5. coastal - The Coast is Clear Gulf Shores Benefit Concert...

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The Coast is Clear Gulf Shores Benefit Concert July 11, 2010 response to BP Horizon disaster
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Lecture 5: Coastal Processes Hurricane Isabelle, Avalon, NJ 9/18/2003 December Nor’easter, LBI, 12/1993 December Nor’easter, LBI, 12/1993 December Nor’easter, LBI, 12/1992
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Waves
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The Perfect Storm
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Coastal Basics Measuring waves Wave height Wavelength Period (= 1/frequency) Velocity Size of waves generated on the open water depends on: 1) Wind strength 2) Duration of wind blowing in a consistent direction 3) Distance over which the wind blows (called the fetch)
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Wave movement
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Figure 9-6 In deep areas, movement of water within a wave is circular, but the size of the circle decreases downward to a depth of about half a wavelength. As waves approach shore and reach areas where the water depth is less than half a wavelength, movement within the wave becomes increasingly elliptical. Slowed by friction with the bottom, the troughs travel more slowly than the crests, causing the wave’s height to increase and its wavelength to decrease. Waves in Deep and Shallow Water
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Waves orbital motion of water (e.g., "bobbing") threshold critical v f(orb. v, grain size and wave period ) at /2, bottom effects result in elliptical orbits λ generates a "to-fro" motion Shoreface shoaling zone to-from low Tide-Mean Wave base breaking zone orbital V> wave v shoreface; <1.3 H (i.e., 3 ft wave breaks in 4 ft water) surf zone turbulence Foreshore swash zone up/down intertidal
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Beach and shoreface
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Most waves approach at angle
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Figure 9-8 Waves that approach shore obliquely undergo refraction, becoming more parallel to the shoreline as friction slows the parts of the waves that enter shallow water first. (b) Refraction focuses wave energy on headlands, resulting in conversion of the headland into an island. Wave Refraction
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Nearshore Currents Longshore drift—movement of sediment by longshore currents Waves wash up the face of the beach at an angle, carrying sediment up the shore Water washes back down the slope of the beach, carrying sediment grains directly back to the shore Beach drift—movement of sediment along the shore These longshore currents also transport sediment along the coast Rip currents—plume-shaped currents conveying the water from breaking waves back through the surf zone
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Figure 9-9 Waves that approach the shore obliquely create longshore currents parallel to the beach that can transport sediment along the coast. They also move sand grains in a zigzag motion along the beach. Longshore Drift
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Rip currents
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Tides
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Tides Sea level fluctuates between 2 high and 2 low tides each day Caused by gravitational interactions among Earth, Moon, Sun But especially between Earth and the Moon Tidal range—amount of rise and fall during a tidal cycle Varies from day to day Varies due to location of the Moon relative to Earth and the Sun Spring tides—2 times in lunar month that tidal ranges are greatest Neap tides—when tidal ranges are the least
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This note was uploaded on 12/16/2011 for the course SEA CHANGE 110 taught by Professor Miller during the Spring '11 term at Rutgers.

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5. coastal - The Coast is Clear Gulf Shores Benefit Concert...

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