strategic flood risk assessment for poole - level
2
STRATEGIC FLOOD RISK ASSESSMENT FOR POOLE - LEVEL 2
contents
1 Recommendations Summary
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2 Introduction
Context
History
National Planning Policy
Flood Zones
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3 SFRA Level 2
Scope of Work
Existing Flood Defences
Scenarios
Climate Change
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4 Purpose
Sequential Approach
Exceptions Test
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5 Conclusions
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6 Recommendations
Maps
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Map 3.1 - Present Day - 1% annual probability event
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Map 3.2 - Present Day - 0.1% Annual probability event
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Map 3.3 - Climate change scenario - 0.5% annual probability for 2086
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Map 3.4 - Climate Change scenario - 0.5% annual probability for 2126
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Figures
Figure 2.1 - Present Day -Base Line Map
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Figure 3.1 - Existing flood defences with elevations
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Figure 3.2 - Water Velocity 0.5% Annual probability Event
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Figure 3.3 - Present Day - 5% annual probability
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Figure 3.4 - Raised Defences for a 0.5% annual probability tide
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1 Recommendations Summary
1.1 The Level 2 Strategic Flood Risk Assessment has identified recommendations that are summarised
below. Poole will require existing flood defences to be improved and new defences to be built in all currently
unprotected areas. This Assessment will help to guide the provision of flood protection for Poole over the
next century.
1.2 The following is a list of the recommendations to come from this work, and includes other general
requirements to address flood risk, and it will provide a steer on how flood mitigation and protection
measures should be employed within this area of the Borough in the future.
Where justified new building in the identified flood risk areas should be flood resilient. Basements
should not be used for habitable purposes. Where basements are permitted for commercial use, it
is necessary to ensure that the basement access points are situated 300 mm above the 0.5%
probability flood level plus climate change.
Undercroft parking, where it is at ground floor level, may be justified as a means of mitigating against
potential sea level rise, by providing first floor habitable accommodation over.
As a precautionary principle a 600mm freeboard will be necessary with new development. This may
be reduced in some circumstances if applicants undertake additional modelling through Flood Risk
Assessments to justify such modification.
The risk of flooding is predicted to significantly increase over the next 100 years without further flood
defence works (due to climate change and sea level rise assumptions). Defences will need to be
raised by at least the same amount as the sea level rise (approximately 0.7m by 2086 and 1.3m by
2126) and extend to zones beyond the regeneration areas to maintain a standard of protection
equivalent to the current standard.
In relation to flood defences the 0.7 metres and 1.3 metres sea level rise will require an additional
200mm freeboard.
To provide protection for the future situation, the Regeneration Areas A and B will both need defences,
such as flood walls or embankments, with elevation sufficient to prevent any significant wave
overtopping for a 0.5% joint probability event. As schemes come forward these developments will
need to provide their own defences and also ensure their defences form part of strategic flood defence
measures required for the Regeneration Area sites.
Additional defences will also be required outside the Regeneration Areas (to combat water overtopping
into adjoining land and so preventing water spreading to the Regeneration Areas and other central
areas like Hamworthy and the town centre) in the following zones:
North of Regeneration Area B, close to the railway station
South of Regeneration Area B, east of Poole Bridge
East of Regeneration Area A, east of Poole Bridge.
The standard of protection of the existing flood defences in the town will need to be investigated in
the future, and any new defences promoted on a benefit/cost basis. (New defences should built in
such a way that they can be modified in response to further predictions and varying circumstances
in the future). This analysis is a recommendation of this SFRA and will need to be undertaken to
identify the exact nature of the necessary works and likely costs. This will be taken forward in the
Infrastructure Planning work that is on-going to support growth in Poole, and linked to the Environment
Agency's Medium Term Plan for schemes.
The Bournemouth and Poole Resilience Group should continue to respond to, and co-ordinate
procedures for, emergency evacuation in Poole (that includes events relating to flooding) in accordance
with its evacuation plan. The 5 emergency shelter points known as 'Primary Rest Centres' should
be retained, with their additional roles clearly safeguarded in future planning.
STRATEGIC FLOOD RISK ASSESSMENT FOR POOLE - LEVEL 2
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one recommendations summary
SUDS should be implemented, where deemed appropriate and necessary, to ensure that run-off
from sites after development is not increased.
As Poole is a low lying urban area adjacent to its Harbour it relies upon pumping stations to dispose
of both foul and surface water. These facilities should be protected in the future, by being flood
proofed and secondary electrical power made available to them.
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2 Introduction
Context
Level 1 SFRA
2.1 A level 1 SFRA was carried out in July 2007. This identified where flooding has occurred, where
there is existing risk and where there could be risk in the future, also having regard to the Environment
Agency's Flood Zones. The SFRA Level 1 identified a future need to specifically carry out the Sequential
Test on Poole's allocated Regeneration Area sites that largely fall within Flood Zone 3. Already there is
limited opportunity to build on alternative sites outside Flood Zone 3, and there are several large, vacant
brownfield sites existing in the central area and in the urban context that are due to come forward for
housing provision and economic growth, that are already at risk from flooding. Many of these site have
been identified in the statutory Poole Local Plan First Alteration 2004.
2.2 Following on from the SFRA Level 1 is the need for the second stage, or Level 2, Strategic Flood
Risk Assessment. This facilitates the detailed application of the Sequential Test and Exception Test. The
purpose of the Sequential Test is to direct new development to areas of lowest flood risk. Where
development cannot be located in zones of lower probability of flooding, the Exception Test needs to be
applied, and this is only appropriate when the the Sequential Test alone cannot deliver acceptable sites.
A Level 2 SFRA needs to include an assessment of the actual protection provided by existing flood defences
for potential development areas previously identified as being at higher risk of flooding. This not only
needs to take into account the condition of existing flood defences but also potential flood defence failure
and the effects of climate change, and therefore it is "breaching and overtopping" modelling that is required
to provide the information for the Assessment. This will directly influence the purpose of SFRA Level 2,
which is to widen the scope of a review of flood hazard to take account of the presence of flood risk
management measures such as flood defences. Included in this widened study will be the review of flood
probability, flood velocity, flood depth and the rate of onset of flooding.
2.3 This led to the appointment of H R Wallingford Ltd (consultant engineers) to carry out an overtopping
and breach analysis to inform Poole's Level 2 SFRA.
Scope of Wallingford's work
2.4 Detailed analysis and mapping has been undertaken of flood hazard due to tidal flooding for the
potential regeneration areas in Poole for both current day and future climate change scenarios over 4
annual probability events (see below). The extent of the study area is shown in the diagram below, with
details of the present day flood zone map. The focus of the study is on the 2 regeneration areas A & B,
Lower Hamworthy (A) and west of Town Quay (B), but also the Town Centre North Area.
2.5 The Environment Agency were consulted on the Brief and the nature of the analysis has been agreed.
STRATEGIC FLOOD RISK ASSESSMENT FOR POOLE - LEVEL 2
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two introduction
Figure 2.1 Present Day -Base Line Map
2.6 The scenarios considered are the 5%, 1%, 0.5% and 0.1% annual probability flood (equivalent to
the 20-year, 100-year, 200-year and 1000-year return period floods). A breach scenario is also considered
near Poole Bridge where the wall protecting the Old Town is at its highest. Climate change scenarios are
modelled for the years 2086 and 2126. These dates correspond to the end of the Local Development
Framework plus a 60-year lifetime for commercial buildings and a 100-year lifetime for residential buildings.
Core Strategy
2.7 The Core Strategy Preferred Options document April 2007, which has been informed by the
Sustainability Appraisal, identifies in paragraph 4.48 the importance of flood risk in a coastal town like
Poole. It sets out the need for a Strategic Flood Risk Assessment to predict and map out the risk of
flooding, and inform necessary prevention measures, such as the height and location of sea defences in
vulnerable locations. Climate change can have direct and indirect impacts on land use and land
management so that it is important to consider its implications for flooding in the future.
The Core Strategy's Preferred Approach 9 sets out as a Core Element our need to reduce our impact on,
and susceptibility to, climate change.
It states :
Evidence 1
The risk and the vulnerability of people to flooding, can minimised be by steering new
development away from the areas of greatest risk and/or putting in place the necessary flood
defences which will protect people and properties from flooding associated with predicted
sea level rises.
2.8 Flood mitigation, through a Strategic Flood Risk Assessment and Sustainability Appraisals, will be
an important step to address this issue.
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2.9 The Core Strategy is due for Submission in May 2008. Within the Submission Document is policy
PCS 35 which has taken the flood risk issue forward further. It is quoted below, but it is stressed that this
is still at an emerging stage.
Target 1
PCS 35 FLOOD RISK
Development in areas at risk from flooding will be required to carry out a detailed Flood Risk
Assessment which identifies necessary adaptation and mitigation measures designed to avoid the
risk of harm from flooding. In order to ensure that such measures avoid harming the integrity of Poole
Harbour SPA and Ramsar sites, such measures will:
i. include the upgrade of water treatment facilities needed to prevent adverse effects upon Poole
Harbour SPA and Ramsar site arising from discharges;
ii. be designed in a manner which facilitates the movement of species within Poole Harbour SPA and
Ramsar sites; and
iii. where necessary, incorporate suitable habitat recreation as part of the measures.
In locations where strategic flood defence or adaptation measures are necessary within the site itself,
proposals will be required to demonstrate how such measures have been incorporated as an intrinsic
part of the scheme in a manner which is compatible with the comprehensive strategy for flood defence
as set out in the Strategic Flood Risk Assessment for Poole.
2.10 Definitions of Flooding Terms
2.11 Return Period:
2.12 When reference is made to a 1 in 100 return period, for example, it means the peak flood flow that
on average will be exceeded only once in a 100 year period. This is known as the 'return period' of the
flood. It does NOT mean it is due in 100 years time. It could happen at any time and more often than once
in 100 years.
2.13 Probability:
2.14 This is probability that an event of a particular magnitude will occur in any one year. For example,
the probability of 1 in 100 year flood occurring in any year is 0.01 (or 1%), and the probability of a 1 in
200 flood occurring in 0.005 (or 0.5%).
2.15 (Source: adapted from Hamill 2001).
2.16 Green Water Overtopping
2.17 This is where waves break over the sea defence.
2.18 Main tide overtopping
2.19 This is where still water is higher than the flood defence, for instance at high tide without waves.
2.20 Wave Overtopping
2.21 This is where waves "overtop" or lap above defences.
STRATEGIC FLOOD RISK ASSESSMENT FOR POOLE - LEVEL 2
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two introduction
2.22 SUDS:
2.23 Sustainable Urban Drainage Systems are the various approaches to surface water drainage
management, that include infiltration devices to allow water to soak into the ground, filter drains, swales
and balancing ponds.
2.24 AOD:
2.25 Above Ordnance Datum.
History
Historical Background
2.26 The aims of PPS25 "Development and Flood Risk" are to ensure that flood risk is taken into account
at all stages of the planning process to avoid inappropriate development in areas at risk of flooding. Where
there is an overriding necessity or need for new development in areas at highest risk the aim is to make
that development safe without increasing flood risk elsewhere, and where possible to reduce flood risk
overall.
2.27 It was following the preparation of the SFRA Level 1 that it became apparent that in view of the
number of development sites in areas at relatively high risk from flooding that Sequential Testing would
need to be carried out. Once this has been undertaken it will be possible to determine whether the Exception
Test is required.
2.28 The modelling work carried out is intrinsic in this process and will help to update the Flood Maps
and forecast where areas of vulnerability will be in the future so that we can plan for it, taking into account
flood events that have occurred in the past. This will ensure that the SFRA Level 2 will hold the best
information that can be used to guide the site selection process for future developments.
National Planning Policy
Planning Policy Framework
2.29 The UK planning system has a comprehensive hierarchy of policies and plans, beginning with
national guidance which provides a broad framework for regional plans through to development plans at
the local level. Development plans are intended to provide clear guidance to developers and the public,
following public and stakeholder involvement. The Core Strategy for Poole, described briefly in the first
chapter, is such a document that sets the strategic overview for the future planning of Poole. The SFRA
Level 2 will also help to inform the Site Specific Allocations Development Plan Document that is currently
being prepared and intends to direct development to the most appropriate sites in the Borough.
2.30 In terms of National guidance, this takes the form of Planning Policy Statements. PPS 25 (December
2006) is the most relevant as it is entitled "Development and Flood Risk" and it clarifies the Sequential
Test that matches types of development to degrees of flood risk and strengthens the requirement to include
flood risk assessments at all levels of the planning process.
2.31 PPS1 (2005) "Creating Sustainable Communities" identifies sustainable development as a core
planning principle and it encourages the use of sustainable urban drainage systems in new developments.
2.32 The new supplement to PPS1 entitled "Planning and Climate Change" sets out how planning should
contribute to stabilising climate change and take into account the unavoidable consequences, and it is
intended that this PPS should take precedence over any other earlier guidance of different emphasis.
Included in its objectives is the aim of securing new development that that will shape places that will
minimise vulnerability, and provide resilience, to climate change. Intrinsic to this aim is addressing flood
risk and minimising its often damaging consequences.
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2.33 PPS3 (2006) on Housing advocates housing policies that minimise environmental impact taking
account of climate change and flood risk.
2.34 There are many PPSs but those above are the most relevant to the preparation of the SFRA Level
2.
2.35 The South-West Regional Flood Risk Appraisal (February 2007) identifies the significant fluvial and
tidal flood risks in Poole, and that even where flood defences already exist there remains a residual risk
of flooding in extreme events or as as result of defence failure. There is a system of tidal flood warnings
to properties in Poole, where 1 - 1000 properties have been identified in the SWR FRA as being at risk,
and evacuation procedures are discussed in Chapter 3.
Flood Zones
Flood Zones
2.36 The Environment Agency's Flood Zones refer to the probability of sea and river flooding only. There
are 3 zones, and it is Flood Zone 3, (sub-divided into both a and b), that is of greatest concern to the
Level 2 SFRA. Zone 3 is of high risk including functional floodplain. This categorisation is intended as an
indication of flood risk only, and does not represent a detailed assessment of the flood risk appertaining
to any specific area within the study area. The map below shows the Flood Zones within the study area.
2.37 Chapter 5 of the SFRA Level 1 report explains in greater detail the flood risk classification.
Picture 2.1 Present Day -Base Line Map
STRATEGIC FLOOD RISK ASSESSMENT FOR POOLE - LEVEL 2
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two introduction
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3 SFRA Level 2
Scope of Work
3.1 Where the need to apply the Exception Test is identified, due to there being an insufficient number
of suitably available sites for development within zones of lower flood risk (see Sequential Approach in
Chapter 4) or due to possible increases in flood risk arising from climate change, the scope of the SFRA
needs to be widened to a Level 2 Assessment, as is the case here.
3.2 This increased scope involves a more detailed review of flood hazard (flood probability, flood depth,
flood velocity, rate of onset of flooding) taking into the account of the presence of flood risk management
measures such as flood defences. This Level 2 SFRA includes breach/overtopping analysis in this regard
also.
3.3 The output of this Level 2 SFRA includes:
Maps showing the distribution of flood risk across different probability events in breach and climate
change scenarios
Guidance on preparation of FRAs for sites within the Regeneration Areas and adjoining sites
An appraisal of the probability and consequence of breach or overtopping of defences
An appraisal of any likely future policy for flood risk management.
Existing Flood Defences
Flood Defences
3.4 The SFRA Level 1 (Chapter 4) describes the existing provision of flood defences in Poole, where
recent work has been carried out and how many properties it protects.
3.5 Coastal defences around the low-lying areas of the town are mainly broad crested earth embankments
and raised ground levels, usually with some form of armouring to prevent their erosion by waves or tides.
Other defences consist of small concrete flood walls. Their standard of protection is dependent on the
level of their crests relative to very high tidal levels. The locations of the coastal defences are shown in
the map below.
STRATEGIC FLOOD RISK ASSESSMENT FOR POOLE - LEVEL 2
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three sfra level 2
Figure 3.1 Existing flood defences with elevations
3.6 Within the study area of this SFRA Level 2 are the flood defences provided around the Asda
development and the RNLI training college. Building here required an AOD of 2.4 metres as protection
from flooding, with a 1.96 metres flood defence (with elevation), and to date no flooding events have
occurred to test this. Whilst the Hamworthy defence line extends to meet New Harbour Road West (the
eastern most point of the line in Hamworthy) it should be noted that the defence here is tied with high
ground.
Water Velocity
3.7 Modelling on the velocity of flood water during a maximum flood depth at a 0.5% annual probability
event has revealed that there is not a significant existing threat from water velocity in Poole. The following
map shows that the speed of water is actually at the lowest level of 5 categories, as depicted in green.
Therefore this is not regarded as an existing major flood risk concern in Poole.
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Figure 3.2 Water Velocity 0.5% Annual probability Event
Evacuation Procedure
3.8 The Bournemouth and Poole Resilience Group are responsible for emergency evacuation procedures
in the Borough, including those events that involve flooding. The likelihood of such events occurring is
considered rare, partly because they tend to be associated with a combination of high tide sea levels
resulting in overtopping and stormy weather conditions, both of which dissipate relatively quickly. However,
impact can be regarded as significant because of the amount of housing in risk areas and the higher
proportion of older people. Further, the risk rating is high (with 'very high' regarded as highest) when events
do occur. There is a capability for water rescue in place with a strategy that would effect a rescue during
the 'slack' tide wherever possible.
3.9 There are 5 emergency shelter or evacuation points, known as the 'Primary Rest Centres', in the
Borough (that are outside the flood risk areas), and these are situated at :
The Lighthouse Arts Centre
Rockley Park Holiday Camp
Broadstone Leisure Centre
Ashdown Leisure Centre, and
Rossmore Leisure Centre.
3.10 These are available for shelter and emergency evacuation purposes, though in reality and in past
experience, it is only about 10% of residents that make use of such facilities with the majority choosing to
stay with relatives or friends. This is particularly relevant because the threat in Poole is from tidal flooding,
which is short term, with emergencies rarely lasting more than 24 hours.
3.11 The Environment Agency operates a flood warning service. This can take various forms, from
on-line advice to telephone notification to registered parties.The information the Environment Agency
collects (eg. the amount of rainfall, tide levels etc) helps to forecast the probability of flooding. There are
four codes used : Flood Watch, Flood Warning, Severe Flood Warning and All Clear. A Flood Warning is
STRATEGIC FLOOD RISK ASSESSMENT FOR POOLE - LEVEL 2
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three sfra level 2
issued if property is expected to flood, Severe Flood Warning if there is extreme danger to life, and All
Clear if flood waters are receding. Flood warning procedures are in place for Poole Harbour.
3.12 Housing developments within areas where overtopping may occur, or where flooding may result,
will generally have commercial premises or undercroft parking at ground floor level, so that residents can
take refuge at first floor or above. In situations where residents need to be evacuated, then the Fire and
Rescue Service is equipped to carry out rescue and evacuation procedures with new vehicles designed
to operate in greater depths of water. However, this may not always be a long term or sustainable solution.
3.13 At the current time, existing defences are protecting 260 properties within the Poole Town Quay
scheme (at a 1:200 year standard), 91 properties protected by the Green Gardens scheme (1:100 year
standard), 72 properties protected by the Hamworthy scheme (1:300 standard), together with Environment
Agency Floodline and public warnings.
3.14 The Resilience Group regard that the existing defences still leave 501 properties in 1:200 year
standard and 954 properties in a 1:1000 year standard at risk in West Quay Road, Lower Hamworthy and
Sandbanks.
History
3.15 There have been no major flooding incidents in Poole since the 1980's when Green Gardens, near
Baiter, was flooded. Since that time flood defences have been raised along this part of the Harbour.
3.16 Whilst there have been 70 incidents requiring evacuation in Poole since 1997, none has related to
flooding.
Scenarios
Present Day Scenarios
3.17 The flood zones shown below have been built using the 5%,0.5% and 0.1% annual probability flood
maps, with no allowance made for climate change .
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Figure 3.3 Present Day - 5% annual probability
STRATEGIC FLOOD RISK ASSESSMENT FOR POOLE - LEVEL 2
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three sfra level 2
Map 3.1 Present Day - 1% annual probability event
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Map 3.2 Present Day - 0.1% Annual probability event
3.18 The green arrows show the areas where green water main tide overtopping would occur and it is
generally at points off Little Channel and Backwater Channel. Main wave overtopping on the other hand
would occur to the south along the freightliner Terminal as well as from Little Channel adjoining the Quay.
3.19 What the maps tell us is that most of the flood defences outside Regeneration Area B (West Quay
to RNLI) provide flood protection against tidal inundation up to the 1000-year return period event. The
only exception is the area near the pontoons behind the breakwater (Old Orchard to the Lifeboat Museum,
crest level 2.1m OD), but the overtopping amount is very small.
3.20 There is wave overtopping for smaller return periods shown as well, but it involves volumes that
are usually small, especially compared to the water that would spread at high tide from undefended areas
(eg West Quay). The areas that would be most affected from wave overtopping are the ferry and freightliner
terminal in Lower Hamworthy and at Old Town Quay, where volumes would be more significant. Most of
the flooding spreads into these areas from an area without flood defences where the tide flows over the
coastal edge.
3.21 A scenario of a breach into the flood wall near Poole Bridge would have no effect on the flood outline
(for both the 20 and 200 year flood). This is because the incoming volume is small compared to the water
spreading at high tide from undefended areas (especially West Quay). Inflow from the breach does
nevertheless cause more rapid flooding to the area immediately adjacent to it.
3.22 The findings also show that flow velocity is very small, gauged by a 0.5% annual probability event,
as the flooding is mostly caused by the tidal water gradually rising and covering lower grounds. The
findings therefore conclude that flood risk to people would have more to do with the function of water
'depth' rather than water velocity. However, this doesn't take account of wave action in the immediate
vicinity of flood defences and which is likely to change if higher defences are constructed, where breaching
would then have a greater impact upon risks to people.
STRATEGIC FLOOD RISK ASSESSMENT FOR POOLE - LEVEL 2
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three sfra level 2
Raising the Defences
3.23 Following the modelling and assessment of the results of the present day, estimates were then
run on on what would happen to the flood risk if the Regeneration Areas were protected to the 0.5% annual
probability standard. This helps to reveal what additional protection would be necessary in other parts of
the town.
3.24 The modelling was therefore revised assuming a sea wall of crest level of 2.5m OD around the
regeneration areas (with no allowance for climate change). This initial crest elevation estimate would
provide protection for a 0.5% annual probability tide (1.95m OD) and should minimise the amount of wave
overtopping and the results are shown in the Appendix B scenario below.
Figure 3.4 Raised Defences for a 0.5% annual probability tide
3.25 Interpreted, the results show that raising the defence in Regeneration Area B would reduce flooding
on Poole Quay only by a relatively small amount. This could be caused by overtopping water actually
returning to the sea through the undefended area in the original scenario, while with this "raised defence"
scenario overtopping water is effectively trapped inland behind the defences. Also, despite the provision
of flood defences along their immediate tidal frontage, these areas still get flooded following overtopping
caused by flooding of adjacent areas. So it is recommended that to protect the regeneration areas additional
defences should be provided at adjoining sites (see Chapter 5 Recommendations).
3.26 The areas east of Poole Bridge on both sides of the channel (In Regeneration Areas A and B) seem
to be the main remaining weak locations in the town's flood defences.
3.27 There has also been a further scenario testing run on the impact of no further defence work being
carried out on land to the north of the Regeneration Area B ( the old RNLI site) and the impact this would
have on the Quay area (see second Appendix B scenario below). The conclusion reached (and shown
in the map below) is that a low area near the RNLI depot at the north of Regeneration Area B would lead
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to flood water spreading inland and travelling southwards towards the Quay following West Quay Road.
Climate Change
Climate change results 2086 and 2126
3.28 The 0.5% annual probability flood has been simulated with sea level rise for the horizons 2086 and
2126 (which corresponds with the timeline of the Local Development Framework plus 60-year lifetime for
commercial buildings and plus 100 years for residential buildings). Sea level rise between 2007 and 2086
is estimated at 0.66m, sea level rise between 2086 and 2126 is estimated at 0.59m.
3.29 The following map shows a climate change scenario for 2086 for a 0.5% annual probability, and
importantly it is for a situation that does not involve any defence works, that is, it has present day
defences.
Map 3.3 Climate change scenario - 0.5% annual probability for 2086
3.30 By 2086 more than 50% of the Old Town and Lower Hamworthy would be flooded by a 0.5% annual
probability event. These predictions are based upon the sea level rise assumptions specified in PPS25
(see Table B.1 in Appendix B), and these sea level rises become the dominant factor in influencing the
magnitude of the flood hazard, with its effect far outweighing the increase in level during extreme events
of different probability for a given period.
3.31 What these findings demonstrate are that in the future the town will require existing flood defences
to be improved and new defences to be built in all currently unprotected areas. New defences should be
built in such a way that their further modification can be carried out in response to future predictions and
circumstances.
3.32 The following map shows a climate change scenario for 2126, at a 0.5% annual probability. The
high level of "blue" demonstrates that nearly 90% of the Old Town and Lower Hamworthy would be flooded.
STRATEGIC FLOOD RISK ASSESSMENT FOR POOLE - LEVEL 2
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three sfra level 2
Map 3.4 Climate Change scenario - 0.5% annual probability for 2126
3.33 To conclude, the climate change scenarios are based on the sea level rise assumptions made in
PPS25, but it is understood that there are significant uncertainties in climate change predictions. There
are 2 main factors at play:
3.34 sea level rise (due to thermal expansion of oceans, and melt water ice sheets and glaciers), and
3.35 the local vertical movement of the land (generally falling in the South East and rising in the North
and West).
3.36 The predicted annual rates of sea level rise are the dominant issue in influencing the magnitude of
the flood hazard, with its effect far outweighing the increase in the level during extreme events of different
probability for a given period. For example, the 20-year return period sea level in 2086 is significantly
higher than the 1000-year return period sea level in 2007.
3.37 Therefore, existing flood defences in the town will need to be improved in the future, and new
defences will need to be built in all currently unprotected areas. Detailed analysis in FRAs in conjunction
with new development proposals will be required to determine the extent, magnitude and programming
of such works to maintain sufficient future
protection.
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4 Purpose
Sequential Approach
SFRA Aims
4.1 The aims of PPS25 "Development and Flood Risk" December 2006 are to ensure that flood risk is
taken into account at all stages of the planning process to avoid inappropriate development in areas at
risk of flooding, and to direct development away from areas at highest risk. The findings of a SFRA can
feed directly into the preparation of Local Development Documents including the Core Strategy and Site
Specific Allocations Development Plan Document.
Allocations
4.2 The Poole Local Plan First Alteration 2004, the Poole Bridge Regeneration Area Action Plan (now
superseded), the Planning Urban Design Guidance Master Plan SPG and the Town Centre North Area
Action Plan all identify areas of brownfield land for future development to achieve the town's strategic
needs in terms of housing, employment uses and retail expansion on areas of Flood Zone 3. To date,
these have been areas that have been previously developed or where flood defence work has been carried
out.
4.3 The areas in question are :Regeneration Area A : Lower Hamworthy, the Pilkingtons Tiles factory site, Sydenhams Timber Yard and
the former Power Station site.
Regeneration Area B : North West of the Quay fronting Back Water Channel from the existing Poole Bridge
to the RNLI.
4.4 The other main constraints in Poole include its high levels of protected Heathland, international
environmental designations on its extensive Harbour, and areas of Green Belt to the north. In these areas
(that amount to approximately 30% of the Borough) development is prohibited where it is considered it
would detrimentally affect the environment, and this puts additional pressure for development on other
areas (some of which are in Flood Zone 3b). This, together with the town's Growth Point status and RSS
requirements for expansion (see Chapter 1), focuses future development provision to the sustainable
locations like the town centre, and brownfield land on the edge of the Harbour, like the identified
Regeneration Areas.
4.5 The Poole Bridge Regeneration Initiative Planning Design Guidance for the Central Area of Poole
SPG, adopted in December 2004, sets out the minimum expectation of the land uses and their capacities
in the the Regeneration Areas.
4.6 The Regeneration Area A proposes 1359 residential units, 25,734m2 employment use, 2,269 m2
retail use and 179m2 leisure function over an area of land of 22.3 hectares, which falls with Flood Zone
3.
4.7 The Regeneration Area B proposes 514 residential units, 10529m2 of employment space, 5710 retail
use plus hotel and sea scouts site, over an area of land 3.79 ha which falls within Flood Zone 3.
4.8 However, the Appropriate Assessment work identifies maximum capacities for the purposes of
calculating environmental, and other, impacts. In terms of housing provision Regeneration Area A could
provide up to 2004 homes, that is 645 more units than its allocation. With regard to Regeneration Area B
717 homes could be provided which is about 200 additional units over and above the initial allocation.
4.9 Urban capacity work, including the on-going Strategic Housing Land Availability Assessment,
acknowledges that whilst Poole is constrained by its environmental designations, it needs to provide
certainty about how much, and where, future housing is going to be located. This work has identified that
STRATEGIC FLOOD RISK ASSESSMENT FOR POOLE - LEVEL 2
22
four purpose
Poole needs to make the best use of its urban and brownfield land to reach its housing targets ( set at
450-500 homes a year until 2026 in the emerging Regional Spatial Strategy). Urban Capacity Studies to
date (June 2005 is the latest) have revealed a supply of land for housing for the next 15 years of 9501,
but this would be phased so that greatest levels of housing would be provided before 2016. By definition
the latest capacity work (known as Strategic Housing Land Availability Assessment ) only identifies sites
that are "suitable, available and achievable", and this has highlighted the lack of greenfield site opportunities
and thereby clearly identifies the Regeneration sites as important in making a significant contribution to
the town's housing need and the sustainability of the town centre. Necessary and identified levels of
development, of this scale, form an essential part of Poole's future land allocation. Provision of vital
services for its population cannot be provided elsewhere in the Borough, that is in areas of Flood Zones
1 or 2, because comparably sized areas are either covered by environmental designations where
development is prohibited, or are in unsustainable locations that could not support the type and mix of
development required in Poole. There are compelling arguments in favour of providing new development
that will contribute to Poole's future prosperity, its sustainable growth and its requirement to cater for the
needs of its population.
4.10 It is concluded that there are no reasonable options available in Flood Zones 1 and 2 to accommodate
the level of development allocated and proposed within Poole's Regeneration Areas. Such Sequential
Testing leads to the need to apply the Exception Test to the Regeneration Sites to ensure that flood risk
is minimised, and not exacerbated in other areas, as a consequence of new development in the
Regeneration Areas.
Exceptions Test
4.11 The Exceptions Test is now applied, because the Sequential Test has demonstrated that there are
no alternative sites in lower category Flood Zones to accommodate the future development allocations
for Poole.
4.12 PPS 25 sets out that the Exception Test. For it to be passed:
a) it must be demonstrated that the development provides wider sustainable benefits to the community
that outweigh flood rsik, informed by an SFRA where one has been prepared. If the DPD has reached
the submission stage the benefits of the development should contribute to the Core Strategy's Sustainability
Appraisal.
b) the development should be on developable previously developed land, or, if not on previously developable
land, that there are no reasonable alternative options on developable previously developed land;
c) a flood risk assessment must demonstrate that the development will be safe, without increasing flood
risk elsewhere, and, where possible will reduce flood risk overall.
a) Sustainable Communities Agenda
4.13 The Regeneration Areas fall within the central area of Poole, and as such occupy a sustainable
location, as defined in the Department of Communities and Local Government's Sustainable Communities
Plan 2003. Poole is a Strategically Significant Town (SSCT) and is identified as one of the most appropriate
areas to accommodate new housing, particularly affordable units and those for key workers, as already
planned for the Regeneration Sites. The need for this development is even more crucial in Poole because
of its high house prices and lower than average earnings, that can have the consequence of driving away
young people to look for work and homes elsewhere.
b) Brownfield Land
4.14 Without utilising its brownfield land the town would fall short of its strategic goal of providing an
economically secure and prosperous town for people to live in for the future. The former Power Station
land in Hamworthy is a vital brownfield site in a central and sustainable location that provides an opportunity
to accommodate a significant proportion of Poole's housing requirement.
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Picture 4.1 Power Station Regeneration Site
4.15 Poole also relies on windfall sites coming forward to provide the majority of its future housing
requirement. Application of the sequential and exception tests will therefore play an important role in
determining acceptability.
c) Flood Risk Assessment
4.16 The Wallingford work reveals that whilst climate change is the greatest threat to future flood risk,
appropriate future defences and properly planned development now can mitigate against the consequences
of rising sea levels and storm conditions in the future. The conclusions of the study are that further flood
defence work is required.
d) Flood Risk Management
4.17 Development within the Regeneration Areas will not only bring about investment to central areas
of Poole, but it may provide a means by which additional flood defence work could be justified around the
Quay area and Harbour. The waterfront regeneration sites will provide mitigation through new flood
defences which will defend both their own and other sites. Such defence work would also provide protection
STRATEGIC FLOOD RISK ASSESSMENT FOR POOLE - LEVEL 2
24
four purpose
to adjoining sites that may not be within Regeneration Areas. Developer contributions may well have an
element that requires monies to be collected for managing flood risk in the future. In this way the
regeneration of Poole can be seen as a vehicle for ascertaining a more "flood secure" environment for
the central part of the town.
Other Flood Risk Areas in the Borough
4.18 Whilst the HR Wallingford work concerns the town centre of Poole, its conclusions that stem from
the sequential testing and requirement for provision to be made for mitigation measures, can be extended
to other Flood Zone areas in the Borough. Therefore, it is reasonable to expect developments proposed
in these similarly categorised areas (Flood Zones 2, 3a and 3b) to incorporate flood defence details and
methods of mitigation that are defined in the recommendations to this document. Where such mitigation
provision can be made as part of Flood Risk Assessments associated with new proposals it would be
expedient to expect a similar level of protection to be employed on such proposals.
4.19 Sequential testing has shown that it is only about 40% of the Town's development needs that can
be met within Flood Zones 1 and 2, and therefore it is accepted that some development will inevitably
have to occur on less favourable sites within Flood Zone 3. In fact, significant development already exists,
(or has existed in the past eg. part of the Power Station site), in the urban area that is Flood Zone 3, and
so, in any event, may require flood defences measures to protect property in the future. Additional
development, therefore, may well provide the opportunity to support flood defence measures in the future.
The exception testing above reveals that there are means by which development can go ahead and
environments and inhabitants can still be safeguarded from flooding in the future. Such methods can be
used across the Borough if it is considered that it is reasonable to build using acceptable defence
mechanisms put forward in individual FRAs.
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5 Conclusions
5.1 Conclusion
5.2 By comparing the present day scenarios and climate change prediction models (Chapter 2) it is
possible to consider the likely differences, and how we can plan for flood risk within the Plan period and
in the life of new development, commercial and residential.
5.3 A significant impact is the effect climate change will have on sea level rise and therefore the need
to raise flood defences for the long term to strengthen flood protection. The risk of flooding will increase
significantly in the next 100 years. So, flood defences will need to be raised by at least the same amount
as the sea level rise, and extending to zones away from the regeneration areas to maintain a standard of
protection equivalent to current standard.
5.4 In terms of present day scenarios, most of the flood defences outside Regeneration Area B provide
protection against tidal inundation up to the 0.1% annual probability event. The frontages without flood
defence (or with lower flood defences) are responsible for most of the flooding by water spreading into
the protected areas. The areas most affected are the regeneration Area B, Poole Quay near the Bridge
and the east of Lower Hamworthy. Defence overtopping is also responsible for flooding of the ferry and
freightliner terminal in Lower Hamworthy and the Poole Quay. The Regeneration Area A starts to be
flooded from a 5% annual probability event, but is only significantly flooded by a 0.1% annual probability
flood. Regeneration Area B is significantly flooded with a a 5% annual probability flood.
5.5 Therefore, to protect against the present situation, the regeneration areas will need defences such
as flood walls, embankment or ground raising, with an elevation sufficient to prevent any significant wave
overtopping for a 0.5% annual probability event.
5.6 The assessment of raising defences to a level of 2.5m OD has shown that building defences at the
immediate frontage of the regeneration areas is not sufficient to protect these areas. Water overtopping
into adjacent land would spread and flood part of the regeneration areas, and therefore additional defences
would be required on adjoining sites.
5.7 However, breaching is not considered to be a significant risk for most of the current coastal defences,
due to their nature (that is, broad flood embankments with crest levels close to the ground).
5.8 This enables us to plan for appropriate flood defences. In connection with new development within
the Regeneration Areas it allows specific heights to new flood defences to be achieved. The findings also
expose the weaker flood defence areas, for instance Poole Quay and north of the RNLI station (north of
Regeneration Area B), that would need to be protected in the future if climate change and flood events
can be defended against in the future.
5.9 Informative Note
5.10 The data and information contained in this Level 2 SFRA contains the best available data at the
time of writing. Data is periodically updated and it is advised that reviews of this SFRA take account of
the latest figures. This will ensure that decisions are based upon the best available data at all times.
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five conclusions
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6 Recommendations
Recommendations
6.1 The SFRA Level 2 finds that Poole's central area will need additional flood protection in the future.
6.2 The following is a list of the recommendations to come from this work, and includes other general
requirements to address flood risk, and it will provide a steer on how flood mitigation and protection
measures should be employed within this area of the Borough in the future.
Where justified, new building in individual flood risk areas should be flood resilient. Basements
should not be used for habitable purposes. Where basements are permitted for commercial use, it
is necessary to ensure that the basement access points are situated 300 mm above the 0.5%
probability flood level plus climate change.
Undercroft parking, where it is at ground floor level, may be justified as a means of mitigating against
potential sea level rise, by providing first floor habitable accommodation over.
As a precautionary principle a 600mm freeboard will be necessary with new development. This may
be reduced in some circumstances if applicants undertake additional modelling through Flood Risk
Assessments to justify such modification.
The risk of flooding is predicted to significantly increase over the next 100 years without further flood
defence works (due to climate change and sea level rise assumptions). Defences will need to be
raised by at least the same amount as the sea level rise (approximately 0.7m by 2086 and 1.3m by
2126) and extend to zones beyond the regeneration areas to maintain a standard of protection
equivalent to the current standard.
In relation to flood defences the 0.7 metres and 1.3 metres sea level rise will require an additional
200mm freeboard.
To provide protection for the future situation, the Regeneration Areas A and B will both need defences,
such as flood walls or embankments, with elevation sufficient to prevent any significant wave
overtopping for a 0.5% joint probability event. As schemes come forward these developments will
need to provide both their own defences and also ensure their defences form part of strategic flood
defence measures required for the Regeneration Area sites.
Additional defences will also be required outside the Regeneration Areas (to combat water overtopping
into adjoining land and so preventing water spreading to the Regeneration Areas and other central
areas like Hamworthy and the town centre) in the following zones:
North of Regeneration Area B, close to the railway station
South of Regeneration Area B, east of Poole Bridge
East of Regeneration Area A, east of Poole Bridge.
the standard of protection of the existing flood defences in the town will need to be investigated, and
any new defences will need to be promoted on a benefit/cost basis. (New defences should built in
such a way that they can be modified in response to further predictions and varying circumstances
in the future). This analysis will need to be undertaken to identify the exact nature of the necessary
works and likely costs. This will be taken forward in the Infrastructure Planning work that is on-going
to support growth in Poole.
The Bournemouth and Poole Resilience Group should continue to respond to, and co-ordinate
procedures for, emergency evacuation in Poole (that includes events relating to flooding) in accordance
with its evacuation plan. The 5 emergency shelter points known as 'Primary Rest Centres' should
be retained, with their additional roles clearly safeguarded in future planning.
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six recommendations
SUDS should be implemented, where deemed appropriate and necessary, to ensure that run-off
from sites after development is not increased.
As Poole is a low lying urban area adjacent to its Harbour it relies upon pumping stations to dispose
of both foul and surface water. These facilities should be protected in the future, by being flood
proofed and secondary electrical power made available to them.