What is Updrift and Downdrift?

What we call the updrift side. That means if you look at one individual groyne, the height of the beach on one side is considerably different to the other. The other side is called the downdrift side.

What is lee side erosion?

The transition area will therefore initially be exposed to a sediment deficit of 5, whereas the area close to the structure will receive 10. This will cause initial erosion as well as sand accumulation on the updrift side of the structure. This is the so-called lee side erosion.

What is a groyne in geography?

A groyne is a shore protection structure built perpendicular to the shoreline of the coast (or river), over the beach and into the shoreface (the area between the nearshore region and the inner continental shelf), to reduce longshore drift and trap sediments.

What is coastal erosion and accretion?

Coastal erosion and accretion are complex processes that need to be investigated from the angles of sediment motion under wind, wave and tidal current action; beach dynamics within a sediment/littoral cell; and human activities along the coast, within river catchments and watersheds and offshore, both at spatial and …

Is a groyne hard or soft engineering?

Groynes are relatively soft hard engineering techniques. They’re low lying wooden walls that extend out to sea. Groynes will remove a lot of the sand that’s present down-drift of the beach which will result in a thinner beach at this area.

How long is a groyne?

The life span of a groyne is around 25 years. They must be replaced periodically to ensure the coastline continues to be protected. The process for removing and replacing each groyne can take up to two months.

Why do beaches have groynes?

Groynes were originally installed along the coastline in 1915. Groynes control beach material and prevent undermining of the promenade seawall. Groynes interrupt wave action and protect the beach from being washed away by longshore drift. Longshore drift is the wave action that slowly erodes the beach.

Are groynes hard or soft engineering?

Examples of hard engineering include: Groynes – Low walls constructed at right angles to retain sediments that might otherwise be removed due to longshore drift. These structures absorb or reduce the energy of the waves and cause materials to be deposited on the updrift side of the groyne facing the longshore drift.

What is a breakwater groyne?

Breakwaternoun. On beaches: a wooden or concrete barrier, usually perpendicular to the shore, intended to prevent the movement of sand along a coast. Groynenoun. a protective structure of stone or concrete; extends from shore into the water to prevent a beach from washing away.

What are the 4 processes of coastal erosion?

Destructive waves erode through four main processes; Hydraulic Action, Compression, Abrasion and Attrition. Image credit: Jeff Hansen, U.S. Geological Survey. Hydraulic Action is the sheer force of water crashing against the coastline causing material to be dislodged and carried away by the sea.

Why is coastal erosion a problem?

Coastal areas have been changing with erosion and sand movement for ages. It becomes a problem when human activity speeds up erosion, or when buildings and roads are close enough to the ocean to be damaged. In these cases, beach erosion can cause flooding, and can even make whole buildings collapse.

How does a groyne work?

How do groynes work? When waves approach a beach at an angle, they tend to move sediment along the beach. When there is a barrier in the beach, such as a groyne, this captures sand which is moving along a coast and thus builds up a beach.