Flood risk and flood risk management

Flood risk is a combination of the probability (likelihood or chance) of an event happening and the consequences (impact) if it occurred. Flood risk is dependent on there being a source of flooding, such as a river, a route for the flood water to take (pathway), and something that is affected by the flood (receptor), such as a housing estate.

Without a pathway linking the source to the receptor, a flood may be a hazard, but not a risk. This concept is known as the source-pathway-receptor model.

The likelihood of a flooding event happening can often be misleading or confusing. Return periods are often used to describe how often a flooding event will occur, but using terms such as 1 in 50 years or 1 in 500 years can mislead the public into thinking that a 1 in 50 year flood event will only occur every 50 years. Return periods are an average of how often a flood event of that magnitude will occur, and so the probability or chance of flooding should be used instead, so for example, a 1 in 50 year flood has a 2 per cent probability of occurring in any one year.

The consequences of a flood depend on two factors, exposure and vulnerability. Exposure is a measure of the number of people or things that may be affected by a flood while vulnerability is a measure of the potential of people or things to be harmed.

For example, the consequences of a flood will be less severe in an area with very few people (low exposure) who are able to evacuate quickly and easily (low vulnerability). Flooding in an area with lots of people (high exposure) who have difficulty with evacuation (high vulnerability) is likely to have more serious consequences.

Historically, some people have regarded flooding as an unforeseeable event. This has perhaps led to excessive focus on the emergency response to events and subsequent recovery.

Flood risk is, however, something that can be estimated, with varying degrees of uncertainty, and its effects are generally predictable. This means that the impacts can be significantly mitigated and response and recovery can be more effective and efficient. In recent years, a ‘step process' has been initiated consisting of:

• prepare
• manage
• respond
• recover

It is also extremely important to emphasise both the role of planning and the mitigation of potential impacts. At a very basic level this approach should embody sound emergency planning and include:

• identifying roles and responsibilities of different agencies
• identifying areas where flooding may be anticipated from specific causes – for example, river, tidal or frequent surface water flooding – including identifying impacts on public transport and traffic
• informing residents and businesses of the potential effects so that they can take appropriate action, such as protecting important documents and other high-value assets – in some cases this may be a simple as keeping them upstairs
• identifying where any protective measures, such as barrier systems or sand bags, may be provided
• identifying locations where people may be evacuated to and the route they will use
• establishing sound communication systems for coordinating the work of stakeholders and passing information to the wider community
• establishing a system for warning those likely to be affected
• ensuring that arrangements are robust, documented, periodically reviewed and updated as necessary
• testing systems in a non-emergency situation
• encouraging the use and uptake of protective measures.

The use to plans, assessments and good practice can also help to provide much better outcomes for communities. These can include:

• preliminary flood risk assessments (PFRA) for surface water flood risk
• strategic flood risk assessment (SFRA) mainly for coastal and fluvial flood risk
• preparing a surface water management plan (SWMP) where this is appropriate for the local area
• site-based flood risk assessments
• exceedence principles and flood routing
• mitigation measures such as setting minimum ground floor levels in new properties relative to expected flood levels
• a more coordinated approach between stakeholders to the implementation of flood relief or flood protection works for existing properties
• using more sustainable drainage techniques to reduce the downstream impacts of new development constructed on higher ground.

For homeowners and local communities, flood insurance is currently provided through an agreement between the Government and the insurance industry called the Statement of Principles.

This agreement commits insurers to continue to offer insurance to existing customers where they are at significant risk, if there are plans in place to reduce that risk within five years.

The current agreement is due to expire in 2013.

Defra is working closely with the insurance industry to ensure that insurance remains widely available in England after this point. However, the Statement of Principles does not apply to homes built since 1 January 2009.

There is therefore no obligation for insurers to offer cover against flood risk for newly-built property. Local authorities and developers therefore have an important role in ensuring that new properties are insurable as having appropriate insurance cover is extremely important to the successful recovery from flood events.

Sustainable planning must take account of flood risk to prevent unwise developments in flood risk areas and ensure homes and businesses can continue to obtain flood insurance. New developments that are placed in high flood risk areas, or developments that increase the risk of flooding both upstream and downstream will have an impact on the ability of homeowners and communities to become insured.

With this in mind, the Association of British Insurers (ABI) and the National Flood Forum have published guidance for local authorities on planning in flood risk areas. The guidance aims to help local authorities in England when producing Local Plans and dealing with planning applications in flood risk areas, and complements the Government's recently-published National Planning Policy Framework.