Coastal Landscapes Flashcards
What are System inputs
different sources of solar and gravitational energy (producing wind and waves) and sediment (from onshore and offshore sources, such as eroding cliffs).
What are system outputs
movements of energy and materials (sediment and water) across the system boundary, leading to their removal from the local coastal environment.
What are system stores
sediment which has been deposited to create beaches and other landforms.
What are system transfers
movements of energy, sediment and water within the system (as a result of the different physical processes which operate in coastal environments).
Terrestrial supplies of sediment to the coastal zone include:
•Debris arriving on a beach following the collapse of a section of cliff.
•Material transported by the wind from an inland site to the coastal zone – this is called aeolian deposition.
•Artificial ‘recharge’ of coastal sediment stores by humans; for example, extra sand that is added to a beach which is used by tourists.
Offshore supplies of sediment to the coastal zone include:
•Seabed material which is transported towards the coastline by waves. During the last ice age, large deposits of shingle were deposited by streams flowing from melting glaciers onto land which now lies some distance offshore. Extensive deposits of gravel and rock fragments lie beneath the present-day coastal waters surrounding the British Isles. Waves have moved some of this material inland.
•Material which is transported offshore from inland locations by rivers before being washed ashore by waves. Fine sediments are transported as part of the suspended load in a river; larger debris is rolled along the river bed (this process is called traction). When it arrives in offshore coastal waters, a proportion of this material is moved back towards the coastline by waves.
What is A sediment cell
a stretch of coastline where movements of sediment budget are thought to be largely self-contained, resulting in a relatively closed system.
What impact does Human activity have on sediment cells
artificial nourishment of beaches with sand and shingle brought from inland locations may lead, in turn, to increased movements of sediment to other beaches within the sediment cell. This is due to the way waves sometimes move material laterally (sideways) from one coastal location to another.
How can equilibrium be applied to the study of coastal systems
Coastal systems are driven by different energy sources, as we have already seen. If energy inputs remain broadly constant over time, we can expect a condition called steady state equilibrium to occur.
From year-to-year, a beach may remain approximately the same size and shape, for example, despite monthly, seasonal and occasional year-to-year fluctuations in beach morphology.
Explain how most of the UK’s coastlines are in a state of dynamic equilibrium.
•Large parts of the UK’s coastline – such as southern England - are gradually sinking at a rate of several mm per year. Over time, this leads to a loss in the size of the beach sediment store; in other locations, it may lead to increased erosion of cliffs (and thus inputs of material).
•Large parts of the UK’s coastline – such as northwest Scotland - are gradually rising at a rate of several mm per year. Over time, this leads to a larger beach and foreshore; it may also lead to reduced cliff erosion (and thus reduced inputs of terrestrial sediments to the beach).
Tell me about tides
•Are a product of gravitational forces acting on water. The movements of the sun and moon give rise to a tidal range that affects coastlines.
•The majority of coastlines experience semi-diurnal tides – two high and two low tides approximately every 24 hours.
•Monthly cycles in the motions of the Earth, moon and sun give rise (each fortnight) to a so-called spring tide, followed a week later by a neap tide.
Tell me about shore normal currents
If the wind drives waves into the intertidal zone at an angle roughly perpendicular to the shoreline, the result is onshore movement, deposition or erosion of sediment. When the tide falls, water and sediment move offshore in the reverse direction. Water returning from the shore can form fast-moving rip currents.
Tell me about Longshore currents
More often than not, approaching waves are not parallel to the shoreline they are approaching. a wave front may be aligned at an angle which is neither parallel nor perpendicular to the shoreline. A longshore current develops: a movement of water is generated which flows along the length of the beach (this flow is the net result of each swash and backwash movement, generating a zig-zag movement of water).
What are Wave characteristics influenced by?
•the strength of the wind (its intensity)
•the length of time the wind has been blowing for (its duration)
•the distance over which the wind has blown (its fetch).
What do Defining characteristics of waves include?
•wavelength (the average distance between wave crests)
•wave height (the vertical distance between the wave’s trough and crest)
•wave period (the average time between successive waves).
Tell me about the orbital movement of water
When waves enter the coastal zone, shallower water results in increased friction from the seabed. This affects the orbital movement of water above and therefore waves become steeper and closer together. The eventual breaking of the wave creates a forward movement of water called the swash. Water which returns to the sea by running back down the beach is called backwash.
Tell me about constructive waves
• is relatively low in height and length. •move material onto a beach because they have a relatively strong swash and weak backwash
•When the orbit of a constructive wave is broken, the water rushes forward in a mass. The wave’s swash pushes material forwards and therefore has a constructive effect by helping to build up beach material.
•The returning water travels more slowly because it lacks the energy of the original wave and relies only on gravity. • less sediment is lost.
•The occurrence of constructive waves is typically associated with non-storm conditions and relatively gentle offshore gradients.
Tell me about destructive waves
•Typically, these are storm waves with greater heights and shorter lengths •Onshore storm winds result in the mass transport of surface water shoreward.
•As they break, they tend to plunge vertically, resulting in a scouring action which flattens the lower section of the beach
Tell me about low energy environments
•has wave action of such low magnitude that widespread deposition of fine-grained sediment can take place.
•Typical locations include sheltered bays and estuaries, which are protected from strong winds.
•In bays, wave energy becomes dispersed, leading to greater deposition of any fine-grained sandy sediments carried by offshore currents or rivers.
•Estuaries are often low-energy environments where the velocity of a river falls as its mouth widens and it encounters coastal water.
•The mixing of salt water and freshwater can encourage the deposition of small clay particles carried as part of the load in the river. Tiny pieces of suspended clay join together in a process called flocculation.
•Extensive deposits of mud and salt marsh may develop over time.
• this can sometimes lead to long-term changes in the position of the main river channel. Here, as elsewhere, the coastal zone is constantly changing with some new land being created while other land is eventually lost.
Tell me about high energy environments
• has wave action of such great magnitude for most of the year that deposition of sediment cannot occur. •the west coast of the British Isles is exposed to prevailing and dominant westerly winds that have travelled a long distance and therefore have considerable power.
Define the fetch
the distance of open water across which wind has blown in order to generate waves.
What is The velocity of waves determined by?
• the depth of water.
• In shallow water, friction from the seabed causes the deceleration of the orbiting water particles which make up waves.
•This causes the waves to slow down, so wave fronts get progressively closer together to one another.
