Download Decision Making Framework and Tools

ESPACE
ESPACE Decision Making Framework and Tools
Phase 2 Piloting Report – Main Volume
June 2005
ESPACE — European Spatial Planning:
Adapting to Climate Events
Environment Agency
Halcrow Group Limited
ESPACE
ESPACE Decision Making Framework and Tools
Phase 2 Piloting Report – Main Volume
June 2005
Environment Agency
Halcrow Group Ltd
The Thames Barrier
Eastmoor Street,Charton
SE7 8LX
Tel +44 (0)208 305 4803
www.environment-agency.gov.uk
Burderop Park
Swindon, Wiltshire
SN4 0QD
Tel +44 (0)1793 812479
www.halcrow.com
ESPACE
ESPACE Decision Making Framework and Tools
Phase 2 Piloting Report – Main Volume
Contents Amendment Record
This report has been issued and amended as follows:
Issue
Revision
Description
Date
Signed
1
0
Draft for comment
01/04/05
MGS
2
0
Final draft, excluding 29/04/05
executive summary
MGS
3
0
Final report – Main 25/06/05
Volume
JMW
Publishing Organisation
Environment Agency, Rio House, Waterside Drive, Aztec West, Almondsbury, BRISTOL, BS32 4UD.
Tel: 01454 624400 Fax: 01454 624409 Website: www.environment-agency.gov.uk
© Environment Agency 2005
June 2005
All rights reserved. No part of this document may be reproduced, stored in a retrieval system, or
transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise
without the prior permission of the Environment Agency.
The views expressed in this document are not necessarily those of the Environment Agency. Its officers,
servants or agents accept no liability whatsoever for any loss or damage arising from the interpretation or
use of the information, or reliance upon views contained herein.
Contents
Executive Summary
1
Glossary
8
1
Background
1.1 The ESPACE project
1.2 The Thames estuary
11
11
13
2
Decision Making Framework
2.1 Introduction
2.2 Guidance, procedures and scenarios
2.3 Decision Testing Tools
2.4 Visualisation and stakeholder engagement
16
16
16
23
26
3
Broad-scale Application
3.1 Introduction
3.2 Broad-scale piloting of the decision making framework
3.3 Results summary and uncertainties
28
28
28
31
4
Local Application
4.1 Introduction
4.2 Local piloting of the decision making framework
4.3 Results summary
34
34
34
37
5
Discussion
39
6
Conclusions and Recommendations
6.1 Conclusions
6.2 Recommendations
47
47
50
References
52
Executive Summary
Adaptation to climate change is essential if we want to minimise the impacts and take advantage
of the opportunities that arise. 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 a changing climate.
One component of the ESPACE project is the development of a Decision Making
Framework and Decision Testing Tools to aid the selection of spatial planning adaptation
measures to cope with climate change. The Environment Agency through its Thames Estuary
flood risk management project, TE2100, is leading on this component of the research project.
The ESPACE Decision Testing Framework Phase 1 report (Environment Agency, 2004)
presented 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 (Climate adaptation: risk, uncertainty and decisionmaking, UKCIP 2003) as summarised in Figure 1.
Figure 1: UKCIP Decision Making Framework
The Phase 1 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
1
identified for piloting (the tools are described in more detail in subsequent sections of this
Executive Summary):






Source-Pathway-Receptor model to help identify the problem and objectives
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
The Phase 2 report focuses on the piloting of the UKCIP Decision Making Framework and the
above tools on the Thames Estuary at the broad and local scale (Figure 2).
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
2
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
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.
3
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 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). This permitted the rapid estimation of direct
economic damages associated with the 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 1-dimensional 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
4
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 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 was undertaken to assess the sensitivity of results to variations in input data
and calculation method. Findings with specific relevance to the Thames Estuary project are
5
contained in the Main Volume discussion section and the Technical Appendix. Generic findings
are listed below.



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 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).
The piloting of the Decision Making Framework and Tools on the Thames Estuary leads to the
following generic findings.




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).
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.
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).
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)
6



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)
7
Glossary
Term
Annual
Average
Damage
Appraisal
Benefits
Climate
change
Consequence
Cost-benefit
analysis
Defence
system
Discount Rate
Drivers
Economic
appraisal
Embayment
Flood Defence
Flood risk
Flood risk
management
Description
The expected value of annual flood damages (or losses) calculated as
the probability of a range of events multiplied by the loss that such an
event would incur (ie the area under the loss–probability curve).
The process of defining objectives, examining options and evaluating
costs, benefits, risks, opportunities and uncertainties before a decision
is made.
Those positive quantifiable and unquantifiable changes that a plan will
produce, including damages avoided.
Long term variations in global temperature and weather patterns both
natural and as a result of human activity, primarily greenhouse gas
emissions.
An impact such as economic, social or environmental
damage/improvement. May be expressed quantitatively, by category
or descriptively.
Comparison of present value scheme benefits and costs as part of an
economic appraisal. The cost-benefit ratio is the total present value
benefits divide by the total present value costs.
Two or more defences acting to achieve common goals (e.g.
maintaining flood protection to a single flood cell/community)
The annual percentage rate at which the present value of a unit of
currency is assumed to fall away through time.
Phenomena that may change the state of the flooding system, such as
climate change, urbanisation. A driver may change, sources,
pathways, receptors or a combination of them.
An appraisal that takes into account a wide range of costs and
benefits, generally those that can be valued in money terms.
Low-lying area defended from tidal flooding which is hydraulically
disconnected from other low-lying areas
A structure (or system of structures) for the alleviation of flooding
from rivers or the sea.
A combination of the probability and consequences of flooding (such
as loss, damage, harm, distress and disruption).
The activity of understanding the probability and consequences of
flooding, and seeking to modify these factors to reduce flood risk to
people, property and the environment. This should take account of
other water level management and environmental requirements, and
opportunities and constraints. It is not just the application of physical
flood defence measures.
8
Term
Flood storage
Floodplain
Joint
probability
Local studies
Measures
Present Value
Probabilistic
method
Residual risk
Responses
Return Period
Risk
assessment
Scenario
Scenarioneutral
SourcePathwayReceptor
Description
The temporary storage of excess runoff or river flow in ponds, basins,
reservoirs or on the flood plain.
Any area of land over which water flows or is stored during a flood
event or would flow but for the presence of flood defences.
The probability of specific values of one or more variables occurring
simultaneously. For example, extreme water levels in estuaries may
occur at times of high river flow, times of high sea level or times
when both river flow and sea level are above average levels. When
assessing the likelihood of occurrence of high estuarine water levels it
is therefore necessary to consider the joint probability of high river
flows and high sea levels.
Studies that are characterised by focusing on either a specific portion
of the geographical setting or in particular physical aspects.
See responses
The future value expressed in present terms by means of discounting.
Method in which the variability of input values and the sensitivity of
the results are taken into account to give results in the form of a range
of probabilities for different outcomes.
The risk that remains after risk management and mitigation. It may
include, for example, risk due to very severe storms (above design
standard) or risks from unforeseen hazards.
Changes to the flooding system that are implemented to reduce flood
risk (usually synonymous to options, interventions and measures).
Responses can be structural and non-structural interventions that
modify flooding and flood risk either through changing the frequency
of flooding, or by changing the extent and consequences of flooding,
or by reducing the vulnerability of those exposed to flood risks.
The average interval in years between events of similar or greater
magnitude (e.g. a flow with a return period of 1 in 100 years will be
equalled or exceeded on average once in every 100 years). However,
this does not imply regular occurrence, more correctly the 100 year
flood should be expressed as the event that has a 1% probability of
being met or exceeded in any one year.
The process of identifying hazards and consequences, estimating the
magnitude and probability of consequences and assessing the
significance of the risk(s).
Used to describe one possible instance of change, eg climate change
scenario or socio-economic scenario.
Used in this report to describe flood risk data that are broadly
independent of the assumptions on climate change or socio-economic
scenario.
Sources are weather related phenomena (rainfall, marine storms etc)
that generate water that can cause flooding.
Pathways are mechanisms by which water travels from its source to
the places where it may affect receptors (eg estuary, defence
9
Term
Stakeholder
Standard of
protection
Sustainable
development
Tidal surge
Uncertainty
Description
overtopping, floodplain inundation).
Receptors are the people, industries and the built and natural
environment that flooding can affect.
A person or organisation with an interest in, or affected by, decisions
made.
The flood return period event (or annual probability) above which
channel capacity or defence level is exceeded.
Development which meets the needs of the present without
compromising the ability of future generations to meet their own
needs.
An increase in tidal water level above the astronomical tide level
caused by low barometric pressure and/or wind acting on the surface
of the sea.
A general concept that reflects our lack of sureness about something,
ranging from just short of complete sureness to an almost complete
lack of conviction about an outcome.
10
1
Background
1.1
The ESPACE project
The ESPACE project addresses Challenge 4 outlined in the Spatial Vision for Northwest Europe:
‘How to protect and manage the cultural and natural resources of Northwest Europe’. Climate
change will be a significant influence on spatial planning in the near future. The need for cooperation across Northwest Europe on the issue of adapting to climate events is high. Despite
climate change being widely accepted, the concept of adaptation is still relatively new. In order to
ensure that natural resources across Northwest Europe are managed in such a way as to be
sustainable in light of the long-term impacts of climate change, transnational co-operation in the
development and implementation of common approaches to new adaptation strategies is key.
In order to support incorporation of adaptation to climate change within spatial planning
mechanisms, a five-year European Union funded research project has been initiated. The
ESPACE project aims to ensure that adaptation to climate change is recognised and to
recommend that it is incorporated within spatial planning mechanisms at the local, regional,
national and European levels. One component of the ESPACE project is the development of a
Decision-Testing Tool to aid the selection of spatial planning adaptation measures to cope with
climate change. The Environment Agency through its Thames tidal flood risk management
project, TE2100, is leading on this work.
During phase 1 of the development of the tool it became clear that what was needed was more
comprehensive than a single decision-testing tool; rather spatial planners require guidance on
decision making considering the extra risks presented by climate change. The Environment
Agency recommends the development of a Decision Making Framework to support spatial
planners adapt to climate change. This framework should be open and clear to allow stakeholders
to see how well differing approaches to decisions perform given differing climate and related
future scenarios. The proposed Decision Making Framework will enable climate change, with its
medium and long-term impact, to be considered alongside the many other drivers affecting
planning. By using the framework, planners will have the confidence to realise that radical
decisions may be needed in the short-term in order to plan the best options for flood risk
management given the uncertainty that climate change presents.
The Decision Making Framework will focus on planning and water management related issues
and will give guidance to decision makers to help answer the following:




What are the climate-change risks that impact water management and spatial planning?
Should climate change influence spatial planning decisions with respect to water
management for the study site?
What adaptation measures are required, and when?
What adaptation measures would be most appropriate?
11
The Environment Agency through TE2100 has responsibility to manage flood risk in the
Thames Estuary but also has a duty to regulate water quality. Both of these sectors will be
impacted by climate change. For this work the focus of the study is to concentrate on flood risk
management. Although this is a reduction in the breadth of the whole ESPACE project, which is
concerned with all issues of water management, the Decision Making Framework as applied to
flood risk management should represent the broader issues of spatial planning and water
management.
As illustrated in Figure 6, it was proposed for phase 2 of the development of the Decision
Making Framework that it should provide guidance, procedures, and recommendations for the
use of scenarios as well as an illustration of the use of ‘Decision Testing Tool(s)’. These
Decision-Testing Tools will be useful to reduce complex modelling and data to enable decision
making. It is also recognised that stakeholder engagement must be a priority and the framework
should cover facilitation of this. In order to focus the project on pertinent issues a series of pilot
studies will be used to help develop the Decision-Making Framework and Tools.
Decision-Making Framework to address:
Pilot Studies
 Guidance — covering: spatial scale, temporal
scale, depth of study, standards, method for
appraisal of adaptation themes and measures
 The pilot studies help
develop the
framework and tools
 Procedures — for application of the DecisionMaking Framework
 Existing guidance,
procedures and tools
provide the starting
point
 Scenarios — guidance on selection of
appropriate climate change scenarios and
impacts for study site
 Stakeholders aid
development of
guidance through
dialogue and
workshops
 Tools — to integrate the climate change
scenarios, appraisal system and adaptation
options through GIS to develop best suite of
measures
 Stakeholder Engagement — guidance for
stakeholder engagement, development of tools
to aid engagement
Figure 6: The ESPACE Decision-Making Framework
This Phase 2 report centres in the piloting of the Decision Making Framework and Tools in the
Thames Estuary.
The ‘ESPACE Decision Testing Framework Phase 1’ report (February 2004) presented the
requirements of the framework and a thorough review of a set of candidate tools. The outcome
of this report is summarised in chapter 2 as background and contextual information that
informed the piloting during this phase of the project.
Two applications of the Decision Making Framework are subsequently described:
12


A broad-scale estuary wide application to support a high level appraisal of estuary-wide
strategic options identified as adaptation measures for the impact of climate change in the
estuary at 2100. This is further described in chapter 3.
A local, more detailed application of the framework and tools on two ‘embayments’ of
the estuary (Dartford and Crayford). This is further described in chapter 4. The term
embayment is used here to describe a discrete flooding sub-system within the estuary.
The purpose of the Decision Making Framework (and tools) is to provide a generic platform for
the analysis of different adaptation measures. Chapter 5 provides a general discussion informed
by the experiences and results obtained from the piloting of the tools to the Thames estuary.
Chapter 6 provides conclusions on the Thames estuary piloting and makes some
recommendations for the general application of the decision making framework and tools in
further ESPACE projects.
1.2
The Thames estuary
The Thames estuary provides a suitable platform for piloting the ESPACE Decision Making
Framework at a broad-scale level as it combines many key issues that are central to the issue of
flood risk, climate change adaptation and society, namely:





1.25 million people live within areas at risk of flooding,
there are £80bn worth of properties at risk of flooding,
the current flood defences are ageing and will require major investment in the next 20-30
years,
increased development pressure: 160,000 new homes, most in protected floodplain,
likely increase in the risk of flooding as a consequence of estimated climate change
scenarios, resulting in increase mean sea level and increases in the occurrence of extreme
conditions such as intense rainfall and / or tidal storm surges.
The Thames Estuary is macrotidal with a mean spring tide range of 5.2 m at Sheerness gradually
increasing upstream to 5.9 m at Tilbury and 6.6 m at London Bridge. The increasing tidal range
upstream is due to the funnelling effect of the estuary, which has gradually been magnified by the
formation and subsequent land-claim of extensive areas of saltmarsh.
The Thames Estuary has historically experienced an increase in the elevation of high water levels.
There has also been an increase in tidal range of around 1-1.1 mm per year for Southend-on-Sea
and 6.4-6.8 mm per year for Tower Bridge. The increase in tidal range is probably due to a
combination of natural and artificial causes. The increase in sea levels giving deeper water in the
North Sea and the Thames Estuary produces a small increase of tidal range. However, at least
part of the observed increase in tidal range is likely to be due to the effects of embanking. Before
construction of embankments much of the water entering the river spread laterally to cover
mudflats and saltmarshes. Embankments have caused a loss of storage volume for the water at
13
high tide levels, thus increasing the height of high water. Other contributory artificial causes may
include the dredging of deeper shipping channels, the damming of tidal creeks and possible
effects of pollution on sedimentation.
Storm surges in the North Sea are generated by low air pressure combined with strong northerly
winds. The biggest surges originate in the Atlantic Ocean associated with a deep depression
moving in an easterly direction. The low air pressure under the centre of the depression allows
sea level to be raised by 10 mm for every millibar drop in air pressure. Even under a deep
depression the increase in level is only about 300 mm, but this hump is about 1500 km in
diameter and may be moving east at 60-80 km per hour.
The dynamic effect of this movement increases the height and, in addition, a further height
increase is produced if the hump moves from the deep water of the Atlantic into the shallower
waters of the northern North Sea. A steep pressure gradient can exist on the western flank of the
depression, giving strong north-easterly and northerly winds which drive the hump south into the
funnel formed by the east coast of England and the west coast of the continent. The Straits of
Dover are too shallow and narrow to allow much water to pass and the Coriolis force pushes the
water on to the English coast. The incidence and magnitude of these surges therefore depend on
the air pressure and the severity of the gales in the North Sea.
Predicted tide levels in the Thames Estuary have been raised by as much as 2.5 m at high water,
and up to 4 m on the rising tide by storm surges. On the 1st February 1953, the storm surge
increased the rising tide by 2.9 m and the high tide level at Tower Bridge by 1.9 m. The 1953
surge breached defences at various places in the Thames Estuary, particularly Canvey Island,
causing extensive flooding and 300 people died.
It is anticipated that climate change will accelerate the rise of sea-level in the south-east of
England. This will mean that the current standard of protection offered by flood defences in the
estuary will slowly fall. It is also anticipated that the frequency and extremes of storm surge may
increase in the next 100 years driven by global climate change. This presents the Environment
Agency with an increase to flood risk, which it will have to manage in order to protect the people
and property of the London and Thames Estuary areas.
Most of the defences in the Thames estuary were constructed or improved in the late 1970s and
early 1980s as part of the Thames Estuary Flood Prevention Scheme. The defences were
designed to last until about 2030 and the Environment Agency has recently started the process of
planning their future strategy for managing flood risk in the estuary in order to ensure that is in
place before large-scale works are required. Within this context, TE2100 is an Environment
Agency initiative charged with developing a flood risk management strategy which must deliver
sustainable decisions given the long-term impacts that climate change presents. Figure 7
illustrates the evolution and progressive adaptation of flood defences along the Thames.
14
Figure 7: Thames estuary flood defences
15
2
Decision Making Framework
2.1
Introduction
Climate change presents an additional risk for water managers and spatial planners. To make sure
that this additional risk is factored into decision making, the TE2100 project team recommends
through their ESPACE work the use of a formal Decision Making Framework. An explicit,
systematic approach should be adopted in order to improve the quality of the decisions and to
provide an audit trail of technical judgements and considerations.
The purpose of the decision making framework, as applied to the Thames Estuary, is to test the
ability of any proposed flood risk management option to provide technically robust, economically
favourable, environmentally sustainable, and politically acceptable and stakeholder endorsed
solutions, given future uncertainty. Because decisions must be made for managing the whole
estuary and delivering small-scale solutions too, the decision-making process must be consistent
across all spatial scales, both estuary-wide and locally.
It has been identified that the ESPACE Decision Making Framework should provide:





Guidance — covering: spatial scale, temporal scale, depth of study, standards, method for
appraisal of adaptation themes and measures
Procedures — for application of the Decision-Making Framework
Scenarios — guidance on selection of appropriate climate change scenarios and impacts
for study site
Tools — to integrate the climate change scenarios, appraisal system and adaptation
options through GIS to develop best suite of measures
Stakeholder Engagement — guidance for stakeholder engagement, development of tools
to aid engagement
This chapter outlines these aspects of the framework in further detail.
2.2
Guidance, procedures and scenarios
The UK Climate Impacts Programme (UKCIP) provides tools and data to help with climate
change risk assessments and developing adaptation strategies. UKCIP tools provide guidance on
handling risk and uncertainty and climate scenarios and socio-economic scenarios.
Guidance and procedures
The UKCIP ‘Risk, Uncertainty and Decision Making’ framework, as illustrated in Figure 8,
provides excellent generic guidance and a set of procedures appropriate for assessing the impact
of climate change, and as such has been adopted as the decision-making framework for the
Environment Agency within this ESPACE study.
16
Figure 8: The UKCIP decision making framework
The framework is structured into eight key stages. The circular nature of the framework supports
the review of decisions as and when new information becomes available. The framework also
emphasises iteration and feedback between stages such that the problem, objectives and option
identification can be refined. Certain stages (3, 4 and 5) are tiered. This allows the identification,
screening, and prioritisation of risks and options, before deciding whether a more detailed risk
assessment and option appraisal is required. The framework also encourages the decision-making
process to be open and explicit, enabling the active engagement with stakeholders and interest
groups in the study area.
The eight stages of the framework are further described as follows. Illustrated examples are
provided as relating to the ESPACE piloting on the Thames estuary.
Stage 1: Identify problems and objectives
Framing the issue represents a critical stage for a project. Before embarking on the decision
making process, it is essential to understand the reasons for the decision being made, the broad
objectives, and the wider context for the decision. It may be necessary to revisit this stage further
on during the decision making process, to ensure that the problem has been correctly defined and
is being addressed properly.
17
Objective setting goes hand-in-hand with identifying the problems we face. Usually, when a
problem has been identified objectives can be set to cope with the problem. Because we are
planning for the future and the full range of problems we face have not been fully identified it is
not entirely straightforward to set objectives. It is necessary then to set objectives against issues
that we expect to face or issues that we manage at present. Examples of objectives could be to
provide an acceptable level of flood risk and to enhance or conserve biodiversity. It is notable
that the Thames estuary piloting has focused on risk associated with estuarial flooding. This is
primarily a pragmatic decision to help bound the piloting of the framework.
Stage 2: Establish decision-making criteria
This stage sets out the criteria for decision-making. The broad objectives that are set out under
Stage 1 need to be translated into operational criteria that can be used in a formal risk assessment,
and against which the performance of different options and the subsequent decision can be
appraised.
The decision-making criteria might include:



residential property to be protected such that there is no more than 0.05% chance per
annum of inundation
0.1% chance per annum of protected species being inundated
reduction in cost to maintain the flood defence assets
The decision-making criteria should reflect uncertainty about the future and future risk, and will
be influenced by the decision maker (e.g., in the Thames estuary piloting the Environment
Agency) and the stakeholders’ attitudes to risk. During this stage the ‘Receptors’ of risk and the
endpoints of when the options appraisal will be achieved must be identified. Table 1 presents an
example for the Thames estuary.
Table 1: Example of Objective, Decision Making Criteria, Receptors and Assessment Endpoints
Objective
Decision Making Criteria
Receptors
Assessment Endpoint
Provide an acceptable level of flood risk
Options must provide a 1:1000 year standard of protection against estuarial
flooding in central London
Resident population
Working population
Cultural and Heritage sites
Infrastructure etc…
90% confidence that estuarial flood risk can be managed to the required standard
of protection
18
Stage 3: Assess risk (tiered)
The primary purpose of undertaking a risk assessment is to:




characterise the nature of the risk
provide qualitative or quantitative estimates of the risk
assess the consequences of uncertainty for decision options
compare sources of risk
This presents the decision maker with a complex set of questions to answer.
As water managers and spatial planners we must manage flood risk and especially the additional
risk presented by climate change. However, our management may in itself have an impact on the
estuary and we must understand this impact. It seems best to use the same model to achieve this.
In the Thames estuary piloting, it is proposed to work with two simple conceptual models, based
on the Pressure System-State Impact Response (PSIR) model. The first model considers estuarial
flood risk, drivers that act to change that risk and the ability of options to effectively manage
estuarial flood risk. This is centred on the flooding system constituted by Source, Pathway, and
Receptor. The second model helps consider all pressures acting on the social, environmental and
economic aspects of the study site, and will identify the significant issues that will help or hinder
the Environment Agency, as decision maker, to achieve our objectives.
The decision maker must make a baseline assessment of the current risk in the study site
designed to achieve the stage 3 objectives. The decision maker must then develop scenarios for
the socio-economic drivers and environmental pressures that will drive change in the study site
— climate change, physical change, socio-economic development, environmental change,
technical change — to understand how risk will change. The measure of risk will be multidimensional, comprising, for example, economic, health, social and environmental measures.
In the Thames estuary piloting, the estuarial flood risk assessment will build on the flood risk
work carried out by the Foresight programme to achieve this. The flood risk model is presented
in Figure 9.
19
Drivers
Processes that change the state of the flooding
system
Response
Flood risk management options ability to affect
flood risk
Flooding System
Source-Pathway-Receptor
Impact
Risk estimate, using economic, social, health,
environmental measures
Figure 9: Conceptual model of risk assessment stage for flood risk
The work of flood risk managers impacts the functioning or state of the study site, economically,
socially and environmentally. Using the PSIR model, as detailed above, Table 2 illustrates some
of the impacts that must be addressed when assessing options. These have been identified as the
‘significant issues’ in the Thames estuary.
Table 2: Developing an understanding of our impacts on the estuary
Pressure
Current
management of
hard defence
Future
management of
hard defence
Current
management of
hard defence
State
Interruption of sediment
transport to salt-marsh
Impact
Stressed inter-tidal
ecology. Loss of
saltmarsh
Raising of tidal walls leading Loss of amenity value
to less access to river for
and interest in river
rowers and anglers
Defence line through central Reduced fish
London keeps river flows
populations
fast. Few chances for fish
to rest during journey from
sea to spawning grounds
Climate Change
Sea level rise and
Loss of inter-tidal
increasing wave action
habitat
Change in policy Desire to realign hard
Loss of reclaimed
of management of defences to provide interland for dock
hard defences
tidal habitat
development
Response
Identify options that
provide compensation
sites
Identify options that
allow better access to
river
Identify options that
provide resting areas for
fish
Identify options that
increase inter-tidal area
Identify options that
provide the required
level of dock
development
It is recognised that there is a need to consider those pressures that act on the study site that are
outside the control of the decision maker. For instance, land development may lead to loss of
habitat. There is a need to understand these impacts, and how these may change in the future, to
understand how objectives may be helped or hindered. By considering the full economic, social
20
and environmental systems within which planning is undertaken, it is possible to identify options
that will provide the best response to all pressures and impacts. Similarly, by performing a
rigorous risk assessment it is possible to investigate how different options provide effective
response to the risk.
There are a number of technical problems that need to be solved to achieve the stage 3
objectives:




How do we compare different hazards?
How do we factor uncertainty into our risk assessment?
Do we define a limited number of standard test events to assess levels of risk or do we
investigate a large number of combinations of hazards?
Do we favour the most likely scenarios for climate or development change over the worst
cases when performing risk assessment?
The tiered structure of assessing risk enables the decision maker to undertake a different depth of
analysis according to the level of decision, understanding and impact of climate change. These
tiers are focused on:



Tier 1 – risk screening
Tier 2 – qualitative, and generic quantitative risk assessment
Tier 3 – specific quantitative risk assessment
Stage 4: Identify options (tiered)
For any particular problem within the study area, there is likely to be a number of different
options that will meet the decision-making criteria. Initially, it is important that a wide range of
potential options are considered to avoid the premature rejection of viable options. This will
include options ranging from ‘do minimum’ to ‘do a lot’.
In terms of options that are robust to future risk, and will help manage their consequences, the
decision maker should attempt to identify the range of least to most acceptable options at the
outset.
Stage 5: Appraise options (tiered)
Options appraisal is closely linked with risk assessment and comprises evaluation of the options
against the decision-making criteria established in Stage 2. Options appraisal informs the
decision: Making the decision is within Stage 6. The prime purpose of the options appraisal stage
is to provide a robust basis upon which to recommend the ‘best’ way (the preferred option) to
meet the overall decision criteria.
21
There are a number of considerations that need to be made to achieve the stage 5 objectives:






How do we compare different criteria that do not have a shared valuation system, e.g.
environmental value and economic cost benefit?
How do we recognise that different decision making criteria are more or less important to
different stakeholders?
How do we involve decision making criteria that are not easily reducible to quantitative
measurement?
How do we represent uncertainty in the appraisal of different options?
How do we appraise options where there may be a large amount of very complex spatial
data on the receptors, can we automate the process?
Do we develop deterministic or probabilistic assessments?
The tiered approach outlined in stage 3 is also applicable in option appraisal. The three tiers
move through a systematic qualitative analysis through to a fully quantified analysis.
Stage 6: Make decision
The aim of Stage 5 options appraisal and the earlier analytical stages is to inform the decision
making process. The final step is to bring the information together, evaluating it against the
objectives and defined decision criteria. This may include a review of whether the decision
objectives and criteria remain appropriate in the light of the preceding analysis. Stage 6 includes
the effective communication of the analysis in a way that will assist the study area stakeholders in
understanding the trade-offs between different courses of action.
In practice, the stages in decision making will not always follow on from one another. It may be
necessary to return to a previous step, for example to take into account a new option that has
only been identified as a result of a first round of risk assessment or options appraisal. In Figure 8
frequently needed re-iteration routes are indicated by dotted lines. In particular, the difficulty and
importance of problem formulation must be recognised. Many issues in the study area may not
yet been fully defined as there may have been a lack of investigation into risk receptors. In other
cases the problems will have to be redefined in order to open a practical set of options.
Most risks cannot be eliminated altogether, and risk management involves making judgements
about what level of risk is acceptable – risk tolerance or risk appetite. Such judgements are often
difficult, both for individual risks and across a programme of activity. The residual risk will need
to be mitigated where possible.
Stage 7: Implement decision and Stage 8: Monitor, evaluate and review
Following the making of a decision that has fully considered risks and uncertainty, it is necessary
to both implement the decision, and to monitor, evaluate and review the decision.
22
It is notable that the main focus of the framework is to help the decision maker make a decision.
However it is also noted that beyond this stage it is important for that decision to be effectively
communicated, and that uncertainty is acknowledged through transparency and clarity of
presentation.
This is beyond phase 4 of the TE2100 project but the TE2100 team should have identified how
the plan could be implemented, considering the spatial planning structure in the UK.
The decision maker should recommend as part of the implementation a set of indicators for long
term monitoring within the study site as an integral part of the review process. The initial
implementation may not be the final solution for the long-term planning horizon but be an
interim solution. Furthermore, it may be the case that decisions made as interim solutions are not
defensible in the longer term because the qualitative and quantitative approaches used to
underpin that decision are too uncertain, or the social framework under which the decision has
been made undergoes paradigmatic change. For both situations it will be important to monitor
the system in question to re-evaluate the decision process.
Scenarios
UKCIP02 climate scenarios were developed by the Tyndall Centre for Climate Change Research
and the Meteorological Office Hadley Centre, providing four scenarios at a scale of 50km for
three future periods (2020s, 2050s and 2080s). These supersede previous 1998 climate change
scenarios. The climate change scenarios are based on IPCC SRES (Special Report on Emissions
Scenarios) emissions scenarios. The UKCIP socio-economic scenarios were developed by the
Science and Technology Policy Research Unit (SPRU) at Sussex University, and were informed
by the IPCC and Foresight scenarios. Four socio-economic scenarios for two future periods
(2020s and 2050s) were developed. These scenarios are useful for sea level rise but are less well
developed for storm surge. The TE2100 team have developed their own scenarios for storm
surge building on advice from UKCIP and the Hadley Centre.
2.3
Decision Testing Tools
The adopted Decision Making Framework contains a variety of different tools used at various
stages of the decision making process. These include tools to: help identify the problem and
objectives of the study (the Source-Pathway-Receptor model), to define climate change scenarios
(IPCC/UKCIP scenarios); to model physical processes (TUFLOW and ISIS hydraulic modelling
software); and tools to post-process results (Excel). This section describes in detail the additional
decision testing tools selected in Phase 1 of the ESPACE project used to calculate economic
flood damage and social impact associated with flood risk (MDSF) and example stakeholder
engagement tools (FloodRanger and FloodRanger Professional).
23
MDSF
The Modelling and Decision Support Framework (MDSF) consists of customised GIS-based
software and procedures originally developed to support operating authorities in the
implementation of Catchment Flood Management Plans (CFMP) and Shoreline Management
Plans (SMP). The MDSF can be used to:





Input GIS and other datasets from Environment Agency databases and other sources
Inspect and manipulate catchment data to support scoping studies
Generate flood hazard maps / shoreline erosion hazard maps for present and future
conditions
Appraise catchment flood management options / shoreline management options using
socio-economic criteria
Assess the uncertainty associated with the predictions.
MDSF offers a range of possibilities for dealing with hazard estimates and mapping: hydrological,
hydraulic modelling and coastline erosion modelling is external to the MDSF software system,
and flood hazard maps may be generated either externally or internally. The evaluation of socioeconomic criteria and the uncertainty procedure are both internal to the MDSF system.
The MDSF tool comprises a customised Geographical Information System (GIS) component
and a data management component that provides a structured framework guiding the user
through the CFMP or SMP process. The data management component is based on a relational
database, and enables users to work through ‘procedures’ developing ‘cases’ for comparative
evaluation: Import Base Data; Import External Model Results; Calculate Flood Extent and
Depth; Calculate Economic Damages; Calculate Erosion Damages1; and, Calculate Social
Impacts. In parallel to developing such cases, the MDSF contains a simple procedure for the
evaluation of uncertainty of calculated economic damages and social impacts. A key feature of
the GIS component is that it creates a number of different ‘views’ of the data held in the MDSF,
appropriate to the different procedural stages of the study. In this way, it helps guide the user
through the process.
The MDSF procedures provide the framework within which to apply the MDSF tool for CFMPs.
It provides an overview of the MDSF tool, guidance on catchment hydrological and hydraulic
modelling, a procedure for estimating uncertainty in the results and supporting technical
information on, for example, land use and climate change scenarios and a methodology for
estimating future development scenarios.
It is important to note that the MDSF has been developed with the purpose of supporting
CFMPs and SMPs and, as such, has as its focus the socio-economic cost of fluvial and coastal
1 The ‘Calculate Erosion Damage’ procedure is appropriate for SMP work only.
24
flooding and coastal erosion, and how these costs are influenced by climate change, land-use
change, flood management / shoreline management policy and uncertainty. The ESPACE Phase
I review acknowledged that there is little consideration given to other factors such as water
resource availability or environmental impact2. Given its focus, the MDSF must also be
considered from the perspective of scale and the accompanying aspects of level of detail and
uncertainty. In one sense, the MDSF tool itself may be considered to be largely scale independent
as much of the modelling of physical processes is carried out external from the tool. The scale of
the MDSF is in large part dependent on the datasets that are introduced into the MDSF tool, and
on the procedures that provide guidance on use of the tool. This may be illustrated by
considering the modelling involved in creating fluvial flood extents and depths, where the level of
detail and accuracy of the results is influenced by the type of modelling used to generate estimates
of water level and the resolution of the DEM used by the MDSF.
FloodRanger and FloodRanger Professional
Stakeholder engagement is crucial as future flood risk options can only succeed if they are widely
supported by those who live in the study area. The process of engaging stakeholders in decisionmaking implies conveying information in the right amount and the right level of complexity so
that it can be clearly understood by all parties involved.
One of the outcomes of the UK Government’s Foresight Future Flooding project is the
‘FloodRanger’ software. FloodRanger was designed as a 3D computer ‘game’ developed to aid
understanding of flood management and climate change issues. It involves the selection of world
future scenarios (informed by the Foresight project) and climate change scenarios (informed by
UKCIP02) and the management of flood risk with respect to the scenario impacts on ‘health of
environment’, ‘public opinion’, ‘regional insurance premium’, ‘water demand’, and ‘areas at risk of
flood’. The game is played in a ‘virtual terrain’ characteristic of a north-eastern coast in Atlantic
Europe.
The ‘rules of the game’ require that the player ‘inserts’ housing and industry in response to the
selected ‘world scenario’, and river and sea defences in response to flood risk. These
interventions are ‘gauged’ according to the internally specified criteria for ‘health of environment’,
‘public opinion’, ‘regional insurance premium’, ‘water demand’, and ‘areas at risk of flood’. These
criteria have been developed as idealised indicators intended to demonstrate the range of issues
that may be considered, rather than scientifically rigorous parameters intended for decision
testing purposes.
2 Whilst the MDSF does not explicitly consider environmental impact, careful editing of datasets used in the
‘economic damage’ calculation can enable a broad assessment of environmental point (e.g., SAMs) and areal (e.g.,
habitat) features.
25
It is notable that FloodRanger has been developed as a tool to demonstrate to a non-flood risk
management professional audience (e.g. local authority planners) and in an educational
environment (e.g. universities and schools) the type of issues that are faced by professional flood
and coastal defence engineers. The focus of the application is in playing a game in a virtual reality
style environment, rather than on scientific rigour of the processes involved. As such, its interest
is as an educational and promotional tool rather than an environment in which decision testing
can be made by the professional community.
Recognising the strengths of FloodRanger, the TE2100 team developed ‘FloodRanger
Professional’, such that real-world examples of flood risk management could be imported and
explored. This development incorporates an open architecture such that flood risk modelling
carried out in other modelling environments (e.g., hydrodynamic inundation modelling, MDSF
evaluation of economic and social impacts) can be incorporated into the FloodRanger
Professional tool, thus enabling the rapid visualisation and exploration of flood risk to a wider
stakeholder community.
FloodRanger Professional has two modes of interaction:


‘constant scenario’ allows the user to select a particular world future scenario and climate
change scenario and to run through a series of time-slices, electing different flood
management options and experiencing different randomly generated flood events to
better understand how flood risk evolves under given futures
‘scenario picker’ allows the user to select all variables – a particular world future scenario,
climate change scenario, flood management option, flood of specified severity and time in
the future – to visualise flood extent and the associated area flooded, population flooded
and economic damage.
An ArcView 3.x extension has been developed to assist in creating FloodRanger Professional
datasets. A DTM, flood frequency grids, event damage grids, event population affected grids and
additional overlays can be created from this extension. Details of the processes involved in the
creation of FloodRanger Professional project and associated datasets is given in the Technical
Annex.
2.4
Visualisation and stakeholder engagement
The participation and support of key organisations and groups from the outset is essential to the
long-term success of the project. It is important to be able to identify the critical stakeholders to
be involved in the project and develop strategies to engage them appropriately in the process.
Stakeholder engagement must take place at all stages of the assessment and planning process and
not be limited to the end as a display of the preferred management measures. It may not be
possible to engage stakeholders who have been alienated by the project and incorporate their
concerns and needs into the project towards the end.
26
Stakeholder engagement can provide many benefits, including:







improved decision making, validating approaches, and enabling scrutiny and testing
resolving conflict, develop consensus by identifying and acknowledging shared views and
objectives
improved management of multiple institutions with similar roles
enhancing co-ordination and extending stakeholders understanding
fostering communication through early and open discussion and clear and transparent
procedures
ensuring that data and information are shared, gaining benefit from information held by
other stakeholders
help avoid adaptation-constraining decisions (that will make it more difficult to cope with
risks in the future)
The Decision Making Framework must include a method for engagement and tools that aid this
stakeholder engagement for the benefits listed above. There are different types of stakeholder
engagement and different types of stakeholder: the TE2100 team must decide on appropriate
styles. Engagement could be participatory or consultative with a gradation in between.
Visualisation is required to aid in stakeholder engagement and should be developed from the
decision testing tool(s) used in the assessment of strategic options. The selection of a visualisation
tool will typically include an assessment of; cost, time, the extent to which engagement will
improve the decision, how to improve the decision making by sharing knowledge and ideas, and
who will undertake the stakeholder engagement. FloodRanger and FloodRanger Professional are
two example stakeholder engagement tools that have been developed for two different types of
stakeholder.
27
3
Broad-scale Application
3.1
Introduction
3.2
Broad-scale piloting of the decision making framework
This chapter describes the broad-scale pilot testing of the Decision Making Framework in the
Thames Estuary. The principal decision testing tools that we have used in this work are MDSF
and FloodRanger Professional, supported by use of the source-pathway-receptor model,
IPCC/UKCIP climate change scenarios, TUFLOW and ISIS hydraulic modelling software and
Excel. These tools are used to help in the risk assessment and options appraisal, as specified for
the tiered stages 3, 4 and 5 of the Decision Making Framework.
Stage 1: Identify problems and objectives
Although the problems facing water management in the Thames Estuary area are numerous, this
piloting exercise only focused on problems associated with flood risk management. Within the
context of the source/pathway/receptor model, the primary sources of flood risk are storm
surge, changes to mean sea level and extreme fluvial flows; the primary pathway of flood risk is
overtopping of the tidal and fluvial defences, and the receptor of flood risk is the people and the
buildings in the flood plain.
The piloting exercise consisted in a broad scale assessment of options in the Thames Estuary for
adaptation to climate change as the driver that further stresses the current sources of flood risk:
storm surge, mean sea level rise and fluvial flow.
Stage 2: Establish decision-making criteria
In any quantitative risk analysis, the objectives need to be translated into measurable assessment
criteria. In this piloting exercise, the adopted measurable criteria were the cost-benefit ratio
(based on the calculation of damage to residential and commercial properties due to tidal
flooding), the number of people flooded and the level of risk to loss of life. This provides the
basis for a well-justified indication of the approximate sums for which it would be economical to
invest in climate adaptation measures.
Stage 3: Assess risk
The appraisal of current and future levels of risk, as required by a typical risk model characterised
by inundation driven hazards, involves the following tasks:


inundation modelling to assess the impact of floods on people and properties,
estimation of the resulting economic damage from floods,
28



post-processing of results to facilitate the strategic appraisal of estuary-wide options,
post-processing of results to aid the visualisation of results and stakeholder engagement,
and,
preliminary sensitivity analysis to identify uncertainties.
Risk assessment was carried out using four different climate change scenarios: the IPCC/UKCIP
‘low’, ‘medium’ and ‘high’ scenarios, and a fourth scenario (‘high+’) based on the ‘high’ scenario
that included an estimate of the climate change impact on tidal propagation and storm surge on
the study area.
The extent of the Thames Broad-scale pilot area is shown in Figure 10.
Tidal Flood Risk Areas
London
Thames
Estuary
Dartford Local
Pilot Area
Thames Broad-scale Pilot Area
Figure 10: Thames Estuary pilot area
Tidal flooding is the key driving mechanism responsible for the hazards in the Thames estuary;
therefore a broad-scale 2D inundation model was set up using TUFLOW (Two Dimensional
Unsteady Flow Model) to simulate the flood extent and associated flood depths for a range of
tidal events.
MDSF was used to estimate direct damage to properties for a range of tidal events. The direct
damage calculations were based on the use of national standard depth-damage curves included in
MDSF and a national property dataset. These relate residential and different categories of
commercial property to damages caused by different depths of flooding. Each 50 m flood depth
29
grid from TUFLOW was imported into MDSF and the corresponding flood extent was
subsequently created.
The social impact analysis carried out with MDSF consisted of estimating the number of people
affected under each of the tidal and defence scenarios for which a damage estimated was
obtained.
A further assessment of the social impact of flooding included the estimation of the annual
probability of loss of life. The broad-scale piloting application precluded from making a detailed
estimation of hazard to life based on water velocity. Therefore it was decided to use the rate of
rise of water on a cell basis as a surrogate for velocity, using a method adapted from Defra/EA
research (Defra/EA, 2003).
Stage 4: Identify options
The piloting of the decision testing tools consisted in the analysis of six strategic climateadaptation options for the entire estuary ranging from a “do nothing” strategy to provision of
large-scale flood defences with varying standards of protection:






Do nothing (DN), i.e. walk away and leave the existing barriers open.
Maintenance Only – Declining Standards (MO), i.e. maintain the level of defences but
increase activity of existing barriers when necessary. Although this will require
maintenance and replacement programmes of existing flood defence assets, the standard
of defence will decline with rising sea levels.
Do something A1 (A1), i.e. provide a 1:1,000 standard of protection (SoP) to the entire
estuary.
Do something B1 (B1), i.e. provide a 1:5,000 SoP to the entire estuary.
Do something A2 (A2), i.e. provide either a 1:1,000 or 1:200 SoP depending on the land
use within the individual embayment. A 1:1,000 SoP will be set for all urban embayments,
whereas the 1:200 SoP will be for the non-urban embayments.
Do something B2 (B2), i.e. provide either a 1:5,000 or 1:200 SoP depending on the land
use within the individual embayment. A 1:5,000 SoP will be set for all urban embayments,
whereas the 1:200 SoP will be for the non-urban embayments.
Stage 5: Appraise options
The overall methodological approach adopted to pilot the Decision Making Framework was
driven by the need to perform high level strategic analysis that provided a rapid assessment of the
economic efficiency of the set of strategic options proposed. Therefore the emphasis was placed
on the identification of technically robust, generic quantitative approaches that could support the
rapid strategic assessment of options.
30
One of the key elements of the methodological approach adopted to appraise the options lies in
the development of a scenario-neutral database populated with event-based damage estimates.
The scenario-neutral approach consists in separating the process of generating results and inputs
from the actual process of appraising options, therefore permitting a rapid assessment of
alternative strategic options. In the context of the piloting to the Thames Estuary, the scenarioneutral approach consists in separating the process of making model runs (for example to predict
the inundation extent) and the damage calculation (MDSF) every time a new strategic option
needs to be analysed. This is exemplified in Figure 11.
Figure 11: Decision Making Framework broad-scale application
In order to arrive at the present value of Annual Average Damage (AAD) for a given strategic
option and for a given UKCIP scenario, a calculation of the AAD at the current time horizon is
carried out first. Then the calculation is repeated for a range of time horizons: 2050 and 2100.
Finally the stream of AADs is generated by interpolating linearly between years and applying the
appropriate discount rates.
3.3
Results summary and uncertainties
The results obtained in the appraisal of options for climate adaptation within the Thames Estuary
enabled the following general observations to be made:

The identification of a (set of) preferred strategic option(s) may be dependent on the use
of a particular climate change scenario. For example, for a UKCIP ‘low’ climate change
scenario there are no differences in the AAD values between the Maintenance Only and
the strategy that includes the provision of a 1:1,000 SoP for the entire estuary. This is a
consequence of the estimated Southend water level for 2050 and 2100 scenario that does
31



not exceed 5.2 mAOD (the assumed maximum Southend level for which the barrier
provides protection for).
For most climate change scenarios, there are no differences in the AAD values between
the strategies that include the same SoP for the entire estuary (i.e. A1 and B1) and the
strategies that vary the SoP with land use (i.e. A2 and B2). Some differences start to
appear for a ‘high+’ climate change scenario at 2100, when Southend levels are above
6.9 mAOD and 7 mAOD (approximately the statutory defence levels for embayments
not protected by the Thames Barrier). This leads onto the conclusion that providing a
differential SoP for embayments with a non-urban land use (i.e. 1:200) would not yield
significant benefits in terms of direct damage avoided as those embayments are already
protected to a much higher standard.
Out of the total of 1.8 million people counted in residences in the estuary, 1 million
people would be affected for the most extreme climate change event (7.81 mAOD at
Southend) at 2100 and with, approximately, the current standard of protection.
Based on a preliminary assessment of the risk to life of people, it could be concluded that,
for the current flood risk (defences at the statutory level with water levels exceeding the
maximum protection provided by the barrier), the individual level of risk is within the
target limit of 1 x 10-5, but this would be exceeded at 2050 and 2100 for the Maintenance
Only strategy under a UKCIP ‘high’ climate change scenario.
Finally for this piloting application, a FloodRanger Professional project file has been created
based on the TUFLOW hydrodynamic inundation modelling and MDSF economic damage
calculation described earlier in this section. The FloodRanger Professional project enables
visualisation and exploration of the flood risk associated with the key previously identified
strategy options (Do Nothing, Maintenance Only and Do Something A1), for a single climate
change scenario that predicts the largest increase in estuarial water levels at 2000, 2050 and 2100
(High +). The current (year 2000) socio-economic ‘world future’ was used.
The use of a high level approach, structured around a scenario-neutral approach and informed by
TUFLOW and MDSF, provided a successful methodology for the preliminary assessment of the
economic efficiency of six estuary-wide strategic options identified for dealing with the
adaptation of spatial planning to climate change.
As part of the piloting exercise, sensitivity analysis was carried out on key decision making areas
in order to analyse a number of issues that, if not properly accounted for, could translate into
large uncertainties conditioning the robustness of the decision adopted. The key issues identified
through the experiences gathered from the broad-scale piloting are:
1. The need to ensure that, if a scenario-neutral approach is adopted, flood depth and extent
(and direct damages, population affected and loss of life) is adequately mapped to specific
climate change and flood management scenarios and event return period. Because this
approach also relies on interpolation of damages, it was noted that the database of flood
32
2.
3.
4.
5.
extents and damages should be densely populated in the range that is most sensitive to the
strategic options to be mapped.
The use of a non-interactive method to simulate river and floodplain interaction could result
in overestimation of the driving tidal levels for the upstream embayments, hence yielding
larger damage figures for options comprising protection measures with low standards.
The need to thoroughly review the contents of the property database, mainly in relation to
the absence of some headline sites, the inclusion of properties that may not be at ground level
and the average floor space data contained in the MDSF database,
The need to appraise options over the entire range of climate change scenarios as a way to
account for the uncertainties contained in climate change predictions, and,
The need to determine as accurately as possible the maximum protection level provided by
the Thames Barrier under different operational circumstances, as it is a key flood control
structure that affect the appraisal of extensive adaptation measures.
33
4
Local Application
4.1
Introduction
The piloting of the ESPACE framework also recognised that a local application would assist with
an evaluation of how issues of scale (e.g. spatial resolution of the DTM) may potentially affect the
performance of the decision testing tools.
The Dartford and Crayford area was selected for the local application of the decision testing
tools. This was aligned with recognition of the programme of existing studies undertaken in the
area.
4.2
Local piloting of the decision making framework
The first two stages of the Decision Making Framework for the local application are aligned with
that of the broad-scale application. Further stages reflect more fully the specific characteristics at
the local scale and that the local application reflects a second iteration of the application of the
framework.
Stage 1: Identify problems and objectives
Although the problems faced for managing water in the Thames Estuary are numerous, this
piloting exercise only focused on problems associated with flood risk management. Within the
context of the source/pathway/receptor model, the primary sources of flood risk are storm
surge, changes to mean sea level and extreme fluvial flows; the primary pathway of flood risk is
overtopping of the tidal and fluvial defences, and the receptor of flood risk is the people and the
buildings in the flood plain.
The piloting exercise consisted of a local assessment of options in the Dartford & Crayford
embayments for adaptation to climate change as the driver that further stresses the current
sources of flood risk: storm surge, mean sea level rise and fluvial flow.
Stage 2: Establish decision-making criteria
In any quantitative risk analysis, the objectives need to be translated into measurable assessment
criteria. In this piloting exercise, the adopted measurable criteria were the cost-benefit ratio
(based on the calculation of damage to residential and commercial properties due to tidal
flooding), the number of people flooded and the level of risk to loss of life. This provides the
basis for a well-justified indication of the approximate sums for which it would be economical to
invest in climate adaptation measures.
34
Stage 3: Assess risk
The appraisal of current and future levels of risk, as required by a typical risk model characterised
by inundation driven hazards, involves the following tasks:





inundation modelling to assess the impact of floods on people and properties,
estimation of the resulting economic damage from floods,
post-processing of results to facilitate the strategic appraisal of estuary-wide options,
post-processing of results to aid the visualisation of results and stakeholder engagement,
and,
preliminary sensitivity analysis to identify uncertainties.
In contrast to the broad-scale application, risk assessment at the local scale was restricted to
considering the ‘high+’ climate change scenario, based on the IPCC/UKCIP ‘high’ scenario and
climate change impact on tidal propagation and storm surge on the study area.
The extent of the Dartford and Crayford pilot area, in relation to the broad-scale pilot area, is
shown in Figure 12.
Tidal Flood Risk Areas
London
Thames
Estuary
Dartford Local
Pilot Area
Thames Broad-scale Pilot Area
Figure 12: Dartford and Crayford local pilot area
Tidal flooding is the key driving mechanism responsible for the hazards in the local pilot area;
therefore a local 2D inundation model was set up using TUFLOW (Two Dimensional Unsteady
Flow Model) to simulate the flood extent and associated flood depths for a range of tidal events.
35
MDSF was used to estimate direct damage to properties for a range of tidal events. The direct
damage calculations were based on the use of national standard depth-damage curves included in
MDSF and a national property dataset. These relate residential and different categories of
commercial property to damages caused by different depths of flooding. Each 10 m flood depth
grid from TUFLOW was imported into MDSF and the corresponding flood extent was
subsequently created.
The social impact analysis carried out with MDSF consisted of estimating the number of people
affected under each of the tidal and defence scenarios for which a damage estimated was
obtained. A further assessment of the social impact of flooding included the estimation of the
Annual Probability of Loss of Life. The same approach as used in the broad-scale piloting
application was used for the local application.
Stage 4: Identify options
Four strategic options for the flood risk management of the Dartford and Crayford area, were
analysed, aligned with those identified during the broad-level application:




Do nothing (DN), i.e. walk away and leave the existing Darent barrier open.
Maintenance Only – Declining Standards (MO), i.e. maintain the level of defences but
increase activity of existing Darent barrier when necessary. Although this will require
maintenance and replacement programmes of existing flood defence assets, the standard
of defence will decline with rising sea levels.
Do something A1 (A1), i.e. provide a 1:1,000 standard of protection to the Dartford &
Crayford area.
Do something B1 (B1), i.e. realign the defences to provide extra flood storage during
estuarial flooding; maintain defence levels at year 2000 1:1,000 standard of protection
(hence the standard of defence will decline with rising sea levels).
Stage 5: Appraise options
In contrast to the ‘scenario-neutral’ methodological approach adopted in the broad-scale
application, a “scenario-specific” approach was followed, in which the inundation modelling was
undertaken for specific scenarios, defined by a combination of flood risk management option,
climate change scenario and rarity of flood event (probability of occurrence). Figure 13 illustrates
the scenario-specific approach. Such an approach requires that the early stages of the adopted
decision making framework are clearly defined such that the scenarios modelled explicitly
describe the risk and range of considered options. In this instance, the ‘scenario-neutral’
modelling undertaken in the broad-level application of the tools has been used to inform the
selection of scenarios modelled for Dartford and Crayford.
Climate (change) scenarios were identified for 2000, 2050 and 2100; the event rarity was selected
to represent relatively frequent events (1:10 year return period), an event that approximates the
36
current standard of protection provided by the existing defences (1:1,000 year return period) and
a particularly rare event (1:10,000 year return period).
Figure 13: Decision Making Framework local application
The AADs have been calculated for each strategic option as modelled using TUFLOW and
MDSF at 2000, 2050 and 2100.
4.3
Results summary
The results obtained in the appraisal of options for climate adaptation for the Dartford and
Crayford embayments enabled the following general observations to be made:


The economic analysis undertaken illustrates that a restricted number of properties tend
to account for the majority of direct economic damage. Typically, approximately 10-20 %
of the properties account for approximately 90 % of the damage. However, it is also
noted that these relative percentages vary according to the strategic option considered and
the time horizon (degree of climate change). For example, for the ‘Do Nothing’ option,
the percentage of properties giving rise to the same percentage of damage lessens from
2000 (20 %) through to 2100 (10 %).
The results of the social impact analysis indicate that under the ‘do nothing’ strategic
option, by 2050 when the existing defences are considered to have deteriorated to ground
level, both the estimated 10 year and 1000 year flood will likely directly impact on
flooding people and their residences. Under all strategic options, the 10,000year return
period flood is estimated to directly impact on flooding people and their residences. By
2100, approximately 8 % of the embayment population are estimated to be directly
impacted upon by the 10,000 year tidal flood. The total population counted in the
37

residences contained within the Dartford & Crayford embayment yielded a value of
120,000 people.
Based on a preliminary assessment of the risk to life of people, it could be concluded that,
for the current flood risk (defences at the statutory level with water levels exceeding the
maximum protection provided by the barrier), the individual level of risk is within the
target limit of 1 x 10-5, but this would be exceeded at 2100 for the Maintenance Only
strategy under a UKCIP ‘high+’ climate change scenario.
Finally for this piloting application, a FloodRanger Professional project file has been created
based on the TUFLOW hydrodynamic inundation modelling and MDSF economic damage
calculation described earlier in this section. The FloodRanger Professional project enables
visualisation and exploration of the flood risk associated with the key previously identified
strategy options (Do Nothing, Maintenance Only and Do Something A1), for a single climate
change scenario that predicts the largest increase in estuarial water levels at 2000, 2050 and 2100
(High +). The current (year 2000) socio-economic ‘world future’ was used.
The use of a high level approach, structured around a scenario-specific approach and informed
by TUFLOW and MDSF, provided a successful methodology for the preliminary assessment of
the economic efficiency of four local strategic options identified for dealing with the adaptation
of spatial planning to climate change. It is noted that a key part of appraising options at the local
level using a scenario-specific approach was the decision making carried out at the broad-level
that clearly defined the identified options and the risk drivers.
38
5
Discussion
This chapter provides a general discussion on the testing of the Decision Making Framework,
informed by the experiences gathered throughout the piloting applications carried out in the
Thames Estuary at a broad-scale and at the local level. The discussion focuses on stages 3-5 of
the Decision Making Framework:



Stage 3 – Assess risk
Stage 4 – Identify options
Stage 5 – Appraise options
Stage 3 - Assess risk
Hazard identification
The first step in the assessment of the risk process is the identification of hazards and their
consequences. For a broad level application it is important to prioritise hazards according to their
impacts in relation to spatial planning. From the piloting experience in the Thames estuary and
the use of the source-pathway-receptor model, expert knowledge recognised that despite the
multitude of drivers and impacts, tidal flooding is the hazard identified as being the most
influenced by climate change and also the one that would pose the most serious stress to spatial
planning. The dominant hazard for the area under study will drive the subsequent development
and implementation of approaches to arrive at a quantitative assessment of risk.
The Foresight Future Flooding programme identifies other important hazards that need to be
qualitatively assessed using expert knowledge at an early stage (e.g., groundwater flooding and
resources, fluvial flooding and resources, environmental impacts).
Probability of occurrence
For the piloting exercise in the Thames estuary, the probability of occurrence was carried out by
estimating the return period associated to different tidal levels in the downstream end of the
estuary. As tidal flooding was the single dominant hazard, a constant fluvial flow at the upstream
end of the system has been used, adopting the long-term average flow that is exceeded 10% of
the time, Q10.
Two other issues could be explored in other studies:

the need to carry out a joint probability analysis of more than one hazard, where it is not
possible to clearly identify a dominant one, and
39

the need to analyse the impact of climate change in the magnitude of future hazards that
could lead to non-stationarity issues in relation to the probability of occurrence of events.
Assessment of consequences
For the applications carried out in the Thames estuary, the assessment of hazard consequences
on properties and people was informed by mathematical modelling of the floodplain inundation
processes. However, other approaches can be adopted for other systems that could be database
driven instead of simulation-base driven. Examples of data base driven assessments are those
based on the interpretation of satellite imagery, the use of regression analysis or any other
method based on simple and empiric relationships between cause and consequences.
In the broad-scale application, a numerical 2D inundation model was developed in order to
predict flood extent, depth and duration for different tidal events. A simplification was made in
the modelling and full river-floodplain interaction was not modelled; instead the simulation of
river flows (in-bank) was decoupled from the simulation of the inundation in the embayments.
This model simplification was found useful as simulations were carried out faster and simpler.
However inundation depths can be overestimated as the decoupled approach cannot account for
the effect of downstream flooding on upstream water levels. A sensitivity analysis was carried out
finding that the assessment of damage would be less sensitive to variations in water levels in
those scenarios that involve an increase in the standard of protection rather than in those that
preserve the current defence levels.
MDSF proved to be a suitable tool to assess the consequences of flooding in properties. The
assessment of damages is directly related to the quality of the property database. During the
broad-scale application, a number of aspects were identified as relevant when assessing a property
damage database for calculation of damages, for example:






Currency of data. It is common to use census data that represents population statistics at a
particular moment in time. This can become quickly out of date.
Distribution of population. Residential and night-time concentrations of population could
significantly alter the pattern of exposure to the flood hazard used in the calculation of
damages.
Spatial extent and coverage of floodable areas with property data.
Inclusion of highly valuable assets. These may not be adequately described by available data
sets.
Flood depth – damage relationships. Readily available datasets may not contain sufficient detail
to adequately represent property damage due to flooding, due to the classification of
properties or how damage values are given (per property or per m2 of property).
Identification of properties not at ground level. In the event of locations with a large proportion
of flood proofed properties, it is important that these are clearly marked in the property
database so that they are realistically reflected in the calculation of damages.
40

Prediction of growth in the number of properties. To maintain consistency in the assessment of
future risks (i.e. due to future climate conditions) it is important that an estimate is made
of the future number of properties likely to be exposed by a given hazard.
However the experience gathered from the local application suggests that significant
simplifications in the analysis are possible by identifying and focussing on the major contributors
to overall risk. For example, for the local pilot study, typically 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 (along the line of the factors highlighted
above) should focus on the major contributors to overall risk.
Extensive flooding of the nature encountered during the appraisal of climate change impact in
the Thames estuary can pose a severe threat to human life. Threat to human life could arise for a
multiple number of reasons, such as: water flowing at high velocities; sudden flood onsets; deep
floodwaters; collapse of existing structures; extensive low lying and densely populated areas; lack
of adequate flood warning; and, the health and age situation (social vulnerability) of the flood
prone population. As part of the application in the Thames estuary, it was found that climate
change events could lead to severe overtopping events and that the rate of rise of water (for
example the time taken for the water to rise to a 1 m or a 2 m depth) can be an adequate
parameter to characterise the risk to life.
Dealing with specific issues
Each particular study area will have peculiarities that will have to be addressed by the Decision
Making Framework for assessing risk and appraising options. Within the application to the
Thames estuary, the following specific issues were encountered and dealt with at an appropriate
level of detail for the stage of the Decision Making Framework, reflecting its tiered and iterative
nature:




River and floodplain interaction. A non-dynamic link was chosen at the expense of
overestimating some flood levels in the upstream part of the system.
Floodplain drainage following an overtopping event. The drainage from the floodplain
back to the river once a defence is overtopped was not simulated and therefore flood
depths can be overestimated after successive stresses by tidal cycles.
Representation of flood control structures. The Thames Barrier was not explicitly
modelled (instead impacts on receptors were set to zero where the Barrier was considered
to provide protection). This approach ignores the reflected wave and extreme events
where the Barrier could provide partial protection.
Interaction between processes. Within the Thames estuary fluvial flooding was decoupled
from tidal flooding. However there are other circumstances that would require careful
41

consideration of interacting processes such as those related to groundwater and surface
water interaction in flatland areas.
Breaching of defences. For the piloting exercise the failure of defences was only
considered to occur from overtopping and thus breaching of defences (and failure to
operate for moveable structures) was ignored. This assumption is appropriate for certain
levels of flood risk assessment but where decisions are affected by breaching then it
should be explicitly included in the analysis.
Stage 4 – Identify options
A set of generic strategic options was identified for testing as part of the broad-scale application
while more specific options, tailored to the detailed conditions in the embayment, were tested in
the local application exercise. In particular, the broad-scale application in the Thames Estuary
was useful to help screening some of the options prior to a more detailed appraisal.
Stage 5 – Appraise options
Methodological approach of flood plain modelling
Chapter 3 described the scenario-neutral approach adopted for the broad-scale application in the
Thames estuary, whereas Chapter 4 presented the scenario-specific approach used for the local
application to the Dartford and Crayford embayments.
The scenario-neutral approach decouples the generation of the input data required to inform the
appraisal of options from the actual process of appraising a particular option and is considered
appropriate when strategic options are in the process of being iteratively defined and refined.
The scenario-specific approach requires that the generation of input data match the specific
characteristics of a particular option, and as such is considered more appropriate once an agreed
set of strategic options has been identified.
The experiences gained through the application of both approaches are summarised in Table 3.
42
Table 3: Appraisal of Options. Summary of advantages and disadvantages of the scenario-neutral and
scenario-specific approaches, based on their application to the Thames estuary
Description of piloting
exercise carried out
Facility to map
scenarios to strategic
options
Main advantages
Scenario-neutral
This approach consists of performing a
series of TUFLOW and MDSF runs for
pre-defined combinations of water
levels and defence levels.
Mapping scenarios to strategic options
is carried out independently of the
definition of the scenarios, relying on
interpolation of direct damages to
derive a value of AAD for each strategic
option.
A single set of model runs can be used
to test a wide range of strategic
options.
The process of appraisal of options is
fast and robust as it does not depend
on the runtime of models and handling
of large amounts of data.
Main disadvantages
The tool designed to carry out the
appraisal of options can be easily
transferred increasing the exposure to
a wider number of decision-makers and
increasing the number of options that
can be tested. This is the case as
models do not need to be transferred.
Needs an external interface (i.e. the
workbook) to use the model results for
the appraisal of options.
Linear interpolation of direct damages
(from MDSF) can result in large errors if
sufficient data are not available at
break points in the damage-level curve.
Model results tend to be generic and
therefore the operation of flood control
structures may not be accurately
represented.
Needs a more experience user to
adequately map scenarios to strategic
options.
43
Scenario-specific
This approach was adopted for the local
application in Dartford and Crayford and
consisted of performing TUFLOW and
MDSF runs for a single climate change
scenario, three return periods and three
time slices.
Mapping scenarios to strategic options is
carried out prior to the execution of the
simulations so there is no need to perform
any potentially inaccurate interpolation to
derive a value of AAD for strategic options.
The results used to inform the appraisal of
options are more accurate as they are
specifically derived for the option being
analysed.
No interpolation is required to arrive at the
final direct damage in the appraisal of
options.
More accurate representation of the
operational functioning of the flood control
structures.
The strategic options need to be defined
well in advance of the modelling exercises.
Lack of flexibility to quickly test (adapt)
further options once the base model runs
are carried out.
Increased time required per appraisal of a
single option.
As part of devising a suitable methodological approach for the appraisal of options, it was found
that assuming flood damage is a sole function of relative water level (expressed as local river
water level minus flood defence crest level) could potentially save time in the computational
process. However, the exploratory analysis carried out 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 detailed above).
Sensitivities and uncertainties
The piloting of the Decision Making Framework has demonstrated that there are important
‘thresholds’ in the analysis associated with option appraisal beyond which there are changes in the
relative importance of variability in input data:





The estuary wide annual average flood damage values are relatively insensitive to the sea
level rise prediction changing from 7 mm/year to 8.9 mm/year for the strategic option
‘Do something A1’ that maintains 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.
Including in the analysis detailed actual defence levels throughout an extensive region can
be difficult and laborious for an initial appraisal of options due to the lack of availability
of appropriate data. Damage estimates can be more sensitive to a variation of defence
levels for tidal events with levels around the actual defence levels, but it would be less so
for events that cause significant overtopping.
Dealing in detail with flood control structures in large-scale applications needs to be
treated in a simplified manner within a scenario-neutral type of approach. For example, in
the application for the Thames estuary, the Thames Barrier was not explicitly included in
the inundation modelling exercise in order to encompass the wide range of options that
may or may not include the operation of the barrier. The effect of the barrier was then
externally treated within the Excel workbook that was developed to post-process data and
appraise options. This can lead to uncertainties related to the maximum level of
protection provided by the barrier and to the effect that the barrier closure can have on
increasing downstream water levels (the reflective wave). As noted before, all the impact
of these uncertainties is noted to vary according to the strategic option considered.
The scenario-neutral approach relies on a linear interpolation algorithm to determine the
damage associated with each strategic option. During the broad-scale application it was
found that not having enough scenario-neutral estimates around the key range of water
levels could distort the appraisal of options and the sensitivity analysis if they involve
water levels that are all masked within a single range in the scenario-neutral database.
Within the scope of the piloting exercise, capping of individual property damages based
on individual asset valuation was not carried out. This highlights an area of uncertainty if
44
the total present value of damages (over 100 years) is more than the asset value. It is
notable that the principal involved in capping damages would mean that parts of London
would have to be considered in the economic appraisal to be ‘set back’ to allow flooding.
It would be instructive in future applications to identify the distribution of those
properties where damages should be capped.
The calculation of the stream of annualised average damage figures was carried out using
linear interpolation between three time horizons. This could be considered consistent
with the uncertainty inherent in the climate change predictions. However a finer temporal
resolution might be required in order to match the calculation of AAD figures with
medium term planning time horizons, design life of structures and land use
developments.

Scale and methodological issues
A comparison was made between the results (event damages, AAD and number of deaths)
obtained using the ‘scenario-neutral’ broad-scale piloting and the ‘scenario-specific’ local piloting
of the Decision Making Framework on the Thames estuary. To enable direct comparison of scale
and methodology, comparisons were made where climate change drivers, strategic options
considered and event frequency were the same:

Climate change scenario: ‘high+’,

Strategic options: Do Nothing and Maintenance Only,

Return periods: 10, 1000 and 10,000.
The results from the local application were obtained directly from MDSF (as reported in Chapter
4), while the results from the broad-scale application were obtained from the Excel workbook
but applied to only the Dartford and Crayford embayments.
The following tables (Table 4 and Table 5) show the results from the comparison of damages and
loss of life. In both cases the same pattern of results can be observed; the largest differences
occur for the lower return period events. This also translates to significant differences in the final
AAD value.
These differences are related to differences in assumptions in the representation of ground and
infrastructure features achieved with each model resolution. Barriers to flow (embankments and
roads) are better represented in a higher resolution model as used for the local application and
therefore flood extents and depths tend to be lower, hence lower damage figures. In the lower
resolution model, as used in the broad-scale application, the level of roads and embankments can
be underestimated as the model uses an average ground level for each model cell crossed by one
of these features. Also, the local scenario-specific approach can represent some local features,
such as secondary barriers and local defences that can also be responsible for differences in the
results obtained in comparison with the broad-scale model.
45
However, it is also notable that seemingly small differences in assumptions between the two
approaches may significantly impact on the results produced. This is particularly noted when
considering the 1,000 year return period modelled using the two approaches. This return period
is close to the standard of protection offered by defences and as such is very sensitive to model
assumptions (e.g. whether defence levels are considered equivalent to the actual defence level, or
to a reported standard of protection, and interpolation between explicitly modelled water levels in
the scenario-neutral broad-scale approach).
Table 4: Comparison of scenario-specific and scenario-neutral approaches - Damages
Option
Do Nothing (DN)
Maintenance
(MO)
Approach
Scenariospecific
Scenarioneutral
Only Scenariospecific
Scenarioneutral
Damage (in million pounds)
10 yrs
1,000 yrs
393
871
10,000 yrs
1,594
AAD
240.8
764
1,109
1,264
437.7
0
0
1,573
0.86
0
670
1,221
34.1
Table 5: Comparison of scenario-specific and scenario-neutral approaches – Loss of life
Option
Maintenance
(MO)
Approach
Only Scenariospecific
Scenarioneutral
Number of deaths
10 yrs
1,000 yrs
0
0
10,000 yrs
1,758
0
1,668
568
High level visualization of results for stakeholder engagement
A Floodranger Professional project was developed as part of the both broad-scale and local
piloting of the Decision Making Framework, proving that the application of this type of tool can
help communicate the consequences of differing strategic options to stakeholders. An analysis of
the functioning of this program was carried out comparing the results obtained from Floodranger
with those obtained with MDSF, highlighting limitations inherent in the interpolation methods
used to predict flood extent for a given return period within the FloodRanger Professional
software.
46
6
Conclusions and Recommendations
6.1
Conclusions
The objective of the piloting of the ESPACE Decision Making Framework on the Thames
estuary has been to assess how well the selected Decision Making Framework and Decision
Testing Tools meet the stated aims of the ESPACE project in supporting planners adapt to
climate change. Throughout the piloting of the framework and tools, the following key questions
have been explicitly considered:




What are the climate-change risks that impact water management and planning?
Should climate change influence spatial planning decisions with respect to water
management for the study site?
What adaptation measures are required, and when?
What adaptation measures would be most appropriate?
The piloting of the Decision Making Framework and Decision Testing Tools explicitly
recognised that a systematic approach is required in order to improve the quality of decision
making, providing a clear and comprehensive audit trail describing the application of scientific
knowledge and expert judgement used in such decision making. The Decision Framework
applied has explicitly considered the need for guidance, procedures, scenarios, tools and
stakeholder engagement, and how these are practically applied to a study site, as summarised in
Figure 14.
Decision Making Framework to address:
Pilot Studies
 Guidance — covering: spatial scale, temporal
scale, depth of study, standards, method for
appraisal of adaptation themes and measures
 The pilot studies to
help develop the
framework and tools
 Procedures — for application of the Decision
Making Framework
 Existing guidance,
procedures and tools
provide the starting
point
 Scenarios — guidance on selection of
appropriate climate change scenarios and
impacts for study site
 Stakeholders to aid
in development of
guidance through
dialogue and
workshops
 Tools — to integrate the climate change
scenarios, appraisal system and adaptation
options through GIS to develop best suite of
measures
 Stakeholder Engagement — guidance for
stakeholder engagement, development of tools
to aid engagement
Figure 14: ESPACE Decision Making Framework
47
The UKCIP ‘Risk, Uncertainty and Decision Making’ framework has been adopted to provide
the guidance and procedures necessary for assessing the ESPACE ‘key questions’. Throughout
the piloting, this has provided clear structured guidance on decision-making, highlighting both
the sequential stages involved in decision-making and the need to iterate between various stages.
Eight stages to decision making are highlighted:
1.
2.
3.
4.
5.
6.
7.
8.
Identify problem and objectives
Establish decision-making criteria
Assess risk
Identify options
Appraise options
Make decision
Implement decision
Monitor
The adoption of the Source-Pathway-Receptor 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 buildings and people as the main ‘receptor’ of this risk. The main
decision-making criteria were thus identified as providing cost-effective protection to buildings
and people given future likely climate change scenarios over the next 100 years.
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, piloting focussed on the first two tiers of these stages and usefully considered
these stages at different scales, or levels of detail.
Within assessing risk, 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 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 selected Decision
Testing Tools. The principal tool used during this stage of the piloting was the MDSF (Modelling
and Decision Support Framework). This permitted the rapid estimation of direct economic
damages associated with the flooding of residential and commercial properties, and an estimation
48
of the number of people affected by flooding. This tool was supported by the use of 1dimensional and 2-dimensional hydraulic modelling of the study area that provided information
on estimated flood extent, depth and rate of flooding. This information was further processed to
enable the calculation of risk of loss of life.
Importantly, the application of the MDSF 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. Such an approach enabled a wide variety of strategic options to be
considered without the need for each strategic option to be explicitly modelled.
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 a ‘local’ area within the
wider study area. 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 assessment were not
completed. 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 with the decision making stage.
The piloting of the Decision Making Framework and Tools on the Thames Estuary leads to the
following generic findings.
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 (e.g. 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 Decision Making Framework tiered approach enabled the development of a scenarioneutral approach to strategic option appraisal to be undertaken to provide rapid quantitative
estimates of risk. This approach enables the identification 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). It is considered that one of the important benefits of
this approach is that it enables a quantitative assessment of both scale and method applied to
risk assessment
4. 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
49
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.
5. Necessarily, the piloting of a Decision Making Framework requires that pragmatic decisions
have to be made that may limit the general applicability of the adopted framework. In this
instance, it is recognised that at an early stage of the piloting, the identification of the
problem and decision-making criteria limited the application of the Decision Making
Framework to a consideration of tidal flooding and the resultant impact on buildings and
people. As such, other sources and receptors of risk have not been further considered. This
early decision necessarily determined the use of particular Decision Testing Tools.
6. Therefore, no single Decision Testing Tool will be appropriate for all studies. However it is
likely that tools (i.e. structured methodologies and/or software products) will be required to:
 Help identify the problem and objectives (e.g. Source-Pathway-Receptor)
 Define appropriate climate change scenarios (e.g. 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).
6.2
Recommendations
The experiences gained through the piloting of the Decision Making Framework and Decision
Testing Tools on the Thames estuary pilot leads to the following set of general recommendations
that should be taken into account for future applications of the framework and tools:3
Problems and Objectives
Other issues related to climate change and land use planning should be targeted, identifying other
sources, pathways and receptors of risk. This should include expert assessment of all water resources
aspects, for example those related to threats to water scarcity and deterioration of land and water
eco-habitats that could impact on highly sensitive environmental features. Ensuring technical,
environmental and social sustainable water resources uses should be one of the prime objectives
in the agenda for piloting the Decision Making Framework.
Assessment of risk
Piloting the Decision Testing Tools to address different problems and objectives will necessarily
lead to different hazard characterisations and consequences to be assessed. For example, issues to
be explored can include the impact of climate change in short and long duration rainfall regimes,
the characterisation of recharge to aquifers (in quality and quantity) and the effect of water
scarcity and reduction of draw down levels in eco-habitats and the environment.
3 Additional recommendations specific to the Thames Estuary are given in the Technical Annex.
50
Other decision testing tools will need to be used to assess risk within the overall Decision Making
Framework, in particular trying to cover other aspects such as water quality, meteorological
modelling and ecological impact assessment.
The application to the Thames Estuary project relied heavily on the use of event-based
inundation modelling events. Further piloting exercises could be carried out to test other
simulation methods, for instance those based on statistical analysis, regression curves, long term
simulations and interpretation of sequential satellite imagery.
Identification of options
Other than flood mitigation options, the framework should be piloted through different type of
options targeted to wider environmental and water resources issues, such as: environmental
mitigation options, analysis of water supply schemes based on the conjunctive and sustainable
use of water resources and generally non-structural land use planning measures focused to the
pathway and receptor levels of the conceptual cycle of risk.
Appraisal of options
The application of a scenario-neutral approach proved to be very advantageous for testing largescale strategic options. Along these lines, the Excel workbook for high-level appraisal succeeded
in implementing the conceptual aspects of the scenario-neutral approach. It is recommended that
the user friendliness of the workbook should be improved (i.e. through the development of a
VBA application) so that it can be incorporated, in the future, as part of the tools that support
the decision-making framework.
Also, individual tools (those piloted here or others) could be further interlinked within a Decision
Support System that could facilitate the systematic application of the entire Decision Making
Framework providing a shell to host the different tools and developments (like the workbook).
Stakeholder involvement
Further evaluation of the FloodRanger Professional is required in order to suit this type of highlevel visualization to other types of problems. In particular, it is important to strike a good
balance between user-friendliness and technical robustness and therefore, further efforts should
be made in order to develop sound interpolation techniques maximising the use of externallyloaded data.
51
References
Climate adaptation: Risk, uncertainty and decision-making. UKCIP Technical Report. May 2003.
Climate Change Scenarios for the United Kingdom: The UKCIP02 Scientific Report. DEFRA,
Tyndall Centre and Hadley Centre. April 2002.
ESPACE Decision Testing Framework. Phase 1 Report. Environment Agency. February 2004.
Flood and Coastal Defence Project Appraisal Guideline. Approaches to Risk. FCDPAG4.
February 2000.
Flood Risk to People, Phase 1. Defra/Environment Agency. Flood and Coastal Defence R&D
Programme. R&D Technical Report FD2317/TR. July 2003.
Evans, E., Ashley, R., Hall, J., Penning-Rowsell, E., Sayers, P., Thorne, C. and Watkinson, A.
(2004) Foresight. Future Flooding. Scientific Summary: Volume II Managing future risks. Office
of Science and Technology, London.
52