Coastal sediment is primarily transported by wave action along the coastline. This movement is largely facilitated by a process known as longshore drift.
Understanding Longshore Drift
Longshore drift is the dominant mechanism for coastal sediment transport. It occurs because waves rarely approach the shoreline perfectly parallel.
- Angled Wave Approach: Waves typically approach the coast at an angle.
- Swash: The swash (water rushing up the beach) moves sediment up the beach at the same angle as the approaching wave.
- Backwash: The backwash (water returning down the beach) flows directly back down the slope due to gravity.
- Net Movement: This creates a zig-zag pattern, resulting in a net movement of sediment along the coastline.
Other Contributing Factors
While longshore drift is the primary method, other factors can contribute to coastal sediment transport:
- Tidal Currents: Strong tidal currents can move sediment, particularly in estuaries and inlets.
- Storms: Storms generate larger waves and stronger currents, capable of transporting significant amounts of sediment over short periods. This includes erosion and deposition.
- River Input: Rivers carry sediment from inland areas to the coast, which then becomes subject to coastal transport processes.
- Wind: Wind can directly transport fine sediment, particularly sand, creating dunes and influencing beach morphology.
Human Impacts
Human activities can also influence coastal sediment transport:
- Coastal Defenses: Structures like groynes, breakwaters, and seawalls can disrupt longshore drift patterns, leading to sediment accumulation in some areas and erosion in others.
- Dredging: Dredging activities can remove sediment from the coastal system, altering sediment budgets and potentially increasing erosion.
- Dam Construction: Dams trap sediment upstream, reducing the amount of sediment that reaches the coast and potentially exacerbating erosion problems.
Summary
In conclusion, coastal sediment is transported primarily by longshore drift, which is driven by the angled approach of waves to the shoreline. Other factors, such as tidal currents, storms, river input, and human activities, also play a role in this dynamic process.
