Looking forward to flood risk

10 December 2008

In 2004 the UK’s Environment Agency launched 76 Catchment Flood Management Plans (CFMPs). Designed to encourage a new way of thinking about flooding and flood risk, the purpose of CFMPs was to encourage an integrated approach to these issues based on a better understanding of all the factors involved.

The plans were required to evaluate not just the current situation but also any foreseeable future scenarios.

Faber Maunsell | AECOM had worked with the Environment Agency for a number of years and was commissioned to undertake eight CFMPs as part of the Environment Agency’s Strategic Flood Risk Management Framework contract.

‘Within each river catchment we assessed the existing flood risk factors based on a number of parameters and also tried to predict the likely consequences of climate change, changes in land usage and the rate of urban development,’ explained Faber Maunsell | AECOM’s Sam Wingfield.

‘In many cases this required extensive computer modelling, looking at predicted increases in river flow rates and sea levels, as well as land use changes. This enabled us to analyse the most likely scenarios and develop a better understanding of future as well as current risk – often identifying risk areas that were not previously listed.

‘The key thing is that each catchment area is different and has to be treated as a separate entity with recommendations based on a range of criteria. For example, the cost of traditional flood defences need to be balanced against the potential cost benefits but where there is a high risk to people this could override other considerations,’ he added.

The differences between catchments arise from a number of factors. For example, some take in large urban conurbations – where the financial and human cost of flooding would be very high. In many of these situations, it is relatively easy to justify the expense of physical flood defence systems, particularly where it is not practically or politically feasible to relocate or redevelop away from the flood plains.

Other catchments may serve largely rural areas where the dispersed settlements are of intrinsically low monetary value, but often contain communities which are reliant on the local farming industry. Some of the rural areas attract large numbers of tourists so there may be seasonal variation in the level of risk to people. This is a particularly important consideration as the UK is apparently developing more continental weather patterns with heavy storms in the summer. Such a manifestation of climate change increases the risk of summer flooding at facilities that may have been considered low risk before, such as camping sites.

Similarly, there may be small, steep river catchments that have low population densities but receive water directly from mountains, so they are subject to high velocity water flows that pose a danger to anyone in the area at times of high rainfall.

‘In general, we’re moving away from a ‘one size fits all’ approach and recommending strategies that provide the best, most sustainable overall solution based on local needs and the requirements of all stakeholders,’ Sam Wingfield noted.

‘This may involve moving water away from populated areas to areas where it will do less harm and could also benefit the environment. Or we may have to accept that we cannot prevent flooding everywhere so certain built areas may flood occasionally. In these locations we would encourage people to take responsibility through awareness and other low cost but effective measures.

‘For example, a surprisingly low proportion of the people living in high risk flood areas avail themselves of existing flood warning systems so they need to be encouraged to keep themselves informed. In these areas people should also ensure they have sufficient provisions and means of communication,’ he continued.

‘For new developments, raising floor levels is another option, though this simply displaces the flood water to adjacent areas. Similarly, if you build a flood defence system near a town it has the knock-on effect of increasing water levels all along the river, so any such actions need to be carefully thought through,’ Wingfield continued.

In areas where flooding is to be allowed, the CFMPs also need to consider issues such as how long people may be cut off and how emergency services can gain access when required. This information will form an integral part of future flood management plans.

Striking a balance

The complexity of such decisions can be found in a number of towns across England and Wales that are at risk of flooding. Plans for extensive regeneration, often focussed around the rivers, have to be balanced against the potential increase in flood risk to people. Any strategy, therefore, needs to take account of a town’s need for regeneration and balance that against the risk and the cost of minimising that risk.

‘Sustainable development is likely to be the answer to the tension between flood risk and regeneration,’ said Wingfield. ‘This is possible by changing the character of the urban footprint of a town through re-development by better layout and a greater resilience to flooding. This will need partnership between the Environment Agency, local planning authorities and developers and innovative approaches to ensure flood risk is not increased elsewhere.’

Possibilities that have been considered for some locations include storing water and managing runoff in upstream locations by allowing areas of agricultural land to flood through environmental stewardship schemes and changing the way land is managed.

However, with the growing appetite for self-sufficiency in food in the UK there are objections to decreasing the amount of agricultural land and the National Farmers Union (NFU) has expressed concerns about these proposals. On the other hand, some farmers are happy to be paid to allow their land to occasionally flood as it provides valuable additional revenue as well as environmental and flood risk management benefits.

This clearly illustrates the complexity of the decision making process, as the majority of projects will attract input from a range of stakeholders. In addition to the Environment Agency, typical stakeholders will include the local authority, the local water company, Natural England and other conservation groups, the NFU and, for some navigable rivers, British Waterways. This is one of the reasons that the CFMPs need to be exhaustively researched and evaluated.

As each CFMP is completed it is submitted to the Environment Agency’s Quality Review Panel prior to inviting public consultation and further regional planning.

The effectiveness of Faber Maunsell | AECOM’s approach is exemplified by the Panel’s response to the River Lune CFMP, describing it as ‘very well produced’ and approving it with almost entirely positive feedback.

For more information contact Bill O’Neill at Faber Maunsell | AECOM bill.oneill@fabermaunsell.com

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