Report produced by Dr Lindsey McEwen

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Contextual summary

1. Flood risk in the South-West from climate change context

Key concerns for flood hazard management are (i) the likely changes to the magnitude, frequency, seasonality and duration of flooding in rivers of different scales (main river and non-main river) and estuaries; and (ii) the changes that will take place to the maximum floods that are found in a given location. Coastal impacts, including flooding, were considered in a separate workshop. Factors that affect the changing nature of flood risk and its impact within the South-West region are summarised below.

(a) Causal factors for flooding - climatic
Anticipated climate changes for the 2050s, indicated in computer-generated scenarios, are summarised as follows. Latest IPCC scenarios suggest that these shifts may be under-estimates and significant changes will have occurred by the 2020s (see CCCF summary sheet). Predictions indicate winters will be wetter and more stormy; summers will be drier and more drought-prone. The headlines are that (i) winter snowfalls will be extremely rare; (ii) more extreme weather events with intense winter precipitation will be more frequent, increasing the risk of flooding; and (iii) higher storm surges will occur around the south-west coasts and inlets, associated with rising sea levels. Overall there will be greater regional variability in climate.

(b) Intensifying factors for flooding
Factors that intensify risk of flooding occur at basin, network and channel levels. Individual water courses will respond differently to the same rainfall conditions due to variations in catchment area, character and landuse. Threatened areas in scoping studies include the Severn Estuary (see the Severn Estuary Strategy, 2000); the low-lying Somerset levels (susceptible to flood risk due to sea-level rises) and the steep-sided valleys in south-west England (e.g. Polperro and Pentewan; particularly vulnerable to flash floods when localised intense rainfalls occur over small catchments).

(c) Impacts of increased flooding
Key concerns in terms of water quantity will be changes to the speed and quantity of runoff and to patterns of storage. There is a need to establish which floodplain areas are going to be most vulnerable to these changes, and the likely ramifications for other natural processes such as landslip hazard. The Severn is a vulnerable estuary - increased risk of coastal and estuarine flooding has implications for coastal infrastructures and habitats. Agricultural activity in the Somerset levels is particularly susceptible to changing patterns of inundation. Water quality issues linked to increased flood frequency include (i) the flushing of pollutants in heavy rains following droughts; (ii) accelerated soil erosion leading to sedimentation of water courses; and (iii) risk of toxic sediments in estuaries being remobilised with increased precipitation and flooding.

2. Provocateurs contributions - scene-setting

Paul Bailey (Flood Defence and Water Resources Manager, Environment Agency; Midlands Region, Tewkesbury

Themes set out to fuel the debate included:

• The nature of the predictions for increased flood risk in coastal and inland areas;
• The emphasis on the whole drainage cycle when assessing the impact of more frequent and heavy rain (to include soil erosion on disturbed ground; impact on water courses of all sizes and structures on them; pressures for new and improved defences and the need to retreat defences and to increase/ restore floodplains)
• Hard decisions are required on what to protect, what standards to aim for and the urban versus rural balance in flood protection;
• The economic justification and environmental impact of approaches taken to manage increased flood risk;
• The different possible options/ measures to implement changes - to include legislation, policies, public support and education.

Richard Bradford (Level and Moor Officer, Somerset County Council)

Issues set out to fuel the debate included:

• Flooding as a national issue rather than merely a local matter;
• Problems of public perception between climate change and flood;
• Problems of getting public to think beyond the 'one-off event' to long-term implications for flood risk;
• Impact of changes in land management on catchment response;
• Need to strike a balance amongst expectations about what flood defence can achieve;
• Problems associated with development in areas of known flood risk;
• Importance of tacking flood management at a catchment scale as part of integrated rural planning;
• Importance of multi-stakeholder approach, as adopted in Parrett catchment, Somerset;
• Importance of management strategies that take a long-term view;
• No single or simple solution - combined short-term and long-term initiatives.

Workshop Discussion

3. Mitigation: How should the sector respond to climate change?

Prevention is better than a cure There was a strong consensus that land management for flood prevention needs to take place at a catchment scale, involving all areas of the catchment and starting at the headwaters. Flood mitigation should not be simply reactive, as demonstrated by the building of floodwalls of increasing height in the lower reaches of rivers. Preventative measures should aim to increase natural floodplain storage and reduce rates of downstream transfer of runoff by restoring flood plains in middle to upper catchments. In the same way as the percentage of catchment above storage reservoir is significant for downstream flood control, so the proportion of the catchment that has the potential to slow or retain water is significant in sustainable flood management. Storage should be considered broadly in a rural context, to embrace not only floodplains but also small-scale farm-based storage. Agricultural policy (landuse and soil policy) and forestry (deforestation) policies need to be tightened up to slow runoff.

RSPB representatives indicated their preferred approach to flood management was to increase storage as high up catchment as possible. Distance of storage from the area to be protected is, however, key for the protection of settlements. The target to increase floodplain storage can provide integrated opportunities to meet other biodiversity targets (such 'win, win' situations were again promoted by RSPB representatives). It was strongly felt by workshop participants that catchment management to reduce flooding needs to be integrated with agricultural incentives for land management (and MAFF and EU approaches to agri-environment). In the major review of agri-environment schemes in 2003, there needs to be understanding of the effectiveness of different management options in ameliorating runoff rates, the hydrological effects of different crops and different landuse practices and good soil management and cultivation techniques. Investment in integrated landuse planning with flood management as one of several key objectives must take a long-term view.

4. Adaptation: how should the sector respond to climate change?

(a) Appropriateness of engineering structures and design standards The workshop debated the extent to which engineering approaches to flood defence would continue to be appropriate. If existing flood defence systems are more often taken to and beyond their design limits, what should be the new design levels of protection and where should they be implemented? There was consensus that strategies and standards for flood defence need reappraising in a context of increased flood risk. Public expectation tends to be that 'everything should be protected'. At the same time, it is not possible to keep jacking up all defences in the face of increasing levels of flood risk. Wide-spread engineering options are not sustainable economically or environmentally in the long-term. The building of further engineering structures with higher design limits needs strong economic justification - the benefits of protection have to continue to exceed the costs of work. Workshop consensus was that mature informed debate is needed about what established activities should be protected and to what standards. The question of design standards for withstanding flood discharges does not just effect levees and dams but also capacities for increased volumes of storm sewerage.

(b) Sustainable management options In planning for increased flood risk, there was consensus that focus needs to be on determining sustainable solutions for the region. The following approaches therefore need to be evaluated to obtain consensus amongst stakeholders in the answers to key but difficult questions.

Approach 1: Floodplain restoration or managed retreat Schemes that give floodplains back to more natural processes, should be reviewed for their viability as potential management options. Restoration of the natural capacity of storage is a more sustainable way to lower flood levels than to protect properties from artificially heightened flood levels as a result of reduced storage.

(i) How can sites with the potential for managed retreat be evaluated? Key issues are what to protect, what to return to nature and on what criteria these decisions should be made. The Public needs to be made aware that strategic decisions have to be made about what to continue protect and what land to give back to the river. It is not a viable strategy to continue to protect everything. If flood risk is too great (however that threshold is defined) then decisions must be made (by stakeholder consensus?) as to whether individuals or communities should move back from floodplains. This retreat could involve releasing land and/or the relocation of buildings. Questions include the circumstances in which relocation should be encouraged or required, and by what degree of compulsion? The sorts of packages that should be put together to compensate individuals or groups, e.g. farmers, for such shifts also need to be debated.

(ii) How can the necessary changes be implemented to allow management retreat? For example, on the lower Severn there are old structures to protect agricultural land against floods of 1 to 5-year return period. Environment Agency representatives made the observation that it is much easier to build defences than to try and break them down to restore floodplains.

(iii) Can managed retreat help meet other strategic targets? The optimum is where it is possible to combine sustainable flood management with other strategic targets for wetland enhancement and biodiversity improvements.

Other preventative measures not explicitly mentioned in the workshop but which merit further investigation include the merits of floodplain zoning and associated flood warning schemes as mitigation options.

Approach 2: Effective planning control How can the planning system prevent inappropriate floodplain development? There needs to be better development planning control to keep property out of the floodplain. There are serious questions as to why there is any new building on floodplains given the context of increasing flood risk. The workshop debated some of the issues about exercising development control on brown field sites with problems of 'established use'. Here the building standards need dictating, both from SUDS and flood protection perspectives. PPG 25 Development and Flood Risk, from the DETR, represents a precautionary approach to the development in flood risk areas. The workshop view was that a stronger PPG 25 than evidenced by the consultative version (June 2000) is required to ensure Local Authority Planning Committees undertake stronger developmental control.

Approach 3: Sustainable Urban Drainage At a catchment level, it is key to avoid smothering significant portions of catchments with impermeable surfaces and storm sewerage that encourage fast rates of surface runoff into watercourses. The urban or sub-urban surface should be constructed to encourage the retention and slow release of water and the adjustments need not necessarily be major or costly. Sustainable Urban Drainage system (SUDS) methodologies aim to minimise the impact of urbanisation on natural drainage pathways and to encourage the release of retained floodwaters when the main flood peak has passed downstream. Such approaches are considered essential in reducing the vulnerability of existing and new areas of development to flood risk. Critical here is how SUDS methodologies can best be adopted (required for adoption?) or retrofitted by architects and developers.

(c) Integration of Government policy on flood management Integration of government policy for flood management is seen as an important goal. In terms of barriers, there was concern about the number of organisations, including MAFF/EA/EU with responsibilities in flood defence and management. The possibility of a Flood and Coastal Authority was muted. Environment Agency representatives anticipated problems in responding in emergencies if organisations were split and became too small to marshall the necessary additional staff resource to manage major flood incidents.

(d) Cost-benefit analysis in the evaluation of flood management options The workshop debated the extent to which traditional methods of assigning a monetary cost to flood probabilities need adapting in context of increased flood risk. Key concerns were the incorporation of social and welfare and environmental costs into cost-benefit analysis.

5. Barriers to adaptation

at occurred in Autumn 2001, to concentrate peoples' minds and make the general public aware of tangible impacts. There was, however, debate as to the extent to which the public linked increased flood incidence with changing climate. Factors which influence public understanding, education and general awareness of risk were viewed to need urgent research to inform strategies for improvement. A major issue is the lack of longevity of public memory of flood scale and impact - as well-proven in environmental perception studies. Key issues are how to capitalise on the momentum after extreme floods and how to maintain the public will and preparation to act over intervening dry spells.

6. Future research needs

(a) More sophisticated hydrological modeling at a catchment scale There is a need to model the generation of floods from source to sea so that changing hydrological processes can be understood more accurately, rather than just modelling the passage of a flood wave through a town. This science should inform the catchment flood management strategy. A short-coming of the current evaluation of design limits for flood defence and associated costs is that it considers the previous 100 years rather than using assessment of future risk. Any assessment of the impact of moving structures to increase storage is also based on historic records. There is no established current process to look at impact on future flood levels.

(b) Better and more timely links between research and policy There should be further investigation of the welfare and social impacts of floods so this information can be properly integrated into cost-benefit analysis. A research literature exists on how to quantify misery and stress, as these intangible costs are frequently more significant than tangible costs. There was a concern about the timescale to implement research outcomes as policy. There was a strong feeling that this timescale should be minimised. In some cases, it was not possible to wait until research outcomes in 2003 before acting. New thinking on how to incorporate risk of changing flood zones or intense rainfall events needs to be developed and implemented now.

(c) Better information tailored to specific stakeholder needs More information about the anticipated changing frequency and severity at regional scales, with increased resolution, is required by stakeholders. Better, accessible information is needed on extreme weather events, as useful reference points to explain the potential impacts of climate change. The workshop again recognised previous extreme events as powerful drivers for action.

References

CCCF summary sheet: Climate-Change scenarios for the South-West (adapted from the Climatic Challenge http://www.ex.ac.uk/ccvc/present/hulme.htm)

The Severn Estuary Strategy (2000) Environment Agency, Lower Severn Region.

Somerset County Council (2000) A future when it rains…. A new partnership for jobs, people and wildlife in Somerset in times of flood. Information about the Parrett Catchment Project

Dr Lindsey McEwen
Geography and Environmental Management Research Unit
Cheltenham & Gloucester College of Higher Education
March 2001