The coastal system Flashcards
(31 cards)
what is negative feedback?
It’s when a change in the system causes other changes that have the opposite effect eg. as a beach is eroded the cliff behind it gets exposed to wave attack, the sediment eroded from the cliff is deposited on the beach causing it to grow in size again
what is positive feedback?
It’s when change in the system causes other changes that have a similar effect eg as a beach forms it slows down waves which can cause sediment to be deposited, increasing the size of the beach
what are the sources of energy in the coastal system?
wind, waves, tides and currents
how does wind create energy in the coastal system?
- winds are created by air moving from high to low pressure
- during storms the pressure gradient is high and winds can be strong
- strong winds generate powerful waves, with strong prevailing winds creating higher-energy waves than winds that change direction
How do waves create energy in a coastal system?
- waves are created by friction caused by wind giving it a circular motion
- effect it has on the shore depends on the height which is affected by wind speed and fetch, high wind and long fetch create high and powerful waves
- waves break at shore, with the friction of the sea bed slowing the bottom of the waves making their motion more elliptical
- the stronger the swash and weaker the backwash means sediment is deposited
what is the fetch?
The distance that the wind has travelled across open water whilst creating waves
what are constructive waves?
A wave with a low frequency and are low and long, that deposits material up the beach after it breaks, deposits it, building up the beach. The swash is stronger than the backwash.
what are destructive waves?
High and steep waves with a high frequency, the backwash is stronger than the swash which erodes material from the beach
how do tides create energy on a coastline?
- tides are caused by the gravitational pull of the moon and sun and are the periodic rise and fall of the ocean surface
- tides affect where the wave breaks on the beach, with the area between high and low tide where most land forms are created and destroyed
how do currents supply energy to a coastline?
- current can be caused by wind or variations in water temperature and salinity
- currents move material along the coast
- rip currents
- upwelling- is the movement of cold water deep in the ocean to the surface, replacing the warmer water with nutrient rich currents
what are some inputs on the coast?
- eg. sediment can be brought into the system in various ways, but energy inputs are wind, waves, tides and currents
- geology
- sea level change
what are some outputs on the coast?
- eg. sediment can be washed out to sea, or deposited further along the coast
- dissipation of wave energy
what are some transfers on the coast?
processes such as erosion, weathering, transportation and deposition
what are some stores on the coast?
land forms such as beaches, dunes and spits
What are high energy coasts?
- They receive high energy inputs from large, powerful waves which are caused by strong winds, long fetches and steeply shelving offshore zones.
- Steady prevailing winds
- They tend to have sandy coves and rocky land forms such as cliffs or caves
- higher rate of erosion than deposition
what are low energy coasts?
- They receive low inputs of energy in the form of small, gentle waves
- They can be caused by gentle winds, short fetches and gently sloping offshore zones
- Some might have a reef or island offshore
- They often have salt marshes and tidal mudflats
- The rate of deposition is often higher than the rate of erosion
- Typical landforms are beaches and spits
Where are inputs of sediment brought to coastal systems from?
- Rivers carry eroded sediment from inland
- Sea levels rising can flood river valleys, forming estuaries
- Eroded from cliffs
- Waves, tides and currents can transport sediment into the coastal zone from offshore deposits
What is the sediment budget?
- The difference between the amount of sediment that enters the system and the amount that leaves
- And requires identifying all sediment sources and sinks to calculate it
What does a negative sediment budget lead to?
retreating coastline
What are sediment cells?
Lengths of the coastline that are self contained for the movement of sediment, which means that processes going on in 1 cell doesn’t affect the movement of sediment in another- making it a closed system
How many sediment cells are there in the UK?
11
What type of equilibrium do coastal systems normally operate in, and what does it mean?
- Dynamic equilibrium
- inputs and outputs are balanced
What are the specific zones on the coastline/beach?
- Backshore
- Foreshore
- Inshore
- Offshore
- Nearshore
What is the backshore?
- area between the high water mark and the landward limit of marine activity
- Changes only normally take place here during storms
