Sand dune = large heap of sand that forms on
the dry backshore of a sandy beach
● Succession = the change of species over time
● Zonation = the change of species over space
● Xerophyte = a plant adapted to living in a dry,
arid habitat like a sand dune
● Embryo dune = newly formed sand dune , closest
to the sea
● Marram grass = a plant found in sand dunes that
have long, binding roots
● Saltation = how sand is bounced along by the
wind
● Crest = the top of the sand dune
● Water table = upper horizontal limit of wet sand
● Dune slack = where there is a trough or low point
in a line of dunes
● Leeward slope = the slope that faces away from
the wind
● Windward slope = the slope that faces the wind
Formation:
● Formed when sand deposited by longshore drift is moved up
the beach by the wind
● Conditions needed for formation:
○ A large flat beach
○ Large supply of sand
○ Large tidal range → sand needs time to dry
○ Onshore wind → allow sand to move to the back of
the beach
○ Obstacle (eg/ driftwood) for the dune to form against
● Wind moves sand in 3 ways →
1. When there are obstacles (eg/ driftwood) → heaviest
grains of sand will settle against driftwood and form
a small ridge
2. Lighter grains are transported and settle on other
side of obstacle
3. Area facing wind begins to reach a crest → pile of sand becomes steep
○ Becomes unstable and collapses under its own weight
4. Lighter grains of sand fall down on leeward side
○ Sand stops slipping once a stable angle has been achieved ( 30 – 34 degrees )
5. Repeats the cycle → causes sand dune migration inland over time
6. Sand dune itself becomes an obstacle for more dunes to form in front of it
○ Height of dunes depend on wind strength
○ Stronger winds create higher dunes
Characteristics:
● Unstable, steep leeward slope (30 – 34 degrees)
● Gentle slope on windward side
● Crests → heights vary up to approximately 15 m
● Colonised by plants and grasses
○ eg/ marram grass
Zonation of sand dunes:
● Dune succession = several lines of dunes running parallel to shore
○ There is a change in vegetation with increased distance inland
● Process:
1. Dunes grow taller (eg/ mature dunes may be up to 15 m high )
2. Size increases inland and long-rooted marram grass /other vegetation bind the sand together
○ Marram grass → grows quickly and aids sand accumulation
○ Long roots bind to the sand → help build up height of the dunes
3. Inland dunes become increasingly colonised by vegetation
○ Vegetation stabilises the sand and encourages more sand to accumulate there
■ Forms small dunes called “embryo dunes”
4. Overtime, oldest dunes migrate inland as newer embryo dunes are formed
5. Each line of dunes is separated by a trough called a slack
○ Slacks = formed by the ongoing removal of sediment at the base of the leeward side and
up the windward side
■ Slacks can be eroded so much that they reach as far as the water table
■ Results in salty ponds between dunes
6. Sometimes, a dune may develop a huge depression called a blowout
○ Blowout = strong winds remove sand from an area that has lost its vegetation cover
Coastal Management: Hard Engineering
→ Hard engineering = uses expensive heavy machinery to build artificial structures which work against nature
● Effective
● Do not blend in with natural environment
● Includes:
○ Sea walls
○ Groynes
○ Rock armour
○ Gabions
Sea walls:
● Sea walls = walls that provide a barrier
between waves and land
● Placed along the back of a beach
● Recurved sea walls are more effective in
reflecting waves/reduce overtopping
○ Recurved sea walls = rotates wave
backwards → energy is reflected
back out to sea
■ Impedes next wave
■ Reduces energy
■ Reduces erosive power
Groynes:
● Groynes = wooden/stone structures built in
the foreshore → look like fences/walls
○ Built at right angles to beach
○ Spaced at regular intervals –
approximately 50 m apart
○ Traditionally made of hardwood
timber
● Trap sediment transported by LSD
○ Builds up the beach on updrift side of
groyne
● Larger beach provides more effective buffer
→ absorbs waves’ energy
● Groynes are mainly effective when used in
conjunction with beach nourishment
Rock armour:
● Rock armour = 1000s of tonnes of huge
boulders/hard rock to act as barrier between
sea and land (eg/ granite (hard rock)
● Generally big enough not to be moved by
storm waves
● Downward slope arrangement to sea –
deflects wave energy
○ When water enters gaps between
rocks – pressure is released and
reduces waves’ energy
● Highly effective
Gabions:
● Gabions = steel, wire-mesh cages filled with
pebbles/ rocks
● Placed at the back of sandy beaches →
create a low, wall-like structure
● Water enters cages and wave energy is
absorbed and dissipated → reduces rate of
erosion
● Gabions may also be placed in front of cliff –
may be covered in vegetation
○ Gives stability to cliff
○ Reduces risk of landslides
