The document discusses various natural phenomena that affect harbors, including winds, waves, tides, and currents. It describes the characteristics and impacts of each phenomenon. Winds can cause waves and currents. Waves are periodic undulations generated by wind moving over water. Tides are rises and falls in ocean waters caused by gravitational forces from the sun and moon. Currents are horizontal water movements caused by factors like tides, wind, and wave breaking. These natural phenomena produce forces that must be considered in harbor and marine structure design to ensure stability and durability.

1. “NATURAL PHENOMENA”
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PREPARED BY : ASST. PROF. VATSAL D. PATEL
MAHATMA GANDHI INSTITUTE OF
TECHNICAL EDUCATION &
RESEARCH CENTRE, NAVSARI.

2. INTRODUCTION
 In an harbour there are many activities of the water but are
affected by the natural phenomena.
 These then to have an impact to the harbour by different
kinds of the motion of the water caused by these
phenomena. The major natural phenomena are as follows:
 Winds
 Waves
 Tides
 Currents

3. WINDS
 Wind is horizontal movement of air due to differences in air
pressure which are caused by differential heating and
cooling.
 In short wind means air in motion.
 Wind Characteristics:-
Direction of wind usually specified by compass.
Frequency of wind is the percentage of the time in a
year it will blow from a particular direction.
Intensity gives the velocity of the wind.
 Speed of wind is expressed in “knots” and wind strength is
measured in km/hr. (1 knot = 1.852 km/hr)

4. WAVES
 Waves are periodic undulations of the sea surface. Water
waves are generated by transfer of energy from air moving
over the water.
 Causes of Sea Waves:-
Wind,
Revolution of the earth,
Gravitational force of the moon and sun,
Earthquake,
Land slide and seashore,

5. WAVES
 There are different types of sea waves. These are listed
below:
1. Deep Sea Waves.
2. Shallow Sea Waves.
3. Oscillatory Waves. (unbroken waves, travelling in
deep water)
4. Translatory Waves. (oscillatory waves that break
when reached shallow water)
5. Capillary Waves or Ripples.
 Surfs (low height and long waves produced by
wind)
 Surges (produced by cyclone)
 Tsunamis (produced by eruption of volcano or
earthquake)

6. DEEP SEA WAVE OSCILLATORY WAVES
SHALLOW SEA WAVES
CAPILLARY WAVES

7. CHARACTERISTICS of
WAVES
The highest point of a
wave is called crest.
The lowest point of a
wave is called trough.
The distance between
two successive crests
is called wavelength
(L).
The vertical distance
from the crest to the
trough is called wave
height (H).
The time taken for a
wave to travel a
distance of one
wavelength is called
wave period (T).

8. CHARACTERISTICS OF WAVES
 The reciprocal of wave period (T) is called the wave
frequency (f).
f= 1/T
 The velocity of wave, V=L/T.
 The angular frequency of wave, ω = 2π/T

9. DETERMINATION OF WAVE VELOCITY,
FETCH, WAVE HEIGHT AND WAVELENGTH
 Wave Velocity:-
Where,
L = Length
T = Wave Period
 Fetch:- Straight line stretch of open water available for
wave growth without the interruption of land is called fetch.
Where,
H = Wave Height (m)
F = Fetch (km)

10. DETERMINATION OF WAVE VELOCITY,
FETCH, WAVE HEIGHT AND WAVELENGTH
 Wave Length:-
Where,
L = Length of wave (m) =
T = Wave Period (sec)

11. Wave
Breaking
Waves break when
the forward velocity
of the crest particles
exceeds the velocity
of the wave
propagation itself in
deep water
 Ocean waves on breaking against
marine structure give rise to….
 Compression due to direct horizontal force,
 Shearing action at the projection on the face of
the wall,
 Suction effect due to return water,
 Sea bed & Foundation disturbance due to
downward force.
 Above effects results in…..
 Inertia Force
 Vibration
 Internal Pressure
 Expansion and contraction of cavities of the structure.

12. WAVE REFLECTION
 Non breaking waves are acting on a vertical wall (break
water), do not loose their energy by the impact but are
reflected.
 Due to continuous interaction of the incidents and reflected
waves, a wave of higher height (2 to 3 times) is formed
which is called Standing Waves (Clapotis).

13. WAVE REFLECTION
 Methods To Minimize Wave Reflection Inside The
Harbour:-
 Break water must in such a way that the reflected waves
are not diverted towards piers or any other structure.
 The interior slopes of breakwater can be designed for the
wave to break, which spend the wave energy.
 Special spending beaches can be planned at points of
maximum waves take place.

14. WIND ROSE
 The wind data i.e., direction, duration and intensity are
graphically represented by a diagram called wind rose.
 Data collection : 5 year study
 Irregular shape resembling rose.

15. WIND ROSE
 In this figure, the radial lines indicate the wind direction
and each circle represent the duration (frequency) of the
wind. The irregular lines show the intensity (speed) of the
wind.

16. TIDES
 Due to gravitational force of sun and moon there is rise and
fall in ocean waters called Tides.
The rise in water level is called high tide and
The fall in water level is called low tides.
 In Mediterranean sea, height of tide is 0.5 to 1.0 m.
 In the Gulf of fundy, height of tide is 15 to 20m.
Mediterranean Sea Bay of Fundy

17. CLASSIFICATION OF TIDES
TIDES
Spring Tides:- These are highest tides which occur when sun, moon and earth
fall in line.
Neap Tides:- These are lowest tides which occur when the lines connecting the
earth with the sun and the moon form right angle.
Semi-diurnal Tide:- These are the tides which occurs twice each lunar day
(Lunar Day means time taken by moon to make a complete revolution
around the earth.)
Diurnal Tide:- These are high tides occur only one time a day. E.g. at Florida.
Mixed Tide:- If one of the two daily high tides does not reach the height of the
previous tide, it is called a mixed tide. E.g. U. S. A, California.
Tidal Bore:- These are high crested waves caused by the rush of flood tide up a
river. Regular occurrence in bay of fundy.

19. Cont...
 Uses of Tides:-
Tides can be used for harnessing the power.
Tides are used for entry and exit of ships in the harbour.
Fisherman takes an advantage of tides.
Ports remain clean due to tides.
High tide water can be used for harvesting salt.

20. CURRENTS
Currents are essentially
a horizontal movement
of water.
 Causes of Currents:-
 Tides,
 Wind blowing over ocean,
 Difference in temperature,
 Turbidity of water,
 Wave breaking at an angle of a beach.
 Effects of Currents:-
 Scouring and erosion,
 Deposition(silting),
 Increase in corrosion rate,
 Delay in construction operations,
 Significant forces on marine structure,
 Loads on moored vessels.

21. CLASSIFICATION OF CURRENTS
CURRENTS
Primary ocean
currents
Turbidity
currents
Tidal and
Wind drift
currents
Wind stress
currents
Littoral
currents
These are produced by the density
difference caused by difference of
temperature and water salinity.
These are caused by the mixing of
bottom sediments with the sea
water resulting in density increase.
Great importance to a engineer in
planning and design of fixed and
floating structures.
Wind blowing over the ocean
surface tends to drag the surface
layers of water
These are caused by the Littoral
Drift alongshore at an angle to the
beach which pile water to the coast

22. LITTORAL DRIFT
 The alongshore sediment movement takes place in the
narrow zone along the coast where the waves break. In this
zone, the waves create the longshore current transporting
the sediment which is then brought in to suspension by the
breaking waves.
 Beyond the breaker zone the longshore sediment
movement decreases rapidly in a seaward direction of
drifting sand in a zig-zag line in the proximity of coasts is
known as littoral drift.

23. SEDIMENT TRANSPORT
 Sediment refers to the conglomerate of materials, organic
and inorganic, that can be carried away by water, wind or
ice. While the term is often used to indicate soil-based,
mineral matter (e.g. clay, silt and sand), decomposing
organic substances and inorganic biogenic material are also
considered sediment.

24. SEDIMENT TRANSPORT
 In an aquatic environment, sediment can either be
suspended (floating in the water column) or bedded (settled
on the bottom of a body of water). When both floating and
settled particles are monitored, they are referred to as
SABS: Suspended And Beded Sediments.

25. SEDIMENT TRANSPORT
 Sediment transport is the movement of organic and
inorganic particles by water. Water flow can be strong
enough to suspend particles in the water column as they
move downstream, or simply push them along the bottom
of a waterway. Transported sediment may include mineral
matter, chemicals and pollutants, and organic material.

26. EFFECTS ON HARBOR & STRUCTURE
DESIGN
 In this time of climate change we have been witness to
many natural phenomena which have caused the
destruction of man-made structures.
 They have created external forces which have produced
stresses on the materials that we use to build buildings,
bridges and roads.
 Stability and design may be affected.
 Life span of some structure can reduce.

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