coastal processes Flashcards
tides
waves with extremely long wavelengths and periods that travel across the ocean and are modified by the geomorphology of the coastline
Tsunami are tidal waves.
TRUE or FALSE
FALSE
everywhere experience equal tides.
TRUE or FALSE
FALSE, influenced by location of the ocean basins and position of the land masses
semi-diurnal tide cycle
2 similar high and low tides
diurnal tide cyle
1 high and 1 low tide per day
on tidal charts, how are different height high tides distinguished?
higher high water and lower high water
mixed tide cycle
no pattern
most places on earth experience how many neap and spring tides per month
2
tidal range
difference between neap (lowest low) and spring tide (highest high)
how many days after a spring tide will a neap tide occur?
7 days
what is the arrangement of planets in a spring vs neap tide?
spring: moon, earth, sun all aligned.
neap: moon 90 degrees to sun and earth
king tides
full moon and closest orbit to the earth coinciding. Results in exceptionally high tidal ranges.
king tide and deep low pressure weather system can result in
widespread coastal flooding
tide terminology: HAT = MHST = MHNT = MIN HT = MIN LT = LAT =
tide terminology: HAT = high astronomical tide MHST = mean high spring tide MHNT = mean high neap tide MIN HT = minimum high tide MIN LT = minimum low tide LAT = lowest astronomical tide
where is the maximum shore width?
at HAT and LAT
3 things affecting height, wavelength and period of WAVES
- wind speed
- length of time wind blows
- fetch
define fetch
distance the wave has travelled across open water
sea state
describes the prevailing wave climate
3 main types of wave
- ocean swell
- storm waves
- nearshore waves
at what depth below a wave is the water unaffected by wave energy?
half the wavelength deep
ocean swell into breakers
Ocean swell is created by distant storms in the ocean. The swell generally has a long wavelength and low amplitude. As the swell approaches the coastline, water depth decreases and the wave height increases. As the height increases, the front of the wave steepens due to a speed reduction caused by friction with the seabed. As the wave continues to slow and become nearshore waves they reach shallow water and the oscillation becomes so great that the wave front collapses as breakers. The morphology of a breaking wave is dependent on the nearshore bathymetry
plunging breaker vs spilling breaker
steep offshore slopes = plunging
gentle slope = spilling
storm surges
caused by very low offshore pressure systems. Combined with winds makes for a very destructive situation
how deep below a wave is the water affected, leading to sediment mobilisation
water depth = 2 x wavelength
Storm water base (SWB) vs Fair weather wave base (FWWB)
SWB is deeper
wave refraction
angle between swell and submarine contours change so waves break parallel to contours. Concentrate energy and accelerate transport and erosion
longshore currents and longshore drift
narrow shore-parallel currents as a result of wave refraction. Primary mechanism for sediment transport in the coastal zone = longshore drift. Sediment is moved from one end of a coastal cell to another.
sea level rise effect on coastal flooding
increases magnitude and frequency of flooding
two sea level rising mechanisms
- eustatic
2. isostatic
shoreline erosion
- coastlines are high energy environments
- high energy erodes and transports sediments
- major economic hazard
- trends show its increasing
2 coastline subcategories
- rocky coasts
2. sediment dominated
rocky coasts erosion
- erode at slow rates
- erode due to UNDERCUTTING
- in weak rocks landslides are a risk
engineers can stop coastal cliff recession
TRUE or FALSE
FASLE, we can only slow it
is coastal cliff regression continuous or episodic?
episodic
Hard engineering
short term and expensive option with high environmental impact
hard engineering solutions
- groynes
- sea walls
- revetments
- rock armour
- breakwaters
- floodgates
Groynes
rigid hydraulic structures made of wood, concrete and rockfill, whose purpose is to limit longshore drift.
Create a wide beach on updrift side and prevent erosion on the downdrift side.
Cliffs are protected by the wider beach and are relatively stable.
sea walls
Sea walls protect the coastline from erosion, but they impede the natural longshore drift.
They have a curved shape which helps dissipate the wave energy. Very expensive to build and maintain
breakwaters
They are constructed 100-500m offshore and cause the waves to break early. however, erosion is increased downdrift of the structure
floodgates
protect low-lying estuarine areas from the effects of storm surges.
Most expensive and complex coastal protection structure
3 soft engineering interventions
- beach replenishment
- dune stabilisation
- managed retreat
beach replenishment
replace sediment lost by longshore drift and create a wider beach which can absorb more energy and protect the coastline
dune stabilisation
dunes help dissipate wave energy. They can be stabilised by vegetation, mesh, fences and controlling human activity.
managed retreat
previously protected areas are allowed to naturally flood and form natural coastal landforms. Restores natural sediment movement dynamics.
Philosophy that coastal erosion is a natural process and to prevent it would be futile.
