#5 Destructive vs constructive waves

On today's episode, I’m diving into the fascinating world of constructive and destructive waves. To understand these concepts, we first need to introduce the idea of an equilibrium beach profile—a shape formed by the constant interplay of destructive and constructive forces. Whenever these forces change, the beach profile adjusts until a new balance is achieved.

Destructive Forces

Destructive waves typically move sediment offshore. The main forces involved are:

1. Gravity

   • Keeps the sediment profile as flat as possible.

   • Fine sand forms gentler slopes, while coarser materials like gravel form steeper slopes.

   • Gravity acts independently of wave period.

2. Turbulence from Breaking Waves

   • Destabilizes sediment.

   • Often works with gravity to move sediment offshore.

3. Undertow

   • A current that moves water and sediment offshore.

   • Balances the water pushed toward the coast by incoming waves.

Constructive Forces

Constructive waves move sediment onshore, helping build up the beach profile. These forces include:

1. Bed Shear Stress

   • Caused by the asymmetrical movement of waves.

   • Results in a net onshore movement of sediment.

2. Wave Streaming

   • A current that moves towards the coast, aiding sediment transport.

3. Sediment Size and Fall Velocity

   • Larger particles fall faster through water.

   • This affects whether they move onshore or offshore.

The Role of Wave Period

The wave period plays a crucial role in shaping beach profiles:

• Longer wave periods

  • Waves break sooner with less turbulence.

  • Promote onshore sediment movement.

• Shorter wave periods

  • Create more turbulence.

  • Enhance offshore sediment movement.

Final Thoughts

Understanding these dynamics is essential for coastal management and education. It’s a complex concept, but I hope this explanation brings some clarity.

Until the next episode, thanks for listening.