coastal defence

Question 1

Groynes

Answer 1

A groyne is a wall made either of concrete or strong wooden posts and planks. It extends from the coastline to the level of low tide. It is designed to halt longshore drift. The groyne acts as a sand trap. Sand piles up on the side facing the direction from which longshore drift advances. Usually a series of groynes is built along a beach. Piers and breakwaters have a similar effect on longshore drift to groynes

Groynes are successful in preventing a beach from being removed. In some places, such as a tourist resort, it is essential to keep a large beach from being eroded away. Tourists visit the resort so that they can relax on the beach. But groynes can stop sand from reaching places further down the coast. These places can experience more severe erosion.

Question 2

Sea walls

Answer 2

In places where there are violent waves, the coast can be protected from erosion by the building of sea walls. Many sea walls have a concave vertical face to deflect the force of the waves. Some sea walls have a long sloping ramp on the seaward side. This helps to dissipate the energy of the waves. Sea walls have the disadvantage of blocking out views of the sea

Question 3

Breakwaters

Answer 3

Breakwaters are generally shore-parallel structures that reduce the amount of wave energy reaching the protected area. They are similar to natural bars, reefs or near-shore islands and are designed to dissipate wave energy. The reduction in wave energy slows the littoral drift, produces sediment deposition and a shoreline bulge or “salient” feature in the sheltered area behind the breakwater. Some longshore sediment transport may continue along the coast behind the nearshore breakwater.

Question 4

Headland Breakwaters

Answer 4

A series of breakwaters constructed in an “attached” fashion to the shoreline and angled in the direction of predominant wave approach such that the shoreline behind the features evolves into a natural “crenulate” or log spiral embayment

Question 5

Detached Breakwaters

Answer 5

As the name implies, these are breakwaters that are constructed away from the shoreline, usually a slight distance offshore. They are detached” from the shoreline, and are designed to promote beach deposition on their leeside.

Question 6

Single Breakwater

Answer 6

Single breakwaters may be attached or detached depending on what they are being designed to protect. A single detached breakwater may protect a small section of shoreline. A single attached breakwater, may be a long structure designed to shelter marinas or harbors from wave action

Question 7

Beach nourishment

Answer 7

Beach nourishment is carried out in places where the sand is being eroded, or where a beach is an important recreational resource. Sand and shingle are brought to the new beach from elsewhere. Alternatively, sediments are dredged and pumped from one side of a groyne to the other.