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What is coastal flooding and what causes it?

Coastal flooding and erosion are major challenges for communities, infrastructure, and nature across the globe. At the National Oceanography Centre (NOC), we blend advanced modelling, cutting-edge observations, and real community engagement to understand these hazards. Our goal is to build resilience and help manage our coastlines effectively.

Coastal flooding happens when seawater inundates the land. We usually see this when the sea level rises above natural barriers or built defences due to storm surges, high tides, and large waves. 

It can also occur as ‘compound flooding,’ where water from different sources, such as the sea, swollen rivers, and heavy rain, combines. This is quite common in estuaries where river flows meet ocean surges. Sadly, climate change and rising sea levels are making the extreme water levels that cause this flooding more frequent.

Why is coastal flooding such a serious threat?

Why is coastal flooding such a serious threat?

It is one of the most dangerous threats facing coastal areas today. The impacts are severe and include: 

  • Social impacts: 
    • Loss of life 
    • Long-term health issues 
  • Economic impacts: 
    • Damage to buildings and infrastructure 
    • Agricultural losses 
  • Environmental impacts: 
    • Loss of coastal ecosystems 
    • Accelerated erosion 

Because this flooding involves saltwater, it damages agricultural fields and habitats deeply. This often requires a long time and significant resources to fix. In the UK alone, 6.1 million people currently live in flood-prone areas, with annual damages costing around £540 million. These numbers will likely rise as sea levels go up.

Impact

Coastal erosion is the loss of land along the shoreline. It is primarily driven by: 

  • The sea wearing away the coast through tides, waves, and currents. 
  • Landslides caused by unstable ground due to rainfall or groundwater. 

Human activities, such as sand mining or building infrastructure, play a part here too, as does climate change. Because erosion depends heavily on local geology, the impacts can vary hugely from one beach to the next. With sea levels rising, we expect to see a significant increase in risks to buildings and coastal communities over time.

Erosion typically results in the permanent loss of land, which makes bouncing back difficult. The consequences include: 

  • Total loss of homes and infrastructure. 
  • The loss of cherished landmarks and coastal features.
  •  Changes to coastal habitats. 
  • Reduced natural protection against future flooding. 

The release of pollutants from old coastal landfill sites. These issues have a knock-on effect, impacting livelihoods, property values, and the vital services our coasts provide.

We know that climate change is already increasing the frequency and severity of these events, and the trend is set to continue. 

In the UK, sea levels could rise between 0.4 m and 0.7 m by 2100. This rising baseline means extreme flooding will happen more often, erosion will speed up, and the risk to coastal communities will grow significantly. This makes the need for protective action urgent.

Research

We use a mix of methods to predict what is coming and provide evidence on how best to manage our coastal zones. We integrate three key approaches: 

  • High-resolution numerical models to simulate coastal dynamics. 
  • Theoretical models to deepen our understanding of the science. 
  • Innovative observations taken from space and in the field. 

We use these tools to test if solutions, such as nature-based defences, will actually work. This provides critical information to help communities become more resilient.

We look at everything from the scale of Northwest Europe down to a single estuary. Our models resolve the motion of water, waves, and sediments. We use top-tier, validated models like NEMO, Delft3D-FM, FVCOM, and XBeach. These allow us to simulate real-world scenarios across the UK and internationally. We also lead the development of NEMO for coastal applications. By combining these applied models with theoretical methods, we can better understand the processes at play and apply our results more broadly.

We use a blend of trusted tools and new technology. 

In situ observations: 

  • Tide gauges: Established tech that measures sea levels. 
  • Novel tech: New inventions like ‘Wirewall’ that monitor waves crashing over sea defences. 

Remote sensing: 

  • Satellite data: Mapping the seabed and intertidal zones. 
  • Land-based radars: For detailed monitoring of the coast. 
  • Satellite altimetry: Measuring water heights from space. 

This variety allows us to capture the full complexity of the coast and double-check our models.

What projects is NOC currently working on?

We have been leading the charge on several major projects, including CHAMFER, Co-Opt, #gravelbeach, SPLASH, CreamT, Wirewall, the SMUK Tide Gauge Network, SWOT-UK, and HURACAN. These initiatives bring together large networks of researchers from leading institutes and universities in the UK and abroad, fostering a collaborative approach to these complex challenges.

Beach stones

gravelbeach

What have we learned about nature-based solutions?

Our research shows that while nature-based solutions are powerful, they have limitations. 

High-resolution high-fidelity computer simulations predict both intended (reduced water levels) and unintended (raised water levels elsewhere) impacts of the managed realignment scheme. Meanwhile, at the village of Airth, we found that a ‘hybrid’ approach combining hard engineering with nature-based solutions might offer the best protection (Matsoukis et al., 2025). This highlights why we need comprehensive assessments for every location.

Our Co-Opt project highlighted that we must engage with coastal communities and work across different discipline so that we achieve a shared understanding of our coastal systems.

By doing this, we generated new knowledge and policy insights to support the shift from hard ‘grey’ infrastructure to softer ‘green’ solutions. This aligns with global net-zero goals. We have also improved our understanding of how sediment moves and how storms and tides interact, which is essential for managing coasts in a changing climate.

How does NOC’s research influence policy and practice?

Our science leads to better tools for predicting flooding. It also feeds directly into policymaking. We provide the evidence that decision-makers need to choose strategies that protect communities while considering the environment and economy. 

The transition toward nature-based and hybrid solutions that we champion also contributes to broader climate goals, such as reducing carbon emissions.

For example, our work led to tangible policy change with a new option for intertidal habitat creation having been included in the draft Falkirk Coastal Strategy 2025. In North West England, our work helps shape local management decisions by informing existing projects (e.g. Our Future Coast) towards supporting the design of practical, innovative flood resilience measures.

We regularly hold workshops with the people living on the front lines. For the Co-Opt project, we brought together consultants, councillors, national agencies, and local residents. 

This engagement ensures that our research addresses real needs, incorporates local knowledge, and helps develop solutions collaboratively. It guarantees our science is useful for the people who need it most.

What scientific publications has this research produced?

Our work is widely published in peer-reviewed journals. Key publications include:

Enhancement of coastal flood mitigation by implementing hybrid flood defences integrating hard engineering and nature-based solutions

Publication year

2025

Publication type

Article

Three-dimensional sediment dynamics in well-mixed estuaries: importance of the internally generated overtide, spatial settling lag, and gravitational circulation

Publication year

2017

Publication type

Article

Impact of storm propagation speed on coastal flood hazard induced by offshore storms in the North Sea

Publication year

2019

Publication type

Article

Interested in learning more?

Explore our work and discover how science helps safeguard marine ecosystems.