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Waves and Coastal Interactions

Waves and Coastal Interactions. Stan Piotrowski. What is a wave?. Types of Waves. Type of wave produced is dependent on the type of swell, wind direction, slope of sea bed, and bathymetric features (canyons, ridges) Groundswell- far off coast Wind swell- formed from local winds (choppy)

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Waves and Coastal Interactions

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  1. Waves and Coastal Interactions Stan Piotrowski

  2. What is a wave?

  3. Types of Waves • Type of wave produced is dependent on the type of swell, wind direction, slope of sea bed, and bathymetric features (canyons, ridges) • Groundswell- far off coast • Wind swell- formed from local winds (choppy) • Offshore/Onshore winds • Deep water waves- h/λ> 1/4 • Shallow water waves- 1/20 > h/λ

  4. Winds • Generate waves – wind speed, duration, and fetch • Onshore – blow over wave crests, causing them to break in a rough froth • Offshore – push the face of the wave up, generally steepen waves

  5. Why do waves break? • Shoaling- amplitude increases, wavelength remains constant • Deep water waves- break when wave steepness exceeds 0.17– H > 0.17λ • Shallow water waves- individual waves break when their wave height H is larger than 0.8 times the water depth (h)– H > 0.8h

  6. Types of Breaking Waves • Spilling • Plunging • Surging • Iribarren Number (surf familiarity parameter) • Breaker Depth Index

  7. Spilling Breakers • ξ < 0.5 • Gently sloping coasts where waves break slowly and over a long distance • Relatively gentle waves

  8. Plunging Breakers • 0.5 < ξ < 3.3 • Steeper coastlines • Form on reefs or sandbars • Wave face becomes vertical, then drops onto the trough, releasing most of its energy at once • Tube/Closeout

  9. Teahupoo • No “back” of the wave • Parts of the reef are only 20 inches deep • Depths plummet to 1,000 feet 1/3 mile offshore

  10. Surging Breakers • ξ < 0.5 • Rapid drop offs – no shoaling zone

  11. Longshore Currents • Currents running parallel to the shoreline • Occur most often when waves approach shoreline at an angle • Larger waves – faster currents • Strongest currents generated on gently sloping beaches

  12. Rip Currents • Strong seaward flowing channel • Typically flow at 1-2 ft/s, and can be as fast as 8 ft/s • Wave set-up • Generally only temporary, but can persist for long periods of time due to man-made structures

  13. Wave Power • Single buoy can generate enough electricity to power 40 homes in NJ • Future wave power station in Oregon, comprised of 10 buoys, will generate 1.5 megawatts – enough electricity to power about 1,000 homes

  14. Sources • www.noaa.org • www.meted.ucar.edu • www.oceanpowertechnologies.com

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