Appendix 8.1 Flood Risk Assessment - Peel

SOUTH CLYDE ENERGY CENTRE, GLASGOW
FLOOD RISK ASSESSMENT
Final Report v2.1
MAY 2012
Weetwood
Suite 4 East House
33-41 Chiltern Ave
Amersham
HP6 5AE
Tel: 01494 725448
info@weetwood.net
www.weetwood.net

Peel Environmental Ltd
Flood Risk Assessment – South Clyde Energy Centre, Glasgow
Report Title:
Client:
South Clyde Energy Centre, Glasgow
Flood Risk Assessment
Final Report v2.1
Peel Environmental Ltd
Date of Issue: 14 May 2012
Prepared by:
Checked by:
Approved by:
Sarah Cowie BSc
Project Manager
Geoff Waite BSc CEng C.WEM MICE MCIWEM
Director
Andrew Grime BEng MBA CEng C.WEM MICE FCIWEM
Managing Director
This document has been prepared solely as a Flood Risk for Peel Environmental Ltd. Weetwood
Services Ltd 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.
©Weetwood
www.weetwood.net
i 1727 SCEC/FRA_Final v2.1
14 May 2012

Peel Environmental Ltd
Flood Risk Assessment – South Clyde Energy Centre, Glasgow
CONTENTS
Signature Sheet
Contents
List of Figures & Appendices
Page
i
ii
iii
1 INTRODUCTION ............................................................... 1
1.1 SITE LOCATION .........................................................................................1
1.2 EXISTING AND PROPOSED DEVELOPMENT ....................................................2
1.3 SITE LEVELS .............................................................................................2
1.4 ACCESS AND EGRESS.................................................................................2
2 SCOTTISH PLANNING POLICY............................................. 3
2.1 SCOTTISH ENVIRONMENT PROTECTION AGENCY FLOOD MAP .........................3
2.2 DEVELOPMENT AND FLOOD RISK.................................................................3
2.3 STRATEGIC FLOOD RISK ASSESSMENT.........................................................4
3 FLOOD RISK .................................................................... 5
3.1 RIVER CLYDE.............................................................................................5
3.2 UNNAMED WATERCOURSE ..........................................................................6
3.3 GROUNDWATER FLOODING.........................................................................9
3.4 SURFACE WATER FLOODING ..................................................................... 10
3.5 ACCESS AND EGRESS............................................................................... 11
4 CONCLUSIONS............................................................... 12
©Weetwood
www.weetwood.net
ii 1727 SCEC/FRA_Final v2.1
14 May 2012

Peel Environmental Ltd
Flood Risk Assessment – South Clyde Energy Centre, Glasgow
LIST OF FIGURES
Figure 1: Site Location.......................................................................................1
Figure 2: SEPA Flood Map ..................................................................................3
Figure 3: River Clyde.........................................................................................5
Figure 4: Extract from Sewer Records .................................................................6
Figure 5: Unnamed Watercourse.........................................................................7
Figure 6: Inlet to 450mm Culvert Under Site ........................................................7
Figure 7: LiDAR Data.........................................................................................9
LIST OF APPENDICES
Appendix A:
Appendix B:
Appendix C:
Appendix D:
Appendix E:
Site Location Plan
Site Photos
Development Proposals
Topographic Survey
Public Sewer Records
©Weetwood
www.weetwood.net
iii 1727 SCEC/FRA_Final v2.1
14 May 2012

Peel Environmental Ltd
Flood Risk Assessment – South Clyde Energy Centre, Glasgow
1 INTRODUCTION
Weetwood were instructed to undertake a Flood Risk Assessment by Peel
Environmental Ltd in connection with the proposed development of an energy
from waste plant (South Clyde Energy Centre) on a site situated off Bogmoor
Road, Glasgow. The assessment has been prepared in accordance with the
requirements of Scottish Planning Policy (2010) and its supporting guidance
documents including Planning Advice Note 69 (PAN69): Planning and Building
Standards Advice on Flooding. The report has also been prepared with
reference to the Flood Risk Management (Scotland) Act (2009).
This report is based on studies of relevant detail and consultation with
Glasgow City Council (CC) and the Scottish Environmental Protection Agency
(SEPA). Weetwood has also produced a separate Drainage Impact Assessment
(DIA) 1 for this site in order to assess any likely impact of the proposals on
surface water runoff.
1.1 SITE LOCATION
The site is located off Bogmoor Road, at Ordnance Survey National Grid
Reference NS 529 654 (see Figure 1.)
King George V Dock
River Clyde
Hillington Road
Bogmoor Road Site
Bogmoor Road
Johnstone Avenue
Sheildhall Road (A8)
Railway Line
M8
Image reproduced with permission of Ordnance Survey and Ordnance Survey of Northern Ireland
Figure 1: Site Location
A more detailed site location plan is provided in Appendix A, which shows the
existing site layout and location of relevant features in the vicinity of the site.
Photos of the site and relevant features are provided in Appendix B.
1 “South Clyde Energy Centre, Glasgow: Drainage Impact Assessment”, Report. Ref: 1727 SCEC/DIAv2.1, 14 May
2012
©Weetwood
www.weetwood.net
1 1727 SCEC/FRA_Final v2.1
14 May 2012

Peel Environmental Ltd
Flood Risk Assessment – South Clyde Energy Centre, Glasgow
1.2 EXISTING AND PROPOSED DEVELOPMENT
The site has been previously developed, but is now vacant. The site consists of
areas of hardstanding with some overgrown, permeable land. The current
masterplan showing the development proposals is included in Appendix C.
The proposals are for construction of a waste management facility – an Energy
from Waste (EfW) plant.
1.3 SITE LEVELS
A topographic survey of the site has been undertaken and is included as
Appendix D of this report. The survey indicates that site levels increase from
7.50m Above Ordnance Datum (mAOD) in the north of the site to 10.00mAOD
in the south.
1.4 ACCESS AND EGRESS
Access and egress to the site is provided directly off Bogmoor Road to the
southeast of the site (Figure 1). Levels along this route are shown to fall from
8.54mAOD near the site to 8.02mAOD to the northeast.
©Weetwood
www.weetwood.net
2 1727 SCEC/FRA_Final v2.1
14 May 2012

Peel Environmental Ltd
Flood Risk Assessment – South Clyde Energy Centre, Glasgow
2 SCOTTISH PLANNING POLICY
2.1 SCOTTISH ENVIRONMENT PROTECTION AGENCY FLOOD MAP
According to the latest SEPA flood map for this area (Figure 2), the site is
located outside those areas defined as being at risk of flooding from rivers
and/or the sea.
Figure 2: SEPA Flood Map
2.2 DEVELOPMENT AND FLOOD RISK
The Risk Framework outlined in Scottish Planning Policy defines flood risk
using the following three categories:
1. Little or no risk – Annual probability of watercourse, tidal or coastal
flooding is less than 0.1% (1:1000)
2. Low to medium risk – Annual probability of watercourse, tidal or coastal
flooding is in the range 0.1% - 0.5% (1:1000 – 1:200)
3. Medium to high risk – Annual probability of watercourse, tidal or coastal
flooding is greater than 0.5% (1:200)
According to the SEPA flood map the site is considered to be at little or no risk
of flooding from rivers and/or sea. This is discussed in more detail in Section
3.
©Weetwood
www.weetwood.net
3 1727 SCEC/FRA_Final v2.1
14 May 2012

Peel Environmental Ltd
Flood Risk Assessment – South Clyde Energy Centre, Glasgow
2.3 STRATEGIC FLOOD RISK ASSESSMENT
Glasgow CC have not yet published their Strategic Flood Risk Assessment 2 .
SEPA have produced a “Local Plan Districts and Potentially Vulnerable Areas”
report in line with the requirements of the Flood Risk Management (Scotland)
Act (2009). The information contained has been used to inform this report.
Glasgow CC guidance 3 states that a Flood Risk and Drainage Impact
Assessment (FRA) “is now required for any residential development comprising
more than 5 dwellings and for industrial or commercial developments of more
than 250m 2 …The FRA will be required to certify that any flood risk associated
with the development can be managed now and in the future, taking into
account climate change and illustrate how the development will not increase
the risk of flooding elsewhere.”
2 Confirmed in email from David Russell (Gralsgow CC) to Sarah Cowie (Weetwood) dated 14 February 2011
3 Flood Risk Assessment and Drainage Impact Assessment: Planning Guidance for Developers, Glasgow City Council,
October 2009
©Weetwood
www.weetwood.net
4 1727 SCEC/FRA_Final v2.1
14 May 2012

Peel Environmental Ltd
Flood Risk Assessment – South Clyde Energy Centre, Glasgow
3 FLOOD RISK
3.1 RIVER CLYDE
The River Clyde (see Figure 3) flows in a westerly direction to the north of the
site. The site does not benefit from flood defences for the River Clyde.
Figure 3: River Clyde
This section of the River Clyde is tidally dominated. The site is shown to lie
outside the area at risk of flooding (see Figure 2). SEPA were contacted for
information concerning the level of risk to the site. Their response 4 stated
that, “Review of the Indicative River & Coastal Flood Map (Scotland) 200-year
flood outline (i.e. the flood with a 0.5% chance of occurring in any single year)
indicates that this area lies out-with this envelope.”
Glasgow CC were also consulted regarding the level of flood risk to the site.
Their response 5 stated that, “The Bogmoor Road site referred to is located
within the (general) vicinity of the River Clyde and is out-with an area
currently identified as likely to flood during a design flood event. Development
of the Bogmoor Road site does not represent an increased flood risk to the
River Clyde catchment and…a Flood Risk Assessment is not required in this
instance with regard to the River Clyde.”
Glasgow CC have not identified any records of flooding at the site.
The site is therefore not considered to be at risk of flooding from the River
Clyde.
4 Email from Nicola Rae (SEPA) to Sarah Cowie (Weetwood) dated 15 December 2010
5 Email from John Lowe (Glasgow CC) to Sarah Cowie (Weetwood) dated 15 December 2010
©Weetwood
www.weetwood.net
5 1727 SCEC/FRA_Final v2.1
14 May 2012

Peel Environmental Ltd
Flood Risk Assessment – South Clyde Energy Centre, Glasgow
3.2 UNNAMED WATERCOURSE
A railway line runs along the western boundary of the site. A small unnamed
watercourse is located to the west of the railway. The sewer records in
Appendix E show that this watercourse approaches the site from the south
via a 675mm culvert. The culvert outfalls into a section of open channel which
flows alongside the railway line. Figure 4 is an extract from the sewer records
and shows the location of relevant features discussed in the following sections.
1200mm surface
water sewer
450mm culvert
Site
Railway Line
900x1,350mm
combined sewer
450mm culvert inlet
375mm surface
water sewer
Open Channel
675mm culvert outlet
Figure 4: Extract from Sewer Records
©Weetwood
www.weetwood.net
6 1727 SCEC/FRA_Final v2.1
14 May 2012

Peel Environmental Ltd
Flood Risk Assessment – South Clyde Energy Centre, Glasgow
During the site visit 6 , it was seen that water within the channel was generally
stagnant with little obvious flow. The only outlet from this section of open
channel appeared to be via a 450mm culvert located approximately half way
along the channel length (see Figure 4 and Figure 6). The 450mm culvert
conveys flows north across the site and connects into a 1,200mm public
surface water sewer (manhole number 7701). The 1,200mm sewer then runs
northeast under the site towards the River Clyde.
A 375mm public surface water sewer is shown in Appendix E and Figure 4 to
connect with the 450mm culvert near the offtake from the open channel. This
pipe was not seen during the site visit, so it is believed to run under the open
channel into the 450mm culvert, rather than outfalling into the channel itself.
Figure 5: Unnamed Watercourse
Figure 6: Inlet to 450mm Culvert Under Site
6 Undertaken on 14 January 2011
©Weetwood
www.weetwood.net
7 1727 SCEC/FRA_Final v2.1
14 May 2012

Peel Environmental Ltd
Flood Risk Assessment – South Clyde Energy Centre, Glasgow
SEPA have confirmed 7 that they hold no information regarding the risk of
flooding from the unnamed watercourse. Glasgow CC have also not raised any
concerns regarding flooding from this watercourse. The catchment area of the
unnamed watercourse has been investigated on the FEH CD v3 produced by
the Centre for Ecology and Hydrology. The minimum catchment size on the
FEH CD is 0.5 km 2 . The catchment area for this watercourse is not shown,
inferring that it is less than 0.5 km 2 .
3.2.1 Risk of Flooding from Unnamed Watercourse
In order for the site to be at risk of flooding from the unnamed watercourse,
floodwaters would need to overtop the channel and the railway line. The most
likely location for overtopping would be upstream of the 450mm culvert under
the railway line (see Figure 6). The 450mm culvert is smaller than the
675mm culvert upstream of the open channel and may well restrict flows
leaving the open channel. The culvert entrance may also be prone to blockage,
especially given the amount of debris in the open channel upstream (see
Figure 5). Should water from the open channel be unable to discharge
through the culvert under to the site due to blockage, floodwaters would build
up within the channel.
The catchment of the unnamed watercourse is believed to be less than 0.5km 2
in area and highly urbanised. The urbanisation means that the catchment is
likely to have a rapid response time. However, it also means that the
catchment will probably drain mainly via the public sewer system. In the
vicinity of the site, the public surface water sewer system includes a 1,200mm
public surface water sewer running through the site, and the combined sewers
under Bogmoor Road (Appendix E). One of these combined sewers measures
900mm x 1,350mm in size. The capacity of the surface water drainage system
in the vicinity of the site is therefore much larger than the capacity of the
culverts associated with the unnamed watercourse. Given this, the
watercourse catchment is believed to drain primarily via the public sewer
system, with only minor flows reaching the open channel near the site.
Observations during the site visit support this conclusion. Despite the fact that
it was raining during the site visit, water within the open channel was
generally stagnant with no significant rates of flow observed. In addition, the
open channel has a relatively large capacity in relation to the observed flow. It
is therefore not considered that the site is at risk of flooding from the
unnamed watercourse.
In the unlikely event that the open channel filled to capacity (e.g. if the
450mm outflow culvert became completely blocked) water would need to
overtop the railway line before reaching the site. LiDAR data has been
obtained for the site and surrounding area. The cross sections in Figure 7
overleaf show that the depth of water within the open channel would need to
exceed 1.5m before overtopping the railway line. Floodwaters would then
spread out to cover the large area of low-lying land available in the vicinity of
the site rather than building up to a depth sufficient to pose a risk to users of
the site.
7 See footnote 2
©Weetwood
www.weetwood.net
8 1727 SCEC/FRA_Final v2.1
14 May 2012

Peel Environmental Ltd
Flood Risk Assessment – South Clyde Energy Centre, Glasgow
Recognising the above, it is not considered that the site is at significant risk of
flooding from the unnamed watercourse.
Open Channel
Railway Line
Site
Open Channel
Railway Line
Site
Cross Section 1 Cross Section 2
Open Channel
Railway Line
Site
Cross Section 3
Figure 7: LiDAR Data
3.3 GROUNDWATER FLOODING
Groundwater flooding generally occurs during intense, long-duration rainfall
events, when infiltration of rainwater into the ground raises the level of the
water table until it exceeds ground levels. It is most common in low-lying
areas overlain by permeable soils and permeable geology, or in areas with a
naturally high water table.
Paragraph 21 of PAN69 states that ‘water tables are not rising generally in
Scotland, but there can be localised problems in some areas’. SEPA’s “Local
Plan Districts and Potentially Vulnerable Areas” report 8 states that there is
potentially a “low to moderate” risk of groundwater flooding within part of the
catchment area, but does not provide any details of potential problems in the
vicinity of the site.
8 “Local Plan Districts and Potentially Vulnerable Areas – Flood Risk Management (Scotland) Act 2009 – 11 Clyde and
Loch Lomond” SEPA, 2011
©Weetwood
www.weetwood.net
9 1727 SCEC/FRA_Final v2.1
14 May 2012

Peel Environmental Ltd
Flood Risk Assessment – South Clyde Energy Centre, Glasgow
The British Geological Society Groundwater Flooding Hazard Maps indicate that
Glasgow is situated within an area with very low to low groundwater
vulnerability. Glasgow CC have not provided 9 any information on groundwater
flooding. Groundwater flooding is therefore not considered to be a significant
source of flood risk to the site.
3.4 SURFACE WATER FLOODING
Surface water flooding comprises pluvial flooding, sewer flooding and
flooding from highway drains and gullies.
3.4.1 Pluvial Flooding
Pluvial flooding results from rainfall-generated overland flow, before the runoff
enters any watercourse or sewer, or where the sewerage/drainage systems
and watercourses are overwhelmed and therefore unable to accept surface
water. Pluvial flooding is usually associated with high intensity rainfall events
but may also occur with lower intensity rainfall where the ground is saturated,
developed or otherwise has low permeability resulting in overland flow and
ponding within depressions in the topography.
Glasgow CC have not identified any problems with pluvial flooding at the site.
Any issues with regard to surface water flooding will be addressed through the
surface water drainage scheme as outlined in the Drainage Impact
Assessment.
3.4.2 Sewer Flooding
Sewer flooding occurs when the sewerage infrastructure has to deal with flow
rates beyond its design capacity. This occurs most often as a result of high
intensity rainfall events and, as detailed in paragraph 16 of PAN69, is
exacerbated by the fact that the sewage infrastructure in many parts of
Scotland constitutes an old combined system, taking both foul sewerage and
surface water.
Scottish Water have not indicated any records of historical sewer flooding
within this area.
Scottish Planning Policy and PAN69 encourage new developments to separate
surface and foul water discharges to reduce the volume of water entering the
public sewer system. Scottish Planning Policy promotes the use of Sustainable
Drainage Systems (SUDS) to address surface water drainage. SUDS are
designed to manage the flow of surface water which could otherwise find its
way into the public sewer network or receiving watercourse. By reducing the
volume of surface water in a sewer, SUDS will subsequently reduce the
likelihood of sewer or watercourse flooding.
This is considered in further detail in the Drainage Impact Assessment with
respect to the proposed development site.
9 Email from John Lowe (Glasgow City Council) to Sarah Cowie (Weetwood) dated 15 December 2010
©Weetwood
www.weetwood.net
10 1727 SCEC/FRA_Final v2.1
14 May 2012

Peel Environmental Ltd
Flood Risk Assessment – South Clyde Energy Centre, Glasgow
3.5 ACCESS AND EGRESS
Access to the site will be provided via Bogmoor Road to the north. Bogmoor
Road lies outside any areas at risk of flooding from the River Clyde. It is
considered unlikely that the unnamed watercourse to the west of the site
would flood the area of Bogmoor Road to the extent and depths required to
preclude access of egress for the site.
Safe access and egress from the site may therefore be provided via Bogmoor
Road.
©Weetwood
www.weetwood.net
11 1727 SCEC/FRA_Final v2.1
14 May 2012

Peel Environmental Ltd
Flood Risk Assessment – South Clyde Energy Centre, Glasgow
4 CONCLUSIONS
There are proposals for construction of an EfW plant on an area of land located
off Bogmoor Road, Glasgow. According to SEPA’s flood map the proposed
development site is located within an area at little or no risk of flooding.
The site is not considered to be at risk of flooding from the River Clyde. Flood
risk from an unnamed watercourse to the west is considered to be low.
The site is not considered to be at risk from groundwater flooding or surface
water flooding.
Access and egress will be provided via Bogmoor Road, which is expected to
remain safe for use in the event of a flood.
©Weetwood
www.weetwood.net
12 1727 SCEC/FRA_Final v2.1
14 May 2012

Peel Environmental Ltd
Flood Risk Assessment – South Clyde Energy Centre, Glasgow
APPENDIX A:
Site Location Plan
©Weetwood
www.weetwood.net
1727 SCEC/FRA_Final v2.1
14 May 2012

Peel Environmental Ltd
Flood Risk Assessment – South Clyde Energy Centre, Glasgow
APPENDIX B:
Site Photographs
©Weetwood
www.weetwood.net
1727 SCEC/FRA_Final v2.1
14 May 2012

Peel Environmental Ltd
Flood Risk Assessment – South Clyde Energy Centre, Glasgow
APPENDIX C:
Development Proposals
©Weetwood
www.weetwood.net
1727 SCEC/FRA_Final v2.1
14 May 2012

Peel Environmental Ltd
Flood Risk Assessment – South Clyde Energy Centre, Glasgow
APPENDIX D:
Topographic Survey
©Weetwood
www.weetwood.net
1727 SCEC/FRA_Final v2.1
14 May 2012

Peel Environmental Ltd
Flood Risk Assessment – South Clyde Energy Centre, Glasgow
APPENDIX E:
Public Sewer Records
©Weetwood
www.weetwood.net
1727 SCEC/FRA_Final v2.1
14 May 2012