Aeolian Transport

The first process of coastal dune formation is known as Aeolian Transport and involves the movement and weathering of sand particles behind and parallel to the shoreline.

There are three main processes involved in Aeolian Transport;

Suspension

The finer sand particles are moved by the wind, high in the air. They are not affected by gravity and therefore can travel thousands of kilometres before they land on earth again. When they land, it is often because they have combined with raindrops and fall with the rain.

Saltation (The most common form of sand transport)

When the wind hits the ground, it causes turbulence, disturbing the sand particles. If the wind has enough velocity, it will cause the particles to start moving (initially just along the ground). The required level of velocity is called critical velocity and varies depending on grain size, vegetation present and the moisture levels of the sand (which holds the sand down, requiring the critical velocity to be greater) As the sand moves, it hits other grains which cause them to bounce up in the air. The wind then picks these airborne particles up and carries them. Gravity causes them to fall back down. If sand lands on a hard surface e.g. rock, it will bounce off again, being carried further. If it lands on a sandy surface, it will cause other particles to be disturbed, bounce up and they too will be carried, thus starting off a chain reaction.

Surface creep

The larger particles are too heavy to be picked up and carried by the wind so instead, they move along the ground. When they become dislodged by the falling ones, they roll along the ground. Through this process, they are not only moved but by moving against other particles, they erode into smaller particles which can be moved by saltation or suspension.

Coastal Dunes

Coastal Dunes refers to the building up of sediment which is transported by the waves and wind, resulting in a series of sand ridges. The Hydrosphere, lithosphere biosphere and atmosphere all interact to form the ecosystem of the coastal dune.

Coastal erosion:

Fore dunes are a protection against the force of the waves and harsh wind.They supply sand for the beach to prevent damage and erosion. Coastal erosion is achieved when sand is pulled off the beach by wave action and deposited offshore, in or behind the surf zone. Damage or deductions of vegetation within the dunes makes the sand dunes vulnerable to harsh coastal winds and waves which result to dune sand drifts.Dune restoration can help eroded or degraded dunes by rebuilding through techniques such as fencing, sand fill and re vegetation.

Dune Formation

Dunes form where constructive waves encourage the accumulation of sand, and where current onshore winds blow this sand inland. There need to be obstacles such as , vegetation, pebbles and soil to trap the moving sand grains. As the sand grains get trapped they start to accumulate, starting dune formation.

Factors which affect Coastal Dune formation:

- Beach storm erosion

- Reduced coastal environment

- Flooding due to storm waves surge

- Sand movement

- Landslides and rock fall.

Prevailing Winds:

Prevailing winds are the winds which are blown predominantly from the same direction, for that area. They have the ability to shape, form and erode the sand dunes. In coastal areas, the dunes tend to position themselves perpendicular to the path of the prevailing winds.