I. Introduction Jubb Have Been Instructed by Galliford Try Construction to Provide Engineering Input Relating to Drainage and Fl

Barry Waterfront School C4294-JUBB-XX-XX-RP-CS-501 Job No: 20111

Title: Drainage Strategy (for planning only) Date: 21/01/2021

I. Introduction Jubb have been instructed by Galliford Try Construction to provide engineering input relating to drainage and flooding for the development of a new junior school. The site is approximately 2ha in size and is located on National Grid Reference (ST) 11074 67358. The site is currently undeveloped and is part of the wider Barry Docks development, with a 2 form entry primary school for 420 pupils, a nursery for 96 pupils and associated sports pitches proposed. Barry Docks is approximately 170m away towards the east of the site.

II. Drainage Strategy As part of the advancement in Sustainable Drainage Systems (SuDS) design, legislature was implemented on 7th January 2019 in Wales to enforce Schedule 3 of the Flood and Water Management Act 2010. This led to the establishment of SuDS Approval Bodies (SABs) for each LLFA. In the case of this development and under requirements of the above legislature, Vale of Glamorgan Council (VoG) would look to review and approve any surface water drainage design proposed for the development, with the intention of adopting possible SuDS features. Any SuDS proposed would need to conform to CIRA C753, ‘The SuDS Manual’ and any additional guidance or information provided by the LLFA. Any drainage design previously proposed to connect to a Dwr Cymru Welsh Water (DCWW) surface water (SW) or highway asset would now be subject to a detailed application & formal approval process, prior to construction and/or communication of drainage flows from the development.

An outline SAB pre-application was submitted to the Vale of Glamorgan with a formal response received in January 2021. The application response summarised that the SuDS Approval Body in line with Welsh Governments Statutory Standards for Sustainable Drainage Systems offered no objection in principle to the proposed drainage scheme based on the details provided with the pre-application,

The developer is committed to working closely with the VoG SAB officers to develop the drainage design in line with their comments in advance of submitting a SAB full application.

Refer to JUBB drawing C4294-JUBB-XX-XX-DR-CS-0500-Proposed Drainage Layout, within Appendix A for details of the proposed strategy.

i. Surface Water Strategy ▪ Subject to SAB approval and agreement with DCWW, the proposed development will discharge to an existing 600Ø sewer which eventually discharges to the nearby Barry docks.

C4293-JUBB-XX-XX-RP-CS-0501 – Barry Waterfront 1

Barry Waterfront School C4294-JUBB-XX-XX-RP-CS-501 Job No: 20111

▪ A number of SuDs features are proposed to treat surface water, like swales/wetlands, attenuation basins and permeable paving. ▪ The permitted rates of discharge are to be discussed and agreed in writing with VoG and DCWW as part of the SABs application process. ▪ Infiltration systems are not considered feasible due to ground conditions. There are also areas of contaminated land that will not be suitable for infiltration. ▪ Due to the scale of the site, multiple swales and basins have been proposed which treat road and roof runoff. The two basins at the eastern side of the side are fitted with vortex flow controls within outfall manhole chambers limiting discharge flows to the downstream network. The swale north west of the site has a swale outlet at high level to allow water to flow out at extreme flood levels. A further swale is located in the centre of the roundabout. ▪ The drawing indicates proposed basins which have been sized to include a 0.3m freeboard.

ii. SuDS Features ▪ Runoff from impermeable roadways, hardstanding, footpaths and car parking is proposed to be conveyed into tanked permeable paving and discharged via carrier-pipes within the subbase. Where this is not possible, the runoff will be conveyed to swales. Any remaining areas which cannot feasibly be conveyed to a SuDS feature will be drained via traditional gully/line drains. As part of the management train, the surface water will then discharge to the attenuation basins as a second form of treatment. ▪ Proposed rainwater pipes from buildings or structures are to pass through the attenuation basins to aid treatment, improve water quality and reduce peak flow rates. ▪ The SuDS features proposed have been selected based upon mitigation index values given within Tables 26.2 & 26.3 of CIRIA C753, with Highways & car parking considered to be medium pollution and roof runoff considered to be low pollution. The SuDS features proposed are suitable up to medium pollution hazard level. We note that not all SuDS features are equal in their ability to treat surface water, and the three main categories of pollutants; total suspended solids (TSS), metals & hydrocarbons. ▪ Any proposed drainage connection will require a S106 agreement prior to the completion of works and/or communication of flows to the DCWW network.

iii. Foul Water Strategy ▪ Foul water (FW) discharging from the proposed school building will discharge to the foul drainage in the adjacent road east of the site. ▪ Any proposed drainage connection will require a S106 agreement prior to the completion of works and/or communication of flows to the DCWW network. ▪ If a section of pipework is to cross the outside of the ownership boundary or pass through 3rd land it would require a S104 adoption agreement with DCWW.

iv. Flooding ▪ Drainage strategy has been developed in line with the information contained within report CDGS-9796-REP01-R2-FCA refer to Appendix B for details.

C4293-JUBB-XX-XX-RP-CS-0501 – Barry Waterfront 2

Barry Waterfront School C4294-JUBB-XX-XX-RP-CS-501 Job No: 20111

▪ It is proposed to redevelop a brownfield site to provide Barry Waterfront School which is located in Flood Zone B and recognised as an area known to have flooded in the past. ▪ A finished site level of at least 9.13m AOD is recommended to satisfy TAN15 two design criterion seeking a flood free solution in the 0.5% AEP (1 in 200 year) and tolerating up to a maximum depth of 600mm in the 0.1% AEP (1 in 1000 year) flood event. ▪ Surface water flooding has been identified as a present-day risk to the development site. The report indicated that a flow bath from Broad Street, across the railway line and Hood Road to the north. ▪ The surface water flood extent has been overlaid to the topographical survey and an on-site flood level of approximately 8.3m AOD has been extrapolated which represents a maximum depth of circa 300mm. ▪ Due to the proposed development raising site levels, A minimum of 530m³ compensatory flood storage is required. This is achieved by reducing levels to the U9 football pitch and providing a depression to the northern triangular area. A ditch to the northern boundary will also be required to convey overland flow to the lower area provided for compensatory flooding.

C4293-JUBB-XX-XX-RP-CS-0501 – Barry Waterfront 3

Barry Waterfront School C4294-JUBB-XX-XX-RP-CS-501 Job No: 20111

Appendix A – C4294-JUBB-XX-XX-DR-CS-0500-Proposed Drainage Layout

C4293-JUBB-XX-XX-RP-CS-0501 – Barry Waterfront

DRAINAGE NOTES:- KEY SURFACE WATER SEWER 1. THIS DRAWING TO BE READ IN CONJUNCTION WITH ALL N RELEVANT ENGINEER'S & ARCHITECT'S DRAWINGS, FOUL WATER SEWER TOGETHER WITH THEIR LATEST SPECIFICATIONS. ANY DISCREPANCIES ARE TO BE REPORTED TO THE ENGINEER OVERLAND FLOW SEWER (JUBB) IMMEDIATELY

SUDS FEATURE INDICATIVE 2. ALL EXISTING MANHOLE INVERTS TO BE CHECKED AND (SWALE, WETLAND, RAINGARDEN) REPORTED TO THE ENGINEER PRIOR TO THE NORTH COMMENCEMENT OF DRAINAGE WORKS. PERMEABLE PAVING 3. WHERE REQUIRED, EXISTING PIPE CONNECTIONS ARE TO RED LINE/PLANNING BE CCTV SURVEYED AND INSPECTED BY THE ENGINEER BOUNDARY (REFER TO AND LOCAL AUTHORITY. IF THE PIPE CONNECTION IS ARCHITECTURAL LAYOUTS) FOUND TO BE DAMAGED OR IN DISTRESS, THE CONTRACTOR IS TO CARRY OUT REMEDIAL WORKS OR PROVIDE A NEW CONNECTION TO THE EXISTING SEWER (PIPE SIZE AND GRADIENT TO BE DETERMINED BY THE ENGINEER

4. DEVELOPMENT SITE SUBJECT TO SAB APPROVAL PRIOR TO THE COMMENCEMENT OF WORKS.

5. MH COVERS AND FRAMES TO CONFORM TO BS EN 124. ALL TRAFFICKED COVERS TO CONFIRM TO C250 LOAD CLASS AND ALL NON-TRAFFICKED COVERS TO CONFORM TO B125.

6. PIPE WORK BEDDING; TYPE S BEDDING AND SURROUND TO ALL PIPES EXCEPT IN THE FOLLOWING CIRCUMSTANCES, IN WHICH TYPE Z BEDDING AND SURROUND ARE TO BE USED:- 6.1. IN LANDSCAPED AREAS (INACCESSIBLE TO VEHICLES) WHERE DEPTH TO CROWN OF PIPE IS LESS THAN 0.35m Cut/Fill Summary 6.2. IN AREAS OF SUBJECT TO POSSIBLE VEHICULAR Volume LOADING (E.G. DRIVEWAYS OR ROADS) WHERE DEPTH IS LESS THAN 1.2m 669 Cu. M. 7. ALL SURFACE WATER DRAINAGE TO BE MINIMUM, DN150mm TWINWALL AND MANUFACTURED TO BS-EN 1401 AND BS 4660 UNLESS NOTED OTHERWISE.

8. ALL RWPs TO BE FITTED WITH RODDABLE GULLIES AT JUNCTURE WITH GROUND

ARROW INDICATS LOW POINT OF ADJACENT SITE AND 9. ALL PROPOSED DRAINAGE TO BE INSTALLED TO SEWERS POINT OF ENTRY OF OVERLAND FLOW AS IDENTIFIED FOR ADOPTION 7th EDITION STANDARD AND BUILDING WITHIN CD GRAY REPORT - CDGS-9796-REP01-FCA-02 NOVEMBER 2020 REGULATIONS PART H REQUIREMENTS.

DITCH TO FRONT OF WALL TO 10. SuDS FEATURES TO BE DESIGNED, CONSTRUCTED & COVEY OVERLAND FLOW PERMEABLE PAVING MAINTAINED IN LINE WITH GUIDANCE OF CIRIA REPORT TOWARDS AREA PROVIDED AS TO CAR PARK SPACES C753 'THE SuDS MANUAL' & 'STATUTORY SuDS STANDARDS FLOOD COMPENSATION FOR WALES 2018'

SURFACE WATER (SW) DRAINAGE STRATEGY FLOW 11. PRIORITY LEVEL4; DISCHARGE TO SURFACE WATER SWALE/WETLAND TO 26 SEWER; (DESTINATION PRIORITY LEVELS AS PER NORTH OF PITCH BASIN 1 STATUTORY SuDS STANDARDS FOR WALES 2018) :- TWL 8.70m DURING 1IN100YR + 40% IL 7.50m SWALE OUTLET AT HIGH LEVEL TO 44 ATTENUATION VOLUME 142m³ RUNOFF FROM PROPOSED IMPERMEABLE AREAS TO BE ALLOW WATER TO FLOW OUT BASIN DIMENSIONS INCLUDED 1:3 SIDES COLLECTED & TREATED IN LINE WITH THE CIRIA SUDS MANUAL FOLLOWING EXTREME FLOOD EVENTS. 40 & 0.3m ALLOWANCE FOR FREEBOARD C753 MITIGATION INDICES. A COMBINATION OF PERMEABLE PAVING, SWALE/RAIN GARDENS AND ATTENUATION BASINS ARE Swale PROPOSED TO TREAT MEDIUM CONTAMINATED ROAD RUNOFF. ROOF RUNOFF IS CONSIDERED TO BE LOW POLLUTION AND 1 EV TREATED VIA ATTENUATION BASIN ONLY. A VORTEX FLOW Sprinklers EV Habitat 33 MH W/T VORTEX FLOW CONTROL IS PROPOSED TO LIMIT DISCHARGE. BASINS TO CONTROL LIMITING FEATURE SUITABLE MIXED PLANTING AT SURFACE (PLANTING TO HATCHED AREA INDICATES AREA OF DISCHARGE. REFER TO SK0501 OVER LAND FLOW COMPENSATORY 27 FOR DISCHARGE RATES. ALSO DISCOURAGE ENTRY TO BASIN) AND SURROUNDED IN STORAGE UP TO LEVEL OF 8.3mAOD FENCING TO PREVENT ACCESS BY SCHOOL CHILDREN. A 0.3m FW CONNECTION TO EXISTING FREEBOARD HAS BEEN ALLOWED FOR IN THE BASIN DESIGN. Swale 225mm∅ SEWER

FLOW 12. JUBB ARE IN DISCUSSION WITH DCWW TO AGREE A SWALE/RAIN GARDEN AT CENTRE DISCHARGE RATE FOR THE STORMWATER DRAINAGE OF ROUNDABOUT, WITH SW CONNECTION TO NETWORK DISCHARGING INTO THEIR EXISTING SEWER CARRIAGEWAY FALLS DIRECTING EXISTING 600mm∅ SEWER FLOW TO THE CENTRE NETWORK. THE FINAL DISCHARGE RATE WILL BE AGREED IN ADVANCE OF THE SUBMISSION OF THE FULL SAB APPLICATION TO VALE OF GLAMORGAN. BASIN 2 TWL 8.70m DURING 1IN100YR + 40% U9 Football Pitch IL 7.50m 13. THE SPECIFICATION IN ALL RESPECTS SHALL BE IN MUGA Swale ATTENUATION VOLUME 116m³ ACCORDANCE WITH THE CURRENT VALE OF GLAMORGAN PITCH LOWERED TO PROVIDE REQUIRED FLOOD STORAGE VOLUME BASIN DIMENSIONS INCLUDE 1:3 SIDES & COUNCIL SPECIFICATION AND CONSTRUCTION FOR HISTORICAL SURFACE WATER FLOODING. OVERLAND FLOW 0.3m ALLOWANCE FOR FREEBOARD ROUTE DIRECTING FLOWS TOWARDS SWALE/WETLAND BEFORE PUBLICATIONS IN FORCE IN THE COUNTY AT THE TIME OF DISCHARGING INTO HIGH LEVEL SWALE OUTLET. Bike Rack BASINS TO BE SURROUNDED WITH CONSTRUCTION. FENCING TO PREVENT PUPILS GAINING

ACCESS. FENCE DIMENSIONS TBC. FLOW P1 21.01.21 Preliminary issue ME GS

FLOW Plaza Rev Date Description By Apvd

PROJECT: BARRY WATERFRONT SCHOOL

TITLE: PROPOSED DRAINAGE LAYOUT

CLIENT: U11 Football Pitch U7 Football Pitch GALLIFORD TRY CONSTRUCTION

SCALE@A1: 1:500

PROJECT REF: 20111 DRAWING No: REV: (Existing Provided) C4294-JUBB-XX-XX-DR-CS-0500 P1 N 167256115 Revision Referencing E 311102904 P = Preliminary A = Approval T = Tender C = Construction

Bristol, Cardiff, Plymouth, Winchester jubb.uk.com 2A Oak Tree Court, Cardiff Gate Business Park, Cardiff +44(0)292 052 4444 Barry Waterfront School C4294-JUBB-XX-XX-RP-CS-501 Job No: 20111

Appendix B – CD Gray – Flood Consequence Assessment – Barry Waterfront School Site – CDGA-9796- REP01-FCA-R2

C4293-JUBB-XX-XX-RP-CS-0501 – Barry Waterfront

FLOOD CONSEQUENCE ASSESSMENT

Barry Waterfront School Site Barry Waterfront Consortium

CDGA-9796-REP01-FCA-R2 November 2020

C D GRAY & ASSOCIATES LTD 5-6 DERYN COURT WHARFEDALE ROAD PENTWYN CARDIFF CF23 7HB

T: 029 20 733 181 F: 029 20 734 445 E: [email protected]

@C_D_Gray Web: www.cdgray.co.uk

…DELIVERING A REPUTATION YOU CAN BUILD ON

Disclamer

This report has been prepared for the sole and exclusive use of the Barry Waterfront Consortium for whom it was commissioned and has been prepared in response to their particular requirements and brief. This report may not be relied upon by any other party.

The Contracts (Rights of Third Parties) Act 1999 shall not apply to this report and the provisions of the said Act are expressly excluded from this report.

This report may not be used for any purpose other than that for which it was commissioned.

This report may not be reproduced and/or made public by print, photocopy, microfilm or any other means without the prior written permission of C D Gray & Associates Limited.

Any information contained in this report which has been provided by others, has neither been checked or verified by C D Gray & Associates Ltd.

Document Control

Rev Comment Date Prepared By Reviewed By R0 First Issue 23/07/20 L Jones R Monkley MEng (Hons) CEng MICE FFB MBA IEng MICE MIHT Updated NRW Data & School Site R1 08/09/20 L Jones R Monkley Plan MEng (Hons) CEng MICE FFB MBA IEng MICE MIHT R2 Compensatory Storage Proposals 09/11/20 L Jones R Monkley MEng (Hons) CEng MICE FFB MBA IEng MICE MIHT

Contents 0 INTRODUCTION ...... 3 1 THE SITE ...... 4 1.1 Site Location ...... 4 1.2 Site Description ...... 5 1.3 Main Watercourses ...... 5 1.4 Flood Zone Classification ...... 5 2 SITE LEVELS...... 6

3 FLOOD ALLEVIATION MEASURES ...... 7 4 ACCESS & EVACUATION ROUTES ...... 8 4.5 Rate of Inundation ...... 9 5 POTENTIAL FLOODING SOURCES ...... 10 5.1 Tidal ...... 10 5.2 Fluvial ...... 10 5.3 Pluvial ...... 10 5.4 Groundwater ...... 10 6 FLOOD HISTORY ...... 11 7 STRUCTURES INFLUENCING FLOW ...... 12

8 PROBABILITY OF FLOODING ...... 13 8.1 Tidal ...... 13 8.2 Fluvial ...... 14 8.3 Pluvial ...... 14 8.4 Groundwater ...... 14 9 PROPOSED DEVELOPMENT ...... 15 10 IMPACT OF FLOODING ...... 16

11 DRAINAGE IMPLICATIONS ...... 18 12 WATER DISPLACED BY DEVELOPMENT ...... 20

13 IMPACT OF DISPLACED WATER ...... 21 14 LONG TERM IMPACT OF DEVELOPMENT ...... 23 15 ALLOWANCES FOR FUTURE ...... 24

16 RESIDUAL RISKS ...... 25 17 SUMMARY / CONCLUSIONS ...... 26

APPENDIX A: DEVELOPMENT DRAWINGS ...... A APPENDIX B: NRW FLOOD DATA ...... B

0 INTRODUCTION

0.1 It is proposed to redevelop a brownfield site to provide the new Barry Waterfront School as part of the wider regeneration scheme being delivered by the Barry Waterfront Consortium.

0.2 Guidance within Planning Policy Wales and Technical Advice Note (TAN) 15 prescribes a minimum standard of flood protection for any new development within flood risk areas. Mapping is based on Natural Resource Wales’ extreme flood outlines (Zone C) and British Geological Survey drift data (Zone B). Zone B data originally published in 2004, updated in 2017 and Zone C data revised quarterly.

0.3 The development site is located within Flood Zone B, recognised as an area known to have flooded in the past. As a public building, the school development category is considered ‘highly vulnerable’ in accordance with TAN15 Section 5, Figure 2.

0.4 This Flood Consequence Assessment (FCA) is intended to support the first phase works and primarily seeks to address the flood risk posed to and impacted upon by the work elements associated with the enabling and remediation contract comprising; vegetation strip, turn and compact and ground surcharging. Proposals for the second phase school delivery are in their infancy and will be presented as a separate planning application in due course. This document is therefore limited to making high level recommendations for consideration in the second phase.

0.5 This FCA follows the numbering of the seventeen points listed in paragraph A1.17 of TAN15 Appendix 1 with relevant site specific information on the development and its setting described under the appropriate headings.

0.6 This assessment is based on a topographical survey commissioned specifically for this development. Base mapping used in some drawings contains Ordnance Survey data, © Crown copyright and database right 2020.

0.7 This report contains information supplied by NRW and subject to their respective copyright and database right (referenced ATI-19065a).

3 Barry Waterfront School CDGA-9796-REP01-R2-FCA

1 THE SITE

1.1 Site Location

1.1.1 The site is located approximately 1km southwest of Barry Town Centre and approximately 1km northwest of the coastline.

1.1.2 The surrounding area is an urbanised catchment which has been subject to significant redevelopment and regeneration in recent years.

Figure 1.1 – Site Location

1.1.3 The site is bound to the east by Ffordd Y Mileniwm, referred to as Barry Island Link Road, Council owned land to the north and the recently constructed West Pond residential development to the south.

1.1.4 The site is centred at approximate Ordnance Survey co-ordinates E: 311040, N: 167323. 4 Barry Waterfront School CDGA-9796-REP01-R2-FCA

1.2 Site Description

1.2.1 The site of approximately 2.07ha (20,700m²) is irregular in shape.

1.2.2 The northern section of the site consists of an existing tarmac finished surface car park. The southern portion of the site is brownfield / scrubland that has been levelled ahead of redevelopment.

1.3 Main Watercourses

1.3.1 The nearest controlled watercourse is Barry Docks located some 200m to the east of the development site. There are no ordinary watercourses or main rivers in the vicinity.

1.4 Flood Zone Classification

1.4.1 The majority of the development site is located with Flood Zone B recognised as an area known to have flooded in the past.

Figure 1.2 – Development Advice Map (DAM)

Source: http://data.wales.gov.uk/apps/floodmapping/

5 Barry Waterfront School CDGA-9796-REP01-R2-FCA

2 SITE LEVELS

2.1 A detailed topographical survey has been commissioned for the site, extracted below and available at larger scale in Appendix A.

2.2 In broad terms, the site consists of two gently sloping plateaus. The northern existing car park is relatively level falling from the Northwest (8.5m AOD) to the southeast (8.1m AOD). There is currently a small earthwork batter on the eastern site boundary with a circa 1m level difference to the higher level access road that bounds the site. The southern plateau does not have a consistent directional fall with levels largely in the range of 9.0m AOD – 8.15m AOD with the exception of a small spoil heap near the southern boundary.

Figure 2.1 – Extract of Topographical Survey

2.3 The site is to undergo extensive earthwork reprofiling to raise ground levels in both the temporary and permanent conditions. The first phase requires surcharging as a ground improvement technique which seeks to avoid settlement in the permanent condition where levels are to be raised to counter tidal flood risk. Once the ground improvement exercise is complete, the excess material will be removed and a 600mm clean capping layer introduced in accordance with the remediation strategy. Proposed development levels are discussed further in the sections to follow.

6 Barry Waterfront School CDGA-9796-REP01-R2-FCA

3 FLOOD ALLEVIATION MEASURES

3.1 The nearby Docks are a controlled watercourse which offers some regulation / flood alleviation to the local area but there are no formal defences in place at this location.

3.2 There are no proposals to introduce wider flood defences or other forms of protection as part of this scheme.

7 Barry Waterfront School CDGA-9796-REP01-R2-FCA

4 ACCESS & EVACUATION ROUTES

4.1 Primary access is currently gained directly off Ffordd y Mileniwm on the northeast corner of the car park with a secondary / informal gated access point providing access to the southern portion of the site. As part of the proposed works, a new dedicated school access is proposed between the existing two accesses.

Figure 4.1 – Proposed Access Location

Proposed New Access Ffordd y Mileniwm

4.2 The proposed access is shown to be flood free and unaffected by extreme tidal events (0.5% AEP (1 in 200 year) and 0.1% AEP (1 in 1000 year)) at current day. The access is however indicated to be affected by surface water flooding although this is ‘low’ risk and on the outer extent of the flood area and would remain passable throughout. The flood risk shown within the development site will be mitigated by raising ground levels and should be ignored for the purpose of assessing access and egress routes.

Figure 4.2 - Surface Water Flood Risk at Proposed Access

Proposed New Access

8 Barry Waterfront School CDGA-9796-REP01-R2-FCA

4.3 As consideration is given to the influences of climate change on sea levels and tidal flood risk over the lifetime of the development, the access and egress route may become increasingly compromised in future years. There is ordinarily advanced warning of high tides and extreme tidal events which would give the School adequate time to initiate their emergence evacuation procedures. Should climate change predictions be proven accurate, the resulting hazard scores (which are a product of flood depth and velocity) are such that if flooding reaches the site’s access junction, safe refuge should be sought within the School site and evacuation should not be attempted without the support of emergency services.

4.4 The most direct evacuation route to a ‘flood free’ area which permits access to the wider highway network in both tidal and pluvial flood events would be to exit the site and head north east on Ffordd y Mileniwm.

4.5 Rate of Inundation

4.5.1 With tidal risk considered the dominant source, the rate of inundation would be limited to that of the rising tide and there is ordinarily a good degree of warning associated with high tide events.

4.5.2 Whilst the magnitude and impact of other source flood events would be smaller, pluvial flood events could represent a more frequent flood risk. These events, caused by localised rainfall, are much harder to predict and the degree of warning would be significantly lower. The proposed access position is however on the outer extent of pluvial flood risk area and would remain passable with caution in all design flood scenarios.

9 Barry Waterfront School CDGA-9796-REP01-R2-FCA

5 POTENTIAL FLOODING SOURCES

5.1 Tidal

5.1.1 Tidal flood risk is considered the dominant source of flood risk posed to the development site.

5.1.2 A Tidal Inundation model extending the coastal boundary to include Barry Docks is part of the model referenced above and the outputs provided by the NRW data request used to inform this FCA.

5.2 Fluvial

5.2.1 The fluvial effects of the River Cadoxton and its tributaries; the East Brook, Sully Brook and Cold Brook are all represented alongside Tidal Risk in the modelling outputs provided by the NRW data request used to inform this FCA.

5.3 Pluvial

5.3.1 Pluvial sources of flood risk are considered to originate from public sewerage networks, highways drainage and local private infrastructure in the immediate vicinity of or within the proposed development.

5.3.2 An existing DCWW 300mm combined sewer currently serves the existing car park to the north. There is also existing DCWW surface and foul water assets within FFordd y Mileniwm as well as evidence of existing positive highway drainage infrastructure in the vicinity of the development.

5.3.3 The drainage infrastructure in this area is under tidal influence with some outfalls operating under tidelock during periodic high tide.

5.4 Groundwater

5.4.1 Groundwater flooding occurs when water levels within the ground rise above surface elevations.

5.4.2 Intrusive site investigation undertaken by Integral Geotechnique indicated groundwater strikes between 3.72m and 4.32m with one shallower strike at 2.86m below existing ground level. Risk of groundwater flooding is therefore considered minimal.

10 Barry Waterfront School CDGA-9796-REP01-R2-FCA

6 FLOOD HISTORY

6.1 NRW interactive mapping does not indicate any historic flood events to have affected the development site.

6.2 Consultation with the Vale of Glamorgan Council in their capacity as Lead Local Flood Authority (LLFA) advised of no specific records of flooding in this area but their response caveated (previously) non-residential land use may have negated flood reports from the public.

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7 STRUCTURES INFLUENCING FLOW

7.1 Not applicable.

12 Barry Waterfront School CDGA-9796-REP01-R2-FCA

8 PROBABILITY OF FLOODING

8.1 Tidal

8.1.1 The development site is currently outside of the 0.5% (1 in 200 year) and 0.1% AEP (1 in 1000 year) flood extents and will therefore remain flood free in events of this magnitude at present day.

8.1.2 However, when the effects of climate change are taken into account, the site may experience flooding in future years if sea levels increase in line with predictions and further interventions such as increasing flood defences is not sought.

Figure 8.2 – Tidal Flood Depth 0.5% AEP (1 in 200 Year) Plus Climate Change (2114)

Figure 8.3 – Tidal Flood Depth 0.1% AEP (1 in 1000 Year) Plus Climate Change Upper Confidence Intervals (2114)

13 Barry Waterfront School CDGA-9796-REP01-R2-FCA

8.2 Fluvial

8.2.1 Included in combination as part of combined tidal model assessment outputs above.

8.3 Pluvial

8.3.1 NRW flood mapping indicates that the northern portion of the site, covering the entirety of the existing car park and just encroaching slightly further south, could be impacted by surface water and each year there is a chance of flooding greater than 3.3% AEP (1 in 30 year).

Figure 8.2 – NRW Flood Risk From Surface Water & Small Watercourses

8.4 Groundwater

8.4.1 Whilst it is acknowledged that groundwater levels can vary seasonally, based on the site-specific ground investigation, it is considered low risk for levels to rise as high as surface level and cause flooding.

8.4.2 There are no proposed basement levels which may be vulnerable to groundwater ingress and the proposed ground raising to facilitate the school development will afford additional protection.

14 Barry Waterfront School CDGA-9796-REP01-R2-FCA

9 PROPOSED DEVELOPMENT

9.1 Full details of the intended sequence of work for the ground surcharging are provided in Coffey’s Surcharge Design Report and subsequent Addendum (reference 01915AM_R_001A_MJW and 01915AM_R_002A_RDB respectively).

9.2 As the proposed school building will have a piled founding solution, the ground improvement exercise will be limited to treating the surrounding hardstanding areas including the access road, car park and MUGA to prevent undue settlement over time. The programme of surcharge, inclusive of wick drain installation, is anticipated to take 2 months to reach the settlement values required.

9.3 The proposed layout for the school is currently being developed and will be considered via separate planning application and as such is presented to discuss principles of design intent and for information only at this stage.

Figure 9.1 – Proposed School Layout

9.4 Some adjustments along the northern boundary will be required to accommodate flood risk and recommendations for minimum finished floor levels, vulnerable areas and access / egress routes are discussed in the sections to follow.

9.5 Any significant changes to the School proposals would need to be mimicked in the surcharging layout as the two are intrinsically linked.

15 Barry Waterfront School CDGA-9796-REP01-R2-FCA

10 IMPACT OF FLOODING

10.1 Surface water flooding has been identified as a present-day risk to the development site.

10.2 Surface water flood mapping indicates that a flow path from Broad Street, across the railway line and Hood Road to the north. Should a flood event occur, overland flows would propagate on the development site’s northern boundary and would currently spread into the site, ponding at relative low spots.

10.3 The surface water flood extent has been overlaid to the topographical survey and an on-site flood level of approximately 8.3m AOD has been extrapolated which represents a maximum depth of circa 300mm.

Figure 10.1 – NRW Surface Water Flood Extent

10.4 Raising of ground levels will protect against encroachment of surface water flooding into the site but consideration must be given to ensure that floodwaters are not displaced to cause detrimental impact to the third party land to the north which is understood to be under consideration for development by Cardiff and Vale College (CAVC). Compensatory storage is therefore discussed in Sections 12 and 13 to follow.

10.5 Tidal risk becomes the increasingly dominant source of flood risk in longer term scenarios and the site may in time experience tidal flooding when consideration for the predicted effects of climate change are applied over the lifetime of the development.

16 Barry Waterfront School CDGA-9796-REP01-R2-FCA

10.6 The full NRW data set is available within Appendix B and summarised flood levels are presented below;

Table 10.1: Extract of NRW Flood Data: Tidal Flood Risk – Maximum Flood Levels with Climate Change (including upper confidence intervals)

0.5% AEP (1 in 200 Year) 0.1% AEP (1 in 1000 Year)

2014 2089 2114 2014 2089 2114

Defended Modelled Nil 8.43 9.00 8.43 9.30 9.65 Maximum Flood Level (Elevation) m AOD

Table 10.2: Extract of NRW Flood Data: Tidal Flood Risk – Maximum Flood Levels with Climate Change (including upper confidence intervals)

0.5% AEP (1 in 200 Year) 0.1% AEP (1 in 1000 Year)

2020 2095 2120 2020 2095 2120

Interpolated Flood Level Nil 8.52 9.09 8.45 9.38 9.73 (Elevation) m AOD

10.7 A finished site level (post surcharge and removal of excess material) of at least 9.13m AOD is recommended to satisfy TAN15 two design criterion seeking a flood free solution in the 0.5% AEP (1 in 200 year) and tolerating up to a maximum depth of 600mm in the 0.1% AEP (1 in 1000 year) flood event.

10.8 A preliminary finished floor level of 9.4mAOD has been discussed for the School which would provide in excess of 300mm freeboard.

10.9 Highly vulnerable areas such as the school building and its primary access / egress route should be given careful consideration and any areas selected to lie at lower level which could be vulnerable to flooding should be identified and advice provided on how this would be managed operationally by the end users.

10.10 A separate FCA will be required to support the School’s planning application once definitive proposals are in place and it is recommended that a flood management and evacuation plan clearly identifying safe routes, procedures and responsibilities form part of the school’s emergency plans.

17 Barry Waterfront School CDGA-9796-REP01-R2-FCA

11 DRAINAGE IMPLICATIONS

11.1 With reference to the extract of the DCWW public sewer records below, the existing local drainage infrastructure is shown to comprise of a mixture of combined and separate foul and surface water assets.

Figure 11.1 – DCWW Public Sewer Records

11.2 The existing car park area appears to be served by the 300mm combined sewer crossing the site.

11.3 There are a number additional existing surface water systems with outfalls to the nearby Docks and further record information on the existing local infrastructure is available in Appendix A.

11.4 During the temporary condition of ground improvement works, the Surcharge Design Report (Section 5.2) makes reference to the intention for drainage provision to drain away any water at the surface, with suitable ditches / stone trenches and sumps, together with gravity drainage or pumping.

11.5 It is intended to introduce a ditch around the western, southern and eastern boundaries which will intercept surface water flows generated by the site itself during a storm event. Positive conveyance will not be provided and flows will be retained and pumped / tankered away as appropriate as a pollution prevention control measure.

11.6 Flow rates have been generated by FEH / REFH2 methods and estimate that the 2 hectare site would generate a volume of 144 m³ during a Q100 (1 in 100 year return period) 6 hour storm event.

18 Barry Waterfront School CDGA-9796-REP01-R2-FCA

Figure 11.2 – REFH2 – Rainfall Generation (Q100 6 Hour)

11.7 The perimeter ditch to be provided will be a minimum of 370mm deep, with a 1 metre wide base and side slopes of a 1:2 profile which will provide a volume of 242m³ which is in excess of the storage volumes required during the Q100 6 hour storm event. More detailed proposals, inclusive of sectional profiles, are available for reference in Appendix A.

11.8 In the permanent condition, it is intended that the proposed School makes use of the local drainage infrastructure serving this area which operates under tidal influence. Any network with outfall to the Dock is therefore anticipated to be permitted without restriction to discharge rates. Consideration should be given to the potential effects of a surcharged outfall which could become submerged under tidelock during a storm event. Positive drainage provision should also be considered for areas where a decision is made to permit flooding i.e on the surface of functional external areas such as pitches / MUGA to allow drain down as floodwaters recede – this is discussed in more detail in section 13.

11.9 The drainage proposals for the permanent School application are subject to separate consultation and SAB approval.

19 Barry Waterfront School CDGA-9796-REP01-R2-FCA

12 WATER DISPLACED BY DEVELOPMENT

12.1 The surface water flood mapping indicates that there is no conveyance path through the site that needs to be retained for continuity and floodwater is simply being stored on the surface in a flood event.

12.2 Any raising of existing levels within the indicated surface water flood extent would displace flood water and most directly locally impact upon the council owned land to the north.

12.3 Volumetric analysis has been undertaken interfacing a surface water flood level of 8.3m AOD to the existing topographical survey surface. This suggests that under flood scenario, the existing car park provides storage volume in the order of 524m³ on the surface of the existing car park.

12.4 It is proposed to introduce compensatory storage to mitigate for this effect.

20 Barry Waterfront School CDGA-9796-REP01-R2-FCA

13 IMPACT OF DISPLACED WATER

13.1 It is proposed to manage the displacement of water by intercepting the overland flow path on the northern boundary and directing flows to an area which will be kept at a low level relative to the wider side and provide equivalent compensatory storage.

13.2 To ensure flood water is not displaced onto the land to the north, the equivalent compensatory storage volume must be achieved with a maximum permitted flood level of 8.3m AOD, to mimic the existing flood water level.

13.3 It is proposed to achieve the compensatory storage required with a solution that compliments the school’s end use proposals. Figure 13.1 illustrates the intent to introduce an interception channel along the northern boundary and a lowered pitch area (indicated by blue hatch) to collectively achieve the compensatory storage volumes required.

Figure 13.1 – Compensatory Flood Storage

Key Parameters:

• Northern Boundary Channel : 1m wide • Plan Area 3,535m² • Max Base Level 8.15m AOD (max flood depth 150mm) • Batter / retaining structure requirements to be considered in permanent condition.

Storage Volume provided to flood level of 8.3m AOD = 530m³

13.4 Further details including site sections are available in Appendix A.

13.5 Some reconfiguration to the current school proposals (car park and sprinklers) will be required to accommodate the proposed compensatory flood storage area as shown.

21 Barry Waterfront School CDGA-9796-REP01-R2-FCA

13.6 A retaining structure rather than an earthwork batter could be introduced to resolve the level difference and minimise the impact and encroachment into the school development site.

13.7 Boundary treatments will need to be considered to ensure that any overland floodwater is permitted to enter the School site and the flow path is not obstructed along the northern boundary.

13.8 Positive drainage provision should be considered for areas where a decision is made to permit flooding on the surface of functional external areas such as pitches / MUGA to allow drain down as floodwaters recede.

13.9 It should be noted that should the CAVC owned land to the north come forward for development and be required to similarly raise levels to mitigate for flood risk or as part of its own remediation strategy then the action of lifting levels would obstruct the overland flow path, afford the school site with protection against overland flows and potentially make the compensatory storage area redundant in the future.

22 Barry Waterfront School CDGA-9796-REP01-R2-FCA

14 LONG TERM IMPACT OF DEVELOPMENT

14.1 There are no long term, adverse impacts associated with the proposed development.

23 Barry Waterfront School CDGA-9796-REP01-R2-FCA

15 ALLOWANCES FOR FUTURE

15.1 TAN15 requires the possible impact of climate change to be taken into account in the assessment of flooding for a 100 year lifetime for highly vulnerable development. Climate change factors including upper confidence intervals (+/- 95%) are included for in the modelling outputs used to inform this FCA.

24 Barry Waterfront School CDGA-9796-REP01-R2-FCA

16 RESIDUAL RISKS

16.1 Once the compensatory storage volume is profiled along the northern boundary, the remaining development plateau will not be at risk of flooding and the first phase works associated with ground surcharging would be unaffected by a flood event.

16.2 Similarly, the school will only potentially become at risk of flooding in future years if sea levels rise in line with climate change predictions and further intervention and protection measures are not introduced in the interim.

16.3 A separate FCA will be required to support the School’s planning application once definitive proposals are in place and it is recommended that a flood management and evacuation plan clearly identifying safe routes, procedures and responsibilities form part of the school’s emergency plans.

25 Barry Waterfront School CDGA-9796-REP01-R2-FCA

17 SUMMARY / CONCLUSIONS

17.1 It is proposed to redevelop a brownfield site to provide Barry Waterfront School which is located in Flood Zone B and recognised as an area known to have flooded in the past.

17.2 The site is to be constructed in a two phase approach with an enabling ground improvement programme ahead of the second phase works delivering the school. This FCA has primarily sought to address the risk and impacts of the first phase associated with ground surcharging and a separate FCA will be required to support the School and its respective planning application.

17.3 The site is currently indicated to be at risk of surface water flooding. Ground raising is proposed to counter this and compensatory storage along the site’s northern boundary is proposed to mitigate against the effects of displacement and ensure that the land to the north is not detrimentally impacted.

17.4 Volumetric analysis has been undertaken and determined that an equivalent compensatory storage volume of 524m³ (below the flood level of 8.3m AOD) would be required along the site’s northern boundary to mimic the existing storage provided by the site and ensure no displacement of floodwater in an extreme event.

17.5 In implementing this solution, the remaining development site is not considered to be at risk of flooding from any source during the first phase ground improvement works.

17.6 The introduction of a ditch on the eastern, southern and western boundary is intended to intercept and store surface water run-off generated by the site itself. The ditch is sized to cater for a Q100 (1 in 100 year) 6 hour storm event. As a pollution prevention / control measure this will not have positive conveyance during the temporary works and will be pumped / tankered away as appropriate.

17.7 Whilst the site is positioned outside of the current tidal flood extent, tidal risk becomes the increasingly dominant source of flood risk in longer term scenarios and the site may experience tidal flooding in future years when consideration for the predicted effects of climate change are applied over the lifetime of the development.

17.8 A finished site level (post surcharge and removal of excess material) of at least 9.13m AOD is recommended to satisfy TAN15 two design criterion seeking a flood free solution in the 0.5% AEP (1 in 200 year) and tolerating up to a maximum depth of 600mm in the 0.1% AEP (1 in 1000 year) flood event.

17.9 Highly vulnerable areas such as the school building and its primary access / egress route should be given careful consideration and any areas selected to lie at lower level which could be vulnerable to flooding should be identified and advice provided on how this would be managed operationally by the end users.

17.10 A separate FCA will be required to support the School’s planning application once definitive proposals are in place and it is recommended that a flood management and evacuation plan clearly identifying safe routes, procedures and responsibilities form part of the school’s emergency plans.

17.11 The effects of flood risk on and resulting from the proposed development have been fully considered. This FCA considers flood risk posed by all sources and demonstrates that the development site can effectively manage the impact / consequence of flooding over the lifetime of the development as prescribed under TAN15.

26 Barry Waterfront School CDGA-9796-REP01-R2-FCA

APPENDIX A: DEVELOPMENT DRAWINGS

A Barry Waterfront School CDGA-9796-REP01-R2-FCA

MH3 Ex. MH2. Ex.

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6 Start pointwalling End ofGabion 7 5 m 1 m . 0

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m 1 MH3

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5 0 1 0 1 m 0 m . 0 d 0 i

m a 0 PETROL INTERCEPTOR 6 d i a FilterDrain

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Surround UTG9502 Concrete surround Surround UTG9502 Concrete Ecopass separator Class 2 (Heavy Duty) Ecopass separator(Heavy Class2 Products) FRP Type NF 110.0 (Fibre Reinforced

PETROL INTERCEPTOR 0 Outfall MH8 Co-plastic. TypeHinge Double OutletValve Flap

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in 1 3 4

B 7 . 3 0 E 0 0 0 0 A m m N

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LocationDia. of 800mm rising main. 1

in B 1 3 L 4 B O E A C N Y Location of 800mmLocationDia. of rising main. K B S L O C K S

B E A

N Y

B L

MH10A O

C K

O B

F N

C K Manhole Schedule Manhole Number 15 14 13 12 11 10 1 * Type C Brick built Manhole (Reference Sewers for Adoption) * Type for C Brick built ManholeSewers (Reference 8 9 7 6 5 3 4 2 8.500 8.6758.500 1.595 8.500 8.650 8.571 8.600 2.963 8.594 8.560 8.596 8.399 8.563 8.663 0.932 7.809 9.101 Cover Level Depth(mm) Manhole 1.537 1.150 1.810 1.536 1.604 1.415 3.428 3.349 3.225 3.110 2.865 2.951 Diam.(mm) Manhole 1800 1350 1800 1050 1800 1800 1800 1050 1050 1800 2400 TypeC* TypeC* TypeC* TypeC* A B AS CONSTRUCTED SJG 24.11.00 05/99 LTG 1.008 1.007 1.006 5.735 1.005 6.150 1.004 1.003 1.002 05/99 6.002 8.000 6.001 6.000 5.001 5.000 7.001 6.963 7.000 CWJ PN Contractissue Manhole10 A added HOOD ROAD IMPROVEMENTS TENDER ISSUE Pipes Out Pipes 5.151 750 5.275 750 5.440 750 5.637 750 6.750 225 6.796 7.080 450 7.500 7.060 7.121 7.371 675 4.381 (m) IL 1:1000 893/ph2ascon DRAINAGE DETAILS DRAINAGE (AS CONSTRUCTED) (AS drg893-02-501b (mm) Dia 1350 300 300 750 750 750 675 225 PHASE 2 1.007 1.006 5.637 750 1.005 1.004 1.003 1.002 1.001 7.371 675 8.000 6.002 6.001 5.151 750 6.000 5.2857.000 750 5.001 6.690 5.000 6.800 225 3.001 PN A 893 PipesIn 5.233 6.380 6.963 5.735 6.613 6.150 6.871 7.121 4.981 (m) IL B (mm) Dia 300 675 675 750 750 450 225 750 450 750 02/501 Gat Gat 06.06.99 03.02.00 16.05.00 SAFETY, HEALTH AND ! ENVIRONMENTAL INFORMATION !

ALL WORK TO BE CARRIED OUT IN ACCORDANCE WITH CURRENT CDM REGULATIONS 2015 AND HSG150. IN ADDITION TO THE HAZARDS/RISKS NORMALLY ASSOCIATED WITH THE TYPES OF WORK DETAILED ON THIS DRAWING, PLEASE NOTE THE FOLLOWING:

KEY

LOW RISK FLOOD AREA

MEDIUM RISK FLOOD AREA

HIGH RISK FLOOD AREA

SITE BOUNDARY

SITE FLOOD LEVEL ESTIMATED AT 8.30 FLOOD VOLUME ESTIMATED AT 524m³

CAVC (IQ SOUTHERN DEVELOPMENT SITE)

PROPOSED SITE

- - - - REV DESCRIPTION BY DATE

status FOR INFORMATION

5-6 Deryn Court, Wharfedale Road, Pentwyn, Cardiff, CF23 7HB Tel: 02920 733181 Web: www.cdgray.co.uk

client BARRY W/FRONT CONSORTIUM

project BARRY WATERFRONT SCHOOL

drawing title NRW SURFACE WATER FLOOD AREAS

drawn GJ chkd LKJ project no. 9796 date drg no. rev. drawn 20.07.2020 scale SK01 P1 @A1 1:500 C:\Users\Laura Jones\Desktop\CDG - March 2020\9796 - Barry Waterfront\02-Drawings\CDGA-9796-NRW SW Flood Risk SAFETY, HEALTH AND ! ENVIRONMENTAL INFORMATION !

ALL WORK TO BE CARRIED OUT IN ACCORDANCE WITH CURRENT CDM REGULATIONS 2015 AND HSG150. IN ADDITION TO THE HAZARDS/RISKS SECTION B-B (SOUTHERN BOUNDARY) NORMALLY ASSOCIATED WITH THE TYPES OF WORK DETAILED ON THIS DRAWING, PLEASE NOTE THE FOLLOWING: SCALE: H 1:1000,V 1:1000. DATUM: 5.000 SECTION LOCATION PLAN - INSERT FROM SURCHARGE LAYOUT 01915AM_D_002B CAVC (1:1000 @ A1) (IQ SOUTHERN DEVELOPMENT SITE) BOUNDARY DITCH 15 SECTION A-A (SOUTHERN BOUNDARY) - 1:2 SIDE PROFILES 370mm DEEP 14 SURCHARGED AREA (10.4 METRES AOD) SECTION E-E - DITCH BASE 1 METRE WIDE 13 SCALE: H 1:1000,V 1:1000. DATUM: 5.000 12 Level 11 CAVC (IQ Southern Development Site) 10 10 Linestyle denotes possible future road re-alignment works

Level 9 9

8 8 BOUNDARY DITCH 00 7 - 1:2 SIDE PROFILES 370mm DEEP 7

- DITCH BASE 1 METRE WIDE 6 6 10 Swale Staff Car Park

5 5 SECTION C-C Habitat Sprinklers 20 paving

Chainage Chainage paving 24 paving 00.000 02.000 04.000 06.000 08.000 09.895 00.000 02.000 04.000 06.000 08.000 09.895 Drop off Swale

U9 Football 61m x 43m (Grass)

109 Bins 100

60 00 50 paving 40 30

20 10 Swale

00 Existing Levels Existing Levels 10 9.061 9.080 9.086 9.074 9.049 9.037

9.614 9.673 9.653 9.633 9.595

Kitchen 18 3 Court MUGA

PROPOSED SITE PLAZA

Lightwell above Lightwell paving

paving 16

SCHOOL Soft 10 Proposed Levels Proposed Levels Social 9.080 8.717 9.265 9.494 9.303 9.663 9.580 9.502 9.442 SECTION D-D above Lightwell 00 10.174 10.400 10.400 Soft U11 Football Social Hard Social 79m x 52m U7 Football Hard Social (Grass) 43m x 33m (Grass)

Lightwell above Lightwell SECTION F-F

Hard Social

Soft 10 Social Habitat 00 00 SECTION B-B

SECTION A-A

BOUNDARY DITCH COMPENSATORY STORAGE AREA SECTION C-C (COMPENSATORY STORAGE AREA) - 1:2 SIDE PROFILES 370mm DEEP BASE LEVEL AT 8.15 AOD. - DITCH BASE 1 METRE WIDE FLOOD LEVEL AT 8.30 AOD. SCALE: H 1:1000,V 1:1000. DATUM: 5.000

15 14 SURCHARGED AREA (10.4 METRES AOD) 13 1:2 BANK PROFILE FROM BASE LEVEL (8.15 METRES AOD) 12 TO SURCHARGED AREA (10.4 METRES AOD) 10.4 METRES Level 11 10 8.15 METRES 9 8 KEY 7 6 PROPOSED GROUND 5 Chainage EXISTING GROUND 40.000 42.000 44.000 46.000 48.000 20.000 22.000 24.000 26.000 28.000 60.000 62.000 64.000 66.000 68.000 00.000 02.000 04.000 06.000 08.000 30.000 32.000 34.000 36.000 38.000 50.000 52.000 54.000 56.000 58.000 70.000 72.000 74.000 76.000 78.000 80.000 82.000 84.000 86.000 88.000 90.000 92.000 94.000 96.000 98.000 10.000 12.000 14.000 16.000 18.000 108.801 100.000 102.000 104.000 106.000 108.000 COMPENSATORY FLOOD STORAGE

Existing Levels PERIMETER DITCH 8.771 8.611 8.321 8.765 8.767 8.777 8.759 8.738 8.718 8.698 8.677 8.667 8.653 8.635 8.623 8.598 8.582 8.583 8.599 8.616 8.633 8.648 8.662 8.675 8.660 8.629 8.597 8.555 8.512 8.470 8.427 8.374 8.355 8.338 8.303 8.282 8.270 8.265 8.260 8.254 8.249 8.244 8.240 8.236 8.232 8.228 8.217 8.205 8.185 8.165 8.153 8.152 SURFACE WATER PROFILE

Proposed Levels 8.422 8.723 8.690 8.618 8.549 8.482 8.255 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 8.150 9.139 10.139 10.400 10.400 10.400 10.400 10.400 10.400 10.400 10.400 10.400 10.400 10.400 10.400

SECTION E-E (1 METRE WIDE NORTHERN BOUNDARY DITCH) SECTION F-F (SOUTH EASTERN BOUNDARY) SECTION D-D (WESTERN BOUNDARY DITCH) SCALE: H 1:1000,V 1:1000. DATUM: 5.000 SCALE: H 1:1000,V 1:1000. DATUM: 5.000 1 METRE WIDE STRIP BELOW FLOOD P2 Section F-F Added RE 29/10/2020 SCALE: H 1:1000,V 1:1000. DATUM: 5.000 LEVEL TO INTERCEPT OVERLAND FLOW REV DESCRIPTION BY DATE 15 1 METRE WIDE STRIP BELOW FLOOD15 BOUNDARY DITCH 14 SURCHARGED AREA (10.4 METRES AOD) LEVEL TO INTERCEPT OVERLAND14 FLOW status - 1:2 SIDE PROFILES 370mm DEEP 10 13 13 - DITCH BASE 1 METRE WIDE Level 9 12 12 PRELIMINARY Level Level 8 11 11 7 10 10 6 9 9 5-6 Deryn Court, Wharfedale Road, 5 8 8 Pentwyn, 7 7 Cardiff, CF23 7HB 6 6 Tel: 02920 733181 Chainage 5 5 Web: www.cdgray.co.uk 00.000 02.000 04.000 06.000 08.000 10.000 12.000 14.000 16.000 18.000 18.484

client Chainage Chainage 00.000 02.000 04.000 06.000 08.000 20.000 22.000 23.859 10.000 12.000 14.000 16.000 18.000 00.000 02.000 04.000 06.000 08.000 10.000 12.000 14.000 16.000 16.228 BARRY W'FRONT CONSORTIUM Existing Levels 8.761 8.791 8.744 8.768 8.775 8.782 8.786 8.776 8.768 8.786 8.790 project Existing Levels Existing Levels BARRY WATERFRONT 8.221 8.241 8.271 8.251 8.260 8.259 8.250 8.255 8.248 8.246 8.245 8.240 8.239 9.031 8.661 9.086 9.107 8.874 8.648 8.634 8.616 8.629 8.630 SCHOOL Proposed Levels 8.682 8.744 8.547 8.737 8.599 8.517 8.436 8.356 8.228 8.150 8.150 drawing title PROPOSED FLOOD Proposed Levels Proposed Levels

8.150 9.090 COMPENSATION MODELLING 9.018 8.540 8.928 9.417 9.914 10.090 10.400 10.400 10.400 10.400 10.400 10.400 10.400 10.400 10.400

drawn RE chkd LJ project no. 9796 date drg no. rev. drawn 28-10-2020 scale 100 P2 @A1 AS STATED F:\Jobs\9700-9799\9796 - Barry Waterfront\05-Documents\02-Drawings\C3D\Combined Storage Features (Use for displaying sections - NOT for calcs of volume)

APPENDIX B: NRW FLOOD DATA

B Barry Waterfront School CDGA-9796-REP01-R2-FCA

ATI-19065a – Development at Barry Waterfront, Barry E: 311124 N: 167313

1. Current Flood Map

Figure 1 shows the current Flood Map (version 202001) at this location. The Flood Map represents a combination of the undefended fluvial and tidal flood extents derived from detailed local models and national generalised model data. Undefended scenarios are provided as being a possible worst case scenario in the event of defence failure.

Please note that the current tidal flood outlines shown on the Flood Map in Figure 1 are based on an NRW Tidal Projection Mapping study (2013) that uses sea level nodes within the Severn Estuary. Each node represents a set of extreme sea levels which were generated by the Environment Agency in 20111 for current day (in the studies case, 2008). These levels were projected in-land over a digital terrain model to produce depth and elevation grids as well as tidal mapped outlines for both the 0.5% (1 in 200) AEP (annual exceedance probability) and the 0.1% (1 in 1000) AEP; including climate change and upper confidence intervals (+/-95%).

These outlines offer a more precautionary picture of tidal flood risk and therefore supersede the localised hydraulic modelled outlines described in Section 2 below.

More information on the Flood Map can be obtained from the Natural Resources Wales website http://www.naturalresources.wales/floodriskmap

2. Local Flood Risk Mapping Study

Model Summary The results summarised in the tables below are taken from two hydraulic models developed as part of the ‘Cadoxton Strategic Flood Risk Assessment’. These are:

a. A multi-domain 1D-2D ESTRY/TUFLOW model assessing fluvial and tidal flood risk from the River Cadoxton and its tributaries – the East Brook, Sully Brook and Cold Brook – from just upstream of Dinas Powys to the Cadoxton sea outfall2. The fluvial outputs below are provided from this model.

b. A Tidal Inundation model extending the coastal boundary to include Barry Docks3. The above fluvial/tidal model was adopted and modified to allow broad-scale tidal flooding within the lower Cadoxton River catchment. This model is subject to substantially more tidal inundation flooding and as such has been used to provide tidal outputs below.

Results – Site of Interest The polygon shown in the figures represents the site in question and has been used to query the height, depth, velocity & hazard grids to provide the results in Tables 1-6 below. NULL values indicate that the site is flood free during a particular scenario.

The elevation results have been interpolated to include the climate change increment from the DEFRA guidance on extreme sea level data to show current day scenarios (see Tables 5 & 6 below).

95% confidence bounds for these values were also derived using the confidence intervals for the Newport Extreme Sea Level node.

Example depth grids for the defended tidal 1 in 200 (2114) and 1 in 1000 (2114) including confidence intervals are produced in Figures 2 & 3 below.

Page 1 of 4 A hazard grid for the defended tidal 1 in 1000 (2114) including Confidence Interval is represented in Figure 4. The hazard rating below relates to the Hazard to People Classification using the hazard matrix4.

Flood Hazard Colour Hazard to People Classification Rating (HR) Code Less than 0.75 Very low hazard – Caution 0.75 to 1.25 Danger for some – includes children, the elderly and the infirm 1.25 to 2.0 Danger for most – includes the general public More than 2.0 Danger for all – includes the emergency services

Table 1: Defended Fluvial Level Data

1 in 1 in 1 in 1 in 1 in 2 1 in 5 1 in 10 1 in 30 1 in 50 1 in 75 100 200 100CC 1000 Model Grid Size 1 1 1 1 1 1 1 1 1 1 (m) Wet Cells 0 0 0 0 0 0 0 0 0 0 Depth, mean (m) NULL NULL NULL NULL NULL NULL NULL NULL NULL NULL Depth, max (m) NULL NULL NULL NULL NULL NULL NULL NULL NULL NULL Elevation, mean NULL NULL NULL NULL NULL NULL NULL NULL NULL NULL (mAOD) Elevation, max NULL NULL NULL NULL NULL NULL NULL NULL NULL NULL (mAOD) Velocity, mean NULL NULL NULL NULL NULL NULL NULL NULL NULL NULL (m/s) Velocity, max (m/s) NULL NULL NULL NULL NULL NULL NULL NULL NULL NULL Hazard, mean NULL NULL NULL NULL NULL NULL NULL NULL NULL NULL Hazard, max NULL NULL NULL NULL NULL NULL NULL NULL NULL NULL

Table 2: Undefended Fluvial Level Data

1 in 1 in 100 1000 Model Grid Size 1 1 (m) Wet Cells 0 0 Depth, mean (m) NULL NULL Depth, max (m) NULL NULL Elevation, mean NULL NULL (mAOD) Elevation, max NULL NULL (mAOD) Velocity, mean NULL NULL (m/s) Velocity, max (m/s) NULL NULL Hazard, mean NULL NULL Hazard, max NULL NULL

Page 2 of 4 Table 3: Defended Tidal Level Data with Climate Change (excluding upper confidence Intervals)

1 in 200 1 in 1000

2014 2089 2114 2014 2089 2114

Model Grid Size 2.5 2.5 2.5 2.5 2.5 2.5 (m) Wet Cells 0 0 961 0 961 2784 Depth, mean (m) NULL NULL 0.14 NULL 0.14 0.46 Depth, max (m) NULL NULL 0.58 NULL 0.58 1.14 Elevation, mean NULL NULL 8.40 NULL 8.40 9.00 (mAOD) Elevation, max NULL NULL 8.43 NULL 8.43 9.00 (mAOD) Velocity, mean NULL NULL 0.09 NULL 0.09 0.34 (m/s) Velocity, max (m/s) NULL NULL 0.97 NULL 0.97 1.42 Hazard, mean NULL NULL 0.64 NULL 0.64 1.18 Hazard, max NULL NULL 1.34 NULL 1.34 2.03

Table 4: Defended Tidal Level Data with Climate Change (including upper confidence Intervals)

1 in 200 1 in 1000

2014 2089 2114 2014 2089 2114

Model Grid Size 2.5 2.5 2.5 2.5 2.5 2.5 (m) Wet Cells 0 961 2784 961 3105 3173 Depth, mean (m) NULL 0.14 0.46 0.14 0.69 1.02 Depth, max (m) NULL 0.58 1.14 0.58 1.43 1.79 Elevation, mean NULL 8.40 9.00 8.40 9.29 9.64 (mAOD) Elevation, max NULL 8.43 9.00 8.43 9.30 9.65 (mAOD) Velocity, mean NULL 0.09 0.34 0.09 0.47 0.55 (m/s) Velocity, max (m/s) NULL 0.97 1.42 0.97 1.42 1.46 Hazard, mean NULL 0.64 1.18 0.64 1.44 1.67 Hazard, max NULL 1.34 2.03 1.34 2.64 2.91

Table 5: Interpolated Tidal Results 2016 (excluding upper confidence interval)

1 in 200 1 in 1000 2020 2095 2120 2020 2095 2120 Elevation, max NULL NULL 8.52 NULL 8.52 9.09 (mAOD)

Page 3 of 4 Table 6: Interpolated Tidal Results 2016 (including upper confidence interval)

1 in 200 1 in 1000

2020 2095 2120 2020 2095 2120

Elevation, max NULL 8.52 9.09 8.45 9.38 9.73 (mAOD)

Results – Emergency Access to Site An access route has not been provided.

Table 7: Sea level rise, mm per year Assumed vertical land 1990-2025 2025-2055 2055-2085 2085-2115 movement -0.5 3.5 8.0 11.5 14.5

3. Additional Information

We do not hold any historic flooding information for the area of interest.

The local authority may be able to provide information on issues such as localised flooding from sewers, drains and culverts.

4. References

1 Environment Agency (2011) ‘Coastal flood boundary conditions for UK mainland and islands – SC060064’ 2 JBA Consulting (2015) ‘Cadoxton Flood Risk Study Hydraulic Model User Report’ 3 JBA Consulting (2015) ‘Cadoxton Flood Risk Study Tidal Inundation Model – Model User Report and Results Discussion Final’ 4 Supplementary note on flood hazard ratings and thresholds for development planning and control purpose (May 2008) 5 Flood and Coastal Defence Appraisal Guidance: FCDPAG3 Economic Appraisal. Supplementary Note to Operating Authorities – Climate Change Impacts; October 2006; Department for Environment, Food and Rural Affairs.

5. Notes

The scope of the model is the mapping of flood risk, it is not intended for detailed design. The model should be considered as the starting point for more detailed modelling, commensurate with the consequences of flooding at the site of interest.

NRW models are available under licence agreement for the purpose of further development. Contact Natural Resources Wales Data Distribution team for details of terms, conditions and pricing.

If the data is used in support of an FCA, please include the reference number.

Please refer to NRW standard terms and conditions.

Flood Risk Analysis 18/08/2020

Page 4 of 4

Legend

Site Location

Flood Zone 3 (1 in 100 year undefended fluvial and 1 in 200 year undefended tidal extents)

Flood Zone 2 (1 in 1000 year undefended fluvial and tidal extents)

Areas benefiting from defences !

! Defences

Flood Storage Area

Main Rivers

Site

Project Development at Barry Waterfront,Barry [Ref: ATI-19065a]

Drawing Figure 1: Current Floodmap [v202001]

± Date 18th August 2020

Scale 1:5,000 Legend

Site Location

Flood Depth (m)

0.0 - 0.3 >0.3

>0.6

>1.0

>2.0

Site

Project Development at Barry Waterfront,Barry [Ref: ATI-19065a]

Drawing Figure 2: Tidal Depth Grid for 0.5% AEP (1 in 200) year event - defended including upper confidence intervals (2114) ± Date 18th August 2020

Scale 1:5,000 Legend

Site Location

Flood Depth (m)

0.0 - 0.3 >0.3

>0.6

>1.0

>2.0

Site

Project Development at Barry Waterfront,Barry [Ref: ATI-19065a]

Drawing Figure 3: Tidal Depth Grid for 0.1% AEP (1 in 1000) year event - defended including upper confidence intervals (2114) ± Date 18th August 2020

Scale 1:5,000 Legend

Site Location

Flood Hazard

< 0.75

0.75 - 1.25

1.25 - 2.00

> 2.0

Site

Project Development at Barry Waterfront,Barry [Ref: ATI-19065a]

Drawing Figure 4: Tidal Hazard Grid for 0.1% AEP (1 in 1000) year event - defended including upper confidence intervals (2114) ± Date 18th August 2020

Scale 1:5,000