coastal Flashcards
what type of system is a coast
it is an open system as it recieves inouts from outside systems and trasnfers outputs away from the coast into other systems. however you need to consider it as a closed system as the costal system inpacts and is impacted by the oceans.
what are sediment cells
sections of a coats wich are often borderd by prominent headlands. within these sections the movement of sediment is almost contained and the flows of sediment act in dynamic equalibrium. within sediment cells there are smaller subcells
what is dynamic equalibrium
the maintenence of a balance in a natural system, despite it being in a constant state of change. the system counteracts any changes imposedon the system in order to keep the balance
what is dynamic equalibrium in sediment cells
where input and output of sediments are in a constant state of change but remian in balance.
what can interupt the dynamic equalibrium
it can be upset in the long term by human interventions or in the short ter, by natural variations.
inputs def and exapmles
material or energy inputs. they include: marine- waves, tides, salt spray atmosphere- sun, air pressure, wind speed and direction humans- pollution, recreation, settlements, defences
outputs def and examples
material or energy outputs. e.g. ocean currents, rip tides, sediment transfer, evapouration
stores/sinks def and examples
stores and sinks of sediment and materail. e.g. beaches, sand dunes, spits, bars and tombolos, headlands adn bays, nearshore sediment, cliffs, wave cut platforms, caves, arches, stacks, stumps, salt marshes, tidal flats, offshore bands and bars
transfers/flows def and examples
the proccesses that link the inputs, outputs and stores in the coastal system. e.g windblowm sand, mass movement proccesses, long shore drift, weathering, erosion, transportation, deposition
energy def and exapmles
the power and driving force behind the transfers and flows in the system. e.g. wind, gravitational, flowing water.
what is the negative feedback loop
it lessens any change wich has occured within the system. when a system is taken out of dynamic eualibrium the negative feed back loop will balance it brining it back to dynakic equalibrium.
example of a negative feedback loop
- when the destructive waves from storm loose their energy excess sedimeny is deposited as an offshore bar.
- the bar dissipates the waves energy wich protects the beach from further erosion
- overtime the bar gets eroded instead of the beach
4.once the bar has gone normal conditions ensue and the system goes back to dynamic equalibrium.
what is a positive feedback loop
this exaggarates the change making the system more unstable and taking it away from dynamic eualibrium
example of a positive feedback loop
- people walking over sand dunes destroys vegetation growing there and causes erosion.
- as the roots from the vegetation have been holding the sadn dunes together, damaging the vegetation makes the sand dunes more suspetible to erosion. this increases the rate of erosion. 3. eventually the sand dunes will be completely eroded leaving more of the beach open to erosion taking the beach further awau from its original state
how is a river a sediment resource
most of the sediment in the coastal zone is a result of an input from rivers, especially in high-rainfall enviroments where signinfiant river erosion occurs. sediment may be deposited in estuaries wich are brackish (salty) areas where rivers flow into the sea. they are important wildlife habitats. the sediment is then transported throughout the coastal system by waves, tides and currents
how is cliff erosion a sediment source
it is very important in areas with unconsolidated cliffs that are easily eroded. in some area, coastlines retreat by up to 10m per year, providing a significant sediment input. most erosion occurs during the winter months due to more frequent storms
how is wind a sediment resource
it is an energy source and can cause sand to be blown along or up a beach. sediment transport by winds may occur where there are sand dunes or in glacial and desert enviroments wich provide sediment inputs.
how are glaciers sediment sources
in some coastal systems glaciers flow directly into the ocean depostiting sediment that was stored in the ice. this occurs when glaciers calve(ice breaks off)
how is offshore a sediment source
sediment is transfered to the coastal zone when waves, tides and currents erode off shore sediment sinks such as offshore bars. the sediment is transported onto the beach, helping build up the beach. storm surges or tsunami waves may also transfer sediment into the caostal zone.
how is longshore drift a sediment source
sediment is moved along the beach due to prevaling winds which alter the direction of the waves. this allows sediment to be transported form one section of the coast to another stretch of caostline. the swash approaches the coast at an angle due to the prevaling winds, transferring sediment along the beach. the backwash pulls the sediment direvtly back down the beach. the swsh then transfers the sediment along the coastline and the proccess repeats
what are sediment budgets
they use data of inputs,outputs, stores and trasfers to sases the gains an losses of sediment within a sediment cell. in principle a system will operate in a state of dynamic equalibrium where input and outputs of sediment are equal.
what is the littoral zone
the area of land beteen the clifs or dunes on the coast and the offshore area that is beyond the influence of waves. it is therefore covered by the sea at different points in time.
what are the long term adn short term factors that affect the littoral zone
short-term: tides and storm surges
long-term: changes in sea level and human intervention
shore/shoreline def
the boundary betweeen the sea and the land
offshore def
the area beyond the influence of waves
onshore def
the area of lanf not covered by the sea but is very close to it
what is the main source of energy at the coast
the main source of energy is form waves wich are formed pffshore, wich are most commnoly generated by wind or less frequently tectonic activity or underwater landslides causing tsunami waves
how do waves form
wind moves across the surface of the water, causing frictional drag wich creates small ripples and waves. this leads to a circular orbital motion of water particles in the ocean. as the seadbed becomes shallower towards the coastline, the orbit of the water particles become more elliptical, leading to more horizontal movement of the waves. the wace height increases, but the wave length and ave velocity bith decrease. this causes water to back up from behind the wave until the wave breaks and surges up the beach
