2. Sources Of Energy In Coastal Environments Flashcards
Describe how wind acts as the primary source for other processes.
Creates waves due to fractional drag
Length of fetch determines the size and energy of waves
Many coastlines have a prevailing wind direction
Spatial variation in energy as the result of varying wind strength and duration
Energy of a wave depends on the strength of wind, it’s duration and the length of fetch
What is a wave?
Undulations on the surface of the sea driven by wind
What are the key features of a wave?
Height
Length
Frequency
Define wave height.
The difference between the crest and trough of a wave
Define wave length.
The distance between two crests (or troughs)
Define wave frequency.
The time between one crest and the following crest passing a fixed point
Describe the functioning of a wave.
Wave enters shallow water Friction with the seabed increases Wave slows Increases in height Plunges or breaks into shoreline
What is the difference between swash and backwash?
Swash is the wash of water up the beach
Backwash is the drag of water back down the beach
Describe constructive waves.
Low, long length (up to 100m) Low frequency (6/8 per minute) Gentle approach to shoreline Swash loses volume and momentum, leading to weak backwash so sediment movement off the beach is low Material is slowly moved up the beach Forms berms
Describe destructive waves.
High, steep High frequency (10/14 per minute) Rapid approach to shoreline Little swash, powerful backwash so sediment is pulled away from the beach Little material moved up the beach Forms storm beaches
What is wave refraction?
The process by which waves break into an irregularly shaped coastline, such as a headland separated by two bays
Becoming increasing parallel to the coastline
Describe the function of wave refraction.
Wave drag in the shallow water approaching a headland
Wave becomes high, steep and short
Part of the wave in deeper water moves forward faster
The wave bends
The low energy wave spills into the bays as most of the wave is concentrate on the headland
What are currents?
The permanent or seasonal movement of water in the seas and oceans
Three types
What are the three types of current?
Longshaw currents
Rip currents
Upwelling
Describe longshaw currents.
Most waves approach the shoreline at an angle
This creates a current of water running parallel to the shoreline
Effect: transports sediment parallel to the shoreline
Describe rip currents.
Strong currents moving away from the shoreline due to a build up of seawater and energy along the coastline
Effect: hazardous for swimmers
Describe upwelling.
The global pattern of currents circulating in the oceans can cause deep, cold water to move toward the surface, displacing the warmer surface water
Effect: a cold current rich in nutrients
ADD TIDES IN
tiddies
What is fetch?
The distance of open water over which a wind blows uninterrupted by major land obstacles
How are waves formed?
By the transfer of energy from the wind blowing over the sea surface
How does wind act as an agent of erosion?
Wind can pick up and remove sediment which can be used to erode other features (abrasion)
How does shallow water change a wave?
Friction with the seabed occurs
The base of the wave slows down
Wave height and steepness is increased
The upper part plunges forward and the wave breaks on shore
Define tides.
The periodic rise and fall of the level of the sea in response to the gravitational pull of the sun and moon
How does the moon impact tides?
It is closer to earth than the sun
It pulls water towards it, creating high tides
There is a compensatory bulge on the opposite side of the earth
In between the two blushes, the tide is at its lowest
