As wind-driven waves approach the shoreline at a slight angle, sediments are carried along the coast. Waves move sediments along the beach in a zigzag fashion (red arrows). The majority of sediment is transported in the surf zone. The movement of sand along the shoreline is known as beach drift.

Longshore drift plays a large role in the evolution of a shoreline, as if there is a slight change of sediment supply, wind direction, or any other coastal influence longshore drift can change dramatically, affecting the formation and evolution of a beach system or profile.

Wave types When a wave breaks, water is washed up the beach. This is called the swash . Then the water runs back down the beach, which is called the backwash . With a constructive wave, the swash is stronger than the backwash.

Longshore Drift (littoral drift) Longshore drift is a process responsible for moving significant amounts of sediment along the coast. The swash moves beach material along the beach and the backwash, under gravity, pulls the material back down the beach at right angles to the coastline.

Methodology

1. Decide on an appropriate distance to measure longshore drift over, for example 10 metres.
2. Lay out tape measure close to water and mark start and finish points.
3. Place your float into water in the breakwater zone at the start point.
4. Observe and time the object’s movement across the pre-set distance.

Longshore drift is the movement of material along the shore by wave action. Longshore drift happens when waves moves towards the coast at an angle. Longshore drift provides a link between erosion and deposition. Material in one place is eroded, transported then deposited elsewhere.

Longshore drift also builds barrier beaches and barrier islands. Barriers are long narrow strips of sand and gravel that are separated from the main shore by lagoons, marshes and mud flats. Sometimes people will build fences or walls to try and slow down longshore drift.

wave erosion Particles are dragged back and forth by wave action, abrading the bedrock along the coast and abrading each other, gradually wearing pebbles into sand. Thus, features extended out into the lake will receive more wave energy, and the tendency is to smooth out an irregular coastline.

When waves approach the beach at an angle, the part of the wave that reaches shallow water earliest slows down the most, allowing the part of the wave that is farther offshore to catch up. In this way the wave is refracted (bent) so that it crashes on the shore more nearly parallel to the shore.

Gentler summer waves deposit sand from offshore bars onto the beach, ultimately widening it and increasing its elevation. Conversely, stronger winter waves with more energy, pick up those particles deposited in the summer, and carry them back offshore in bars, thus narrowing the beach.

The peak frequency ranges from about 0.2 waves per second (12 per minute) up to about 0.4 waves per second (24 per minute).

As waves come into shore, they usually reach the shore at some angle. As a wave comes into shore, the water ‘feels’ the bottom which slows down the wave. So the shallower parts of the wave slow down more than the parts that are further from the shore. This makes the wave ‘bend’, which is called refraction.

Waves don’t always flow towards the shore, it just appears that way. Waves don’t always flow towards the shore, it just appears that way. Sea waves are mostly formed by winds moving across the surface of the sea water, pushing the surface water along until it forms waves of energy.

1 As waves approach shore they “touch bottom” when the depth equals half of the wavelength, and the wave begins to slow down.

As the wave moves into increasingly shallow water, the bottom of the wave decreases speed. There comes a point where the top of the wave overtakes it and starts to spill forward — the wave starts to break. We’re surfing! In general a wave will start to break when it reaches a water depth of 1.3 times the wave height.

4.18 A). When deep-water waves move into shallow water, they change into breaking waves. When the energy of the waves touches the ocean floor, the water particles drag along the bottom and flatten their orbit (Fig. When this happens, the front surface of the wave gradually becomes steeper than the back surface.

Surging breakers occur when long wave period, low amplitude waves approach moderately steep shores. The wave doesn’t spill or curl; it builds up and then slides rapidly up the beach with less foam or spray than the other two breakers.