What is the difference between beach drift and longshore current

Unit 2. Unit 3. Unit 4. Unit 5. Unit 6. Unit 7. Unit 8. Unit 9. Unit Learning Objectives. Review Quiz. When a particular oceanic wave reaches the beach, different segments of the wave reach the beach before others.

This phenomenon causes the wave segments to slow down. Here, the oceanic wave tends to bend and get the shape of the shoreline. Therefore, these waves tend to reach the beach parallel to the shoreline. However, these waves do not always reach the shoreline in a parallel way; the waves come in a slight angle. The current that comes with this wave and is parallel to the shoreline is named as the longshore current.

Figure 1: Longshore Current. The nature of a longshore current is affected by the velocity and the angle of a wave. If the longshore current breaks the beach in a more acute angle, then it encounters a steep beach slope. Similarly, a wide breaking angel indicates a gentle beach slope. In either case, the longshore current moves towards the beach and comes back to the ocean.

During this moving forward and backward process, the longshore current can carry sediments on and off the beach. For example, if the waves appoach the shoreline from the south, longshore current moves from south to north. But longshore current and the resulting transport of sediment is only one of the dynamic processes that constantly alter the shoreline. As waves repeatedly hit the shore, water moves onto the beach and then retreats in a continuous cycle.

However, the waves are not all that moves on the shoreline. In fact, the sediment on the shore is also always on the move. Great energy is expended on the beach as waves crash against the shoreline. This energy allows the water to transport sediment. The grains are lifted as the waves in the swash zone move onto the beach, and then the grains are deposited again as the water retreats. In this case, no real net movement of sand occurs in the swash zone. However, waves generally do not form parallel to the shoreline, and thus, usually approach the shore at an angle.

Consequently, beach sand will have a net movement up or down the beach, depending on the direction of incoming waves. This net movement of the beach sand is known as beach drift. Figure 2 illustrates how beach drift operates. Notice on the diagram the angle at which the waves hit the beach.