waves and tides

Waves Overview

• Introduction to Waves

  • Discusses the significance and impact of waves in various contexts.

• Importance of Waves

  • Surfing:

  • Waves provide recreational opportunities through surfing.

  • Economic impact on tourism and local economies.

  • Beach Erosion:

  • Waves contribute to beach erosion, affecting tourism and necessitating sand replenishment efforts.

  • Storm Surge & Coastal Flooding:

  • Waves influence storm surges, leading to coastal flooding, and require mitigation planning.

  • Navigation Hazards:

  • Affect ship routing and necessitate insurance for cargo lost at sea.

  • Climate Influence:

  • Waves and bubbles mediate ocean uptake of CO2, influencing climate change dynamics.

  • White caps on waves enhance albedo by reflecting sunlight.

  • Weather Interaction:

  • Waves facilitate the exchange between the atmosphere and the ocean, impacting weather patterns.

Types of Waves

• Wave Formation

  • Waves form primarily due to wind and can be classified based on their properties:

  • Main types include:

  • Wind-generated Waves:

    • Occur due to the wind's interaction with the ocean surface.

  • Deep-water Waves:

    • Waves that exist where the water depth is greater than half the wavelength.

  • Shallow-water Waves:

    • Waves that occur in water shallower than half their wavelength.

  • Tsunamis:

    • Large ocean waves caused by underwater seismic activity.

  • Seiches:

    • Standing waves caused by atmospheric pressure changes or seismic events.

  • Wave Energy:

    • The potential energy carried by waves can be harnessed for power generation.

• Waves Move Energy, Not Water

  • Waves primarily transport energy across the ocean surface rather than significant volumes of water itself.

Key Properties of Waves

• Wave Characteristics

  • Crest:

  • The highest point of a wave.

  • Trough:

  • The lowest point of a wave.

  • Wavelength (L):

  • Distance between two consecutive crests or troughs.

  • Frequency (f):

  • The number of wave crests passing a fixed point in one second (measured in Hz).

  • Period (T):

  • The time taken for one full wavelength to pass a fixed point; related to frequency as $(f = \frac{1}{T})$.

  • Wave Height (H):

  • The vertical distance between the crest and trough.

  • Steepness:

  • Ratio of wave height to wavelength ($H/L$).

    • If steepness ratio exceeds 1/7, waves tend to break.

Types of Disturbing Forces and Restoring Forces

Wind Waves & Beaufort Wind Force Scale

• Creating Wind Waves

  • Occur due to:

  • Strong wind:

    • The force of wind must be strong to create significant waves.

  • Duration:

    • Waves are influenced by how long the wind blows.

  • Fetch:

    • The distance over which the wind blows uninterruptedly will also affect wave development.

• Beaufort Wind Force Scale

  • A scale used to measure wind speed and its effects on the sea.

  • Originally devised by Sir Francis Beaufort in 1805, it describes wind conditions based on observed sea states.

  • The scale ranges from:

  • 0 (Calm):

    • Smoke rises vertically; no significant wave action.

  • 1 (Light Air):

    • 1-3 mph, leaves rustle, small ripples appear.

  • 2-5:

    • Ranges from light to fresh breezes, with increasing wave action.

  • 6-12 (Gale, Storm, Hurricane):

    • Describes conditions from strong breezes to severe storms with significant wave heights and destruction.

Mathematical Foundations of Waves

• Wave Speed Calculations

  • Wave speed can be calculated depending on the characteristics of deep and shallow water waves.

  • For deep-water waves, the speed (C) increases with wavelength.

  • Wave height and particle speed variations occur based on the water depth relative to wavelength.

Behaviors of Waves in Relation to Water Depth

• Transitional Waves:

  • Waves transition between shallow and deep waters influence behavior.

• Influence of Water Depth:

  • Deep-water waves ($depth > \frac{1}{2}L$) maintain speed and wavelength over large distances.

  • Shallow-water waves change speed and height as they approach land, leading to wave breaking.

Tsunamis

• Formation & Characteristics:

  • Tsunamis form primarily due to seismic activities such as underwater earthquakes.

  • They can travel as fast as 450 mph in oceans, making tsunami detection crucial.

  • Considered identifiable as shallow-water waves despite their large wavelengths due to their behavior influenced by ocean depth.

• Understanding Tsunami Movement:

  • Tsunami waves carry more energy compared to regular waves and can result in substantial destruction when they reach coastal areas.

Tides

• Basic Characteristics of Tides:

  • Caused by gravitational interactions between Earth, Moon, and the Sun, leading to water bulging out on opposite sides of Earth.

  • Tidal cycles consist of two high and two low tides approximately every 24 hours and 50 minutes due to the Moon's orbit.

• Tidal Types:

  • Diurnal Tides:

  • One high and one low tide per day.

  • Semidiurnal Tides:

  • Two high and two low tides per day.

  • Spring & Neap Tides:

  • Spring Tides: Occur during full and new moons when tidal forces are aligned for maximal impact.

  • Neap Tides: Occur during the first and third quarters of the moon when solar and lunar forces are at right angles.

Practical Applications & Future Considerations

• Wave Prediction Models:

  • Various coastal data programs create models to predict wave behavior for safety and economic considerations.

  • Wave energy harnessing holds potential for sustainable energy development, with theoretical potentials reaching significant numbers (e.g., 2.64 trillion kW hrs in U.S. coastal waters).

• Climate Change Implications:

  • Changes in climate affecting wind patterns may lead to changes in wave behavior and associated risks along coasts.

• Testing Understanding:

  • Key review questions and understanding checks regarding wave dynamics and tidal behaviors discussed throughout the document serve as a self-assessment tool for comprehension.