Depositional Landforms (Beaches)

Formation of Beaches

Beaches are formed by the deposition of sediment carried by waves along the coast. When waves lose energy, they drop the sediment they are carrying, building up the beach over time.

Constructive waves play a key role in building beaches. These waves have a strong swash (movement of water up the beach) and a weak backwash (movement of water back to the sea). This means more material is deposited than removed, gradually creating a beach.

Longshore drift is the process that moves sediment along the coast. Waves approach the shore at an angle, carrying sediment up the beach with the swash and back down with the backwash at right angles. This zigzag movement transports sediment along the coastline, helping to build and shape beaches.

Beaches have different features in their profile:

• Berms: Flat areas or ridges on the upper part of the beach formed by deposited sediment during calm conditions.
• Ridges: Raised lines of sediment that run parallel to the shoreline, often marking the high tide mark. (Note: In GCSE geography, these features are sometimes also called 'cusps'.)

For instance, on a sandy beach, constructive waves deposit fine sand forming gentle berms, while on shingle beaches, ridges of pebbles are common.

Example: If constructive waves deposit 2 cubic metres of sand each day on a beach, and destructive waves remove 0.5 cubic metres, the net gain is 1.5 cubic metres daily, gradually building the beach.

Types of Beaches

There are three main types of beaches found around the UK coastline:

• Sandy beaches: Made mostly of fine sand particles. These beaches are common where there is a plentiful supply of sand, such as at Bournemouth. Sandy beaches tend to be wide and have gentle slopes because lighter sand is moved easily by waves with lower energy.
• Shingle beaches: Composed mainly of pebbles and small stones. These beaches are steeper and narrower, like Chesil Beach in Dorset, which is a famous shingle beach. The larger, heavier pebbles are deposited where wave energy is higher.
• Mixed beaches: Contain both sand and shingle. The distribution depends on wave energy and sediment supply. An example is the beach at Whitby, which has areas of both sand and shingle.

The type of beach affects its shape, slope, and the habitats it supports.

Processes Leading to Deposition

Deposition occurs when waves lose energy and can no longer carry sediment. Several factors reduce wave energy, encouraging deposition:

• Wave energy reduction: When waves enter sheltered areas such as bays or behind headlands, they slow down and deposit sediment.
• Sheltered areas: Bays and estuaries are common places for sediment to accumulate because they are protected from strong wave action.
• Sediment supply sources: Sediment comes from eroded cliffs, rivers, and offshore sources. A plentiful supply means more material is available to form beaches.
• Seasonal changes: In summer, constructive waves dominate, building beaches by depositing sediment. In winter, destructive waves remove sediment, making beaches narrower.

For example, the sandy beaches of the south coast of England often grow in summer due to constructive waves, then shrink in winter due to stormy conditions.

Example: A sheltered bay receives sediment from a nearby eroding cliff. The wave energy reduces as waves enter the bay, causing sediment to settle and form a beach.

Human Impact and Management

Beaches are popular tourist destinations, but human activity can affect their natural state:

• Tourism effects: Large numbers of visitors can cause erosion of dunes and damage to habitats. Foot traffic compacts sand, reducing its ability to absorb water.
• Beach nourishment: This involves adding sand or shingle to a beach to replace material lost by erosion or storms. It helps maintain beach size and protects the coast.
• Coastal defences impact: Structures like groynes (wooden or rock barriers built at right angles to the coast to trap sediment) and sea walls can interrupt natural sediment movement, sometimes causing sediment to build up in one area but erode in another.
• Sustainable management approaches: These include managing visitor numbers, protecting dunes with fencing, and using natural materials for beach nourishment to maintain the beach environment.

Example: At Bournemouth, beach nourishment is regularly used to maintain the sandy beach, protecting the town from coastal erosion and supporting tourism.