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Field Trip Preparation

Field Trip Preparation. When: Tues. Mar. 30th, 2008, 8am - 6pm Where: Leave from Williamson Loading Dock

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Field Trip Preparation

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  1. Field Trip Preparation When: Tues. Mar. 30th, 2008, 8am - 6pm Where: Leave from Williamson Loading Dock What: ~3 stops, one paleo-coastal, the rest modern coastal, we’ll measure beach profiles, dig a trench, do a short beach walk, talk about waves, tides, and currents, and have lunch (either bring your own or ?) Who: You all and me. Vehicles? Check the weather and dress appropriately * We will discuss particulars in greater detail on Thursday in class.

  2. Early Numerical Models

  3. Early Numerical Models

  4. More Recent Numerical Models

  5. More Recent Numerical Models Solitary Wave Runup on a beach

  6. More Recent Numerical Models 3-D Weakly Plunging Breaking Wave on a Beach

  7. More Recent Numerical Models 3-D Weakly Plunging Breaking Wave on a Beach

  8. Wave Breaking Condition – g (gamma) - ratio of Hb to hb Is this a constant? some disagreement = 0.73 --> 1.03, from lab studies of monochromatic waves For a given wave steepness, the higher the beach slope, the greater the value of b

  9. Breaker Height Prediction - various forms Munk (1949) - based on Solitary Wave Theory Komar and Gaughan (1972) - based on Airy Wave Theory Kaminsky and Kraus (1993) - based on Lab Measurements

  10. Wave Breaking Exercise – Solitary Solution >> H=1; T=20; L=9.8*(T^2)/(2*pi), S=H/L, Hb_s=H/(3.3*((S)^(1/3))) L =623.8874 S = 0.0016 Hb_s = 2.5893 >> H=2; T=10; L=9.8*(T^2)/(2*pi), S=H/L, Hb_s=H/(3.3*((S)^(1/3))) L = 155.9718 S = 0.0128 Hb_s = 2.5893 >> H=3; T=8; L=9.8*(T^2)/(2*pi), S=H/L, Hb_s=H/(3.3*((S)^(1/3))) L = 99.8220 S = 0.0301 Hb_s = 2.9240 >> H=4; T=15; L=9.8*(T^2)/(2*pi), S=H/L, Hb_s=H/(3.3*((S)^(1/3))) L = 350.9366 S = 0.0114 Hb_s = 5.3860 >> H=5; T=15; L=9.8*(T^2)/(2*pi), S=H/L, Hb_s=H/(3.3*((S)^(1/3))) L = 350.9366 S = 0.0142 Hb_s = 6.2499

  11. Breaker Height Prediction - reconfigured Data span 3 orders of magnitude of breaker heights Remarkably well-behaved data ----->

  12. Plunge Distance

  13. Surf Zone Wave Decay and Energy Dissipation Steep, reflective beaches - Wave breaking (and energy dissipation) is concentrated through plunging breakers. Broken wave surges up the beach as runup. Villano Beach Wave energy dissipation pattern depends on morphology of the beach Low-slope, dissipative beaches - Extensive, wide surf zone over which spilling breakers dissipate energy. At any time, several broken wave bores, and smaller unbroken waves, are visible. Anastasia Island

  14. Reasons for understanding surf zone wave decay Understanding the patterns of wave decay in the surf zone is important for two significant reasons: Wave energy dissipation is inversely related to the alongshore pattern of wave energy delivery -- so it can help identify relative vulnerability of coastal property. Wave energy expenditure is partially transformed into nearshore currents, which are responsible for sediment transport and beach morphologic modification.

  15. Thornton & Guza (1982) - Torrey Pines Beach Torrey Pines Beach – fine sand with minimal bars and troughs. Wave staffs and current meters - measurements from 10 m water depth to inner surf zone. Published the distributions of wave breaking within the surf zone on a natural beach

  16. Measurements of Wave Breaking Distributions Histograms of breaking wave height distributions illustrate a greater fraction of broken waves at shallower depths. Histograms of all waves in nearshore (broken and unbroken) show skewed distributions -- many small waves and few large waves -- comparable to that of a Rayleigh distribution, which also describe the distribution of deep water wave heights. Histograms of broken waves only (cross hatched pattern) show a more uniform distribution. 1. Constant H and T - Lab channel - easy to determine breaking conditions. 2. Natural setting - range of H and T, so surf zone witnesses range of broken/unbroken waves/bores. Unbroken = Rayleigh distributions Broken = Modified distributions

  17. Energy Saturation of Broken Waves

  18. Surf wave heights after initial breaking

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