ESPACE - Decision Testing Framework

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 Burderop Park Eastmoor Street,Charton Swindon, Wiltshire SE7 8LX SN4 0QD Tel +44 (0)208 305 4803 Tel +44 (0)1793 812479 www.environment-agency.gov.uk 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 MGS executive summary

3 0 Final report – Main 25/06/05 JMW Volume

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

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 11 1.1 The ESPACE project 11 1.2 The Thames estuary 13

2 Decision Making Framework 16 2.1 Introduction 16 2.2 Guidance, procedures and scenarios 16 2.3 Decision Testing Tools 23 2.4 Visualisation and stakeholder engagement 26

3 Broad-scale Application 28 3.1 Introduction 28 3.2 Broad-scale piloting of the decision making framework 28 3.3 Results summary and uncertainties 31

4 Local Application 34 4.1 Introduction 34 4.2 Local piloting of the decision making framework 34 4.3 Results summary 37

5 Discussion 39

6 Conclusions and Recommendations 47 6.1 Conclusions 47 6.2 Recommendations 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 decision-making, 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

1 beneficial for particular studies. For application to the TE2100 project, the following tools were 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

2 Figure 1) and the need to iterate between stages (particularly stages 3, 4 and 5). Completion of the formal questions posed in the UKCIP Framework provide a very valuable audit trail which will encourage a systematic approach to the decision making and provide documentation suitable for stakeholder scrutiny.

The adoption of the Source-Pathway-Receptor (Figure 3) model helped to both identify the problem and objectives and to establish the decision-making criteria. Through the application of expert knowledge, a comprehensive list of risk components were identified and ranked. This process enabled the identification of tidal flood risk as the main ‘source’ of risk in the Thames estuary, and the resultant impact on properties and people as the main ‘receptor’ of this risk. The main ‘drivers’ were identified as climate change (increasing sea levels and surges) and land 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 Pathways Receptors System Risk rainfall fields, rivers people analysis sea level drains, roads properties economic storms floodplains infrastructure social etc flood defences ecosystems environmental flood storages etc etc 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).

4 Figure 4: Scenario-neutral database of modelling results supports appraisal of strategic options

Once a limited number of strategic options had been identified, a further iteration of the appraisal stage was undertaken at a more detailed spatial resolution for the Dartford ‘local’ pilot area within the wider study area (see Figure 2). This iteration included the explicit modelling of strategic option scenarios, enabling both a comparison of scale and method to be undertaken.

Further stages of the UKCIP Decision Making Framework were not applied during this piloting as a full assessment of preceding stages using specific quantitative risk 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

5 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 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

6 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)  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 Description Annual The expected value of annual flood damages (or losses) calculated Average as the probability of a range of events multiplied by the loss that Damage such an event would incur (ie the area under the loss–probability curve). Appraisal The process of defining objectives, examining options and evaluating costs, benefits, risks, opportunities and uncertainties before a decision is made. Benefits Those positive quantifiable and unquantifiable changes that a plan will produce, including damages avoided. Climate Long term variations in global temperature and weather patterns change both natural and as a result of human activity, primarily greenhouse gas emissions. Consequence An impact such as economic, social or environmental damage/improvement. May be expressed quantitatively, by category or descriptively. Cost-benefit Comparison of present value scheme benefits and costs as part of analysis an economic appraisal. The cost-benefit ratio is the total present value benefits divide by the total present value costs. Defence Two or more defences acting to achieve common goals (e.g. system maintaining flood protection to a single flood cell/community) Discount Rate The annual percentage rate at which the present value of a unit of currency is assumed to fall away through time.

Drivers 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. Economic An appraisal that takes into account a wide range of costs and appraisal benefits, generally those that can be valued in money terms. Embayment Low-lying area defended from tidal flooding which is hydraulically disconnected from other low-lying areas Flood Defence A structure (or system of structures) for the alleviation of flooding from rivers or the sea. Flood risk A combination of the probability and consequences of flooding (such as loss, damage, harm, distress and disruption). Flood risk The activity of understanding the probability and consequences of management 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

8 Term Description physical flood defence measures.

Flood storage The temporary storage of excess runoff or river flow in ponds, basins, reservoirs or on the flood plain. Floodplain 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. Joint The probability of specific values of one or more variables probability 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. Local studies Studies that are characterised by focusing on either a specific portion of the geographical setting or in particular physical aspects. Measures See responses Present Value The future value expressed in present terms by means of discounting. Probabilistic Method in which the variability of input values and the sensitivity method of the results are taken into account to give results in the form of a range of probabilities for different outcomes. Residual risk 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. Responses 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. Return Period 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. Risk The process of identifying hazards and consequences, estimating assessment the magnitude and probability of consequences and assessing the significance of the risk(s). Scenario Used to describe one possible instance of change, eg climate change scenario or socio-economic scenario. Scenario- Used in this report to describe flood risk data that are broadly neutral independent of the assumptions on climate change or socio-

9 Term Description economic scenario. Source- Sources are weather related phenomena (rainfall, marine storms etc) Pathway- that generate water that can cause flooding. Receptor Pathways are mechanisms by which water travels from its source to the places where it may affect receptors (eg estuary, defence overtopping, floodplain inundation). Receptors are the people, industries and the built and natural environment that flooding can affect. Stakeholder A person or organisation with an interest in, or affected by, decisions made. Standard of The flood return period event (or annual probability) above which protection channel capacity or defence level is exceeded. Sustainable Development which meets the needs of the present without development compromising the ability of future generations to meet their own needs. Tidal surge 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. Uncertainty 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 co-operation 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?

11  What adaptation measures would be most appropriate?

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 The pilot studies help scale, depth of study, standards, method for develop the appraisal of adaptation themes and measures framework and tools Procedures — for application of the Decision- Existing guidance, Making Framework procedures and tools provide the starting Scenarios — guidance on selection of appropriate point climate change scenarios and impacts for study site Stakeholders aid development of Tools — to integrate the climate change scenarios, guidance through appraisal system and adaptation options dialogue and through GIS to develop best suite of measures workshops 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.

12 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:

 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

13 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 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.

14 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.

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 Provide an acceptable level of flood risk Decision Making Options must provide a 1:1000 year standard of protection Criteria against estuarial flooding in central London Receptors Resident population Working population Cultural and Heritage sites Infrastructure etc… Assessment Endpoint 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 multi-dimensional, 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 Response Processes that change the state of the Flood risk management options ability flooding system to affect flood risk

Flooding System Impact Source-Pathway-Receptor 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 State Impact Response Current Interruption of Stressed inter- Identify options that management sediment transport to tidal ecology. provide of hard salt-marsh Loss of saltmarsh compensation sites defence Future Raising of tidal walls Loss of amenity Identify options that management leading to less access value and allow better access of hard to river for rowers and interest in river to river defence anglers Current Defence line through Reduced fish Identify options that management central London keeps populations provide resting of hard river flows fast. Few areas for fish defence chances for fish to rest during journey from sea to spawning grounds Climate Sea level rise and Loss of inter-tidal Identify options that Change increasing wave habitat increase inter-tidal action area Change in Desire to realign hard Loss of reclaimed Identify options that policy of defences to provide land for dock provide the management inter-tidal habitat development required level of of hard dock development

20 Pressure State Impact Response defences

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 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.

21 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.

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.

22 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.

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.

23 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).

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 socio-economic 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

1 The ‘Calculate Erosion Damage’ procedure is appropriate for SMP work only.

24 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 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 decision-making 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.

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 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.

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.

26 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.

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 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.

3.2 Broad-scale piloting 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.

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.

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

29 50 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 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 climate- adaptation 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

30 placed on the identification of technically robust, generic quantitative approaches that could support the rapid strategic assessment of options.

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 scenario-neutral 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

31 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 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:

32 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 extents and damages should be densely populated in the range that is most sensitive to the strategic options to be mapped. 2. 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. 3. 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, 4. 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, 5. 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.

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.

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

35 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 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

36 ‘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 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

37 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 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).

40  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.  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.

41  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 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

Scenario-neutral Scenario-specific Description of This approach consists of This approach was adopted for piloting exercise performing a series of TUFLOW the local application in Dartford carried out and MDSF runs for pre-defined and Crayford and consisted of combinations of water levels performing TUFLOW and MDSF and defence levels. runs for a single climate change scenario, three return periods and three time slices. Facility to map Mapping scenarios to strategic Mapping scenarios to strategic scenarios to options is carried out options is carried out prior to the strategic options independently of the definition execution of the simulations so of the scenarios, relying on there is no need to perform any interpolation of direct damages potentially inaccurate to derive a value of AAD for interpolation to derive a value of each strategic option. AAD for strategic options. Main advantages A single set of model runs can The results used to inform the be used to test a wide range of appraisal of options are more strategic options. accurate as they are specifically derived for the option being The process of appraisal of analysed. options is fast and robust as it does not depend on the No interpolation is required to runtime of models and handling arrive at the final direct damage of large amounts of data. in the appraisal of options.

The tool designed to carry out More accurate representation of the appraisal of options can be the operational functioning of the easily transferred increasing flood control structures. 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. Main Needs an external interface The strategic options need to be disadvantages (i.e. the workbook) to use the defined well in advance of the model results for the appraisal modelling exercises. of options. Lack of flexibility to quickly test Linear interpolation of direct (adapt) further options once the damages (from MDSF) can base model runs are carried out. result in large errors if sufficient data are not available Increased time required per at break points in the damage- appraisal of a single option. level curve.

43 Scenario-neutral Scenario-specific

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.

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

44 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 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.

45 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.

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 Approach Damage (in million pounds) 10 yrs 1,000 yrs 10,000 yrs AAD Do Nothing (DN) Scenario- 393 871 1,594 240.8 specific Scenario- 764 1,109 1,264 437.7 neutral Maintenance Scenario- 0 0 1,573 0.86 Only (MO) specific Scenario- 0 670 1,221 34.1 neutral

Table 5: Comparison of scenario-specific and scenario-neutral approaches – Loss of life

Option Approach Number of deaths 10 yrs 1,000 yrs 10,000 yrs Maintenance Scenario- 0 0 1,758 Only (MO) specific Scenario- 0 568 1,668 neutral

46 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.

47 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 The pilot studies to help scale, depth of study, standards, method for develop the appraisal of adaptation themes and measures framework and tools Procedures — for application of the Decision Existing guidance, Making Framework procedures and tools provide the starting Scenarios — guidance on selection of appropriate point climate change scenarios and impacts for study site Stakeholders to aid in development of Tools — to integrate the climate change scenarios, guidance through appraisal system and adaptation options dialogue and through GIS to develop best suite of measures workshops Stakeholder Engagement — guidance for stakeholder engagement, development of tools to aid engagement

48 Figure 14: ESPACE Decision Making Framework

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. Identify problem and objectives 2. Establish decision-making criteria 3. Assess risk 4. Identify options 5. Appraise options 6. Make decision 7. Implement decision 8. 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.

49 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 of the number of people affected by flooding. This tool was supported by the use of 1-dimensional 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.

9. 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). 10. 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. 11. The Decision Making Framework tiered approach enabled the development of a scenario- neutral approach to strategic option appraisal to be undertaken to provide rapid quantitative estimates of risk. This approach enables the identification of robust strategic

50 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 12. 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. 13. 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. 14. 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.

3 Additional recommendations specific to the Thames Estuary are given in the Technical Annex.

51 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.

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 large-scale 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 high-level 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 externally-loaded data.

52 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.