land off mancot lane, deeside...jba project manager howard keeble 2nd floor mersey bank house...

DFJ-JBAU-XX-XX-RP-Z-0001-A3-C01-Flood_Consequence_Assessment.docx i

Land off Mancot Lane,

Deeside Flood Consequence Assessment

May 2020

www.jbaconsulting.com

Wales & West Housing

Tŷ Draig

St Davids Park

EWLOE

Flintshire

CH5 3DT

http://www.jbaconsulting.com/

DFJ-JBAU-XX-XX-RP-Z-0001-A3-C01-Flood_Consequence_Assessment.docx i

JBA Project Manager

Howard Keeble

2nd Floor

Mersey Bank House

WARRINGTON

Cheshire

UNITED KINGDOM

WA1 1WA

Revision History

Status Revision Ref/Date

Date Originated Checked Approved

S3 P01 01/05/2020

J Landells-

Molloy

Assistant

Engineer

H Keeble

Technical

Director

H Keeble

Technical

Director

A3 C01 03/06/2020

J Landells-

Molloy

Assistant Engineer

H Keeble

Technical

Director

H Keeble

Technical

Director

Contract

This report describes work commissioned by Emma Hancock, on behalf of Wales & West

Housing, by an email dated 31st January 2020. Joseph Landells-Molloy of JBA Consulting

carried out this work.

Prepared by .................................. Joseph Landells-Molloy MEng

Assistant Engineer

Reviewed by .................................. Howard Keeble MPhil BEng BSc CEng CEnv

CSci CWEM MICE MCIWEM MCMI IMaPS

Technical Director

Purpose

This document has been prepared as a Draft Report for Wales & West Housing. JBA

Consulting accepts no responsibility or liability for any use that is made of this document

other than by the Client for the purposes for which it was originally commissioned and

prepared.

JBA Consulting has no liability regarding the use of this report except to Wales & West

Housing.

Copyright

© Jeremy Benn Associates Limited 2020.

DFJ-JBAU-XX-XX-RP-Z-0001-A3-C01-Flood_Consequence_Assessment.docx ii

Carbon Footprint

A printed copy of the main text in this document will result in a carbon footprint of 132g if

100% post-consumer recycled paper is used and 168g if primary-source paper is used.

These figures assume the report is printed in black and white on A4 paper and in duplex.

JBA is aiming to reduce its per capita carbon emissions.

DFJ-JBAU-XX-XX-RP-Z-0001-A3-C01-Flood_Consequence_Assessment.docx iii

Contents

1 Introduction 1 1.1 Overview 1 1.2 Scope 1 2 Development Location and Description 1 2.1 Location 1 2.2 Description 2 2.3 Topography 3 3 Review of Flood Risk 4 3.1 Fluvial & Tidal 4 3.1.1 Development Advice Map (DAM) 4 3.1.2 Planning Requirements 5 3.1.3 Breach Scenario 7 3.2 Surface Water 10 3.3 Groundwater 10 4 Safe Site Access and Egress 11 5 Outline Drainage Strategy 12 5.1 Sustainable Drainage Systems Standards for Wales 12 5.2 Surface Water Management 13 5.3 SuDS Maintenance 14 5.4 Water Quality 14 6 Foul Drainage 15 7 Conclusions 16 8 Appendices 17

A 2020 Ground Investigation Report 18

B Drainage Layout 19

C Micro Drainage Modelling Results 20

D Greenfield Runoff Rates 21

E Welsh Water Sewer Plan 1

F Welsh Water Response 1

DFJ-JBAU-XX-XX-RP-Z-0001-A3-C01-Flood_Consequence_Assessment.docx iv

List of Figures

Figure 2-1 - Wider Location Plan 2 Figure 2-2 - Proposed Development Layout 3 Figure 2-3 - Site Topography 4 Figure 3-1 - NRW Development Advice Map (DAM) 5 Figure 3-2 - Summary of TAN15 Policy Requirements (Section 9, TAN15 2004) 6 Figure 3-3 - 2017 Flintshire SFCA Modelled Breach Locations 7 Figure 3-4 - Climate Change 0.5% AEP Tidal Breach Depth Map 8 Figure 3-5 - Climate Change 0.1% AEP Tidal Breach Depth Map 9 Figure 3-6 – NRW’s updated Flood Map for Surface Water 10 Figure 4-1 - Primary Egress Route (fluvial/tidal sources) 11

List of Tables

Table 2-1 - Site Description 2 Table 5-1 - Standard S1 Discussion 12 Table 5-2 - Calculated Greenfield Runoff Rates 13 Table 5-3 - Required Volumes of Attenuation 14

DFJ-JBAU-XX-XX-RP-Z-0001-A3-C01-Flood_Consequence_Assessment.docx

1

1 Introduction

1.1 Overview

This Flood Consequence Assessment (FCA) has been prepared following instruction from

Emma Hancock, on behalf of Wales & West Housing, by an email dated 31st January 2020.

It aims to demonstrate that the proposed development of 24 residential units at Land off

Mancot Lane is compliant with the requirements of both Technical Advice Note 15:

Development and Flood Risk1 (TAN15) and Sustainable Drainage Systems Standards for

Wales2.

1.2 Scope

This FCA has been undertaken with consideration of TAN15 and is based on a desktop

review of available information, including tidal River Dee breach mapping from the 2017

Flintshire Strategic Flood Consequence Assessment (SFCA).

In addition to reviewing flood risk at the site, an Outline Drainage Strategy has been

undertaken to quantify attenuation requirements and inform preparation of the separate

SuDS Approving Body (SAB) Pre-Application Form.

2 Development Location and Description

2.1 Location

Land off Mancot Lane is located in Mancot, Deeside as indicated by the red line boundary in

Figure 2-1. It is bounded by existing residential development to the south and by Mancot

Lane to the west which is proposed for site access. Pentre Drain South West is located to

the north of the site and adjacent to Chester Road (B5129), it converges with Queensferry

Drain and flows northwards before bending eastwards, parallel to A494 and outfalling into

the tidal River Dee.

It is noted that Flintshire SAB could require discharge to a surface water body (Pentre Drain

South West) in accordance with National SuDS Standards for Wales, therefore, third party

land ownership issues must be confirmed and considered prior to SAB pre-application.

Based on a review of Google Earth, there is one field between areas of site ownership and

Pentre Drain South West, equivalent to a horizontal distance of between 125 and 150

metres depending on the alignment of potential conveyance infrastructure through third-

party land.

It is noted that Pentre Drain South West and Queensferry Drain are NRW Main Rivers.

————————————————————————————————————————————

1 Technical advice note (TAN) 15: development and flood risk | GOV.WALES 2 https://gov.wales/sites/default/files/publications/2019-06/statutory-national-standards-for-sustainable-

drainage-systems.pdf

https://gov.wales/technical-advice-note-tan-15-development-and-flood-risk

https://gov.wales/sites/default/files/publications/2019-06/statutory-national-standards-for-sustainable-drainage-systems.pdf



2

Figure 2-1 - Wider Location Plan

2.2 Description

Table 2-1 - Site Description

Site Name Land off Mancot Lane

Site Area (ha) 1.55

Existing Land Use Greenfield

Proposed Land Use Residential

Proposed Vulnerability Classification Highly Vulnerable

OS-NGR SJ 322 674

Local Planning Authority (LPA) Flintshire County Council


3

Figure 2-2 - Proposed Development Layout

It is understood that the developer is proposing to erect 24 residential units (see Figure

2-2), eight of which are bungalows (single-storey). In accordance with TAN15, this

constitutes a change of use of the land from greenfield to highly vulnerable development

(residential). It is understood that northern areas of the site are to accommodate a

children’s play area and associated footpaths, else this area will remain as open green

space.

It is proposed that SuDS attenuation features are also located within this area.

2.3 Topography

In accordance with National SuDS Standards for Wales, if infiltration drainage has been

appropriately discounted, Flintshire SAB require that discharge to watercourse be

considered. LiDAR indicates that the area falls away to the north east towards the tidal

River Dee (see Figure 2-3), however, the gradient of topography shallows within the red

line boundary which would likely have implications for gravity discharge of surface water

runoff to Pentre Drain South West.

In Figure 2-3, the spot level of 5.53 metres Above Ordnance Datum (mAOD) indicates

existing ground levels within northern areas of the site where attenuation features are to

be located.

Associated ground levels for Pentre Drain South West are between 5.22mAOD and

5.10mAOD.

Comparison of site levels and Drain levels indicates a difference in levels of approximately

0.43m, equivalent to a gradient of 1 in 470.

To maintain greenfield runoff rates surface water attenuation basins will be required. It is

highlighted that attenuation features would need to be excavated to provide any


4

meaningful storage volume. Therefore, it is not practical for proposed development to

discharge via gravity to Pentre Drain South West. A pumped solution would be required.

As a result, discharge to ground or sewer should be considered.

Figure 2-3 - Site Topography

3 Review of Flood Risk

3.1 Fluvial & Tidal

3.1.1 Development Advice Map (DAM)

The Natural Resources Wales’ (NRW) Development Advice Map (DAM) is presented in

Figure 3-1 and indicates that six of the proposed residential are located within DAM Zone

C1 and a further four in DAM Zone B. DAM Zone maps are based on Natural Resources

Wales extreme flood outlines (Zone C) and the British Geological Survey 10k Superficial

Geology data (Zone B). It is noted that NRW’s Development Advice Map is based on the

modelled undefended scenario.

DAM Zone C1 represents "areas of the floodplain which are developed and served by

significant infrastructure, including flood defences" and covers 51% of the total site area.

Areas in Mancot benefit from the tidal River Dee flood defences as defined in Figure 2-1,

therefore, could be at risk from a potential tidal breach scenario.

It is noted that the remaining 14 residential units are located within DAM Zone A and

“considered to be at little or no risk of fluvial or tidal/coastal flooding” hence the

justification test is not applicable and there is no need to consider flood risk further in this

location.


5

Figure 3-1 - NRW Development Advice Map (DAM)

3.1.2 Planning Requirements

In accordance with TAN15, new development should be directed away from zone C and

towards suitable land in Zone A, otherwise to Zone B, where river or coastal flooding will be

less of an issue.

However, in Zone C, the tests outlined in sections 6 and 7 (of TAN15) will be applied,

recognising, however, that highly vulnerable development and Emergency Services in Zone

C2 should not be permitted.

It is recognised that a preferred solution would be for residential units to be located within

areas of land defined as Zone A (i.e. considered to be at little or no risk of fluvial or

tidal/coastal flooding) only, however, this would have negative implications for residential

yields. However, given that the River Dee is tidally influenced at this location, land raising

to elevate all residential units above flood level should be considered.

In accordance with TAN15, for highly vulnerable development in DAM Zone C1, the

planning requirements defined in Figure 3-2 (an extract from TAN15) must be

demonstrated for proposals to be considered acceptable in terms of flood risk.


6

Figure 3-2 - Summary of TAN15 Policy Requirements (Section 9, TAN15

2004)


7

3.1.3 Breach Scenario

Based on the 2017 Flintshire SFCA, the site is not considered to be at risk from the

modelled breach scenarios (of the River Dee flood defences) during present day tidal flood

events at the locations defined in Figure 3-3 below. Flintshire County Council and NRW

specified potential breach locations to be modelled at locations near to some of Flintshire

County Council’s concept development sites and at areas that are considered to be more

prone to risk, such as outfall structures. It is noted that no further breach modelling has

been undertaken as part of this FCA.

Figure 3-3 - 2017 Flintshire SFCA Modelled Breach Locations


8

In relation to flood risk at Land off Mancot Lane, Figure 3-4 indicates that the proposed

development is not at risk of a tidal breach event at Queensferry during the climate change

0.5% Annual Exceedance Probability (AEP) event. Predicted flooding within the wider site

boundary, including areas to the north and a highly localised area of the new, dedicated

highway is to a depth of less than 300 mm.

Figure 3-4 - Climate Change 0.5% AEP Tidal Breach Depth Map

It is noted that the most extreme modelled flood event was the climate change 0.1% AEP

which is presented in Figure 3-5 and, under this event, six properties are predicted to flood

to a depth less than 300 mm based on existing ground levels. In this event, the maximum

flood level within residential areas of the development is predicted to be 5.96 mAOD. It is

recommended to set finished floor levels (FFLs) above this level including allowance for

freeboard, assuming to be 200mm at this stage. It is noted that development is usually

raised above surrounding ground levels and this shallow flooding could be accommodated

within kerb and property threshold levels.


9

Figure 3-5 - Climate Change 0.1% AEP Tidal Breach Depth Map


10

3.2 Surface Water

NRW’s updated Flood Map for Surface Water (uFMSW) is presented in Figure 3-6 and

indicates that the proposed development is at low risk if surface water flooding, however,

there is an area in the 3.33% (high risk) and 1% AEP (medium risk) of surface water

ponding in the northern area of the site which is to remain free from significant

hardstanding development. It is noted that surface attenuation features could be sized

with additional capacity to accommodate this area of ponding. It is understood that

northern areas will accommodate a children’s play area and associated footpaths, and

surface attenuation features. It is noted that the children’s play area should be designed to

take surface water risks into account.

SuDS and attenuation features should be formed outside of this mapped surface water

flood extent to prevent inundation and interaction with off site impacts.

Figure 3-6 – NRW’s updated Flood Map for Surface Water

3.3 Groundwater

Based on a 2020 ground investigation report for this proposed development (refer to

Report No. 19WWH002/GI), shallow groundwater was encountered across the site. In trial

pits of depths varying between 1.40 and 1.60 metres below ground level (mbgl), there was

observed slow groundwater ingress at the base of each pit rising to up to 1.00 mbgl.

In Section 16.3 (Control of Groundwater), the report recommends that further site

investigation will be required if sewer construction is proposed at a greater depth than

those of the trial pits. Whilst this does not constitute a risk to development levels, it will

influence soakaway potential and the potential depth of surface water attenuation facilities.


11

4 Safe Site Access and Egress

Based on the proposed development layout, the majority of properties are located on a

new, dedicated highway off Mancot Lane, with six properties accessed directly off Mancot

Lane itself.

2017 SFCA modelled breach scenarios indicate that the site can be safely accessed and

egressed via Mancot Lane heading south-west during all flood events, however, the

proposed new highway within the development is predicted to flood to depths less than 300

mm in the climate change 0.1% AEP event based on existing ground levels. It could be

necessary to land raise both properties and road levels above this predicted flood extent to

enable safe access and egress during all flood events.

Based on the uFMFSW, Mancot Lane is at medium risk of flooding, equivalent to the 1%

AEP event, to the north and south of the site, however, this flooding is largely contained

within kerb lines, therefore, depths of flooding on the road are likely to be relatively shallow

and pavements are unlikely to flood. In the event of an emergency, this depth of flooding

is unlikely to prevent emergency access to the properties.

It is, therefore, recommended that a safe access and egress route following Mancot Lane to

the south as defined in Figure 4-1 below is proposed during a tidal breach scenario. Under

surface water flood conditions this route is dry in the 3.33% AEP event.

Figure 4-1 - Primary Egress Route (fluvial/tidal sources)

It is noted that the areas of the site that are located within DAM Zone C1 are also located

within the NRW Flood Warning Area: Hawarden Bank. It is recommended that the six

properties in Zone C1 sign up to the NRW Flood Warning Service.


12

5 Outline Drainage Strategy

It is proposed that surface water runoff will be attenuated in a detention basin to greenfield

runoff rates (with discharge to the adjacent existing surface water sewer beneath Mancot

Lane). However, in accordance with Sustainable Drainage Systems Standards for Wales3,

surface water runoff destination, in order of priority, is as follows: collected for use,

infiltrated to ground, discharged to a surface water body, discharge to a surface water

sewer and finally, discharge to a combined sewer; as much of the runoff as possible

(subject to technical or cost constraints) should be discharged to each destination before a

lower priority destination is considered, this is discussed in more detail in Table 5-1.

Table 5-1 - Standard S1 Discussion

Priority Level Surface Water Runoff

Destination

Comments

1 Collected for use Demand for non-potable water

is limited

2 Infiltrated to ground 2020 ground investigation

concluded that existing ground

conditions are unsuitable for

soakaway

3 Discharged to a surface water

body

Discharge to Pentre Drain

South West discounted based

on levels (see Section 2.3),

where proposed detention

basin bed levels (including

250mm freeboard) are too low

for discharge to the Drain

4 Discharged to a surface water

sewer, highway drain, or

another drainage system

Discharge to a surface water

sewer is proposed based on a

fully attenuated system

Further consultation is required

5 Discharged to a combined

sewer

N/A

It is noted that the potential site demand for non-potable water is limited. Based on Report

No. 19WWH002/GI (see Appendix A) - a 2020 ground investigation report at the site

including infiltration testing, concluded that due to the presence of a significant depth of

cohesive strata, standing surface water, and high groundwater tables, the use of infiltration

is not deemed a suitable surface water drainage option.

A provisional drainage layout drawing is provided in Appendix B.

Micro Drainage modelling results are provided in Appendix C.

5.1 Sustainable Drainage Systems Standards for Wales

This Outline Drainage Strategy has been undertaken in accordance with SuDS Standards

for Wales, however, it remains a high-level strategy that will need to be reviewed as part of

a formal FCA submission. To prevent development worsening flood risk elsewhere, surface

water runoff must be managed on site.

————————————————————————————————————————————

3 https://gov.wales/sites/default/files/publications/2019-06/statutory-national-standards-for-sustainable-

drainage-systems.pdf




13

In accordance with SuDS Standards for Wales, proposed measures for surface water

management must comply with the following criteria:

Table G2.1 (Interception of runoff)

Interception methods that can be assumed to be compliant for zero runoff for the first 5mm

rainfall for 80% of events during the summer and 50% in winter:

Detention basins

Areas of the site drained to detention basins with a flat unlined base (without specific

provision for routing low flows directly to the outlet) can be assumed to comply where

the drained impermeable surface area is less than 5 times the vegetated surface area

receiving the runoff for any soil type.

Runoff volume control

Where controlling runoff to greenfield volumes is considered unachievable, then the runoff

volume should be reduced as much as possible and any additional volume should be stored

and released at a low rate which will not increase downstream flood risk (normally 2 l/s/ha

is considered an appropriate rate) using either of the following approaches:

1. The additional runoff volume (i.e. the difference between the predicted development

runoff volume and the estimated greenfield runoff volume, often called Long-Term

Storage) should be discharged from the site at a rate of 2 l/s/ha or less, while still

allowing greenfield runoff peak flow rates to be applied for the greenfield runoff

volume.

2. All the runoff from the site for the 1:100 year event should be discharged at either a

rate of 2 l/s/ha or the average annual peak flow rate (i.e. the mean annual flood,

QBAR), whichever is the greater.

5.2 Surface Water Management

Based on an a calculated impermeable area of 0.494 ha and calculated greenfield runoff

rates (see Table 5-2 below and Appendix D), Table 5-3 defines the required volumes of

attenuation for critical flood events.

Table 5-2 - Calculated Greenfield Runoff Rates

Rainfall Event (% AEP) Greenfield Runoff Rate (l/s)

Qbar 2

100 2

3.33 4

1 5

0.5 5

In accordance with SuDS Approval Body (SAB) requirements, all the runoff from the site for

the 1% AEP event is assumed to discharge at the average annual peak flow rate (i.e. the

mean annual flood, Qbar). Further to this, the invert area of the proposed detention

basin(s) is assumed to be 0.099 ha (approximately 6% of the total site area) where the

drained impermeable surface area (assumed to be 0.494 ha) is less than 5 times the

vegetated surface area receiving the runoff (0.099 ha).

In accordance with SuDS Standards for Wales and the required storage for the 3.33% AEP

+ 40% CC event (see Table 5-3), the depth of the proposed basin should be 0.325 m

excluding any freeboard allowance to attenuate the design event. At this stage, a 250mm

freeboard is envisaged.


14

Table 5-3 - Required Volumes of Attenuation

Design flood

event

(incl climate

change)

Critical

storm

duration

Hrs

Inflow

volume

m3

Outflow

volume

m3

Attenuation

required

m3

Time to

empty

(assuming

no

infiltration)

Hrs

3.33% AEP +

20% CC

5.5 298 69 229 18.1

3.33% AEP +

40% CC

6.5 362 82 280 22.2

1% AEP + 20%

CC 6.5 414 82 332 (103

exceedance

storage)

26.3

1% AEP + 40%

CC 7.5 497 95 403 (123

exceedance

storage)

31.9

It is noted that discharge to the existing surface water sewer beneath Mancot Lane is

subject to Welsh Water consultation and confirmation. Whilst initial discussions were

undertaken by the client and Welsh Water, the results to Ground Investigation were still

pending.

5.3 SuDS Maintenance

1 in 3 side slopes to the detention basin have been assumed for safe access for operatives.

Further to this, the basin is shallow (approx. 500mm) and designed to be dry under normal

conditions – reducing potential risk to operatives

It is assumed that the detention basin will be managed and maintained by a third-party

appointed by the developer. Owing to the proximity of the proposed playground facilities,

the basin will need to be designed for safety and egress. This may include consideration of

barrier planting, clear pathways, shallow banks and fencing if required.

5.4 Water Quality

In meeting S2 interception requirements, this has reduced the number of runoff events

discharged from the site, therefore, reducing contaminant loadings. Based on the proposed

land use type, the Pollution Hazard Level is classified as Low. It is recognised that Welsh

Water may have additional water quality requirements.

Using the Simple Index Approach, as defined in CIRIA’s The SuDS Manual, a detention

basin is considered to provide sufficient pollution mitigation for the proposed land use type.

It is proposed to set the invert level of the basin outfall above the basin invert to provide

the potential to provide adequate residency time for the first 5mm of rainfall.


15

6 Foul Drainage

It is noted that the proposed development site is crossed by a 225mm and 300mm

diameter foul gravity public sewer which has been incorporated into the development

layout to include for an appropriate standoff of three metres either side. Welsh Water’s

sewer network plan is provided in Appendix E.

Based on previous consultation with Welsh Water (see Appendix F), it is understood that it

is unlikely that the local public sewerage system has sufficient capacity for the anticipated

foul flows from the development. However, Welsh Water indicated that foul flows could be

pumped to the siphon which is located to the west of the site. Consent for this connection

is not yet in place.

Development plans include for a pumped discharge (see Figure 2-2) – no further reference

is made in this FCA.

Further to this, Welsh Water indicated that no problems are envisaged with the Waste

Water Treatment Works for the treatment of domestic discharges from this site.


16

7 Conclusions

This Flood Consequence Assessment (FCA) has been prepared following instruction from

Wales & West Housing, by an email dated 31st January 2020.

24 residential units, eight of which are bungalows (single-storey) are proposed for the Land

off Mancot Way site. In accordance with TAN15, this constitutes a change of use of the

land from greenfield to highly vulnerable development (residential). It is understood that

northern areas of the site are to accommodate a children’s play area and associated

footpaths, else this area will remain as open green space. SuDS features are proposed to

be accommodated here also.

NRW mapping indicates that six of the proposed residential plots are located within DAM

Zone C1 and a further four are located in DAM Zone B. DAM Zone C1 could be at risk from

a potential tidal breach scenario (River Dee).

Flintshire County Council undertook tidal Dee breach modelling as part of the 2017 SFCA.

As part of this study, the most extreme modelled flood event was the climate change 0.1%

AEP and, under this event, six properties are predicted to flood to a depth less than 300

mm based on existing ground levels. In this event, the maximum flood level within

residential areas of the development is predicted to be 5.96 mAOD. It is recommended to

set finished floor levels (FFLs) above this level including allowance for freeboard, assuming

to be 200mm at this stage. It is noted that development is usually raised above

surrounding ground levels and this shallow flooding could be accommodated within kerb

and property threshold levels. It is further noted that critical flood risk at the site is tidal

(hence tidal breach modelling), therefore, ground level raising is acceptable without

increasing flood risk elsewhere.

NRW’s uFMSW indicates that the proposed development is at low risk if surface water

flooding, however, localised areas of flooding are to be avoided in terms of attenuation

features.

2020 ground investigations highlighted that groundwater could impact excavations to

depths greater than 1.60 mbgl. Whilst this does not constitute a risk to development

levels, it will influence soakaway potential and the potential depth of surface water

attenuation facilities.

A safe access and egress route are achievable via Mancot Lane in a south-westerly direction

under tidal breach conditions.

It is proposed to pump foul flows to a siphon located to the west of the site.

Infiltration testing has been discounted based on 2020 ground investigations, therefore, in

accordance with SAB requirements, runoff from the site for the 1% AEP event is to be

attenuated in surface attenuation features and assumed to discharge at Qbar to a public

surface water sewer beneath Mancot Lane (subject to Welsh Water consultation and

confirmation). Discharge to Pentre Drain South West has been discounted based on levels,

where proposed detention basin bed levels (including 250mm freeboard) are too low for

discharge to the Drain. (See Table 5-1 summary)

In conclusion, the site can be safely developed providing that units are raised to a safe

development level about the extreme climate change 0.1% AEP tidal breach event and that

surface water is fully attenuated on site.


17

8 Appendices

A – 2020 Ground Investigation Report

B - Drainage Layout

C – Micro Drainage Modelling Results

D - Greenfield Runoff Rates

E – Welsh Water Sewer Plan

F – Welsh Water Response


18

A 2020 Ground Investigation Report


19

B Drainage Layout


20

C Micro Drainage Modelling Results


21

D Greenfield Runoff Rates


1

E Welsh Water Sewer Plan


1

F Welsh Water Response


2


3

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