Coastal ProcessesWave Processes and Shore ErosionSlide 3Slide 4Slide 5Slide 6BeachesWave Refraction and Cliffed Coasts Refer to pages 361-362.Erosional Remnants of Cliffed Coastlines Eroded by Wave RefractionLongshore Drift Refer to pages 361-362.Seasonal Beach Winter/Summer Beach Profile Refer to pages 363-365.Storm Response Loss of Sand from the Beach Refer to pages 364-367.Barrier IslandsSlide 14Slide 15Barrier islands are places of change and motion.Slide 17Slide 18Barrier islands are places of change and motion. Refer to pages 367-371.Slide 20SeawallsSeawalls Refer to pages 374-376.Sea CliffsGroins Refer to pages 374-376.Jetties Refer to pages 374-376.Breakwaters and Artificial Reefs Refer to pages 374-376.Beach Replenishment Refer to pages 376-380.Beach Replenishment Refer to pages 376-380.1Coastal ProcessesChapter 13Waves, Beaches And Coastal ErosionRivers of Sand2Wave Processes and Shore ErosionWaves form as wind blows over the ocean surface. Waves increase in size with the following factors: •greater wind velocity•greater amount of time the wind blows•greater fetchRefer to pages 356-360.Wave Processes and Shore Erosion3Wave height and wavelength increase with increasing energy.•wave height -- the vertical distance from low point (trough) to high point (crest)•wavelength -- the horizontal distance from one crest to the next crestRefer to pages 356-360.4In deep water the wave form itself moves, but the water does not have net forward motion -- instead the water travels in circlular orbits (right). The circular motion of the water fades downward to a depth equal to ~half the wavelength, called wave base (below).Refer to pages 356-360.Wave Processes and Shore Erosion5Wave Processes and Shore ErosionAt a water depth equal to or less than half the wave length, the waves begin to ‘feel bottom’. The crest of the wave moves forward as the base drags on the bottom. This causes the waves to bunch up (wavelengths decrease) and grow taller (wave heights increase). Refer to pages 356-360.6Wave Processes and Shore ErosionEventually the waves oversteepen, causing them to tumble toward the shore, or break, and the water moves landwardRefer to pages 356-360.Beaches7Beaches are accumulations of sand or gravel supplied bySea Cliff Erosionand byRiver Transport of Sediment to the Coast.The sand and gravel supplied to the coast is then moved by wave action.8Wave Refraction and Cliffed CoastsRefer to pages 361-362.Wave refraction is the bending of waves to conform to the shape of the coastline.Wave refraction concentrates wave energy on headlands and deposits the products of that erosion in bays, ultimately straightening the coastline.9Erosional Remnants of Cliffed Coastlines Eroded by Wave RefractionLongshore DriftRefer to pages 361-362.10Longshore drift in parts of coastal California averages 750,000 m3/year, or the equivalent of 2,000 10m3 dumptrucks per day.Longshore drift along the East Coast averages 75,000 m3/year.The gradual migration of sand along the shoreline.Sand grains are pushed up onto the beach in the direction of wave travel. Gravity pulls it back directly down the slope of the beach.We measure longshore drift by the volume of sand moved in cubic meters per year.11Seasonal BeachWinter/Summer Beach ProfileRefer to pages 363-365.Storm Response Loss of Sand from the BeachRefer to pages 364-367.12Top: This beach in California was eroded by waves during a storm event.Right: But was naturally rebuilt by 1998Larger waves and storm surge erode sand from the shallow portion of the beach and transport much of it just offshore. Much of the eroded material comes from the surface of the beach, eroding it to a flatter profile.Barrier Islands13Barrier islands are long, narrow, offshore deposits of sand that parallel the coast line, separated from the main land by a shallow sound, bay or lagoon. They are the products of dynamic coastline processes: erosion, deposition, longshore drift, and wind transport.Barrier Islands14Barrier islands are often found in chains along the coast line and are separated from each other by narrow tidal inlets.A baymouth barrier is a barrier beach that is attached at both ends to the mainland and backed by a bay or lagoon. A spit is a protrusion or linear beach extending from the mainland.Barrier Islands15Most barrier islands in North America are along the Atlantic Coast. The photograph at left shows the barrier islands off of Long Island and New Jersey. These islands extend almost continuously south to Georgia.Barrier islands are places of change and motion. 16Longshore drift moves sand from one beach to another.Islands grow and shrink depending on the amount of sediment available (dams, sand mining, hardening). Sea level rise causes them to erode and to shift toward the mainland over time. An island that is migrating toward the mainland is termed retrograding. In most cases an island that is retrograding undergoes a process known as "island rollover".17Two forms of evidence that show an island is rolling over are washovers and exposed marsh mud and oyster shells on the beach.Barrier islands are places of change and motion.18Barrier islands are places of change and motion. This figure shows how Hog Island, Virginia, has changed over the past 150 years, as a result of hurricanes and wave erosion. The dashed lines show the former shorelines of the island. Entire towns, such as the once-thriving community of Broadwater, have disappeared into the ocean as the barrier has shifted toward the mainland.19Barrier islands maintain their equilibrium profile by migrating shoreward with rising sea level. Because many barrier islands are now covered with buildings, the island cannot migrate but is progressively eroded. Barrier islands are places of change and motion.Refer to pages 367-371.20Seawalls21Seawalls are structures constructed parallel to the coastline and are generally used as a last resort to protect property landward of an already eroded, small beach. They may be constructed of concrete, large stones (riprap), wood, or other material and are essentially built to repel the sea.22SeawallsRefer to pages 374-376.Seawalls accelerate erosion as water hits the sea wall with high energy and retreats with high energy. The beach narrows and becomes steeper and the water in front of the seawall deepens. As a result, bigger waves approach closer to shore, hastening erosion and removal of the beach.Seawalls require costly repair. Large storm waves
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