Introduction to Waves
There are two types; constructive and destructive waves. As their names suggest constructive adds to the beaches and coastlines whilst destructive takes away and destroys.
Swash & Backwash
Swash is the water that rushes up the beach and as it rushes up the beach. It can push sand, sediment, and even pebbles and rocks.
In contrast, backwash as the name suggests is the opposite. Once the water has pushed up as far as it can, it then rushes back down the beach with the force of gravity. As it rushes back down it carries with it sand and pebbles.
Destructive Waves
We can tell this is a destructive wave because it has a weak swash and a strong backwash. This means that very little sediment will be pushed higher up the beach or deposited. Instead, the water will rush back to sea and carry with it sand and sediment from the beach. Thus destroying the beach over time. The weak swash and strong backwash are in part created by the fact the destructive wave has a forward-moving crest that crashes down at about a 120-degree angle. This directs the energy downwards at the beach. They are common when slow-moving waves approach a steep shingle beach. The wave frequency is about 13 to 15 per minute. Additionally, the motion of the water in the wave remains circular because of a deeper nearshore zone,
Constructive Waves
Constructive works in the opposite way. They are usually found where nearshore depths are shallow such as a gentle sandy beach. In contrast to destructive waves that often have a steep approach. The swash is more powerful than the backwash, and sediment is moved up a beach, making it wider. Waves break with a frequency of about 6 to 8 per minute. This allows each wave to complete its cycle so the swash is not interrupted. The motion of water in the wave is elliptical, giving a strong forward movement. The energy of the backwash is reduced as the water percolates through the beach material, rather than running off the surface. If the wave is approaching at an angle to the beach it may push sediments into semicircles, creating a feature known as beach cusps.
Types of Wave Summary Table
| Feature | Constructive Waves | Destructive Waves |
|---|---|---|
| Swash Strength | More powerful swash, moving sediment up the beach, making it wider | Weak swash, very little sediment pushed higher up the beach |
| Backwash Strength | Weaker backwash, allowing sediment to percolate through the beach material | Strong backwash, carrying sand and sediment back to the sea |
| Wave Crest Direction | Forward-moving crest with a gentle approach | Forward-moving crest crashing down at a 120-degree angle, directing energy downwards at the beach |
| Beach Impact | Builds up the beach over time, making it wider and depositing sediment | Destroys the beach over time, carrying away sand and sediment |
| Frequency of Waves | About six to eight waves per minute | About 13 to 15 waves per minute |
| Motion of Water in the Wave | Elliptical motion, providing a strong forward movement | Circular motion, directed downwards at the beach due to the 120-degree angle of the crest |
| Beach Appearance | May push larger sediments into semicircles, creating beach cusps | Little sediment pushed, leading to a narrower and eroded beach |
