Shoreline Processes and Features Chapter 16.3 Shoreline Processes and Features

A beach is the accumulation of sediment found along the shore of a lake or ocean. Each beach is very unique and different.

Forces Acting on the Shoreline Waves are constantly eroding, transporting, and depositing sediment. This changes the shape of the shoreline.

Wave Impact During storms waves can be very erosive. They can be large and have a lot of energy. This can cause crack and crevices in cliffs, coastal structures, and anything else the wave hits. Water is forced into every opening making the cracks.

Abrasion Abrasion is the sawing and grinding action of rock fragments in the water. This is why there are smooth, rounded stones and pebbles on the shore. Rock fragments can also cut into the land as they are pushed back and forth by a wave.

Wave Refraction Wave refraction is the bending of waves. This is caused by the shape of the shoreline. This causes wave energy to be different at different spots along the shore. This will impact the amount of erosion, sediment transport, and deposition that will take place. This means that erosion takes place fast on areas the jut out from the shore vs. for example a bay.

Longshore Transport Longshore current is when waves come into a beach at an angle. The water in the surf zone is turbulent. This makes it easy for longshore currents to move fine suspended sand and to roll larger sand and gravel along the bottom.

Erosional Features Shoreline features will be different based on the type of rock, the intensity of waves, the nature of coastal currents, and whether the coast is stable or not. Any shoreline feature that is make from mostly erosion are called erosional features. Depositional features are those that are made where materials have been deposited. In California the coast is being eroded 15-30 cm every year. We also have uplift of coastal land from plates. This causes features like cliffs and platforms, sea arches, and sea stacks.

Wave-Cut Cliffs and Platforms This is made from the cutting action of the surf against the base of coastal land.

Sea Arches and Sea Stacks Headlands that extend into the sea are eroded by waves. The softer and fractured rocks erode fastest. This may form a sea cave. When 2 caves open on opposite sides of a headland unite a sea arch forms. The arch will eventually fall in leaving part of the arch called a sea stack.

Depositional Features Spits – this is an elongated ridge of sand that goes from land to the mouth of a bay. A baymouth bar is a sand bar that closes off a bay. A tombolo is a ridge of sand that connects an island to the mainland or another island.

Barrier Islands Barrier islands are narrow sandbars that are separate from the shore but parallel to it.

Stabilizing the Shore Erosion at the coast causes a lot of damage and quickly. For those who live along the coast, they need to find ways to lessen the impact of erosion.

Protective Structures Groins, breakwaters, and seawalls and some protective structures that are built to lessen erosion or prevent the movement of sand along a beach. Groins are make to maintain or widen beaches that are losing sand. It is a barrier that traps sand that is moving. A breakwater protects boats from large waves. A seawall is similar. Seawalls will take much of the energy expended by waves.

Beach Nourishment This is the addition to large amounts of sand to a beach. The problem with is that these beaches will be washed away the same way that it washed the original beach away. This can harm marine life because many times different sand is brought in and it can affect the water.