1.1.1 - the operation of the coast as a system
- Coastal system (inputs, outputs, stores and Coastal system (inputs, outputs, stores and
transfers of energy and materials)
transfers of energy and materials)
- Terrestrial and offshore supplies of sediment
Coastal zones - dynamic environments in which
- Coastal sediment cells
landscapes develop by the interactions of waves,
- Dynamic equilibrium in the coastal system and
winds, currents and terrestrial and marine sediments.
zone of rapid changes
Inputs, outputs, erosional components and depositional
components work together to ensure processes and
landforms can work together and be in balance with
one another.
Landforms are created by energy and sediment.
Energy - brings change and modifies landscape
Sediment - plays a role in certain processes of erosion
and cycles around a system to form stores of
deposition.
Inputs - different sources of solar energy (generates
wind that generates waves and currents), gravitational
energy (pull of the sun and moon generates tides
which can affect coastlines) and sediment (from
onshore and offshore surfaces, such as through LSD,
eroding cliffs and beach nourishment).
Store - sediment that has been deposited to create
beaches and other landforms (deposition components
eg beaches, tombolos, sand dunes, cuspate foreland)
Transfers - movements of energy, sediment and water
within a system as a result of physical process that
operate in coastal environment (eg
cliff-cave-arch-stack-stump sequence)
Outputs - movement of energy and materials across
the system boundary, leading to their removal from the
local coastal environment (physical ways eg dissipation
of wave energy and accumulation of sediment above
tidal limit, human ways eg dredging)
Terrestrial and offshore supplies of sediment
Process-response method - the morphology (shape) pf
any coastal landform is the product of the process
operating in the system (processes driven by energy
and sediments)
Sediment budget - how much sediment is available, its
source, its store and how it leaves a particular coastal
section
Terrestrial sediment - sediment from the land
Examples:
- Debris arriving on a beach after cliff collapse
- Aeolian deposition (material transported by the
wind)
- Artificial recharge by humans such as beach
nourishment, which is adding sand to beaches
to combat erosion.
- 90% of sediment comes from terrestrial
sediment that turns into offshore sediment.
Offshore sediment - sediment from the sea
Examples:
, - Seabed material transported by the waves.
During the last ice age, sea levels were lower
and large deposits of shingle were deposited by
streams from melted glaciers. As a result,
extensive deposits of gravel and rock fragments
lie beneath present day coastal waters in
Britain and over time, waves have moved this
material inland.
- Material is transported by rivers and washed
ashore by waves. Fine sediments are
transported via suspension and larger
sediments by traction. When it arrives, some of
this material is moved back.
Coastal sediment cells
Sediment/littoral cell - a length of coastline and its
associated nearshore area within which the movement
of coarse sediment (sand and shingle) is largely self
contained. Interruptions to the movement of coarse
sediment within one cell shouldn’t affect beaches in a
neighbouring sediment cell (defined by DEFRA).
Inputs - sources of sediment
- Cliff erosion, fluvial sediment, eroding
depositional features, beaches, dunes, spits,
beach recharge, offshore bars and sediments,
erosion of wave cut platforms
Transfers - transportation
- LSD, currents, saltation
Outputs - sinks
- sinks/permanent storage,m estuary, submarine
canyon, offshore bar/bank, dredging, sub
sinks/temporary stores, beach/dune/spit/bar
Characteristics:
- Discrete and function separately from each
other as theory are bounded by significant
disruptions to the coastline (headlands,
estuaries, currents and the LSD direction).
- Sediment in sourced, transferred and stored
within each (fine sediment in suspension can
go in between but coarse sediment can’t)
- Sub sinks erode and sediment re-enters system
over time
- Sediment in the sink is away from LSD and
wave action so becomes an output as it’s not
being worked by processes within the cell.
- Sediment budget (already defined)
Human activity in sediment cell:
- Disrupts supply of sediment and sediment
budget
- Groynes trap sediment in essential beaches to
protect cliffs, defences, leisure amity and
economic prosperity. (Rural areas have more
problem as groynes are in built up areas)
- Groynes, jetties, harbour walls block
movement, eads to beach erosion downdrift
, Dynamic equilibrium in the coastal system and
zone of rapid changes
Balanced budget - input and output volumes should be
in equilibrium (volume of sediment in = volume of
sediment store + volume of sediment out).
Anthropogenic actions decline inputs and there won’t
be equilibrium if replacement stores can’t be found
(volume of sediment in < volume of sediment store +
volume of sediment out). It produces a net loss of
sediment to the budget and increases erosion.
Dynamic equilibrium - coasts are dynamic zones of
rapid changing energy conditions (energy changes =
energy dissipated). If beach morphology changes
month to month but doesn’t see a permanently
long-term change, this is because inputs and outputs
are the same. The coast responds to disturbance if the
sediment entering and leaving the beach isn’t equal.
The system changes to restore it.
Examples:
- Coastlines in South England are gradually
sinking by several mm per year, leading to a
loss in beach sediment. However, this will lead
to increased erosion of cliffs in other areas,
balancing the inputs and outputs.
- Coastlines in Northwest Scotland are gradually
rising by several mm per year, leading to a
larger beach and foreshore. However, this will
lead to reduced cliff erosion so there are less
terrestrial inputs.
Positive feedback - enhances or amplifies change,
moving a system away from equilibrium and making it
unstable. For example, strong storm waves breach the
ridge of a coastal sand dune, therefore leaving them
susceptible to wave erosion.
Negative feedback - an opposing force, which
encounters change, lessening it and holding the
system into a more stable equilibrium. For example, a
storm erodes foredunes on a beach and deposits
material offshore as sand bars. This helps protect the
beach from further erosion by reducing wave energy
and further erosion. Then when the storm calms,
normal wave conditions rework sediments from the
offshore bar and back to the beach.
Human/anthropogenic actions to restore balance:
Hard engineering - groynes (stops LSD within its
sediment cell)
1.1.2 - temporal variations and their influence
on coastal environments Diurnal tides, offshore and onshore currents
- Diurnal tides, offshore and onshore currents Tides - long-period waves that appear to move through
- Constructive and deconstructive wave types, their the oceans due to the gravitational forces exerted by
characteristics and their seasonal variations the moon and sun. Their apparent movement towards
the coast creates a rise of the sea surface.
