flows from the Proposed Development shall connect into the existing

Thames Water 300mm diameter foul sewer (TWUL Ref No.8903) located along the eastern bank of the Harlowbury Brook via a gravity sewer connection.

4.1.2 Peak foul flow estimates for the Proposed Development have been prepared by WSP. The predicted peak foul flow is 55/s. Refer to Appendix R for details.

4.1.3 A capacity check on the existing public foul system has been carried out by Thames Water taking into account the anticipated peak foul flows from the Proposed Development. Thames Water has confirmed that there is sufficient capacity within the public foul sewerage network to accommodate the predicted foul discharge from the Proposed Development without any off site reinforcement works. Refer to Appendix J for details.

4.1.4 An indicative foul drainage strategy for the Proposed Development has been prepared and can be viewed within Appendix S, hydraulic calculations can be viewed within Appendix T. This does not rely on the provision of any pumping stations. The locations of manholes etc will be the subject of revision as the detailed design of the housing phases comes forward.

4.1.5 Connection to the public sewer will be subject to a Section 104/106 agreement with Thames Water.

17

5 Conclusion 5.1.1 This report sets out the principles for the Site in terms of how the surface and foul water runoff will be

dealt with for the Proposed Development.

5.1.2 The report sets out that SuDS will be implemented throughout the development in order to provide source control and attenuation of surface waters whilst also providing water quality and bio diversity enhancement.

5.1.3 Surface water runoff will be attenuated on-site for events up to and including the critical 1 in 100 year storm rainfall event with a 30% allowance for climate change and released into the onsite ordinary watercourse at rates no greater than the existing greenfield runoff rates.

5.1.4 It is proposed that all SuDS and exceedance features within communal areas and green Infrastructure will be maintained by the management company set up under the terms of S106 obligations to maintain the SuDS devices throughout the lifetime of the development.

5.1.5 Initial Health and Safety Risk Assessments have been produced for the SuDS and surface water drainage arrangements. It is considered that the all risks can be adequately managed.

5.1.6 It is proposed that the foul flows from the Proposed Development shall connect into the existing Thames Water 300mm diameter foul sewer located along the eastern bank of the Harlowbury Brook via a gravity sewer connection. Thames Water have stated that adequate capacity existing within the existing public foul sewer network.

5.1.7 This report has set out the principles for dealing with surface water and foul water runoff for the Proposed Development and shown that it can be dealt with in a sustainable manner, in accordance with the consented Flood Risk Assessment, Environment Agency and NPPF requirements and best practice guidelines.

Project number: 50600547 Dated: 04/09/2014 Revised:

Appendices

Appendix A – Site Location Plan

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Contains Ordnance Survey data © Crowncopyright and database right 2014.

TITLE: FIGURE No:

GILDEN WAYHARLOW SITE LOCATION PLAN

KeySite Boundary

Easting 548200Northing 212200Postcode CM17 0JN


Appendix B – Topographical Survey

44.24

43.97

43.81

43.85

44.11

44.91

45.93

46.95

48.04

48.97

49.80

50.30

50.54

49.88

50.18

50.31

50.50

50.79

51.07

51.39

51.77

52.15

52.56

52.94

53.25

53.47

53.66

53.96

55.18

54.80

54.48

54.28

54.22

54.08

53.82

53.46

53.09

52.70

52.44

52.32

52.26

52.18

52.07

51.87

51.67

51.54

51.15

50.52

51.90

52.52

52.86

53.10

53.33

53.53

53.73

53.88

53.95

53.96

54.01

54.12

54.29

54.46

54.67

54.87

54.98

55.05

55.01

54.94

55.00

55.34

55.85

56.20

56.13

56.00

55.83

55.62

55.48

55.30

55.11

55.02

54.94

54.88

54.83

54.88

54.84

54.77

54.67

54.65

54.66

54.66

54.58

54.46

54.30

54.12

53.94

53.75

53.51

53.21

52.85

52.38

51.81

51.17

50.45

51.01

51.37

51.54

51.65

51.88

52.28

52.77

53.19

53.41

53.55

53.62

53.62

53.58

53.61

53.65

53.74

53.80

53.87

53.98

54.09

54.13

54.15

54.16

54.21

54.29

54.44

54.64

54.82

55.07

55.24

55.43

55.54

55.67

54.20

54.16

54.16

54.12

54.11

54.13

54.08

53.87

53.62

53.31

53.01

52.83

52.70

52.73

52.78

52.90

53.00

53.09

53.13

53.14

53.10

53.08

53.01

52.92

52.77

52.55

52.23

51.86

51.41

50.87

50.29

49.87

49.31

48.56

47.67

46.80

46.02

45.33

44.52

44.31

44.09

44.11

44.34

44.72

45.34

46.09

46.79

47.55

48.41

49.25

49.99

50.60

51.15

51.60

51.95

52.1752.16

52.29

52.32

52.32

52.15

51.90

51.60

51.27

51.00

50.88

50.96

51.12

51.2151.22

51.26

51.23

51.17

51.1251.14

51.0751.06

51.00

50.9950.92

50.85

50.73

50.71

50.70

50.24

50.05

49.47

48.33

47.17

46.53

47.47

47.49

47.56

47.62

47.65

47.71

47.83

47.95

48.07

48.19

48.29

48.51

48.81

49.23

49.72

50.09

50.40

50.52

46.15

46.02

45.99

46.06

46.13

46.23

46.24

46.32

46.2246.07

46.08

46.09

46.22

53.33

53.37

53.42

53.41

53.38

53.45

51.62

51.63

51.65

51.60

51.45

51.28

51.08

50.90

50.77

50.83

50.90

50.94

50.88

45.74

45.77

45.75

45.80

45.89

45.82

45.77

45.71

45.65

45.70

45.63

45.66

45.69

45.61

45.59

45.3645.34

45.32

45.34

45.28

45.56

45.42

45.44

45.53

45.58

45.53

45.52

45.48

45.44

45.32

45.18

45.06

45.22

45.71

46.25

46.42

45.81

45.45

45.49

45.35

45.25

45.2145.39

45.25

45.13

44.92

44.82

44.82

44.81

44.78

44.8845.68

45.57

45.41

45.54

45.49

45.49

45.41

45.2145.69

46.1245.69

44.92

45.94

45.80

45.91

44.63

44.44

44.44

44.51

44.53

44.67

44.64

44.93

44.82

45.15

45.2545.84

44.60

44.4944.40

45.31

45.30

45.7545.77

45.5545.29

45.0944.42

50.02

50.01

49.89

49.68

49.54

49.52

49.47

49.42

49.33

49.24

49.26

49.25

49.35

52.93 52.45

52.38

51.79

51.75

48.18

48.20

48.19

48.01

48.10

47.64

47.64

47.73

47.70

47.78

47.95

48.15

48.56

48.58

48.31

48.08

47.78

47.78

48.15

48.39

48.72

48.8048.41

48.12

48.05

47.9048.22

48.40

48.72

49.28

49.18

48.77

48.31

48.14

48.25

48.56

49.02

48.82

48.61

48.34

47.90

47.49

47.45

47.64

47.71

47.64

47.05

47.17

47.01

47.21

47.3647.01

46.6746.9947.1547.0147.34

47.90

47.33

47.3547.39

47.14

47.28

47.30

47.21

46.98

46.71

47.48

47.3947.36

47.34

47.63

47.4647.56

47.55

47.40

47.19

46.86

46.79

46.93

47.14

47.26

47.18

47.13

47.18

47.11

47.18

47.26

47.33

47.49

47.56

47.66

47.80

47.43

47.54

47.49

50.94

51.20

51.33

51.18

51.2351.34

51.42

50.98

48.96

48.74

48.41

48.14

48.19

48.49

48.78

48.93

49.08

49.04

49.14

49.01

48.75

48.9048.61

48.89

49.24

49.21

49.06

48.9048.59

48.79

48.77

48.90

49.11

49.07

48.90

48.80

48.69

48.36

48.17

48.10

48.34

48.56

48.72

48.86

48.96

48.89

48.71

48.66

48.4548.65

48.71

49.09

48.86

48.79

48.62

48.47

48.55

48.86

48.89

48.95

48.76

48.6648.66

48.56

48.38

48.12

48.04

47.98

48.06

48.20

48.34

48.64

48.57

48.83

48.85

48.66

48.48

48.68

48.70

48.87

49.08

49.01

48.88

48.74

48.49

48.32

48.25

48.41

48.61

48.79

48.53

48.19

48.08

47.97

47.52

47.74

47.51

47.35

47.8147.97

47.79

48.03

48.54

48.62

48.31

48.42

48.18

48.27

48.40

48.83

49.01

49.27

49.73

49.55

49.47

49.34

48.93

48.71

48.31

48.30

48.20

48.08

48.10

48.1548.17

48.59

48.37

47.95

47.58

47.50

47.60

47.72

47.98

48.39

48.7848.55

48.44

48.40

48.41

48.48

48.58

48.55

48.96

49.39

49.60

49.76

49.84

49.97

50.39

50.24

50.11

49.96

49.86

49.70

49.64

49.33

48.84

48.58

48.45

48.54

48.57

48.53

48.50

48.46

48.33

47.90

48.45

48.47

48.56

48.84

49.06

49.16

49.76

49.93

50.24

50.35

50.71

51.12

51.17

53.09

53.10

53.1753.07

52.9953. 28

53.4753.59

55.69

55.03

55.87

55.8255.82

55.94

55.56

55.29

55.20

55.17

55.46

55.85

55.55

55.4255.32

55.50

55.75

55.78

55.5254.76

54.93

54.70

5 3.1

35 3

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53.195 2. 48

5 2.445 2.40

49.85

50.75

51.66

51.7751.85 51.97

50.45

50.54

50.42

50.45

50.25

50.40

50.38

50.16

50.12

50.33

50.29

51.17

51.12

53.72

53.74

47.14 47.24 47.23

47.17

47.1647.10

47.2247.28 47.32

47.2247.2247.18

47.14

47.33

47.3547.39

47.39

47.3147.17

47.1747.06

46.80

47.00

47.14

47.28

47.2547.25

47.1546.86

46.8247.09

47.2047.30

47.21

46.9846.86

46.7646.76

46.81

46.79

46.8546.86

46.7146.80

46.80

46.81

46.75

46.78

46.79

46.65

46.79

47.06

47.20

47.22

47.26

47.3947.36

47.34

47.06 47.0947.14

47.15

47.36

47.2747.25

47.63

47.51

47.46

47.51

47.54

47.47

47.53

47.4147.42

47.56

47.45

47.4047.42 47.44

47.43

47.30

47.3547.34

47.28

46.78

46.86

46.86

46.79

47.14

47.26

47.18

47.42

47.37

47.31

47.21

47.13

47.18

47.11

47.18

47.26

47.33

47.49

47.56

47.66

47.80

47.43

47.54

47.49

55.16

55.12

55.02

54.89

54.67

54.45

54.13

53.79

53.42

53.05

52.70

52.35

52.04

51.76

51.48

51.23

51.00

50.78

50.60

50.43

50.25

50.05

49.85

49.64

49.43

49.19

49.01

49.95

49.90

50.07

50.32

50.59

50.84

51.03

51.25

51.43

51.58

51.77

51.96

52.14

52.29

52.45

52.60

52.75

52.92

53.08

53.26

53.42

53.60

53.77

53.96

54.16

54.43

59.93

55.12

59.90

59.75

59.7759.5959.3659.3359.23

59.16

59.10

58.92

58.57

58.35

58.15

58.04

57.75

57.37

57.02

56.71

56.41

56.03

55.51

48.18

48.20

48.19

48.01

48.10

47.64

47.64

47.73

47.70

47.78

47.95

48.15

48.56

48.58

48.31

48.08

47.78

47.78

48.15

48.39

48.72

48.8048.41

48.12

48.05

47.9048.22

48.40

48.72

49.28

49.18

48.77

48.31

48.14

48.25

48.56

49.02

48.82

48.61

48.34

47.90

47.55

47.49

47.45

47.64

47.71

47.64

49.80

49.12

48.44

48.21

48.11

48.04

48.00

47.98

47.96

47.98

47.05

47.17

47.01

47.21

48.7448.58 48.59 48.57

48.81

47.3647.01

46.6746.9947.1547.0147.34

47.90

47.33

47.3547.39

47.14

47.28

47.30

47.21

46.98

46.71

46.78

47.48

47.3947.36

47.34

47.40

47.50

47.63

47.72

47.77

47.63

47.4647.56

47.55

47.40

47.19

50.67

50.5350.34

50.39

50.50

50.15

49.96

50.10

50.01

49.87

49.90

47.90

47.83

47.93

48.03

48.18

48.48

48.81

49.18

49.53

49.83

50.08

50.36

50.58

50.79

53.13

52.98

52.88

52.79

52.77

52.76

52.77

52.77

52.64

52.49

52.30

52.10

51.83

51.56

51.33

51.09

50.86

50.61

50.40

50.17

49.89

49.67

49.44

51.03

51.06

51.18

51.45

51.71

52.01

52.31

52.65

52.96

53.21

53.55

53.87

54.12

54.29

54.51

54.64

54.67

54.64

54.64

54.64

54.71

54.78

54.91

55.05

55.20

55.35

55.51

55.58

55.64

55.83

57.70

57.72

57.69

57.61

57.52

57.38

57.23

57.09

56.99

56.91

56.81

56.68

56.59

56.60

56.49

56.26

56.12

55.91

55.62

55.26

54.97

54.66

54.33

53.96

53.66

53.34

52.99

52.73

52.59

55.04

55.13

55.46

55.81

56.08

56.38

56.59

56.82

57.06

57.24

57.44

57.61

57.77

57.93

58.05

58.16

58.37

58.57

58.70

58.82

58.88

58.94

58.98

59.02

59.06

59.10

59.08

58.99

59.00

59.51

59.49

59.51

61.51

61.38

61.17

61.04

60.90

60.68

60.47

60.32

60.11

59.95

59.80

59.65

59.46

59.27

59.07

58.99

58.93

58.87

58.85

58.85

58.70

58.53

58.48

58.37

58.28

58.07

57.95

57.81

57.65

57.42

57.20

57.06

56.88

56.71

56.61

56.56

56.41

46.08

46.19

46.07

46.16

46.41

46.59

46.60

46.59

46.59

46.54

46.48

46.66

46.76

46.79

46.75

46.66

46.53

46.51

46.67

46.75

46.79

46.81

46.82

46.64

46.78

46.86

46.86

46.79

46.93

47.14

47.26

47.18

47.42

48.28

48.10

48.22

47.63

47.44

47.31

47.37

47.35

47.26

47.13

47.18

47.11

47.18

47.26

47.33

47.49

47.56

47.66

47.80

47.43

47.54

47.49

47.44

47.36

47.33

47.36

47.33

47.28

47.30

47.35

47.36

47.43

47.32

47.23

47.40

47.49

47.50

47.47

47.47

47.47

47.50

47.61

47.60

47.7347.69

47.64

47.67

47.57

47.56

47.51

47.51

47.55

47.53

47.51

47.53

47.57

47.65

47.71

47.74

47.69

47.70

47.62

47.62

47.65

47.66

47.59

47.59

47.62

47.87

47.94

47.99

48.09

48.09

47.86

47.85

47.83

47.95

47.97

48.01

48.07

48.14

48.37

53.16

53.46

53.78

54.17

54.57

54.89

55.21

55.52

55.77

56.01

56.22

56.42

56.62

56.77

56.90

57.05

57.14

57.15

57.11

57.07

57.03

56.95

56.87

56.73

56.52

56.31

56.07

55.80

55.54

55.33

55.32

51.02

51.27

51.54

51.79

51.97

52.18

52.29

52.42

52.52

52.62

52.65

52.54

52.37

52.31

53.64

53.77

54.06

54.29

54.52

54.67

54.75

54.82

54.85

54.81

54.75

54.71

54.61

54.46

54.27

54.03

53.76

53.47

53.17

52.87

52.50

52.16

51.87

51.50

51.20

50.92

50.69

50.59

50.44

50.34

50.24

50.22

50.63

50.51

50.70

50.90

51.11

51.31

51.65

51.92

52.27

52.65

53.00

53.30

53.66

54.00

54.30

54.54

54.76

54.96

55.17

55.33

55.44

55.50

55.54

55.51

55.49

55.45

55.36

55.20

55.04

54.85

54.58

54.30

54.16

54.78

54.92

55.21

55.50

55.82

56.01

56.15

56.33

56.41

56.38

56.39

56.42

56.38

56.26

56.15

56.02

55.90

55.73

55.52

55.32

55.09

54.78

54.48

54.14

53.79

53.40

53.00

52.61

52.20

51.87

51.4751.49

51.35

49.93

49.95

49.93

49.94

49.90

49.91

49.97

50.14

50.32

50.50

50.74

50.96

51.12

51.14

51.16

51.10

51.06

50.99

50.86

50.79

50.65

50.57

50.50

50.47

50.38

50.3550.35

50.39

50.50

50.65

50.69

60.05

60.04

60.00

59.98

59.9459.94

59.86

59.70

59.49

58.97

58.59

58.23

57.97

57.74

57.50

57.30

57.08

56.84

56.00

56.23

56.63

57.0557.51

57.8558.17

58.51

58.80

59.01

59.21

59.37

59.49

59.59

59.72

59.82

59.90

59.9459.96

60.02

60.10

60.17

60.24

60.32

60.46

60.5860.65

60.7460.94

61.1961.50

61.69

61.83

61.84

61.80 61.7061.61

61.52 61.4161.36 61.32

61.41

61.53

61.62

61.71

61.82

61.88

61.86

61.7461.69

61.49

61.29

61.11

60.93

60.77

60.74

60.72

60.64

60.53

60.52

60.50

60.43

60.42

60.43

60.38

60.44

60.49

60.49

60.46

60.40

60.32

60.16

59.94

59.69

59.33

59.01

58.73

58.53

58.37

58.23

58.07

57.89

57.70

57.52

57.32

57.7857.88

58.09

58.37

58.58

58.87

59.10

59.28

59.49

59.65

59.85

60.09

60.27

60.50

60.69

60.81

60.91

61.03

61.08

61.12

61.21

61.24

61.28

61.30

61.30

61.30

61.27

61.28

61.27

61.25

61.24

61.41

61.54

61.64

61.70

61.75

61.74

61.74

61.72

61.6861.67

61.69

61.67

61.60

61.62

61.57

61.49

61.43

61.40

61.26

61.52

61.62

61.73

61.78

61.73

61.71

61.64

61.49

61.38

61.21

61.24

61.28

61.20

61.13

61.10

61.11

61.10

61.06

60.95

61.00

61.1061.10

61.11

61.14

61.19

61.22

61.19

61.20

61.13

61.06

60.96

60.88

60.82

60.68

60.55

60.43

60.28

60.11

59.93

59.75

59.54

59.27

59.04

58.7458.73

58.52

58.23

57.95

57.67

57.42

57.15

55.68

55.91

56.18

56.47

56.78

57.10

57.35

57.63

57.92

58.16

58.32

58.49

58.61

58.75

58.91

59.03

59.15

59.31

59.46

59.60

59.72

59.78

59.88

59.91

60.01

60.00

59.99

59.99

59.96

59.90

59.87

60.00

60.09

60.11

60.24

60.38

60.56

60.76

60.84

60.90

61.09

61.29

61.45

61.53

61.51

61.43

61.34

61.27

61.12

60.99

60.87

60.73

60.59

60.53

60.42

60.33

60.21

60.12

59.99

59.77

59.52

59.25

58.97

58.78

58.69

58.56

58.38

58.27

58.31

58.32

58.26

58.25

58.16

58.06

57.94

57.89

57.76

57.64

57.50

57.36

57.21

57.06

56.91

56.80

56.71

56.60

56.52

56.45

56.41

56.35

56.22

56.02

55.83

55.6255.5255.48

55.4655.42

55.49

58.5258.48 58.59

58.80

58.95

59.02

59.11

59.22

59.34

59.47

59.59

59.73

59.91

60.08

60.23

60.40

60.54

60.67

60.8560.94

61.13

61.01

60.84

60.62

60.45

60.33

60.14

59.97

59.82

59.64

59.45

59.30

59.13

58.99

58.85

58.69

58.62

58.52

58.44

58.37

58.35

58.34

58.29

58.24

58.20

58.09

57.88

57.61

57.29

56.91

56.49

56.11

55.72

55.48

55.07

55.8556.66

56.95

56.97

57.04

57.43

57.87

58.36

58.70

59.01

59.35

59.48

59.62

59.89

60.04

60.26

60.47

60.78

61.08

61.20

61.32

61.48

61.64

61.68

61.93

62.03

61.85

62.02

62.00 61.9261.80

61.59 61.6361.52 61.39 61.24

61.09 60.94 60.72 60.64 60.57 60.04

53.61

54.10

54.60

55.27

55.92

56.18

56.53

56.31

46.06

46.00

46.00

46.06

46.14

46.28

46.20

45.95

46.18

46.60

46.97

47.38

47.86

48.55

49.02

49.61

50.23

50.94

51.56

52.13

52.66

53.19

53.61

54.02

54.48

54.93

55.34

55.75

56.07

56.44

56.81

57.33

45.58

46.02

46.56

47.12

47.68

48.19

48.79

49.37

49.91

50.49

51.04

51.56

52.19

52.69

53.21

53.70

54.15

54.56

55.06

55.48

55.88

56.27

56.68

56.99

57.13

56.75

56.41

55.95

55.58

55.19

54.84

54.42

54.05

53.62

53.20

52.83

52.42

52.01

51.57

51.10

50.63

50.10

49.53

49.02

48.49

47.97

47.45

46.99

46.37

46.11

45.68

45.98

46.55

47.38

47.88

48.34

48.76

49.13

49.57

50.00

50.54

51.04

51.43

51.88

52.23

52.64

56.59

56.33

55.94

55.57

55.23

54.85

54.50

53.96

53.59

52.84

52.16

51.47

50.79

50.15

49.60

48.96

48.38

47.84

47.27

46.74

46.20

56.44

56.16

55.88

55.54

55.13

54.65

54.05

53.40

52.73

52.01

51.26

50.51

49.75

48.94

48.10

47.34

46.63

45.94

50.66 50.6450.45

50.25

50.21

50.39

50.92

49.93

50.67

51.45

51.28

50.46

49.62

49.79

59.75

59.80

59.74

59.61

59.42

59.25

59.02

58.73

58.47

58.12

58.35

58.70

59.05

59.26

59.44

59.55

59.63

59.58

59.47

59.57

59.79

60.00

60.16

60.27

60.43

60.56

60.78

60.81

60.85

60.88

60.95

60.99

60.03

60.04

60.04

60.08

60.12

60.14

60.14

60.12

60.12

60.14

60.15

60.13

60.09

60.00

59.93

59.94

59.94

59.9159.92

59.86

59.82

59.75

59.57

59.29

59.01

58.75

58.50

58.16

57.82

57.4257.86

58.25

58.58

58.91

59.20

59.41

59.59

59.75

59.79

59.73

59.66

59.81

59.99

60.10

60.17

60.27

60.35

60.42

60.52

60.64

60.73

60.77

60.77

60.84

60.82

58.15

58.19

57.97

57.7457.29

57.10

57.28

57.63

57.91

58.22

58.55

58.75

59.04

59.31

59.60

59.80

59.97

60.11

60.14

60.16

60.13

60.09

60.08

60.09

60.07

60.03

59.97

59.96

59.90

59.87

59.85

59.75

59.67

59.63

59.59

59.67

58.96

58.88

59.02

59.10

59.23

59.38

59.48

59.60

59.68

59.76

59.87

59.98

60.09

60.25

60.40

60.47

60.53

60.52

60.43

60.23

60.00

59.77

59.54

59.29

59.04

58.79

58.48

58.21

57.91

57.62

57.31

56.98

56.64

53.2353.26

55.50

55.85

56.36

56.83

57.21

57.56

57.86

58.25

58.61

58.88

59.16

59.46

59.69

59.95

60.21

60.40

60.56

60.72

60.80

60.84

60.78

60.67

60.48

60.31

60.15

60.03

59.90

59.80

59.74

59.56

59.41

59.21

58.97

58.83

58.60

58.57

57.99

57.99

58.15

58.47

58.71

58.90

59.09

59.26

59.34

59.55

59.69

59.79

59.91

60.04

60.13

60.26

60.38

60.46

60.53

60.52

60.43

60.39

60.24

60.09

59.96

59.81

59.57

59.38

59.15

58.84

58.49

58.11

57.77

57.35

56.87

56.29

55.63

54.89

54.08

53.14

52.31

51.04

51.87

52.65

53.46

54.34

55.12

56.04

56.67

57.19

57.59

57.92

58.22

58.52

58.81

59.03

59.19

59.35

59.48

59.61

59.7759.79

59.93

60.01

60.08

60.18

60.20

60.20

60.20

60.17

60.07

59.96

59.88

59.80

59.73

59.60

59.47

59.35

59.15

58.90

58.67

58.45

58.21

57.98

57.74

57.45

57.20

57.11

47.51

47.60

47.57

47.47

47.26

46.93

46.52

46.08

45.56

45.16

44.63

44.25

44.7445.15

46.08

46.93

47.79

48.61

49.39

50.11

50.71

51.20

51.53

51.70

51.71

51.63

51.46

51.16

50.85

50.76

54.16

54.20

54.25

54.33

54.43

54.56

54.69

54.76

54.79

54.74

54.57

54.35

54.06

53.63

53.11

52.53

51.87

51.19

50.45

49.68

49.74

50.15

50.73

51.36

51.95

52.52

53.16

53.79

54.36

54.89

55.31

55.71

56.04

56.27

56.41

56.44

56.44

56.44

56.41

56.42

56.44

56.36

56.20

56.03

55.86

55.76

55.74

56.37

56.63

56.78

56.90

56.99

57.08

57.16

57.28

57.40

57.50

57.55

57.65

57.66

57.63

57.54

57.45

57.33

57.11

56.81

56.47

56.05

55.67

55.33

54.95

54.5754.44

57.88

58.01

58.23

58.38

58.44

58.48

58.51

58.47

58.45

58.46

58.47

58.47

58.41

58.31

58.16

57.98

57.86

57.71

57.59

57.41

57.24

57.08

56.89

56.69

56.46

55.52

55.83

56.13

56.37

56.67

56.99

57.31

57.63

57.91

58.15

58.41

58.63

58.78

58.91

59.02

59.07

59.08

59.15

59.19

59.26

59.30

59.13

59.15

59.5459.4659.3859.29

59.2059.15

59.10

58.99

58.83

58.56

58.35

58.19

57.92

57.58

57.25

56.89

56.53

56.15

55.87

55.56

55.19

54.75

WSP Group Ltdc

Appendix C – Existing Drainage Catchment Plan

WSP Group Ltdc


Appendix D – Illustrative Scheme Layout

TOB

Metal P & W

/M

I/R

Conc P & W/M

TOB

TOB

C/B

C/B

C/B

C/B

TOB

TOB

TOB

TOB

BO

B

BOB

TOB

TOB

TOB

TOB

TOB

TOB

C/B

Conc P & W

/M

Conc P & W/M

Con c P & W/M

46.39

46.33

46.42

46.31

46.39

46.3 6

46.21

46.30

53.93

53.59

53.16

52.51

52.28

51.94

51.64

51.16

50.80

50.40

50.12

49.68

49.27

48.8

2

48 .84

48.83

48.71

48.66

48.72

49.04

49.19

49.29

49 .61

49.7 0

46 .0 9

46.19

4 6.07

46 .1 0

46 .0 2

44.79

44.83

44.83

45.06

44.90

45.00

45.10

45.37

45.58

45.70

45 .65

45.80

45.81

45.85

45.81

45.76

45.84

45.82

45.88

45.98

46.08

46.00

45.90

45.77

4 6.1

44 6

.27

46.3

546

. 22

46.0746.18

44.8

3

44.73

51.06

50. 32

49 .1947. 67

46. 79

4 6.4 846.14

46.0146.04

50.56

50.92

51.17

51.04

50.85

50.86

51.24

51.49

51.51

51.69

51.79

51 .83

51.79

51 .72

51.19

47.27

48.63

49.86

52.51

52.09

51.54

51.20

50.81

50.50

50.21

53.76

53.29

53.31

50.06

49.98

49.80

49.13

47.89

46.90

46.3

6

46.0

4

49.88

50.18

50.31

50.50

50.79

51.07

51.39

51.77

52.15

52.56

52.94

53.25

53.47

53.66

53.96

55.18

54.80

54.48

54.28

54.22

54.08

53.82

53.46

53.09

52.70

52.44

52.32

52.26

52.18

52.07

51.87

51.67

51.54

51.15

50.52

51.90

52.52

52.86

53.10

53.33

53.53

53.73

53.88

53.95

53.96

54.01

54.12

54.29

54.46

54.67

54.87

54.98

55.05

55.01

54.94

55.00

55.34

55.85

56.20

56.13

56.00

55.83

55.62

55.48

55.30

55.11

55.02

54.94

54.88

54.83

54.88

54.84

54.77

54.67

54.65

54.66

54.66

54.58

54.46

54.30

54.12

53.94

53.75

53.51

53.21

52.85

52.38

51.81

51.17

50.45

51.01

51.37

51.54

51.65

51.88

52.28

52.77

53.19

53.41

53.55

53.62

53.62

53.58

53.61

53.65

53.74

53.80

53.87

53.98

54.09

54.13

54.15

54.16

54.21

54.29

54.44

54.64

54.82

55.07

55.24

55.43

55.54

55.67

52.83

52.70

52.73

52.78

52.90

53.00

53.09

53.13

53.14

53.10

53.08

53.01

52.92

52.77

52.55

52.23

51.86

51.41

50.87

50.29

49.87

49.31

48.56

47.67

46.80

46.02

44.11

44.34

44.72

45.34

46.09

46.79

47.55

48.41

49.25

49.99

50.60

51.15

50.24

50.05

49.47

48.33

47.17

46.53

46.15

46.02

45.99

46.06

46.13

46.23

46.24

46.32

46.22

46.07

46.08

46.09

46.22

53.33

53.37

53.42

53.41

53.38

53.45

51.62

51.63

51.65

51.60

51.45

51.28

51.08

50.90

50.77

50.83

50.90

50.94

50.88

V

PLOUGHED ARABLE

45.0

7

44.96 44.87

44.9345 .09

4 5.3 7

45. 48

45. 53

45.57

45.40

45.40

45.47

45.57

45.49

45 .3 3

45.3

8

4 6.51

46.48

46.10

45 .89

45 .67

45 .8 2

45.78

45.7545.77

45.65

45.75

45.7045.86

45.82

45.71

45.71

45.6845.6845

.74

45.77

45.83

45.83

45.45

45.7745.71

45.74

45.77

45.75

45.80

45.89

45.82

45.77

45.71

45.65

45.70

45.63

45.66

45.69

45.61

45.59

45.3645.34

45.32

45.34

45.28

45.56

45.42

45.44

45.53

45.58

45.53

45.52

45.48

45.44

45.32

45.18

45.06

45.22

45.71

46.25

46.42

45.81

45.45

45.49

45.35

45.25

45.13

44.92

44.82

44.82

44.81

44.78

44.88

45.94

45.80

45.91

4 5.65

WOODLAND

WOODLAND

WOODLAND

HE

DG

E

HE

DG

E

HE

DG

E

HE

DGE

HE

DGE

TREE

S

50.02

50.01

49.89

49.68

49.54

49.52

49.47

49.42

49.33

49.24

49.26

49.25

49.35

HO

US

E

1 .3m HT

ROUGH GRASS

CONC SL

ABS

TA

RMA

C

HTTop 0.60mHTUnd 0.31m

HTTop 1.13mHTUnd 0.56m

HT App10m

HT App10m

HT App10m

HT App10m

HT App10m

HT App10m

HT

App1

0m

HT

Ap p

10m

HT App10m

HT

Ap

p10m

HT App10m

HT App10m

Width 1.34mHTTop 0.60mHTUnd 0.31m

HTTop 1.13m







HT 10.02m













HTTop 2.31m


4mDECIDUOUS




TRAF

FIC

No Ht

HtTop 2.65mHtTop 2.55m

Width 0.63mHtTop 1.68mHtUnd 1.32m

Width 0.72mHtTop 0.56mHtUnd 0.34m

dth 1.0mTop 0.60m

nd 0.34m

48m


HtTop 1.64mWidth 0.61m

HtUnd 1.98m

BURY ROAD

OLD R

OA

D

SHEER

ING RO

AD

SHEER

ING RO

AD

SHEER

ING RO

AD

SH

EER

ING

RO

AD

GILDE

N WAY

10m

GRA

SS

1.2

mH

T

2.0mH

T

4.9mHT

7.5mHT

4.9mHT

4.9mHT

4.9mHT

SAP

LING

GRASS

4 9.3 049 .1 0

49.0 9

49.2

249

.43

49.2

6

49.4

3

49.6

4

49.7

0

49.8

5

50.11

50.34

50.5

5

50.7

7

50.65

50.45

50.2

8

50.0

4

49.8

8

49.6

9

49.5

1

49.1

9

49.1

54 9

. 25

49.0

9

49. 024 9. 15

4 9 .2 2

50.9 7

50.8 4

50.6 8

50.5

4

50.3

3

50.1

8

50.0

7

49.9

9

49.8

549

. 81

49.7

64 9

.71

49.654 9. 71

49.73

4 9 .8 14 9.7 8

49.8 1

49.8

049

.78

49.8

3

49.9

6

50.0

9

50.1

6

50.2

3

50.3

3

50.4

9

50.61

50.79

50.7

9

1.9m

HT

1. 5m

HE

DGE

HE

DGE

2. 5m

0.60 m

HT

1.0

mH

T

1.0

mH

T

0.60 m

HT

0.60

mHT

TAR

MAC

TAR

MAC

TARM

AC

TARM

AC

CO

NC

TAR

MA

C

TAR

MA

C

TAR

MA

C

CO

NC

RETE

52.02

52.10

51.90

51.7951.82

GRA

SS

GRASS

GRASS

1.8m

HE

DGE

10m

DECIDUOUS

30mDECIDUOUS

HE

DGE

1.8m

HE

DGE

1.8m

1.8m

HE

DGE

DECIDUOUS4.0m

0.80 m

HT

1.8m

HE

DGE

5m

12m

DECIDUOUS

DECIDUOUS

HEDG

E

2.5m

12mDECIDUOUS

2.5m

12m

12m

DECIDUOUS

DECIDUOUS

12mDECIDUOUS

DECIDUOUS12m

DECIDUOUS30m

45.4145.62

45.71

45.62

45.46

45.55

45.51

47.4447.53

47 .3 147. 41

48.0

947

.93

47. 9

9

48.0 8

48.04

47.89

48.0 8

48.04

48.0848.00

48.18

48.20

48.19

48.01

48.10

47.64

47.64

47.73

47.70

47.78

47.95

48.15

48.56

48.58

48.31

48.08

47.78

47.78

48.15

48.39

48.72

48.80

48.41

48.12

48.05

47.90

48.22

48.40

48.72

49.28

49.18

48.77

48.31

48.14

48.25

48.56

49.02

48.82

48.61

48.34

47.79

47.73

47.69

47.5847.59

47.63

47.64

47.76

47.44

47.94

47.4

6

45.73

45.82

45.9746.10

45.73

45 .66

45 .75

45.69

45.644 5.47

45.40

WL 45.17

WL 4 5.12

WL

45.14

WL 45

.31

WL 45.

29

WL

45.4

1

WL 45.40

WL 45.43

WL 45.35

WL 45.42

WL 45.45

WL 45.56

WL 45.57

46.42

4 6.4

346

.49

46.4

0

46.1

5

46.2

7

45.98

WL

46.2

5W

L 46

.20

WL

4 6. 2

0W

L 4 6

.12

WL

46.0

6

WL

46.0

5

WL 46 .0 1

WL 46.02

WL 46.25

WL 46.33

WL 46.31

WL 46.33

46.2

2

46.2

8

4 6. 3

146

. 50

46.44

46.4

0

46.50

46.49

46.73

46.77

47.11

46.96

46.59

46.45

47.19

48.1047.90

47.55

47.49

47.45

47.64

47.71

47.76

47.73

47.64

46.71

48.1

0

47.60

46.6

7

47.1

647

. 22

BR

I CK

RE

TAIN

ING

WAL

L

CO

NC W

ALL

HEDG

E

Met al P & W

/M 1 .58m HT

C/B 1.9 5

m HT

GRASS

SHRUBS

IL 46.93mPIPE DIA 0.32m

47.05

47.17

47.01

47.21

TOB

Conrete Walls

47.3647.01

46.67

46.9947.15

47.0147.34

47.90

47.33

47.35

47.39

47.14

47.28

47.30

47.21

46.98

46.71

47.48

47.39

47.36

47.34

47.63

47.46

47.56

47.55

47.40

47.19

47.6547.58

47.70

47.93

SP

SP

CL 47.65IC

CL 47.91IC

PP

P

P

46.86

46.79

46.93

47.14

47.26

47.18

47.13

47.18

47.11

47.18

47.26

47.33

47.49

47.56

47.66

47.80

47.43

47.54

47.49

46.19

45.99

45 .77

46.97

47.8

1

47.5046.

62

45.92

46 .16

47.78

47.52

47.55

47.52

47. 3

9

47.3

4

47. 0

4

47.0

1

4 7. 0

6

47.3

3

47.3

7

47.6

3

47.6

94 7

. 78

47.59

47.54

47.57

47.52

47.80

IL 4

6.681

Dia

0.29m

46.92

46.63

47.07

47.20

47.27

4 7.2 7

47.31

47.22

47.30

47.26

47.48

47.5

5

TOB

TOB

TOB

B rick Wall

TOB

I /R

Stone W

all

I/R

I /R

BRICK WALL

TOB

TOB

Gate

TOB

50.94

51.20

51.33

51.18

51.2351.34

51.42

50.98

BO

BBO

B

TOB

48.96

48.74

48.41

48.14

48.19

48.49

48.78

48.93

49.08

49.04

49.14

49.01

48.75

48.9048.61

48.89

49.24

49.21

49.06

48.90

48.59

48.79

48.77

48.90

49.11

49.07

48.90

48.80

48.69

48.36

48.17

48.10

48.34

48.56

48.72

48.86

48.96

48.89

48.71

48.66

48.45

48.65

48.71

49.09

48.86

48.79

48.62

48.47

48.55

48.86

48.89

48.95

48.76

48.6648.66

48.56

48.38

48.12

48.04

47.98

48.06

48.20

48.34

48.64

48.57

48.83

48.85

48.66

48.48

48.68

48.70

48.87

49.08

49.01

48.88

48.74

48.49

48.32

48.25

48.41

48.61

48.79

48.53

48.19

48.08

47.97

47.52

47.74

47.51

47.35

47.81

47.97

47.79

48.03

48.54

48.62

48.31

48.42

48.18

48.27

48.40

48.83

49.01

49.27

49.73

49.55

49.47

49.34

48.93

48.71

48.31

48.30

48.20

48.08

48.10

48.15

48.17

48.59

48.37

47.95

47.58

47.50

47.60

47.72

47.98

48.39

48.78

48.55

48.44

48.40

48.41

48.48

48.58

48.55

48.96

49.39

49.60

49.76

49.84

49.97

50.39

50.24

50.11

49.96

49.86

49.70

49.64

49.33

48.84

48.58

48.45

48.54

48.57

48.53

48.50

48.46

48.33

47.90

47.87

48.29

48.44

48.43

48.45

48.47

48.56

48.84

49.06

49.16

49.43

49.76

49.93

50.24

50.35

50.71

51.12

51.17

50. 0449 .95

4 9. 8 04 9.7 5

CL 50.08MH

CL 51.341MH

51.64

51.3851.41

51 .40

51.5

1

51.8

7

4 9. 7749 .77

49. 8

349

. 94

50.0

5

50. 1

0

51.39

51.40

51.37

51.29

51.24

51.14

51.01

50.8450.63

50.41

50 .1 950 .0 2

49. 8849.80

51.38

51.35

51.30

51.26

51.23

51.19

51.16

51.12

51.0250.97

50.98

50.92

50.88

50.95

50.87

50.78

50.66

50.53

51.2251.30

51.23

51.24

51.23

51.19

50.98

51.0551.15

51.0551.07

51.0951.07

51.08

51.17

51 .15 51.1 4

51.25

51.1751.29

51.18

51.2151.33

51.2351.27

51.3351.30

51.2751.35

51.4

1

51.27

51.33

51.28

51.37

51.24

51.32

51.11

51.17

51.07

51.11

51.03

51.1251.2

4

51.2651.24

51.17

51.3

7

51.7

2

50 .32

51.4951.13

50.9 1

50.74

5 0.53

50 .3350.12

50 .2050. 11

49. 9249. 90

49. 93

49. 8249.7549.78

49.8149.73

49.644 9.6 74 9. 64

4 9.6 0

49.92

49. 9

249

.81

49.7149 .65

49 .73

49. 85

50.00

50 .1 8

50 .62

50.81

50.99

51.18

49 .6049.63

49. 7

249

. 84

49.92

49. 9

649

.89

49.9

349

.90

4 9. 884 9 .8 6

49.8 649.8 1

4 9.7 24 9. 75

49.80

49.89

49. 96

50. 0650 .23

50 .2 5

50 .4 5

5 0.64

51.11

50.78

50.90

51.02

50. 01

50. 08

50. 17

50. 36

50 .56

50.75

50.89

51.04

51.18

51.24

51.30

51.40

51.3751.34

51.28

51.2051.10

50.97

50.7750.66

50 .4 8

50 .3050. 14

50 .0 549.9 7

49.884 9. 79

4 9. 8049.8 7

49. 8

949

. 90

51.19

51.27

51.35

51.37

51.46

51.42

51.37

51.33

51.30

51.26

51.21

51.11

5 1.02

50.8 9

50.9 1

50.85

50.80

50.70

50.63

50.48

51.36

51.33

51.28

51.24

51.20

51.16

51.13

51.04

50.98

50.87

50.83

50.75

50.67

50.58

50.48

50.3250.39

50.55

50.64

50.76

50.82

50.89

50.92

51.00

51.08

51.16

51.21

51.25

51.31

51.34

51.38

51.43

50.58

50.69

50.80

50.9

5

51.10

51.01

51.43

50.67

50.79

50.89

51.0

7

51.23

51.21

51.41

GRA

SS

CO

NC

50.82

50.81

B rick

Wall

P/R

T OB

BOB

BO

B

DK

P /R

Gate

TOB

BOB

TOB

BOB

BOB

DK

P/W

P/W

P/W

P/W

BOB

TOB

TOB

TOB

TOB

TOB

BO

B

C/B

BOB

TOB

DK

DK

Metal P & W/M

C/B

P/RC/B

TOB

Bric k Wall

Gate

Metal P

& W

/ M

P/R

C/B

Metal P & W/M

P/R

P/R

P/R

P/R

P/R

Gat e

P/R

P /R

I /R

TOB

C/B

TOB

DK

C/B

GateC/B

Gate

C/ B

Bric k W

a ll

Br ick W

all

I/RI/R

Ga t

eI/R

DK

DK

DK

Brick W

a ll

P/R

Gat

eP

/RG

ate

P/R

DK

DK

DK

Brick W

all

Brick W

all

DK

Brick W

a ll

Gate

Brick W

all Gate

C/B

B rick

Wa ll

DK

DK

DK

DK

B rick W

all

C/B

P/R

P/R

P/R

P/W

Gat e

P/R

Ga te

I/R

I/R

TOB

C/B

GRAVE

L

61.94

GRASS

61.55

61.53

61.6

5

61.66

61.57

61.50

61.26

61.2

1

61.26

61.4261.20

61.19

61.0

5

BUS SHELTER2.98mHT

TARMA

C

ROUGH GRASS

62.3

6

61.8

0

61.93

62.08

62.16

61.96

61.84

61.74

61.60

61.50

61.32

61.19

61.03

60.85

8mDECIDUOUS

62.45

62.45

62.23

62.15

61.18

61.72

G

61.18

61.33

61.47

61.63

61 .0 9

61.28

61.41

61.52

61.72

61.81

61.96

61.98

62.08

61.62

SPLIT BOLE

61.15

61.09

61.92

61.80

61.63

61.62

61.50

61.36

61.23

61.04

60.96

60.8561.01

61.2061 .00 60.78 60.7

960.8

6

60.95

61.07

61.15

61.25

61.39

61.50

SP

60.6 6

60.9 4

61.12

6m

6m

DECIDUOUS

DECIDUOUS

DECIDUOUS

TARMA

C

TARM

AC

TARMAC

TARM

AC

TARM

AC

ROUGH GRASS

ROUGH GRASS

GRASS

GRASS

GRASS

20m

20m

DECIDUOUS

DECIDUOUS

61.41

61.6960.

9461.00

61.17

61.28

61.52

61.53

61.54

61.67

61.73

61.80

61.86

61.98

62.06

61.52

61.38

61.31

61.17

61.03

60.88

60.9

1

5m

2m

DECIDUOUS

61.36

61.55

61.32

61.1

0

61.06

61.12

61.10

60.90

60.55

60.41

60.21

60.00

59.82

59.79

59.49

59.33

59.09

58.87

58.38

58.24

58.02

57.83

57.63

60.8460 .54

53.77

53.81

53.93

54.08

54.23

54.41

54.58

54.76

54.92

55.10

55.28

55.46

55.63

55.81

55.97

56.15

56.34

56.51

56.68

56.85

57.04

57.19

57.40

57.57

57.73

57.90

58.07

58.24

58.40

58.58

58.75

58.91

59.08

59.43

59.60

59.93

60.10

60.28

60.42

60.53

60.6

760

.87

61.05

53.78

61.94

61.82

61.68

61.49

61.33

61.16

61.04

60.89

60.72

60.49

60.35

60.18

60.02

59.85

59.69

59.52

59.34

59.18

59.00

58.84

58.67

58.49

58.34

58.15

58.00

57.88

57.65

57.49

57.29

57.11

56.94

56.76

56.59

56.42

56.24

56.05

55.89

55.72

55.54

55.36

55.20

55.03

54.85

54.66

54.49

54.31

54.14

53.97

53.81

15mDECIDUOUS

15mDECIDUOUS

HEDG

E

ROUGH GRASS

61.3

0

61.20

61.19

61.05

60.87

60.79

60.64

60.48

60.39

60.25

60.11

59.92

59.78

59.45

59.30

59.04

58.87

58.71

58.56

58.34

58.19

58.24

58.26

58.16

56.21

56.15

56.00

58.03

57.90

57.76

57.68

57.61

57.46

57.30

57.13

56.93

56.76

56.62

56.56

56.41

56.36

55.83

55.50

55.31

55.2355.2955.28

55.25

55.04

55.1854.77

TOB

TOB

TOB

TOB

TOB

TOB

TOB

TOB

53.2853.14

53.0

7

53.1

0

52.99

52.0852.22

52.35

53.5

5

53.5153.60

53.71

54.46

53.18

53.74

53.6553.5653.4653.38

53.28

53.23

53.18

53.10

53.0353.01

53.00

53.10

53.17

61. 10

6 1.2

8

60.74

60.64

60.44

60.29

60.11

59.91

59.76

59.58

59.40

59.23

59.05

58.92

58.73

58.50

58.36

58.17

58.03

57.86

57.62

57.45

57.39

57.21

57.02

56.85

56.68

56.54

56.40

56.20

56.05

55.83

55.64

55.43

55.36

55.20

55.06

54.86

54.73

54.53

54.40

54.17

53.96

53.88

53.8253.7253.6453.5653.45

53.39

53.2753.23

53.19

53.15

53.21

53.4053.56

53.5953. 57

CONC

CONCRETE

53.1

953

. 60

53. 7

654

.33

53.5

3

53.4

8

53.2

4

53.0

5

53.0

2

52.9

6

52.9

0

52.8

1

53.09

53.10

53.1753.07

52.99

53.04

53.07

53.13

53.13

53.1753.11

53.08

52.75

52.90

53.02

53.12

53.05

52.95

52.785

3.06

53.3

953

.80

52.7

952

.87

Documents

DRAINAGE AND SUDS DESIGN STATEMENTconsultation-online.co.uk/UserFiles/harlow/Drainage and SUDS Design... · DRAINAGE AND SUDS DESIGN STATEMENT Gilden Way Harlow 04/09/2014 Client