COASTAL EROSION
Processes Causing Coastal Erosion
WHAT DO THESE WORDS MEAN?
- Erosion - the process by which the surface of the earth is worn away by the action of water, glaciers, winds, waves, etc.
- Plunging wave -generally occurs where the amplitude reaches the point that the crest of the wave actually overturns
- Spilling wave -turbulent white water spilling down the face of the wave.
- Prevailing wind -winds that blow predominantly from a single general direction over a particular point on Earth's surface
- Swash - turbulent layer of water that washes up on the beach after an incoming wave has broken.
- Backwash - the water that rolls back down a beach after a wave has broken
- Deposition - process by which material is added to a land form or land mass.
- Long shore drift -transportation of sediments (generally sand but may also consist of coarser sediments such as gravels) along a coast at an angle to the shoreline.
- Undercutting - To create an overhang by cutting material away from, as in carving.
- Slip plain – a plain on which one type of rock sits another causing the upper rock to slip
- Erosion - the process by which the surface of the earth is worn away by the action of water, glaciers, winds, waves, etc.
- Plunging wave -generally occurs where the amplitude reaches the point that the crest of the wave actually overturns
- Spilling wave -turbulent white water spilling down the face of the wave.
- Prevailing wind -winds that blow predominantly from a single general direction over a particular point on Earth's surface
- Swash - turbulent layer of water that washes up on the beach after an incoming wave has broken.
- Backwash - the water that rolls back down a beach after a wave has broken
- Deposition - process by which material is added to a land form or land mass.
- Long shore drift -transportation of sediments (generally sand but may also consist of coarser sediments such as gravels) along a coast at an angle to the shoreline.
- Undercutting - To create an overhang by cutting material away from, as in carving.
- Slip plain – a plain on which one type of rock sits another causing the upper rock to slip
Diagrams showing different wave types, beach erosion, & sea cliff erosion.
As well as wave action processes, two other processes co exist. These processes are erosional processes and meteorological processes (weather), meteorological processes are discussed in the flooding section.
Physical Changes to the land due to coastal erosion
Sand Dune Removal
When the wave action processes are so strong, they may take sand dunes away. This can effect people living on the coast either directly or indirectly.
Vegetation Loss
When the sea erodes away at the sand dunes - vegetation is lost. When this vegetation is taken away the sand dune becomes unstable as there is nothing in the dune to support the sand - therefore more sand is taken away. In measures to protect the vegetation on a sand dune the dune itself will be fenced off to protect it from the public walking on them and disturbing them.
Sand Removal
Sand removal occurs at almost every beach. When sand is taken from a beach it is quite often returned, however, in some case the sand will be taken permanently leaving a rocky beach such as the one in the photo.
Longshore Drift
The sand is slowly moved along the shore. When the wave retreats the sand is taken out with the wave. When the wave rushes back onto the shore it takes sand with it on an angle creating long shore drift, This process can move sand hundreds of kilometers.
Sand Bar Development
When the sand is taken out by the backwash it is deposited off shore in a sand bar. For anyone who is into surfing or fishing you will quite often be able to witness the sandbar when you are out in the water.
Cliff Collapse
When water saturates the cliffs enough the cliff face will become unstable therefore slipping into the sea.
Cave, Arch & Sea Stack Formation
Caves are formed when a weak area of rock is eroded. Wave action processes eventually erode a small cave into the rock face which eventually turns into a larger cave and then into an arch. When the top of the arch becomes weak then it collapses creating a sea stack.
Coastal Erosion effects on people
Coastal erosion has many different effects on people. The two types we will look at are direct impact and in direct impact.
Direct Impact
•Sand dunes erode
•Cliffs Collapse
•Human activities and property are affected immediately
Indirect Impact
•Sand dunes and cliffs weakened by the storms later erode further or collapse
•Human activities and properties are affected later
Direct Impact
•Sand dunes erode
•Cliffs Collapse
•Human activities and property are affected immediately
Indirect Impact
•Sand dunes and cliffs weakened by the storms later erode further or collapse
•Human activities and properties are affected later
Coastal Erosion increasing and decreasing the effects
There are many ways that people are able to increase and decrease the effects of a flood. The first section looks at how people increase the effects.
INCREASING THE EFFECTS OF A FLOOD
INCREASING THE EFFECTS OF A FLOOD
Possible protection measures
Seawalls
Seawalls are a great measure to stop erosion. However seawalls are extremely expensive and timely to build. Seawalls also create reflection therefore when waves bring sand in (swash) the waves are reflected back out to sea taking the sand with them. There is not room for deposition, especially in rough storms.
Groynes and sand sausages
Groynes and sand sausages stop the transportation of sand along the beach (long shore drift). These are another great protection measure, however, they are pretty ugly looking and can be a hazard for surf lifeguards getting vehicles along the beach. They are also vulnerable to vandalism.
Sand replenishment
In certain areas sand is replaced on the beach so that long shore drift can take the sand along the beach. This is an expensive and timely measure but extremely successful.
Sand Dune Development
By planting on sand dunes it encourages new growth which is able to stabilize the dunes in a storm. The only difficulty in this situation is keeping people off the dunes so they don't disturb the new growth.
Offshore breakwaters
Off shore breakwaters the beach from erosion. They also slow the process of long shore drift. They act as an off shore reef. Breaking any big surf that travels ashore.
Activity 1
In the diagram below - list all of the measures used to protect a community from coastal erosion. Regulation and Relocation have been given to you already but you should be able to get a few more in each of those columns. For answers CLICK HERE.