O

Wave base

Offshore

B

Mainland Bay

Lagoon

Barrier beach

Spit

6 Infobase Publishing

Ocean

Summer profile or gently landward sloping. The backshore area is usually dry and above the high-water mark except during large storms, so the backshore area is mainly affected and shaped by wind. some backshore areas are characterized by multiple berms, and others have none. on gravel beaches, found in high-energy environments, the backshore area may be replaced by a storm ridge marked by a ridge of gravel that may be several to 10 feet (3 m) high. These ridges form because incoming waves have the velocity to move gravels up the beach face, but since these gravels are porous, the water sinks into the gravel before it can drag the gravel back down the beach face, causing its accumulation in a large ridge.

Beaches are highly variable in the width and heights of these various zones. some beaches are steep, whereas others are flat. Beaches that have flat slopes are said to be dissipative in that they take the energy from waves and gradually dissipate it across the intertidal zone. These types of beaches often have multiple sand bars in the nearshore environment. Reflective beaches are those with steep gradients, and these tend to take much of the wave energy and reflect it back to sea. Reflective beaches do not gener ally have nearshore bars and are erosive. Dissipative beaches tend to be depositional, as they are actively accreting sediment.

The shape of a beach is largely controlled by the nature of the waves, tides, currents, and, to a lesser extent, wind. Waves move the sediment onshore, and are then transported along the beach face by the longshore currents, and perhaps blown to the backshore by wind. Tides change the areas to which waves direct their energy vertically up and down, bringing the sediment alternatively to different sections of the beach. out of all these processes, the currents produced by the waves on the beach are the most important. These currents include longshore currents, rip currents, onshore-offshore currents produced in the swash zone, and combined currents.

Beaches are very dynamic environments and are always changing, being eroded and redeposited constantly from day to day and from season to season. They are typically eroded to thin strips, known as storm beaches, by strong winter storms and built up considerably during summer, when storms tend to be less intense. The wide summer beaches are known as accretionary beaches. The processes controlling this ft!

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