Coasts as natural systems

Welcome to Coastal Systems!

In this chapter, we are going to look at the coastline not just as a place for a summer holiday, but as a dynamic, working system. Imagine the coast is like a giant machine: energy goes in, materials get moved around, and the shape of the land changes as a result. By the end of these notes, you’ll understand how winds, waves, and sediments all work together to create the stunning landscapes we see at the seaside.

1. The Coast as an Open System

In Geography, a system is simply a set of objects that are linked together. The coast is an open system. This means it can exchange both energy and matter with the world around it (like the ocean and the atmosphere).

To make this easy, think of a bank account:

• Inputs: This is the money you pay in (like sand being added to a beach).
• Stores: This is the balance sitting in your account (the beach itself).
• Transfers: This is moving money between accounts (sand moving along the coast).
• Outputs: This is money you spend (sand being washed out to sea).

Key Components of the Coastal System:

Inputs: These are things that "enter" the system. Examples include kinetic energy from wind and waves, thermal energy from the sun, and sediment from eroding cliffs or rivers.

Outputs: These are things that "leave" the system. Examples include evaporation, and sediment being moved far offshore into deep ocean stores.

Stores/Components: These are the "landforms" where material stays for a while, such as beaches, spits, and sand dunes.

Flows/Transfers: These are the processes that move material from one place to another, like longshore drift or rip currents.

Quick Review: An open system transfers both energy and matter across its boundary. If you remember "Inputs → Processes → Outputs," you’ve got it!

Key Takeaway: The coast is a balancing act of energy and material moving in, staying for a while, and eventually moving out.

2. Sources of Energy: What Drives the System?

Energy is the "fuel" that makes the coastal system work. Without energy, the water wouldn't move, and the rocks wouldn't erode.

Wind: The Primary Driver

Wind is created by differences in air pressure. It is vital because it creates waves. Two things matter here:

• Wind Speed: Faster wind = more energy.
• Fetch: This is the distance of open water over which the wind has blown. A long fetch (like the Atlantic Ocean hitting Cornwall) means huge, powerful waves.

Waves: The Great Shapers

Waves are the most visible form of energy. We categorize them into two main types:

1. Constructive Waves: These "build" the beach. They are low, long, and have a strong swash (water moving up the beach) and a weak backwash (water moving back down).

2. Destructive Waves: These "destroy" or erode the beach. They are high, steep, and have a weak swash but a very strong backwash that pulls sand away.

Did you know? You can calculate wave energy using this formula: \( P = H^{2}T \), where \( P \) is power, \( H \) is wave height, and \( T \) is the time between wave crests. Basically, if you double the height of a wave, you quadruple its power!

Tides and Currents

Tides are the periodic rise and fall of the sea level caused by the moon's gravity. They determine where the wave energy hits the shore. Currents are the "rivers" of water within the ocean that transport sediment over long distances.

Key Comparison: High-Energy vs. Low-Energy Coasts

• High-Energy Coasts: Think of rocky, stormy places like Scotland. Strong waves, high rates of erosion, and bold landforms like cliffs.
• Low-Energy Coasts: Think of sheltered bays or the Mediterranean. Gentle waves, more deposition, and landforms like beaches and salt marshes.

Key Takeaway: Wind creates waves. Constructive waves build beaches, while destructive waves take them away.

3. Sediment: The Material of the Coast

If energy is the fuel, sediment (sand, pebbles, silt) is the "building material" of the coast.

The Sediment Budget

Geographers use a sediment budget to see if a beach is growing or shrinking:

• Positive Budget (Surplus): Inputs are greater than outputs → The beach grows.
• Negative Budget (Deficit): Outputs are greater than inputs → The beach erodes and shrinks.

Sediment Cells

The coastline is divided into sediment cells. These are sections of the coast that are mostly "self-contained." Material moves within the cell, but very little sand crosses over the boundaries (usually headlands). There are 11 major sediment cells around England and Wales.

Memory Aid: Think of a sediment cell like a recycling bin. Most of what happens inside stays inside, but occasionally something might fall out!

Key Takeaway: Coasts are managed in "cells." We track the "budget" of sand to understand if a coast is eroding or growing.

4. Equilibrium and Feedback Loops

Coastal systems like to stay in balance. This balance is called dynamic equilibrium. If something changes (like a big storm), the system tries to correct itself.

Negative Feedback (The "Good" Kind)

This is when the system reacts to a change by trying to push things back to normal. It creates stability.

Example: A storm erodes a large amount of sand from a beach. This sand is deposited offshore in a "sandbar." The sandbar then forces waves to break further out at sea, protecting the beach from further erosion until the sand can eventually move back.

Positive Feedback (The "Escalating" Kind)

This is when a change triggers more change in the same direction. It creates instability.

Example: Global warming melts ice, which leads to sea-level rise. As the sea rises, it erodes more cliffs. This erosion might destroy coastal vegetation that was holding the land together, leading to even faster erosion.

Don't worry if this seems tricky! Just remember: Negative feedback negates the change (cancels it out). Positive feedback adds to the change (makes it bigger).

Key Takeaway: Dynamic equilibrium is a state of balance. Feedback loops are the "internal thermostats" of the coastal system.

5. Landforms and Landscapes

It is important to know the difference between these two terms:

• Landform: An individual feature created by erosion or deposition. Example: A single sea stack or a beach.
• Landscape: The "big picture." It is the overall appearance of an area, made up of many related landforms. Example: A "high-energy rocky coastline" made of cliffs, arches, and wave-cut platforms.

Common Mistake: Students often use these words interchangeably. Remember: A landform is one piece of the puzzle; the landscape is the whole finished puzzle!

Key Takeaway: Individual landforms (like a spit) combine to create characteristic coastal landscapes.

Quick Review: Check Your Understanding

1. Is the coast an open or closed system? (Answer: Open)

2. What do we call the distance wind blows over water? (Answer: Fetch)

3. Which wave type has a stronger backwash than swash? (Answer: Destructive)

4. What happens in a "negative feedback" loop? (Answer: The system restores balance)