Systems (Coasts) Flashcards
What type of system are coasts?
Coasts are “natural open systems”
Where do inputs of sediment come from?
Where does energy come from?
What are the main flows/ transfers?
What are the stores of sediment?
Rivers, flooded river valleys called estuaries, cliff costal erosion, waves wind and tides bringing in offshore deposits.
Wind, Waves, Tides, Currants
Erosion, Weathering, Mass movement, Transportation
Beaches, dunes, spits, offshore bars, tombolo.
Define a sediment cell?
A largely self contained stretch of coastline, usually defined by two headlands.
A CLOSED SYSTEM, however can be disturbed during storm events.
Has its own inputs and outputs of sediment. “discrete”
Sediment is sourced, transferred and stored and is away from local wave action and LSD.
Define sediment budget?
The relationship between erosion and deposition that can be used to predict the changing shape of the coastline.
What is the effect of a positive and negative sediment budget?
POSITIVE= beach gain NEGATIVE= beach loss
Give an example of dynamic equilibrium at the coast?
Coasts are generally in dynamic equilibrium.
WAVE TYPE AND BEACH GRADIENT
eg: constructive waves deposit sediment and beach gradient becomes steeper——- encourages destructive waves that plunge instead of surge leading to wave quarrying and h.d.a——- destructive waves erode and remove sediment and beach gradient decreases.
Positive feedback example at the coast?
Erosion takes place leading to a need for coastal management implementation——- groynes are put in place to trap sediment and interfere with LSD—— groynes save implementation area, but accelerate and increase costal erosion elsewhere.
Negative feedback example at coast?
Rates of cliff erosion increase——- eroded material forms a “scree slope” that slumps down the cliff face and protects it from sub-aerial processes and erosion———- rates of cliff erosion decrease.
Define wind?
How is wind created?
Wind is the movement of air from a high pressure to a low pressure.
Created as fluctuating temperatures lead to the formation of “pressure systems”.
What are the prevailing (dominant) winds within the UK?
The “westerlies” from the SW. Travel from sub-tropical areas over a vast expanse of the Atlantic Ocean.
What three factors effect wave energy?
- The strength of the wind (determined by the PRESSURE GRADIENT)
- The duration the wind blows for
- The FETCH - the distance the wind blows over
Describe the process of wave formation?
- Air moves over the water and frictional drag is created causing small ripples to form.
- Close to the shore, locally, water moves in an orbital motion
- Initially a circular orbit of water within the wave is created.
- However, due to increased friction and shallower waters a elliptical movement is created.
- As the wave reaches the shore, VELOCITY AND WAVELENGTH DECREASES, but WAVE HEIGHT increases.
- Swash breaks up the beach and backwash falls back down.
Compare the two types of wave- constructive and destructive?
CONSTRUCTIVE DESTRUCTIVE
- low frequency (6-8/ min) -high frequency (10-14/min)
- low wave height + velocity -high wh and velocity
- Circular orbit -Elliptical orbit
- beach gain -beach loss
Define Tides?
What is the tidal range?
Changes in the relative level of seas and oceans caused by the GRAVITATIONAL PULL of the moon and to lesser extent, the sun.
The difference between the high tide and the low tide.
Define neap tides?
Draw a neap tide:
Neap tides take place when the sun and moon are at right angles to each other, cancelling out the gravitational pull.
TIDAL BULDGE SMALL TO MOONS
Define spring tides?
Spring tides take place when the sun and moon align, causing the gravitational pull to be amplified
Higher high tides can be seen.
What are High Energy coastlines?
Environments with high wave power, rocky beaches and EROSIONAL features as erosion exceeds deposition eg: wave cut platforms, headlands.
EG: The West Coast of the British Isles
What are Low Energy coastlines?
Environments with low wave power, sandy beaches, and DEPOSITIONAL features as deposition exceeds erosion eg: spit, tombolo.
EG: The East Coast of the British Isles (small fetch across the North Sea)
Define wave refraction?
The DISTORTION of wave fronts as they approach the shoreline.
What causes wave refraction and what happens to wave energy?
- Shallow waters around hard rock headlands leading to friction.
- High and low energy stretches and DISCORDANT coastlines.
- Energy is COCENTRATED at headlands (chalk and limestone) and DISSIPATED at bays (clay and sands).