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CARDIFF COUNCIL
LAMBY WAY SOLAR FARM
DRAINAGE STRATEGY
JANUARY 2019
Wardell Armstrong 2 Devon Way, Longbridge, Birmingham, West Midlands, B31 2TS, United Kingdom Telephone: +44 (0)121 580 0909 www.wardell-armstrong.com
Wardell Armstrong is the trading name of Wardell Armstrong LLP, Registered in England No. OC307138.
Registered office: Sir Henry Doulton House, Forge Lane, Etruria, Stoke-on-Trent, ST1 5BD, United Kingdom
UK Offices: Stoke-on-Trent, Birmingham, Cardiff, Carlisle, Edinburgh, Glasgow, Greater Manchester, Central Manchester, London, Newcastle upon Tyne, Sheffield, and Truro. International Offices: Almaty and Moscow.
ENERGY AND CLIMATE CHANGE ENVIRONMENT AND SUSTAINABILITY
INFRASTRUCTURE AND UTILITIES LAND AND PROPERTY
MINING AND MINERAL PROCESSING MINERAL ESTATES
WASTE RESOURCE MANAGEMENT
DATE ISSUED: JANUARY 2019
JOB NUMBER: CA11469 REPORT NUMBER: 0002
VERSION:
STATUS:
V0.1
DRAFT
CARDIFF COUNCIL
LAMBY WAY SOLAR FARM
DRAINAGE STRATEGY
JANUARY 2019
PREPARED BY:
Adriana Garcia Engineer
REVIEWED BY:
Kerry Whitehouse Associate Director
APPROVED BY:
Graham Whitehouse Technical Director
This report has been prepared by Wardell Armstrong LLP with all reasonable skill, care and diligence, within the terms of the Contract with the Client. The report is confidential to the Client and Wardell Armstrong LLP accepts no responsibility of whatever nature to third
parties to whom this report may be made known.
No part of this document may be reproduced without the prior written approval of Wardell Armstrong LLP.
CARDIFF COUNCIL LAMBY WAY SOLAR FARM DRAINAGE STRATEGY
CA11469/DRAFT JANUARY 2019
CONTENTS
EXECUTIVE SUMMARY ............................................................................................................... 1
1 INTRODUCTION .................................................................................................................. 2
Purpose of Report ....................................................................................................... 2
Acknowledgement ...................................................................................................... 2
2 EXISTING SITE CONDITIONS ............................................................................................... 3
Site Location and Description ..................................................................................... 3
Proximity to Watercourses ......................................................................................... 4
Geology ....................................................................................................................... 4
3 POTENTIAL SOURCES OF FLOODING .................................................................................. 5
Fluvial and Tidal Flooding ............................................................................................ 5
Pluvial/Surface Water Flooding .................................................................................. 6
Groundwater Flooding ................................................................................................ 7
Existing Drainage ......................................................................................................... 7
Reservoirs, Canals and Lakes ....................................................................................... 8
Historic Flooding: ........................................................................................................ 8
4 DEVELOPMENT PROPOSAL ................................................................................................ 9
5 SURFACE WATER MANAGEMENT STRATEGY .................................................................. 11
Landfill Existing Water Management Plan ................................................................ 11
Additional Water Management Measures ............................................................... 12
6 CONCLUSIONS .................................................................................................................. 14
DRAWINGS TITLE SCALE
CSP11070-104 Landfill Reinstatement Details NTS
LAM-DWG002 Site Layout Plan 1:1250 @A1
CA11469-004 Drainage Catchment Plan 1:2500 @A1
CARDIFF COUNCIL LAMBY WAY SOLAR FARM DRAINAGE STRATEGY
CA11469/DRAFT JANUARY 2019
Page 1
EXECUTIVE SUMMARY
This Drainage Strategy is part of a suite of documents that supports the planning application
by Cardiff Council, for a development of a solar farm and ancillary development on land at
Lamby Way.
The development covers a total area of approximately 16.89 hectares of former landfill land
and comprises the installation of solar panels and associated infrastructure, including an
access route and a cabling route to a substation nearby.
This Drainage Strategy outlines the risk of flooding from all sources, including from fluvial,
tidal, surface water, groundwater, existing and proposed drainage infrastructure and other
artificial sources.
This Drainage Strategy outlines the existing surface drainage regime of the site and how this will be retained to ensure runoff is disposed at greenfield runoff rates.
The Proposed Development is therefore considered to be safe and appropriate in this regard
and can be suitably drained for the lifetime of the development.
CARDIFF COUNCIL LAMBY WAY SOLAR FARM DRAINAGE STRATEGY
CA11469/DRAFT JANUARY 2019
Page 2
1 INTRODUCTION
1.1.1 Wardell Armstrong (WA) was instructed by Cardiff Council (The Applicant) to produce
a Drainage Strategy for the development of a Solar Farm on land at Lamby Way,
Cardiff.
1.1.2 This Report details the proposed surface water drainage strategy.
Purpose of Report
1.2.1 The purpose of this report is to provide a technical appraisal of the flood risk pre- and
post-development by assessing all potential sources of flood risk. In addition, this
report provides a comprehensive site wide surface water strategy. This report will
form part of a larger suite of information to support the planning application for the
proposed development of the site.
1.2.2 WA 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.
Acknowledgement
1.3.1 Within this report, data from the BGS website has been ‘Reproduced with the
permission of the British Geological Survey © Natural Environment Research Council (NERC). All rights reserved’. Reproductions of any BGS materials does not amount to
an endorsement by NERC of any of its employees of any product or service and no
such endorsement should be stated or implied.
1.3.2 Data from Natural Resources Wales has also been included within this report. Flood
Zone data is now classed as Open Data. ‘Open Data can be accessed, used and shared
by anybody. It allows access to our data under the Open Government Licence – free
of charge and free of restriction, even for commercial use’.
CARDIFF COUNCIL LAMBY WAY SOLAR FARM DRAINAGE STRATEGY
CA11469/DRAFT JANUARY 2019
Page 3
2 EXISTING SITE CONDITIONS
Site Location and Description
2.1.1 The proposed development at Lamby Way, to the east of Cardiff is centred on
National Grid Reference ST 321900 177800.
2.1.2 The site comprises the western most portion of the former landfill site, bounded to
the west by the Rhymney River, to the south by the Severn Estuary, to the north by
Lamby Way, and to the east by further former landfill site land.
2.1.3 The proposed site is approximately 16.89 Hectares in total.
2.1.4 The site address is Lamby Way, Rumney, Cardiff, CF3 2HP. See Figure 1 below for site
location:
Figure 1 – Site Location Plan
(Source: Google Earth)
2.1.5 Topographical information has been provided, this is shown in Drawing CA11469-004.
The site slopes slightly from approximately 25m AoD in the East to 21m AoD to the
West with a slight depression around the pond at 20m AoD and rising again to 24.5m
towards the south west. Using the Pond as a reference the sites slopes slightly to the
north to approximately 16m AoD and to the south to 15m.
Approximate Solar Farm Site Boundary
CARDIFF COUNCIL LAMBY WAY SOLAR FARM DRAINAGE STRATEGY
CA11469/DRAFT JANUARY 2019
Page 4
Proximity to Watercourses
2.2.1 The development site is bounded to the west, northwest and southwest by the
Rhymney River. The confluence of the Rhymney River with the Severn Estuary is
approximately 300m directly South of the site. To the east of the development site,
separated by the remaining eastern part of the historic landfill site, is an unnamed
drainage channel approximately 1.2km in length. 500m to the north of the
development site is Parc Tredelerch Lake. There is a small pond area towards the
northeast of the site, covering approximately 3,000m2.
Geology
2.3.1 British Geological Survey (BGS) records suggest the entirety of the site is underlain by
bedrock geology of Mercia Mudstone. Superficial deposits, including clays, silts and sand, consistent with those from Tidal Flats, have been recorded in the vicinity.
2.3.2 The development is proposed on the site of a former landfill which has been capped.
The reinstatement details are shown in Drawing CSP11070-104.
CARDIFF COUNCIL LAMBY WAY SOLAR FARM DRAINAGE STRATEGY
CA11469/DRAFT JANUARY 2019
Page 5
3 POTENTIAL SOURCES OF FLOODING
3.1.1 The main sources of flooding identified by Planning Policy Wales, Edition 10 December
2018 (PPW) are ‘…from rivers and the sea, directly from rainfall on the ground surface
and rising groundwater, overwhelmed sewers and drainage systems, and from
reservoirs, canals and lakes and other artificial sources’.
3.1.2 These sources will be considered in turn in the following sections.
Fluvial and Tidal Flooding
3.2.1 Fluvial (river) flooding occurs when the capacity of watercourses (including streams,
brooks and ditches etc.) are exceeded due to intense rainfall. Natural Resources Wales
have produced mapping to indicate areas which may be at risk of fluvial flooding,
called Flood Zones, depicted on the Flood Map for Planning.
3.2.2 Following review of the existing Natural Resources Wales flood maps, the proposed
development area of the site is located within flood risk zone1, due to its elevated
position against neighbouring sites (See Figure 2 below).
Figure 2- Flood Map for Planning (Rivers and Sea)
(Source: https://maps.cyfoethnaturiolcymru.gov.uk)
Approximate Solar Farm Site Boundary
CARDIFF COUNCIL LAMBY WAY SOLAR FARM DRAINAGE STRATEGY
CA11469/DRAFT JANUARY 2019
Page 6
3.2.3 As a flood Zone 1 site this development area comprises land assessed as having a less
than 1 in 1,000 annual probabilities of river or sea flooding (<0.1%). Therefore, this
area of the site is suitable for development in terms of fluvial / tidal flood risk.
Pluvial/Surface Water Flooding
3.3.1 Pluvial flooding is caused by intense rainfall events, which collect onto surfaces at such
a rate that prohibits the efficient drainage and runoff of water into watercourses or
drainage infrastructure. This then contributes to surface water flooding where the
drainage systems become inundated, or permeable areas become saturated creating
an impermeable area effectively which eventually leads to surface water flooding.
Natural Resources Wales ‘Risk of Flooding from Surface Water’ Map examines the risk
of flooding from surface water without accounting for infiltration or the influence of
drainage systems.
3.3.2 The likelihood of surface water flooding is split into four categories; ‘Very Low’, ‘Low’,
‘Medium’ and ‘High Risk’. The ‘Very Low’ category indicates areas that have a chance of flooding of less than 1 in 1000 (0.1%) each year. ‘Low’ risk is defined as an area that
has a chance of flooding of between 1 and 1000 (0.1%) and 1 in 100 (1%) in any year
with a depth of water between 0-300mm. The ‘Medium’ risk category is defined as an area that has a chance of flooding of between 1 in 100 (1%) and 1 in 30 (3.3%) with a
depth of water between 300mm-900mm, and the ‘High’ risk category has a chance of
flooding of greater than 1 in 30 (3.3%) with a depth of water of over 900mm.
3.3.3 The Natural Resources Wales surface water flooding map indicates that the majority
of the site is at very low risk of surface water flooding, meaning it has less than 0.1%
annual probability of flooding. However, there is an isolated area of the site which is
indicated to have a low surface water flood risk (See Figure 3 below), giving an annual
flooding probability of 0.1% to 1%. This area corresponds to the existing pond on the
site. The identified surface water flood risk is therefore accommodated within the
existing surface water drainage system.
3.3.4 The site is therefore considered to be at low risk of surface water flood.
CARDIFF COUNCIL LAMBY WAY SOLAR FARM DRAINAGE STRATEGY
CA11469/DRAFT JANUARY 2019
Page 7
Figure 3 - Risk of Flooding from Surface Water
(Source: https://maps.cyfoethnaturiolcymru.gov.uk)
Groundwater Flooding
3.4.1 Groundwater flooding can occur anywhere where groundwater levels rise above the
ground surface. Groundwater flooding can be difficult to predict and identify and is
often associated with surface water flooding.
3.4.2 As the site is a capped landfill, with a leachate drainage system, groundwater flooding
is not an issue for the site.
Existing Drainage
3.5.1 Flooding from sewers and drains can occur when capacity is exceeded or there is a
blockage or collapse in the network.
3.5.2 The surface water information provided by Cardiff Council indicates a series of
Manholes located to the south and west of site which direct the rainwater from the
landfill geocomposite drainage layer to a land drain bordering the edge of the site to
the west. The flows are then conveyed to the River Rhymney. Should flooding of the
sewers occur, flows would be contained within the land drainage at the edge of the
site.
Approximate Solar Farm Site Boundary
CARDIFF COUNCIL LAMBY WAY SOLAR FARM DRAINAGE STRATEGY
CA11469/DRAFT JANUARY 2019
Page 8
3.5.3 The site is considered to be at low risk of flooding from existing sewers and drains.
Reservoirs, Canals and Lakes
3.6.1 Flooding from reservoirs, canals and lakes occurs when their associated dams,
embankments or other retaining structures fail or are breached.
3.6.2 There are no reservoirs near the site. Natural Resources Wales ‘Risk of Flooding from
Reservoirs’ mapping indicates that the site is not at risk of reservoir flooding. Please
refer to Figure 4 for details.
Figure 4 - Risk of Flooding from Reservoirs
(Source: https://maps.cyfoethnaturiolcymru.gov.uk)
Historic Flooding:
3.7.1 No historic flooding has been identified on the proposed development site.
Approximate Solar Farm Site Boundary
CARDIFF COUNCIL LAMBY WAY SOLAR FARM DRAINAGE STRATEGY
CA11469/DRAFT JANUARY 2019
Page 9
4 DEVELOPMENT PROPOSAL
4.1.1 The proposals are for an 8.7MW ground-mounted solar farm on approximately 16.89
Hectares of gently sloping land forming part of the waste landfill site at Lamby Way,
Rumney. A Site Layout Plan containing the solar panels array is reproduced in drawing
LAM-DWG002.
4.1.2 The solar panels will be formatted in rows across the site, in an appropriate south
facing direction at an angle of approximately 20 to 25 degrees from the ground.
4.1.3 The installation will include an estimated 30,688 individual panels combined to form
arrays that are arranged in rows. Each array will be supported by a galvanized steel
mounting structure supported in surface mounted concrete pads. The arrays are not
proposed to exceed 2.8m in height and the lower edge will be approximately 750mm above ground level.
4.1.4 Rows of panels will be separated by 5.18 metres minimum depending on the angle of
the panel. Please refer to Figure 5 for details. Figure 6 shows a typical structural support unit.
4.1.5 The Solar Panels will be secure into ballasted fixings with no penetrative works
required and no demolition works proposed to avoid any disturbance to the landfill engineered cap.
Figure 5 - Solar Panel Framing System – Side
CARDIFF COUNCIL LAMBY WAY SOLAR FARM DRAINAGE STRATEGY
CA11469/DRAFT JANUARY 2019
Page 10
Figure 6 – Typical Structural support unit
(Source: http://www.arpower.co.uk/images/wysiwyg/kx56uxgk.jpg)
CARDIFF COUNCIL LAMBY WAY SOLAR FARM DRAINAGE STRATEGY
CA11469/DRAFT JANUARY 2019
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5 SURFACE WATER MANAGEMENT STRATEGY
5.1.1 A sustainable strategy for the management of surface water runoff from the proposed
development has been prepared to ensure that flood risk to the site and the wider
area is not increased.
Landfill Existing Water Management Plan
5.2.1 The restored landfill at Lamby Way, Cardiff was fully capped using a geosynthetic
capping system comprised of a geocomposite drainage and protection layer,
impermeable geomembrane and protection geotextile. Please refer to Figure 7 and 8
for details.
Figure 7- Landfill Capping System Detail (Cardiff Council)
Figure 8 - Landfill Geocomposite Drainage Layer Detail (Cardiff Council)
5.2.2 The contaminated water (leachate) from the landfill currently discharge to the East of
the site where the effluent is treated prior to its discharge to the River Rhymney. See
Drawing CA11469-004 for details.
5.2.3 Surface water currently infiltrates into the soil cover where it is collected by the
Geocomposite draining layer and directed to a filter drain that runs along the west
CARDIFF COUNCIL LAMBY WAY SOLAR FARM DRAINAGE STRATEGY
CA11469/DRAFT JANUARY 2019
Page 12
and south of the site at the edge of the landfill. The effluent captured by the filter
drain is discharged at various points to the river Rhymney. See Drawing CA11469-004
for location and details.
5.2.4 In addition to this the part of the site drains to the attenuation pond in the centre of
the site, as shown on Drawing CA11469-004. This discharges to the River Rhymney to
the west via and open channel.
Additional Water Management Measures
5.3.1 It is proposed that the rainfall landing on the proposed solar panels will drain through
rainwater gaps and infiltrate into the ground beneath and between each row of
panels. From where it will infiltrate into the existing landfill capping drainage layer.
Figure 9 shows the cross section of a typical solar panel structural support unit.
Figure 9 – Typical Solar Panel Structural Support Unit – Cross Section
5.3.2 Ancillary equipment will be contained in small cabinets. Due to the size of the buildings
it is proposed that roof water will be discharged directly onto the surrounding ground
and infiltrates into the existing landfill capping drainage layer.
5.3.3 Soil compaction and disturbance of the capping layer should be kept to a minimum.
Any disturbances caused by the installation of the solar farm should be harrowed and
seeded prior to final commissioning.
CARDIFF COUNCIL LAMBY WAY SOLAR FARM DRAINAGE STRATEGY
CA11469/DRAFT JANUARY 2019
Page 13
5.3.4 Maintenance of the solar farm is unlikely to cause any major compaction of the soil;
Thus, the proposed development would not change the pre-development infiltration
rate of the underlying ground, which currently discharges at greenfield runoff rates.
5.3.5 Upon completion of the Solar Farm the vegetative cover of the site should be
maintained reducing the risk of soil erosion and reducing potential runoff.
CARDIFF COUNCIL LAMBY WAY SOLAR FARM DRAINAGE STRATEGY
CA11469/DRAFT JANUARY 2019
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6 CONCLUSIONS
6.1.1 The development of Land at Lamby Way will comprise the installation of a Solar Farm
which could produce 8.7MW of power on top of the restored landfill.
6.1.2 The proposal includes a provision for ground mounted solar panels with no
penetrative works required and no demolition works proposed. Minimising the impact
of installation in the engineered capping of the landfill.
6.1.3 Natural Resources Wales mapping indicates that the site is located wholly in Flood
Zone 1. The site is at low risk of flooding from all other sources.
6.1.4 Existing drainage features will be retained, with no increase in the current greenfield
run off from the site.
6.1.5 Rainfall falling on to the solar panels would runoff directly to the ground below and between the rows of panels and infiltrate into the landfill engineered cap. The
Geocomposite drainage layer will convey the flows to the existing system as it is
currently doing.
6.1.6 The site should remain vegetated through construction and operation of the solar
farm to prevent soil erosion.
6.1.7 The proposed drainage strategy anticipates that the installation of the solar farm will have no impact upon the current surface water regime for the site.
6.1.1 On consideration of the above, and on implementation of this strategy, it is considered
that the development will be appropriate in terms of flood risk and can be suitably drained for the development lifetime.
CARDIFF COUNCIL LAMBY WAY SOLAR FARM DRAINAGE STRATEGY
CA11469/DRAFT JANUARY 2019
DRAWINGS
Total Power = 8983.2 kWZone 1 = 200.64 kWZone 2 = 839.04 kW
Zone 3+4 = 72.96 kW
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48 Charlotte StreetLondon, W1T 2NSTel: 0203 7010381
Email: [email protected]: www.SOLRAC.co.uk
TOTAL POWER:
No. of MODULES:
MODULE POWER:
INVERTERS:
No. of CCTV:
NOTES:
PROJECT DETAILS
DESIGN KEY
C SOLRAC Ltd
Gates:
PROJECT:
DESCRIPTION:
DRAWING No.
DRAWN by:
CHECKED by:
APPROVED by:
Date:
ISSUE:
SCALE:
Lamby Way
Site Layout Plan
LAM-DWG002
Davide Orio
Carlos Javier
Carlos Javier
10/01/2019
V1
1:1250 @ A1
Lamby WayUnnamed Road,Rumney, CardiffCF3 2HP
8,746.08 kWp (DC)
30,688
285Wp
120x60kVA@25CTotal 7,200kW (AC)
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OVERLAND FLOW
ROUTE FROM POND
P0Preliminary Issue 11/01/19
Copyright Reservedc
DRAWN BY CHECKED BY
CLIENT
PROJECT
DRAWING TITLE
SCALE DATE
APPROVED BY
APP'DCHK'D
REVISION DETAILS DATE DRAWN
DO NOT SCALE FROM THIS DRAWING
N:\CA\CA11469 - LAMBY WAY SOLAR FARM PS\03 - DESIGN\AUTOCAD\CA11469-004-P0.DWG
DRG No.
DRG SIZE
REV
A1
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ENERGY AND SUSTAINABILITY
CARDIFF COUNCIL
LAMBY WAY SOLAR FARM PS
DRAINAGE CATCHMENT PLAN
CA11469-004
P0
1:2500 11/01/19
HRK
0m 50m 100m 150m 200m 250m
SCALE 1:2500
REFERENCE
DIRECTION OF FALL
LAND DRAINING TO ATTENUATION
POND
LAND DRAINING TO FILTER DRAIN
ASSUMED LINE OF FILTER DRAIN
ASSUMED LINE OF LEACHATE
DRAINAGE SYSTEM PIPE
ASSUMED SURFACE WATER MANHOLE
ASSUMED LEACHATE MANHOLE
ASSUMED SURFACE WATER PIPE TO
OUTFALL
OVERLAND FLOW ROUTING FROM
ATTENUATION POND TO RIVER
RHYMNEY
SITE BOUNDARY
