C -> 3.1 - 3.4 Flashcards
Glass Beach, California
- tourist attraction, 1-2000 people a day
- gradually diminishing
- a need for replenishment
traction
sediment rolls along
suspension
its carried along, making the water all muddy
saltation
it bounces along 2-10cm above the beach
solution
its dissolved, but it doesn’t happen very much
sediment cells
- stretches of coastline where the movement of material is mainly self contained
- closed systems of inputs (erosion), transport, outputs (deposition)
- the key question: is sediment transferred from one cell to another
dynamic equilibrium
- negative - when erosion leads to block fall mass movement, collapsed debris act as barrier protecting base, lowering erosion. Or when major erosion of sand dunes could lead to excessive deposition offshore, creating offshore bar that reduces energy, allowing dunes time to recover.
Positive - when wind erosion of dune section during high velocity storms may remove stabilising vegetation.
Longshore drift
(drift aligned beach)
swash comes in at an angle 30 is the most efficient because of the wind
backwash out perpendicular 90o because gravity
are they closed or open systems
- closed: large natural barriers might stop sediment being moved between, or out of cells - e.g. Thames Estuary, Start Point Headland.
- semi closed: small material could make it out of cells, or between sub-cells, e.g. Christchurch Harbour
- Open: Wind, tides, or tidal currents might remove material
deposition into stores
- when waves no longer have sufficient energy to continue to transport material
- gravity settling (energy is too low), or Flocculation (small clay particles attracted, clump together)
- might be beach, eg. Slapton sands, or offshore, e.g. Dolphin Bank
Inputs
- from cliffs, headlands, rivers, lagoons by coastal erosion processes (HA, Att, Ab, Cor)
- OR: deposited by rivers in coastal environments
transport
by littoral drift/ currents / wind
Real example - Christchurch Bay
source 1 - cliff erosion, e.g. Highcliffe Barton Sands/ Barton clay
Sink 2 (Source 3) - Offshore bars, e.g. Dolphin Bank
point of open cell - double spit (Christchurch Harbour) - sediment can skip over
sink 1 - Hurst Spit
closed cell - river disrupts longshore drift at Hurst Narrows
transport processes - longshore drift, west to east
what is a sediment cell?
littoral cell - linked system of sources/ inputs, transfers and sinks/ outputs of sediment along a section of a coastline
- 11 sediment cells within UK and Wales, boundaries are formed by major headlands or estuaries
examples of inputs + what is it
were sediment is generated from eg. cliff erosion, onshore currents, river transport, aeolian sediment, sub aerial processes
cliff erosion
unconsolidated material after mass movement
river transport
saltation, traction, suspension, solution
aeolian sediment
wind blown sediment
transfers
sediment is moved along shore through longshore drift and offshore currents
sinks
locations where dominant process is deposition and depositional landforms are created, eg. spits and offshore bars
swash aligned
directly faces prevailing wind, wave fronts approach it aligned parallel to the coast, swash aligned beaches often exhibit well defined berms
drift aligned
aligned at an angle to prevailing wind direction, wave fronts approach coast at an angle, so there is transport by LSD. May exhibit some sorting of sediment with smaller more rounded at furthest end
interference
transport of material is stopped or changed, eg river flow, wind
wave refraction
energy levels of the waves are changed/ reduced direction material transport is probably changed