INTRODUCTION

  1.  London is prone to flooding from five sources: tidal, fluvial, groundwater, surface and sewer flooding. Climate change will increase the probability of flooding from all these sources except groundwater, whilst London's growth may increase the consequence of any flood.

  2.  The unseasonably heavy rainfall of July this year affected 15 London Boroughs, with significant numbers of homes, schools and other essential social infrastructure being flooded, despite London not experiencing the amount of rainfall that caused flooding elsewhere in the UK.

  3.  The management of flood risk is critical to London's future. Flood risk in London is increasing due to climate change, but also due to ageing flood defence infrastructure, the fact that much of the infrastructure was designed to meet lower flood standards, a low level of public flood risk awareness and their capacity to respond to a flood.

Who and what is at flood risk in London?

  4.  The Mayor defines "risk" as the product of probability, vulnerability and consequence. These components are assessed below to provide an indication of the current flood risk.

Probability

  5.  Nearly 15% of London is at fluvial or tidal flood risk. Despite having some of the best standards of tidal flood defence in the world, London has poor standards of flood defence on the tributaries to the Thames. Figure 1 shows the tidal and fluvial flood defence standards in London. It can be seen that the standards of protection on the tributaries to the Thames are significantly lower than the 1 in 75 year (0.3% annual probability) threshold determined by the Association of British Insurers as the level above which their members can provide affordable flood risk insurance.

Source: Environment Agency

Consequence

  6.  The Mayor has prepared a draft Regional Flood Risk Appraisal (RFRA) to identify "who and what" is at risk of flooding in London for the areas shown at flood risk in Figure 1. The draft RFRA has revealed that as well as an estimated 1.25 million people and 593,000 properties, there is extensive social and civil infrastructure at high flood risk. It is important to note that 82%[1] of these properties are at "low" flood risk, but that 100,000 properties at "moderate" or "significant" risk.

  7.  It is essential to determine which elements of this infrastructure need to remain operational during a flood, either to manage the flood response, or to ensure that the parts of London not flooded can continue to function as normal. Table 1 below identifies the key social and civil infrastructure at flood risk in London. Further work is required to identify the utilities (electricity, gas and water networks) at flood risk.

Vulnerability

  8.  Vulnerability is the third factor that defines risk. Whilst measuring the consequence provides information on who and what is at risk, it does not provide an indication of how vulnerable those people and assets are to a flood.

  9.  There are a number of factors that make an individual more vulnerable to flooding than the average person. These can be divided into two categories:

—  Personal—for example, age (the very young and old), health, disability and proficiency of spoken English.

—  Situational—for example, income, living on the ground or lower-ground floor, having advance warning of a flood, having insurance.

  10.  Independently or in combination, these factors may mean that an individual may be:

—  less likely to be aware of the flood risk they live at;

—  physically more at risk from a flood if flooding occurs;

—  less likely to know what to do and be able to do it;

—  less likely to receive and use information on what to do through regular communications channels; and

—  less likely to be able to recover independently, or access services to aid recovery.

  11.  Other factors which contribute to reducing vulnerability are:

—  Advance warning. Advance warning of a flood provides the opportunity to take action before a flood occurs. This warning time can be used by individuals to take personal action to protect themselves, their family and their assets, and for the emergency services and Boroughs to initiate their flood plans. Many of the tributaries in London that have a low standard of protection are also liable to flash flooding. The Environment Agency states that it is unable to provide more than three hours warning on these catchments.

—  The Environment Agency provides a flood warning service, called Floodline Warning Direct, where an automated flood warning is sent by facsimile or phone to people registered for the service when a flood is predicted. Fewer than 1% of Londoners living or working in areas of flood risk London have registered to receive this advance warning. This compares with a national uptake of approximately 12%.

—  Public Awareness. Prior to the construction of the Thames Barrier, regular flood drills were held in London. The presence of the Barrier and upgraded defences has meant that people have become oblivious to the risk of flooding. The Environment Agency estimate that 30% of people would not know what action to take following a flood warning.[2]

—  Insurance. Flood risk insurance is generally provided within standard insurance cover. The uptake of insurance (both buildings and contents insurance) tends to be lower than average in low-income households[3] and it is estimated that less than 1 in 5 households living in social housing make use of the Housing Associations "insurance with rent" schemes[4]. This is significant because, if flooded, these low-income households would not be able to pay for replacing essential household goods, or repair their homes by claiming on insurance.

Assessment

  12.  Analysis of "who and what" is at a flood risk shows that:

—  a significant proportion of London's population lives and works at risk of flooding, though the probability of them being flooded is considered low;

—  the poorest in the city are more likely to live at flood risk[5] (though more affluent people also live in areas of fluvial flood risk);

—  there is a low level of public awareness of flood risk and what action to take to prepare, or respond to a flood;

—  there is a lower uptake of insurance for people in social housing or on low-incomes;

—  very few people at flood risk are registered to receive flood warnings, so are unable to make use of even short advance warnings of a potential flood; and

—  a significant proportion of London's critical infrastructure lies in areas of flood risk, including emergency services that London would be reliant upon to manage the impacts of a flood.

Storm Drainage and surface water flooding

  13.  London's impermeable urban realm means that the city is reliant upon storm drains to conduct rainwater away to prevent flooding. Many of these storm drains discharge into local watercourses, or the combined sewer system, so may contribute to flooding elsewhere. The probability of surface water flooding in London is much higher in comparison to tidal flooding, and will increase for the following reasons:

—  the predicted increase in winter rainfall and extreme rainfall events;

—  the reduced permeability of the urban realm due to development using impermeable materials and waterlogged soils;

—  the fact that most drainage systems are designed for high frequency, low volume rainfall (1 in 20 year occurrences or less); and

—  lack of maintenance of surface water sewers—see below.

  14.  A report by the London Assembly[6] identified that an area in excess of 22 Hyde Parks had been paved to create private parking on front gardens of domestic dwellings. The Mayor believes that this loss of permeability, in combination with the finite capacity of the drainage network, will lead to increased surface water flooding in the future as rainfall intensifies.

  15.  The Mayor's Water Strategy (see Appendix) proposes that a forum of agencies responsible for drainage should be formed to collate data on drainage ownership, capacity and management to assess the capability of the drainage system in London under a changing climate. This forum, known as "Drain London" met for the first time in October and is preparing to commission a scoping report to better understand London's surface water and sewer flooding issues.

RECOMMENDATIONS

  16.  The Mayor recommends that the Committee consider the following issues:

—  Better coherency between plan making authorities in undertaking Strategic Flood Risk Assessments: Strategic Flood Risk Assessments in London have generally been developed in an uncoordinated and ad hoc fashion. The London Regional Flood Risk Appraisal recommends groupings of Boroughs collaborate in undertaking their Strategic Flood Risk Assessments according to common hydrology.

—  Better links between spatial and emergency planners and emergency services: In our experience, in the development of Strategic Flood Risk Assessments, emergency planners and emergency services are seldom involved, or are any involved at the consultation stage, and therefore unable to effect significant change.

—  Lack of leadership on surface water flooding: Responsibility for managing and maintaining drainage networks is held by too many agencies and the historic transfers of responsibility have meant that the quantity and quality of data on the drainage networks is poor. The Mayor believes that the Drain London forum previously referred to should be recognised as good practice. The Mayor supports the Making Space for Water proposal that the Environment Agency should be given strategic overview for drainage, provided that this function is properly funded.

—  Using the Climate Change Bill to require statutory undertakers to identify, and act sustainably on climate risks: The Mayor supports the recommendation trailed in the second reading of the Climate Change Bill that public authorities should identify, prioritise and act sustainably on climate risks. Appropriate guidance will be required to ensure that drainage undertakers consider "soft" measures such as sustainable urban drainage as well as more traditional "hard" engineering.

—  More emphasis on rainwater harvesting: The Mayor believes that rainwater harvesting can supplement limited mains water supplies for non-potable uses and reduce flood risk. New development should be required to include rainwater-harvesting systems through the planning system (for example the Code for Sustainable Homes), and existing development should be encouraged through financial incentives.

—  Sustained investment in managing surface water flooding: The Regional Flood Risk Appraisal and the Climate change Adaptation Strategy identify that surface water flooding is a significant and growing risk for London. It is important that sustained funding for managing surface water flooding is found and the mechanism for assessing potential solutions encourages both soft and hard solutions.

Mayor of London

November 2007

2   Environment Agency, pers comms. Back

3   ONS (2005) ONS Family Spending 2005 : A report on the 2004-05 Expenditure and Food Survey. Back

4   ABI pers comms. Back

5   Environment Agency (2006), Addressing environmental inequalities : Flood Risk. Back

6   London Assembly (2005), Crazy Paving. The environmental importance of London's front gardens. Back