How are they made?
The process of sediment moving in one direction down a beach due to a prevailing wind. Most of the material is moved on the beach, or in the nearshore zone
The swash arrives at an obtuse angle to the beach, with the backwash returning to the sea at 90 degree to the beach.
This forms long, large beaches.
Issues with Longshore drift
This can cause silt to deposit in inconvenient locations, such as at the mouth of a river or port. It can also remove the beach from areas that need protection from the waves.
Why are beaches useful?
Beaches are a good natural defence against coastal erosion. From a tourism perspective, it can cause a loss of income as beaches are removed
GB Sediment cells
Sediment moves along the coast in sediment cells. The coastline of England and Wales was split into 11 sections, each section is the responsibility of the local authority. any action that takes place in one part of the cell impacts the rest of the cell. each cell operates between physical barriers that prevent sediment from moving between them, such as estuaries.
These sediment cells act as systems, in dynamic equilibrium. Each has a "sediment budget", how much sediment is available in that area
dynamic equilibrium: overall stays the same, but small changes over short periods of time
- There are many different sources of coastal sediment, not just from eroded cliffs
- Where sediment comes from
- How sediment moves
- Where sediment is stored
|Erosion of cliffs||Longshore drift||Backshore depositional landforms|
|Onshore currents||Wave transport||Foreshore depositional landforms|
|Land sediment eroded by rivers||Tides||Nearshore depositional landforms|
|Wind blown (aeolian) sediments from land||Local or large scale currents||Offshore sediment deposition to deep offshore waters|
|Subaerial processes||Wind along shore|
flow of seawater in a particular direction driven by wind, water density, salinity and temperature
|Traction||Sediment is rolled along by the water currents||the sound of rolling pebbles and shingle can be heard on a beach||pebbles, cobble and boulders|
|Saltation||Sediment bounces along, due to water or wind||on a dry but windy day, a layer of sand can be seen just above the beach surface||Sand and small particles|
|Suspension||sediment is carried in the water||on soft coasts, sea is often muddy due to sediment||silt|
|Solution||dissolved material is carried by the river||of limited importance||water soluble rocks, limestone|
Longshore drift effectively continues around a gap in the coastline, such as a estuary, in a straight line. the material is then deposited in this location, forming mounds of sand. this continues out into the estuary until the river currents are too strong to continue. often spits form a curved end due to a change in prevailing wind, or due to wave refraction
Behind a spit, salt marshes or mudflats can form due to high deposition in the protected area.
Commonly found in bays, wave refraction creates a low-energy environment. A beach can be:
waves break in line with the coast, forming concave, curved beached
Example: Lulworth Cove, Dorset
Waves break at an obtuse angle to the coast, but backwash runs perpendicular to the beach. These are areas of high Longshore drift
Example: Walton-on-the-Naze, Suffolk
Beach Features & characheristics
A ridge composed of the biggest boulders from the largest waves. Shows the highest tide point during a storm
Riges marking successively lower high tides, formed by constructive waves.
Semicurcular shaped depressions formed when waves beak directly on the beach. They show where the sea meets the beach most of the time
Ridges and depressions in the sand caused by a small tide and little water movement. Underground water movement creates ridges. In the low tide area, often submerged
Ridges and runnels
Forming in the foreshore zone, [more data here]
A beach/spit that connects a small island and the mainland
Example: Chesil Beach, connecting the Isle or Portland
Offshore bars, known as sandbars, are submerged at high tide, and created by offshore waves. on the coast destructive waves erode sand from the beach due to their strong backwash, forming deposits out at sea. Sandbars can also be formed from contructive wave on a shllow coastlin, when energy is lost at sea
Example: Bramble Bank, Solent
where a beach or spit extends across a bay and joins two headlands together, forming a lagoon.
Example: Slapton sands, Devon
a triangular shaped headland out from the main coastline , formed when a coast is suceptable to long shore drift from two different directions. vegetation grows stabalising it. they can be small (3m) or larger than 4km in length. Example: Dungeness, Kent