How do waves affect coasts on different timescales?
There are powerful forces on coasts such as:
- Long-term regular wave action (slow costal erosion)
- Storm Surges (faster erosion)
- Tsunamis & Hurricanes (significant erosion & damage, can reshape coastline)
How do you calculate wave velocity?
Wave Velocity (V) =
Wave Length (L)/Wave Period (T)
V = L / T
Can waves be felt all the way to the bottom?
No, water particles below the surface move in stationary circular orbits that get smaller and smaller to a depth of about 0.5 L
Why do waves crash at the shore?
When the waves approach the shore, the depth of the ocean floor decreases, causing the bottom of the wave to slow down. This slows the wave down, making the top of the wave move faster than the bottom. As a result, the wave begins to break, or crash, as its energy is transferred from the horizontal motion to the vertical
Why do waves bend?
when a wave moves from deep water into shallow water, the speed of the wave decreases because the water becomes shallower and its density increases. As a result, the wave front bends and moves toward the shore. The amount of bending depends on the angle at which the wave is moving relative to the shoreline and the change in speed of the wave as it enters the shallow water
How does the longshore current move sand?
When waves approach the shore at an angle, some of the water is deflected along the shore and creates a current, known as the longshore current. As the longshore current flows along the shore, it picks up sand and sediment from the bottom of the ocean and moves it down the beach. The longshore current can transport sand and sediment great distances, even moving it from one beach to another.
How are spits formed?
Spits are narrow, elongated stretches of land that extend from the shore into the water. They are formed by the accumulation of sand and sediment transported by longshore drift, which is the movement of material along the shore due to waves approaching the shore at an angle.
How does the surf affect beach topography?
The surf, or breaking waves, can have a significant impact on beach topography by shaping and reshaping the beach and seafloor over time though:
- Erosion - removing sand and sediment and altering the shape of the shoreline resulting in a loss of beach width and the creation of cliffs and sea caves.
- Sediment transport - help to reshape the beach and create new features such as sandbars and spits.
- Beach profile - can also affect the slope or profile of the beach, causing it to become steeper or more gradual
- Formation of features - such as ripples, dunes, and berms on the beach
What are Rip Currents?
Rip currents are narrow, fast-moving channels of water that flow away from shore. They are formed when waves break near the shoreline and the water flows back into the ocean through a gap in the sandbar or through a channel in the seafloor. The flow of water in a rip current can be strong and fast, and can move directly away from shore, making it difficult for swimmers to return to shore.
What are natural causes of erosion?
- Hydraulic action
- Abrasion
- Attrition
- Solution
What are human causes of erosion?
- Development
- Dams
- Groins / Jetties
- Climate warming (sea level rise)
What caused the erosion in Tuktoyaktuk, N.W.T.?
- Sea level rise
- Less sea ice
- Substrate (thawing, loose soils)
- Poor planning
(More open water = more waves)
What are possible mitigation strategies for erosion?
- Sandbags
- Boulders
- Concrete Slabs
- Relocation
- Beach Nourishment
Why is beach nourishment not that great?
- Expensive
- Short-term solution
- May erode faster
- False sense of security
What are Groins?
Groins are structures that are built perpendicular to the shoreline and are used to trap and retain sand along the beach by breaking longshore current. They are often built to protect shorelines from erosion or to rebuild eroding beaches.
What are Detached Breakwaters?
Detached breakwaters are offshore structures built parallel to the shore line and are used to break incoming waves and reduce erosion.
What are Attached Breakwaters?
Attached breakwaters are structures that are built parallel to the shoreline to reduce wave energy and protect the beach and adjacent areas from erosion. They are similar to detached breakwaters, but are built directly adjacent to the shoreline, rather than being placed farther offshore.
What are Jetties?
Jetties are structures that are built along the shoreline to regulate the flow of water in and out of harbors, bays, and inlets. They are often built in areas where the flow of water is difficult to control due to strong currents, tides, or other physical characteristics.
What are Seawalls?
Seawalls are structures that are built along the shoreline to protect coastal areas from wave energy and erosion. They are commonly used in areas where shorelines are at risk of erosion and damage from wave action, such as in urban areas with high-value infrastructure and buildings close to the shore. They are typically made of concrete, rocks, or other materials, and are designed to prevent the movement of sand and to absorb the energy of incoming waves.
How must seawalls be maintained?
Regular monitoring of the seawall and the adjacent coastal environment is important to identify any changes or impacts that may be affecting the effectiveness of the seawall
How are corals natural protection against erosion?
They act as a physical barrier to the energy of incoming waves, reducing the impact of waves on the shore and helping to prevent erosion.
How are corals endangered by ocean acidification?
Ocean acidification refers to the process by which the world’s oceans are becoming increasingly acidic due to the absorption of carbon dioxide (CO2) from the atmosphere. As CO2 dissolves in seawater, it forms carbonic acid, which reduces the pH of the water and makes it more acidic. This increase in ocean acidity has significant impacts on coral reefs and the organisms that rely on them. Corals rely on the process of calcification to build their skeletons, which are formed from calcium carbonate. As the ocean becomes more acidic, it becomes more difficult for corals to extract the calcium carbonate they need to build their skeletons. Over time, this can weaken and dissolve the coral’s skeleton, making it more vulnerable to damage from storms, disease, and other threats.
How are corals endangered by mining?
Mining can have a range of impacts on coral reefs, including the physical removal of reefs for building materials, the discharge of waste materials and pollutants into the ocean, and the destruction of habitats that support coral and other reef-dwelling species.
How are corals endangered by disrespectful / inexperienced divers?
- Physical Damage
- Anchor Damage
- Stirring up sediments
- Breaking off coral specimens
- Introduction of disease
