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CHAPTER 8 Waves and Water Dynamics. Origin of waves Most waves wind-driven Most waves wind-driven Moving energy along ocean/air interface Moving energy.

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Presentation on theme: "CHAPTER 8 Waves and Water Dynamics. Origin of waves Most waves wind-driven Most waves wind-driven Moving energy along ocean/air interface Moving energy."— Presentation transcript:

1 CHAPTER 8 Waves and Water Dynamics

2 Origin of waves Most waves wind-driven Most waves wind-driven Moving energy along ocean/air interface Moving energy along ocean/air interface Wind main disturbing force Wind main disturbing force Boundary between and within fluids with different densities Boundary between and within fluids with different densities Air/ocean interface (ocean waves) Air/ocean interface (ocean waves) Air/air interface (atmospheric waves) Air/air interface (atmospheric waves) Water/water interface (internal waves) Water/water interface (internal waves)

3 Internal waves Fig. 8.1a Associated with pycnocline Associated with pycnocline Larger than surface waves Larger than surface waves Caused by tides, turbidity currents, winds, ships Caused by tides, turbidity currents, winds, ships Possible hazard for submarines Possible hazard for submarines

4 Other types of waves Splash wave Splash wave Coastal landslides, calving icebergs Coastal landslides, calving icebergs Seismic sea wave or tsunami Seismic sea wave or tsunami Sea floor movement Sea floor movement Tides Tides Gravitational attraction among Moon, Sun, and Earth Gravitational attraction among Moon, Sun, and Earth Wake Wake Ships Ships

5 Types of ocean waves Fig. 8.2

6 Wave motion Waves transmit energy Waves transmit energy Cyclic motion of particles in ocean Cyclic motion of particles in ocean Particles may move Particles may move Up and down Up and down Back and forth Back and forth Around and around Around and around Particles in ocean waves move in orbital paths Particles in ocean waves move in orbital paths

7 Progressive waves Waves travel without breaking Waves travel without breaking Longitudinal Longitudinal Transverse Transverse Orbital Orbital Orbital or interface waves Waves on ocean surface Waves on ocean surface Crest, trough, wave height (H) Crest, trough, wave height (H) Wavelength (L) Wavelength (L)

8 Fig. 8.3

9 Orbital waves Wave characteristics Wave characteristics Wave steepness = H/L Wave steepness = H/L If wave steepness > 1/7, wave breaks If wave steepness > 1/7, wave breaks Wave period (T) = time for one wavelength to pass fixed point Wave period (T) = time for one wavelength to pass fixed point Wave frequency = inverse of period or 1/T Wave frequency = inverse of period or 1/T

10 Circular orbital motion Water particles move in circle Water particles move in circle Movement up and down and Movement up and down and Back and forth Back and forth Fig. 8.4

11 Orbital motion Diameter of orbital motion decreases with depth of water Diameter of orbital motion decreases with depth of water Wave base = ½ L Wave base = ½ L Hardly any motion below wave base due to wave activity Hardly any motion below wave base due to wave activity Fig. 8.3C

12 Deep-water waves Water depth is greater than wave base (>1/2L) Water depth is greater than wave base (>1/2L) Wave speed (celerity) proportional to wavelength Wave speed (celerity) proportional to wavelength Fig. 8.5a

13 Shallow-water wave Water depth is < 1/20L Water depth is < 1/20L Celerity proportional to depth of water Celerity proportional to depth of water Fig. 8.5b

14 Transitional waves Characteristics of both deep and shallow-water waves Characteristics of both deep and shallow-water waves Celerity depends on both water depth and wavelength Celerity depends on both water depth and wavelength Fig. 8.5c

15 Wave development Most ocean waves wind-generated Most ocean waves wind-generated Capillary waves (ripples) formed first Capillary waves (ripples) formed first Rounded crests, very small wavelengths Rounded crests, very small wavelengths Increasing energy results in gravity waves Increasing energy results in gravity waves Symmetrical waves with longer wavelengths Symmetrical waves with longer wavelengths Increasing energy results in trochoidal waveforms Increasing energy results in trochoidal waveforms Crests pointed, troughs rounded, greater wave heights Crests pointed, troughs rounded, greater wave heights Sea = area where waves generated by storm Sea = area where waves generated by storm

16 Wave development Fig. 8.7

17 Wave development Fig. 8.8

18 Wave energy Factors that control wave energy Factors that control wave energy Wind speed Wind speed Wind duration Wind duration Fetch Fetch

19 Maximum wave height Reliable measurement Reliable measurement Wave height 34 m or 112 ft Wave height 34 m or 112 ft Fig. 8.10

20 Wave energy Fully developed sea Fully developed sea Maximum wave height, wavelength for particular fetch, speed, and duration of winds at equilibrium conditions Maximum wave height, wavelength for particular fetch, speed, and duration of winds at equilibrium conditions Swell Swell Uniform, symmetrical waves that travel outward from storm area Uniform, symmetrical waves that travel outward from storm area Long crests Long crests Transport energy long distances Transport energy long distances

21 Swell Longer wavelength waves travel faster and outdistance other waves Longer wavelength waves travel faster and outdistance other waves Wave train = group of waves with similar characteristics Wave train = group of waves with similar characteristics Sorting of waves by their wavelengths is wave dispersion Sorting of waves by their wavelengths is wave dispersion Wave train speed is ½ speed of individual wave Wave train speed is ½ speed of individual wave

22 Swell wave train Fig. 8.12

23 Wave interference patterns Different swells coming together Different swells coming together Constructive interference Constructive interference In-phase wave trains with about the same wavelengths In-phase wave trains with about the same wavelengths Destructive interference Destructive interference Out-of-phase wave trains with about the same wavelengths Out-of-phase wave trains with about the same wavelengths Mixed interference Mixed interference Two swells with different wavelengths and different wave heights Two swells with different wavelengths and different wave heights

24 Wave interference patterns Fig. 8.13

25 Waves approach shore Deep-water swell waves shoal Deep-water swell waves shoal Transitional waves Transitional waves Shallow-water waves Shallow-water waves Wave speed decreases Wave speed decreases Wavelength decreases Wavelength decreases Wave height increases Wave height increases Wave steepness increases Wave steepness increases Waves break Waves break Period remains constant Period remains constant

26 Shoaling waves Fig. 8.15

27 Breakers in surf zone Top of wave topples over base because of decrease in wave speed due to friction with sea floor Top of wave topples over base because of decrease in wave speed due to friction with sea floor Wave form not sustained Wave form not sustained Different types of breakers associated with different slope of sea floor Different types of breakers associated with different slope of sea floor

28 Spilling breaker Water slides down front slope of wave Water slides down front slope of wave Gently sloping sea floor Gently sloping sea floor Wave energy expended over longer distance Wave energy expended over longer distance

29 Plunging breaker Curling crest Curling crest Moderately steep sea floor Moderately steep sea floor Wave energy expended over shorter distance Wave energy expended over shorter distance Best for board surfers Best for board surfers

30 Surging breaker Breakers on shore Breakers on shore Steepest sea floor Steepest sea floor Energy spread over shortest distance Energy spread over shortest distance Best for body surfing Best for body surfing

31 Wave refraction As waves approach shore, they bend so wave crests are nearly parallel to shore As waves approach shore, they bend so wave crests are nearly parallel to shore Wave speed proportional to depth of water (shallow-water wave) Wave speed proportional to depth of water (shallow-water wave) Different segments of wave crest travel at different speeds Different segments of wave crest travel at different speeds

32 Wave refraction Fig. 8.17a

33 Wave energy distribution at shoreline Fig. 8.17b Energy focused on headland Energy focused on headland Headland eroded Headland eroded Energy dissipated in bay Energy dissipated in bay Bay filled up with sediment Bay filled up with sediment

34 Wave reflection Waves and wave energy bounced back from barrier Waves and wave energy bounced back from barrier Reflected wave can interfere with next incoming wave Reflected wave can interfere with next incoming wave Fig. 8.18

35 Standing waves Two waves with same wavelength moving in opposite directions Two waves with same wavelength moving in opposite directions Water particles move vertically and horizontally Water particles move vertically and horizontally Water sloshes back and forth Water sloshes back and forth Fig. 8.19

36 Tsunami or seismic sea wave Sudden changes in sea floor caused by Sudden changes in sea floor caused by Earthquakes, submarine landslides, volcanic eruptions Earthquakes, submarine landslides, volcanic eruptions Long wavelengths (> 200 km or 125 m) Long wavelengths (> 200 km or 125 m) Shallow-water wave Shallow-water wave Speed proportional to water depth so very fast in open ocean Speed proportional to water depth so very fast in open ocean Sea level can rise up to 40 m (131 ft) when tsunami reaches shore Sea level can rise up to 40 m (131 ft) when tsunami reaches shore

37 Tsunami or seismic sea wave Fig. 8.20a

38 Tsunami or seismic sea wave Most occur in Pacific Ocean (more earthquakes and volcanic eruptions) Most occur in Pacific Ocean (more earthquakes and volcanic eruptions) Damaging to coastal areas Damaging to coastal areas Loss of human lives Loss of human lives Example, Krakatau eruption (1883) in Indonesia created tsunami that killed more than 36,000 people Example, Krakatau eruption (1883) in Indonesia created tsunami that killed more than 36,000 people Example, Aura, Japan (1703) tsunami killed 100,000 people Example, Aura, Japan (1703) tsunami killed 100,000 people

39 Tsunami watches and warnings Pacific Tsunami Warming Center Pacific Tsunami Warming Center Seismic waves forecast possible tsunami Seismic waves forecast possible tsunami Tsunami watch Tsunami watch Tsunami warning Tsunami warning Evacuate people from coastal areas and send ships from harbors Evacuate people from coastal areas and send ships from harbors Increasing damage to property as more infrastructure constructed near shore Increasing damage to property as more infrastructure constructed near shore

40 Waves as a source of producing electricity Lots of energy associated with waves Lots of energy associated with waves Mostly with large storm waves Mostly with large storm waves How to protect power plants How to protect power plants How to produce power consistently How to produce power consistently Environmental issues Environmental issues Building power plants close to shore Building power plants close to shore Interfering with life and sediment movement Interfering with life and sediment movement Offshore power plants? Offshore power plants?

41 Wave power plant at Islay, Scotland Fig. 8.25b

42 Global coastal wave energy resources Fig. 8.26

43 End of CHAPTER 8 Waves and Water Dynamics Fig. 8A


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