2B Coastal recession, sea level change and coastal flood risk

Introduction: Why Should We Care About Changing Coastlines?

Welcome to one of the most dynamic parts of geography! In this chapter, we explore why some coastlines seem to vanish into the sea while others stay put. We also look at how rising sea levels and massive storms are putting millions of people at risk. Understanding these processes isn't just about rocks and water; it’s about the future of where people live, work, and build communities.

In this section, we will focus on three big ideas: 1. Why some coasts recede (retreat) faster than others. 2. The difference between global and local sea level changes. 3. Why coastal flooding is becoming a bigger threat to human life and the economy.

Note: This builds on what you learned about the littoral zone and marine processes in previous chapters. If you need a refresher, remember that the "littoral zone" is just the area where the land meets the sea!

1. Coastal Recession: Why the Land Retreats

Coastal recession is just a fancy way of saying "the coastline is moving inland" because of erosion and weathering. But it doesn't happen at the same speed everywhere. Some coasts lose 10 meters a year, while others don't change for centuries.

Factors Influencing Recession Rates

Recession is like a tug-of-war between the strength of the land and the power of the sea. Here are the main "players" in this struggle:

• Lithology (Rock Type): Soft rocks like unconsolidated glacial till (clays and sands) erode very quickly. Harder rocks like igneous granite are much more resistant. Think of it like trying to wash away a sandcastle vs. a brick wall.
• Geological Structure: If the rock layers (strata) dip toward the sea, they are more likely to slide down during a storm. If they dip inland, they are more stable.
• Marine Factors: High-energy waves (destructive waves) and a large fetch (the distance wind blows over water) increase erosion.
• Subaerial Processes: This includes weathering and mass movement (like landslides). Sometimes, the rain weakens the cliff from the top before the sea even touches the bottom!

Human Influence on Recession

Humans often accidentally make recession worse. For example, building a sea wall in one place might stop waves there, but it can starve beaches "down-drift" of sediment, making those areas erode faster. This is a key example of how Actions (A) have unintended consequences.

Quick Review: Coastal recession happens fastest when you have soft rock, high-energy waves, and heavy rainfall causing landslides.

2. Sea Level Change: Eustatic vs. Isostatic

This is a topic that trips many students up, but here is a simple trick to remember the difference: Eustatic is "Everywhere" (Global), and Isostatic is "Island-specific" (Local).

Eustatic Change (Global)

This is a change in the volume of water in the global ocean. - Climate Change: As the planet warms, glaciers and ice sheets melt, adding more water to the "bathtub." - Thermal Expansion: When water gets warmer, the molecules move more and take up more space. This is actually a huge cause of sea level rise! - Equation for Volume Change: If \( V \) is the volume of the ocean and \( \Delta T \) is the change in temperature, the change in volume \( \Delta V \) is proportional to the increase in heat.

Isostatic Change (Local)

This is a change in the level of the land relative to the sea. - Post-Glacial Rebound: During the last Ice Age, massive ice sheets weighed down the land (like sitting on a cushion). Now that the ice has melted, the land is slowly "springing back" up. - Example: In the UK, the North and West are rising (rebounding), while the South and East are sinking (subsiding). This makes the South-East of England much more vulnerable to flooding.

Contemporary Sea Level Rise

Currently, sea levels are rising globally at about \( 3.2mm \) per year. This creates huge Uncertainties (F) for the future. Scientists use complex models to predict how much the sea will rise, but because we don't know exactly how much CO2 humans will emit, the predictions vary.

Key Takeaway: Sea level rise is a combination of the water rising (Eustatic) and the land potentially sinking (Isostatic).

3. Coastal Flood Risk: Who is at Danger?

Low-lying coastal areas are at the highest risk. A "storm surge" is often the trigger for a disaster. This is a temporary rise in sea level caused by very low atmospheric pressure and high winds pushing water onto the land.

Physical Factors Increasing Risk

• Low-lying Topography: Areas only a few meters above sea level (like the Maldives or parts of Bangladesh) have no "buffer" zone.
• Vegetation Removal: Mangroves and salt marshes act as natural sponges and breakwaters. When humans remove them for shrimp farming or tourism, the coast loses its natural protection.
• Estuaries: The "funnel" shape of some river mouths can concentrate the force of a storm surge, pushing water higher and further inland.

The Human Aspect: Vulnerability

Risk isn't just about the physical environment; it’s about the Players (P) involved. - Population Density: Millions of people live on coastal floodplains because the land is flat and good for farming or trade. - Economic Development: Wealthier nations can afford expensive sea defenses (hard engineering). Developing nations may lack the resources, making their populations more vulnerable.

Did you know? A storm surge in 1953 killed over 300 people in the UK. This led to the Attitude (A) change that resulted in the building of the Thames Barrier to protect London!

4. Synoptic Themes: Players, Actions, and Futures

To get the top marks in Geography, you need to link your ideas to these three themes:

• Players (P): These include local residents (who want to save their homes), environmental groups (who want to protect habitats), and governments (who have to decide where to spend money). Often, these players disagree!
• Attitudes and Actions (A): Do we build a wall (Hard Engineering), or do we let the sea take the land (Managed Realignment)? Our actions depend on our "Cost-Benefit Analysis"—is the land worth the price of the wall?
• Futures and Uncertainties (F): Global warming is a "wildcard." If the Antarctic ice sheet melts faster than expected, all our current coastal defenses might become useless. We are planning for an uncertain future.

Chapter Summary Checklist

Before you move on, make sure you can:
- Explain why lithology and structure affect how fast a cliff erodes.
- Define Eustatic and Isostatic change without getting them mixed up.
- List three reasons why some people are more at risk from coastal flooding than others.
- Identify the different Players involved in coastal decision-making.

Don't worry if this seems tricky at first! Just remember that coastlines are always changing; humans are just trying to figure out how to live alongside that change. Keep practicing your definitions, and you'll do great!