Soft sediment coasts
sandy shores, sand dunes,
marsh lands and estuarine
shores
Frances Mowling
Coastal & Aeolian Geomorphology
Soft landforms
3 Dune forms
Foredunes ± incipient dunes
Parallel dunes
Transgressive dunes
Spits, barriers
Estuaries, lacustrine systems
Embayed beaches
Coastal Dunes
Foredune and Parallel
Foredune and parallel dune
forms are common landforms.
Parallel dunes are sometimes
called secondary dunes, in that
the foredune is the first dune
located at the backshore of the
beach, and parallel dunes are
located behind the foredune.
Good examples: Templestowe
and Lagoons Beaches,
Binalong Bay, Taylors,
Boobyalla, and Waterhouse
Beaches, Noland Bay.
Transgressive dunes
Transgressive dunes –
Peron Dunes St Helens,
Cape Portland to Great
Forester River, Sandy
Point, St Albans Bay, and
Five Mile Bluff .
Foredune & parallel dunes (p.18)
Spits and barriers (see p15 of report)
18 landform features incorporating mid-bay spits,
spits and barrier in region.
Spits and barriers are elongate accumulations of
sand formed by waves, tides and winds. These
landforms can be reworked by rising sea levels.
These features are formed and grow in the
predominant direction of longshore sediment flow
caused by waves. Generally, spits are backed by
estuarine or lacustrine systems with salt marshes
and lagoons.
Lacustrine system Henderson Lagoon
Embayed beaches
Regular geometric planforms in beaches formed in
response to wave refraction.
Soft Estuarine Shores and Saltmarsh (p.21)
Geomorphic types
(a) Boobyalla, Little
Forester.
(b) Big, Musselroe, and
Little Musselroe Lagoons,
Scamander, Georges Bay.
(d) Henderson Lagoon
Application of a
worldwide typology of
geomorphic settings in
which saltmarshes occur
provides a good
comparative benchmark of
regional diversity.
Soft estuarine: Swash bars & delta
Coastal Dune Management - Natural
Vegetation, Mobility and Reactivation
Coastal dunes function as a buffer:
protecting hinterland from storm surge
frontal dunes act as a storage and transfer zone of beach
sediment
vegetation determines the stability of a sand dune.
Acceleration of coastal erosion by humans
Causes of blowouts
• off-road vehicles in dunes or mud-flats,
• alignment of access tracks to beach (pedestrian and vehicle)
water run-off from hard surfaces, into estuarine systems
• Pollution, sediment inputs.
Major causes of dune erosion
Wave erosion of foredunes leading to removal of
vegetation. the destruction or modification of natural
vegetation by fire.
Human recreation and alteration of composition of native
plant species.
Grazing by introduced animals, such as, sheep, cattle,
rabbits or native browsing animals in large numbers.
Dieback of natural vegetation within the dune system due to
Prolonged drought.
Off-road vehicles in dunes or mud-flats,
Alignment of access tracks to beach (pedestrian / vehicle).
Determining dune mobility status (p.40)
Triggered by Tasmanian State Coastal Policy (1996)
clause 1.4.2 ”Development on actively mobile landforms
such as frontal dunes will not be
permitted.”
Comparison of aerial photography – 1949± to latest photo
runs to acquire temporal and spatial components of coastal
dunes.
Short term hours through to months;
Medium term – several months to several decades.
Planning timeframes - Australian and International
Standards to be in the order of 50 to 100 years.
Dune mobility status – current (p. 40/95)
Character
(00 - 99)
00
10
11
12
20
21
22
Current dune mobility status
(Currmob
Unclassified
100% vegetation cover
(fixed dune)
70% - 100% vegetation cover (transitory)
50% - 70% vegetation cover (transitory)
30% - 50% vegetation cover (transitory)
10% - 30% vegetation cover (actively mobile dune)
<10% vegetation cover
(actively mobile dune)
Dune mobility status – Historic (p.40/95)
Character
(00 - 99)
00
30
31
32
33
34
35
Historic dune mobility status
(Histmob)
Unclassified
100% vegetation cover
(fixed dune)
70% - 100% vegetation cover (transitory)
50% - 70% vegetation cover (transitory)
30% - 50% vegetation cover (transitory)
10% - 30% vegetation cover (actively mobile dune)
<10% vegetation cover
(actively mobile dune)