Coastal Systems
COASTS AS NATURAL SYSTEMS
3.1.3.1 Coasts as Natural Systems
Systems in physical geography: systems concepts and their application to the development of coastal landscapes –
inputs, outputs, energy, stores/components, flows/transfers, positive/negative feedback, dynamic equilibrium. The
concepts of landform and landscape and how related landforms combine to form characteristic landscapes.
The Gaia hypothesis proposes that living organisms interact with their inorganic surroundings on
Earth to form a synergistic and self-regulating, complex system that helps to maintain and perpetuate
the conditions for life on the planet
Types of systems:
Morphological (connections between different components)
Cascading (movement of specific matter/energy e.g. water)
Open
o both energy and matter move in/out
o linked by transfer of energy and material
o EXAMPLE- Selwick Bay: stream discharges water and inputs sediment into the sea
Closed
o energy moves in/out but matter stays within
o E.g. water cycle
Isolated (no inputs/outputs e.g. universe)
Components of systems:
Inputs and output
Flows of matter and energy
Stores of matter and energy
Processes (action which creates change)
Dynamic equilibrium (feedback mechanisms)
Thresholds/tipping points
Dynamic Equilibrium:
Stability
Balanced state of a system when inputs and outputs are balanced over time
If one element changes the equilibrium is upset so other components of the system change
System adjusts to go back to equilibrium by process of positive and negative feedback system
o Positive: when transfer leads to growth
EXAMPLE: sea walls transfer big waves to other parts of the coast
o Negative: when transfer leads to decline
EXAMPLE: mass movement produces a scree slope which overtime protects cliff
from subaerial processes leading to less mass movement & weathering causing
less damage
Dynamic Metastable Equilibrium: idea that natural systems change in episodic, more rapid
changes
Albedo: surface reflectivity
How much solar radiation is absorbed or reflected by the planet’s surface
Ice: best natural reflector (high albedo of 90%)
o When this melts, the earth gets warmer, melting
more ice
Water: worst natural reflector (low albedo of 10%)
o It's transparent so radiation goes into it (up to 50m)
Threshold and Tipping Point
Once tipping point is reached there is a permanent change
,Iceland, Dyrholaey
Waves from antarctica (south) transfer lots of energy into coastal energy in south Iceland
o Transfers sediment, causing erosion
Created distinct features:
o Coastal Plains: due to sea level drop, leaving coastal landforms e.g. stacks
o New Vegetation: made new ecosystems
o Black Sand: volcanic basalt has been transported by rivers, wind & glaciers
SOURCES OF ENERGY
3.1.3.2 Systems & Processes
Sources of energy in coastal environments: winds, waves (constructive and destructive), currents and tides. Low
energy and high energy coasts.
Coastal Zone: the narrow zone where the land and sea overlap and interact (haven for life)
Backshore: areas above the average high tide limit
High and dry most of the time
Maybe reached during Spring tides or storms
Foreshore: intertidal zone
Few nutrients
Have to live in air and water
Few creatures can survive
Inshore: permanently underwater
Zone of wave influence
How are waves formed?
Transfer of kinetic energy from atmospheric motion to the surface of the oceans
Wind moves from high to low pressure
o Greater difference in pressure = greater wind speed & strength
o Higher strength & longer duration = higher wave strength
o Wind moves across water, causing ripples which develop into waves
Fetch: distance that the wind can blow over (length of open sea)
o Longer fetch = larger wave
As waves develop, they create more surface area for the wind to press against (wind stress)
o They become more rounded, longer and travel faster Prevailing wind
o Maximum speed: as fast as the wind
In the wave, base of the water is calm
Constructive Waves:
Low energy As waves approach the shore, friction slows
the base of the wave, causing the orbit to
Strong swash, weak backwash become elliptical until top of wave breaks over
Long wavelength, low wave height
Smaller longshore bars & spilling breakers
6- 8 waves per minute 9-12 waves per min
is in transitional
Destructive Waves: period between
High energy constructive and
destructive
Weak swash, strong backwash
Short wavelength, high wave height
Larger longshore bars & plunging breakers
13 - 15 waves per minute
, Tides
Spring tide
Twice a month
o Time it takes for the moon to go around the earth
On full and new moon as when sun is in alignment with moon,
the gravitational pull is stronger
o Highest high tides and lowest low tide
o Highest tidal range
Neap Tide
Twice a month
o Time it takes for the moon to go around the earth
On third and first quarter moon, sun is at right angle to moon so gravity is weakest
o Lowest high tide and highest low tide
o Lowest tidal range
Tidal range: difference between high and low tide
Micro (<2m):Caribbean, Mediterranean, Australia
Meso (2-4m)
Macro (>4m)
Factors effecting tidal range
Degree of coastal shelter
Coriolis Effect (spin exerted on moving gases and liquids caused by earth's rotation)
Southampton:
Only place in the world that gets 4 high tides a day, therefore can get twice as many ships in and out
the port per day so does very well economically as a port
Rip Currents
Current going out to sea that’s why the surf doesn’t break
Often in clusters
Escape by swimming parallel to direction of rip
You can't swim against it
Swash pushes in and before backwash recovers, next swash comes in
o When critical frequency is reached a rip is formed
You get lateral movement of water as gravity is still trying to pull it down
Tends to develop in small coves and bays
Wave diffraction
Wave Refraction
Anything which makes the wave change direction
Example of negative feedback: formation of headlands and bays
lead to wave refraction which disperses wave energy, thus lowering
the erosional effect of the waves
Less resistant parts of coastline get less energy (& vice versa) due
to wave refraction
