Coastal erosion and engineering aspect

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INRODUCTION
A coastline or seashore is the area where land meets the sea or ocean. Coastal erosion is the
wearing a way of land and the removal of beach or dune sediments by wave action, tidal currents,
wave currents, or drainage.
Every land mass on Earth has miles of coast at the interface between the hydrosphere
and the lithosphere. Natural forces such as wind, waves and currents are constantly shaping the
coastal regions. The combined energy of these forces moves land materials.
The landward displacement of the shoreline caused by the forces of waves and currents
is termed as coastal erosion. It is the loss of sub-aerial landmass into a sea or lake due to natural
processes such as waves, winds and tides, or even due to human interference. While the effects of
waves, currents, tides and wind are primary natural factors that influence the coast the other aspects
eroding the coastline include: the sand sources and sinks, changes in relative sea level,
geomorphological characteristics of the shore and sand, etc. Other anthropological effects that
trigger beach erosion are: construction of artificial structures, mining of beach sand, offshore
dredging, or building of dams or rivers.
SHORELINE
A shore or shoreline is the fringe of land at the edge of a larger body of water, such as an ocean,
sea, or lake.
COASTEL CLASSIFICATION
PRIMARY COAST
Primery coast is coast whitch is essentially in same condition when sea level stabilized after the
last ice age. Primary coast are young coast. Terrestrial (land) influence dominate primary coast
 LAND EROSION COAST
 SUBARIAL DEPOSITION COAST
 VOLCANIC COAST
 ICE COAST
SECONDERY COAST
Secondary coast shaped primarily by marine agents or by marine organism. May or may not have
been primary coast before being shaped by the sea
 Wave erosion coast
 Marine deposition coasts
 Coast build by organism
EROSIONAL AND DEPOSITIONAL COAST
Depending on whether their primary features were created by erosion of land or deposition
of eroded material.
 EROSIONAL COASTS are those that developed where active erosion by wave action
occurs or where rivers or glaciers caused erosion when sea level was lower than it presently
is; these include cliffs or rocky shores
 DEPOSITIONAL COASTS develop where sediments accumulate either from a local source
or after being transported to the area in rivers and glaciers or by ocean currents and waves;
these include deltas, mangrove swamps, salt marshes, barrier islands, and beach-sand dunes

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A beach is a landform along the shoreline of an ocean, sea, lake or river. It usually consists of loose
particles which are often composed of rock, such as sand, gravel, shingle, pebbles or cobblestones
BEACH
A beach is a landform along the shoreline of an ocean, sea, lake or river. It usually consists of
loose particles which are often composed of rock, such as sand, gravel, shingle, pebbles or
cobblestones
TYPES OF BEACHES
Tropical Beaches
 Formed of fine sand brought to coast by rivers
 Beach rock - cemented sand with calcium carbonate from dissolved shells
Storm Beaches
 At highest point of beach
 Pebbly and steep slope
 Pebbles moved by storm waves
Barrier Beaches
 Elongated sand or pebble banks lying parallel to, but separate from the coastline.
WAVES
Shorelines are dynamic systems involving the energy of waves and currents. Wind-generated
waves provide most of the energy for erosion, transportation, and deposition of sediment. Waves
approaching a shore are bent, or refracted, so that energy is concentrated on headlands and dispersed
in bays.
TIDES
Tidal Tides are produced by the gravitational attraction of the Moon and the centrifugal force of
the Earth–Moon system. They affect coasts in two major ways:
(1) By initiating a rise and fall of the water level and
(2) By generating currents.
OCEAN CURRENTS
An ocean current is a continuous, directed movement of ocean water generated by the forces
acting upon this mean
flow, such as breaking
waves, wind, Carioles
effect, caballing, tempera
ture and salinity
salinity differences
and tides caused by the
gravitational pull of
the Moon and the Sun.
DEPOSITION
Material that is
transported by the waves
along a coastline is
eventually deposited

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forming distinctive deposition features. There are four main deposition features that you need to
learn the formation of. These are:
1.Beaches
2.Spits
3.Bars
4. Tombolos
LANDFORM CAUSED BY COASTEL EROSION
 BAY
 LAGOON
 SPITS
 BARRIER ISLAND
 TOMBOLO
 PENINSULA
SPITS
Spits are long narrow
ridges of sand and shingle which
project from the coastline into
the sea. The formation of a spit
begins due to a change in the direction of a coastline - the main source of material building up a spit
is from long shore drift which brings
material from further down the coast.
TOMBOLOS
Tombolos are formed where a
spit continues to grow outwards joining
land to an offshore island
BAY
A bay is an area of water mostly
surrounded by land. Bays generally
have calmer waters than the surrounding
sea, due to the surrounding land
blocking some waves and often
reducing winds.
BARRIER ISLAND
Barrier Islands, a coastal landform and a type of barrier system, are relatively narrow strips of
sand that parallel the mainland coast. They usually occur in chains, consisting of anything from a few
islands to more than a dozen
PENINSULA
Peninsula is a piece of land that is bordered by water on three sides but connected to mainland
COASTEL DYNAMICS
Coastal dynamic is the change or movement of coast. Costal dynamics includes erosion,
transportation & deposition by waves, tides, currents, Currents, waves and winds constantly affect
the margins of land adjacent to bodies of water. These processes differ along the various types of

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coasts and in diverse climates. Coasts are composed of many kinds of materials, including sand,
rocky sediments, mud and biological substances. Because of these variations, coasts respond
differently to the natural forces acting upon them.
In this section deals more about the ways that coasts change and the events that affect them.
Although coasts are unique, all types of coastlines change over time in significant ways.
EROSION
Erosion is the process by which materials are removed from the surface and transported to another
location. Coastal erosion is the wearing of land and the removal of beach or dune sediments by wave
action, tidal current wave currents.
RATE OF DESTRUCTION
Habitat Destruction along the coast and in the ocean results from harmful fishing practices
such as trawling or dynamite fishing , poor land use practices in agricultural, coastal development
and forestry sectors and other human activities such as mining and anchoring. Destroyed habitats
include sea grasses, marshes, corals and mangroves – all of which are important nurseries for fish
and critical for buffering coasts from storm damage. Damaging habitat can lead to increased erosion
and sedimentation, increased impact from storms, fewer nursery grounds and fewer places for
animals and plants to live.
Rate of destruction (weathering) along the coast is due to human activity and also due to natural
agencies. Rate of destruction is not uniform in all coasts. Rate of destruction is controlled by several
factors that are
1. Slope of the coast
2. Intensity of waves tides
3. Wind velocity
4. Topography of coast (sandy, rocky, etc)
RATE OF DESTRUCTION AT DIFFERENT LOCATION IN INDIA
Long shore sediment transport rate (LSTR) reported for different locations along the Indian
coast shows local reversals in the transport direction in a number of locations along the west coast. It
was found that the annual gross sediment transport rate was high along the coast of south Orissa and
south Kerala.
Coastal Erosion in India
The Indian coastline is about 7517 km, about 5423 km along the mainland and2094 km the Andaman
and Nicobar, and Lakshadweep Islands. The coastline comprises of headlands, promontories,
rocky shores, sandy spits, barrier beaches, open beaches, embayment, estuaries, inlets, bays,
marshy land and offshore islands. According to the naval hydrographic charts, the Indian mainland
consists of nearly 43% sandy beaches, 11% rocky coast with cliffs and
46% mud flats and marshy coast. Oscillation of the shoreline along the Indian coast is seasonal.
Some of the beaches regain their original profiles by March/April. Fifty per cent of the beaches that
do not regain their original shape
Over an annual cycle undergo net erosion. Shoreline erosion in the northern regions of Chennai,
Encore, and Visakhapatnam and Para dip ports has resulted duet construction of breakwaters of the
respective port. At present, about 23% of
Shoreline along the Indian main land is affected by erosion.
Erosion Process:

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Waves start by attacking the main points of weakness in the rock such as the joints and any fault that
there may be in the rock. The point of weakness is increased until it becomes a cave. The waves
continue to attack the cave, which finally results in an arch being formed through the headland. The
arch is then attacked by both coastal and sub - aerial erosion and finally the roof of the arch falls into
the sea. This then leaves behind a stack, which is then slowly eroded down to become a stump.
Low outcrop of rock formed by the erosion of a coastal stack. Unlike a stack, which is exposed at all
times, a stump is exposed only at low tide. Eventually it is worn away completely.
The easiest way of describing the overall effect of coastal erosion is that, if left unchecked, all the
coastlines would be, low wave cut platforms. Most erosion
Takes place around high tide and will be carried out in one of three ways. The first is Hydraulic
erosion which has an effect of a small explosive charge. The sudden impact of a wave on to the cliff
face forces air into any cracks that they might be or along the bedding planes, compressing the air
briefly then releasing the pressure. The changes in pressure causes the cracks to widen and go further
into the cliff, material breaks away and washed out of the cliff by following waves. The material
washed away becomes means for further erosion. The debris is washed against the base of the cliff in
a process known as corrosion and acts in a grinding motion. In this process, not only does erosion
take place at the foot of the cliff but the sediment itself is worn down and rounded in a process
known as attrition. The third type of erosion is chemical, particularly in limestone and chalk cliffs
where chemicals within the sea water attack the rocks eroding the weaker sections and gradually
causing the cliff to collapse.
Coastal lands may experience long-term erosion under some conditions. For instance, if sea level is
rising, the beach may eventually migrate landward or drown. This causes coastal land behind the
beach to erode. Also, if the amount of sand from the seaward side is reduced, a beach will erode the
land behind it to maintain a constant sand supply. This creates a condition called coastal erosion.
Beaches on eroding coasts undergo seasonal profile adjustments, but they slowly shift their position
landward as the land erodes. Hardening a shoreline can interfere with necessary profile adjustments
because the dune can no longer share its sand with the beach. As a retreating beach encounters a
seawall or revetment it can no longer draw upon a landward sand supply and it begins to Waves start
by attacking the main points of weakness in the rock such as the joints and any faults that there may
be in the rock. The point of weakness is increased until it becomes a cave. The waves continue to
attack the cave, which finally results in an arch being formed through the headland. The arch is then
attacked by both coastal and sub - aerial erosion and finally the roof of the arch falls into the sea.
This then leaves behind a stack, which is then slowly eroded down to become a stump.
Low outcrop of rock formed by the erosion of a coastal stack. Unlike a stack, which is exposed at all
times, a stump is exposed only at low tide. Eventually it is worn away completely.
The easiest way of describing the overall effect of coastal erosion is that, if left unchecked, all the
coastlines would be, low wave cut platforms. Most erosion
Takes place around high tide and will be carried out in one of three ways. The first is Hydraulic
erosion which has an effect of a small explosive charge. The sudden impact of a wave on to the cliff
face forces air into any cracks that they might be or along the bedding planes, compressing the air
briefly then releasing the pressure. The changes in pressure causes the cracks to widen and go further
into the cliff, material breaks away and washed out of the cliff by following waves. The material
washed away becomes means for further erosion. The debris is washed against the base of the cliff in
a process known as corrosion and acts in a grinding motion. In this process, not only does erosion
take place at the foot of the cliff but the sediment itself is worn down and rounded in a process

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known as attrition. The third type of erosion is chemical, particularly in limestone and chalk cliffs
where chemicals within the sea water attack the rocks eroding the weaker sections and gradually
causing the cliff to collapse.
Coastal lands may experience long-term erosion under some conditions. For instance, if sea level is
rising, the beach may eventually migrate landward or drown. This causes coastal land behind the
beach to erode. Also, if the amount of sand from the seaward side is reduced, a beach will erode the
land behind it to maintain a constant sand supply. This creates a condition called coastal erosion.
Beaches on eroding coasts undergo seasonal profile adjustments, but they slowly shift their position
landward as the land erodes. Hardening a shoreline can interfere with necessary profile adjustments
because the dune can no longer share its sand with the beach. As a retreating beach encounters a
seawall or revetment it can no longer draw upon a landward sand supply and it begins erode.
Erosion Rate:
Erosion rates vary over time and space. These variations occur in response to many factors.
Among them are: soil slope and composition
• Credibility of material
• Near shore seabed shoals and slopes
• Storm wave energy and duration
• Precipitation
• Ground water and soil conditions
• Ice cover
• Shoreline orientation
• Beach composition, width and slope
• shore protection structures
It has been observed that sea level rise of 1 mm per year could cause a recession of shoreline in the
order of about 0.5 m per year.
Effects of Coastal Erosion
Coastal erosion, or coastal instability, threatens property and businesses and puts people living
near cliffs and shoreline risk. The great concentration of national resources in coastal zones makes it
imperative that coastal change is well understood.
LANDSLIDES:
The term landslide refers to the downward movement of masses of rock and soil. Landslides are
caused by one or a combination of the following factors: change in slope gradient, increasing the
load the land must bear, shocks and vibrations, change in water content, ground water movement,
frost action, weathering of shocks, removal or, changing the type of vegetation covering slopes.
Landslide hazard areas occur where the land has certain characteristics which contribute to the risk
of the downhill movement of material. These characteristics include:
I A slope greater than 15 percent.
ii Landslide activity or movement occurred during the last 10,000 years.
iii Stream or wave activity which has caused erosion, undercut a bank or cut into a bank to cause the
surrounding land to be unstable.
iv The presence or potential for snow avalanches.
v The presence of an alluvial fan which indicates vulnerability to the flow of debris or sediments.

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vi The presence of impermeable soils, such as silt or clay, which aremixed with granular soils such
as sand and gravel.
Landslides can also be triggered by other natural hazards such as rains, floods, earthquakes, as well
as human-made causes, such as grading, terrain cutting and filling, excessive development, etc.
Because the factors affecting landslides can be geophysical or human-made, they can occur in
developed areas, undeveloped areas, or any area where the terrain has been altered for roads, houses,
utilities, buildings, etc.
TYPES OF DISASTER:
Natural
 cyclone
,hurricane,
typhoon
 earthquakes
 tsunamis
 landslides
 storms
 floods
Man made
 an airplane
crash,
 a major fire,
 oil spill,
 epidemic,
 terrorism, etc.
Causes of landslides:
 There are
several causes of landslide. Some of the major causes are as follows:
 1. Geological Weak material: Weakness in the composition and structure of rock or soil may
also cause landslides.
 2. Erosion: Erosion of slope toe due to cutting down of vegetation, construction of roads
might increase the vulnerability of the terrain to slide down.
 3. Intense rainfall: Storms that produce intense rainfall for periods as short as several hours or
have a more moderate intensity lasting several days have triggered abundant landslides.
Heavy melting of snow in the hilly terrains also results in landslide.
 Human Excavation of slope and its toe, loading of slope/toe, draw down in reservoir, mining,
deforestation, irrigation, vibration/blast, Water leakage from s
 5. Earthquake shaking has triggered landslides in many different topographic and geologic
settings. Rock falls, soil slides and rockslides rom steep slopes involving relatively thin or
shallow dis-aggregated soils or rock, or both have been the most abundant types of landslides
triggered by historical earthquakes.
 6. Volcanic eruption Deposition of loose volcanic ash on hillsides commonly is followed by
accelerated erosion and frequent mud or debris flows triggered by intense rainfall.
Disaster management:
Is a systematic process (i.e., is based on the key
management principles of planning, organising, and leading which includes coordinating and
Controlling).

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Aims to reduce the negative impact or consequences of adverse events (i.e., disasters cannot always
be prevented, but the adverse effects can be minimised.
Adverse Effects:
 The most common elements at risk are the settlements built on the steep slopes, built at the
toe and those built at the mouth of the streams emerging from the mountain valley. All those
buildings constructed without appropriate foundation for a given soil and in sloppy areas are
also at risk.Roads, communication lines are vulnerable.
Disaster management cycle:
Steps in disaster management of landslides:
 Pre-disaster studies
 Post disaster
PRE-DISASTER STUDIES:
 Includes landslide hazards zonation mapping are the different parts of the country
 Assessment of the slope stability aspects at the sites of different infra structural facilities
 Landslide hazards zonation on macro (1:50000 or 1:25000 scale) and meso ( 1:10000 or 1:
5000 scale ) has been taken y the geological survey of India.
 Efforts are made to use GIS and data mapping tools are made
 Landslides zonation mapping in parts of Ravi Basin, Himachal Pradesh, Yamuna Basin
Uttrakhand, Imphal, Manipur, Kohima, Nagaland, Cachar , Mezoram,
 Landslides hazard zonation in macro scale includes Guwahati Assam , Kannur
area Idukki Kerala Nilagiri Tamilnadu .
POST DISASTER STUDIES:
 The landslides information reporting preformed was developed for reporting Occurrence
landslides to the DMS Control room GSI New Delhi
 Landslide pre study include reconnoiter studies followed y detailed analysis, preliminary
monitoring of a few landslides and efforts to stabilize the disasters landslides
 The preliminary/ reconnoiter studies of specific slides were carried out – to asses the
magnitude, suggest remedies and identified slides that required detail study
 The work carried out included 34 incidents in HP 65 in Uttarakand, 20 in Jammu Kashmir ,
111 in West Bengal , 4 in Guwahati –
Assam, 6 in Manipur
Possible risk reduction measures:
 Hazard mapping locates areas prone
to slope failures. This will help to
avoid building settlements in such
areas. These maps will also serve as a
tool for mitigation planning.
 Land use practices such as:
 Areas covered by degraded
natural vegetation in upper
slopes are to be afforested with
suitable species.
 Any developmental activity
initiated in the area should be
taken up only after a detailed

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study of the region has been carried out.
 In construction of roads, irrigation canals etc. proper care is to be taken to avoid
blockage of natural drainage
 Total avoidance of settlement in the risk zone should be made mandatory.
 Relocate settlements and infrastructure that fall in the possible path of the landslide
 No construction of buildings in areas beyond a certain degree of slope
 Retaining Walls can be built to stop landfrom slipping (these walls are commonly seen along
roads in hill stations). These are constructed to prevent smaller sized and secondary
landslides that often occur along the toe portion of the larger landslides.