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BROAD SCALE TIDAL FLOOD RISK ASSESSMENT FOR LONDON USING MDSF
AND FLOODRANGER
Tim Reeder
Regional Climate Change Project Manager
Environment Agency
Bill Donovan
ESPACE Development Officer
Environment Agency
Jon Wicks
Associate Director
Halcrow Group Ltd
ABSTRACT
Understanding current flood risk and changes to flood risk over time periods of
decades should be a key component in both flood risk management and spatial
planning. As part of the European Union funded ESPACE (European Spatial
Planning Adapting to Climate Events) project, a Decision Testing Framework has
been developed which makes use of the MDSF and FloodRangerPro software tools
to improve assessment, visualisation and stakeholder engagement of flood risk at the
broad scale (eg catchment or whole estuary).
This paper describes the application of MDSF and enhanced FloodRanger to London
and the Thames Estuary. The application provides an initial broad scale flood risk
assessment for use within the Environment Agency’s Thames Estuary 2100 project
which is developing a flood risk management plan for London and the Thames
Estuary for the next 100 years.
The findings from the Thames Estuary application are generalised to provide advice
on the appropriateness of the Decision Testing Framework (including MDSF and
FloodRanger) within broad scale flood risk assessment. Key issues described
include: interpretation of climate change scenarios, appropriate spatial resolution,
broad scale flood risk management measures, need for modelling and relative
importance of different types of input data.
Key words: Flood risk assessment, climate change, decision making, Thames
Estuary
INTRODUCTION
Climate change and its inherent uncertainties for the future presents a totally new
challenge to decision makers in the broad field of spatial planning. In view of this the
Environment Agency proposed the development of appropriate tools to simulate and
test long term decisions in the light of changing future. This proposal was embedded
as part of the formation of the ESPACE (European Spatial Planning: Adapting to
Climate Events) project. The ESPACE research project is an ambitious four-year
European project that aims to promote awareness of the importance of adapting to
climate change and to encourage adaptation within spatial planning mechanisms at
local, regional, national and European levels. Focussing on North West Europe,
ESPACE is looking at how we manage our water resources and plan for a future with
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a changing climate. It has been running now for nearly two years and is working with
Dutch, Belgian and German partners to develop and compare tools for the future
management of these issues.
The Environment Agency is piloting the development of decision making frameworks
and tools through its Thames Estuary 2100 project, which is looking at the future of
flood risk management for the Thames Estuary over the next 100 years. The initial
phase of the research included an assessment of the requirements of the framework
and a thorough review of a set of candidate tools. The review concluded that a
suitable generic Decision Making Framework is provided by the UKCIP Decision
Making Framework(1) as summarised in Figure 1.
Figure 1: UKCIP Decision Making Framework
DECISION TESTING FRAMEWORK AND TOOLS
The review did not identify a specific decision-testing tool that is appropriate for all
sectors, locations and scales. Instead, it recognised that there is a range of tools that
may be beneficial for particular studies. For application to the TE2100 project, the
following tools were identified for piloting on the Thames Estuary at the broad and
local scale (Figure 2Figure 2) - the tools are described in more detail in subsequent
sections of this paper:
 Source-Pathway-Receptor model to help identify the problem and objectives (as
used in Foresight Future Flooding(2)).
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 IPCC/UKCIP climate change scenarios to define climate change scenarios and
their impact on the sources of flooding (primarily sea level rise and surges)
 TUFLOW and ISIS hydraulic modelling software to convert changes in extreme
sea level to water depths at the receptors (primarily properties and people)
 MSDF software to calculate flood risk (consequences x probability) by
translating scenario-neutral water depths at receptors into economic flood
damage and social impact
 Excel Workbook to post process results and map the scenario-neutral data to
specific strategic options
 FloodRanger Professional software as a strategic option exploration and
visualisation tool for stakeholders
Tidal Flood Risk Areas
London
Thames
Estuary
Dartford Local
Pilot Area
Thames Broad-scale Pilot Area
Figure 2: Thames Estuary pilot area showing flood risk areas (‘embayments’)
The UKCIP Decision Making Framework provided clear structured guidance on
decision making, highlighting both the sequential stages involved in decision making
(stages 1 to 8 in Figure 1) and the need to iterate between stages (particularly stages
3, 4 and 5). Completion of the formal questions posed in the UKCIP Framework
provide a very valuable audit trail which will encourage a systematic approach to the
decision making and provide documentation suitable for stakeholder scrutiny.
The adoption of the Source-Pathway-Receptor (Figure 3) model helped to both
identify the problem and objectives and to establish the decision-making criteria.
Through the application of expert knowledge, a comprehensive list of risk
components were identified and ranked. This process enabled the identification of
tidal flood risk as the main ‘source’ of risk in the Thames estuary, and the resultant
impact on properties and people as the main ‘receptor’ of this risk. The main ‘drivers’
were identified as climate change (increasing sea levels and surges) and land
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development pressures in the Thames Gateway. ‘Responses’ were identified at two
levels of detail: at the broad scale responses were represented in terms of generic
strategic options (such as maintain existing defence system or maintain existing
standard of protection); whereas at the local scale responses included specific
defence level and defence realignment options. For the piloting the decision-making
criteria were the identification of cost-effective flood risk management strategies for
properties and people given future likely climate change scenarios over the next
100 years. (Note that full TE2100 project has a wider remit and will, for example,
include environmental benefit in the criteria).
Drivers
Processes that change the
state of the system
System descriptors
Sources
rainfall
sea level
storms
etc
Pathways
fields, rivers
drains, roads
floodplains
flood defences
flood storages
etc
Receptors
people
properties
infrastructure
ecosystems
etc
System
analysis
Risk
economic
social
environmental
etc
Responses
Interventions that change the
state of the system
Figure 3: Drivers and responses can change the sources, pathways and receptors of
risk
A distinctive feature of the UKCIP Decision Making Framework is the iterative
application of stages 3 to 5 – assessing risk, identifying options and appraising
options. This explicitly recognises that different approaches to risk assessment are
required according to the level of understanding of the problem, structuring this
approach through: risk screening; qualitative and generic quantitative risk
assessment; and specific quantitative risk assessment. Within the Thames Estuary
study area, the piloting focussed on the first two tiers of these stages at both the
broad (Estuary wide) and local (Dartford embayment) scale.
For the risk assessment, a number of climate change scenarios based on IPCC
SRES (Special Report on Emissions Scenarios) emissions scenarios were
developed to provide a range of possible future tidal water levels to 2100. During
piloting, it was recognised that UKCIP02 climate change scenarios (3) provided a good
starting point for the development of these scenarios, but did not include
consideration of key components of Thames estuary tidal water levels, namely, storm
surge and tidal propagation. These two components were therefore added to the
sea-level rise climate change estimates.
Generic quantitative risk assessment was undertaken through the application of the
selected Decision Testing Tools. The principal tool used during this stage of the
piloting was the MDSF (Modelling and Decision Support Framework) (4). This
permitted the rapid estimation of direct economic damages associated with the
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flooding of residential and commercial properties, and an estimation of the number of
people affected by flooding. This tool was supported by the use of the ISIS 1dimensional and TUFLOW 2-dimensional hydraulic modelling software applied to the
study area to provide information on estimated flood extent, depth and rate of
flooding. These data were further processed to enable the calculation of risk of loss
of life based on a rate of rise in flood water criterion.
Importantly, the application of the MDSF decision testing tool enabled the wide
evaluation of strategic options and the identification and appraisal of options that
were robust to climate change impacts. This appraisal was undertaken iteratively at a
broad-scale to filter strategic options. During this process, a scenario-neutral
approach was undertaken to modelling and application of the MDSF decision testing
tool. An initial matrix of modelling was undertaken independently of climate change
scenario and strategic option. This initial matrix was subsequently mapped across to
particular strategic options using an Excel Workbook (the computationally intensive
inundation modelling was thus decoupled from the economic damage calculation and
strategic option). Such an approach enabled a wide variety of strategic options to be
considered without the need for each strategic option to be explicitly modelled (see
Figure 4).
Figure 4: Scenario-neutral database of modelling results supports appraisal of
strategic options
Once a limited number of strategic options had been identified, a further iteration of
the appraisal stage was undertaken at a more detailed spatial resolution for the
Dartford ‘local’ pilot area within the wider study area (see Figure 2). This iteration
included the explicit modelling of strategic option scenarios, enabling both a
comparison of scale and method to be undertaken.
Further stages of the UKCIP Decision Making Framework were not applied during
this piloting as a full assessment of preceding stages using specific quantitative risk
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assessment were not completed (ie the process stopped at step 6 of Figure 1).
However, the development and trialling of ‘FloodRanger Professional’ as a
visualisation and strategic option exploration tool was undertaken, both to assist with
option appraisal and stakeholder engagement (Figure 5 shows example screen
shots). The version of FloodRanger developed through the ESPACE project (called
‘Professional’ to differentiate it from the previous ‘educational game’ version) was
able to import the MDSF generated Thames Estuary flood risk data (for current
conditions, 2050 and 2100) and interpolate between these time slices to enable
estimates of flood risks for 10-year time slices. The software concept is considered a
significant innovation as it allows non-modellers to view outputs of potentially
complicated modelling and risk assessment calculations in an intuitive and visually
appealing software product. Further development of the concept is recommended to
provide a simplified fit-for-purpose tool that will enable flood risk managers and other
stakeholders to be able to assess, and to communicate to others, the positive and
negative impacts of proposed development.
Figure 5: FloodRanger Professional visualises MDSF results for the Thames Estuary
SENSITIVITY ANALYSIS
Sensitivity analysis was undertaken to assess the sensitivity of results to variations in
input data and calculation method. The analysis found that significant ‘short cuts’ in
the analysis are possible by identifying and focussing on the major contributors to
overall risk. For example, for the local pilot study, less than 20% of all properties
contributed over 90% of the risk (measured in terms of annual average economic
flood damage). Thus, results are likely to be insensitive to sensible changes in data
quality for most of the property data set and any effort to improve data quality should
only address the major contributors to overall risk.
There are likely to be important ‘thresholds’ in the analysis beyond which there are
changes in the relative importance of variability in input data. For example, the
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estuary wide annual average flood damage values are relatively insensitive to the
sea level rise prediction changing from 7mm/year to 8.9mm/year for the strategic
option to maintain a 1:1000 year standard of protection (damages increase by only
5%). However, the same variation in sea level rise for the ‘maintenance only –
declining standards’ strategic option results in a 350% increase in flood damage.
Similarly, there are also likely to be important calculation method ‘thresholds’. An
example of this is the potentially time saving assumption of expressing flood damage
per embayment as only a function of relative water level (expressed as local river
water level minus flood defence crest level). Sensitivity testing showed that while this
relationship was valid for some river and defence levels, it became inappropriate for
the most important river levels (and thus flood damage had to be related to both river
level and defence level in the scenario-neutral database).
CONCLUSIONS
The following conclusions can be drawn from the piloting of the Decision Making
Framework and Tools on the Thames Estuary:
1. The application of the UKCIP ‘Risk, Uncertainty and Decision Making’ Framework
provides excellent generic guidance and a set of procedures appropriate for
assessing the impact of climate change on spatial planning. Despite its ‘UK’ title,
it is appropriate for use throughout the ESPACE partner countries and outside
flood risk management (eg for scarcity of water resources, threat to biodiversity,
threat to water quality).
2. The Framework proposes an iterative and tiered approach to the assessment of
risk, identification of options and appraisal of options. This enables a level of
analysis that is appropriate to both the level of decision and the level of
understanding of the risk problems and objectives.
3. The tiered approach is consistent with the development of the scenario-neutral
approach to strategic option appraisal (as used in the broad scale piloting) which
provides rapid quantitative estimates of risk. This approach enables the
identification of sets of robust strategic options that can be further assessed using
more detailed, scenario-specific quantitative methods (and the early screening out
of ‘non-sensible’ options).
4. No single Decision Testing Tool will be appropriate for all studies. However it is
likely that tools (ie structured methodologies and/or software products) will be
required to:
 Help identify the problem and objectives (eg Source-Pathway-Receptor)
 Define appropriate climate change scenarios (eg IPCC/UKCIP)
 Assess the impact of drivers and responses on risk using an appropriate
level of scientific rigour (TUFLOW, ISIS, MDSF and Excel were used in
the piloting)
 Help communicate the consequences of action and lack of action to
stakeholders (FloodRanger Professional was used in the piloting)
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ACKNOWLEDGEMENTS
The broad scale risk assessment was undertaken for the Environment Agency
TE2100 team. Their help and encouragement is gratefully acknowledged although
the views and opinions expressed in this paper do not necessarily reflect those of the
Agency. The research in this paper was part funded by the European Commission
Interreg 3c ESPACE (European Spatial Planning: Adapting to Climate Events)
project. The authors acknowledge the contribution to the work presented in this paper
by Kevin Morris (Discovery Software Ltd – developer of FloodRangerPro), Matt Scott
and Rodolfo Aradas (Halcrow) and members of the TE2100 team.
(1)
REFERENCES
Climate adaptation: Risk, uncertainty and decision-making. UKCIP Technical
Report. May 2003.
(2)
Evans, E, Ashley, R, Hall, J, Penning-Rowsell, E, Sayers, P, Thorne, C and
Watkinson, A (2004) Foresight. Future Flooding. Scientific Summary: Volumes I
and II. Office of Science and Technology, London. 2004
(3)
Climate Change Scenarios for the United Kingdom: The UKCIP02 Scientific
Report. DEFRA, Tyndall Centre and Hadley Centre. April 2002.
(4)
Penning-Rowsell, EC, Evans, EP, Ramsbottom, DM, Wicks, JM, Packman, JC.
Catchment Flood Management Plans and the Modelling and Decision Support
Framework. ICE Proceedings, Civil Engineering, Vol 150, Special Issue 1, May
2002, 43-48.
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