Studied by 61 people
beach
land that extends from mean lower low water to dunes/bluffs/cliffs
shoreline
where the land and ocean meet
spit
linear extension of land; forms from an accumulation of sediment and is maintained by tides
barrier
a spit or island seaward from land; usually is parallel to land
bars/troughs
seabed features in surf zone
berm
relatively flat region of beach behind shoreline
foreshore
seaward sloping; area seaward of berm
backshore
berm and dunes
flood-tide delta/washover delta
features formed when beach sediment is transported landward due to tides/storms respectively
longshore drift/transport
movement of water and sediment parallel to beach
MSL
mean sea level
winter berms
higher up a beach relative to summer berms due to more active tides and storms
summer berms
lower down a beach relative to winter berms due to calmer tides and less storms
swash
upward movement of waves when they break
why is swash more capable of moving sediment than backwash?
some of the water goes into pore spaces rather than returning to ocean
backwash
downward movement of water after waves have broken
what is the single most important physical process on beaches?
surface waves
what snuffs out surface waves?
gravity
what propagates surface waves?
wind stress
wavelength
the distance from the crest of one wave to another (or other analogous point)
wave height
distance between the trough and crest of a wave
still water level
mean between trough and crest heights; approximately where water would sit if it wasn't disturbed
crest
the highest point of a wave
trough
the lowest point of a wave
how does water move in waves?
in an orbital fashion
wave period
amount of time it takes for two adjacent wave crests to cross the same point; proportional to wave length
in deep water, wave speed increases with...
wavelength and period
as waves move away from the source, they...
sort themselves out; larger waves move ahead of smaller waves
swell
waves with large wavelengths that reach beaches first
the energy of a wave is proportional to
the wave height
as you move down to wave base, sediment transport capacity...
lowers
as waves move across sea, they become...
muted due to gravity
once a wave forms, it will keep going until...
it breaks on a beach
fetch
distance a wind blows
bigger waves are the result of
strong winds, longer duration of winds, bigger fetches
sea condition waves
very jumbled structure (not organized with swell ahead of smaller waves); confused waves
post-generation wave conditions
waves are now organized; single wave shape characteristic
surf
where waves break on shore; pointed wave crest characteristic
in deeper water, how do things move in waves?
in a more circular orbit; influence decreases with depth
wave base
1/2 wavelength
in shallow water, how do things move in waves?
in a more elliptical orbit; as you go deeper, orbit gets thinner until it's just moving back and forth in a line
transition zone
occurs when waves are 10-50 m of shore (wherever water depth is less than or equal to 1/2 of wave base)
what happens to the seabed at the transition zone?
gets eroded; mud in suspension, sand as bedload
as depth decreases, what happens to wave speed and wavelength?
decreases as well (due to friction of bed); leads to wave refraction (change in wave direction)
as depth decreases, what happens to wave height?
increases; crest increases until height-length ratio is greater than 1/7, in which case wave breaks
what determines break shape of a wave?
gradient of seabed and grain size
spilling breakers
occur at nearly horizontal beaches with fine sediment
plunging breakers
occur at steeper beaches with sandier sediment
surging breakers
occur at steepest beaches with biggest grain sizes
water infiltration
when water seeps into permeable beach sediment; again, this reduces sediment transport capacity of backwash
how does water infiltration affect beach gradient?
coarser sediments have more pore spaces between them allowing more water to seep in; thus further reduces backwash's transport capacity; thus bigger ratio between landward and seaward transportation (landward is much bigger); thus beaches that have coarse grain sizes are steeper; this also contributes to formation of berms
what controls berm elevation?
wave energy and tidal range
rip currents (riptides)
method for water to return to sea after breaking on beach; moves in parallel direction to longshore transport until washing out to rip head (location of this depends on gradient and wave morphology)
undertow
a weak, non-dangerous riptide
wave refraction
bending of the wave crest
swash can move up at an angle due to refraction. what about backwash?
no, it stays perpendicular because it is driven by gravity
wave ray
imaginary line that moves perpendicular to wave crest to allow us to see movement of energy
when waves approach a straight shoreline, what happens?
wave refraction due to lowering of speed
when waves approach an irregular shoreline, what happens?
shallow water of headlands gets hit with most energy, backlands not hit with as much energy; leads to erosion of headlands and sediment deposition at backlands
what causes longshore transport?
wave refraction of swash (angled) and perpendicular direction of backwash
summer beach characteristics
tall dunes and wide berm
winter beach characteristics
dune and berm erosion, washover, and offshore bar/higher berm formation
to put it simply, the beach grows seaward when?
in the summer
to put it simply, the beach recedes landward when?
in the winter
storm surge
occurs in winter; when strong wind and waves push against shore with high energy, eroding it
what happens to the sediment eroded during storm surge?
builds offshore bars/winter berms; washes through dunes during washover and forms washover deposits
what happens to the sediment stored offshore during the summer?
gets pushed back back up to shore; forms summer berm
longshore bar
deposit of sediment just off the shore that has been eroded during storm surge
why are spits and barrier islands common on trailing edge margins?
gentle gradients and little tectonic uplift/subsidence
can spits/barrier islands appear on collision margins?
yes, only if the sediment load is abundant
where are these coastal barriers migrating today?
landward due to sea level rise (however, some places see seaward migration due to being right next to river mouths)
how do spits form?
longshore transport; inlets maintained by tides
barrier island characteristics
tidal inlets are both ends; elevation depends on wind/sand supply
what determines length of barrier islands?
tidal prism (vertical amount of water flowing in and out during tides)
large prism
short barrier island
small prism
long barrier island
can barrier islands be covered by washover?
yes, if they are low enough
two kinds of coastal barriers
spits and barrier islands
what are the three ways a barrier island forms?
spit elongation, bar submergence, and bar emergence
how are spits built?
built from tip out seaward
spit elongation
when a spit becomes too long for water to efficiently transport across it, an new inlet will form, making the spit a barrier island
bar submergence
when an old dune or other topographic high is surrounded by water as sea-level rises
bar emergence
when a longshore bar is formed and then rises out of sea when storm surge subsides
what is the time interval for tide fluctuations?
24 hours, 50 minutes
diurnal tide
one high and one low each day
semidiurnal tide
two nearly-equal highs and two nearly-equal lows each day (most common type of tide)
mixed semidiurnal tide
two unequal highs and two unequal lows each day
when are currents strongest in regards to tides?
during period of greatest water level change
slack water
period of least movement of water; occurs during max high and max low
what are the two causes of tides?
gravitational attraction of the sun and moon and centrifugal force around earth
tidal range
the vertical difference between max high and max low during SRPING TIDE; can be cm or m
ebb tide
when water level falls
flood tide
when water level rises
how often do the sun and moon cycle to affect the tides?
every 28 days or so
spring tides
larger tidal range
neap tides
smaller tidal range
every 28 days, how many neap and spring tides are there?
2 neap tides and 2 spring tides
when do neap tides occur?
during first quarter and third quarter moons (moon and sun are working against each other)
when do spring tides occur?
during new and full moons (moon and sun work together)
can local geometry differences influence tidal range?
yes; can increase or decrease depending on how much flow the seabed allows
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Flashcard (32)