branksome care home extension - high peak, derbyshire
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Branksome Care Home Extension
Flood Risk Assessment
June 2014
Document Ref 020PDL-002
Document Control Record
Rev Date Description/Amendment Author Appr’d
1 02/06/2014 Final for issue to client EA JW
This document is the property of Phoenix Adam Ltd. It must not be reproduced in whole or in part or otherwise disclosed without prior written consent from Phoenix Adam Ltd. The official controlled copy of this document is the PDF document on the Phoenix Adam Ltd network server and visible to all authorized users. All printed copies, and all electronic copies and versions except the ones described above, are considered uncontrolled copies used for reference only. This document is controlled as a single entity, as any change – however slight, even a single character – to any part of the document by definition changes the entire document. For this reason, as well as the fact that the concept of “page” varies with the publication format, page-level revision is not practiced with this or any other Phoenix Adam Ltd document.
Originator:
Eric Agyemang
Date 27/01/2014
Approved By
John Ward.
Date 02/06/2014
Revision No
001
Doc Ref 020PDL-002 Page 2 of 14
Contents
1. Introduction ............................................................................................................. 3
2. Development Description, Location and Soil Type................................................... 4
2.1. Development Description ........................................................................................... 4
2.2. Development Location ............................................................................................... 4
2.3. Soil Type .................................................................................................................... 4
3. Sequential and Exception Tests .............................................................................. 5
4. Definition of the Flood Hazard ................................................................................. 6
4.1. Potential Flooding Sources ........................................................................................ 6
4.2. Ground Water ............................................................................................................ 6
4.3. Surface Water ............................................................................................................ 7
4.4. Piped Drainage .......................................................................................................... 8
5. Flooding Probability ................................................................................................. 9
5.1. Flood Risk Map .......................................................................................................... 9
5.2. Strategic Flood Risk Assessment ............................................................................. 10
5.3. Climate Change ....................................................................................................... 11
6. Detailed Development Proposals .......................................................................... 11
7. Flood Risk Management Measures ....................................................................... 11
8. Off Site Impacts ..................................................................................................... 12
9. Residual Risks ...................................................................................................... 12
10. Conclusions ....................................................................................................... 13
11. Recommendations ............................................................................................. 13
12. Report Authors................................................................................................... 13
13. Disclaimer .......................................................................................................... 14
Originator:
Eric Agyemang
Date 27/01/2014
Approved By
John Ward.
Date 02/06/2014
Revision No
001
Doc Ref 020PDL-002 Page 3 of 14
1. Introduction
Phoenix Adam Limited (PAL) was appointed by Pharaoh Designs (West Midlands) Ltd to
undertake a Flood Risk Assessment (FRA) in support of a full planning application by
Four Seasons Health Care for a proposed extension of Branksome Care Home in
Buxton, Derbyshire.
The proposed redevelopment site lies within the Environment Agency’s (EA) Flood Zone
1, which means that it has a low probability risk of flooding from rivers.
This document details the findings of the FRA undertaken in May 2014. The degree of
detail entered into any FRA is dependent upon the scale and potential impact of the
proposed development. This FRA has been developed based on guidance from the
National Planning Policy Framework (NPPF) March 2012 and its accompanying
technical guide and considers flooding from all sources, not just main rivers.
Originator:
Eric Agyemang
Date 27/01/2014
Approved By
John Ward.
Date 02/06/2014
Revision No
001
Doc Ref 020PDL-002 Page 4 of 14
2. Development Description, Location and Soil Type 2.1. Development Description
The proposed development is an extension of the existing Branksome Care Home
building, at St Johns Road, Buxton. The 12 bedroom extension will comprise ground
floor and first floor levels. Other external works will comprise landscaping, planting and
additional car parking.
2.2. Development Location
The development site is located in the historic spa town of Buxton in the Peak District,
the Branksome Care Home is situated close to all local amenities. The River Wye lies
approximately 30m to the south.
The town centre lies to the east. The Grid Reference of the site is E404898 N373428.
2.3. Soil Type
The broad classification soil types, or superficial deposits (formerly known as drift
geology), as described by the British Geological Survey for the area are indicated in the
map below.
The site lies within the pale yellow map zone which is described in detail below.
Site Location
Originator:
Eric Agyemang
Date 27/01/2014
Approved By
John Ward.
Date 02/06/2014
Revision No
001
Doc Ref 020PDL-002 Page 5 of 14
Superficial deposits are the youngest geological deposits formed during the most
recent period of geological time, the Quaternary, which extends back about 2.6 million
years from the present. They rest on older deposits or rocks referred to as bedrock.
The superficial deposits for this site are described as;
‘Alluvium - Gravel, Sand, Silt And Clay. Local environment previously dominated by
rivers. These rocks were formed from rivers depositing mainly sand and gravel
detrital material in channels to form river terrace deposits, with fine silt and clay from
overbank floods forming floodplain alluvium. Normally soft to firm consolidated,
compressible silty clay, but can contain layers of silt, sand, peat and basal gravel. A
stronger, desiccated surface zone may be present’.
3. Sequential and Exception Tests
The NPPF Technical Guide paragraphs 3 and 4 describe the FRA procedure. There are
two tests to be applied in the initial assessment; these are called the sequential test and
the exception test.
The aim of the Sequential Test is to direct development away from areas at risk of
flooding. Development should be directed to Flood Zone 1 wherever possible, and then
sequentially to Flood Zones 2 and 3, and to the areas of least flood risk within Flood
Zones 2 and 3.
Site Location
Originator:
Eric Agyemang
Date 27/01/2014
Approved By
John Ward.
Date 02/06/2014
Revision No
001
Doc Ref 020PDL-002 Page 6 of 14
From undertaking the sequential test it is clear that the proposed development lies within
Flood Zone 1 which is assessed as having a less than 1 in 1000 annual probability of
river flooding in any year (<0.1%).
The development is classified as ‘more vulnerable’ according to Table 2 of the NPPF
Technical Guide.
As the proposed development lies within Flood Zone 1 - Low Probability, the Exception
Test is not applicable.
Under the current NPPF Technical Guide the proposed development is considered
appropriate for planning consent.
4. Definition of the Flood Hazard 4.1. Potential Flooding Sources
Flood Source Relevant to Site?
Justification
River / Watercourse No Outside the functional flood plain of the River Wye
Sea / tidal influence No Non coastal and outside the zone of tidal influence
Ground Water Yes Geographic location and nature of the underlying soil
Surface Water Yes Geographic location and nature of the underlying soil
Piped Drainage Yes Both wastewater and storm water systems lie close to the site boundary.
4.2. Ground Water
The SFRA conducted by Halcrow Group in 2008 did not find any specific problems with
flooding from groundwater in this area.
However, as the site is low lying compared to the land immediately to the north east and
is also located adjacent to the river Wye the water table may be relatively close to the
surface. It is possible that natural seasonal variation in water table depth could result in
groundwater flooding at the site. It is also possible, given the geography and the nature
of the underlying soils, noted in section 2.3 above, that rainfall induced changes in
ground water level may also pose a flood risk.
Originator:
Eric Agyemang
Date 27/01/2014
Approved By
John Ward.
Date 02/06/2014
Revision No
001
Doc Ref 020PDL-002 Page 7 of 14
Ground water flooding is unlikely to reach depths that would cause significant disruption
to the normal use of the site. On balance, the hazard arising from this flooding source is
low.
4.3. Surface Water
The land slopes mildly from an elevation of 343m above sea level at the A5004
Manchester Road (North of the site) to 300m above sea level at the site location. This
equates to a fall of 43m over a distance of around 500m, an average gradient of 1 in 12.
During severe rainfall events there is a risk of surface water runoff being routed by
overland flow paths to the site location. This is known commonly as ‘flash flooding’.
The hazard from flash flooding will be greatest during the summer months during high
intensity, short duration storms may exceed the capacity of the below ground drainage in
the area.
Localised overland flood routing would be along Carlisle Road towards Branksome Care
Home. Overland flows would split at the junction with the Paddock heading west and
south of the site. The site itself is protected by a high stone wall which would divert flow
View north along Carlisle Road with
Branksome Care Home to the left.
View north south towards Branksome
Care Home from Carlisle Road.
Originator:
Eric Agyemang
Date 27/01/2014
Approved By
John Ward.
Date 02/06/2014
Revision No
001
Doc Ref 020PDL-002 Page 8 of 14
away from the building. The building itself is low lying compared to the road and there is
some residual risk of road channel flows overtopping the driveway entrance level.
The impact of flash flooding is likely to be of short duration with shallow flows of high
velocity along Carlisle Road. However, any overland flow reaching the site would slow
down and ‘pond’ around the building before finding an exit route to the river wye. Flows
across the site would be shallow and of low velocity.
The hazard from this flooding source is low.
4.4. Piped Drainage
Public sewer records held by Severn Trent Water Ltd indicate both wastewater and
storm water piped drainage systems along The Paddock to the north, Carlisle Road to
the east and St John’s Road to the south, as shown in the plan below.
The 225mm diameter pipelines shown in red are wastewater sewers which also take
some surface water. These are known as combined sewers and can be considered to
be a flood risk for the site during extreme rainfall events.
The 225mm diameter pipeline shown in blue is a surface water sewer which takes roof
and road runoff only. This too can be considered to be a flood risk for the site during
extreme rainfall events.
Flood register from Severn Trent Water does not show any historical flooding at the site
and its immediate vicinity over the past 20 years.
Site Location
Originator:
Eric Agyemang
Date 27/01/2014
Approved By
John Ward.
Date 02/06/2014
Revision No
001
Doc Ref 020PDL-002 Page 9 of 14
The site location is low lying compared to the surrounding drainage network. However,
this is not considered a risk factor as we understand the site is hydraulically separated
from the gravity network in Carlisle Road by a private pumping station.
The hazard from this flooding source is low
5. Flooding Probability 5.1. Flood Risk Map
The EA Flood Risk Maps identify the likelihood and severity of flooding across the
England and Wales. The areas shown in blue on each side of a river channel is Flood
Zone 3 and the extended area in cyan is Flood Zone 2. All other areas on the map are
Flood Zone 1.
At its closest, the River Wye lies just 20m from the southern edge of the proposed
building extension. However, the latest EA flood maps indicate that the development site
is outside the functional flood plain of the river.
54 67 97 130
SK04739597
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SK04739593
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SK04739695
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SK04739597311.361
SK04739593311.360
SK04739591316.118
--
SK04739401.1150
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SK05730491.1225
305.370303.792
SK04739597.1225
307.731305.490
SK04739593.1225
308.560307.761
-225
313.448308.570
SK04739695.1225
315.944313.468
Nodeground (m AD)
Linkwidth (mm)us inv (m AD)ds inv (m AD)
m AD
303.0
319.0
305.0
307.0
309.0
311.0
313.0
315.0
317.0
m
The Paddock
Carlisle Road
Originator:
Eric Agyemang
Date 27/01/2014
Approved By
John Ward.
Date 02/06/2014
Revision No
001
Doc Ref 020PDL-002 Page 10 of 14
It is evident from the Flood Risk Map that the proposed development falls within Flood
Zone 1 – Low Probability risk of flooding from rivers or sea. This zone comprises land
assessed as having a less than 1 in 1000 annual probability of river or sea flooding in
any year (<0.1%).
5.2. Strategic Flood Risk Assessment
The SFRA produced for the Peak District Sub Region by Halcrow Group has been used
to inform the relevant sections of this report. This study was completed and the final
report published in September 2008.
A key outcome of the SFRA process is the establishment of the Sequential Test in
accordance with paragraph 3 of the NPPF Technical Guide. The SFRA informs the
planning process, by taking into account flood risk through all sources and the impacts
of climate change. The SFRA categorises the area in terms of the likelihood (or
probability) that flooding will occur.
Site Location
Originator:
Eric Agyemang
Date 27/01/2014
Approved By
John Ward.
Date 02/06/2014
Revision No
001
Doc Ref 020PDL-002 Page 11 of 14
5.3. Climate Change
The UK Climate Impacts Programme (UKCIP) is responsible for promoting use of the
UK Climate Projections, alongside other tools and guidance, to help organisations to
prepare for the unavoidable impacts of climate change. UKCIP co-ordinated the
stakeholder input into the development of the Projections. UKCIP is principally funded by
Defra, and provides its services free of charge. UKCP09 is the short name for UK
Climate Projections. Detailed guidance on the use of the Projections can be found on
the UKCP09 website http://ukcp09.defra.gov.uk alongside information on how to access
further training in using them.
There is an increasing body of scientific evidence that the global climate is changing as
a result of human activity. As a result, sea levels will rise globally. In addition to this
there is a predicted increase in rainfall and stormy weather. This could all have
significant impacts on the likelihood and frequency of flooding.
Within the Derbyshire / Peak District area winter precipitation is predicted to increase by
between 10% and 20% by the 2080s. It seems highly likely that one of the effects of
climate change will be flooding on a larger scale in most winters than has previously
been recorded.
UKCP09 also predicts increases in summer drought followed by heavier rainfall which
could increase the frequency of flash flooding.
6. Detailed Development Proposals
The proposed 12 bedroom extension will comprise ground floor and first floor levels.
Other external works will comprise landscaping, planting and additional car parking. No
absolute levels were available but we understand that the proposed finished level of the
ground floor is to be around 300mm below the existing building floor level.
Based on Table 2 of NPPF Technical Guide, Flood Risk Vulnerability Classification, the
land use for residential care homes is “More Vulnerable”. This means that the Building is
required to be operational even during a flooding event.
7. Flood Risk Management Measures
It is unlikely that groundwater, surface water or piped drainage flooding would breach
the door thresholds. The site slopes towards the river and any surface water would find
natural overland flow paths away from the building.
Originator:
Eric Agyemang
Date 27/01/2014
Approved By
John Ward.
Date 02/06/2014
Revision No
001
Doc Ref 020PDL-002 Page 12 of 14
Based on the assessment of current data, no specific flood risk management measures
are required at this site.
However, some flooding resilience measures are appropriate. The layout and
landscaping of the site should aim to route flood water away from the building and avoid
creating hazards to access and egress routes. The CIRIA publication ‘C635 Designing
for exceedance in urban drainage’ provides design guidance and examples of good
practice.
8. Off Site Impacts
There will be a slight increase in the overall impermeability of the site due to the
development works. The current surface water and wastewater discharges will
marginally increase.
Wastewater flow increase will reduce the capacity of the wastewater network which
could increase flood risk from local piped drainage. We understand that wastewater
from the site is transferred to the public sewer system via a private pumping station. Any
increase in discharge rate would need to be agreed with Severn Trent Water Ltd.
Surface water flow increase, if connected to the surface water pipe network may have a
significant localised impact on flood risk. To mitigate this risk the EA strongly
encourages a Sustainable Drainage Systems (SuDS) approach to the management of
surface water for all new developments. The SuDS principle is to try to replicate natural
drainage systems using cost effective solutions with low environmental impact.
SuDS offer significant advantages over conventional piped drainage systems in reducing
flood risk by reducing the quantity of surface water run-off from a site and the speed at
which it reaches water courses, promoting groundwater recharge, and improving water
quality and amenity. The range of SuDS techniques available means that a SuDS
approach in some form will be applicable to any development.
9. Residual Risks
As flood resilience measures only are considered advised for this development,
flooding from the sources described above remains a residual risk, though the risk is
considered low.
Projected climate change effects may increase the risk of flooding from all sources.
However these effects are not considered significant over the anticipated design life of
the proposed building.
Originator:
Eric Agyemang
Date 27/01/2014
Approved By
John Ward.
Date 02/06/2014
Revision No
001
Doc Ref 020PDL-002 Page 13 of 14
10. Conclusions
This FRA demonstrates that flood risk issues at this site are manageable and that future
site users can be safeguarded for the lifetime of the development.
This FRA demonstrates that:
• The development site is situated in Flood Zone 1, having a less than 1 in
1000 annual probability of river flooding in any year (<0.1%).
• There is a low risk of flooding at the site from all other sources.
• The development should have minimal off site impact on flood risk to others.
11. Recommendations
Flood resilience measures are recommended. The layout and landscaping of the site
should aim to route flood water away from the building and avoid creating hazards to
access and egress routes. The CIRIA publication ‘C635 Designing for exceedance in
urban drainage’ provides design guidance and examples of good practice.
The use of SuDS to control surface water runoff from the development site is
recommended. SuDS offer significant advantages over conventional piped drainage
systems in reducing flood risk by reducing the quantity of surface water run-off from a
site and the speed at which it reaches water courses, promoting groundwater recharge,
and improving water quality and amenity.
12. Report Authors
Eric Agyemang graduated with an MSc in Water and Environmental
Engineering from the University of Surrey in 2004. Eric has over 8 years
water industry experience specialising in hydraulic and hydrological
modeling of urban drainage networks to alleviate flooding and river water
quality issues.
John Ward is a Chartered Water and Environmental Manager. John has
over 25 years water industry experience in urban drainage network
hydraulic, hydrological and water quality modelling. He has specialised in
urban drainage area planning and strategic options development to meet
EU directives on flooding.
Originator:
Eric Agyemang
Date 27/01/2014
Approved By
John Ward.
Date 02/06/2014
Revision No
001
Doc Ref 020PDL-002 Page 14 of 14
13. Disclaimer This assessment report has been prepared by PAL with all reasonable skill, care and
diligence and taking account of the scale and nature of the development. Information
presented in the report is based on interpretation of the data collected which has been
accepted from third parties in good faith as being current, accurate and valid.
This report is for the exclusive use of Four Seasons Health Care. No warranties or
guarantees are expressed or should be inferred by any third parties. This report may not
be relied upon by other parties without written consent from PAL.
PAL disclaims any responsibility to the client and others in respect of any matters
outside the agreed scope of the assessment.
Phoenix Adam Ltd
Unit 7 Riverside Business Park
Buxton Road
Bakewell
DE45 1GS
Tel: 01629 813330 email: info@phoenixadam.com web: www.phoenixadam.com
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