Coastal Oceanography Notes

Coastal & Estuarine Processes
Md Ibrahim, Oceanography, CU 1
Topic-1: Shore and Shore Process
What is coast?
Coast is the edge of land along the sea or other large body of water. The coast is the zone where the
land meets the sea/ocean. The coastline is a line that is considered the boundary between sea and land.
Coasts are shaped by the sea and the action of waves,
What is coastal zone?
The coastal zone is that the interface between the land
and sea, which comprised of a continuum of coastal
land, intertidal area, and aquatic system as an example
network of rivers & estuaries, inter-tidal places, salt
marshes.
A general workable definition is:
The part of the land affected by its proximity to the sea,
and that part of the sea affected by its proximity to the
land as the extent to which man's land-based activities
have a measurable influence on water chemistry and
marine ecology.
(US Commission on Marine Science, Engineering and Resources, 1969)
What is the major coastal process?
Coastal zones are very sensitive and are not static but rather dynamic environments that involve
transformation mass and energy through different forces, producing rocky coasts as well as beaches,
dunes, barriers and tidal inlets.
The 3 principle marine processes that influence coasts are:
• Erosion-breaking down of the land by the force of waves.
• Transportation-when waves and tides transfer broken; eroded materials somewhere else.
• Disposition-process by which winds and tides lose energy, cease to transport and release
eroded materials, thus depositing them.
These processes are driven by various types of driving forces such as waves, tides, currents, coastal
erosion and accretion, weathering, sea level rise, temperature, precipitation, and winds.
Erosion is the wearing away of the land by the sea. This often involves destructive waves wearing
away the coast. There are five main processes which cause coastal erosion. These are corrasion,
abrasion, hydraulic action, attrition and corrosion/solution.
• Corrasion is when waves pick up beach material (e.g., Pebbles) and hurl them at the base of a cliff.
• Hydraulic action. Air becomes trapped in joints and cracks in the cliff face. When a wave breaks, the
trapped air is compressed which weakens the cliff and causes erosion.
• Abrasion. Bits of rock and sand in waves are flung against the cliff face. Over time they grind down cliff
surfaces like sandpaper.
• Attrition. Waves smash rocks and pebbles on the shore into each other, and they break and become smaller
and smoother.
• Solution. Weak acids contained in sea water will dissolve some types of rock such as chalk or limestone.

Transportation is the movement of material in the sea and along the coast by waves. The movement
of material along the coast is called longshore drift.
Longshore drift is the main transport method for
movement of material along the shore by wave action.
Longshore drift happens when waves move towards the
coast at an angle. The swash (waves moving up the
beach) carries material up and along the beach. The
backwash carries material back down the beach at right
angles. This is the result of gravity. This process slowly moves material along the beach. Longshore
drift provides a link between erosion and deposition. Material in one place is eroded, transported then
deposited elsewhere.
• Solution. Minerals are dissolved in sea water and carried in solution. The load is not visible.
Load can come from cliffs made from chalk or limestone, and calcium carbonate is carried
along in solution.
• Suspension. Small particles are carried in water, e.g., silts and clays, which can make the water
look cloudy. Currents pick up large amounts of sediment in suspension during a storm, when
strong winds generate high energy waves.
• Saltation. Load is bounced along the sea bed, e.g., small pieces of shingle or large sand grains.
Currents cannot keep the larger and heavier sediment afloat for long periods.
• Traction. Pebbles and larger sediment are rolled along the sea bed.
Deposition is when eroded material is dropped by constructive waves. It happens because wave have
less energy. Deposition creates a range of landforms.
Give an overview of coastal zone.
A coastal zone is the interface between the land and water. These zones are important because a
majority of the world's population inhabit such zones. Coastal zones are continually changing because
of the dynamic interaction between the oceans and the land. This zone is being continually attacked by
cyclones, sea level rise, storm surge which have caused terrible impacts on this low-lying coastal area.
Waves and winds along the coast are both eroding rock and depositing sediment on a continuous basis,
and rates of erosion and deposition vary considerably from day to day along such zones. Sea level
changes affect the coast.
In general, coastal zones include the splash zone, the high intertidal zone, the low intertidal zone, and
the low tide zone. The coastal zone is the zone in which most of the infrastructure and human activities
directly connected with the sea are located. The coastal zone of Bangladesh covers an area of 47,201
km2
, 32% of the country, being the landmass of 19 districts. Around 35 million people, representing
29% of the population, live in the coastal zone. Humans have attempted various coastal stabilization
measures.
The energy reaching the coast can become high during storms, and such high energies make coastal
zones areas of high vulnerability to natural hazards. Thus, an understanding of the interactions of the
oceans and the land is essential in understanding the hazards associated with coastal zones.

Describe the coastal features.
Coastal landforms, any of the relief features present along any coast, the result of a combination of
processes, sediments, and the geology of the coast itself. There are two major types of coastal
morphology: one is dominated by erosion and the other by deposition.
Beaches
A consideration of the beach must also include the seaward adjacent nearshore environment because
the two are intimately related. The nearshore environment extends from the outer limit of the longshore
bars that are usually present to the low-tide line. In areas where longshore bars are absent, it can be
regarded as coincident with the surf zone. The beach extends from the low-tide line to the distinct
change in slope and/or material landward of the unvegetated and active zone of sediment accumulation.
It may consist of sand, gravel, or even mud, though sand is the most common beach material.
Shore
A shore or a shoreline is the fringe of land at the edge of a large body of water, such as an ocean, sea,
or lake. In physical oceanography, a shore is the wider fringe that is geologically modified by the
action of the body of water past and present, while the beach is at the edge of the shore, representing
the intertidal zone where there is one. In contrast to a coast, a shore can border any body of water,
while the coast must border an ocean or a sea. Therefore, in that sense, a coast is a type of shore.
However, the word "coast" often refers to an area far wider than the shore, often stretching miles into
the interior.
Shores are influenced by the topography of the surrounding landscape, as well as by water induced
erosion, such as waves. The geological composition of rock and soil dictates the type of shore which
is created. So, shore can be defined as the zone that lies between the low tide line and the highest
area of land affected by storm waves/storm surge.
Sea cliffs
The most widespread landforms of erosional coasts are sea cliffs. These very steep to vertical bedrock
cliffs range from only a few meters high to hundreds of meters above sea level. Their vertical nature
is the result of wave-induced erosion near sea level and the subsequent collapse of rocks at higher
elevation. Cliffs that extend to the shoreline commonly have a notch cut into them where waves have
battered the bedrock surface.
Sea stacks
Erosion along rocky coasts occurs at various rates and is dependent both on the rock type and on the
wave energy at a particular site. As a result of the above-mentioned conditions, wave-cut platforms
may be incomplete, with erosional remnants on the horizontal wave-cut surface. These remnants are
called sea stacks, and they provide a spectacular type of coastal landform.

Sea arches
Another spectacular type of erosional landform is the sea arch, which forms as the result of different
rates of erosion typically due to the varied resistance of bedrock. These archways may have an arcuate
or rectangular shape, with the opening extending below water level. The height of an arch can be up
to tens of meters above sea level. It is common for sea arches to form when a rocky coast undergoes
erosion and a wave-cut platform develops.
Coastal dunes
Immediately landward of the beach are commonly found large, linear accumulations of sand known
as dunes. (For coverage of dunes in arid and semiarid regions, see sand dune.) They form as the wind
carries sediment from the beach in a landward direction and deposits it wherever an obstruction hinders
further transport.
Coastal boundaries of Bangladesh according to Bangladesh coastal zone policy
2005:
The Coastal Zone Policy, formulated by the
Ministry of Water Resources (mowr),
intends provide a general guidance to all
agencies and institutions concerned for the
management and development of the coastal
zone in a manner that provides a secure and
conducive environment for coastal
communities to pursue their life and
livelihoods. Amongst several objectives it
identifies the following: the creation of
sustainable livelihoods; intensifying the
coverage of safe drinking water facilities;
reducing vulnerabilities (including to
climate change) and closing the gender
gap.
Three indicators have been considered for determining the landward boundaries of the coastal zone of
Bangladesh. These are: influence of tidal waters, salinity intrusion and cyclones/storm surges. 19
districts2 of the country are being affected directly or indirectly by some of these phenomena. The
districts are considered including all pails/thanas. A total of 48 upazilas/thanas are considered as
‘exposed’ directly to vulnerabilities from natural disasters. The exclusive economic zone (EEZ) is
regarded as the seaward coastal zone. One-third of the country belongs to the coastal zone. According
to 2001 population census, population of the coastal zone is 3 crore and 48 lakhs.
The coastal zone of Bangladesh lies within the tropical zone between 21-23° N and 89-93° E. The
coast of Bangladesh is about 700 km long and can be broadly divided into three regions: the deltaic
eastern region (Pacific type), the deltaic central region, and the stable deltaic western region (Atlantic
type). It is characterized by a vast network of rivers (24,000 km in length) covering an area of 9380
km2, a large number of islands between channels, a submarine canyon (Swatch of no Ground), the
funnel shaped part of the northern bay of Bengal, huge amount of sediment transportation (annually
about 2.4 x 109 m tons), low relief (1.2-4.5 m above mean sea level) and horrendous tropical cyclones.

Weathering
Weathering describes the breaking down or dissolving of rocks and minerals on the surface of the
Earth. Water, ice, acids, salts, plants, animals, and changes in temperature are all agents
of weathering. Weathering is breaking down rocks, soil, and minerals as well as wood and artificial
materials by contacting the atmosphere, water, and biological organisms of the Earth. Weathering takes
place in situ, i.e., in the same place, with little or no movement.
How is erosion different to weathering?
Erosion and weathering are the processes in which the rocks are broken down into fine particles.
Erosion is the process in which rock particles are carried away by wind and water. Weathering, on the
other hand, degrades the rocks without displacing them.
Erosion Weathering
It is the displacement of solids by wind, water and
ice.
It is the decomposition of rocks, soil and minerals
by direct contact with the atmosphere.
The eroded materials are displaced. The weathered materials are not displaced.
The different types of erosion are water, wind, ice,
thermal and gravity erosion
The different types of weathering include physical,
chemical and biological weathering
Wind, water, ice and human activities are some of
the causes of erosion.
Weathering is caused due to atmospheric factors
like air pressure.
Physical weathering
Physical weathering consists of breaking apart rocks and crystals through different processes without
changing their chemical composition. The results of physical weathering are smaller components of
the same material that is being weathered. There is no change in chemical composition.
Physical weathering tends to produce mostly sand-sized sediment and larger grains because most of
the fracturing occurs along mineral boundaries. Physical weathering of fine grained or finely
crystalline rock can produce abundant very fine grains, but most of the sediment from these rock types
consists of rock fragments called lithic clasts. Lithic clasts produced from physical weathering range
in size from very fine silts and clays to large boulders and gravel.
There are two main types of physical weathering:
• Freeze-thaw occurs when water continually seeps into cracks, freezes and expands, eventually
breaking the rock apart.
• Exfoliation occurs as cracks develop parallel to the land surface a consequence of the reduction
in pressure during uplift and erosion.
Freeze-thaw: Freeze-thaw weathering is a process of erosion that happens in cold areas where ice
forms. A crack in a rock can fill with water which then freezes as the temperature drops. As the ice
expands, it pushes the crack apart, making it larger.

Where does it occur?
In mountainous regions like the Alps or Snowdonia.
How does it occur?
Exfoliation: Exfoliation is a form of mechanical
weathering in which curved plates of rock are stripped from
rock below. This results in exfoliation domes or dome-like
hills and rounded boulders. Exfoliation domes occur along
planes of parting called joints, which are curved more or
less parallel to the surface.
Where does it occur?
Typically, in upland areas where there are exposures of
uniform coarsely crystalline igneous rocks.
Rainwater or
snow-melt
collects in
cracks in the
rocks.
At night the
temperatures
drops and the
water freezes
and expands.
The increases
in volume of
the ice exerts
pressure on
the cracks in
the rock,
causing them
to split
further open.
During the
day the ice
melts and the
water seeps
deeper into
the cracks
At night the
water freezes
again….etc.

How does it occur?
Changes in pressure can also contribute to exfoliation due to weathering. In a process called unloading,
overlying materials are removed. The underlying rocks, released from overlying pressure, can then
expand. As the rock surface expands, it becomes vulnerable to fracturing in a process called sheeting.
Chemical weathering
Weathering of rocks caused by the chemical action of water containing atmospheric oxygen, carbon
dioxide, and some organic acids in solution on the rock-forming minerals leading to an adjustment of
the mineralogical composition with the formation of new minerals, like hydrous phyllosilicates, iron
oxides/hydroxides, soluble salts, and other alteration products, consisting of rock decay by chemical
decomposition.
Oxidation is the reaction of rock minerals with oxygen, thus changing the mineral composition of the rock.
When minerals in rock oxidize, they become less resistant to weathering. Iron, a commonly known mineral,
becomes red or rust colored when oxidized.
The rock mass at depth
is under high pressure
from underlying rocks.
It tends to be uniform
and lack fractures.
As progressive erosion
occurs, the rock mass
is subjected to
progressively lower
pressure of overlying
rocks which leads to
tension in directions at
right angles to the land
surface.
This tension is
relieved by formation
of cracks which follow
the land surface - they
are relatively flat on
plateaus, but can be
steep on the flanks of
mountains which are
called exfoliation
domes.
Once the cracks
develop, water enters
and causes chemical
weathering leading to
the formation of new
low-density minerals.
This enhances the
cracks and encourages
slabs of rock to detach
from the surface.

Carbonation is the process of rock minerals reacting with carbonic acid. Carbonic acid is formed
when water combines with carbon dioxide. Carbonic acid dissolves or breaks down minerals in the
rock. As its solutes the rock it also called solution process.
CO2 + H2O → H2CO3
(Carbon dioxide + water → carbonic acid)
Caco3 + H2CO3 → Ca2+
+ 2HCO3-
(calcite + carbonic acid → calcium + bicarbonate)
Hydrolysis is a chemical reaction caused by water. Water changes the chemical composition and size
of minerals in rock, making them less resistant to weathering. Click on the video clip below to
see Hydrolysis of a relatively weathering resistant mineral, feldspar. When this mineral is completely
hydrolyzed, clay minerals and quartz are produced and such elements as K, Ca, or Na are released.
A hydrolysis reaction of orthoclase (alkali feldspar), a common mineral found in igneous rock, yields
kaolinite, silicic acid, and potassium.
2kaisi3o8 + 2H+
+ 9H20 → H4Al2Si2O9 + 4h4sio4 + 2K+
(orthoclase + water → kaolinite + silicic acid + potassium)
Biological weathering
Biological weathering is the weakening and
subsequent disintegration of rock by plants,
animals and microbes.
Growing plant roots can exert stress or
pressure on rock. Although the process is
physical, the pressure is exerted by a
biological process (i.e., growing roots).
Biological processes can also produce
chemical weathering for example where
plant roots or microorganisms produce
organic acids which help to dissolve minerals.
Microbial activity breaks down rock
minerals by altering the rock’s chemical composition, thus making it more susceptible to weathering.
One example of microbial activity is lichen; lichen is fungi and algae, living together in a symbiotic
relationship. Fungi release chemicals that break down rock minerals; the minerals thus released from
rock are consumed by the algae. As this process continues, holes and gaps continue to develop on the
rock, exposing the rock further to physical and chemical weathering.
Burrowing animals can move rock fragments to the surface, exposing the rock to more intense
chemical, physical, and biological processes and so indirectly enhancing the process of rock
weathering.
Although physical, chemical, and biological weathering are separate processes, some or all of the
processes can act together in nature.

Topic-3&4: Beach and Beach Material
A beach is a narrow strip of land separating a body of water from inland areas. Beaches are usually
made of sand, tiny grains of rocks and minerals that have been worn down by constant pounding by
wind and waves. This beach, in Pebble Beach, California, has both sandy and rocky features
Backshore: The beach area between the foreshore and the foot of the dunes. This zone is between the
shoreline and coastline. Normally the backshore is dry; waves only reach this area during storms. (H)
Bar (Sandbar): An embankment of sand, gravel, or other particles deposited in shallow water by
waves and currents that are parallel to the shore. Bars may be submerged or emerged. There can be
several rows of bars.
Beach (Shore): Zone of loose sand, gravel, and other material that extends landward from the low tide
waterline to the coastline.
Beach Berm: Long wedge of sand parallel to the shoreline that is normally in the backshore of the
beach. Berms have different slopes on their seaward and landward sides; the steep side of a berm faces
the ocean, the side that faces land has a gentler slope or is flat. Beach berms are formed by waves
depositing material. Berms can resemble terraces, with several beach berms on a beach. Or, a beach
may have no berms.
Breaker Zone: Area where deep-water waves touch bottom and become shallow-water waves,
changing from rounded swells to unstable, peaked waves that start to break.
Coast: A strip of land of indefinite width (up to several miles) extending from the coastline inland
toward the first major change in land features that are not influenced by coastal processes.
Coastline: The line that forms the boundary between the coast (land) and the beach (shore). It is
marked by the start of permanent vegetation or where there is a marked change in substrate or landform
morphology (shape), for example, from a relatively flat beach to hilly dunes.
Dunes: Ridges or mounds of loose, windblown material, usually sand. Dunes are often vegetated, that
is, they have plants growing on them.
Foreshore: That part of the beach (shore) between the water level at low tide and the upper limit of
the wave wash at high tide (the shoreline).
High tide: The highest water level of each rising tide.
Low tide: The lowest water level of each falling tide.
Nearshore; The zone extending seaward from the water level at low tide (the foreshore) to beyond the
breaker zone. This area is indefinite and is affected by nearshore currents. So, it is the area from low
water tide line to where waves break at low tide.
Offshore: The direction seaward of the nearshore zone. The area beyond low tide breaking waves.
Shoreline: The line formed when the water touches the beach at high tide. The shoreline divides the
beach into the foreshore and backshore.

Composition of Beaches
A beach is a landform alongside a body of water which consists of loose particles. Beaches are made
up of eroded materials that have been transported from elsewhere and deposited by the sea. Sometimes
it is formed by locally available material. The particles composing a beach are typically made from
rock, such as sand, gravel, shingle, pebbles, etc., or biological sources, such as mollusk shells or
coralline algae. It may be coarse of fine-grained sediment, boulders from local cliff, sand or mud from
rivers. Sediments settle in different densities and structures, depending on the local wave action and
weather, creating different textures, colors and gradients or layers of material. Most beach materials
are the products of weathering and erosion. Over many years, water and wind wear away at the land.
The continual action of waves beating against a rocky cliff, for example, may cause some rocks to
come loose.
A broad classification of beaches was presented by Trask (1952), consisting of three divisions: sand,
gravel, shingle, and cobble beaches; muddy, silty, or clayey beaches; and bedrock and reef beaches.
Sand movement along beach
Beach sand will have a net movement up or down the beach or perpendicular depending on the
direction of incoming waves. This net movement of the beach sand is known as beach drift.
Two major types
1.Perpendicular to shoreline (toward and away)
• Swash – is the movement of
water that is washed up the
beach when a wave breaks and is
often observed as a foaming
mass of moving water.
• Backwash – water drains back
to the ocean so the water that
runs back down the beach
following the swash. Water
rushes up the beach
2.Parallel to shoreline (up-
coast or down-coast)
• Longshore current –
transports sand along the beach.
Longshore drift from longshore
current is a geological process
that consists of the
transportation of sediments
(clay, silt, pebbles, sand,
shingle) along a coast parallel to the shoreline, which is dependent on the angle incoming wave
direction. Oblique incoming wind squeezes water along the coast, and so generates a water current
which moves parallel to the coast. Longshore drift is simply the sediment moved by the longshore
current. This current and sediment movement occur within the surf zone. The process is also known
as littoral drift.

Longshore current
Longshore currents are common at any
beach that is exposed to breaking surf. A
longshore current is an ocean current that
moves parallel to shore. It is caused by large
swells sweeping into the shoreline at an
angle and pushing water down the length of
the beach in one direction. Longshore
currents usually extend from the shallow
waters inside the breaking waves to
breaking waves on the outside. They vary
depending on the size, strength, and
direction of the approaching swell, and the
length of the beach. The more prominent the
swell size and direction, and the longer and
straighter the beach is, the more powerful
and swift the long-shore current will be.
They are responsible for many rescues along
the coast by sweeping swimmers and surfers
down the beach into a variety of hazards. They also have a large impact on the shoreline.
Winter & Summer Beach Profiles
Scientists refer to beaches’ profile (a cross-shore measure of elevation from the dune to the water
across the beach), and there are both summer and winter profiles for each beach due to variation in
wind and wave energy between seasons.
Winter time
In general, along the mid-Atlantic, seasonal
variation in prevailing wind direction and
speed results in larger waves in the winter
months.
Wind speed is greater in the winter because
of the increased temperature difference
between the poles and equator. Air
movement is caused by uneven heating, so
as the difference between the temperature
of the poles and equator increases, so does
wind speed because the temperature
gradient causes warm air rising from the
equator to be more quickly replaced by air
from the poles. Wind speed, direction, and
fetch create waves meaning that the
increase in wind speed and a change in
direction will result in bigger winter waves
that cause greater erosion and result in two very different beach profiles.

Summer Time
Gentler summer waves deposit sand from offshore bars onto the beach, ultimately widening it and
increasing its elevation. Conversely, stronger winter waves with more energy, pick up those particles
deposited in the summer, and carry them back offshore in bars, thus narrowing the beach. These
offshore bars work to help buffer the beach during the winter from erosion as they cause waves to
break further offshore.
The differences between summer and winter on beaches in areas where the winter conditions are
rougher and waves have a shorter wavelength but higher energy. In winter, sand from the beach is
stored offshore (Steven Earle, “Physical Geology”).
Describe the basic characteristics of erosional and depositional coasts in brief.
Erosional coast:
A coastline where sediment is not accumulating and wave action grinds away at the shore. These are
new coast in which the dominant processes are those that remove coastal material.
Characteristics:
• Erosional coast is shaped and attached from land by
stream erosion, the abrasion of wind driven grit, the
alternating freezing and thawing of water in rock
cracks, the probing of plant roots, glacial activity and
dissolution by acids from soil and slumping.
• Usually, rocky coasts are more susceptible to erosion
by these processes.
• The rate at which a shore erodes depends on the
hardness and resistance of rock, the violence of the
wave shock to which it is exposed and the local range
of tide.
• A shore with little tidal variation can erode quickly
because the wave action is concentrated near one level
for longer times.
• Erosion is usually most rapid on high energy coasts
and the low energy coasts are only infrequently
attached by large waves.
Example: Rocky coasts of Marine in South America, British Columbia Coasts.

Depositional coast:
The coasts that are created by the deposition of sediments carried by wave and currents in the
continental margin are called depositional coast.
Characteristics:
• Accumulation and distribution of a layer of
protective sediments along a coast insulate that coat
from erosion.
• Most of the depositional coasts are created by long-
shore drift.
• These long-shore drift carries huge amount of
sediments and accumulated then in a suitable place
of deposition along the continental margin.
• Near shore currents may distribute some of the
sediments to the edge of the shelf break but most of
the sediments are distributed in the surf zone by
waves.
• The most common features of a depositional coast
is the beach.
Example: The sandy coastline from New Jersey to Florida, Broad beaches of Southern California
Cox’s Bazar, Chittagong.

Beach Materials
A beach is a narrow, gently sloping strip of land that lies along the edge of an ocean, lake, or river.
Materials such as sand, pebbles, rocks, and seashell fragments cover beaches.
Most beach materials are the products of weathering and erosion. Over many years, water and wind
wear away at the land. The continual action of waves beating against a rocky cliff, for example, may
cause some rocks to come loose. Huge boulders can be worn town to tiny grains of sand.
Beach materials may travel long distances, carried by wind and waves. As the tide comes in, for
example, it deposits ocean sediment. This sediment may contain sand, shells, seaweed, even marine
organisms like crabs or sea anemones. When the tide goes out, it takes some sediment with it.
What is sand made of?
Sand is made of rocks eroded by rivers, the skeletons and shells of invertebrates, as well as calcium
carbonate from marine animals.
A lot of the sand (both beach and desert) is made from eroded rock. As rivers flow downstream from
their origin, their movement (often violent) erodes rocks down to very small grains of minerals and
carries these small portions of rock along with it as it travels. Along the river’s journey, the pebbles
continue to break down into smaller pebbles, which finally become sand by the time the river reaches
its end. As the river empties into the ocean, it deposits some sand along the land. The waves constantly
shift the sand deposited by the river, creating the gorgeous coastlines we lounge on during summer
vacations. Smaller sediments are carried even further into the sea.
Sand is made from the skeletons and shells of marine life. Life forms also contribute to sand. In fact,
sand is made up of the skeletons of many invertebrates, such as clams, coral and other creatures with
shells that live in the sea. The waves carry them to the shore, where they settle. They too slowly erode
to become finer grains of sand. Sand is made of organic matter. Beach sand is also replete with living
life. Algae are very common inhabitants of sand.
Sand will look slightly different in different parts of the world, depending on which types of rocks the
river eroded.

Beach Colors
Sand’s color is derived from its mineralogy, or the physical structure of the crystals that populate the
sand. These minerals can come from erosion of nearby landscape, volcanic eruptions, and even the
grounding up of sea shells over decades, so the color and content of sand reflect the makeup of the
surrounding landscape and even the beach’s inhabitants.
Beaches can be many different colors. Coral beaches, common on warm, tropical islands, are white
and powdery. They are made from the skeletons of tiny animals called corals. Some coral beaches
have pink sand. The corals that created these beaches were red. Some islands created by volcanoes
have black beaches. The sand on Punaluu Beach, Hawaii, it was created as black lava hardened in the
ocean. Some beaches are green. The sand on these beaches is made of a mineral called olivine.
Sources of Beach Materials
Beach sediment is categorized by three main types depending on its origin:
• Terrigenous Parent Material (derived from land)
• Volcanic Parent Material (derived from volcanic activity)
• Biogenic Parent Material (derived from shells and skeletons of marine organisms)
Four Sources of Beach Material;
1) Material eroded from headlands dependent on the rock type.
Most beach materials are the products of weathering and erosion. Over many years, water and
wind wear away at the land. The continual action of waves beating against a rocky cliff, for
example, may cause some rocks to come loose. Huge boulders can be worn town to tiny grains
of sand.
2) Sediment moved up onto the beach from the offshore zone.
Beach materials may travel long distances, carried by wind and waves. As the tide comes in,
for example, it deposits ocean sediment. This sediment may contain sand, shells, seaweed, even
marine organisms like crabs or sea anemones.
3) Large rivers carrying material from inland to the sea.
In Bangladesh most of the sediment which become source of beaches is supplied by the Ganges
and Brahmaputra rivers which supply the Lower Meghna delta in Bangladesh and the Hoogly
delta in West Bengal (India). Several other large rivers in Bangladesh and India provide smaller
contributions.
4) Material cycled from one beach along the coast to another.
Tides and ocean currents can carry sediment a few meters or hundreds of kilometers away.
Tides and currents are the main way beaches are created, changed, and even destroyed, as the
currents move sediment and debris from one place to another.
What determines the size of sand on a beach?
A) Energy of the wave
B) The size of the material furnished to the beach

Topic-6&7: Wave Generation, Types and Their Measurement
A wave is the repeating and periodic disturbance that travels through a medium (e.g., Water) from one
location to another location. In the ocean most waves are generated by wind, but Tsunami waves can
also be generated by landslides, and undersea earthquakes.
Waves transmit energy, not water, across the ocean and if not obstructed by anything, they have
the potential to travel across an entire ocean basin. Waves are most commonly caused by wind. Wind-
driven waves, or surface waves, are created by the friction between wind and surface water.
Term (symbol) Meaning
Wavelength
(lambdaλlambda) Distance between adjacent maxima or minima of a wave.
Periodic wave
Wave that repeats over time and space. Also called a continuous
wave.
Crest Highest point on a transverse wave. Also called the peak.
Trough Lowest point on a transverse wave.
Expansion
A point of maximum spacing between particles of a medium for
longitudinal waves.
Compression
A point of minimum spacing between particles of a medium for
longitudinal waves.

What determines the size of wave?
Most waves are generated by wind. Such a wave's size depends on
• How long the wind blows (wind duration): The length of time the wind blows in the same
direction over the swell generating area, or the fetch. The greater the wind velocity, the longer
the fetch, and the greater duration the wind blows, then the more energy is converted to waves
and the bigger the waves. However, if wind speed is slow, the resulting waves will be small,
regardless of the fetch or duration. The longer the duration of wind, the more of its energy is
transferred to the ocean, resulting in larger waves. As seas develop, they can reach at most a 7-
to-1 ratio of wavelength to wave height.
• The strength of the wind (wind speed): Waves are most commonly caused by wind. Waves
are created by the friction between wind and surface water. As wind blows across the surface
of the ocean or a lake, the continual disturbance creates a wave crest. More powerful wave
builds strong waves.
• The fetch: Fetch is area of ocean or lake surface over which the wind blows in an essentially
constant direction, thus generating waves. It is the distance over which the wind blows. Fetch
is an important factor in the development of wind waves, which increase in height with
increasing fetch up to a maximum of 1,600 km (1,000 miles). Wave heights do not increase
with increasing fetch beyond this distance.
The water in a wave moves in a circular orbital pattern downward to a depth of one-half the
wavelength.
Wave speed
Wave speed is the distance a wave travels in a given amount of time, such as the number of meters it
travels per second. Wave speed (and speed in general) can be represented by the equation:
Speed = Distance/Time
The frequency, f, is 1/T, so the equation relating wave speed, frequency, and wavelength is
V = f λ .
Speed = Wavelength x Wave Frequency
Wave speed is related to both wavelength and wave frequency. Wavelength is the distance between
two corresponding points on adjacent waves. Wave frequency is the number of waves that pass a fixed
point in a given amount of time. This equation shows how the three factors are related:
Speed = Wavelength x Wave Frequency

Types of waves on the basis of particle movement direction
One way to categorize waves is on the basis of the direction of movement of the individual
particles of the medium relative to the direction that the waves travel. Categorizing waves on this
basis leads to three notable categories:
• Transverse waves
• Longitudinal wave
• Orbital waves.
A transverse wave is a wave in which particles of the
medium move in a direction perpendicular to the
direction that the wave moves. Suppose that a slinky is
stretched out in a horizontal direction across the
classroom and that a pulse is introduced into the slinky
on the left end by vibrating the first coil up and down.
Energy will begin to be transported through the slinky
from left to right. As the energy is transported from left
to right, the individual coils of the medium will be displaced upwards and downwards. In this case,
the particles of the medium move perpendicular to the direction that the pulse moves. This type of
wave is a transverse wave. Transverse waves are always characterized by particle motion
being perpendicular to wave motion.
A longitudinal wave is a wave in which particles of the
medium move in a direction parallel to the direction that
the wave moves. Suppose that a slinky is stretched out in
a horizontal direction across the classroom and that a pulse
is introduced into the slinky on the left end by vibrating
the first coil left and right. Energy will begin to be
transported through the slinky from left to right. As the energy is transported from left to right, the
individual coils of the medium will be displaced leftwards and rightwards. In this case, the particles of
the medium move parallel to the direction that the pulse moves. This type of wave is a longitudinal
wave. Longitudinal waves are always characterized by particle motion being parallel to wave motion.
An orbital wave is a wave in which particles of the
medium undergo a circular motion. Surface waves are
neither longitudinal nor transverse. In longitudinal
and transverse waves, all the particles in the entire
bulk of the medium move in a parallel and a
perpendicular direction (respectively) relative to the
direction of energy transport. In a surface wave, it is only the particles at the surface of the medium
that undergo the circular motion. The motion of particles tends to decrease as one proceeds further
from the surface.

Types of waves on the basis of depth
Deep-Water Waves
If the water depth (d) is greater than the wave base (L/2), the waves are called deep-water waves
(Figure 9.6). Deep-water waves have no interference with the ocean bottom, so they include all wind-
generated waves in the open ocean, where water depths far exceed wave base. Wave speed (S) is the
rate at which a wave travel. Numerically, it is the distance traveled divided by the travel time; for a
wave, it can be calculated as:
Transitional Waves
Waves that have some characteristics of shallow-water waves and some of deep-water waves are called
transitional waves. The wavelengths of transitional waves are between two times and twenty times the
water depth (Figure 9.5b). The wave speed of shallow water waves is a function of water depth; for
deep-water waves, wave speed is a function of wavelength. Thus, the speed of transitional waves
depends partially on water depth and partially on wavelength.
Shallow-Water Waves
Waves in which depth (d) is less than 120 of the wavelengths (L/20) are called shallow-water waves,
or long waves (Figure 8.7c). Shallow-water waves are said to touch bottom or feel bottom because
they touch the ocean floor, which interferes with the wave s orbital motion. The speed of shallow-
water waves is influenced only by gravitational acceleration (g) and water depth (d). Particle motion
in shallow-water waves is in a very flat elliptical orbit that approaches horizontal (back-and forth)
oscillation. The vertical component of particle motion decreases with increasing depth below sea level,
causing the orbits to become even more flattened

Types of waves on the basis of wave period
Detail Info will be available at
https://onlinelibrary.wiley.com/doi/full/10.1002/9781118476406.emoe077

Standing wave
Standing wave, also called stationary wave.
Standing waves result when two equal waves are going in opposite direction and in this case, you get
the usual up/down motion of the water surface but the waves don't progress.it is combination of two
waves moving in opposite directions, each having the same amplitude and frequency. The phenomenon
is the result of interference; that is, when waves are superimposed, their energies are either added
together or canceled out. These are common in coastal areas where waves reflect off seawalls, ship's
hulls, or breakwaters. They're also common in swimming pools.
Tidal wave
A tidal wave is a shallow water wave caused by the gravitational interactions between the Sun, Moon,
and Earth.
A tidal wave is a regularly reoccurring shallow water wave caused by effects of the gravitational
interactions between the Sun, Moon, and Earth on the ocean. The term "tidal wave" is often used to
refer to tsunamis; however, this reference is incorrect as tsunamis have nothing to do with tides.
What is the difference between a tsunami and a tidal wave?
Although both are sea waves, a tsunami and a tidal wave are two different and unrelated phenomena.
A tidal wave is a shallow water wave caused by the gravitational interactions between the Sun, Moon,
and Earth.
A tsunami is an ocean wave triggered by large earthquakes that occur near or under the ocean, volcanic
eruptions, submarine landslides, or by onshore landslides in which large volumes of debris
Tsunamis
Tsunamis are very long wavelength waves resulting
from seismic events, such as earthquakes, under-water
landslides, or volcanic eruptions. Wavelengths can be
>200km with long wave periods. In the open ocean
(away from shore) they travel very fast (the same speed
as a jet airliner), but have very small amplitude (cm to
a meter or so). Thus, they have very small wave slopes,
and you might not even notice it in the deep ocean,
because the normal

Capillary wave
Capillary wave, small, free, surface-water wave with such a short wavelength that its restoring force
is the water’s surface tension, which causes the wave to have a rounded crest and a V-shaped trough.
Capillary waves represent the initial stage of wave generation. They are the first waves produced by
small vortices in a completely flat sea, and they have a very short wavelength.
The maximum wavelength of a capillary wave is 1.73 centimeters (0.68 inch); longer waves are
controlled by gravity and are appropriately termed gravity waves. Unlike the velocity of gravity
waves, the velocity of capillary waves increases with decreasing wavelength, the minimum velocity
being 23.1 centimeters per second (9.09 inches per second), where the wavelength is the maximum
1.73 cm.
Gravity waves
Gravity waves are waves generated in a fluid medium or at the interface between two media when
the force of gravity or buoyancy tries to restore equilibrium. An example of such an interface is that
between the atmosphere and the ocean, which gives rise to wind waves.
A gravity wave results when fluid is displaced from a position of equilibrium. The restoration of the
fluid to equilibrium will produce a movement of the fluid back and forth, called a wave orbit.[1]
gravity
waves on an air–sea interface of the ocean are called surface gravity waves or surface waves, while
gravity waves that are within the body of the water (such as between parts of different densities) are
called internal waves. Wind-generated waves on the water surface are examples of gravity waves, as
are tsunamis and ocean tides.
wind-waves would catch your attention instead. They may start small-amplitude out at sea, but when
they meet a continental shelf, their wave height increases dramatically, creating a wall of water
approaching the shore.

Rogue waves
Rogue waves (also known as freak waves, monster
waves, episodic waves, killer waves, extreme waves,
and abnormal waves) are unusually large,
unpredictable and suddenly appearing surface waves
that can be extremely dangerous to ships, even to large
ones. They are distinct from tsunamis, which are often
almost unnoticeable in deep waters and are caused by
the displacement of water due to other phenomena
(such as earthquakes). A rogue wave appearing at the
shore is sometimes referred to as a sneaker wave.
A rogue wave is usually defined as a wave that is two times the significant wave height of the area.
The significant wave height is the average of the highest one-third of waves that occur over a given
period. Therefore, a rogue wave is a lot bigger than the other waves that are happening in its vicinity
around the same time.
Wave shoaling
Wave shoaling is the change in shape and behavior as
waves propagate into water of decreasing depth. This
results in decreases in wave speed and wavelength while
wave height increases. In deep water, the waveform
approximates a sinusoid and wave behavior is unaffected by
water depth.
Shoaling happens because waves experience force from the
seabed as the water gets shallower. This slows down the
wave – the shallower the water, the slower the wave. In deep
water, a tsunami moves very fast and has a long wavelength
and a small amplitude.

Wave Interference
Wave interference is the phenomenon that occurs when two waves meet while traveling along the
same medium. The interference of waves causes the medium to take on a shape that results from the
net effect of the two individual waves upon the particles of the medium.
Constructive interference is a type of interference that occurs at any location along the
medium where the two interfering waves have a displacement in the same direction. In this
case, both waves have an upward displacement; consequently, the medium has an upward
displacement that is greater than the displacement of the two interfering pulses.
Destructive interference is a type of interference that occurs at any location along the medium
where the two interfering waves have a displacement in the opposite direction
Mixed interference in most ocean areas, it is likely that two or more swells of different heights
and lengths will come together and produce a mixture of constructive and destructive
interference. In this scenario, a more complex mixed interference pattern develops
Wave dispersion
Dispersion of water waves generally refers to frequency dispersion, which means that waves of
different wavelengths travel at different phase speeds. Water waves, in this context, are waves
propagating on the water surface, with gravity and surface tension as the restoring forces.
Dispersion may be caused either by geometric boundary conditions (waveguides, shallow water) or by
interaction of the waves with the transmitting medium.

Patterns of waves approaching the shoreline
Water waves exhibit the same behaviors as other waves, including electromagnetic and sound waves,
when they encounter a boundary, such as an object. Waves interact with matter in several ways. The
interactions occur when waves pass from one medium to another. The types of interactions are
reflection, refraction, and diffraction.
Refraction
A Physics definition of refraction involves a change in the
direction of waves as they pass from one medium to another.
This is due to energy conservation when a wave changes its
wavelength, and thus wave speed, as it enters a new medium
(like in light or sound waves traveling from air to water). Now,
in terms of ocean waves, refraction also involves a change of
direction when a wave experiences a shift in wavelength and
wave speed. However, this shift generally occurs due to
changes in ocean depth. As a wave travels from deep to
shallow water, the wavelength shortens, the wave speed slows
down, and the wave will refract, or bend, toward the shallow
area in order to conserve its energy. This is commonly seen in
deep water canyons where the wave encounters shallow water
along the canyon’s edges, and the wave will bend/refract
towards the shallow water.
Diffraction
Diffraction occurs when a wave encounters an obstruction in its path and will change direction, or
wrap around it. In ocean waves, we see this occur when a wave
encounters an object like a jetty and the wave rotates around it
(sometimes diffraction also occurs when a wave moves through
a small opening in a seawall or between or two islands). The
‘wrapping’ or turning potential of a wave is larger in waves
with a longer wavelength (i.e., longer period). This is why a
long period Groundswell wave can sometime wrap a full 180
degrees around a barrier/jetty, whereas short-period Wind swell
wave will often shoot straight by it. Diffraction can occur in
shallow or deep water and is separate from refraction since it is not a result of a change in ocean depth.
However, both refraction and diffraction will involve a change in a wave’s direction.
Reflection
Reflection occurs when a water wave bounces off of a
hard surface, such as a seawall or a sea cliff, changing
the direction of the wave. For reflected waves, the
angle of incidence, the angle at which the wave
approaches the surface, equals the angle of reflection.
Both the angle of incidence and the angle of reflection
are measured from a normal line, which is a
hypothetical line perpendicular to the shoreline. For
example, if a wave approaches a seawall at a 45-degree
angle of incidence, the wave direction propagates away from the wall at a 45-degree angle of reflection
(Fig. 5.6). The angle of incidence ranges from zero degrees, which is like a wave approaching a wall
head on, to slightly greater than 90 degrees, which is like a wave approaching parallel to the wall. In
general, the speed, frequency, period, and energy of a wave are not affected by reflection.

Wave breakers at shore
There are three main types of breakers:
• Spilling,
• Plunging,
• Surging.
These are related to the steepness of the bottom, and how quickly the wave will slow down and its
energy will get dissipated.
Spilling breakers form on gently sloping or flatter beaches, where the energy of the wave is dissipated
gradually. The wave slowly increases in height, then slowly collapses on itself. For surfers, these waves
provide a longer ride, but they are less exciting.
Plunging breakers form on more steeply-sloped shores, where there is a sudden slowing of the wave
and the wave gets higher very quickly. The crest outruns the rest of the wave, curls forwards and breaks
with a sudden loss of energy. These are the “pipeline” waves that surfers seek out.
Surging breakers form on the steepest shorelines. The wave energy is compressed very suddenly right
at the shoreline, and the wave breaks right onto the beach . These waves give too short (and potentially
painful) a ride for surfers to enjoy.

Topic-10: Sediment Cycles and Movements in Coastal Water
Sediment is a naturally occurring material that is broken down by processes of weathering and
erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity
acting on the particles.
Sediment is solid material that is moved and deposited in a new location. Sediment can consist of
rocks and minerals, as well as the remains of plants and animals. It can be as small as a grain of sand
or as large as a boulder.
What are the types of marine sediment?
Sediments (and sedimentary rocks) are classified in by origin of source material.
There are 4 sources of sediments (and sedimentary rocks):
a) Cosmogenous: material that falls to the Earth surface from outer space.
b) Hydrogenous: material precipitated directly seawater.
c) Lithogenous: material derived from erosion of other rocks, typically from continental sources.
d) Biogenous: material formed from the accumulation of remains of living organism
Lithogenous sediments are formed by the weathering process and are made up of small particles of
weathered rocks and oceanic volcanoes. They are often formed together when metal and silicate ions
bond. And within Lithogenous sediments there are two sub categories:
Terrigenous sediments are produced as a result of the weathering process of rocks above the
water. These eroded particles are carried by the wind and other natural means to the oceans and
are deposited at the bottom. Although it can be easily found in river beds, not much of this finds
its way to the deep ocean.
Red clay lithogenous sediment, on the other hand, is plentiful in the ocean. It is reddish-brown
(hence the name) and is a combination of terrigenous material and volcanic ash. It is transported
to the oceans by currents and wind and it settles in deep places along the ocean floor.
Biogenous sediments are formed from the insoluble remains of past life forms and parts such as bones
and teeth. In many areas where the water is shallow, a majority of these sediments are the remains of
shells or fragments from shelled sea creatures as well as corals. In the deep sea where there is no such
a high concentration of these life forms, biogenous sediment is made from the microscopic shells that
are deposited by tiny plants, animals, and plankton that live on the water’s surface and eventually make
their way down to the ocean floor.
Hydrogenous sediments are formed by precipitation of minerals from the ocean’s water or can be
formed as a new mineral as a result of chemical reactions between the water of the ocean and sediments
that already exist on the ocean floor. Chemically speaking, this is an interesting sedimentary process
because of the reactions that take place. For instance, the water of earth’s oceans contains ions that
have already been dissolved. When evaporation occurs and large amounts of these ions remain the area
can become saturated with the leftovers from this process, salt.
Cosmogenous sediments are extraterrestrial in nature and are generally like miniature meteorites.
These sediments are the remains of impacts of large bodies of space material (such as comets and
asteroids). They are comprised of silicates and mixtures of different metals and, as one might imagine,
they are not incredibly common to find. This is rather surprising because there is a constant “rain of
these materials that falls to earth daily. The amounts of such sediments also lead researchers to wonder
if these space-driven events might have been responsible for mass extinction and thus these sediments
hold several possible keys to future understanding of ancient life on earth.

What is the source of sediments?
There are four types of sources of sediment:
• Cosmogenous (from outer space),
• Volcanogenous (ash from volcanic eruptions),
• Terrigenous (continents erosion and river runoff)
• Biogenous (skeletons of marine creatures).
Cosmogenous Sediments
Cosmogenous Sediments originated from outer space. Scientists have used satellites to estimate how
much material enters the earth's atmosphere. Current estimates from satellite data suggesting about
100 to 300 tons (mostly cosmic dust) hits earth each day. This is just a tiny fraction of the sediments
generated on earth each day. However, early in the history of our Solar System, Earth and other planets,
moons, comets and asteroids formed from the gravitational accumulation of extraterrestrial material,
but by 4.5 million years ago, most of this cosmogenous accumulation had significantly diminished.
However, cosmogenous materials including iron-nickel and stony meteorites can be found. Although
a relatively insignificant source of sediment, meteor fireballs disintegrating in the atmosphere
contribute dust that can accumulate measurable amounts in parts of some ocean basins.
Extraterrestrial impacts have changed life on Earth repeatedly, including the mass extinction at the end
of the Mesozoic Era associated with the extinction of dinosaurs and many other forms of life on land
and in the oceans. Tektites are silica glass generated by extraterrestrial impacts: asteroids exploding
on the surface and molten material is ejected into the atmosphere where it condenses into a glass-like
material.
Volcanogenous Sediments
Volcanogenous Sediments deposits
occurring in cases of the entry into
ancient and modern sea and ocean
basins of mineral products formed
during volcanic eruptions on the sea
floor, on islands, and along the shores
and upon the precipitation of these
products in the form of strata and
nodules.
Volcanogenic sedimentary deposits
include large stratified deposits of iron
and manganese ores composed of
silicates, carbonates, oxides, and
hydroxides of the above metals, as well as pyriteores containing sulfide compounds of iron, copper,
and zinc and occasionally lead, barite, and gypsum. They are deposited in layers of rock consisting of
lavas, ash, and strata of siliceous rocks alternating with normal marine deposits. Accumulations of
nodular iron and manganese ores, which are found on the bottom of the Pacific, Atlantic, and Indian
oceans and contain admixtures of cobalt, nickel, molybdenum, and other valuable metals, may also
have been produced as a result of submarine eruptions of young volcanoes. Volcanogenic sedimentary
deposits of ancient and modern geological periods are known.

Terrigenous Sediments
Terrigenous sediments are those derived from the erosion of
rocks on land; that is, they are derived from terrestrial (as
opposed to marine) environments. Terrigenous sediment,
deep-sea sediment transported to
the oceans by rivers and wind from land sources.
Terrigeneous sediments that reach the continental shelf are
often stored in submarine canyons on the continental
slope. Turbidity currents carry these sediments down into the
deep sea. These currents create sedimentary deposits called
turbidites, which are layers up to several meters thick composed of sediment particles that grade
upward from coarser to finer sizes. The turbidites build sedimentary deep-sea fans adjacent to the base
of the continental slope. Turbidites also are found below the major river deltas of the world where they
build features called abyssal cones. The largest of these is the ganges fan (also called the ganges cone
or bengal cone) in the bay of bengal east of the indian subcontinent. It measures 3,000 km (about 1,900
miles) long (north-south) by 1,000 km (about 600 miles) wide (east-west) and is up to 12 km (about 7
miles) thick. The bengal cone continues to form from rock material eroded from the himalayas and
transported by the ganges and brahmaputra rivers.
Biogenous Sediments
Biogenous sediments (bio = life, generare = to produce) are sediments made from the skeletal remains
of once-living organisms. These hard parts include a wide variety of particles such as shells of
microscopic organisms (called tests), coral fragments, sea urchin spines, and pieces of mollusc shells.
Biogenous sediments come from the remains of living organisms that settle out as sediment when the
organisms die. It is the “hard parts” of the organisms that contribute to the sediments; things like shells,
teeth or skeletal elements, as these parts are usually mineralized and are more resistant to
decomposition than the fleshy “soft parts” that rapidly deteriorate after death.
The primary sources of microscopic biogenous sediments are unicellular algaes and protozoans
(single-celled amoeba-like creatures) that secrete tests of either calcium carbonate (caco3) or silica
(sio2). Silica tests come from two main groups, the diatoms (algae) and the radiolarians (protozoans)
The most important type of biogenous sediment comes from the tests of one-celled microscopic algae
and protozoans living in the surface waters of the oceans. When these tests comprise greater than 30%
of the particles in the sediment, the sediment is called an ooze. The remainder of the sediment is often
made up of clay.
What are the components of sediment?
Sediment can consist of rocks and minerals, as well as the remains of plants and animals. It can
be as small as a grain of sand or as large as a boulder. Sediment moves from one place to another
through the process of erosion marine sediment, any deposit of insoluble material,
primarily rock and soil particles, transported from land areas to the ocean by wind, ice, and rivers, as
well as the remains of marine organisms, products of submarine volcanism,
chemical precipitates from seawater, and materials from outer space (e.g., meteorites) that
accumulate on the seafloor.
Describe the dynamics of marine sediment
Coasts bordering the seas and oceans consist of large masses of terrigenous sediments eroded from
the continents and deposited on the beach, shore face and shelf. Estimates are that the continents are
worn-down at a rate of about 3 mm per 100 years. Sediments are delivered to the sea by rivers
(roughly 1 to 10 km3 per year; 90% of total input), by glaciers (polar region), by wind, by volcanic
action, by wave-induced cliff/dune erosion and by biogenic production. Sediments of the shore face

and shelf can be transported to the deep oceans via submarine canyons and via turbidity currents and
gravity currents. Short-term deposition rates near coastlines can be as high as 10 m per year in
regions with large river input (Yellow River). Redistribution of sediments over the sea and ocean
floor takes place by waves and currents. The Shelves covering 5% of the Earth's surface, can be seen
as the submerged parts of the continents. Shelves are not so deep; the average depth for the Atlantic
Shelves is about 130 m. All continental shelves have a base of sediments deposited during periods of
fluctuating sea level in the Pleistocene period.
Explain the transport mechanism of marine sediment
Sediment transports in several different way. These are often segregated into
• The bed load - materials bounced along the ocean bottom.
• The suspended load - material carried in suspension in the ocean water.
• The dissolved load - material carried as dissolved solids in the ocean water.
Bed load: Bedload transport is a specific form of sediment transport, which involves coarse particles
(sand, gravel or coarser particles) rolling or saltating along the streambed. There are three main ways
to transport bed load:
• Rolling: Large pebbles and boulders are rolled along the seafloor.
• Sliding: Sliding particles remain in continuous contact with the bed, merely tilting to and
from as they move.
• Saltation: Sand-sized material is bounced along the seafloor. Transportation happens via
forces from the water or wind. A layer of saltation can often be seen 2-10 centimeters above
the beach surface on dry, windy days.
Suspended load: The portion of its sediment uplifted by the fluid's flow in the process of sediment
transportation. It is kept suspended by the fluid's turbulence. The suspended load generally consists
of smaller particles, like clay, silt, and fine sands.
Dissolved load: Dissolved load is the portion of a stream's total sediment load that is carried in
solution, especially ions from chemical weathering. It is a major contributor to the total amount of
material removed from a river's drainage basin, along with suspended load and bed load.
Further Study: http://ecoursesonline.iasri.res.in/mod/page/view.php?Id=2131

Coastal Oceanography Notes

More Related Content

What's hot

Similar to Coastal Oceanography Notes

Recently uploaded

Coastal Oceanography Notes