The Environment Agency has published the key findings of its monitoring review of the Thames Estuary 2100 plan which flag up the growing prospects of flood risk and the need to strengthen flood defences, including the Thames Barrier.

Introducing the review, Emma Howard Boyd, Chair, Environment Agency and Julia King, Baroness Brown of Cambridge, Chair of the Climate Change Committee’s Adaptation Committee, described the Thames Barrier as “the jewel in a 330 kilometre crown” of flood walls, embankments, smaller barriers, pumping stations, and flood gates.

At almost 40 years old and nearing its 200th closure, the Barrier is part a vast and complex network of tidal defences protecting over £321 billion worth of property and 1.42 million people from flooding.

The report points out that the more frequently the Barrier closes, the more costly it is to maintain over the longer term to ensure its reliability. More frequent closures also means less time is available to complete essential maintenance on the Barrier (set at 50 per year on average), The EA can maintain the reliability of the Barrier by keeping the number of closures within a manageable limit - currently set at 50 per year on average.

The two Chairs point out that these structures are all having to work harder as climate change accelerates, commenting:

“In addition to the 1.42 million people directly protected by flood defences, it is worth considering the impact of a major flood in the Thames Estuary. Millions more could be impacted by the closure of major transport hubs and critical infrastructure (such as hospitals and schools), businesses could suffer from lost time and customers, and the region’s reputation as a major business and tourist hub could be at risk.”….

“Individuals, businesses and government need to work together to create a resilient Thames Estuary. By making the right investment decisions at the right time, we can protect millions of people and support sustainable development that is more resilient to rising sea levels and other climate shocks.”

The Environment Agency and its partners published the first Thames Estuary 2100 Plan in 2012 setting out a series of possible ‘pathways’ for managing tidal flood risk in the Thames Estuary.

A full review and update of the recommendations in the Plan is carried out every 10 years. The monitoring review is the first of 3 phases, which will be followed by an economic review (now underway) and then finally publication of the updated Plan in 2022.

For the first time since the Plan was published, the Agency has reviewed data on the number of social and cultural assets in the Plan’s area. There are approximately:

• 3000 ‘social assets’ such as theatres, and community/leisure centres
• 27 km² of open green space
• over 4000 listed buildings
• 4 World Heritage Sites

The report set outs the key findings as 10 high-level ‘indicators of change’:

• sea level rise
• extreme water levels
• river flows
• condition of flood defences
• Thames Barrier operations
• people, property, infrastructure and policy
• extent of erosion and deposition
• habitat
• social, cultural and commercial value
• public and institutional attitudes to flood risk

The headline findings include:

• sea level in the Thames Estuary has risen over the last century
• sea level rise has been accelerating over the last few decades
• recent data shows that river flows are increasing
• 97.5% of the tidal flood defences in the estuary are classified as meeting or exceeding their target condition
• the Agency expects it will need to close the Thames Barrier more frequently as sea level rise accelerates
• the number of people and properties in the Plan area has increased since 2009

The report sets out the next steps the EA is proposing to take, including prioritising work on flood defences that are currently below their target condition and an assessment of any changes needed in numbers of Thames Barrier closures as sea level rise accelerates.

The original Plan set out the following 4 major deadlines for flood defence upgrades.

1. Defence raising downstream of the Thames Barrier - 2040

2. Defence raising upstream of the Thames Barrier - 2065

3. Thames Barrier upgrade/replacement and additional defence raising downstream of the Thames Barrier - 2070

4. Additional defence raising upstream of the Thames Barrier - 2100

The defences downstream of the Thames Barrier (including the Barrier itself) need to be high enough to protect against different sizes of storm tides. The height of the Thames Barrier protects central London against a storm tide with a 1 in 1000 (0.1%) chance of occurring in any year. As sea level continues to rise, the height of storm tides will increase.

The report says that defences downstream of the Barrier will therefore need to be higher to prevent tidal flood risk increasing. In addition, the Thames Barrier will either also need to be upgraded or replaced with a new, higher barrier further downstream to prevent tidal flood risk upstream of the Barrier increasing.

Current condition of flood defences

The Agency monitors the condition of over 3000 fixed flood defences in the estuary - however, it is only responsible for maintaining 12% of them (39% by length of the defences). A range of organisations and land owners manage the remaining defences - the EA works in partnership with them to ensure all defences are adequately maintained.

Photo: erosion of flood defences at Dukeshore Wharf

Photo: Dukeshore Wharf completed flood defence improvements

The Agency uses condition grades (based on regular visual inspections) from ‘1 (very good)’ to ‘5 (very poor)’ to indicate whether flood defences are in an appropriate state of repair. The report says the EA aims to maintain at least 98% of flood defences at or above their required condition to ensure that the flood defence system is resilient during a tidal flood event.

The report says the majority of the defences in the estuary are in ‘good’ condition, but a proportion of them have a lower condition grade than 5 years ago, commenting:

“ This may indicate that the flood defence network is deteriorating at a faster rate than anticipated when the maintenance programme was developed. This is likely to be due to the combined impacts of ageing assets and climate change.”

“When defences are below the required condition it does not necessarily mean that they are structurally unsafe, or that performance in a flood is compromised. Where defences are our responsibility, we will prioritise the 2.5% below their required condition for maintenance or repair through our asset management programme (TEAM2100).”

“We will work with the relevant owners to maintain and repair the remaining assets in this category. We are also now developing our strategic approach to managing the overall decline in flood defence condition. This will help to determine when and where to invest in the estuary in future.”

Barrier reliability

The report says that assessments show that the reliability of the mechanical and electrical systems of the major flood barriers and gates in the estuary remains high overall.

The Agency regularly reviews the reliability of barriers in the estuary taking into account:

• the risk of human or forecasting errors during closures
• how reliable the barriers’ mechanics and electrical systems are
• how resilient the barriers are to internal risks (e.g. fires) and external risks (e.g. strikes by passing ships)

The EA will continue to invest in improvement works as annual closures increase due to rising sea levels, the report says – which means that the barriers “will continue to provide the required standard of reliability” The Agency is currently carrying out a programme of improvements to the Thames Barrier to ensure it is sufficiently reliable (to close when required) in the long-term. This includes upgrading or replacing mechanical, electrical, forecasting and supporting systems.

Critical infrastructure in Thames Estuary includes Tideway Tunnel 

The report also highlights a number of  major critical infrastructure projects which are planned or under construction in several areas of the Thames Estuary 2100 Plan, including:

Thames Tideway Tunnel - Acton (West London) to Abbey Mills Pumping Station, Mill Meads (East London) Wastewater tunnel

Silvertown Tunnel - Silvertown to North Greenwich (East London) Road tunnel

Riverside Energy Park - Bexley (East London) Renewable energy facility

Lower Thames Crossing - Between Gravesend (Kent) and Tilbury (Essex)- Road tunnel

Tilbury2 - Port facility

Thurrock Flexible Generation Plant - Power plant

The report says the EA will consider whether the flood risk management policies for these areas should be reviewed as part of the next phase of the 10-Year-Review.

As part of its regular flood defence visual inspections the Agency has also started a programme of enhanced monitoring across part of the estuary. The enhanced monitoring includes using new technology to detect three-dimensional data via aircraft, drones and boat surveys.

The EA is carrying out studies to determine which areas are being impacted the most by the processes of erosion and deposition s as part of its current asset management programme (TEAM2100).

The Agency will also be prioritising defences that are below their required condition for maintenance through the TEAM2100 programme. For any defences it does not own and maintain, the EA said it will work with other owners to determine and implement the right solutions.

It will also identify which areas of the estuary require future investment in flood defences and when the investment will be needed.

Click here to read to the key findings report online.