Surfs Up!All About Waves at     the Coast         Prof. Tom Herrington  Ocean Engineering Program Director     Stevens Ins...
Tonight’s Lecture• What happens when waves reach the  coast• Surf zone currents• Wave & beach interactions• Shoreline evol...
Anatomy of a Wave                                   L                                         H                  2       ...
Wave Growth
Wave Development Limit
Fully developed seas
Interesting Mathematical Wave Properties• Wave are dispersive  (longer waves move                                 gk tan...
-In Deep-Water -Waves have Ideal Shape and thusPropagate Energy  but not Mass
Deep and Shallow-Water Wave Regions
Wave Motion and Particle Motion            Progressive WavesWaves which interact with the sea floor are known as shallow-w...
Wave Refraction
Wave Refraction:Bending of Shallow-Water Wave Fronts Dueto Change in BottomDepth. The LeadingEdge of a Wave FrontEnters Sh...
Wave Focusing and Spreading
Examples      Headland FocusingEmbayment wave spreading
Wave train breaking                 Really amazing rule of thumbBreaking wave height can be estimated by:       Hb  0.78h
Waves Break by Plunging and Spilling• depends on the  slope of the bottom
Surf Similarity Parameter• Ratio of slope steepness and local wave  steepness  ξ> 2.0 – surging/collapsing breaker  2.0 ...
Plunging wavesPlunging Breaker atAvon-by-the-Sea, NJSpilling Breaker atOcean City, NJ
Surf Zone Physical Processes• Currents in the surf  zone are generated  by the variation in  Wave Height across  surf zone...
Cape May, NJoblique wave approach
Flow in the Surf Zone is Very Complex!            From Svendsen and Lorenz (1989)
Alongshore Current ForcingVL  41.4S gHb sin  b cos b S    : beach slope  g   : gravity Hb     : breaking wave height b...
Longshore Currents
Cross-shore wave generated motion          Svendsen, et al. (1987)
Cross-shore Current ForcingWave setup balancesthe gradient in thecross-shore directedradiation stress     dS xx       dR...
What is a Rip Current?• Narrow seaward  moving current of up  to 3 knots• Related to mass  transfer of water  trough the b...
Flow through gaps in the sandbar            system          Hass, et al. (2000)
Rip Current Formation between Groins
When do Rip Currents Occur?…Extremely Large Wave Events…            …Tropical Cyclone Swells…                             ...
…Low energy Wave Events…July 5, 200344009: Hm0=3 ft, Tp=6 secOver 100 rescues along NJ coast
Analysis of Observed Rip Current Events                 In New Jersey•    Revealed 2 conditions:    1. Extreme waves (> 8 ...
Rip Current Index• In order to weight large swell  higher than wind waves and  smaller swell a Rip Current                ...
Evaluation of Rip Current Index Against known Events in 2003                                                           Isa...
What about Notched Groins?  What are these things?
Current and Sediment Measurements Near Notched                     Groin
-5                              -1010          0             -10      5                             -15              -5   ...
Measured Alongshore Current through Notched                  Groin                Rankin, et al. (2003)
Waves as Agents of Coastal Change• Shoreline Changes occur on many temporal scales:   –   Seconds (Every wave)   –   Daily...
Seasonal Coastal Changes• The cross-shore extent of  the beach undergoes  erosion and accretion on  a seasonal basis   – I...
How Do We Know This?
Seasonal Beach Changes
We even know where motion stops…Depth of ClosureHallermeier (1981) and Birkemeier (1985)                        H e2    ...
…and which way the sand is moving!                                          3                     H          H          ...
Episodic Change:       Driven by 3 Components1. Extreme astronomical tides2. Storm surge  generated by intense storms or p...
Prolonged storm surge at Atlantic   City during March 1962 Nor’easter                                    Water Level recor...
Large-scale DamageOcean City, NJ. Note the transport of water across the island by waves
How can we predict potential storm damage?Not Easily!
ResultsNot so conclusive• Longer storm  duration more  important than  wave height and  surge unless…• If duration is  abo...
Wave Climate Long Term Coastal Change
How do we know this?• Wave Hindcasts based  on historic weather data• Offshore Buoy Data• Neashore Wave Data
Long Term Wave Climate                                       Wave Height Distribution by Month (1980 - 1999)              ...
We can use this to our advantage!                                          WAVE DIRECTION & PERCENT OCCURRENCE            ...
Long Branch Feeder Beach
Shoreline     Evolution• Elevation Change   • Offshore contours     are becoming     parallel to shoreline   • Deflation o...
Long Term Change (Sea-level Rise)
Recent Sea Level Changes            • 18,000 years ago, at the              height of the last              glaciation, se...
Global Temp and Sea level changes for past 18,000 years         based on radiometric age dating of corals
Modern Record Sea level rise about 30 cm/century    speculation: greenhouse gas>>global warming >>melting ice             ...
Falling               Rising 1-3mm               1-3mm Rising            Rising 1-3mm            3-5mmFalling5+mm         ...
Tectonic Factors Affecting        Sea Level     Glacial Rebound
North American Glacial                    ReboundRebound occurs much moreslowly than ice melting.Even though the ice hasbe...
What does the future hold?Projected sea-level rise for the 21st century. The projected range of global-averaged sea-level ...
Considerable Uncertainty
What does this mean for the Coast?        INCREASED FLOOD LEVELS              Adjusted Flood Levels at Atlantic CityStormM...
What does this mean for the Coast?      Change in MHHW Line                                     2100                      ...
Food for Thought ?         May 4, 2012Changes in the speed that ice travels in more than 200 outlet glaciers indicatesthat...
Thank youUseful Data Sources:        Waves: http://www.ndbc.noaa.gov/        Tides: http://tidesandcurrents.noaa.gov/     ...
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East Coast MARE Ocean Lecture May 16, 2012 - Surf's Up! All About Waves at the Coast

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East Coast MARE hosted an Ocean Lecture & Educators’ Night for teachers focused on bringing ocean literacy to students in New Jersey. Dr. Tom Herrington of Stevens Institute of Technology presented the scientific lecture on May 16, 2012. For more information visit http://coseenow.net/mare/opportunities-resources/ocean-lecture-educators-night/.

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East Coast MARE Ocean Lecture May 16, 2012 - Surf's Up! All About Waves at the Coast

  1. Surfs Up!All About Waves at the Coast Prof. Tom Herrington Ocean Engineering Program Director Stevens Institute of Technology
  2. Tonight’s Lecture• What happens when waves reach the coast• Surf zone currents• Wave & beach interactions• Shoreline evolution• Shoreline of the future
  3. Anatomy of a Wave L H 2  h T T (Always Constant for an individual wave)Wave Number: k  2 Wave Phase Speed C  L L T
  4. Wave Growth
  5. Wave Development Limit
  6. Fully developed seas
  7. Interesting Mathematical Wave Properties• Wave are dispersive (longer waves move   gk tanh( ) 2 kh  2  2  2h  2 faster) period and length are not independent!   g tanh  T  L  L • In deep water (h>L/2) Lo  gT 2 C  L  gT 2 T 2 tanh(kh) ~ 1.0• In shallow water (h<L/20) tanh(kh) ~ kh L  ghT C  gh• Between deep and  2  2 2  2h    g tanh  shallow water must use  T  L  L  full equation 
  8. -In Deep-Water -Waves have Ideal Shape and thusPropagate Energy but not Mass
  9. Deep and Shallow-Water Wave Regions
  10. Wave Motion and Particle Motion Progressive WavesWaves which interact with the sea floor are known as shallow-water waves. The orbits of the water molecules become elliptical.
  11. Wave Refraction
  12. Wave Refraction:Bending of Shallow-Water Wave Fronts Dueto Change in BottomDepth. The LeadingEdge of a Wave FrontEnters Shallower Waterand Slows While theRemaining FrontContinues at HigherSpeed. The Net Result isa Rotation of WaveFronts To BecomeParallel with BottomDepth Contours.
  13. Wave Focusing and Spreading
  14. Examples Headland FocusingEmbayment wave spreading
  15. Wave train breaking Really amazing rule of thumbBreaking wave height can be estimated by: Hb  0.78h
  16. Waves Break by Plunging and Spilling• depends on the slope of the bottom
  17. Surf Similarity Parameter• Ratio of slope steepness and local wave steepness ξ> 2.0 – surging/collapsing breaker 2.0 <ξ< 0.4 – plunging ξ< 0.4 – spilling
  18. Plunging wavesPlunging Breaker atAvon-by-the-Sea, NJSpilling Breaker atOcean City, NJ
  19. Surf Zone Physical Processes• Currents in the surf zone are generated by the variation in Wave Height across surf zone and the angle at which the waves approach the coast.• Generates both cross-shore and alongshore currents
  20. Cape May, NJoblique wave approach
  21. Flow in the Surf Zone is Very Complex! From Svendsen and Lorenz (1989)
  22. Alongshore Current ForcingVL  41.4S gHb sin  b cos b S : beach slope g : gravity Hb : breaking wave height b : wave angle at breaking Longuet-Higgens (1970)
  23. Longshore Currents
  24. Cross-shore wave generated motion Svendsen, et al. (1987)
  25. Cross-shore Current ForcingWave setup balancesthe gradient in thecross-shore directedradiation stress dS xx dR   gh dx dx 3 S xx  gdH 2 Masselink and Black (1995) 16
  26. What is a Rip Current?• Narrow seaward moving current of up to 3 knots• Related to mass transfer of water trough the breaker zone
  27. Flow through gaps in the sandbar system Hass, et al. (2000)
  28. Rip Current Formation between Groins
  29. When do Rip Currents Occur?…Extremely Large Wave Events… …Tropical Cyclone Swells… Hurricane FabianApril 18, 2003Ocean City, NJ Sept. 4, 200344009: Hm0=13 ft, Tp =10 sec Surf City, LBISurfer/Lifeguard drowned at this beach 44009: Hm0=5.75 ft, Tp=14 sec
  30. …Low energy Wave Events…July 5, 200344009: Hm0=3 ft, Tp=6 secOver 100 rescues along NJ coast
  31. Analysis of Observed Rip Current Events In New Jersey• Revealed 2 conditions: 1. Extreme waves (> 8 ft) with periods > 8 sec 2. Long-period swell of any height• Rate of wave energy propagation to coast appears to be important P  nEC
  32. Rip Current Index• In order to weight large swell higher than wind waves and smaller swell a Rip Current H Pswell Index (RI) that is the ratio of RI  0.1* * swell energy flux to wind h Pwindwave wave energy flux multiplied by the ratio of the wave height to water depth appears reasonable.• Developed from wave buoy data located 20 n.m. off NJand Stevens Coastal Monitoring Network
  33. Evaluation of Rip Current Index Against known Events in 2003 Isabel July 4th Fabian Juan
  34. What about Notched Groins? What are these things?
  35. Current and Sediment Measurements Near Notched Groin
  36. -5 -1010 0 -10 5 -15 -5 -15 10 -15
  37. Measured Alongshore Current through Notched Groin Rankin, et al. (2003)
  38. Waves as Agents of Coastal Change• Shoreline Changes occur on many temporal scales: – Seconds (Every wave) – Daily (Tides) – Seasonally (Changing wave climate) – Decadal (Extreme storms) – Centuries (Sea level changes) – Millennia (Global climate changes)
  39. Seasonal Coastal Changes• The cross-shore extent of the beach undergoes erosion and accretion on a seasonal basis – In the summer and fall, small waves transport sand up onto the beach – In the winter and spring, large storm waves erode sand – Transition provides natural protection for the beach.
  40. How Do We Know This?
  41. Seasonal Beach Changes
  42. We even know where motion stops…Depth of ClosureHallermeier (1981) and Birkemeier (1985)  H e2  hc  1.75 H e  57.9 2   gT   e 
  43. …and which way the sand is moving! 3 H H   critical   0.00070  wT   L  s  3Profile Transitions between eroded H  H  critical  wT   0.00070 (“bar”) profile and accreted (”berm”)profile on a seasonal basis L  s  Kraus and Larson (1988)
  44. Episodic Change: Driven by 3 Components1. Extreme astronomical tides2. Storm surge generated by intense storms or prolonged onshore winds can generate significant departures from predicted water elevations and wave attack high up on beach berm.3. Large waves generate mass transport of water toward coast, increasing flood levels and extent of wave attack.
  45. Prolonged storm surge at Atlantic City during March 1962 Nor’easter Water Level recorded at Atlantic City Steel PierStorm Evolution March 5 – 8, 1962
  46. Large-scale DamageOcean City, NJ. Note the transport of water across the island by waves
  47. How can we predict potential storm damage?Not Easily!
  48. ResultsNot so conclusive• Longer storm duration more important than wave height and surge unless…• If duration is about equal wave heights dominate
  49. Wave Climate Long Term Coastal Change
  50. How do we know this?• Wave Hindcasts based on historic weather data• Offshore Buoy Data• Neashore Wave Data
  51. Long Term Wave Climate Wave Height Distribution by Month (1980 - 1999) 5.00 4.50 4.00 3.50Wave Height (ft) 3.00 2.50 2.00 127 130 1.50 135 1.00 138 0.50 140 0.00 145 1 2 3 4 5 6 7 8 9 10 11 12 Month of Year Pecent Occurrence of Wave Direction November (1980 - 1999) 12.0 127 130 10.0 135 138 140 8.0 Occurrence (%) 6.0 4.0 2.0 0.0 0 45 90 135 180 225 270 315 360 Direction (deg N)
  52. We can use this to our advantage! WAVE DIRECTION & PERCENT OCCURRENCE Long Branch, NJ 40 35 30 Occurrence (%) 25 20 15 10 5 0 0 45 90 135 180 Direction (deg N)
  53. Long Branch Feeder Beach
  54. Shoreline Evolution• Elevation Change • Offshore contours are becoming parallel to shoreline • Deflation of feeder feature • 100,000 cu.yds. Per year transport to north
  55. Long Term Change (Sea-level Rise)
  56. Recent Sea Level Changes • 18,000 years ago, at the height of the last glaciation, sea level was 130 m lower than today. • Sea level continues to rise by about 1 foot per century in New York City. • A rise in sea level of up to a meter is predicted for the coming century.
  57. Global Temp and Sea level changes for past 18,000 years based on radiometric age dating of corals
  58. Modern Record Sea level rise about 30 cm/century speculation: greenhouse gas>>global warming >>melting ice NJ Tide Gauge Records 3.8 mm/yr in New Jersey
  59. Falling Rising 1-3mm 1-3mm Rising Rising 1-3mm 3-5mmFalling5+mm Rising 5-10mm
  60. Tectonic Factors Affecting Sea Level Glacial Rebound
  61. North American Glacial ReboundRebound occurs much moreslowly than ice melting.Even though the ice hasbeen gone for 10,000years, North America is stillrebounding at 1 to 2 mm/yr.
  62. What does the future hold?Projected sea-level rise for the 21st century. The projected range of global-averaged sea-level rise fromthe IPCC (2001) assessment report for the period 1990–2100 is shown by the lines and shading (thedark shading is the model average envelope for the range of greenhouse gas scenarios considered, thelight shading is the envelope for all models and for the range of scenarios, and the outer lines includean allowance for an additional land-ice uncertainty). The AR4 IPCC projections (90% confidence limits)made in 2007 are shown by the bars plotted at 2095, the magenta bar is the range of model projectionsand the red bar is the extended range to allow for the potential but poorly quantified additionalcontribution from a dynamic response of the Greenland and Antarctic Ice Sheets to global warming.
  63. Considerable Uncertainty
  64. What does this mean for the Coast? INCREASED FLOOD LEVELS Adjusted Flood Levels at Atlantic CityStormMeas. Elev.1Surge2012221003Sept. 1944 8.96 ft 4.17 ft 9.81 ft 11.43 ftMarch 1962 8.80 ft 3.43 ft 9.42 ft 11.05 ftDec. 1992 9.14 ft 4.28 ft 9.39 ft 11.01 ftOct. 1991 8.93 ft 4.48 ft 9.19 ft 10.81 ft1. Relative to MLLW at Atlantic City2. Adjusted for historic sea level rise of 3.8 mm/yr3. Adjusted for IPPC Max Sea Level Rise Projection of 1.9 ft by 2100
  65. What does this mean for the Coast? Change in MHHW Line 2100 1990 80 – 100 ft
  66. Food for Thought ? May 4, 2012Changes in the speed that ice travels in more than 200 outlet glaciers indicatesthat Greenlands contribution to rising sea level in the 21st century could besignificantly less than the upper limits some scientists thought possible.The finding comes from a paper funded by the National Science Foundation(NSF) and NASA and published in todays journal Science.
  67. Thank youUseful Data Sources: Waves: http://www.ndbc.noaa.gov/ Tides: http://tidesandcurrents.noaa.gov/ Stevens: http://hudson.dl.stevens-tech.edu/maritimeforecast/ Stevens Storm Surge: http://hudson.dl.stevens-tech.edu/SSWS/ NJ Beach Data: http://www.gannet.stockton.edu/crc/index.asp

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