coastal engineering

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Prepared by R.Vijayakumar, B.Tech (CIVIL), CCET, Puducherry

COASTAL ENGINEERING

UNIT – 1

1. Define coastal engineering.

Coastal engineering is the study of the processes ongoing at the

shoreline and construction within the coastal zone. The field involves

aspects of near shore oceanography, marine geology, and civil engineering,

often directed at combating erosion of coasts or providing navigational

access.

2. Define coastal zone.

Coastal zone is the interface where the land meets the ocean

encompassing shore line environment as well as adjacent coastal waters. Its

components can include river deltas, coastal planes, wet lands, beaches,

reefs, mangrove forest, lagoons and other coastal features. The coastal zone

is divided into four subzones. They are,

Coast

Shore

Shore face

Continental shelf

3. What is meant by coastal regulation zone?

Under the Environment Protection Act, 1986 a notification was issued

in February, 1991, for regulation of activities in the coastal area by the

Ministry of Environment and Forests (MoEF). As per the notification, the

coastal land up to 500m from the High Tide Line (HTL) and a stage of 100m

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along banks of creeks, estuaries, backwater and rivers subject to tidal

fluctuations, is called the Coastal Regulation Zone(CRZ). CRZ along the

country has been placed in four categories. The above notification includes

only the inter-tidal zone and land part of the coastal area and does not

include the ocean part. The notification imposed restriction on the setting up

and expansion of industries or processing plants etc. in the said CRZ.

4. Define coastal area.

The coastal area is the land and sea areas bordering the shoreline.

5. Define setback area.

A setback area is the strip of land along the coastal zone, where

certain development activities are prohibited or significantly restricted.

6. How coastal regulation zone are classified?

For regulation of developmental activities, the coastal stretches within

500m of HTL on the landward side are classified into four categories, viz.

Category I (CRZ-I)

Category II (CRZ - II)

Category III (CRZ-III)

Category IV (CRZ-IV)

7. List down the factors influencing coastal topography.

Population pressure

Wastewater disposal

Destruction of mangrooves

Increasing urbanization

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Solid waste disposal

Coastal constructions

Natural disasters

8. Write down the coastal types.

Cliff coast

Clayey bank coast

Intertidal / muddy coast

Sand dune coast

Sandy coast

9. Define waves.

When wind blows over water it exerts a drag on water surface and

water by virtue of its fluidity gets disturbed giving rise to waves. Such

waves are referred as wind waves or storm waves. Waves are usually

defined by their height, length and period.

10. Define tides.

Tides are the rise and fall of sea levels caused by the combined effects

of the gravitational forces exerted by the moon and the sun, and the rotation

of the Earth.

11. Define astronomical tide.

The astronomical tide is generated by the rotation of the earth in

combination with the varying gravitational impact on the water body of the

sun, the moon and the planets. These phenomena cause predictable and

regular oscillations in the water level, which is referred to as the tide. The

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astronomical tide at a specific location can be predicted and is published in

Tidal Tables.

12. Define tidal flat.

Shallow and often muddy, the part of foreshore, which are covered

and uncovered by the rise and fall of the tide. As a rule of thumb, a tidal flat

normally develops when the relative tidal range RTR, defined as the ratio

between the mean spring tidal range and the annual average HS, is higher

than 15.

13. What is meant by high tide and low tide?

At most places the tidal change occurs twice daily. The tide rises until

it reaches a maximum height, called high tide or high water, and then falls to

a minimum level called low tide or low water.

14. What are the types of tides?

Diurnal tide

Semi – diurnal tide

Mixed tide

15. Define diurnal tide.

In the diurnal tide, only a single high and single low water occur each

tidal day. Tides of the diurnal type occur along the northern shore of the

Gulf of Mexico, in the Java Sea, the Gulf of Tonkin, and in a few other

localities.

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16. Define semi – diurnal tide.

In the semidiurnal tide, there are two high and two low waters each

tidal day, with relatively small differences in the respective highs and lows.

Tides on the Atlantic coast of the United States are of the semidiurnal type.

17. Define mixed tide.

In the mixed tide, the diurnal and semidiurnal oscillations are both

important factors and the tide is characterized by a large inequality in the

high water heights, low water heights, or in both. There are usually two high

and two low waters each day, but occasionally the tide may become diurnal.

Such tides are prevalent along the Pacific coast of the United States and in

many other parts of the world.

18. Define gravity waves.

As the wind speed increases, the next stage of waves are gravity

waves, named for their restoring force, gravity as the wave height increases,

it overcomes surface tension, and is instead dragged back down by gravity.

19. Define tidal waves.

It is the combined effect of astronomical and meteorological surges -

the popular expression for an unusually high and destructive water level

along a shore. The expression of tidal wave also includes the influence of

the associated waves.

20. Define progressive waves.

If the whole profile moves in the forward direction the wave is a

Progressive Wave.

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21. Define sea water waves.

If winds of local storm blow towards the shore, the generated waves

will reach the beach in nearly the form in which they are generated. Under

these conditions, the waves are steep; i.e. the wave length is 10 to 20 times

the wave height. Such waves are called sea water waves.

22. What is meant by swell?

If waves are generated by a distant storm, they may travel through

hundreds or even thousands of miles of calm areas before reaching the shore.

Under these conditions, waves decay – short, steep waves are eliminated,

and only relatively long low waves reach the shore. Such waves have

lengths from 30 to more than 500 times the wave height and are called swell.

23. How wind waves are generated?

In fluid dynamics, wind waves, or wind-generated waves, are surface

waves that occur on the free surface of oceans, seas, lakes, rivers, and canals

or even on small puddles and ponds. They result from the wind blowing

over an area of fluid surface.

24. Write the classification of waves.

Based on repetition of wave

form

Regular, irregular

Based on wave period Long period, short period

Based on shape Sinusoidal, trochoidal, cnoidal, solitary,

random, progressive, standing, oscillatory,

translatory

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Other types Capillary wave, ultra gravity wave, ordinary

gravity wave, infra gravity wave, ordinary

tide wave, trans - tidal wave

25. What are the types of wave theories?

Linear or Airy’s (or sinusoidal or small amplitude) wave theory

Non-linear (or finite amplitude) wave theory

26. Write the assumptions of wave theories.

The waves have regular profiles

The flow is two dimensional

The wave propagation is unidirectional

The fluid is ideal (i.e.) inviscid, incompressible and irrotational

The sea bed is impermeable and horizontal

27. State the assumptions to be made in linear wave theory.

Fluid is homogeneous and incompressible. Therefore the density is

constant.

Surface tension can be neglected.

Pressure at free surface is uniform and constant.

The fluid is ideal.

The particular wave being considered does not interact with any other

wave motion.

The bed is horizontal, fixed, impermeable boundary which implies

that the vertical velocity at the bed is zero.

The wave amplitude is small and invariant in time and space.

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28. What are the advantages of linear wave theory?

It is the simplest available theory to describe the water wave motion

Provides insight to all periodic wave behavior

Adequate for most of the practical problems

Reliable over a large sequent of the whole wave region

29. What are the disadvantages of linear wave theory?

This theory is unable to account for mass transport due to waves

This theory cannot provide the information correctly either in shallow

water regime or in deep water regime for steeper waves, especially

during wave breaking

30. What is meant by wave celerity?

The speed at which a wave form propagates is termed as phase

velocity or wave celerity, C. Since the distance travelled by a wave during

one wave period is equal to one wave length.

𝐶 = 𝐿

𝑇

31. Define wave energy.

The total energy, E of a wave system is the sum of its kinetic energy,

Ek and potential energy, Ep. According to linear wave theory, the total wave

energy in one wave length per unit crest width is given by,

𝐸 = 𝐸𝑘 + 𝐸𝑝 = 𝜌 𝑔 𝐻2 𝐿

8

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32. What is meant by group velocity?

The speed with which a group of waves or a wave train travels is

generally not identical to the speed with which individual waves within the

group travel. The group speed is called the group velocity, Cg.

33. Define wave amplitude.

The maximum vertical displacement of the sea surface from still water

level (half the wave height).

34. Define wave height, wave length, wave period.

The vertical distance from the top of the crest to the bottom of the

trough is called wave height.

The horizontal distance between the successive crest is called wave

length.

The time between successive crest passing a given point is called

wave period.

35. Define wave energy flux.

Wave energy flux is the rate at which energy is transmitted in the

direction of wave propagation across a vertical plane perpendicular to the

direction of wave advance and extending down the entire depth. The

average energy flux per unit crest width transmitted across a plane

perpendicular to wave advance is given by,

�̅� = �̅� 𝑛 𝐶 = �̅� 𝐶𝑔

Energy flux �̅� is called wave power.

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36. What is high tide line?

“The high tide line means the line on the land up to which the highest

water line reaches during the spring tide". Here the word "highest water line

reaches during the spring tide" refers to the mean high water spring (19

years average of spring water) that is the regular water level fluctuations

caused by changes in relative position of the Sun, Moon and Earth.

37. What is spilling?

The spilling type of breaking occurs in deep water or over gentle bed

slope (m = 1: 50). This involves gradual release of energy and is

characterized by appearance of foam on forward side of the crest.

38. What is surging?

Surging takes place when the sea bed slope is steep with (m = 1: 10)

or so. In this case the entire water gets piled up and the foam is seen on

beach face.

39. Write the expressions for velocity potential function and stream

function.

VELOCITY POTENTIAL FUNCTION:

𝛷 ( 𝑥, 𝑦, 𝑧 ) = 𝑋 (𝑥) 𝑍 (𝑧) 𝑇 (𝑡) = 𝑔 𝐻 cosh( 𝑘 ( 𝑑 + 𝑧 ))

2 𝜔 cosh( 𝑘𝑑 ) sin( 𝑘𝑥 − 𝜔𝑡 )

STREAM FUNCTION:

𝜕𝜓

𝜕𝑥= −𝑣

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𝜕𝜓

𝜕𝑦= 𝑢

40. What is meant by storm surges?

Storms and hurricanes can produce large rises in water level near

coasts, which are known as storm surges or wind set-up. In combination

with springtide conditions the water level rise may reach a critical stage

(flooding).

41. Write the expression for wave celerity in shallow and deep waters.

𝐶𝑜 = 𝑔𝑇

2𝜋

𝐶𝑠 = √𝑔𝑑

Where,

Co = wave celerity in deep water

Cs = wave celerity in shallow water

g = acceleration due to gravity

T = wave period

42. Write down the dispersion relation or scattering formula.

𝜔2 = 𝑔 𝑘 tanh(𝑘𝑑)

43. Mention the expression for group velocity and energy flux.

GROUP VELOCITY:

𝐶𝑔𝑜=

𝐶𝑜

2 (For deep water)

𝐶𝑔 = 𝐶𝑠 = √𝑔𝑑 (For shallow water)

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ENERGY FLUX (OR) WAVE POWER:

𝑃 = 𝑛 𝜌 𝑔 𝐻2

8 𝐿

𝑇= 𝑛 𝐶 𝐸 = 𝐶𝑔 𝐸

44. What is meant by coastal hinterland?

The land that extends landward of the coast and which is not

influenced by coastal processes.

45. What is meant by coast?

The strip of land that extends from the coastline inland to the first

major change in the terrain features, which are not influenced by the coastal

processes. The main types of coastal features are dunes, cliffs and low-lying

areas, possibly protected by dikes or seawalls.

46. Define coast line.

Technically the line that forms the boundary between the coast and

shore,(i.e. the foot of the cliff or the foot of the dunes). In general the coast

line that forms the boundary between the land and the water.

47. Define shore line.

The shore line is the intersection between the mean high water line

and the shore. The line delineating the shoreline on Nautical Charts (Sea

Maps) approximates this Mean High Water Line. The shoreline is not easy

to identify in the nature in contrast to the coastline, which is based on a clear

morphological shift between the shore and the coast.

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48. What is meant by beach or shore?

The zone of unconsolidated material that extends from the mean low

water line to the place where there is a marked change in material or

physiographic form, or to the line of permanent vegetation (the effective

limit of storm waves and storm surge), i.e. to the coastline. The beach or

shore can be divided in the foreshore and the backshore.

49. Define backshore.

The part of the beach is lying between the foreshore and coastline.

The backshore is dry under normal conditions, is often characterized by

berms and is without vegetation. The backshore is only exposed to waves

under extreme events with high tide and storm surge.

50. Define foreshore.

The foreshore, or swash zone, is the region of the profile that is

alternately wet or dry as the waves rush up this steep portion of the profile.

51. Define beach berm.

Beach berms are built naturally by waves to above the highest

elevation reached by normal storm waves. When storm waves erode the

berm and carry the sand offshore, the protective value of the berm is reduced

and large waves can overtop the beach. The width of the berm at the time of

the storm is, thus, an important factor in the amount of upland damage, a

storm can inflict.

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52. What do you understand by the term continental shelf?

It is the shallow seafloor that borders most continents. The shelf floor

extends from the toe of the shore face to the shelf break where the steeply

inclined continental slope begins.

UNIT – 2

1. Define waves of oscillation.

Water particles move in near circular orbits which decrease in

diameter with depth.

2. Define waves of translation.

Water particles actually move forward.

3. What are wave forecasting and its methods?

Forecasting of waves for operational or design purpose can be made

by measuring and analyzing the actual wave data. But considering the

difficulties and costs involved in gathering large scale wave data, many

times, the readily available wind information is gathered and then converted

into corresponding wave information. Though, this procedure is less

accurate than the actual wave analysis.

METHODS:

Simplified or parametric method

Sverdrup – Munk and Bretschneider (SMB)

Hasselmann method

Darbyshire and Draper technique

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Elaborate or numerical method

4. What is meant by wave hind casting?

Wave hind casts refer to the predictions of wind waves on the water

surface for a past event. Wave now casts and forecasts similarly refer to the

predictions in real time and in the future, respectively. But the relations or

models used for predictions for a past, present, or future event are the same.

5. What are the types of transportation occurs within the water?

Solution

Suspension

Saltation

Traction

6. Write short notes on beach profile changes.

Beaches and dunes undergo a seasonal transformation from a

“summer” beach to a "winter" beach. A summer beach has a wide, well-

developed berm often with a vegetated dune where American beach grass

grows seaward onto the berm. A winter beach is lower, may not have a

berm, and often shows signs of loss of beach grass.

7. What are the factors controlling profile variations?

Variation in wave energy

Sediment variability

Nature of sediment transport process over the beach slope

Tidal variations

Wind variations

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8. Draw a typical section of a coastal region.

9. Define the phenomena of wave transformation.

When the waves approach the shoreline, they are affected by the

seabed through processes such as refraction, shoaling, bottom friction and

wave-breaking. However, wave-breaking also occurs in deep water when

the waves are too steep. If the waves meet major structures or abrupt

changes in the coastline, they will be transformed by diffraction. If waves

meet a submerged reef or structure, they will overtop the reef.

10. What is meant by refraction of waves?

When deep water wave crest line strikes the sea bed contours at some

non – zero angle, it tends to change its direction and align its wave crest with

the sea bed contours. This is called the wave refraction.

http://www.coastalwiki.org/wiki/Deep_water

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11. What is meant by reflection of waves?

Wave reflection occurs when waves “bounce back” from an obstacle

they encounter. Reflected waves can cause interference with oncoming

waves, creating standing waves.

12. What is meant by diffraction of waves?

Diffraction can be seen when there are sheltering structures such as

breakwaters. Diffraction is the process by which the waves propagate into

the lee zone behind the structures by energy transmittance laterally along the

wave crests.

13. State the assumptions to be made in the development of diffraction

theories.

Water is an ideal fluid (Inviscid and incompressible)

The small amplitude waves can be calculated by the linear wave

theory

The flow is irrotational and follows a potential function, which

satisfies the Laplace equation

The water depth shoreward of the breakwater is constant

14. What is meant by angle of incidence?

The angle between the wave propagation direction and the normal to

the coastline or the angle between the wave front and the coastline is called

angle of incidence and it is denoted by the symbol α. The deep water angle

of incidence is denoted by α0.

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15. What is meant by deep water?

For a water depth larger than half the wavelength( ℎ > 𝐿

2 ), the phase

speed of the waves is hardly influenced by depth (this is the case for most

wind waves on the sea and ocean surface).

16. What is meant by shallow water?

For a water depth smaller than the wavelength divided by 20( ℎ >

𝐿

20 ), the phase speed of the waves is only dependent on water depth, and no

longer a function of period or wavelength.

17. What is shoaling?

As the wave moves from deep water towards the coast its height

generally increases and its length reduces. This phenomenon is known as

shoaling.

18. Define wave overtopping.

Wave-overtopping takes place when waves meet a submerged reef or

structure, but also when waves meet an emerged reef or structure lower than

the approximate wave height. During over-topping, two processes important

to the coastal processes take place: wave transmission and the passing of

water over the structure.

19. Define white capping.

White-capping or top-breaking is steepness-induced wave-breaking,

which occurs in deeper water when the wave height becomes too large

compared to the wavelength.

http://www.coastalwiki.org/wiki/Wavelength

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20. Write short notes on bottom friction.

Bottom friction causes energy dissipation and thereby wave height

reduction as the water depth becomes more and more shallow. Friction is of

special importance over large areas with shallow water.

21. What is meant by tsunami?

It also known as a seismic sea wave is a series of waves in a water

body caused by the displacement of a large volume of water, generally in an

ocean or a large lake. Tsunami waves do not resemble normal sea waves,

because their wavelength is far longer.

22. How tsunami is formed?

Tsunamis are waves created by ocean bottom earthquakes, submarine

land – slides and volcanic explosions. These long period waves can travel

across entire oceans at speeds exceeding 800 kmph causing extensive

damage to coastal areas.

23. What is meant by sea level rise?

The so-called greenhouse effect or global warming may cause a Sea

Level Rise, which will have a great impact on the long-term coastal

morphology. The possible and gradual Sea Level Rise will cause a general

shoreline retreat and an increased flooding risk and has to be handled

according to the local conditions.

24. What is Mean Sea Level (MSL)?

The sea level halfway between the mean levels of high and low water.

https://en.wikipedia.org/wiki/Tsunamis_in_lakes

https://en.wikipedia.org/wiki/Wind_wave

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25. What is Mean Tide Level?

This is the average between mean low and mean high water, measured

from datum.

26. Define still water level.

The level that the sea-surface would assume in the absence of wind

waves (not to be confused with mean sea level or mean tide level).

27. What is meant by stand?

The period at high or low water during which there is no apparent

change of level is called stand.

28. What is tidal range?

The tidal range is the vertical difference between the high tide and the

succeeding low tide. Tides are the rise and fall of sea levels caused by the

combined effects of the gravitational forces exerted by the Moon and the

Sun and the rotation of the Earth. The tidal range is not constant, but

changes depending on where the sun and the moon are.

UNIT – 3

1. Write short notes on wave forces on piles.

Wave forces on vertical cylindrical structures, such as piles exerted by

non – breaking waves can be divided into two components such as,

Force due to drag

Force due to inertia

https://en.wikipedia.org/wiki/High_tide

https://en.wikipedia.org/wiki/Low_tide

https://en.wikipedia.org/wiki/Tide

https://en.wikipedia.org/wiki/Moon

https://en.wikipedia.org/wiki/Sun

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2. What is meant by breaker zone?

The breaker zone is the zone within which the waves approaching the

coastline commence breaking. The breaker zone is part of the surf zone.

However, the instantaneous width of the breaker zone varies with the

instantaneous wave conditions.

3. Define near shore zone.

The zone extending seaward from the low water line well beyond the

breaker zone; it defines the area influenced by the near shore currents. The

near shore zone extends somewhat further seawards than the littoral zone.

4. Define offshore zone.

The offshore zone is not well defined. In relation to beach

terminology, it is thus not clear if it starts from the littoral zone, from the

breaking or from the near shore zone. In the present context, the offshore

zone is defined as the zone off the near shore zone.

5. Define littoral zone.

This zone extends seaward from the foreshore to some distance

beyond the breaker zone. The littoral zone is the zone in which the littoral

processes take place; these are mainly the long-shore transport, also referred

to as the littoral drift, and the cross-shore transport.

6. Define surf zone.

The surf zone is the region extending from the seaward boundary of

wave breaking to the limit of wave uprush. Within the surf zone wave

breaking is dominant hydrodynamic process.

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7. Define non – breaking waves.

When the depth of water against the structure is greater than about 1 1

2

times the maximum expected wave height, generally the non – breaking

wave conditions occur.

Forces due to non – breaking waves are essentially hydrostatic.

‘Sainflou Method’ may be used for the determination of pressure due to non

– breaking waves.

8. Define breaking waves.

In fluid dynamics, a breaking wave is a wave whose amplitude

reaches a critical level at which some process can suddenly start to occur

that causes large amounts of wave energy to be transformed into turbulent

kinetic energy. There are four types of breaking waves. They are spilling,

plunging, collapsing and surging.

9. Define broken waves.

Locations of certain structures like protective structure will be such

that waves will break before striking them. In such cases, no exact formulae

have been developed so far to evaluate the forces due to broken waves, but

only approximate methods based on certain simplifying assumptions are

available.

10. What is breaking wave height?

Wave height is limited by both depth and wavelength. For given

water depth and wave period there is a maximum height limit above which

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the wave becomes unstable and breaks. This upper limit of wave height is

called breaking wave height.

11. Write the formula used to find the design breaker height.

𝐻𝑏 = 𝑑𝑠

𝛾 − 𝑚𝜏𝑝

Where,

𝑑𝑠 = 𝑑𝑒𝑝𝑡ℎ 𝑎𝑡 𝑠𝑡𝑟𝑢𝑐𝑡𝑢𝑟𝑒 𝑡𝑜𝑒

𝛾 = ℎ𝑏

𝐻𝑏

𝑚 = 𝑛𝑒𝑎𝑟 𝑠ℎ𝑜𝑟𝑒 𝑠𝑙𝑜𝑝𝑒

𝜏𝑝 = 𝑑𝑖𝑚𝑒𝑛𝑠𝑖𝑜𝑛𝑙𝑒𝑠𝑠 𝑝𝑙𝑢𝑛𝑔𝑒 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 = 𝑏𝑟𝑒𝑎𝑘𝑒𝑟 𝑡𝑟𝑎𝑣𝑒𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (𝑥𝑝)

𝑏𝑟𝑒𝑎𝑘𝑒𝑟 ℎ𝑒𝑖𝑔ℎ𝑡 (𝐻𝑏)

12. What is breakwater? Name its types.

Breakwaters are one of the essential coastal structures and these are

constructed to provide a calm basin for ships and to protect harbor facilities.

Since sea waves have enormous power, the construction of structures to

mitigate such power is not easily accomplished. Breakwaters are generally

classified into three major categories according to the functional

requirements. They are,

Mound breakwaters

Vertical breakwaters

Mixed or composite breakwaters

13. What are the points should be considered for the design of breakwater?

The required lifetime of the structure

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The return period of the design conditions

Allowable overtopping

Allowable wave disturbance behind a breakwater

Construction aspects (e.g. crest width and height)

14. What are the boundary conditions should be considered for the design

of breakwater?

The design wave height and period

The design water level (high water and low water)

The bathymetry

The soil conditions

Seismic conditions

15. What are the functions of breakwater?

Protection against waves

Guiding of current

Protection against shoaling

Provision of a dock or quay

16. Define vertical breakwaters.

Vertical breakwaters especially the single unit monolithic types are

sometimes preferred to the rubble mound breakwaters mainly for reasons

such as saving in material due to smaller body with and rapidity in

construction. Obviously, the vertical structure is preferred in deep waters

and when rock quarries are not located near the harbor site and

transportation of large quantities of stones from distant quarries become

expensive.

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17. Define rubble mound breakwater.

A rubble mound breakwater is composed of several layers of random

shaped and randomly placed stones protected with a cover layer of selected

armor units of either natural rock or specially shaped concrete units. The

armor units in the cover layer may be placed at random or in an orderly

manner to obtain good interlocking between the individual units.

18. Define composite breakwaters.

This is a combination of a vertical monolithic breakwater founded on

a rubble mound base. The advantage of a composite breakwater is the

judicious and economical use of materials. It has the advantage of adopting

itself to uneven bottom. The height of the monolith is reduced. The

disadvantages are that the wave break on the structure and the impact forces

are several fold larger than the forces exerted by standing waves.

19. What are the types of failures occurs on vertical walls?

Settling in quicksand when the breakwater is founded on fine sand

Horizontal sliding at the foundation level

Overturning

20. What are the types of vertical breakwater?

Small blocks

Large blocks

Monolithic caissons

Sloping faces

Hanstholm type of breakwater

Cellular sheet pile breakwater

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Vertical parallel sheet piles

Metal box caisson

Perforated breakwater

21. What are the types of rubble mound breakwater?

Berm breakwaters armored with natural rock

Conventional multi layer breakwater with armor over crest

Conventional multi layer breakwater with crown wall

Composite structure incorporating caisson with armor protection

22. How do you calculate the height of break water?

𝐻𝑓 = 𝑅𝑐 + ℎ

𝑅𝑐 = 1.2 𝐻𝑠

Where,

𝐻𝑓 = 𝑏𝑟𝑒𝑎𝑘𝑤𝑎𝑡𝑒𝑟 ℎ𝑒𝑖𝑔ℎ𝑡 (𝑚)

𝑅𝑐 = 𝑓𝑟𝑒𝑒𝑏𝑜𝑎𝑟𝑑 (𝑚)

ℎ = 𝑤𝑎𝑡𝑒𝑟 𝑑𝑒𝑝𝑡ℎ (𝑚)

𝐻𝑠 = 𝑑𝑒𝑠𝑖𝑔𝑛 𝑤𝑎𝑣𝑒 ℎ𝑒𝑖𝑔ℎ𝑡 (𝑚)

23. What are the forces acting on breakwaters?

Hydrostatic pressure

Buoyancy or uplift pressure

Non – breaking wave force on non – overtopping walls

Wave forces on overtopping vertical breakwaters

Impact pressure due to braking waves

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24. What are the advantages of beach nourishment?

Widens the recreational beach

Structures behind beach are protected as long as the added sand

remains

25. What are the disadvantages of beach nourishment?

Beach nourishment sand may erode, because of storms or lack of up-

drift sand sources

Beach nourishment is expensive, and must be repeated periodically

The beach turns into a construction zone during nourishment

The process of nourishment may damage, destroy or otherwise hurt

marine and beach life by burying it

The sand added to the beach is often different from the natural beach

sand. It can be hard to find a perfect match

26. Define clapotis.

When tidal wave is reflected back by solid wall of marine structure,

the reflected water may fall on the incoming tidal wave; increasing height of

water surface, which looks like a wall of water, such a wall of water is

known as clapotis.

27. Write a note on spring tide.

During full moon and new moon periods, we have high tides known

as spring tide.

Sun and Moon on the same side (zero degree)

Sun and Moon at opposite sides

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28. Write a note on neap tide.

When the moon is in its quarter position, low tides occurs known as

neap tide.

Sun and Moon at 90 degrees

Sun and Moon at 270 degrees

29. How is current created?

Ocean currents can be generated by wind, density differences in water

masses caused by temperature and salinity variations, gravity, and events

such as earthquakes. Currents are cohesive streams of seawater that circulate

through the ocean.

30. What are the types of current relevant to coastal engineers?

Ocean circulation

Tidal currents

Near shore currents

Long shore current

Rip current

On shore – off shore current

31. Define tidal current.

The rise and fall of tide is accompanied by horizontal movement of

the water is called tidal current.

32. Define non – tidal current.

Non – tidal current includes all currents not due to the tidal

movement. Non – tidal currents include the permanent currents in the

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general circulatory system of the oceans as well as temporary currents

arising from meteorological conditions. The current experienced at any time

is usually a combination of tidal and non – tidal currents.

33. Define hydraulic current.

A slight departure from the sine form is exhibited by the reversing

current in a strait that connects two different tidal basins, such as the East

River, New York. The tides at the two ends of a strait are seldom in phase or

equal in range, and the current is called hydraulic current.

34. What is meant by slack water?

In rivers or straits, or where the direction of flow is more or less

restricted to certain channels, the tidal current is reversing; that is, it flows

alternately in approximately opposite directions with an instant or short

period of little or no current, called slack water.

35. Define near shore current.

A system of currents that is caused by wave activity within and

adjacent to the breaker zone. The current system includes the shoreward

mass transport of water, long shore currents and seaward-moving rip

currents.

36. Define the term long shore current and rip current.

The long shore current is the dominating current in the near shore

zone; it is running parallel to the shore. The long shore current is generated

by the shore-parallel component of the stresses associated with the breaking

process for obliquely incoming waves, the so called radiation stresses, and

http://www.encyclopedia.com/doc/1O14-breaker.html

http://www.encyclopedia.com/doc/1O14-longshorecurrent.html

http://www.encyclopedia.com/doc/1O14-ripcurrent.html

http://www.encyclopedia.com/doc/1O14-ripcurrent.html

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by the surplus water which is carried across the breaker zone towards the

coastline.

An intermittent strong surface current flowing seaward from the shore

is called rip current.

UNIT – 4

1. What is known as lagoons?

A lagoon is a shallow body of water separated from a larger body of

water by barrier islands or reefs. Lagoons are commonly divided into coastal

lagoons and atoll lagoons. They have also been identified as occurring on

mixed-sand and gravel coastlines. There is an overlap between bodies of

water classified as coastal lagoons and bodies of water classified as

estuaries.

2. What is littoral drift?

Littoral transport is the term used for the transport of non-cohesive

sediments, i.e. mainly sand, along the foreshore and the shore face due to the

action of the breaking waves and the long shore current. The littoral

transport is also called the long shore transport or the littoral drift.

3. What is long shore drift?

Long shore drift is a geographical process that consists of the

transportation of sediments (clay, silt, sand and shingle) along a coast at an

angle to the shoreline, which is dependent on prevailing wind direction,

swash and backwash. This process occurs in the littoral zone, and in or close

to the surf zone.

https://en.wikipedia.org/wiki/Barrier_island

https://en.wikipedia.org/wiki/Reef

https://en.wikipedia.org/wiki/Atoll

https://en.wikipedia.org/wiki/Estuary

http://www.coastalwiki.org/wiki/Littoral_transport

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4. What is stokes drift?

In reality, for finite values of the wave amplitude (height), the particle

paths do not form closed orbits; rather, after the passage of each crest,

particles are displaced slightly from their previous positions, a phenomenon

known as Stokes drift.

5. Mention some of the environmental parameters.

Maximum tidal elevation

Wave characteristics

Storm surge

Long shore transport rate

Current

Soil characteristics of the backfill

6. What are the environmental parameters should be considered by

coastal engineers?

Waves

Tides

Currents

Wind

Storm surge

Sediment transport

7. What is meant by fetch?

The fetch, also called the fetch length, is the length of water over

which a given wind has blown. Fetch is used in geography and meteorology

and its effects are usually associated with sea state and when it reaches shore

https://en.wiktionary.org/wiki/finite

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it is the main factor that creates storm surge which leads to coastal erosion

and flooding.

8. What is meant by scour?

Rubble mounds may be subject to severe toe erosion by undermining

and scour. Scour is a process of removal of materials on the sediment bed.

9. What is coastal erosion?

Coastal erosion is the wearing a way of land and the removal of beach

or dune sediments by wave action, tidal currents, wave currents, drainage or

high winds.

10. List the natural causes of erosion.

Sea level rise

Protruding headlands, reefs or rocks in to the sea

Tidal entrances and river mouths causing interruption of free passage

of sediments along the shore, natural protection of tidal entrances

Shoreline geometry causing rapid increase of drift quantity

Removal of beach material by wind drift

Removal of beach material by sudden outbursts of flood waters

11. List down the man induced causes of erosion.

Construction of dykes, dams and other coastal structures

Construction of breakwaters, groins, jetties, etc

Man-made entrances causing interruption of littoral drift. This

includes construction of jetties

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Fills protruding in the ocean to an extent that they change local

shoreline geometry radically

Removal of material from beaches for construction and other purposes

Digging or dredging of new inlets, channels and entrances offshore

dumping of materials

12. What are the causes of coastal erosion in India?

Rise of sea level

Reduction of sediment supply to shore

Effect of severe cyclonic storms and tides

Natural and manmade littoral barriers

Change in near shore topography

Lack of coastal environmental data

13. What are the effects of coastal erosion?

Dislocation of coastal population and loss of life and property

Loss of beaches, accretion of beach, areas, dislocation of coastal

transport system

Silting of ports, harbours and shipping channels

Stoppage of shore based fisheries

Loss of placer mining grounds

Scenic beauty affected, loss of agricultural land

Influx of saline water into coastal agricultural lands, causes erosion of

beaches due to reduced supply of sediment

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14. What are the remedial measures for coastal protection?

Construction of suitable structures to prevent wave energy from

reaching the erodible shores or to trap and accumulate the littoral drift

material on the beach

Artificial nourishment of the eroding beach to make up for the

deficiency in sand supply. In some cases, a small structure such as a

groyne may be required to reduce the rate of loss of material from the

nourished beach

15. What are the long term and short term measures provided for the

coastal zone management?

SHORT TERM MEASURES:

Seawalls

Anti sea erosion bunds

Revetments

Groynes

Bulkheads

LONG TERM MEASURES:

Offshore breakwaters

Beach nourishment by sand

Sand by passing

Vegetative plantation

Sand dunes

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16. What is dredging?

It is the process of removal of sediments and debris from the bottom

of river bed, lake or sea for the purpose of deepening them. It is an

important operation in navigation canals, harbors, dams etc.

17. Classify the dredging procedure.

Pre – treatment

Extraction

Disposal

18. What are the multiple uses of dredged material?

Construction purpose

Wetland creation

Sediment separation

Creation of harbors

Habitat restoration

Beach nourishment

Top soil creation

19. Mention some of the choice of dredging systems.

Nature of material to be dredged

Depth of dredging

Distance and height at which dredged material is to be deposited

Quantity of material to be dredged

The traffic conditions in area to be dredged

Weather conditions in area to be dredged

Availability of maintenance facilities

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Types of prime movers for dredgers

Kinds of fuel for prime movers

20. What are the types of dredgers?

Mechanical dredger

Hydraulic or suction dredger

21. Mention the types of mechanical dredgers.

Grab dredger

Dipper dredger

Rock breaker

Bucket dredger

Non – propelling type or stationary bucket dredger

Self propelling bucket dredger

22. Mention the types of hydraulic or suction dredger.

Stationary suction dredger

Cutter suction dredger

Suction dredger

Suction dredger with rotating bucket wheels

Hopper suction dredger

Trailing suction dredger

23. Define remote sensing.

Remote sensing is the acquisition of information about an object or

phenomenon without making physical contact with the object and thus in

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contrast to on site observation. Remote sensing is a sub-field of geography.

In modern usage, the term generally refers to the use of aerial sensor

technologies to detect and classify objects on Earth (both on the surface, and

in the atmosphere and oceans) by means of propagated signals (e.g.

electromagnetic radiation). It may be split into active remote sensing (when

a signal is first emitted from aircraft or satellites) or passive (e.g. sunlight)

when information is merely recorded.

24. What are the advantages of remote sensing?

Observation of a large geographical area

Long-term and fast collection of data

Lower collecting costs

"Inaccessible" regions become accessible (e.g. Antarctica)

Object is not being destroyed

25. What are the disadvantages of remotes sensing?

Lower spatial resolution (depending on the type of sensor)

Need for the installation of complex systems (which have a long

testing phase)

Captured data need to be calibrated via in-situ data

Noise caused by another source than the desired one

Atmospheric effects degrade the quality of the images and need to be

corrected

https://en.wikipedia.org/wiki/Geography

https://en.wikipedia.org/wiki/Atmosphere

https://en.wikipedia.org/wiki/Oceans

https://en.wikipedia.org/wiki/Wave_propagation

https://en.wikipedia.org/wiki/Electromagnetic_radiation

https://en.wikipedia.org/wiki/Aircraft

https://en.wikipedia.org/wiki/Satellites

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UNIT – 5

1. Mention the methods of protection of shores.

Shore parallel structures

Seawall

Bulkhead

Revetment

Offshore breakwaters

o Reef breakwater

o Low created breakwaters

o Submerged breakwaters

Shore perpendicular structures

Timber groynes

Concrete groynes

Stone groynes

Cellular groynes

High / low groynes

Beach nourishment

2. What is known as bulkhead?

This is defined as a structure or a partition to retain or prevent sliding

of the land. A secondary purpose is to protect the upland against damage

from wave action. Bulkheads are next in size, their function along to retain

the fill and are generally not exposed to severe wave action. Bulkheads

appear in three forms. They are,

Concrete slab and king pile bulkhead

Steel sheet pile bulkhead

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Timber sheet pile bulkhead

3. What is meant by revetment?

Revetment in general is a sloping face made up of a randomly placed

stones, concrete, etc. built to protect an embankment, or shore structure

against erosion by wave action or currents. They are the lightest because

they are designed to protect the shorelines against erosion by currents or

light wave action. Revetments are of two types. They are,

Concrete revetment

Rip – rap revetment

4. What is meant by sea walls?

Seawall is defined as a structure separating land and water body,

primarily designed to prevent erosion and other damage due to wave action.

In general, seawalls are the most massive of the three types because they

resist the full force of the waves. They are designed to face severe wave

action and are provided with sheet pile cut off walls at the toe to prevent loss

of foundation material by wave induced scour, leaching from wave

overtopping water or storm drainage beneath the wall. Seawalls can be

classified as,

Concrete curved face

Combination of a curve and steps

Step faced

Rubble mound

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5. What is meant by offshore breakwater?

Along certain coastal region, the shoreline is protected by a series of

submerged or raised rubble mound structures positioned intermittently in the

shallow waters. These breakwaters make the incoming waves to break

before they reach the coastline and in the process the beaches are protected

from the fury of the waves. These breakwaters are classified as,

Reef breakwater

Low created breakwater

Submerged breakwater

6. What are the materials to be used for building bulkheads and seawalls?

Concrete

Steel

Timber

7. What is Groynes?

When the stretch of coast to be protected extends over a long distance,

it would be advisable to install shore perpendicular structures for coastal

protection. Usually finger like structures projecting into the sea for a short

distances are constructed at a pre – determined spacing for the entire length

of the coast to be protected. The finger like structures are known as groynes

and a number of such groynes put together form a groyne field.

DEMERITS:

Induces local scour at the toe of the structure

Causes erosion down drift; requires regular maintenance

Typically more than one structure is required

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8. Mention the types of Groynes.

Timber groynes

Concrete groynes

Stone groynes

Cellular groynes

High / low groynes

9. Give a brief description about beach nourishment.

Tidal inlets protected from waves by jetties face accretion along the

up drift coast and erosion on the down drift coast. Under such

circumstances the affected coast is nourished with sand from the up drift

accretion zone. This process has been proven to be effective provided the

process of by – passing the sediments is carried out without any interruption.

The advantage of this system is that the beach maintains its natural beauty.

10. What are the applications of GIS?

Current GIS applications in the coastal zone are diversified and case-

based studies, mainly focusing on vector-based applications. These

applications can be categorized as,

Coastal mapping

Environmental monitoring

Coastal process modeling

Navigation and port facilities management

Coastal environmental / hazard assessment

Coastal management / strategic planning

Coastal ecological modeling

coastal engineering

Engineering