3.1.3.2 Systems and processes in costal envrioments

Inputs

Energy from waves/currents, sediment from rivers/cliffs

Outputs

Sediment moved offshore/along the coast, energy dissipated through waves

Flows/transfers

Sediment transfer, offshore desposition

Source of energy

Sun, wind blowing across the water

Factors affecting the amount of wave energy

Wind speed/duration/fetch

Constructive waves chareceteristics

Low energy, long wavelength, low height (0.5-1 metres), strong swash, weak backwash (deposition)

Destructive wave characteristics

High energy, short wavelength, high height (1-3 metres), weak swash, strong backwash

Formation of waves

Wind blows to form friction ripples that grown into waves. Shallow water causes elliptical shape and waves slow/increase in height before plunging

Wave refraction

Wave energy concentrated on headlands and deposition at bays

Tides

Change in water level of seas and oceans caused by gravity of moon/sun

Tidal range and example

Difference between high and low tide, 3-4 metres Christchurch bay

Neap tide

Moon at right angle to the sun, smaller tidal range

Spring tide

Moon and sun in line to increase the tidal range

Rip currents defintion

Strong underwater currents moving away from the shore

Formation of a rip current

Series of plunging waves cause a build up of water at the top of the beach which is met by resistance of breaking waves. Forces backwash below the surface and through troughs in the beach profile to move sediment offshore and change the beach shape

High energy coastline features and example

Rocky coasts with erosional features from erosion>deposition, Dorset coast

Low energy coastline features and example

Sandy, sheltered stretch where waves are weaker with deposition>erosion. Thames Estuary

Longshore currents

Move sediment alongshore due to angled waves

Offshore currents

Transport sediment away from the coast

Sources of sediment

Cliff erosion (soft, unconsolidated rock), rivers, offshore (storm surges, waves), wind

Sediment cell

11 Self contained units (bounded by headlands) in a state of DE along a coast where sediment is moved (can be divided into sub cells) but as a closed system

Sediment cell example

Christchurch Bay (sub cell), inputs from cliffs west of Barton, stores like The Shingles, transfers such as west to east LSD

Sediment budget

Balance between inputs and outputs of sediment

Weathering

Breakdown of rocks in situ

Types of geomorphic processes

Weathering, Mass movement

Types of weathering

Mechanical (no chemical reactions), biological, chemical

Freeze thaw (mechanical)

Water enters cracks/joint and expands by 10% when frozen to exert pressure and widen the crack

Wetting/drying (mechanical)

Clay rocks expand when wet and fracture/contract when dry

Types of biological weathering

Plant roots grow into small cracks and widen, birds/animals burrow into cliffs

Types of chemical weathering and expkanation

Carbonation - Carbonic acid rainwater reacts with calcium carbonate to from weak calcium bicarbonate that erodes. Oxidation - Minerals reacts with oxygen to form a red powder and become vulnerable

Mass movement

Movement of material downslope due to gravity

Types of mass movement in ‘speed’ ascending order

Soil creep, mudflows, landslide, landslip/slump, runoff, rockfall

Soil creep and examplke

Particles rising due to freezing and falling due to gravity causes slow downward movement. Visible due to terracettes, Chalk Hills - Dorset

Mudflow

Flow of saturated soil due to pore pressure forcing particles apart over unconsolidated rock

Landslide and example

Slip surface becomes lubricated and rock moves downhill along a planar surface, Clay cliffs - Holderness

Landslip/slump with example

Pore pressure rises as permeable rock (unconsilidated) lies over impermeable rock to cause lost internal strength rotational movement on a curved slip plane, Barton on Sea - Hampshire

Runoff

Overland flow moves particles into the littoral zone and acts as an input into the sediment cell

Rockfall

Sudden collapse of fragments to from temporary store/input of scree

Erosion types and rate example

Hydraulic action, abrasion, attrition, solution, cavitation, 1-2m/year Holderness coast

Hydraulic action

Water compresses air into cracks and expands to weaken joints

Abrasion

Sediment scrapes cliffs and shoreline, eroding/smoothing surfaces

Attrition

Rocks collide to become smaller and more rounded

Solution

Acids in seawater can dissolve alkaline rock and transport this in water

Caviation

Bubbles implode under pressure to generate eroding jets of water

Factors affecting rate of erosion

Wave size/type, rock type, geological structure, presence/absence of beach, sub aerial processes, costal management

Transportation methods

Traction, saltation, suspension, solution, longshore drift

Traction

Rolling coarse sediment along the sea bed that’s too heavy to be carried

Saltation

Sediment bounces along the sea bed

Suspension

Fine sediment carried in water

Longshore drift

Waves approach generally in prevailing wind direction, swash carries material obliquely up the beach, backwash pulls material down at right angles due to gravity.