Longshore Drift

Definition

Longshore drift is the process by which sediment is transported along a coastline parallel to the shore, primarily driven by wave action and prevailing currents. This natural movement shapes coastal landforms and is essential for understanding how beaches evolve over time, influencing coastal erosion, sediment supply, and the effectiveness of various coastal management strategies.

5 Must Know Facts For Your Next Test

1. Longshore drift primarily occurs due to oblique wave angles hitting the shore, which causes sediment to be pushed up the beach at an angle and then pulled back down by gravity.
2. This process can lead to the gradual shifting of beaches over time, potentially impacting coastal ecosystems and human structures.
3. Seasonal changes in wave patterns can alter the rate and direction of longshore drift, leading to variations in beach shape and composition throughout the year.
4. Structures like groins and jetties can disrupt longshore drift, leading to increased erosion on one side and sediment accumulation on the other.
5. Longshore drift plays a critical role in maintaining the balance of sediment along coastlines, which is vital for preventing excessive erosion and supporting coastal habitats.

Review Questions

• How does wave action contribute to longshore drift and what impact does this have on coastal landforms?
  • Wave action drives longshore drift by pushing sediment up the beach at an angle as waves approach the shore obliquely. The backwash then pulls the sediment straight down, creating a zigzag pattern of movement along the coast. This continuous process shapes coastal landforms, such as bars and spits, while also influencing beach profiles and overall beach stability over time.
• Discuss how human interventions, such as groins or jetties, affect longshore drift and what consequences this might have for nearby beaches.
  • Human interventions like groins or jetties are designed to stabilize shorelines but can disrupt natural longshore drift. By interrupting sediment transport, these structures can lead to erosion on one side while causing excessive deposition on the other. This imbalance may require further management efforts to maintain beach health, as it can create hotspots of erosion or sediment build-up that alter local ecosystems.
• Evaluate the importance of understanding longshore drift in planning effective coastal management strategies.
  • Understanding longshore drift is crucial for effective coastal management because it helps predict sediment movement and potential erosion hotspots. By analyzing how sediment is transported along coastlines, planners can design targeted interventions like beach nourishment or erosion control structures that work harmoniously with natural processes. Failing to consider longshore drift could lead to inefficient or harmful management practices that exacerbate erosion problems or disrupt local ecosystems.

Related terms

Wave Refraction: The bending of waves as they approach the shore at an angle, causing variations in wave energy and contributing to sediment transport along the coastline.

Beach Nourishment: A coastal management technique that involves adding sand or sediment to a beach to combat erosion and enhance its recreational value.

Tidal Currents: The horizontal movement of water caused by the rise and fall of tides, which can also affect sediment transport along the coast.