WednesdayMarch 28, 2012

(Beach and Shoreline

Processes and Features)

The Launch PadWednesday, 3/28/12

Explain the process of “beach drift.”When waves wash up onto shore, they

don’t always hit at 90o to the beach. They will wash up at the angle of the wind.

However, when the water recedes back from the beach, it is usually at 90o.

Therefore, the angle of swash doesn’t equal the angle of backwash, and a zigzag pattern is set up. This will steadily move

the material on the beach down the coastline.

Assignment Currently Open

Summative or Formative Date Issued Date Due

Date Into Grade Speed

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Quiz 23 S4 3/9 3/9 3/9 3/30

WS – Ocean Water

MovementsF 3/19 3/21

WS – Ocean Surface

CirculationF 3/20 3/22

Quiz 24 S5 3/23 3/23

WS - The Coastal Zone and Waves F 3/27 3/30

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Continue WorksheetThe Coastal Zone and

Waves

Wave ErosionWave erosion is caused by

wave impact and pressure.

Wave erosion breaks down rock material and

supplies sand to beaches.

The sawing and grinding action of water armed with rock fragments is

called abrasion.

Sand Movement on the BeachBeaches are composed of

whatever material is available.

Sand Movement on the BeachSome

beaches have a

significant biological

component.

Sand Movement on the BeachBeach material does not stay

in one place.Wave energy moves large quantities of sand parallel and perpendicular to the

shoreline.

Beach and Shoreline Processes

The result of wave refraction is that wave energy is concentrated against the sides and

ends of headland. Wave erosion straightens an irregular

shoreline

Wave refraction is the bending of a wave so that the wave arrives

parallel to the shore

Beach and Shoreline Processes

Longshore transport consists of the movement of sediments (generally

sand, but may also consist of coarser sediments such

as gravels) along a coast at an angle to the shoreline,

which is dependent on prevailing wind direction.

Beach and Shoreline ProcessesBeach drift is one of the most important transport mechanisms results from wave

refraction.

Since waves rarely break onto a shore at right angles, the upward movement of

water onto the beach (swash) occurs at an oblique angle.

However, the return of water (backwash) is at right angles to the beach, resulting in the net movement of beach material

laterally.

This movement is known as beach drift.

The endless cycle of swash and backwash and resulting beach drift can be observed on all beaches. – sediment

moves in a zigzag pattern along the beach face.

Beach and Shoreline Processes

Longshore current is current that flows in the

surf zone.

Longshore current flows parallel to the shore,

and moves substantially more sediment than

beach drift.

Beach Drift and Longshore Currents

Figure 15.18

Shoreline Features Shoreline features created by

erosional effects include:Wave-cut cliffs

Wave-cut platforms Marine terraces

Sea archesSea stacks

Figure 15.24 A

A Sea Stack and a Sea Arch

Figure 15.21

Shoreline Features Depositional Features

A spit is a ridge of sand extending from

the land into the mouth of an

adjacent bay with an end that often hooks

landward.

Figure 15.24 C

Shoreline Features Depositional Features

A baymouth bar is a sand bar that

completely crosses a bay.

Aerial View of a Spit and

Baymouth Bar Along the

Massachusetts CoastlineFigure 15.22 A

Shoreline Features Depositional Features

A tombolo is a ridge of sand that

connects an island to the

mainland.

Figure 15.24 B

Shoreline Features Depositional Features

Barrier islands occur mainly along the Atlantic and Gulf Coastal Plains.

They run parallel the coast and can originate

in several ways.

Stabilizing the Shore Shoreline erosion is influenced

by several local factors –the proximity to sediment-

laden rivers –the degree of tectonic

activity –the topography and

composition of the land –the prevailing wind and

weather patterns –the configuration of the

coastline

Stabilizing the Shore Responses to Erosion Problems

“Hard stabilization” refers to building structures to lessen the

effects of shoreline erosion.Types of structures

Groins are barriers built at a right angles to the beach that are

designed to trap sand.Breakwaters are barriers built

offshore and parallel to the coast to protect boats from breaking

waves.Seawalls armors the coast against

the force of breaking waves. Often these structures are not

effective.

Stabilizing the Shore Responses to Erosion Problems

Alternatives to hard stabilization:

In beach nourishment, sand is added to the beach

system. Relocating buildings away from a beach

Miami Beach Before and After Beach Nourishment

Figure 15.28 A

Stabilizing the Shore Responses to Erosion Problems

Shoreline erosion problems are different along the different U.S.

coasts.Along the Atlantic and Gulf Coasts, development occurs

mainly on barrier islands that face the open ocean.

These islands receive the full force of storms.

Development has taken place more rapidly than our

understanding of barrier island dynamics.

Stabilizing the Shore Responses to Erosion Problems

Shoreline erosion problems are different along the different U.S. coasts.

The Pacific Coast is characterized by relatively narrow beaches

backed by steep cliffs and mountain ranges.

The major problem here is the narrowing of the beaches.

Sediment for beaches is interrupted by dams and

reservoirs; therefore, rapid erosion occurs along the beaches.