Flood Risk Assessment Replacement Dwelling 8 the Mead Nazeing New Road

Flood Risk Assessment

Replacement Dwelling 8 The Mead Nazeing New Road (B194)

Broxbourne

Hertfordshire

EN10 6SS

Job No: BLI.2019.13

Date: April 2019

Version 1

Flood Risk Assessment Replacement Dwelling – 8 The Mead, Nazeing New Road, Broxbourne, Herts

Revision Schedule

Job No. Revision Date Client Details Prepared by

BLI.2019.13 Version 1 03.04.2019 Mr. C Drake Planning Richard Martin IEng MICE Director

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Limitations

This Report has been prepared by BLI Consulting Engineers Ltd for the sole use of Mr. C Drake (“Client”) in accordance with the Agreement under which our services were performed [letter dated 19 February 2019]. No other warranty, expressed or implied, is made as to the professional advice included in this Report or any other services provided by BLI Consulting Engineers Ltd. This Report is confidential and may not be disclosed by the Client nor relied upon by any other party without the prior and express written agreement of BLI Consulting Engineers Ltd.

The conclusions and recommendations contained in this Report are based upon information provided by others and upon the assumption that all relevant information has been provided by those parties from whom it has been requested and that such information is accurate. Information obtained by BLI Consulting Engineers Ltd has not been independently verified by BLI Consulting Engineers Ltd, unless otherwise stated in the Report.

The methodology adopted, and the sources of information used by BLI Consulting Engineers Ltd in providing its services are outlined in this Report. The work described in this Report was undertaken during February 2019 to April 2019 and is based on the conditions encountered and the information available during the said period. The scope of this Report and the services are accordingly factually limited by these circumstances.

Where assessments of works or costs identified in this Report are made, such assessments are based upon the information available at the time and where appropriate are subject to further investigations or information which may become available.

BLI Consulting Engineers Ltd disclaim any undertaking or obligation to advise any person of any change in any matter affecting the Report, which may come or be brought to BLI Consulting Engineers Ltd’s attention after the date of the Report.

Certain statements made in the Report that are not historical facts may constitute estimates, projections or other forward-looking statements and even though they are based on reasonable assumptions as of the date of the Report, such forward-looking statements by their nature involve risks and uncertainties that could cause actual results to differ materially from the results predicted. BLI Consulting Engineers Ltd specifically does not guarantee or warrant any estimate or projections contained in this Report.

Any unauthorised reproduction, adaption or usage of this report and/or appended documents by any person is strictly prohibited without prior written consent.

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Table of Contents

1 Introduction ...... 1

2 Development Details ...... 2

3 Flood Hazard Review ...... 5

4 Flood Risk Mitigation Measures ...... 21

5 Residual Risk ...... 25

6 Discussion and Conclusion ...... 27

Appendices

Appendix A Existing Site Layout (Topographical Survey)

Appendix B Proposed Development Layout

Appendix C Product 4 Environment Agency Flood Data

Appendix D Environment Agency – Climate Change Allowance/Procedure

Appendix E Climate Change Flood Levels – Stage / Flow Calculations

Appendix F Epping Forest District Council – Level 2 SFRA Extract

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1 Introduction

1.1 BLI Consulting Engineers Ltd have been commissioned by Mr. C Drake to prepare a Flood Risk Assessment in accordance with the:

■ National Planning Policy Framework (NPPF).

■ Flood Risk and Coastal Change Planning Practice Guidance (PPG).

1.2 This report will form part of the supporting technical documentation to accompany a full planning application comprising of a replacement dwelling and associated hard and soft landscaping areas.

1.3 The application will be submitted by Halladay West Limited to Epping Forest District Council and the purpose of this report shall be to:

■ Provide information on the flood risks associated with the application site and to present appropriate mitigation measures for the proposed development where flood risk has been identified.

■ Assist where possible with the application of the Sequential Test and Exception Test.

1.4 This is to enable the development to obtain planning permission without objection from the Local Planning Authority (LPA) or their statutory consultees and so that the site, its occupants and the surrounding development is at the minimum risk of flooding.

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2 Development Details

Site Location

2.1 The application site is located:

■ Site Address: – 8 The Mead, Nazeing New Road (B194), Broxbourne, Hertfordshire

■ Post Code: – EN10 6SS

■ Grid Reference: – TL 905 341

Site

Figure 2.1 – Site Location Plan

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Site

Figure 2.2 – Aerial Photo

Existing Site Layout

2.2 The proposed development boundary as indicated in Figure 2.2 above is defined by:

■ Residential dwellings to the north and south.

■ Open grassland to the east with commercial development beyond.

■ Nazeing New Road to the west with dense woodland beyond.

2.3 A topographical survey of the existing site layout has been undertaken by Survey Solutions and a copy of the survey has been included within Appendix A. The site layout currently comprises of a two storey residential dwelling (2-bedroom) together with a garage, impermeable driveway and rear garden area. Vehicle and pedestrian access to the dwelling is achieved via the private driveway leading off Nazeing New Road to the west of the site.

2.4 The Finished Floor Level (FFL) of the existing residential dwelling is set at 24.83m AOD and drops slightly to 24.77m AOD at the rear of the dwelling. The existing external ground levels to the front (west) of the dwelling are circa 24.40m AOD and rise up to circa 24.85m AOD adjacent to Nazeing New Road. The ground levels within the rear garden are slightly lower at a level of circa 24.10m AOD

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2.5 The existing site layout has an impermeable area of approximately 0.019 ha comprising of roof (0.007 ha) and hardstanding (0.012 ha) areas as detailed above. The impermeable area is served by a positive drainage network and it is likely that the drainage network discharges its surface water runoff into a soakaway located within the rear garden.

2.6 The remainder of the site comprises concrete pathways and permeable grass which infiltrates into the ground with a surface water runoff equal to the greenfield runoff rate.

Development Proposal

2.7 The proposed development as shown in Appendix B and Figure 2.3 below comprises of:

■ The demolition of the existing built development including the residential dwelling, garage, outbuildings and private driveway.

■ The construction of a new two storey residential dwelling (4-bedroom) in the location of the previous building structure together with a new private driveway.

2.8 Vehicular and pedestrian access to the development will continue to be via Nazeing New Road located to the west of the site.

Figure 2.3 – Proposed Development

2.9 The development layout has an impermeable area of approximately 0.025 ha comprising of roof (0.010 ha) and hardstanding (0.015 ha) areas as detailed above.

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3 Flood Hazard Review

Source of Flooding

3.1 Fluvial Flooding - is caused by rivers and occurs when the river channel capacity is exceeded by the flow. Most rivers have a natural flood plain which in built up areas is sometimes encroached upon by development.

3.2 The indicative fluvial and tidal flood mapping available on the GOV.UK website and as shown in Figure 3.1 below, demonstrates that the development site is located within Flood Zone 3 in accordance with Table 1 of the Flood Risk and Coastal Change PPG. The mapping also identifies that the site is located within an area which is provided flood protection from fluvial and/or tidal flooding.

Site

Figure 3.1 – Fluvial and Tidal Indicative Flood Mapping

3.3 To provide a better understanding of the fluvial flood risk at the site location, a Product 4 data request was submitted to the Environment Agency (EA) and their full response has been included within Appendix C. Following a review of the EA’s response, a range of fluvial flood levels and their corresponding flows rate were provided along the Nazeing Drain located to the south-east of the site and the Lee Navigation (Lower) located to the north-west.

3.4 The proposed development site is located adjacent to model Node 1.064 (Nazeing Drain) and model Node WGA56 (Lee Navigation Lower) and a copy of the most critical storm events associated with these Nodes have been provided within Table 3.1 and Table 3.2 below.

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Storm Event 20 Year 100 Year 1000 Year

Flood Level Node 1.064 24.41m AOD 24.56m AOD 25.23m AOD

Table 3.1 – Nazeing Drain Fluvial Flood Levels (Present Day Scenario)

Storm Event 20 Year 100 Year 1000 Year

Flood Level Node WGA56 24.35m AOD 24.74m AOD 25.16m AOD

Table 3.2 – Lee Navigation (Lower) Fluvial Flood Levels (Present Day Scenario)

3.5 A review of the above flood level data against the topographical survey included within Appendix A demonstrates that:

■ the existing building with an FFL of 24.83m AOD is located within Flood Zone 2 as a result of the raised Finished Floor Level.

■ The raised hardstanding areas (driveway & patio) are located within Flood Zone 3a and Flood Zone 2. However, the site specific mapping identifies the site as being located within Flood Zone 2 as a result of the protection provided by the higher surrounding land and the flood defences.

■ The garden area which is set at a lower level is located within Flood Zone 3b. However, the site specific mapping identifies the site as being located within Flood Zone 2 as a result of the protection provided by the higher surrounding land and the flood defences.

3.6 When the effects of future climate change are taken into consideration, the fluvial flood risk to the site and the proposed development will be increased and an assessment of this risk has been undertaken below.

3.7 In accordance with the recently published document ‘Adapting to Climate Change: Advice for Flood and Coastal Erosion Risk Management Authorities’ Table 2 provides advice in relation to changes to peak river flow as a result of future climate change.

3.8 For residential development within the Anglian region, the potential changes anticipated up to the year 2115 range between:

■ Upper End (90th) = +65%

■ Higher Central (70th) = +35%

■ Central (50th) = +25%

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3.9 In accordance with the Environment Agency’s Climate Change Guidance Document included within Appendix D, the following assessment has been made:

■ The proposed development is less than 9No. dwellings and is therefore classified as ‘Minor Development’ (Note 1).

■ The proposed development has a vulnerability classification of ‘More Vulnerable’ and is located within Flood Zone 2. Therefore, the ‘Basic’ approach for assessing climate change allowance is acceptable for ‘Minor Development’ in accordance with Table A.

■ In accordance with Table 2, the ‘Central’ and ‘Higher Central’ climate change allowance should be used to assess ‘More Vulnerable’ development located within Flood Zone 2.

3.10 To undertake a more detailed assessment of future climate change, an intermediate approach instead of a basic approach has been adopted. Using the flood levels and corresponding flow data provided as part of the Product 4 data requested, a staged discharge rating curve has been constructed for the Nazeing Drain and the Lee Navigation (Lower) as shown in Appendix E. The staged discharge rating curves have been used to interpolate the climate change enhanced flood levels as shown within Table 3.3 and Table 3.4 below.

Storm Event 100 Year (+25%) 100 Year (+35%) 100 Year (+65%)

Flood Level Node 1.064 24.98m AOD 25.08m AOD 25.36m AOD

Table 3.3 – Nazeing Drain Fluvial Flood Levels (Climate Change Scenario)

Storm Event 100 Year (+25%) 100 Year (+35%) 100 Year (+65%)

Flood Level Node WGA56 24.92m AOD 24.97m AOD 25.11m AOD

Table 3.4 – Lee Navigation (Lower) Fluvial Flood Levels (Climate Change Scenario)

3.11 When reviewing the stage discharge rating curve of the Nazeing Drain included within Appendix E, the Nazeing Drain appear to have abnormal increase in flood depth during the 1000-year event as a result of a small increase in flow. This has skewed the shape of the rating curve and makes the results unreliable. However, the stage discharge rating curve for the Lee Navigation (Lower) which is the larger watercourse, has a more realistic stage-discharge relationship and would appear to present more appropriate results. Therefore, the flood levels calculated for the Lee Navigation (Lower) and included within Table 3.4 above will be used to review the risk of fluvial flooding at the proposed development site.

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3.12 A review of the climate change enhanced flood level data against the topographical survey included within Appendix A demonstrates that:

■ the existing building with an FFL of 24.83m AOD is located:

– 90mm below the 100-year plus 25% climate change flood level of 24.92m AOD.

– 140mm below the 100-year plus 35% climate change flood level of 24.97m AOD.

– 280mm below the 100-year plus 65% climate change flood level of 25.11m AOD.

■ Ground levels (min. 24.43m AOD) along the existing access and egress route (driveway) towards Nazeing New Road is located:

– 490mm below the 100-year plus 25% climate change flood level of 24.92m AOD.

– 540mm below the 100-year plus 35% climate change flood level of 24.97m AOD.

– 680mm below the 100-year plus 65% climate change flood level of 25.11m AOD.

3.13 Therefore, the site is considered to be at a ‘MEDIUM’ to ‘HIGH’ risk of flooding from this source as a result of impeded access and egress conditions. This will require additional mitigation measures as part of the proposed development as detailed within Section 4 of this report.

3.14 Tidal Flooding - from the sea occurs when high tides and storm surges raise the level of tidal waters above the level of the shore or river bank. They can be sudden and severe but are dependent on a number of factors.

3.15 The Nazeing Drain and the Lee Navigation (Lower) are not tidally influence within the vicinity of the site and therefore, the development is at a LOW risk of flooding from this source.

3.16 Surface Water Flooding – commonly occurs within highly dense urban areas where there are large areas of impermeable surfacing e.g. roof areas, car parking and roads. It is possible during high intensity rainfall storms events for surface water run-off to be unable to soak into the ground, or enter the man-made drainage systems at a quick enough rate. Where this occurs, the excess water can flow across land and potentially cause flooding.

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3.17 The indicative Surface Water Flood Mapping associated with the proposed development site has been included within Figure 3.2 – 3.7 below during the ‘High Risk’, ‘Medium Risk’ and ‘Low Risk’ flood scenarios.

30-Year Storm Event

3.18 Figure 3.2 and 3.3 below represents the ‘High Risk’ flood scenario which equates to flooding of greater than 3.3% probability (30-year event).

3.19 The mapping demonstrates that:

■ The proposed development site is located outside of the anticipated flood extents and has a risk rating of ‘Very Low’.

■ Nazeing New Road and the land surrounding the development site is located outside of the anticipated flood extents and has a risk rating of ‘Very Low’.

Figure 3.2 – Surface Water Indicative Flood Mapping (High Risk Flood Extents/Depth)

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Figure 3.3 – Surface Water Indicative Flood Mapping (High Risk Flood Velocity)

100-Year Storm Event

3.20 Figure 3.4 and 3.5 below represents the ‘Medium Risk’ flood scenario which equates to flooding between the 1.0% and 3.3% probability (30-year event to 100-year event).

3.21 The mapping demonstrates that:

■ The proposed development site is located outside of the anticipated flood extents and has a risk rating of ‘Very Low’.

■ Nazeing New Road and the land surrounding the development site is located outside of the anticipated flood extents and has a risk rating of ‘Very Low’.

■ Surface water flooding has been identified along the channel of the Lee Navigation (Lower) located to the north-west of the site with a modelled flood depth of 300mm – 900mm and flow velocity of greater than 0.25 m/s.

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Figure 3.4 – Surface Water Indicative Flood Mapping (Medium Risk Flood Extents/Depth)

Figure 3.5 – Surface Water Indicative Flood Mapping (Medium Risk Flood Velocity)

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1000-Year Storm Event

3.22 Figure 3.6 and 3.9 below represents the ‘Low Risk’ flood scenario which equates to flooding between the 0.1% and 1.0% probability (100-year event to 1000-year event).

3.23 The mapping demonstrates that:

■ The area of the site where the proposed dwelling is intended to be constructed is located outside of the anticipated flood extents and has a risk rating of ‘Very Low’.

■ Surface water flooding has been identified within the rear garden of the proposed dwelling and has a modelled flood depth of less than 300mm and a flow velocity of less than 0.25 m/s.

■ Nazeing New Road which forms the sites access and egress route is located outside of the anticipated flood extents and has a risk rating of ‘Very Low’.

■ Surface water flooding has been identified along the Lee Navigation (Lower) located to the north-west of the site with a modelled flood depth of 300mm – 900mm and flow velocity of greater than 0.25 m/s.

■ Surface water flooding has been identified along the Nazeing Drain located to the south-east of the site with a modelled flood depth of less than 300mm and a flow velocity of greater than 0.25 m/s.

Figure 3.6 – Surface Water Indicative Flood Mapping (Low Risk Flood Extents/Depth)

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Figure 3.7 – Surface Water Indicative Flood Mapping (Low Risk Flood Velocity)

3.24 In summary, the surface water flood mapping included within Figure 3.2 to Figure 3.7 demonstrates that the proposed development site is located outside the extent of surface water flooding up to the 100-year storm event and the site is considered to be at a ‘LOW’ of flooding from this source.

3.25 To further reduce the risk of surface water flooding to the site and the existing surrounding development, additional mitigation measures as detailed within Section 4 of this report shall implemented into the development design.

3.26 Groundwater Flooding - occurs in areas where the level of groundwater is high. Rainfall that soaks into the ground can raise it to a level where structures within the ground are at a risk of flooding. Structures such as basements or detention ponds can be at risk, although this is dependent upon the ground conditions of the site.

3.27 No intrusive investigation works have been undertaken at this stage and therefore the ground water table has not been accurately defined.

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3.28 A review of the Ground Water Susceptibility Mapping included within the Epping Forest District Councils Strategic Flood Risk Assessment (August 2015) has been undertaken and an extract of the mapping has been included within Figure 3.8 below.

3.29 The Ground Water Susceptibility Mapping is a strategic scale map showing the proportion of each 1km grid square where geological and hydrogeological conditions show groundwater might emerge. It does not show the likelihood of groundwater flooding and only isolated locations within the overall susceptible area are actually likely to suffer the consequences of groundwater flooding.

3.30 The mapping demonstrates that the site is located within a 1.0km grid square with a greater than 75% proportion of the grid identified as an area where ground water might emerge. However, the high risk areas are likely to be associated with the low lying land to the east of the site, adjacent to large open waterways.

Site

Figure 3.8 – Groundwater Susceptibility Mapping

3.31 In addition to the above, the existing building structure has an elevated Finished Floor Level and does not currently show any evidence of flood damage from any source of flooding.

3.32 The proposed replacement dwelling:

■ will also incorporate a raised Finished Floor Level as part of the development design and as detailed within section 4 of this report.

■ does not include any below ground basement construction.

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3.33 However, intrusive investigation works should be undertaken during the detail design stage as groundwater could potentially affect the type of foundations and their method of construction, as well as the type of surface water drainage techniques including potential issues with floatation

3.34 Therefore, at this stage the risk of flooding from this source is considered to be ‘LOW’.

3.35 Non-natural or Artificial Flooding - can include reservoirs, canals and lakes where water is retained above the natural ground level and flooding may occur as a result of the facility becoming overwhelmed or as a result of dam or bank failure. The potential effects of flood risk management infrastructure should also be considered.

3.36 The reservoir flood mapping available on the GOV.UK website and as shown in Figure 3.9 below demonstrates that the proposed development site is located outside of the extent of any reservoir breach flooding scenario.

Site

Figure 3.9 – Reservoir Indicative Flood Mapping

3.37 In addition to the above flood mapping, a review of the OS mapping of the site and surrounding area did not identify any artificial sources of flooding which could affect the proposed development.

3.38 Therefore, the risk of flooding from this source is considered to be ‘LOW’.

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Strategic Flood Risk Assessment

3.39 As part of the site assessment, a desk top review of the following documents has been undertaken.

■ Epping Forest District Council (Level 1) Strategic Flood Risk Assessment (SFRA) – August 2015

■ Epping Forest District Council (Level 2) Strategic Flood Risk Assessment (SFRA) – March 2018

3.40 The above reports did not provide any site-specific comments in relation to flood risk beyond the assessment undertaken above. However, a site specific assessment has been undertaken within the Level 2 SFRA for the commercial development located to east of the site (SFRA Ref: NAZE.E3) and an extract of the findings has been included within Appendix F.

Description of Flooding

3.41 The site is considered to be at a low risk of flooding from all sources except:

■ Fluvial flooding which is considered to present a ‘Medium to High’ flood risk due to the sites location within the fluvial floodplain associated with the Lee Navigation (Lower) located to the north-west of the site and the Nazeing Drain located to the south-east.

3.42 Therefore, the focus of this report will be to mitigate the flood risks posed from this source in accordance with the mitigation measures stated within Section 4 of this report. However, the flood risk from other sources of flooding will not be overlooked and the measures put forward to mitigate the risk of fluvial flooding will also further reduce the already low risk from other potential sources of flooding.

Access and Egress

3.43 In accordance with the NPPF and the Flood Risk and Coastal Change PPG, access and egress to the site during a range of storm events should be considered with preference being over dry land. However, where this is not possible, evacuation should fall within the white cells as classified within Table 13.1 of FD2320_TR2 and shown below.

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Table 13.1 of FD2320_TR2

3.44 The proposed access and egress route for the residential dwelling is included within Figure 3.10 below. During construction, an elevated pedestrian walkway will be constructed along the southern boundary of the private driveway between the residential dwelling and Nazeing New Road. The elevation of the pedestrian walkway and the FFL of the proposed dwelling will be set at 24.85m AOD except where the pedestrian access ties into the existing level of Nazeing New Road at 24.78m AOD.

Access & Egress

Figure 3.10 – Access & Egress Route

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3.45 The flood level data provided by the EA and included within Table 3.1, Table 3.2 and Table 3.4 above has been reviewed against the access and egress routes and will be subject to the following conditions during a range of fluvial storm events.

3.46 The fluvial flows along the access and egress route are likely to be at low velocity (less than 0.5 m/s) due to the location of the access and egress route on the outer extent of the floodplain and the protection provided from the existing surrounding development and boundary walls etc.

■ A maximum flood depth of 0mm (dry) will be experienced during the 20-year storm event.

■ A maximum flood depth of 0mm (dry) will be experienced during the 100-year storm event.

■ A maximum flood depth of 140mm will be experienced during the 100-year (+25%) plus climate change storm event. The anticipated flood depth and velocity (less than 0.5 m/s) would place the access and egress conditions within the white cells of Table 13.1 of FD2320_TR2.

■ A maximum flood depth of 190mm will be experienced during the 100-year (+35%) plus climate change storm event. The anticipated flood depth and velocity (less than 0.5 m/s) would place the access and egress conditions within the white cells of Table 13.1 of FD2320_TR2.

■ A maximum flood depth of 330mm will be experienced during the 100-year (+65%) plus climate change storm event. The anticipated flood depth and velocity (less than 0.5 m/s) would place the access and egress conditions within the orange cells (Danger for most) of Table 13.1 of FD2320_TR2. Therefore, conditions would be considered acceptable for access and egress by the emergency services.

■ A maximum flood depth of 450mm will be experienced during the 1000-year storm event. The anticipated flood depth and velocity (less than 0.5 m/s) would place the access and egress conditions within the orange cells (Danger for most) of Table 13.1 of FD2320_TR2. Therefore, conditions would be considered acceptable for access and egress by the emergency services.

3.47 Therefore, the above access and egress conditions are considered to be acceptable up to the 100-year (+35%) plus climate change storm event and unlikely to require the assistance of the emergency services during these events. However, it is recommended that the occupants of the residential dwelling sign up to the Environment Agency’s flood warning service and following receipt of a flood warning, the site could be evacuated over dry land in a calm and safe manner.

Vulnerability Classification

3.48 Table 2 of the Flood Risk and Coastal Change PPG provides a list of different development types which fall into the vulnerability classifications also defined within the Flood Risk and Coastal Change PPG.

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3.49 The proposed development is intended for residential use and therefore the flood risk classification indicates that this falls within the ''More Vulnerable'' classification.

Sequential & Exception Tests

3.50 The proposed residential dwelling is classified as More Vulnerable development and is shown to be located within Flood Zone 2 during the current day storm conditions and within Flood Zone 3a when climate change is taken into consideration. In accordance with Table 3 (see below) of the Flood Risk and Coastal Change PPG, More Vulnerable development is considered appropriate within Flood Zones 2 and Flood Zone 3a subject to passing the Exception Test.

3.51 It should also be note that the proposed development is for a replacement dwelling only and therefore the current use of the site is not being amended. From a Sequential and Exception Test perspective, the replacement dwelling would be considered similar to a building extension (less 250m2) intended to provide additional living space with a classification of minor development.

3.52 The Flood Risk and Coastal Change PPG states:

You also don’t need to do the sequential test if either the following apply:

■ your development is a minor development

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■ your development involves a change of use (eg from commercial to residential) unless your development is a caravan, camping chalet, mobile home or park home site

3.53 In addition to the above, one of the notes appended to Table 3 of the Flood Risk and Coastal Change PPG states:

■ The Sequential and Exception Tests do not need to be applied to minor developments and changes of use, except for a change of use to a caravan, camping or chalet site, or to a mobile home or park home site

3.54 Therefore, the Sequential Test and Exception Test are not considered to apply to the proposed development which comprises of a replacement residential dwelling.

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4 Flood Risk Mitigation Measures

4.1 To enable the site to be considered in line with the NPPF and the Flood Risk and Coastal Change PPG, appropriate flood mitigation measures need to be set in place. The measures laid out below, are put forward as those that will be incorporated within the detailed design and operation of the proposed development.

Level Regime

4.2 The proposed residential dwelling shall have a minimum Finished Floor Level (FFL) of 24.85m AOD which is 20mm higher than the existing residential dwelling which is set at 24.83m AOD.

4.3 High level refuge will also be provided at first floor level which will be set at a minimum level of 27.05m AOD.

4.4 An elevated pedestrian walkway will be constructed along the southern boundary of the private driveway between the residential dwelling and Nazeing New Road. The elevation of the pedestrian walkway will be set at 24.85m AOD except where the pedestrian access ties into the existing level of Nazeing New Road at 24.78m AOD.

Flood Warning & Evacuation

4.5 The site is located within an area where the Environment Agency operates a Flood Warning Service, as shown in Figure 4.1 below.

Site

Figure 4.1 – Flood Warning & Flood Alert Mapping

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4.6 This scheme is free to join and provides early warning prior to the flood event, allowing for early and calm evacuation. Under the Scheme, there are three levels of flood warning, as shown within Table 4.1 below.

Flood Warning Code Description

Flood Alert:

• Flooding is possible, be prepared. • Two hours to two days in advance of flooding.

Flood Warning:

• Flooding is expected, immediate action required. • Half an hour to one day in advance of flooding.

Severe Flood Warning:

• Severe flooding, danger to life. • When flooding poses a significant threat to life.

Table 4.1 – Flood Warning Category

4.7 If the occupants of the site decide not to remain within the safe refuge of the property, the access and egress review undertaken between para 3.43 – 3.47 has confirmed that the access and egress conditions are considered to be safe for the occupants up to the 100-year (+35%) plus climate change storm event and unlikely to require the assistance of the emergency services during these events.

4.8 However, it is recommended that:

■ the occupants sign up to the Environment Agency's early Flood Warning service as described above;

■ an Evacuation Plan is undertaken during the detailed design stage and provided to the occupants.

4.9 This will enable early and safe evacuation for all storm events over the lifetime of the development should the occupants not wish to remain with the property.

Flood Resilient Construction Techniques

4.10 The use of flood resilient construction techniques in accordance with ‘Improving the Flood Performance of New Buildings: Flood Resilient Construction’ and ‘Prepare your Property for Flooding’ will be incorporated into the final design of the proposed development up to a minimum level of 25.83m AOD.

This level equates to 600mm above the 1000-year flood level of 25.23m AOD.

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Flood Compensation Storage

4.11 The proposed residential dwelling has a plan area of 100m2 which is 30m2 greater that the existing site development. Therefore, the proposed development will occupy approximately 16.2m3 of additional flood plain storage during the 100-year (+35%) plus climate change storm event. However, there is no available land to provide flood compensation storage on a level for level and volume for volume basis.

4.12 It should be noted, that if the proposed development comprised of an extension to the existing residential dwelling (less than 250m2), the development would be considered to have a minor impact on flood risk and the provision of compensation storage would not normally be required.

4.13 However, the proposed development is for a replacement dwelling only and the current use of the site is not being amended. Therefore, the replacement dwelling would be considered similar to a building extension (less 250m2) by providing a larger living area and the development should also be considered to have a minor impact on flood risk.

Surface Water Drainage Strategy

4.14 In the absences of a suitable watercourse or public surface water sewer within the proximity of the site, it is believed that the existing site development discharges it surface water runoff via an infiltration drainage system (soakaway). Based on the site topography and the amount of suitably available land away from the existing building structures, the location of the soakaway would be in the rear garden of the site.

4.15 Therefore, it is intended that the proposed surface water drainage system also discharges to an infiltration drainage system as detailed below:

■ Runoff from the impermeable roof area will discharge to a soakaway located within the rear garden.

■ Runoff from the impermeable hardstanding areas will discharge via a permeable paving construction and/or to a soakaway located within the rear garden.

4.16 During the detailed design stage an intrusive investigation will be undertaken, including percolation testing in accordance with BRE 365. Using the soil infiltration rates obtained from the percolation testing, the design of infiltration structure(s) should be undertaken to meet the following design criteria.

■ The infiltration drainage system should contain the critical 100-year storm event with a 40% increase in rainfall intensity to allow for the effect of climate change;

■ The infiltration drainage system should have a half drain time of less than 1440 minute (1 day) unless additional storage is provided to contain subsequent storm events.

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4.17 The above drainage system will also be required to comply with the design requirements of Part H of the Building Regulations and will be subject to inspection and approval by the Building Control inspector.

Detailed Design

4.18 It is proposed that the mitigation measures set out above are controlled by conditions to the planning consent which will be approved by the LPA and their consultees.

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5 Residual Risk

Remaining Flood Risk

5.1 The main residual flood risk to be considered are:

■ A breach within the fluvial flood defences located to the north-west and south-east of the site.

■ A blockage occurring within the surface water drainage system serving the proposed development

Flood Defence Breach

The fluvial flood defences are under the ownership of the Environment Agency who are responsible for their future maintenance and repair. The flood defences currently have a Condition Rating of ‘2 - 3’ and a breach within these particular defences is currently considered to be unlikely.

To further reduce the risk associate with a breach scenario, it is recommended that:

■ The future occupants of the residential dwelling sign up to the Environment Agency's early Flood Warning service as described above. This will enable the early and calm evacuation of the residential dwelling prior to the flood event occurring.

■ A site-specific Flood Evacuation Plan is undertaken during the detailed design stage and provided to the occupants of the residential dwelling as part of the home buyers welcome pack.

Surface Water Drainage System

5.2 The maintenance of the private surface water drainage network serving the proposed development shall be dealt with through the implementation of a simple maintenance regime which would be provided to the future occupants.

5.3 The initial maintenance regime recommended for the private surface drainage network is set out below and has been undertaken in accordance with the CIRIA SuDS Manual:

■ Undertake regular inspection and removal of litter and other debris (leaves) from the drainage catchment, including roads, car parks and soft landscaping areas.

■ Inspection and clearance of all gutters and filter meshes installed to protect the RWPs outlet points should be undertaken on an annual basis.

■ Inspection and clearance of all pre-treatment structures including catchpit gullies, inspection chambers (IC) and manholes to be undertaken on an annual basis.

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■ Inspection and clearance of the geo-cellular soakaway tank to be undertaken on an annual basis. This should include inspection of the inlets, outlets, vents and overflows to ensure that they are in good condition and operating as design.

■ Undertake a survey of the geo-cellular soakaway tank for sediment build-up every 5 years and remove if necessary.

■ Regular sweeping of permeable paving with a stiff brush to ensure removal of loose debris and litter.

5.4 The maintenance regime recommended above is put in place to minimise the risk of blockages occurring and to prevent water surcharging from the inspection chambers and manholes. However, the final maintenance regime should be established during the detailed design of the drainage system in consultation with the design consultant.

5.5 The maintenance plan should be considered as a live document and should be updated over the lifetime of the development and adapted where necessary to ensure a system failure does not occur and the risk of flooding is minimised.

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6 Discussion and Conclusion

6.1 This Flood Risk Assessment has been undertaken in accordance with the National Planning Policy Framework (NPPF) and the Flood Risk and Coastal Change Planning Practice Guidance (PPG).

6.2 The report demonstrates that the proposed development:

■ is located within Flood Zone 2 during the current day storm conditions and within Flood Zone 3a when climate change is taken into consideration over the life time of the development. However, the development and it occupants are considered to be safe when the suggested mitigation measures as stated within Section 4 of this report have been implement into the development design.

■ is considered to be at a low risk of flooding from all other sources and this risk will be further reduced with the suggested mitigation measures as stated within Section 4 implemented into the development design.

■ comprises of a replacement dwelling and passes the requirements of the Sequential and Exception Tests.

■ will incorporate a Sustainable Surface Water Drainage Strategy to drain the proposed development's impermeable area and ensure flood risk is not increased.

■ will reduce flood risk to the site and the future occupants when compare to the existing site development.

6.3 Therefore, the proposed development is considered appropriate from a flood risk and surface water drainage perspective subject to the implementation of the recommended mitigation measures put forward as part of this report.

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Appendices

Flood Risk Assessment Replacement Dwelling – 8 The Mead, Nazeing New Road, Broxbourne, Herts

Appendix A

Existing Site Layout (Topographical Survey)

TOPOGRAPHICAL & MEASURED BUILDING SURVEYS ABBREVIATIONS & SYMBOLS

AH Arch Head Height FH Fire Hydrant RSJ Rolled Steel Joist 537980.000mE 206600.000mN 537920.000mE 537940.000mE Private gardens 537960.000mE 206600.000mN AR Assumed Route FBD Floor Board Direction SI Sign Post AV Air Valve FH Fire Hydrant SP Arch Spring Point Height BB Belisha Beacon FL Floor Level SV Stop Valve EL 5 The Mead BH Bore Hole FP Flag Pole SW Surface Water 27.42 Two storey rendered dwelling EL BL Bed Level FW Foul Water SY Stay 29.50 BO Bollard GG Gully Grate Tac Tactile Paving BrP Brace Post GV Gas Valve TC Telecom Cover Pier RL BS Bus Stop HH Head Height TH Trial Pit Indicative 31.40 NORTH WM Driveways & gardens BU Bush IC Inspection Cover THL Threshold Level 25.07 25.11 B/W Barbed Wire Fence IL Invert Level TL Traffic Light 25.00 BX Box (Utilities) I/R Iron Railings ToW Top of Wall Pier UK 12h, approx position Wall 0.5h C/B Close Board Fence KO Kerb Outlet TP Telegraph Pole CH Cill Height LP Lamp Post TV Cable TV Cover 25.07 CL Cover Level MH Manhole UB Universal Beam 24.96 Pier C/L Chain Link Fence MP Marker Post UC Unknown Cover C-Lev Ceiling Level NB Name Board UK Unknown Tree

Single white line Col Column OHL Overhead Line (approx) USB Under Side Beam 25.08 LP Pier C/P Chestnut Paling Fence Pan Panel Fence UTL Unable To Lift 25.03 C/B 1.1h Concrete Private gardens Conifer 8h CR Cable Riser PB Post Box VP Vent Pipe WM Private access 24.15 Dilpidated Concrete 24.13 Private land DC Drainage Channel PM Parking Meter WB Waste Bin 24.09 & Storage RL 6 The Mead 24.15 DH Door Head Height PO Post WH Weep Hole 31.90 Three storey brick dwelling 24.08 P/W 0.9h PO Green 24.19 DP Down Pipe P/R Post & Rail Fence WL Water Level 24.97 PO Concrete house Flat roof 24.07 24.97 31.73 DR Drain P/W Post & Wire Fence WM Water Meter Wall 0.2h foundations Driveways & gardens 24.09 Grass PO 24.10 24.08 EL Eaves Level P/Wall Partition Wall WO Wash Out PO PO 24.10 24.14 24.10 24.14 EL PO 24.13 EP Electric Pole RE Rodding Eye X.XX Floor to Ceiling Height PO Polytunnel PO Concrete Grass Single white line 29.57 frame 24.11 Pan. 1.8h 24.10 ER Earth Rod RL Ridge Level RL 24.05 C/B 0.7h Concrete POPolytunnel Asphalt EL 28.38 P/W 0.9h 24.06 24.19 24.08 frame ET EP+Transformer RP Reflector Post X.XX F/C Floor to False Ceiling Ht 27.46 PO 24.20 UK 3h RS Road Sign BU PO 24.09 PO FB Flower Bed 25.02 24.06 24.08 Shrubs 1.8h Concrete 24.13 Conc. base FBD Floor Board Direction RSD Roller Shutter Door Survey Control Station 24.08 24.95 24.25 EL Weed matting 24.91 C/B 1h UK 4h 24.08 Concrete Storage 25.01 27.26 24.12 Sapling for flower bed I/R 1.3h 24.25 DRAWING NOTE Single white line Top of fence 24.17 7 The Mead 26.42 24.07 24.33 Brick paved 24.05 24.12 EL OHL 24.08 24.98 Private access Two storey brick/rendered dwelling 24.13 26.70 Topographical Surveys 206580.000mN 24.89Dashed white line Unable to survey, 206580.000mN Bushes 2h PO BUs Pan 1.75h Dilpidated 24.07 24.16 WM OHL OHL BU 24.12 Trees are drawn to scale showing the average canopy spread. Descriptions and BU 24.29 UK 5h 24.12UK 6h Group 24.01 24.08 Concrete 24.89 Stumps Grass RL heights should be used as a guide only. 24.50 24.87 RL 24.08 28.17 31.32 24.13 24.82 Driveways & gardens Border 0.15h 24.13 24.08 Ret. wall 0.1h Brick outbuilding Pan 1.85h 24.20 24.11 Conc.base All building names, descriptions, number of storeys, construction type including PO ST05 24.12 PO Wall 0.65h 24.55 Pan 1.75h GG Concrete slabs EL FB 24.07 24.09 roof line details are indicative only and taken externally from ground level. 24.86 24.95 EL Concrete Concrete 24.14 26.89 DP 24.85 29.35 UK 6h 24.47 24.57 EL EL 24.53 26.95 FB 24.19 IC 100Ø 24.08 24.13 24.1324.09 All below ground details including drainage, voids and services have been 27.20 Border 0.1h CL 24.17 24.98 THL THL 24.17 Pan 1.65h 24.19 IL 23.84 24.15 identified from above ground and therefore all details relating to these features 24.76 24.77 C/B 1.2h ST04 24.18 Concrete Conc. 24.39 24.07 Concrete including; sizes, depth, description etc will be approximate only. All critical Gas pipe RL 24.16 Unable to survey, GG Wall remains Canopy FB 24.14 FB 27.46 Drainage Step up Bushes 4h 24.86 24.37 24.49 basin 24.11 BU dimensions and connections should be checked and verified prior to starting 24.91 24.19 24.19 24.92 Sag level EL RL EL 24.47 24.26 Step up 24.16 work. 30.10 27.70 Pan. 1.6h 24.38 31.54 26.84 24.33 24.18 8 The Mead Step up BU 24.93 24.46 IC 100Ø EL 24.20 24.21 24.14 Gravel/Concrete Two storey RL CL 24.59 24.84 24.84 EL 24.64 26.42 UK 5h Detail, services and features may not have been surveyed if obstructed or not Private access 24.39 rendered dwelling 27.20 IL 24.10 Dashed white line 24.33 29.69 Disused storage 24.62 24.17 reasonably visible at the time of the survey. ToW Approx. VP Brick garage 24.23 RL Conc. base C/B 1.2h 24.33 RL 26.47 24.32 24.84 31.57 RL Wall 27.02 BU 27.43 RL Canopy Pan. 1.9h Measured Building Surveys 24.93 24.94 24.82 WM 24.72 PO 24.32 THL RL 24.39 27.20 24.27 Private gardens 24.54 Disused 24.83 28.00 EL 24.83 24.91 24.21 29.71 Gas Cabinet EL EL Concrete EL 24.48 Measurements to internal walls are taken to the wall finishes at approx 1m Shrubs 1h 27.36 27.05 PO 29.75 24.87 Step up fades 24.28 above the floor level and the wall assumed to be vertical. 24.81 24.38 Steps 24.39 Grass & 24.28 24.43 24.41 Single white line exposed slabs Concrete 24.44 DR Concrete DP24.43 I/R 0.9h DP Concrete P/R 0.5h (above ground) Sag level Sag level 24.35 Cill heights are measured as floor to the cill and head heights are measured Single white line Grass SLOW C/B 0.65h 30.09 30.12 from cill to the top of window. Concrete fades Edging fades Pan. 1.85h 24.33 Brick setts Single white line 24.36 24.37 24.37 24.42 24.30 General 24.44 EL Nazeing New Road (B194) 24.56 24.92 Step up Concrete 29.77 24.66 9 The Mead The contractor must check and verify all site and building dimensions, levels, DrivewayConcrete Pan. 1.45h 24.89 Brick setts Two storey brick dwelling 24.81 24.36 EL utilities and drainage details and connections prior to commencing work. Any 24.82 24.78 24.48 29.73 errors or discrepancies must be notified to Survey Solutions immediately. Dashed white line 24.43 30mph Asphalt 24.73 RL EL 24.62 30.43 OHLs RL GG Asphalt 29.70 24.81 24.78 33.47 The accuracy of the digital data is the same as the plotting scale implies. All 206560.000mN 24.53 RL 206560.000mN GG WM 32.43 dimensions are in metres unless otherwise stated. 24.79 24.74 hedgeUnable levels, to survey, obstructed by wall EL LP 29.68 The survey control listed is only to be used for topographical surveys at the 24.79 24.90 Conifer hedge 4h EL 24.82 Wall 0.6h 24.89 29.73 OHL stated scale. All control must be checked and verified prior to use. KO

RL © Land Survey Solutions Limited holds the copyright to all the information GG Canopy 32.36 24.92 OHL ST01 24.79 contained within this document and their written consent must be obtained 24.91 24.89 24.80 before copying or using the data other than for the purpose it was originally 24.87 RL Sag level 33.42 supplied. 30.83 24.87 10 The Mead OHL 24.81 Dashed white line Two storey brick dwelling Do not scale from this drawing. 24.89 GG Brick paved Driveways & gardens Kerb line fades in to undergrowth 24.78 Private access Sag level Private gardens 30.58 EL Grass 29.66 RL REV DESCRIPTION DRAWN APPR DATE WMs 24.93 30.37 24.84 24.85 24.84

Asphalt

OHL 24.94 TP EL TC 29.49 Single white line 24.93 24.95 24.88 Wall 0.5h RL SURVEY CONTROL CO-ORDINATES Single white line OHL 31.35 STATIONS EASTINGS NORTHINGS LEVEL DESCRIPTION 11 The Mead Ipswich Coventry Yeovil Norwich Perth Nottingham Brentwood Two storey rendered dwelling ST01 537929.409 206557.000 24.888 Hilti nail Wall continues ST02 537946.363 206519.563 25.324 Hilti nail 25.01 24.99 Driveways & gardens Tel No: 0845 0405 969 Fax No: 0845 0405 970 Brick setts ST03 537911.374 206614.472 25.251 Hilti nail www.survey-solutions.co.uk [email protected] 206540.000mN ST04 537954.384 206573.687 24.561 Hilti206540.000mN nail 25.01 24.94 RL 24.91 31.37 ST05 537961.454 206576.578 24.123 Peg & Hilti nail LAND SURVEYING BUILDING SURVEYING UNDERGROUND SURVEYING Dashed white line WM Brick paved 24.93 Sag level 32.45 Private access 24.93 24.95 EL 24.96 31.40 24.92 24.99 PROJECT TITLE 25.02 EL 25.05 Grass 29.20 8 THE MEAD, NAZEING NEW ROAD, 25.07 25.00 SURVEY GRID AND LEVEL DATUM BROXBOURNE, HERTFORDSHIRE, EN10 6SS.

Single white line Asphalt Brick setts 25.07 DRAWING DETAIL Dashed white line The coordinate system established for this survey is related to Ordnance Survey (OS) national grid at a single point using Smartnet, then orientated to grid north TOPOGRAPHICAL SURVEY TC with a scale factor of 1.000. 25.11 The level datum established for this survey is related to Ordnance Survey (OS) CLIENT SCALE 25.13 using GPS Smartnet. 25.06 HALLIDAY WEST LIMITED 1:200 To avoid discrepancies any coordinated data used in conjunction with this survey must be derived directly from this control data. SURVEYOR SURVEY DATE CHECKED BY APPROVED BY DWG STATUS

25.13 25.07 PMB 07.01.2019 DWB TJF FINAL 537980.000mE 537960.000mE 537940.000mE 537920.000mE DRAWING NUMBER REVISION ISSUE DATE 23480se-01 08.01.2019

©Land Survey Solutions Limited 01/01/2010 Original Sheet Size A2H

Flood Risk Assessment Replacement Dwelling – 8 The Mead, Nazeing New Road, Broxbourne, Herts

Appendix B

Proposed Development Layout

Flood Risk Assessment Replacement Dwelling – 8 The Mead, Nazeing New Road, Broxbourne, Herts

Appendix C

Product 4 Environment Agency Flood Data

Flood Map for Planning centred on: 8 The Mead, Nazeing New Road, EN10 6SS - 14/03/2019 - HNL 118820 AS

Environment Agency Alchemy,

Lee Lee Navigation (Lower) Bessemer Road, Welwyn Garden City, Hertfordshire, Spital Brook

Nazeing Drain AL7 1HE Lee Navigation (Lower)

Lee Navigation (Lower) 0 150 300 600 Metres Lee Navigation (Lower) Lee Navigation (Lower) Legend Lee Navigation (Lower) Main Rivers Site location Lee Navigation (Lower) Flood Map for Planning Flood Storage Area

Lee Navigation (Lower) Areas Benefiting from Flood Defences Flood Zone 3

Broxbourne Ditch Flood Zone 2

Nazeing Drain

Flood Map for Planning (assuming no defences)

Nazeing Brook Flood Zone 3 shows the area that could be affected by flooding: Nazeing Drain - from the sea with a 1 in 200 or greater chance of happening each year - or from a river with a 1 in 100 or greater

Lichen Brook chance of happening each year.

Flood Zone 2 shows the extent of an extreme flood from rivers or the sea with up to a 1 in 1000 chance of occurring each year.

Broxbourne Ditch Produced by: Partnerships & Strategic Overview, This map is based upon Ordnance Survey Material with the permission of Ordnance Survey on behalf of the controller of Her Majesty's Stationery Office Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution or civil proceedings. Environment Agency 100024198, 2018 Hertfordshire & North London Detailed FRA centred on: 8 The Mead, Nazeing New Road, EN10 6SS - 14/03/2019 - HNL 118820 AS

Lee Navigation (Lower)

Environment Agency

Lee Navigation (Lower) Alchemy, Bessemer Road, Welwyn Garden City, Hertfordshire, AL7 1HE

0 50 100 200 Lee Navigation (Lower) Nazeing Drain Metres Legend Main Rivers Site location Defended Flood Outlines Nazeing Drain 1 in 2 (50%) Defended 1 in 5 (20%) Defended 1 in 10 (10%) Defended 1 in 20 (5%) Defended

The data in this map has been extracted from the River Lee 2D Flood Mapping Study (CH2M Hill, 2014). This was a catchment-scale mapping study, so may need local updates for site-specific decisions. It should be noted that it was not created to produce flood levels for specific development sites within the catchment. Modelled outlines take into account catchment-wide defences. Nazeing Drain Updates to model M03 were undertaken by the Lower Hall Sluices Operational Scenario Modelling (CH2M Hill, 2014), and updates to model M04 by the Lower Lee Tributaries Economic Appraisal project (CH2M Hill, 2015). https://www.gov.uk/guidance/flood-risk-assessments- climate-change-allowances Produced by: Partnerships & Strategic Overview, This map is based upon Ordnance Survey Material with the permission of Ordnance Survey on behalf of the controller of Her Majesty's Stationery Office Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution or civil proceedings. Environment Agency 100024198, 2018 Hertfordshire & North London Detailed FRA centred on: 8 The Mead, Nazeing New Road, EN10 6SS - 14/03/2019 - HNL 118820 AS

Lee Navigation (Lower)

Environment Agency

Lee Navigation (Lower) Alchemy, Bessemer Road, Welwyn Garden City, Hertfordshire, AL7 1HE

0 50 100 200 Lee Navigation (Lower) Nazeing Drain Metres Legend Main Rivers Site location Defended Flood Outlines Nazeing Drain 1 in 50 (2%) Defended 1 in 75 (1.33%) Defended 1 in 100 (1%) Defended 1 in 100+20% (*CC) Defended

Lee Navigation (Lower)

Environment Agency

Lee Navigation (Lower) Alchemy, Bessemer Road, Welwyn Garden City, Hertfordshire, AL7 1HE

0 50 100 200 Lee Navigation (Lower) Nazeing Drain Metres Legend Main Rivers Site location Defended Flood Outlines Nazeing Drain 1 in 200 (0.5%) Defended 1 in 1000 (0.1%) Defended

!( WGD2

Lee Navigation (Lower)

WGD1 Environment Agency !( Lee Navigation (Lower) Alchemy, Bessemer Road, Welwyn Garden City, Hertfordshire, AL7 1HE

WGA56 0 50 100 200 Lee Navigation (Lower) !( Nazeing Drain Metres

WGA55 !( Legend Main Rivers NM21Usd !( Site location NM21U !( Nazeing Drain 1D Node Results !( Node Results NM21d !( 1.065 !( 1.064 !( 1.063!( 1.062!( 1.058 1.06 !( 1.057!(!( !( !( !( 1.061 The data in this map has been extracted from the River Lee !( 1.059 2D Flood Mapping Study (CH2M Hill, 2014). 01.057d 1.056 This was a catchment-scale mapping study, so may need local !( updates for site-specific decisions. It should be noted that it was 1.055 NM19 not created to produce flood levels for specific development sites !( !( within the catchment. Modelled outlines take into account catchment-wide defences. 1.054 Nazeing Drain Updates to model M03 were undertaken by the Lower Hall !( Sluices Operational Scenario Modelling (CH2M Hill, 2014), and updates to model M04 by the Lower Lee Tributaries 1.053 Economic Appraisal project (CH2M Hill, 2015). !( NM18 !( 1.052 !( 1.051 !( 1.05 !( 1.049 NM17 https://www.gov.uk/guidance/flood-risk-assessments- !( !( climate-change-allowances 1.048 !( Produced by: Partnerships & Strategic Overview, This map is based upon Ordnance Survey Material with the permission of Ordnance Survey on behalf of the controller of Her Majesty's Stationery Office Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution or civil proceedings. Environment Agency 100024198, 2018 Hertfordshire & North London Environment Agency ref: HNL 118820 AS

The data in this map has been extracted from the River Lee 2D Modelling study (CH2M Hill, 2014).

Flood risk data requests including an allowance for climate change will be based on the 1 in 100 flood plus 20% allowance for climate change, unless otherwise stated. You should refer to ‘Flood risk assessments: climate change allowances’ to check if this allowance is still appropriate for the type of development you are proposing and its location. You may need to undertake further assessment of future flood risk using different allowances to ensure your assessment of future flood risk is based on best available evidence. https://www.gov.uk/guidance/flood-risk-assessments-climate-change-allowances

Caution: This model has been designed for catchmentwide flood risk mapping. It should be notedthat it was not created to produce flood levels for specific development sites within the catchment. Modelled outlines take into account catchment wide defences.

All flood levels are given in metres Above Ordnance Datum (mAOD) All flows are given in cubic metres per second (cumecs)

MODELLED FLOOD LEVEL Return Period Node Label Easting Northing Watercourse 2 yr 5 yr 10 yr 20 yr 50 yr 75 yr 100 yr 100 yr + 20% 200 yr 1000 yr 1.048 537922 206256 Nazeing Drain 23.85 23.9 23.93 23.95 23.96 23.97 24 24.72 24.32 24.9 1.049 537923 206276 Nazeing Drain 23.85 23.9 23.93 23.95 23.96 23.97 24 24.72 24.33 24.9 NM17 538211 206276 Nazeing Drain 22.95 23.25 23.36 23.57 23.81 23.96 24.24 24.65 24.43 24.98 1.05 537933 206309 Nazeing Drain 23.86 23.9 23.93 23.95 23.97 23.97 24 24.72 24.33 24.91 1.051 537942 206333 Nazeing Drain 23.86 23.91 23.93 23.96 23.97 23.97 24 24.72 24.33 24.91 1.052 537945 206356 Nazeing Drain 23.86 23.91 23.93 23.96 23.97 23.98 24.01 24.73 24.34 24.92 NM18 538246 206379 Nazeing Drain 22.96 23.27 23.38 23.59 23.83 23.97 24.25 24.66 24.45 25 1.053 537955 206384 Nazeing Drain 23.86 23.91 23.93 23.96 23.97 23.98 24.01 24.73 24.34 24.92 1.054 537958 206410 Nazeing Drain 23.86 23.91 23.94 23.96 23.97 23.98 24.01 24.73 24.34 24.92 1.055 537965 206436 Nazeing Drain 23.86 23.91 23.94 23.96 23.97 23.98 24.01 24.73 24.34 24.93 NM19 538264 206441 Nazeing Drain 22.96 23.28 23.39 23.61 23.84 23.99 24.26 24.67 24.45 25 1.056 537969 206451 Nazeing Drain 23.86 23.91 23.94 23.96 23.98 23.98 24.01 24.73 24.34 24.93 01.057d 537969 206456 Nazeing Drain 23.89 23.95 23.97 23.99 24 24.01 24.03 24.73 24.34 24.91 1.057 537981 206471 Nazeing Drain 23.91 23.96 23.99 24.01 24.02 24.03 24.05 24.79 24.38 25.16 1.061 538069 206474 Nazeing Drain 24 24.06 24.07 24.09 24.1 24.11 24.14 24.87 24.46 25.22 1.06 538043 206475 Nazeing Drain 23.99 24.05 24.06 24.09 24.1 24.1 24.13 24.87 24.46 25.22 1.059 538023 206476 Nazeing Drain 23.99 24.05 24.06 24.08 24.09 24.1 24.13 24.86 24.45 25.22 01.058d 537988 206478 Nazeing Drain 23.98 24.03 24.05 24.07 24.08 24.08 24.11 24.81 24.42 25.2 1.058 537998 206479 Nazeing Drain 23.99 24.05 24.06 24.08 24.09 24.1 24.13 24.86 24.45 25.22 1.062 538094 206483 Nazeing Drain 24.01 24.07 24.08 24.1 24.11 24.12 24.15 24.87 24.46 25.22 1.063 538108 206492 Nazeing Drain 24.01 24.07 24.09 24.11 24.12 24.13 24.16 24.87 24.46 25.22 01.064d 538121 206501 Nazeing Drain 24.01 24.07 24.09 24.11 24.12 24.13 24.16 24.87 24.46 25.22 1.064 538127 206508 Nazeing Drain 24.16 24.31 24.35 24.41 24.45 24.46 24.56 24.87 24.69 25.23 1.065 538130 206523 Nazeing Drain 24.16 24.31 24.35 24.41 24.45 24.46 24.56 24.87 24.69 25.23 NM21d 538260 206542 Nazeing Drain 22.98 23.31 23.42 23.64 23.87 24.02 24.3 24.72 24.49 25.11 NM21U 538249 206595 Nazeing Drain 24.02 24.15 24.18 24.24 24.29 24.35 24.49 24.82 24.64 25.18 NM21Usd 538248 206610 Nazeing Drain 24.02 24.15 24.18 24.24 24.29 24.35 24.49 24.82 24.64 25.18 WGA55 537693 206651 Lee Navigation (Lower) 24.23 24.26 24.28 24.33 24.55 24.59 24.7 24.9 24.82 25.09 WGA56 537825 206701 Lee Navigation (Lower) 24.25 24.28 24.3 24.35 24.59 24.64 24.74 24.96 24.87 25.16 WGD1 537908 206801 Lee Navigation (Lower) 24.26 24.29 24.31 24.36 24.61 24.66 24.77 24.99 24.9 25.21 WGD2 538007 206886 Lee Navigation (Lower) 24.31 24.34 24.36 24.41 24.66 24.71 24.82 25.05 24.95 25.26 MODELLED FLOWS Return Period Node Label Easting Northing Watercourse 2 yr 5 yr 10 yr 20 yr 50 yr 75 yr 100 yr 100 yr + 20% 200 yr 1000 yr 1.048 537922 206256 Nazeing Drain 0.31 0.39 0.42 0.45 0.47 0.48 0.52 1.83 1.09 3.65 1.049 537923 206276 Nazeing Drain 0.31 0.39 0.42 0.45 0.47 0.48 0.52 1.83 1.09 3.65 NM17 538211 206276 Nazeing Drain 40.87 69.27 77.76 91.81 99.62 104.14 112.52 134.31 121.48 161.25 1.05 537933 206309 Nazeing Drain 0.31 0.39 0.42 0.45 0.47 0.48 0.52 1.84 1.09 3.65 1.051 537942 206333 Nazeing Drain 0.31 0.39 0.42 0.45 0.47 0.48 0.52 1.84 1.09 3.65 1.052 537945 206356 Nazeing Drain 0.31 0.39 0.42 0.45 0.47 0.48 0.52 1.84 1.09 3.65 NM18 538246 206379 Nazeing Drain 40.84 69.13 77.75 91.81 99.66 104.13 112.53 134.33 121.43 161.24 1.053 537955 206384 Nazeing Drain 0.31 0.39 0.42 0.45 0.47 0.48 0.52 1.84 1.09 3.65 1.054 537958 206410 Nazeing Drain 0.31 0.39 0.42 0.45 0.47 0.48 0.52 1.84 1.09 3.65 1.055 537965 206436 Nazeing Drain 0.31 0.39 0.42 0.45 0.47 0.48 0.52 1.84 1.09 3.65 NM19 538264 206441 Nazeing Drain 40.79 69.21 77.74 91.82 99.64 104.13 112.57 134.39 121.48 161.24 1.056 537969 206451 Nazeing Drain 0.31 0.39 0.42 0.45 0.47 0.48 0.52 1.84 1.09 3.65 01.057d 537969 206456 Nazeing Drain 0.31 0.4 0.42 0.45 0.47 0.48 0.52 1.84 1.09 3.65 1.057 537981 206471 Nazeing Drain 0.31 0.4 0.42 0.45 0.47 0.48 0.52 1.84 1.09 3.65 1.061 538069 206474 Nazeing Drain 0.31 0.4 0.42 0.45 0.47 0.48 0.52 0.55 0.55 0.66 1.06 538043 206475 Nazeing Drain 0.31 0.4 0.42 0.45 0.47 0.48 0.52 0.55 0.55 1 1.059 538023 206476 Nazeing Drain 0.31 0.4 0.42 0.45 0.47 0.48 0.52 1.85 1.1 2.48 01.058d 537988 206478 Nazeing Drain 0.31 0.4 0.42 0.45 0.47 0.48 0.52 1.84 1.1 2.2 1.058 537998 206479 Nazeing Drain 0.31 0.4 0.42 0.45 0.47 0.48 0.52 1.84 1.1 2.2 1.062 538094 206483 Nazeing Drain 0.31 0.4 0.42 0.45 0.47 0.48 0.52 0.55 0.55 0.55 1.063 538108 206492 Nazeing Drain 0.31 0.4 0.42 0.45 0.47 0.48 0.52 0.55 0.55 0.56 01.064d 538121 206501 Nazeing Drain 0.31 0.4 0.42 0.45 0.47 0.48 0.52 0.55 0.55 0.56 1.064 538127 206508 Nazeing Drain 0.31 0.4 0.42 0.45 0.47 0.48 0.52 0.55 0.55 0.56 1.065 538130 206523 Nazeing Drain 0.31 0.4 0.42 0.45 0.47 0.48 0.52 0.54 0.54 0.54 NM21d 538260 206542 Nazeing Drain 40.72 69.36 77.72 91.82 99.67 104.13 112.59 134.43 121.51 161.26 NM21U 538249 206595 Nazeing Drain 40.72 69.36 77.72 91.82 99.67 104.13 112.59 134.43 121.51 161.26 NM21Usd 538248 206610 Nazeing Drain 40.72 69.37 77.72 91.82 99.69 104.13 112.65 134.42 121.55 161.28 WGA55 537693 206651 Lee Navigation (Lower) 16.39 17.45 18.18 20.39 29.63 31.34 35.88 46.06 41.4 58.26 WGA56 537825 206701 Lee Navigation (Lower) 16.4 17.45 18.18 20.39 29.63 31.34 35.88 46.06 41.4 60.49 WGD1 537908 206801 Lee Navigation (Lower) 16.41 17.46 18.18 20.39 29.63 31.34 35.88 46.56 41.44 55.63 WGD2 538007 206886 Lee Navigation (Lower) 16.42 17.46 18.18 20.39 29.64 31.34 35.88 46.58 41.45 56.61 Detailed FRA centred on: 8 The Mead, Nazeing New Road, EN10 6SS - 14/03/2019 - HNL 118820 AS

Environment Agency Alchemy, Bessemer Road, Welwyn Garden City, Hertfordshire, AL7 1HE

0 15 30 60

Metres Legend Main Rivers Site location 2D Node Results: Heights 1 in 2 (50%) Defended M02

24.16 24.16 24.16

24.16 24.16

24.16 24.16 24.16 The data in this map has been extracted from the River Lee 2D Flood Mapping Study (CH2M Hill, 2014). This was a catchment-scale mapping study, so may need local 24.16 24.16 24.16 updates for site-specific decisions. It should be noted that it was not created to produce flood levels for specific development sites within the catchment. Modelled outlines take into account catchment-wide defences. 24.16 24.16 Updates to model M03 were undertaken by the Lower Hall Sluices Operational Scenario Modelling (CH2M Hill, 2014), and updates to model M04 by the Lower Lee Tributaries Economic Appraisal project (CH2M Hill, 2015). Nazeing Drain https://www.gov.uk/guidance/flood-risk-assessments- climate-change-allowances Produced by: Partnerships & Strategic Overview, This map is based upon Ordnance Survey Material with the permission of Ordnance Survey on behalf of the controller of Her Majesty's Stationery Office Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution or civil proceedings. Environment Agency 100024198, 2018 Hertfordshire & North London Detailed FRA centred on: 8 The Mead, Nazeing New Road, EN10 6SS - 14/03/2019 - HNL 118820 AS

Environment Agency Alchemy, Bessemer Road, Welwyn Garden City, Hertfordshire, AL7 1HE

0 15 30 60

Metres Legend Main Rivers Site location 2D Node Results: Heights 24.31 1 in 5 (20%) Defended M02

24.31 24.31 24.31

24.31 24.31 24.31 The data in this map has been extracted from the River Lee 2D Flood Mapping Study (CH2M Hill, 2014). This was a catchment-scale mapping study, so may need local 24.31 24.31 24.31 24.31 updates for site-specific decisions. It should be noted that it was not created to produce flood levels for specific development sites within the catchment. Modelled outlines take into account catchment-wide defences. 24.31 24.31 24.31 24.31 Updates to model M03 were undertaken by the Lower Hall Sluices Operational Scenario Modelling (CH2M Hill, 2014), and updates to model M04 by the Lower Lee Tributaries 24.31 24.31 24.32 Economic Appraisal project (CH2M Hill, 2015). Nazeing Drain https://www.gov.uk/guidance/flood-risk-assessments- climate-change-allowances Produced by: Partnerships & Strategic Overview, This map is based upon Ordnance Survey Material with the permission of Ordnance Survey on behalf of the controller of Her Majesty's Stationery Office Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution or civil proceedings. Environment Agency 100024198, 2018 Hertfordshire & North London Detailed FRA centred on: 8 The Mead, Nazeing New Road, EN10 6SS - 14/03/2019 - HNL 118820 AS

Environment Agency Alchemy, Bessemer Road, Welwyn Garden City, Hertfordshire, AL7 1HE

0 15 30 60

Metres Legend Main Rivers Site location 2D Node Results: Heights 24.35 1 in 10 (10%) Defended M02

24.35 24.35 24.35

24.35 24.35 24.35 The data in this map has been extracted from the River Lee 2D Flood Mapping Study (CH2M Hill, 2014). This was a catchment-scale mapping study, so may need local 24.35 24.35 24.35 24.35 updates for site-specific decisions. It should be noted that it was not created to produce flood levels for specific development sites within the catchment. Modelled outlines take into account catchment-wide defences. 24.35 24.35 24.35 24.35 Updates to model M03 were undertaken by the Lower Hall Sluices Operational Scenario Modelling (CH2M Hill, 2014), and updates to model M04 by the Lower Lee Tributaries 24.35 24.35 24.35 Economic Appraisal project (CH2M Hill, 2015). Nazeing Drain https://www.gov.uk/guidance/flood-risk-assessments- climate-change-allowances Produced by: Partnerships & Strategic Overview, This map is based upon Ordnance Survey Material with the permission of Ordnance Survey on behalf of the controller of Her Majesty's Stationery Office Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution or civil proceedings. Environment Agency 100024198, 2018 Hertfordshire & North London Detailed FRA centred on: 8 The Mead, Nazeing New Road, EN10 6SS - 14/03/2019 - HNL 118820 AS

Environment Agency Alchemy, Bessemer Road, Welwyn Garden City, Hertfordshire, AL7 1HE

0 15 30 60

Metres Legend Main Rivers Site location 2D Node Results: Heights 24.42 24.42 1 in 20 (5%) Defended M02

24.42 24.42 24.42

24.42 24.42 24.42 24.41 The data in this map has been extracted from the River Lee 2D Flood Mapping Study (CH2M Hill, 2014). This was a catchment-scale mapping study, so may need local 24.42 24.42 24.41 24.41 updates for site-specific decisions. It should be noted that it was not created to produce flood levels for specific development sites within the catchment. Modelled outlines take into account catchment-wide defences. 24.42 24.42 24.41 24.41 Updates to model M03 were undertaken by the Lower Hall Sluices Operational Scenario Modelling (CH2M Hill, 2014), and updates to model M04 by the Lower Lee Tributaries 24.42 24.42 24.42 Economic Appraisal project (CH2M Hill, 2015). Nazeing Drain https://www.gov.uk/guidance/flood-risk-assessments- climate-change-allowances Produced by: Partnerships & Strategic Overview, This map is based upon Ordnance Survey Material with the permission of Ordnance Survey on behalf of the controller of Her Majesty's Stationery Office Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution or civil proceedings. Environment Agency 100024198, 2018 Hertfordshire & North London Detailed FRA centred on: 8 The Mead, Nazeing New Road, EN10 6SS - 14/03/2019 - HNL 118820 AS

Environment Agency Alchemy, Bessemer Road, Welwyn Garden City, Hertfordshire, AL7 1HE

0 15 30 60

Metres Legend Main Rivers Site location 2D Node Results: Heights 24.45 24.45 24.45 1 in 50 (2%) Defended M02

24.45 24.45 24.45

24.45 24.45 24.45 24.45 The data in this map has been extracted from the River Lee 2D Flood Mapping Study (CH2M Hill, 2014). This was a catchment-scale mapping study, so may need local 24.45 24.45 24.45 24.45 updates for site-specific decisions. It should be noted that it was not created to produce flood levels for specific development sites within the catchment. Modelled outlines take into account catchment-wide defences. 24.45 24.45 24.45 24.45 Updates to model M03 were undertaken by the Lower Hall Sluices Operational Scenario Modelling (CH2M Hill, 2014), and updates to model M04 by the Lower Lee Tributaries 24.45 24.45 24.45 24.45 Economic Appraisal project (CH2M Hill, 2015). Nazeing Drain https://www.gov.uk/guidance/flood-risk-assessments- climate-change-allowances Produced by: Partnerships & Strategic Overview, This map is based upon Ordnance Survey Material with the permission of Ordnance Survey on behalf of the controller of Her Majesty's Stationery Office Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution or civil proceedings. Environment Agency 100024198, 2018 Hertfordshire & North London Detailed FRA centred on: 8 The Mead, Nazeing New Road, EN10 6SS - 14/03/2019 - HNL 118820 AS

Environment Agency Alchemy, Bessemer Road, Welwyn Garden City, Hertfordshire, AL7 1HE

0 15 30 60

Metres Legend Main Rivers Site location 2D Node Results: Heights 24.47 24.47 24.47 1 in 75 (1.33%) Defended M02

24.47 24.47 24.47

24.47 24.47 24.47 24.47 24.47 The data in this map has been extracted from the River Lee 2D Flood Mapping Study (CH2M Hill, 2014). This was a catchment-scale mapping study, so may need local 24.47 24.47 24.47 24.47 24.47 updates for site-specific decisions. It should be noted that it was not created to produce flood levels for specific development sites within the catchment. Modelled outlines take into account catchment-wide defences. 24.47 24.47 24.47 24.47 Updates to model M03 were undertaken by the Lower Hall Sluices Operational Scenario Modelling (CH2M Hill, 2014), and updates to model M04 by the Lower Lee Tributaries 24.47 24.47 24.47 24.47 Economic Appraisal project (CH2M Hill, 2015). Nazeing Drain https://www.gov.uk/guidance/flood-risk-assessments- climate-change-allowances Produced by: Partnerships & Strategic Overview, This map is based upon Ordnance Survey Material with the permission of Ordnance Survey on behalf of the controller of Her Majesty's Stationery Office Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution or civil proceedings. Environment Agency 100024198, 2018 Hertfordshire & North London Detailed FRA centred on: 8 The Mead, Nazeing New Road, EN10 6SS - 14/03/2019 - HNL 118820 AS

Environment Agency Alchemy, Bessemer Road, Welwyn Garden City, Hertfordshire, AL7 1HE

0 15 30 60

Metres Legend Main Rivers Site location 2D Node Results: Heights 24.56 24.56 24.56 1 in 100 (1%) Defended M02

24.56 24.56 24.56 24.56

24.56 24.56 24.56

24.56 24.56 24.56 24.56 24.56 The data in this map has been extracted from the River Lee 2D Flood Mapping Study (CH2M Hill, 2014). This was a catchment-scale mapping study, so may need local 24.56 24.56 24.56 24.56 24.56 updates for site-specific decisions. It should be noted that it was not created to produce flood levels for specific development sites within the catchment. Modelled outlines take into account catchment-wide defences. 24.56 24.56 24.56 24.56 Updates to model M03 were undertaken by the Lower Hall Sluices Operational Scenario Modelling (CH2M Hill, 2014), and updates to model M04 by the Lower Lee Tributaries 24.56 24.56 24.56 24.56 Economic Appraisal project (CH2M Hill, 2015). Nazeing Drain https://www.gov.uk/guidance/flood-risk-assessments- climate-change-allowances Produced by: Partnerships & Strategic Overview, This map is based upon Ordnance Survey Material with the permission of Ordnance Survey on behalf of the controller of Her Majesty's Stationery Office Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution or civil proceedings. Environment Agency 100024198, 2018 Hertfordshire & North London Detailed FRA centred on: 8 The Mead, Nazeing New Road, EN10 6SS - 14/03/2019 - HNL 118820 AS

24.93 24.89 24.89 24.89 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87

24.82 24.89 24.89 24.88 24.88 24.88 24.88 24.88 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87

24.89 24.88 24.88 24.88 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87

24.88 24.88 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 Environment Agency Alchemy, Bessemer Road, 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 Welwyn Garden City, Hertfordshire, 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 AL7 1HE

24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 0 15 30 60

24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 Metres 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 Legend

24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 Main Rivers Site location 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 2D Node Results: Heights 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 1 in 100+20% (*CC) Defended M02

24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87

24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87

24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 The data in this map has been extracted from the River Lee 2D Flood Mapping Study (CH2M Hill, 2014). This was a catchment-scale mapping study, so may need local 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 updates for site-specific decisions. It should be noted that it was not created to produce flood levels for specific development sites within the catchment. Modelled outlines take into account catchment-wide defences. 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 Updates to model M03 were undertaken by the Lower Hall Sluices Operational Scenario Modelling (CH2M Hill, 2014), and updates to model M04 by the Lower Lee Tributaries 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 24.87 Economic Appraisal project (CH2M Hill, 2015). 24.87 24.87 24.87 24.87 24.87 24.87 24.86 24.87 Nazeing Drain 24.86 24.86 https://www.gov.uk/guidance/flood-risk-assessments- 24.81 24.81 climate-change-allowances Produced by: Partnerships & Strategic Overview, This map is based upon Ordnance Survey Material with the permission of Ordnance Survey on behalf of the controller of Her Majesty's Stationery Office Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution or civil proceedings. Environment Agency 100024198, 2018 Hertfordshire & North London Detailed FRA centred on: 8 The Mead, Nazeing New Road, EN10 6SS - 14/03/2019 - HNL 118820 AS

24.77 24.78 24.75 24.75 24.66 24.66 24.66 24.67

24.77 24.77 24.77 24.77 24.77 24.74 24.75 24.75 24.75 24.73 24.66 24.66 24.66 24.66 24.66 24.67 24.67 24.67

24.77 24.77 24.77 24.75 24.74 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.67 24.67 24.67 24.67 24.67

24.77 24.77 24.66 24.68 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.67 24.67 24.67 24.67 24.67 24.67 24.67 Environment Agency Alchemy, Bessemer Road, 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.67 24.67 24.67 24.67 24.67 24.67 24.67 Welwyn Garden City, Hertfordshire, 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.67 24.67 24.67 24.67 24.67 24.67 24.67 AL7 1HE

24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.67 24.67 24.67 24.67 24.67 24.67 0 15 30 60

24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.67 24.67 24.67 24.67 24.67 24.67 Metres 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.67 24.67 24.67 24.67 24.68 Legend

24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.67 24.67 24.67 24.68 24.69 Main Rivers Site location 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.68 24.69 24.69 2D Node Results: Heights 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.69 24.69 24.69 1 in 200 (0.2%) Defended M02

24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.68 24.69 24.69 24.69 24.69

24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.67 24.69 24.69 24.69

24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.68 24.69 24.69 24.69 24.69 The data in this map has been extracted from the River Lee 2D Flood Mapping Study (CH2M Hill, 2014). This was a catchment-scale mapping study, so may need local 24.66 24.66 24.66 24.66 24.66 24.65 24.66 24.63 24.66 24.69 24.69 24.69 24.69 24.69 updates for site-specific decisions. It should be noted that it was not created to produce flood levels for specific development sites within the catchment. Modelled outlines take into account catchment-wide defences. 24.66 24.66 24.6 24.62 24.63 24.58 24.64 24.69 24.69 24.69 24.69 Updates to model M03 were undertaken by the Lower Hall Sluices Operational Scenario Modelling (CH2M Hill, 2014), and updates to model M04 by the Lower Lee Tributaries 24.66 24.66 24.59 24.59 24.56 24.55 24.62 24.69 24.69 24.69 24.69 Economic Appraisal project (CH2M Hill, 2015). 24.56 24.56 24.49 24.58 Nazeing Drain https://www.gov.uk/guidance/flood-risk-assessments- climate-change-allowances Produced by: Partnerships & Strategic Overview, This map is based upon Ordnance Survey Material with the permission of Ordnance Survey on behalf of the controller of Her Majesty's Stationery Office Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution or civil proceedings. Environment Agency 100024198, 2018 Hertfordshire & North London Detailed FRA centred on: 8 The Mead, Nazeing New Road, EN10 6SS - 14/03/2019 - HNL 118820 AS

25.15 25.2 25.2 25.2 25.2 25.21 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.23

25.15 25.19 25.2 25.2 25.2 25.2 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.23

25.2 25.21 25.21 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22

25.21 25.21 25.21 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 Environment Agency Alchemy, Bessemer Road, 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 Welwyn Garden City, Hertfordshire, 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 AL7 1HE

25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 0 15 30 60

25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 Metres 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 Legend

25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 Main Rivers Site location 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.23 2D Node Results: Heights 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.23 25.23 1 in 1000 (0.1%) Defended M02

25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.23 25.23 25.23

25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.23 25.23 25.23 25.23

25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.23 25.23 25.23 25.23 The data in this map has been extracted from the River Lee 2D Flood Mapping Study (CH2M Hill, 2014). This was a catchment-scale mapping study, so may need local 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.23 25.23 25.23 updates for site-specific decisions. It should be noted that it was not created to produce flood levels for specific development sites within the catchment. Modelled outlines take into account catchment-wide defences. 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.23 25.23 25.23 Updates to model M03 were undertaken by the Lower Hall Sluices Operational Scenario Modelling (CH2M Hill, 2014), and updates to model M04 by the Lower Lee Tributaries 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.23 25.23 25.23 Economic Appraisal project (CH2M Hill, 2015). 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.21 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.22 Nazeing Drain 25.2 25.22 25.22 25.22 25.22 25.22 25.22 25.22 25.2 https://www.gov.uk/guidance/flood-risk-assessments- 25.21 25.21 25.22 25.22 25.22 25.22 25.22 25.22 climate-change-allowances Produced by: Partnerships & Strategic Overview, This map is based upon Ordnance Survey Material with the permission of Ordnance Survey on behalf of the controller of Her Majesty's Stationery Office Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution or civil proceedings. Environment Agency 100024198, 2018 Hertfordshire & North London Historic Flood Map centred on: 8 The Mead, Nazeing New Road, EN10 6SS - 14/03/2019 - HNL 118820 AS

Environment Agency Alchemy,

Lee Lee Navigation (Lower) Bessemer Road, Welwyn Garden City, Hertfordshire, Spital Brook

Nazeing Drain AL7 1HE Lee Navigation (Lower)

Lee Navigation (Lower) 0 150 300 600 Metres Lee Navigation (Lower) Lee Navigation (Lower) Legend Lee Navigation (Lower) Main Rivers Site location Lee Navigation (Lower) Flood Event Outlines 2000

Lee Navigation (Lower) 1990 1983

Broxbourne Ditch 1947

Nazeing Drain

Nazeing Brook The historic flood event outlines are based on a combination of anecdotal evidence, Environment Agency staff observations and Nazeing Drain survey. Our historic flood event outlines do not provide a definitive record of flooding.

Lichen Brook It is possible that there will be an absence of datain places where we have not been able to record the extent of flooding. It is also possible for errors occur in the digitisation of historic records of flooding.

Broxbourne Ditch Produced by: Partnerships & Strategic Overview, This map is based upon Ordnance Survey Material with the permission of Ordnance Survey on behalf of the controller of Her Majesty's Stationery Office Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution or civil proceedings. Environment Agency 100024198, 2018 Hertfordshire & North London Structures and Defences centred on: 8 The Mead, Nazeing New Road, EN10 6SS - 14/03/2019 - HNL 118820 AS

Lee Navigation (Lower)

Environment Agency

Lee Navigation (Lower) Alchemy, Bessemer Road, Welwyn Garden City, Hertfordshire, AL7 1HE

0 50 100 200 Lee Navigation (Lower) Nazeing Drain Metres Legend Main Rivers Site location NAFRA_STRUCTURE Nazeing Drain ASSET_ID 202300 453163 489004 489005 NAFRA_DEFENCE ASSET_ID

Nazeing Drain 7706 7707 7708 7709

The following information on defences has been extracted from the Asset Information Management System (AIMS)

Produced by: Partnerships & Strategic Overview, This map is based upon Ordnance Survey Material with the permission of Ordnance Survey on behalf of the controller of Her Majesty's Stationery Office Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution or civil proceedings. Environment Agency 100024198, 2018 Hertfordshire & North London Structures and Defences centred on: 8 The Mead, Nazeing New Road, EN10 6SS - 14/03/2019 - HNL 118820 AS

Lee Navigation (Lower)

Environment Agency

Lee Navigation (Lower) Alchemy, Bessemer Road, Welwyn Garden City, Hertfordshire, AL7 1HE

0 50 100 200 Lee Navigation (Lower) Nazeing Drain Metres Legend Main Rivers Site location

Nazeing Drain NAFRA_DEFENCE ASSET_ID 12842 13057 41772 91678 93304

Nazeing Drain

The following information on defences has been extracted from the Asset Information Management System (AIMS)

Lee Navigation (Lower)

Environment Agency

Lee Navigation (Lower) Alchemy, Bessemer Road, Welwyn Garden City, Hertfordshire, AL7 1HE

0 50 100 200 Lee Navigation (Lower) Nazeing Drain Metres Legend Main Rivers Site location

Nazeing Drain NAFRA_DEFENCE ASSET_ID 93305 93306 101982 101983 470203

Nazeing Drain

The following information on defences has been extracted from the Asset Information Management System (AIMS)

Defences Condition of Design Standard of Downstream Upstream Asset ID Asset Type Asset Protection Asset Comment Asset Description Defences (1=Good, protection (years) Crest Level Crest Level 5 = Poor)

Natural vegetated earth 7706 high_ground fluvial Natural Bank 5 No Data No Data 2 defence.

Natural vegetated earth 7707 high_ground fluvial Natural bank 5 No Data No Data 2 defence.

SEE LAKE DEFENCE 7708 high_ground fluvial Natural Bank 100 24.73 24.73 3 LINE DETAILS.

SEE LAKE DEFENCE 7709 high_ground fluvial Natural Bank 5 24.88 24.88 3 LINE DETAILS.

Vegetated earth embankment with prolific 12842 high_ground fluvial Flood Relief Channel 1a RB 50 23.22 24.73 3 self-set vegetation. Steel sheet piling to mid-section

Ex gravel pit, now used for amenity and flood flows. Nazeing Mead South Lake 13057 high_ground fluvial 5 No Data No Data 3 Natural vegetated earth (A.K.A) Rusheymead Lake banks.

Vegetated earth embankment with prolific 41772 high_ground fluvial Flood Relief Channel 1a LB 50 23.26 24.88 3 self-set vegetation. Steel sheet piling to mid-section

Natural vegetated earth 91678 high_ground fluvial defence. Brickwork Natural Bank 2 24.98 25.76 2 revetment at Lock house.

Natural vegetated earth 93304 high_ground fluvial defence. No maintenance Natural Bank 25 24.63 24.87 3 appears to exist.

Predominately pre-cast concrete piles with some 93305 high_ground fluvial Lined Channel 100 24.82 24.94 3 sections of masonry revetment.

Natural vegetated earth 93306 high_ground fluvial defence. No maintenance Natural Bank 2 24.82 No Data 2 appears to exist.

Insitu r/concrete lined lock and approaches. 101982 high_ground fluvial Lined Channel 5 24.2 26.05 3 Revetment for moorings at u/s end.

Channel side lined concrete through lock with 101983 high_ground fluvial Lined concrete channel. 5 24.73 25.96 2 Pre-cast concrete piles for remainder.

This asset does not provide Embankment to stop 470203 embankment fluvial any flood protection, vehicles being driven onto No Data No Data No Data 3 security and safety purpose EA land Structures

Condition of Asset ID Asset Type Asset Protection Asset Comment Asset Description Structures (1=Good, 5 = Poor)

In-situ concrete lock chamber with steel gates. SLUICE GATE Carthegena 202300 control_gate fluvial Footbridge to D/S 2 Lock end.Length along watercourse 45m.

One of two manually operated penstock sluices, located either side of the central outlet channel. These enable upstream 1 of 2 penstock gates in the 453163 control_gate fluvial levels to be lowered for 3 Nazeing Labyrinth Weir maintenance purposes and provide a sweetening flow to the LFRC during periods of dry weather. O&M Manual 53/21.

The marker boom comprises of floating polystyrene/concrete booms attached to timer piles placed at intervals Nazeing Labyrinth Weir 489004 screen fluvial 3 across the channel. Its marker boom purpose is to identify the safety hazzard created by the weir. O&M Manual 53/21.

One of two manually operated penstock sluices, located either side of the central outlet channel. These enable upstream 1 of 2 penstock gates in the 489005 control_gate fluvial levels to be lowered for 3 Nazeing Labyrinth Weir maintenance purposes and provide a sweetening flow to the LFRC during periods of dry weather. O&M Manual 53/21.

Flood Risk Assessment Replacement Dwelling – 8 The Mead, Nazeing New Road, Broxbourne, Herts

Appendix D

Environment Agency – Climate Change Allowance/Procedure

Environment Agency OFFICIAL

Flood risk assessments: Climate change allowances Application of the allowances and local considerations East Anglia; Essex, Norfolk, Suffolk, Cambridgeshire and Bedfordshire

1) The climate change allowances

The National Planning Practice Guidance refers planners, developers and advisors to the Environment Agency guidance on considering climate change in Flood Risk Assessments (FRAs). This guidance was updated in February 2016 and is available on Gov.uk. The guidance can be used for planning applications, local plans, neighbourhood plans and other projects. It provides climate change allowances for peak river flow, peak rainfall, sea level rise, wind speed and wave height. The guidance provides a range of allowances to assess fluvial flooding, rather than a single national allowance. It advises on what allowances to use for assessment based on vulnerability classification, flood zone and development lifetime.

2) Assessment of climate change impacts on fluvial flooding

Table A below indicates the level of technical assessment of climate change impacts on fluvial flooding appropriate for new developments depending on their scale and location. This should be used as a guide only. Ultimately, the agreed approach should be based on expert local knowledge of flood risk conditions, local sensitivities and other influences. For these reasons we recommend that applicants and / or their consultants should contact the Environment Agency at the pre- planning application stage to confirm the assessment approach, on a case by case basis. Table A defines three possible approaches to account for flood risk impacts due to climate change, in new development proposals: . Basic: Developer can add an allowance to the 'design flood' (i.e. 1% annual probability) peak levels to account for potential climate change impacts. The allowance should be derived and agreed locally by Environment Agency teams. . Intermediate: Developer can use existing modelled flood and flow data to construct a stage- discharge rating curve, which can be used to interpolate a flood level based on the required peak flow allowance to apply to the ‘design flood’ flow. . Detailed: Perform detailed hydraulic modelling, through either re-running Environment Agency hydraulic models (if available) or construction of a new model by the developer.

Table A – Indicative guide to assessment approach

VULNERABILITY FLOOD DEVELOPMENT TYPE

CLASSIFICATION ZONE MINOR SMALL-MAJOR LARGE-MAJOR Zone 2 Detailed ESSENTIAL Zone 3a Detailed INFRASTRUCTURE Zone 3b Detailed Zone 2 Intermediate/ Basic Intermediate/ Basic Detailed HIGHLY Zone 3a Not appropriate development VULNERABLE Zone 3b Not appropriate development Zone 2 Basic Basic Intermediate/ Basic MORE Zone 3a Intermediate/ Basic Detailed Detailed VULNERABLE Zone 3b Not appropriate development Zone 2 Basic Basic Intermediate/ Basic LESS Zone 3a Basic Basic Detailed VULNERABLE Zone 3b Not appropriate development Zone 2 None WATER Zone 3a Intermediate/ Basic COMPATIBLE Zone 3b Detailed Note: Where the table states 'not appropriate development', this is in line with national planning policy. If in exceptional circumstances such development types are proposed in these locations, we would expect a detailed modelling approach to be used.

Environment Agency October 2016 Environment Agency OFFICIAL

NOTES:

The assessment approach should be agreed with the Environment Agency as part of pre- planning application discussions to avoid abortive work.

3) Specific local considerations

Where the Environment Agency and the applicant and / or their consultant has agreed that a ‘basic´ level of assessment is appropriate the figures in Table B below can be used as a precautionary allowance for potential climate change impacts on peak ‘design’ (i.e. 1% annual probability) fluvial flood level rather than undertaking detailed modelling.

Table B – Local precautionary allowances for potential climate change impacts

Essex, Norfolk and Suffolk

Hydraulic Model (Watercourse) Central Higher Central Upper Blackwater & Brain - 500mm 600mm 900mm Blackwater between TL7520925623 and TL7820324314 Brain between TL7373323312 and TL7683821321 Chelmer - between TL6872107082 and 350mm 450mm 750mm TL7161609422 and TL7436306592 Colne (Model Extent) 450mm 600mm 950mm Gipping – Downstream of Needham Market 400mm 500mm 850mm Gipping – Needham Market and upstream including 200mm 250mm 400mm Somersham W/C Norwich Downstream of TG2332009072 450mm 600mm 950mm Norwich Upstream of TG2332009072 600mm 800mm 1200mm Wensum (Model Extent) 400mm 500mm 800mm Yare (Model Extent) 200mm 250mm 450mm Broads (2008 Model Extent) Please use the current 1 in 1000 (0.1%) annual Bure and Ant (2012 Model Extent) probability including climate change allowance For other main rivers, tributaries and ordinary watercourses that are not stated above, basic allowances have not been calculated. In this instance you can either:  If flow data is available you can request this Other main rivers, tributaries and ordinary data from us and can conduct an watercourses intermediate assessment yourself  Or alternatively, you can choose to undertake a Detailed Assessment and “perform detailed hydraulic modelling, through either re-running our hydraulic models (if available) or constructing a new model

Environment Agency October 2016 Environment Agency OFFICIAL

Cambridgeshire and Bedfordshire

Watercourse / Model Central Higher Central Upper End Alconbury Brook 600mm 700mm 900mm River Kym Lower Ouse (Model 700mm 800mm 1100mm Extent) Mid Ouse (Cold 700mm 800mm 1100mm Brayfield to Bromham – between SP9156852223 and TL0132950919) Mid Ouse (East of 700mm 850mm 1200mm Bedford to Roxton – between TL0791848903 and TL1618854543) River Hiz and River 400mm 450mm 550mm Purwell River Ivel 500mm 600mm 750mm Pix Brook 450mm 500mm 600mm Potton Brook 500mm 600mm 700mm River Cam and 600mm 700mm 950mm tributaries (excluding the Cam Lodes and the Slade System) Great Barford (ordinary 500mm 550mm 650mm watercourses) Bromham (ordinary 550mm 650mm 850mm watercourse)

NOTES:

Urban areas excluded from the ‘basic’ approach: St Ives, Holywell, Godmanchester, Swavesey, Over, Bedford, Newport Pagnell, Buckingham and Leighton Buzzard. More detailed assessment of climate change allowances will need to be undertaken in these locations.

Use of these allowances will only be accepted after discussion with the Environment Agency.

Environment Agency October 2016 Environment Agency OFFICIAL

4) Fluvial food risk mitigation

For planning consultations where we are a statutory consultee and our Flood risk standing advice does not apply we use the following benchmarks to inform flood risk mitigation for different vulnerability classifications. These are a guide only. We strongly recommend you contact us at the pre-planning application stage to confirm this on a case by case basis. For planning consultations where we are not a statutory consultee or our Flood risk Standing advice applies we recommend local planning authorities and developers use these benchmarks but we do not expect to be consulted.

 For development classed as ‘Essential Infrastructure’ our benchmark for flood risk mitigation is for it to be designed to the ‘upper end’ climate change allowance for the epoch that most closely represents the lifetime of the development, including decommissioning.

 For highly vulnerable or more vulnerable developments in flood zone 2, the ‘central’ climate change allowance is our minimum benchmark for flood risk mitigation, and in flood zone 3 the ‘higher central’ climate change allowance is our minimum benchmark for flood risk mitigation. In sensitive locations it may be necessary to use the higher central (in flood zone 2) and the upper end allowance (in flood zone 3).

 For water compatible or less vulnerable development (e.g. commercial), the ‘central’ climate change allowance for the epoch that most closely represents the lifetime of the development is our minimum benchmark for flood risk mitigation. In sensitive locations it may be necessary to use the higher central (particularly in flood zone 3) to inform built in resilience.

For a visual representation of the above, please see Tables 1 and 2 overleaf.

5) Development in Tidal Areas There is no change to the way we respond to sites affected solely by tidal flood risk as the sea level allowances are unchanged.

6) Our Service

Non-chargeable service

We will give a free opinion on:

• What climate change allowance to apply to a particular development type

• Which technical approach is suitable in the FRA

Chargeable service:

• Review of climate change impacts using intermediate and detailed technical approaches (i.e. modelling review)

• Assessment and review of proposals for managed adaptation.

Environment Agency October 2016 Environment Agency OFFICIAL

Table 1 peak river flow allowances by river basin district (use 1961 to 1990 baseline) River Allowance category Total potential Total potential Total basin change change potential district anticipated for anticipated for change ‘2020s’ ‘2050s’ anticipated (2015 to 39) (2040 to 2069) for ‘2080s’ (2070 to 2115) Anglian Upper end 25% 35% 65% Higher central 15% 20% 35% Central 10% 15% 25% Thames Upper end 25% 35% 70% Higher central 15% 25% 35% Central 10% 15% 25%

Table 2: Using peak river flow allowances for flood risk assessments Flood Essential Highly More Less Water Zone Infrastructure Vulnerable Vulnerable Vulnerable Compatible 2 higher central higher central central and central none of the and upper end and upper end higher central allowance allowances allowances allowances allowances 3a upper end X higher central central and central allowance and upper end higher central allowance 3b upper end X X X central allowance allowance X – Development should not be permitted If (exceptionally) development is considered appropriate when not in accordance with flood zone vulnerability categories, then it would be appropriate to use the upper end allowance.

There may be circumstances where local evidence supports the use of other data or allowances. Where you think this is the case we may want to check this data and how you propose to use it.

Environment Agency October 2016

Flood Risk Assessment Replacement Dwelling – 8 The Mead, Nazeing New Road, Broxbourne, Herts

Appendix E

Climate Change Flood Levels – Stage / Flow Calculations

Stage - Discharge Calculations (Nazeing Drain)

Site: 8 The Mead, Nazeing New Road, Broxbourne, Hertfordshire Client: Mr. C Drake Job No. BLI.2019.13 Date: 02.04.2019

Naveing Drain Fluvial Model Data (Node 1.064) Storm Event Stage (m AOD) Flow (Cumecs) 2 24.16 0.31 5 24.31 0.40 10 24.35 0.42 20 24.41 0.45 50 24.45 0.47 75 24.46 0.48 100 24.56 0.52 200 24.69 0.55 1000 25.23 0.56

Stage - Discharge Relationship

25.50

y = 1.3262ln(x) + 25.556 25.00

24.50 Stage (m AOD) (m Stage

24.00

23.50 0.25 0.35 0.45 0.55 0.65 0.75

Flow (Cumec)

Stage - Discharge Relationship Stage = 1.3262In(Flow) + 25.556 Storm Event Flow (Cumecs) Climate Change (%) Flow + CC Stage 100 0.52 25 0.65 24.98 100 0.52 35 0.70 25.08 100 0.52 65 0.86 25.36 Stage - Discharge Calculations (Lee Navigation Lower)

Site: 8 The Mead, Nazeing New Road, Broxbourne, Hertfordshire Client: Mr. C Drake Job No. BLI.2019.13 Date: 02.04.2019

Lee Navigation (Lower) Fluvial Model Data (Node WGA56) Storm Event Stage (m AOD) Flow (Cumecs) 2 24.25 16.40 5 24.28 17.45 10 24.30 18.18 20 24.35 20.39 50 24.59 29.63 75 24.64 31.34 100 24.74 35.88 200 24.87 41.40 1000 25.16 60.49

Stage - Discharge Relationship

25.50

y = 0.6918ln(x) + 22.284 25.00

24.50 Stage (m AOD) (m Stage

24.00

23.50 15.00 25.00 35.00 45.00 55.00 65.00

Flow (Cumec)

Stage - Discharge Relationship Stage = 0.6918In(Flow) + 22.284 Storm Event Flow (Cumecs) Climate Change (%) Flow + CC Stage 100 35.88 25 44.85 24.92 100 35.88 35 48.44 24.97 100 35.88 65 59.20 25.11

Flood Risk Assessment Replacement Dwelling – 8 The Mead, Nazeing New Road, Broxbourne, Herts

Appendix F

Epping Forest District Council – Level 2 SFRA Extract

EB913

Strategic Flood Risk Assessment – Site Assessments Epping Forest District Council

Site Assessment Summary – NAZE.E3 Bridge Works and Glassworks

Allocation Reference: Address: Area (ha): Proposed Use: Vulnerability Classification: NAZE.E3 Nazeing New Road, Broxbourne, EN10 6SY 2.12 Employment Less Vulnerable

Fluvial Flood Risk

Flood Zone 1: Flood Zone 2: Flood Zone 3a: Flood Zone 3b: - 19% 81% -

Flood Zones and Flood Defences To the west of the site flows a complex network of channels that form the Lower Lee Navigation, Flood Relief Channel and Nazeing Drain. The majority of the site is identified as Flood Zone 3a (81%), with the central part classified as Flood Zone 2 (19%). The site is shown to benefit from the presence of flood defences, namely the management of flood water through the flood relief channels. The flood risk is therefore residual, in the event of failure of the flood defence system. The site is not shown to be located within Flood Zone 3b Functional Floodplain. However the areas to the east of the site, and that adjacent to the Lower Lee Navigation to the west, are defined as such and are therefore identified as land where water has to be stored in time of flood.

(Contains Ordnance Survey data © Crown copyright and database right 2017. Contains Environment Agency data © Environment Agency and database right 2017). Figure A Flood Map for Planning (Rivers and Sea) Historic Records The Environment Agency Historic Flood Map records fluvial flooding in this area during the flood event of March 1947. There have been no reported historical fluvial flooding events within this site, with the only recorded event within 1km of the site having been reported approximately 0.8km south east of the site. This occurred due to the rising of water within the Nazeing Drain. Climate Change In accordance with the PPG, for Less Vulnerable development proposed in Flood Zone 3, the Central (25%) and Higher Central (35%) climate change allowances should be considered. Analysis of the stage-discharge relationship along the Lee Navigation identifies that the 0.1% AEP (1 in 1000 year) flood level for the undefended model scenario, which corresponds to Flood Zone 2, is greater than the flood levels calculated for the Central and Higher Central climate change allowances. The outline of Flood Zone 2 is therefore appropriate to use as a proxy when considering the impact of climate change on flood risk for this site and surrounding area.

AECOM Project Number: 60561951 AECOM 57 EB913

Strategic Flood Risk Assessment – Site Assessments Epping Forest District Council

Site Assessment Summary – NAZE.E3 Bridge Works and Glassworks

25.4

y = 0.0217x + 23.924 25.2

24.8

24.6

Modelled Flood Events (Defended Scenarios)

Peak River Stage (mAOD) 24.4 Interpolated Flood Event Central 25% Interpolated Flood Event Higher Central 35% 24.2 0.1% AEP Flood Level Undefended (Flood Zone 2)

24 0 10 20 30 40 50 60 70 80 Peak Discharge (m)

Figure B Stage-Discharge relationship at Node WGA56 of the River Lee Modelling Study 2014

Surface Water Flood Risk

Risk of Flooding from Surface Water (RoFSW) The RoFSW mapping indicates that the majority of the site is not at risk from surface water flooding. However, a small region (approximately 5m 2) located in the west of the site lies within a region of low surface water flood risk.

(Contains Ordnance Survey data © Crown copyright and database right 2017. Contains Environment Agency data © Environment Agency and database right 2017). Figure C Risk of Flooding from Surface Water (RoFSW) Geology: The underlying geology is Lambeth Group, comprising gravels, sands, silts and clays. This bedrock geology is overlain by alluvium. In contrast to the bedrock geology, which is typically not very permeable, the superficial deposits contains sufficient, saturated permeable material to yield significant

AECOM Project Number: 60561951 AECOM 58 EB913

Strategic Flood Risk Assessment – Site Assessments Epping Forest District Council

Site Assessment Summary – NAZE.E3 Bridge Works and Glassworks quantities of water to wells and springs, reducing the build-up of surface water across the ground surface, as illustrated by the RoFSW mapping.

Groundwater Flood Risk

The AStGWF mapping (also presented in the Level 1 SFRA, Appendix B Figure 9) shows that the site is located within a 1km square of which >=75% is susceptible to groundwater emergence. The risk of groundwater flooding in this area is therefore generally considered to be high. This will need to be confirmed during site investigation survey. Historic Records: There have been three reported groundwater flooding incidents approximately 10m from the south western boundary of the site, all groundwater seepages occurred in 2007.

Other Sources

The Environment Agency ‘Risk of Flooding from Reservoirs’ mapping indicates that the site is not at risk of flooding in the event of a failure of a reservoir.

Site Specific Recommendations

Fluvial Modelling As part of a site specific FRA for this site at the planning application stage, additional hydraulic modelling will be required comparing a range of probability events to determine the impact of climate change on the risk of flooding at this location. The 1% AEP (1 in 100 year) flood event including the Central (25%) and Higher Central (35%) allowance are of relevance to the proposed Less Vulnerable development. The modelling will also need to address any potential impact the proposed development may have on flood risk to the surrounding area.

Site Layout and Design The drainage strategy for the site must be considered early in the site planning process to ensure adequate inclusion of SuDS, taking care to consider SuDS features in accordance with the hierarchy of SuDS (i.e. considering infiltration measures first wherever possible). The suitability of locating proposed surface water drainage features within the fluvial floodplain, as they may be rendered ineffective during times of fluvial flooding.

Finished Floor Levels Given the proposed use is Less Vulnerable there is no requirement to raise finished floor levels.

Floodplain Compensation Land raising and any built development should be avoided within Flood Zone 3. Where alterations to the floodplain are proposed, compensatory floodplain storage will need to be provided on a level-for-level and volume-for-volume basis with respect to the 1% AEP (1 in 100 year) design event, including an allowance for climate change. The land used to provide compensation storage will need to be in hydraulic connectivity with the existing floodplain, but not already part of the floodplain.

Access / Egress It will be necessary to consider whether safe dry access to and from the site can be achieved. The site is located between two watercourses and corresponding areas of Flood Zone 3a. The main access to the site is provided along Nazeing New Road, which passes over the watercourses.

Safe Refuge Given the proximity to the watercourses and the potential for the access / egress route to be affected by flooding, internal access should be provided to upper floors (first floor or a mezzanine level) to provide safe refuge in a flood event. An area of safe refuge should be located above the 1% AEP fluvial flood level including an allowance for climate change. This refuge will have to be permanent and accessible to all occupants and users of the site. Emergency Planning The site is shown to be within an Environment Agency Flood Warning Area for the Lower River Lee at Hoddesdon and Cheshunt. Site occupants should register to receive the warning service. Due to the proximity of the site to the watercourse, Flood Response Plans should be prepared by residents of the site.

Resilience Measures A number of flood resistance and resilience measures can also be implemented into new developments to mitigate potential flooding. Guidance on resilience measures can be found in the ‘Improving the Flood Performance of New Buildings, Flood Resilient Construction’ published by The Department for Communities and Local Government (CLG).

AECOM Project Number: 60561951 AECOM 59 EB913

Strategic Flood Risk Assessment – Site Assessments Epping Forest District Council

Site Assessment Summary – NAZE.E3 Bridge Works and Glassworks LLFA Consultation It is recommended that potential developers contact Essex CC as the LLFA for further information prior to taking forward site specific plans.

Summary

The proposed development is classified as Less Vulnerable and therefore does not require the formal application of the Exception Test in accordance with the NPPF. The site specific recommendations set out above should be considered as part of a site specific FRA for the site at the planning application stage to ensure that future development on the site is safe and does not increase flood risk to the site or surrounding area.

AECOM Project Number: 60561951 AECOM 60