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

10. 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

11. 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

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

14. 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

16. 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

18. 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

21. Sources www.noaa.org www.meted.ucar.edu www.oceanpowertechnologies.com