Important Announcement The first prelim will be held

Important Announcement • The first prelim will be held during regular class time on Thursday 21 February • A short in-class review will be held Tuesday 19 February to go over student submitted questions • Submit review questions to Yianna Samuel (ys 88@cornell. edu) by Friday 15 February

Why Study Waves?

Wave Prediction and Shipping

Wave Prediction and Construction of Coastal Structures

Wave Prediction and Construction of Off-Shore Structures

Wave-Induced Beach Erosion and Sediment Transport

Wave Prediction and Recreation

Fundamental Principles

Wave Parameters • Wave Period = Time it Takes a Wave Crest to Travel one Wavelength (units of time) • Wave Frequency = Number of Crests Passing A Fixed Location per Unit Time (units of 1/time) • Wave Speed = Distance a Wave Crest Travels per Unit Time (units of distance/time) • Wave Steepness = Wave Height/Wavelength

Constructive, Destructive and Mixed Addition of Two Waves Constructive Destructive Mixed

Ideal Deep-Water Waves Propagate Energy not Mass

Two Critical Points to Note About Wave Speeds • Deep-Water Waves (Bottom Depth > L/2) – Speed is a Function of Wavelength Only – Waves with Longer Wavelength move faster than Waves with Shorter Wavelength • Shallow-Water Waves (Bottom Depth < L/20) – Speed is a Function of Depth Only – Waves Travel Slower in Shallower Water Irrespective of Wavelength as long as Depth < L/20 Note: L = wavelength _________ Note that there is also an intermediate region (L/20 < Depth < L/2) where Wave Speed is a Function of Both Wavelength & Depth

Speed of Deep-Water and Shallow. Water Waves as a Function of Wavelength and Depth

Deep-Water and Shallow-Water Wave Regions

The Size of Wind Generated Waves is a Function of: 1. Wind Speed 2. Duration of Wind 3. Fetch - the distance over which wind can blow without obstruction

The Importance of Fetch

Full Developed Waves (Unlimited by Fetch and Duration)

Lateral Spreading of Wave Energy from a Storm Source (95% of Energy Contained Within ± 45 o of Storm Direction)

Wave Measurement Methods

Wave Height Measured with Bottom-Moored Pressure Sensor

Significant Wave Heights Derived from the Shape of the Returned Beam on the Topex-Poseidon Altimeter

The Distribution of Wave Energy as a Function of Wave Period or Wavelength…

Distribution of Wave Energy in the Ocean as a Function of Wave Frequency or Wavelength

Some Interesting Things About Waves…

Wave Dispersion: Self Sorting of Deep-Water Waves Leaving a Storm Region based on Wavelength. It Occurs Because Longer Wavelength Waves Travel Faster than Shorter Wavelength Waves (for Deep Water).

Wave Refraction: Bending of Shallow-Water Wave Fronts Due to Change in Bottom Depth. The Leading Edge of a Wave Front Enters Shallower Water and Slows While the Remaining Front Continues at Higher Speed. The Net Result is a Rotation of Wave Fronts To Become Parallel with Bottom Depth Contours.

Consequence of Wave Refraction Focusing and Defocusing of Wave Energy on Headlands and Bays, Respectively

Wave Diffraction

Wave Diffraction

Along Shore Sediment Transport

Along-Shore Sediment Transport Obstructed by Groins

Initiation and Propagation of a Tsunami

Motion of Seiche Caused by a Storm Over a Semi-Enclosed Body of Water

Internal Waves Travel along Density Discontinuities in the Ocean Interior

Thin Layers of Phytoplankton Oscillating with an Internal Wave Formed along the Continental Shelf

Kelvin and Rossby Waves - Planetary Waves -

Rossby Waves in the Equatorial Pacific

Summary Points 1. Waves Propagate Energy and not Mass 2. Waves Add Constructively or Destructively 3. Deep-Water Wave Speed is a Function of Wavelength 4. Shallow-Water Wave Speed is a Function of Bottom Depth 5. Wave Dispersion: Sorting of Deep-Water Waves Based on Wavelength 6. Wave Refraction: Bending of Shallow-Water Waves Based on Depth 7. Wave Height Determined by: Wind Speed, Wind Duration and Fetch

8. Waves Hitting a Shore Obliquely Will Cause along Shore Transport of Sediment 9. Constructed Structures such a Groins will Block the Along Shore Sediment Transport 10. Tsunami are Generated by Underwater Earthquakes or Landslides and Propagate across Whole Ocean Basins 11. Seiches are Standing Waves formed in Semi. Enclosed Bodies of Water 12. Internal Waves Propagate along Density Discontinuities (Pycnoclines) in the Ocean Interior 13. Kelvin and Rossby Waves are Important Planetary Wave