Coastal Geography, Beach-dune System Flashcards
Why are beaches so resilient to erosion?
Beaches exist because they are adaptable/malleable. They accomodate wave energy
Landward limit
The end of where water runs up the coast
Seaward limit
Where waves encounter the seafloor
What are the five main components of a beach-dune system?
The berm, beach face, runnel/ridge, low tide terrace, trough/longshore bar
Berm
A nearly horizontal ridge formed by swash deposition
Beach face
The swash/backwash zone
Runnel/ridge
Runnel: A drainage route for tides on the low tide terrace
Ridge: The raised area flanking either side of the runnel
Low tide terrace
A flat, extensive part of the beach composed of fine sand that becomes exposed at low tide
Trough/longshore bar
Trough: A deep part of the beach that is submerged even at low tide
Longshore bar: The top of the trough
Sand dunes
A temporary mound of sand that forms on the beach from desposited sediment
What happens to sand dunes during storms?
The sand is eroded and deposited offshore, usually returning during calmer weather
What are the two types of beach profiles and their implication for the transport of sediment?
Steep profile: Sediment transported and deposited onshore
Flat profile: Sediment transported and deposited offshore
What are the two main controls of beach profile?
Sediment and wave energy
What three parts of sediment influence the beach profile?
Sediment size, percolation, and angle of repose
How does sediment size influence beach profile?
Finer sediment will result in a flatter beach while larger, coarser sediment will result in a steeper beach
Percolation
The rate at which water will pass through sediment
Larger sediment = Greater percoation
How does percolation influence beach profile?
Both well sorted sand and poorly sorted sand with pebbles results in a flatter beach gradient
Contrarily, well sorted pebbles result in a stepper beach gradient
Angle of repose
The angle at which loose material can maintain a slope
How does angle of repose influence beach profile?
A lower angle of repose (sand) results in a flatter beach gradient
Contrarily, a higher angle or repose (gravel and pebbles) results in a steeper beach gradient
What are the two types of wave energy and what types of beaches do they form?
High wave energy: Forms a dissipative beach. Dissipates wave energy
Low wave energy: Forms a reflective beach. Reflects wave energy
What are the characteristics of a dissipative beach?
High energy, flat gradient, wide surf zone, small/fine sediment, spilling waves
What are the characteristics of a reflective beach
Low energy, steep gradient, narrow surf zone, large/coarse sediment, surging waves
In realtion to sediment sorting, what is the relationship between energy and time?
More energy + More time = Better sorting
What two conditions change beach profiles
Summer (swell) conditions and Winter (storm) conditions
What are the five main characteristics of Summer (swell) conditions
Regular waves, onshore sand transport, beach construction, berm-build up, and a steep beach gradient
What are the five main characteristics of Winter (storm) conditions?
High storm waves, offshore sand transport, beach erosion, longshore bar accretion, and low beach gradient
What are bars and how do they form?
Bars are areas of sediment convergence while troughs are areas of sediment divergence
Why do bars migrate?
In high wave events, bars migrate offshore due to increased erosion
Contrarily, in low wave events, bars migrate onshore due to increased deposition
Why does beach erosion occur during storm conditions?
Under storm conditions, more sediment is eroded and transported offshore as backwash remains onshore for a longer period of time
Storm surge
A combination of wind set up (strong winds) and pressure set up (low pressure), causing MSL to rise
Constructive waves
Low energy waves with a weaker backwash that deposits more sediment. Occurs during Summer (swell) conditons
Destructive waves
High energy waves with a stronger backwash that erodes ad transports more sedimentl. Occurs during Winter (storm) conditions
