Types of coast - Soft
- influenced by natural processes
- change at various timescales
Types of coasts - hard
- resist natural forces
- change mostly at very long term timescales
What influences coastal behaviour?
-geological controls (bedrock, natural features…)
- natural forcing (waves, tides, rivers…)
- interaction between different parts of a coastal system
- human intervention
World wave mean height map
- large waves found in vast oceans
- waves small closer to land
Water wave generation
- resulant of wind shear stress acting on the sea surface
- size dependant on; wind speed and direction
two wave categories
- wind (sea) waves
- swell waves
wind waves
- depend on local wind field
- shorter waves and periods
- wide frequency band`
swell waves
- independant on the local wind field
- have long wave lengths and large wave periods
- all waves lengths and large wave periods
- fairly uniform
When both sea and swell waves present
bi - modal sea
linear wave theory
- mathematically describes water waves and their propagation
- provide wave parameters for coastal engineering applications
-can be used to calculate sediment transport and beach change - used to determine wave energy
LWT assumptions
- fluid incompressible
- fluid is inviscid
- flow is irrotational
- surface tension negligible
- gravity waves sinusoidal (cosine) in shape
- sea bed horizontal
- wave two dimensional
- pressure at the free surface is constant
wave number (k)
2(pi) / L
wave celerity
the speed with which a wave crest moves
Wave dispersion
water waves with different frequencies travel at different speeds
- wave period is a constant
- wave length varies with water depth
Approximations - dispersion relationship (deep)
valid if the water depth h is much greater than the wavelength L
Approximations - dispersion relationship (shallow)
valid if the water depth is significantly less than the wavelength
Wave groups - speed
Group speed
-function of wave celerity, wavelength and water depth
water particle velocity
- when in a water column, move when a progressive wave propagates at free surface
- water particles move in circular (deepwater) or elliptical (shallow water) trajectories
- direction and magnitude move in circular/ elliptical trajectories
magnitude dependant on position with respect to wave profile and location in water column
water particle displacement
- magnitude of particle displacement depends on wave height, length, postion with respect to profile and water column
wave pressure
- hydrostatic pressure exerted by water in equilibrium
- water wave motion induce an additional dynamic pressure component
- total pressure under progressive waves is the sum of dynamic and hydrostatic pressure
Wave power
rate of wave energy propagation over one wave period per unit width of the wave
Wave energy
PE - resulting from the displacement of the free surface due to propagating wave
KE - resulting from moving water particles
