Coastal Processes Flashcards
how do waves form?
by friction with air
- energy from wind is transferred to waves on the surface
does the water move in waves?
no
-> only energy transfers
in what motion do water particles move?
circular orbits
does orbit diameter increase or decrease with distance from the bottom?
increases
is there energy loss when waves reflect from objects?
no
-> energy is only transferred not loss
crest
highest point of wave
trough
lowest point of the wave surface -> not the point deep in the water column only the SURFACE
wave length
from crest to crest
height
amplitude
- trough to crest
period
t - sec
- time of passage of successive crests
velocity
L/t for waves in deep water
depth
half of L of a wave
L/2
does the whole water column move horizontally?
NO
- circular motion at the top
what happens with D> L/2?
water motion is negligible
what happens in deep water with waves?
in deep water-> wave action diminishes
what happens to waves in shallow water?
wave action does not diminish, wave energy reflects off the bottom
-> waves feel the bottom
-> water depth is less than half the length (D < L/2) - wave becomes elliptical and particles are displaced
-> when water gets too high it breaks
what happens when H to L ratio is greater than 1/7?
wave is unstable and collapses (breaks)
is the wave stable or unstable when heigh is 1/7 the length?
wave is stable
what does the surface tension of water allow for?
energy to be captured
whats the order of waves?
ripple then swell then waves
how is the final wave height determined?
- average velocity of wind
- length of time the wind blows
- fetch - distance over surface which the wind blows
what are the two types of wind waves?
- local seas: short period, irregular -> wind driven
- swell: long period, reg, independent of local winds -> driven by distant weather conditions
what are rogue waves?
- not wind waves
- usually huge waves without warning
- wave reinforcement -> 2 waves interacts and wave height is added together
- interaction of storms with currents
whats an example of rogue waves?
Draupner Oil Perform
what are tsunamis?
- harbor wave
- not wind waves
- caused by undersea earthquakes -> tectonic plates that slide past each other and get caught and cause a break
- long wave lengths - loses very little energy
- slipping of ocean faults
what is an example of a system that measures tsunamis?
- Neptune Canada ->Ocean Networks Canada
- pressure on sea floor is equivalent to eave height
what drives internal waves?
density driven
- occurs where low density water lies over higher density water
- propagation of the wave occurs at interface -> wave in-between 2 water bodies
- influenced by tides in shallow water -> estuary where fresher water is coming out and saltier water coming in with tide (wedge)
what are internal waves?
stratification of the inner water column
why is the intermediary water and basin water distinct?
the sill keeps the 2 kinds of water separate and creates internal waves
whats an example of famous internal waves?
Tasman Sea
-> one of the few that has waves that move in one direction making it easier to study
tide types?
dinural - once a day
semi-diurnal - twice a day
mixed semidiurnal - diff highs and lows during the day
what causes tides?
gravitational pull of the sun and moon
- pulls the water
- types and number dependent on location
why is the gravitational effect of the moon stronger than sun?
closer to us
- 6x stronger
what does the moon’s rotation around earth give?
monthly cycles
- spring and neap
what are spring tides?
2 of them during new or full moon
- greatest vertical tidal range, highest high or lowest low
what are neap tides?
2 of them during half moon
- smallest vertical tidal range
- perpendicular to sun so forces do not cooperate
what gives daily cycles?
earth’s rotation
what gives annual cycle?
earth’s orbit of sun
what are the tide cycles?
daily: 12h25min, 24h50min (1 per day)
biweekly: 14 days (27.32 days)
half yearly: 6M ( 1yr)
what causes the 12h25min cycle?
- gravitational attraction of moon
- inertial force of the earth-moon sys
- motion of moon in same direction as earth’s rotation
what causes the 24h50min cycle?
gravitational attraction of moon
what causes the monthly cycle?
combo of earth, moon and sun and their alignments
what causes the yearly cycle?
earth, moon, sun and maybe the tilt of earth as it moves around the sun diff regions of earth are closer or further from sun
what are tide cyc;es?
in diff location are function of basin shape, basin size and latitude
what are tidal buldges?
giant incoming waves
- more shallow = more noticeable
what happens in narrowing channels?
amplified or dampened tides or causes tidal bores and Seiches
what affects predicted tides?
coastlines
tidal bore
tide moving up a river channel and outflow is overpowered and creates breaker that pushes water forward
Seiche
standing wave caused by the wave reflecting off shorelines
what factor affects tides?
weather patterns
- atmospheric pressure
- low pressure cause storm surge or storm tides - Irma
