Corporate report

Thames Estuary 2100: 5-year review non-technical summary (2016)

Published 1 February 2021

This was published under the 2019 to 2022 Johnson Conservative government

Applies to England

The Thames Estuary’s most significant flood risk is from a tidal surge event and therefore a system of defences has been constructed to reduce the risk of tidal flooding. This includes:

• the Thames Barrier
• other smaller barriers
• 350 kilometres (km) of flood walls and embankments
• pumping stations
• flood gates

Increasing pressures, including climate change and growth, mean that tidal flood risk will increase over time in London, unless that risk is carefully managed.

The Thames Estuary 2100 (TE2100) Plan was developed to provide strategic direction for managing tidal flood risk in the Thames Estuary to the end of the century and was approved by Defra in 2012. It sets out how the Environment Agency, working with partners, will continue to protect 1.25 million people and £200 billion worth of property from tidal flood risk.

The Thames Estuary 2100 Plan is based on a relative sea level rise estimate of 90 centimetres (cm) by 2100 but is adaptable to differing rates of sea level rise up to 2.7 metres (m) by 2100. The Plan recognises that there are several factors that determine tidal flood risk in the estuary in addition to sea level rise and that these will change over time.

The Plan therefore identified 10 indicators of change to be monitored as part of the Plan. These indicators of change will help us assess whether we need to make the interventions identified in the Plan at an earlier or later date, and whether the actions and interventions that we are taking are adequately managing the flood risk. In addition some indicators help us to identify whether the estuary is changing in a way that is different to that envisaged by the Plan and whether this means that the type of interventions identified in the Plan need reviewing.

The Plan requires a review of the indicators of change to be undertaken after 5 years to provide an early assessment, ahead of the full review of the Plan itself in year 10, as to whether anything in the Plan needs to be updated or amended. This review process is then repeated at 5 and 10 year intervals.

Having completed our first review of the indicators of change, the monitoring results from this review have been used to assess the changes which have been taking place in the Thames Estuary over the last 5 years, and have been compared against what was predicted to occur by the Plan. We have also considered the impact of these changes on the Plan. The results show that changes in the estuary are generally taking place in line with the Plan’s predictions. We have concluded that the timing of the actions identified in the Plan remain appropriate and that it is not necessary to review the flood risk policies or recommendations made in the Plan at this time. However we need to continue monitoring the changes taking place in the estuary and have identified a number of improvements that should be considered to improve our understanding as we prepare for the 10 year review of the Plan in 2020.

The results of the review are presented according to the 10 indicators below. For more detailed information on the review, please refer to the main 5-year review document. The main report includes further information on the methods, the results and the implications for the Plan as well as recommendations for future monitoring.

Indicator of change 1: sea level

We monitor changes in sea level in the estuary over time. We consider this data alongside projections and guidance on future sea level rise to understand how sea level could change in the future.

This information helps us to understand when we will need to raise flood defences and also when we will need to build major flood defences such as a new Thames Barrier. It also helps us to understand how important habitats in the estuary will change as a result of rising sea levels.

Figure 1 - recorded and predicted changes in mean tide levels at Southend

Our monitoring confirms that sea levels in the Thames Estuary are rising. Figure 1 shows how the average sea level (mean tide level) has changed at Southend since 1950 and how sea level is projected to rise until 2050. Taking into account changes in land level, sea level rise between 1999 and 2014 occurred at a rate of approximately 4.5 millimetres (mm) per year. This rate of change is slightly above the projection in the Plan and the central estimate projection in the latest UK specific climate change research (UKCP09). The average rate of change over the last 70 years is however below both these projections.

Using statistical analysis we have calculated a forward projection of sea level rise at Southend and this suggests that change at a significantly greater rate than that projected by the Thames Estuary 2100 Plan and UKCP09 is unlikely. This analysis does not predict the effect of future climate change and continued monitoring of sea level rise is therefore required to identify any significant changes.

Based on the evidence available, sea level rise is taking place within the bounds of what the Plan expected and the timings of the recommendations in the Plan therefore remain appropriate.

Indicator of change 2: peak surge level

Peak surge is the maximum water level which occurs as a result of storms which develop in the estuary. Together with wave conditions this defines the extent of extreme tidal flood events which can occur. We use our understanding of peak surge and wave conditions to understand if unexpected changes are taking place. If required, we can use this information to revise the height to which flood defences need to be built and change the timing of when they need to be raised.

Our analysis of the data available, shows no discernible trend in peak surge, meaning that the maximum water level appears to be stable over time although it does vary between years. As there is no discernible change in peak surge level there is no reason to adjust the timings of the recommendations in the Plan.

No data was available to analyse wave conditions and we propose to address this data gap before the next review. Flood defences are built to a height which includes an allowance for uncertainties such as wave height, known as the freeboard. The guidance on freeboard developed for the plan remains appropriate, including an adequate allowance for wave action. Therefore we have been able to make our assessment for this indicator based on the evidence available for peak surge alone on this occasion.

Indicator of change 3: peak river flows

We use river flow data to design flood defences in the areas of the estuary which are influenced by river flows. We also use it to understand how the use of the Thames Barrier might change in the future as the Barrier is currently closed to help alleviate flooding in west London at time of high river flows.

The monitoring results show no discernible trend in the highest flows recorded on an annual basis. This means that the highest river flow seen in any year in the tidal Thames and its tributaries does not appear to be either increasing or decreasing. We also analysed changes in high river flows which are experienced for longer periods of time, such as for approximately 18 days within a year, and there was no trend through time in this data either.

During the winter of 2013 to 2014 there were prolonged high flows experienced in the Thames which resulted from record breaking rainfall. It is too early to identify whether or not this is part of an emerging longer term trend but we are able to conclude that it is not part of an existing trend.

We have therefore concluded that no changes to the Thames Estuary 2100 Plan are needed at present but that we need to monitor for potential changes in extreme events. To this end we will continue to monitor long term high flows in the River Thames and take into account the outcome of the National Resilience Review. New guidance on how river flows are expected to increase in the future has also been recently published and will be investigated prior to the next review of the Plan to understand if there are any implications for the Plan.

Indicator of change 4: asset (flood defence) condition

Monitoring the condition of flood defence assets tells us how well the flood defence system is likely to perform during a flood event.

Flood defences are inspected regularly and given a condition grade based on a visual assessment. There are approximately 3,800 separate flood defence assets in the estuary and we aim to maintain at least 97% of the flood defences in fair or good condition. By meeting our 97% target, we can be confident that the flood defences will perform as we expect them to during a flood event.

Figure 2 - asset condition

98% of the assets in the estuary are currently in fair or good condition (Figure 2). This exceeds our target but is lower than 2014, when 99% of assets were in fair or good condition. In the future this target will be rising to 98%. Current asset condition in the estuary already meets this higher target.

There are some areas where asset condition has declined over the past year and this has taken place mainly in the outer estuary. The numbers of properties at risk in these areas is lower than in other parts of the estuary but over the next 10 years we will, through our asset management programme, investigate those assets which have shown a decline in condition and will carry out appropriate works to those assets which are our responsibility, where necessary. For those assets which are the responsibility of others to maintain we will work with them to find and implement an appropriate solution.

The current maintenance programme is identifying flood defence assets in need of attention and working to ensure that less than 3% of these fall below the target condition grade. As a result of additional funding we are currently planning more maintenance and improvement works and are working towards increasing the target for the number of assets in fair or good condition.

Indicator of change 5: Barrier operation

We monitor how the operation of the Thames Barrier, and other major flood barriers, are changing over time, including how frequently the barriers need to be operated and how reliable they are. The lifetime of the Thames Barrier needs to be maximised.

One of the ways we do this is by improving how accurately we can forecast the need for a closure. The Thames Estuary 2100 Plan recommends a level of forecast accuracy which should be met in the future to achieve this. If the reliability of the barriers starts to decline through increased use, then additional maintenance will need to be carried out to ensure the level of reliability remains at or above the design standards.

Figure 3 - Thames Barrier closures

As discussed in indicator 3, there is no trend in the number of Thames Barrier closures being made each flood season (September to April), meaning that the number of times the Barrier closes each year does not appear to be either increasing or decreasing over time.

During the winter of 2013 to 2014 the Thames Barrier was used more frequently than in previous years due to the particularly high river flows that occurred during that winter. It is too early to identify whether or not this is part of an emerging longer term trend but we are able to conclude that it is not part of an existing trend.

Reliability of the major flood barriers studied remains high. There is some variation in reliability levels between the different barriers but planned maintenance will ensure any reduction in reliability is addressed early and that design standards continue to be maintained. The accuracy with which we can predict the need to close the Thames Barrier is improving, although it is not yet at the level required by the Thames Estuary 2100 Plan. We expect to be able to increase the level of accuracy in the future as improvements to the forecasting model are made.

Reliability studies are currently being carried out for all the major barriers but with no discernible trend in the number of barrier closures, the Plan recommendations remain appropriate.

Indicator of change 6: development

Indicator 6 - development infographic

An infographic showing that in the Thames Estuary 2100 area there is:

• residential property valued at £275 billion
• 551,000 household properties
• 1.3 million people
• over 40,500 commercial properties

The flood risk management policies recommended in the Plan for each policy unit are informed by the number of people and property at risk of tidal flooding. We review our understanding of this to ensure the policies remain the right approach to managing flood risk. We also take into account where future development is likely to take place in the estuary.

The policies and recommendations can be adapted to take account of any changes in the estuary which were not anticipated by the Plan. The Thames Estuary 2100 study area was considered to be the maximum extent of tidal flood risk in the estuary at the time the Plan was developed. The number of people and properties were calculated for this area during the development of the Plan. This forms a baseline against which the latest statistics can be compared.

The number of residential properties in the Thames Estuary 2100 study area has increased from 500,000 to 551,000 with the total residential property value increasing from £200 billion to £275 billion. The total number of residents has increased from 1.25 million to 1.3 million. The number of commercial properties has increased from 40,000 to 40,500. Development is expected to take place throughout the Estuary with the majority expected in London, Thurrock and Dartford.

The TE2100 Plan anticipated development would take place and that the numbers of people and properties at risk of tidal flooding would increase. The above results are consistent with these expectations. The flood risk policies and recommendations in the Plan therefore do not need reviewing on the basis of recent and expected development. Future monitoring will consider how we identify the areas which should be assessed as part of our monitoring programme to reflect our improved understanding of the area at risk of tidal flooding and also whether flood risk is increasing or decreasing in the estuary.

Indicator of change 7: erosion and deposition

The removal (erosion) of sand, shingle, mud and other material from the foreshore and bed of the Thames is taking place across the estuary. This material is transported and then accumulates in other parts of the estuary (deposition). We are interested in how and where this is occurring as it can have a detrimental impact on the flood defences such as by undermining foundations of flood defence walls. It can also affect the location and extent of important habitats for plants and animals, by removing habitat in some areas and creating habitat in others.

From previous studies we understand the long term changes which have taken place in the estuary. We have less information on the very recent changes which have taken place. We are identifying localised erosion and deposition which is affecting flood defence assets through asset inspections. Any impact on the flood defences from these processes is addressed through asset management programmes. With this system in place the risk from erosion and deposition is being monitored and managed and therefore changes to the Plan relating to erosion and deposition are not required at this time.

Indicator of change 8: habitat

As part of the Thames Estuary 2100 Plan we made commitments to ensuring the amount of important habitat does not decline in the estuary and to ensure we remain compliant with the Conservation of Habitats and Species Regulations 2010.

The important habitats that need to be monitored and replaced include saltmarsh and mudflat (intertidal habitat) and coastal grazing marsh and wetlands (freshwater habitat). Habitat replacement needs to take place before it is lost. We expect to create 1,200ha of replacement habitat over the lifetime of the Plan.

By monitoring the amount of protected habitat in the estuary (both intertidal and freshwater) we can ensure that sufficient habitat is created at the right time.

For this review we have been unable to accurately measure the amount of intertidal habitat in the estuary, it has not been possible to assess the most recent changes. We can be confident that freshwater habitat has not decreased, as this results from managed realignment projects. This is where the position of the flood defences are moved to create space for intertidal habitat. We are yet to commence any of this type of project in the estuary.

The Plan’s recommendations for compensatory habitat creation included additional habitat to allow for uncertainty in how much habitat would be lost. We will therefore continue to work to this conservative estimate until we have more complete monitoring information.

Indicator of change 9: land use planning and development activities

The Plan included objectives for supporting and informing the land use planning process to promote appropriate, sustainable and flood resilient development in the Thames Estuary. There are also objectives for protecting the social, cultural and commercial value of the River Thames, its tidal tributaries and its floodplain. This indicator is used to help us understand how these objectives are being met by those who are helping to carry out the Plan’s recommendations. Monitoring results can be used to make any necessary changes to the recommendations in the Plan to ensure it continues to support these objectives.

The review has focussed on developing a monitoring method for this indicator which can be repeated in the future. This will allow progress to be tracked over the lifetime of the Plan. The monitoring method which has been proposed focuses on reviewing the latest available policy and strategic planning documents, alongside relevant reports and data published by our partners in the estuary.

It also includes using our Key Performance Indicators (KPI’s), which relate to our role as statutory consultee in the planning process, for development proposed in areas at risk of flooding. Without any results for this indicator, we cannot be certain how well these objectives are being delivered or whether changes to the Plan relating to these objectives are required. However these objectives do not affect the level of flood risk protection provided in the Thames Estuary.

We will carry out detailed monitoring in advance of the next review of the Plan, in order to create a useful baseline.

Indicator of change 10: public/institutional attitudes to flood risk

Understanding how those who live and work in the Thames Estuary floodplain feel about flood risk, including their preferred method for managing the risk, needs to be considered throughout the lifetime of the Plan. The Plan’s development included public consultation; this indicator is used to assess whether the views held by those affected by tidal flood risk in the Thames Estuary has changed significantly since this time. If significant changes are seen, the recommendations made in the Plan can be revised accordingly.

This review considered the results of our National Public Opinion survey alongside relevant published research. The results show that at a national scale, the attitudes of the public to flood risk have remained consistent over the past 5 years, although there is some localised variation where communities have been affected by recent flooding.

The Thames Estuary has not experienced significant flooding in recent years. We expect that public awareness and preparedness has not changed significantly, as experiencing flooding has been shown to be a primary influence in increasing preparedness for such events. Therefore we do not need to change the recommendations made in the Plan at this time.

However we are aware that the Thames Estuary has a number of characteristics which mean the results of national scale surveys and research might not be fully representative of those who live and work in the estuary. We will therefore consider the merits of carrying out a survey specific to the Thames Estuary to inform the next review of the Plan.