Coastal Hazards: Processes and Impacts

Introduction to Coastal Hazards

• Coastal areas are dynamic environments, differing in topography, climate, and vegetation
• Hazardous coastal processes have considerable impact due to the high population in coastal regions
• Global warming and sea-level rise exacerbate coastal erosion

Coastal Hazards

• Rip Currents: Strong currents flowing away from the shore
• Coastal Erosion: Loss of land due to wave action and other natural processes
• Tsunamis: Seismic sea waves caused by earthquakes
• Storm Surges: Abnormal rise of water caused by storm
• Tropical Cyclones/Typhoons: Storm systems characterized by a low-pressure center and strong winds

Coastal Processes

• Waves are generated by offshore storms or wind transferring energy to the water
• Waves can travel long distances across the ocean with minimal energy loss
• Wave size is affected by velocity, duration, and fetch

Wave Form

• Wave Height: The vertical distance between a wave's trough and peak
• Wave Length: The distance between successive peaks
• Wave Period: The time (in seconds) for successive waves to pass a reference point
• Swell: Wave groups generated by storms far out at sea
• Wave Fronts: Imaginary line connecting the crests of incoming ocean waves as they approach the shoreline
• Wave Normals: Lines drawn perpendicular to wave fronts, pointing toward the shoreline
• Plunging Breakers: Highly erosive at the shoreline
• Spilling Breakers: Gentle; may facilitate sand deposition on beaches

Beach Characteristics

• Beach: Landform of loose material, such as sand or gravel, accumulated by wave action at the shoreline
• Beaches terminate at a natural topographic and morphologic change such as a seacliff or a line of sand dunes
• Berms: Flat backshore areas on beaches formed by sediment deposition
• Beach Face: Sloping portion of the beach below the berm
• Swash Zone: The area where the backwash of waves occurs
• Surf Zone: The area where turbulent translational waves move toward the shore after breaking
• Breaker Zone: The area where incoming waves become unstable, peak, and break
• Longshore Troughs and Longshore Bars: Elongated depressions and adjacent ridges of sand

Transport of Sand

• Beach sand is not static; wave action keeps it moving in the surf and swash zones
• Longshore sediment transport moves sand along the beach
• Sand is transported along the coast with the longshore current in the surf zone
• The up-and-back movement of beach sand in the swash zone causes the sand to move along the beach in a zigzag path
• Incoming waves striking the coast at an angle produce a longshore current that transports the sand

Rip Currents

• Rip Currents, also known as riptides or undertows, are dangerous currents of water moving away from the shore
• Large waves cause water to pile up on the shore, which then concentrates in narrow zones as it flows back

Beach Budget

• Compares beach erosion and sediment movement to a financial budget
• Input (Deposits): Sand or sediment that arrives at the beach, often through natural coastal processes
• Storage (Balance): The amount of sand that remains on the beach at any given time
• Output (Withdrawals): Sand that leaves the beach due to waves, tides, storms, or human activities
  • If Input > Output: The beach grows
  • If Input = Output: The beach remains stable
  • If Input < Output: The beach erodes

Coastal Erosion Factors

• River Sediment Supply and Dams: Dams trap sediment, preventing it from reaching the coast
• Storms & Extreme Weather: Carve away dunes and deposit sand offshore
• Rising Sea Levels: Allow waves to reach further inland, increasing erosion
• Human Interference with Coastal Processes: Structures like seawalls, jetties, and groins disrupt natural sand movement

Seacliff Erosion

• Seacliffs are exposed to wave action and land erosion processes such as running water and landslides
• Seacliff Erosion Factors:
  • Wave Action
  • Running Water & Rainfall
  • Landslides
  • Seasonal Changes:
    • Summer: Gentle waves deposit sand
    • Winter: Strong waves erode sand
  • Human Activities:
    • Urbanization increases runoff
    • Poor drainage placement
    • Construction: Buildings, pools, and walls near cliff edges add weight and trigger collapses
  • Sea Level Rise
  • Rock Type & Structure
  • Natural Disasters

Coastal Stabilization Approaches

• Hard Stabilization: Engineering structures protect a shoreline from waves, and improves navigation or retard erosion
• Soft Stabilization: Beach Nourishment
• Managed Retreat: Allowing the coastline to move further inland when there is a high risk of flooding or cliff collapse

Hard Stabilization Structures

• Seawalls: Parallel to the coastline to retard erosion; criticized as they can enhance beach erosion
• Groins: Linear structures perpendicular to the shore that can cause irregular beach build up
• Breakwaters: Intercept waves and provide a protected harbor, blocking the natural littoral transport of beach sediment
• Jetties: Constructed in pairs at river mouths or inlets to stabilize channels

Soft Stabilization

• Beach Nourishment: Artificially placing sand on beaches to provide recreation and shoreline erosion protection

Managed Retreat

• Living with beach erosion by using a mixture of hard and soft stabilization; coastline moves inland.

Relationship between Humans & Coastal Erosion

• Human activity can accelerate coastal erosion
• E.g., Texas coastal zones accelerated 30-40%

Examples of Coastal Erosion

• Atlantic Coast: Characterized by barrier islands
• Gulf Coast
• Great Lakes: Coastal erosion during high water stages
• Construction of the Dauin-Bacong port resulted to sediment deprivation and consequent coastal erosion in areas south of the port.

Tropical Cyclones

• Hurricanes: Tropical cyclones in the Atlantic
• Typhoons: Tropical cyclones in the Pacific

Hurricanes

• Hurricanes develop from a Caribbean Indian word for "big wind" or "evil spirit".
• A large system of thunderstorms rotating around a low-pressure area over warm ocean waters
• They rotate counter-clockwise
• Tropical storm if wind speeds reach 63 km/h (39 mph), it becomes a tropical storm and is given a name.
• Classified as hurricane at 119 km/h (74 mph)
• Can reach a diameter as large as 600 km (370 mi).

Hurricane Intensity

• Saffir-Simpson Hurricane Scale: 1 to 5 rating based on the hurricane's present intensity
• Modified Tropical Cyclone Wind Signal (TCWS): A plain text warning to particular land area that may experience winds with at least strong breeze in strength

Coastal Hazards

• Processes that kill most people and often cause the most damage
  • High Winds
  • Flooding
  • Storm Surges

Examples of Storms

• Super Typhoon Yolanda: One of the strongest tropical cyclones, struck the Philippines
• Hurricane Katrina: Category 5 Atlantic hurricane, ravaged the southeastern United States, 2005
• Bhola Cyclone: Deadliest weather event in recorded history, struck Bangladesh in 1970, caused up to 600,000 deaths

Adjustments to Coastal Hazards

• Tropical Cyclones Community:
  • Strengthening the environment with protective structures
  • Improving land-use zoning
  • Enhancing evacuation and warning procedures
• Coastal Erosion Management:
  • Beach nourishment (soft solution)
  • Shoreline stabilization (hard solution, using structures like seawalls)
  • Land-use change (avoiding hazardous areas/relocating buildings)

E-Lines and E-Zones

• E-lines and E-zones based on the rate of coastal erosion.