Earth Surface Processes Unit 9 ReviewCoastal Processes: Waves & Tides

Key Concepts and Terminology

• Coastal zone encompasses the interface between land and sea, including both the terrestrial and marine environments
• Littoral zone extends from the shoreline to the depth where sediment is no longer moved by waves, typically around 10-20 meters deep
• Fetch refers to the distance over which wind blows across open water, influencing wave size and energy
• Wave height measures the vertical distance between a wave's crest and trough, while wavelength is the horizontal distance between two consecutive crests or troughs
• Wave period represents the time it takes for two consecutive crests or troughs to pass a fixed point
• Tides are the rise and fall of sea levels caused by the gravitational pull of the moon and sun, as well as the Earth's rotation
• Spring tides occur during new and full moons when the sun and moon's gravitational forces align, resulting in higher high tides and lower low tides
• Neap tides happen during the first and third quarter moons when the sun and moon's gravitational forces are perpendicular, leading to lower high tides and higher low tides

Coastal Dynamics and Energy Sources

• Coastal dynamics involve the complex interactions between waves, tides, currents, and sediment transport that shape coastlines over time
• Wind stress transfers energy from the atmosphere to the ocean surface, generating waves and surface currents
• Wave energy is proportional to the square of wave height, with larger waves possessing more energy to erode and transport sediment
• Tidal energy is derived from the gravitational pull of the moon and sun, causing regular fluctuations in sea level and generating tidal currents
• Longshore currents are generated by waves approaching the shoreline at an angle, causing water and sediment to move parallel to the coast
• Rip currents are strong, narrow channels of water that flow seaward from the shore, often associated with breaking waves and can pose a hazard to swimmers
• Coastal upwelling occurs when wind-driven currents move surface water offshore, causing deeper, nutrient-rich water to rise and replace it, supporting high biological productivity

Wave Formation and Characteristics

• Waves are generated by wind blowing over the ocean surface, transferring energy from the atmosphere to the water
• As wind speed, duration, and fetch increase, waves become larger and more powerful
• Wave height is influenced by wind speed, fetch, and duration, with stronger winds, longer fetches, and more time leading to higher waves
• Wavelength depends on wave period, with longer period waves having greater wavelengths
• Wave steepness is the ratio of wave height to wavelength, with steeper waves more likely to break and dissipate energy
• As waves approach shallow water, they begin to interact with the seafloor, causing them to slow down, increase in height, and eventually break
• Wave refraction occurs when waves approach the shore at an angle, causing them to bend and align more parallel to the shoreline
  • Refraction focuses wave energy on headlands and disperses it in bays, influencing erosion and deposition patterns

Types of Waves and Their Impacts

• Wind waves are generated by local wind conditions and are the most common type of wave in the coastal zone
  • Wind waves are typically short-period (5-15 seconds) and have a wide range of heights depending on wind conditions
• Swell waves are generated by distant storms and have traveled far from their origin, losing energy and becoming more organized
  • Swell waves have longer periods (10-20 seconds) and are more regular in shape and direction than wind waves
• Tsunami waves are generated by sudden displacements of water, often caused by earthquakes, landslides, or volcanic eruptions
  • Tsunami waves have extremely long wavelengths (up to hundreds of kilometers) and can travel at speeds up to 800 km/h in deep water
• Storm surges are temporary increases in sea level caused by strong winds and low atmospheric pressure associated with storms
  • Storm surges can cause significant coastal flooding and erosion, particularly when combined with high tides
• Rogue waves are exceptionally large and unpredictable waves that can pose a serious hazard to ships and coastal structures
• Internal waves occur within the water column at the interface between layers of different densities, such as thermoclines or haloclines
  • Internal waves can influence mixing and nutrient distribution in coastal waters

Tidal Processes and Patterns

• Tides are driven by the gravitational pull of the moon and sun, as well as the Earth's rotation
• The moon's gravitational influence is about twice that of the sun due to its proximity to Earth
• Tidal range is the vertical difference between high and low tide, varying depending on location and tidal cycle
• Diurnal tides have one high and one low tide per lunar day (24 hours and 50 minutes), common in the Gulf of Mexico and Southeast Asia
• Semidiurnal tides have two high and two low tides per lunar day, with each high and low tide of approximately equal height, prevalent along the U.S. Atlantic coast
• Mixed semidiurnal tides have two high and two low tides per lunar day, but with significant differences in the heights of successive high and low tides, found along the U.S. Pacific coast
• Tidal currents are the horizontal movement of water associated with the rise and fall of tides, influencing sediment transport and navigation
• Tidal prism refers to the volume of water that flows into and out of an estuary or bay during a tidal cycle, influencing water exchange and mixing

Coastal Erosion and Sediment Transport

• Coastal erosion is the removal and transport of sediment from the shoreline by waves, currents, and tides
• Sediment transport occurs through three main processes: bedload, suspended load, and dissolved load
  • Bedload refers to the movement of sediment along the seafloor by rolling, sliding, or saltation
  • Suspended load is the transport of sediment within the water column by turbulence and currents
  • Dissolved load is the transport of ions and molecules in solution, typically negligible in coastal sediment budgets
• Longshore transport is the movement of sediment parallel to the shoreline, driven by oblique wave approach and longshore currents
• Cross-shore transport is the movement of sediment perpendicular to the shoreline, influenced by wave orbital motion and rip currents
• Sediment budget refers to the balance between sediment inputs (e.g., rivers, cliff erosion) and outputs (e.g., longshore transport, offshore transport) in a coastal system
• Human activities, such as dam construction, sand mining, and coastal development, can significantly alter sediment budgets and exacerbate coastal erosion
• Sea-level rise, associated with climate change, can increase the vulnerability of coastlines to erosion by allowing waves to reach higher elevations and increasing the frequency of coastal flooding

Coastal Landforms and Features

• Beaches are accumulations of sediment along the shoreline, shaped by waves and tides
  • Beach profiles typically include a berm (a flat, elevated portion) and a beach face (a sloping section extending into the water)
• Barrier islands are elongated, narrow islands that run parallel to the mainland coast, separated by a lagoon or bay
  • Barrier islands are dynamic features that migrate in response to changes in sea level, sediment supply, and storm activity
• Spits are elongated ridges of sand or gravel that extend from the mainland coast, formed by longshore drift
  • Spits often have a curved or hooked shape due to wave refraction and changing shoreline orientation
• Tombolos are sand or gravel bars that connect an offshore island to the mainland or another island, formed by wave refraction and sediment deposition
• Estuaries are partially enclosed coastal water bodies where freshwater from rivers mixes with saltwater from the ocean
  • Estuaries are highly productive ecosystems that provide critical habitats for many species and support diverse human activities
• Deltas are accumulations of sediment at the mouth of a river, formed by the deposition of sediment as the river flow slows and spreads upon entering the ocean
  • Delta morphology varies depending on the balance between river, wave, and tidal influences (e.g., river-dominated, wave-dominated, or tide-dominated deltas)
• Rocky coasts are characterized by resistant bedrock formations that are eroded by waves and weathering processes
  • Erosional features on rocky coasts include cliffs, sea caves, arches, and sea stacks, which reflect the interplay between rock strength and wave energy

Human Interactions and Coastal Management

• Coastal zones are highly valued for their natural resources, economic opportunities, and recreational amenities, leading to intense human development and use
• Coastal development, such as the construction of buildings, roads, and ports, can alter natural coastal processes and increase the vulnerability of communities to coastal hazards
• Coastal engineering structures, such as seawalls, groins, and breakwaters, are designed to protect shorelines from erosion and flooding, but can have unintended consequences
  • Seawalls can reflect wave energy and cause increased erosion at the base of the structure and on adjacent unprotected shorelines
  • Groins can trap sediment on the updrift side, leading to erosion on the downdrift side
  • Breakwaters can alter wave patterns and sediment transport, potentially causing erosion or accretion in unexpected areas
• Beach nourishment involves the addition of sand to a beach to combat erosion and maintain a desired beach width
  • Beach nourishment can be costly and requires regular maintenance, as the added sand is subject to the same erosional processes as the original beach
• Coastal zone management aims to balance the competing demands on coastal resources and minimize the negative impacts of human activities
  • Integrated coastal zone management (ICZM) is a holistic approach that considers the interdependencies between ecological, social, and economic systems in the coastal zone
• Climate change adaptation is becoming an increasingly important aspect of coastal management, as rising sea levels and changing storm patterns pose growing threats to coastal communities
  • Adaptation strategies may include managed retreat (relocating development away from vulnerable areas), nature-based solutions (e.g., wetland restoration, living shorelines), and improved coastal infrastructure design
• Coastal management policies and practices vary widely around the world, reflecting differences in physical, cultural, and institutional contexts
  • Effective coastal management requires collaboration among diverse stakeholders, including governments, communities, industries, and researchers, to develop sustainable and resilient coastal systems