Coastal Classification and Change Flashcards
Coastal Barrier
any sandy shoreline
shore parallel, accumulation of
sediment formed by waves, tides and aeolian processes
littoral zone
portion of the coastal profile where sediment can be transported by wave action.
seaward limit:
defined by the water depth at which significant sediment transport by wave action ceases (boundary between the offshore and nearshore)
landward limit:
the limit of (normal) wave action.
Offshore zone
portion of the profile where there is no significant transport of sediment by wave action.
Note that the landward boundary is often defined as the outer limit of the breaker zone
coastal zone
broad term for the area influenced by proximity to the coast; onshore and offshore limits are imprecisely defined
swash zone
The area of wave swash (uprush of
water) and backwash (back rush of water)
nearshore zone
portion of the profile extending from the limit of significant sediment transport by waves to the low tide line.
seaward limit: the seaward edge of the breaker line
surf zone
The zone landward of the breaking wave where there is the forward translation of water
area where waves are actively breaking
you go surfing here
waves disentangle from group of waves they started with and are now individual waves
extends from the breaker zone to the foreshore
break zone
The zone of breaking waves
where the surf zone starts
shoaling zone
Where the waves start to feel the seabed and increase in height prior to breaking
where the waves are first touching the bottom
-friction, they slow down, increase in height
seaward of the break zone
foreshore
The sloping portion of the beach between the limits of high tide and low tide swash
backshore
above high tide line, beyond the swash (foreshore)
nearshore bar
Ridge of sand formed at the convergence of transport by waves and currents in the surf zone
- dynamic
- bars are moved by changes in wave structure
- shallowest point offshore
- supply of sand, important for replenishing the beach after a storm
describe the direction (onshore/offshore) a grain of sand moves depending on the weight of the grain (settling velocity), wave period, and wave height
if the grain hits the bottom before another wave hits, the grain moves onshore
(and vice versa)
-heavy sand goes onshore, light sand goes offshore
(heavy sand will fall before the other wave hits it)
-big wave offshore, little wave onshore
(big wave means greater falling distance, another wave will hit before the grain reaches the bottom)
-longer period onshore, shorter period offshore
(a longer period means more time between waves, ie more time for the grain to reach the bottom)
Q1: What determines how dissipative a nearshore will get during a storm?
Q2: Why is Recovery slower than response?
- duration and intensity of storm
- during a storm waves energies are high (able to make a big impact in a short period of time)
why are beaches often in steady state equilibrium
during storms, beaches become more dissipative ->higher energies mean greater wave height and shorter wave periods so sand moves offshore (creates bars)
between storms, lower wave energies cause sand to move onshore (shorter wave height, longer period) making the beach more and more reflective
describe dissipative, intermediate, and reflective beaches
dissipative
-fine sand (lower settling v)
-high wave energies (greater wave height, lower period)
-> sediment moves offshore to form bars
-spilling breakers
-low gradient, gentle slopes
intermediate
-medium grains
-medium energy causes rip currents to dissect bars, forms complex morphology
-plunging breakers
-during storms, higher wave energies will cause erosion, sediment is moved offshore
reflective
-coarse grains (greater settling v)
-low energy (smaller waves, greater wave period)
-> sand moves onshore
-steep slopes->surging breakers
-> wave energy reflects rather than dissipate
-highly impacted by storms as high energy from storms is reflected and beach quickly erodes
what is fall velocity
Ω = H / 𝑤T
greater Ω means sand moves offshore
- big H small T due to high energy
- dissipative
smaller Ω means sand moves onshore
-small H big T due to lower energy
-reflective
steady state vs dynamic vs dynamic metastable equilibrium
Steady State Equilibrium: Numerous variations
around the mean or base level
Dynamic Equilibrium: Numerous
fluctuations around a trending mean value
(flat then gradual decrease, then flat, then gradual decrease)
Dynamic Metastable Equilibrium:
Step changes around a trending
mean value
(flat then 90º drop, flat then 90º drop)
