This document provides an overview of various natural phenomena including wind, tides, currents, and littoral drift. It describes the characteristics of wind including direction, frequency, and intensity which are represented graphically in a wind rose. Tides are defined as the periodic rise and fall of ocean waters caused by gravitational forces of the sun and moon. Types of tides include spring, neap, semi-diurnal, and diurnal tides. Currents are horizontal water movements caused by factors such as tides, wind, temperature/salinity differences, and wave breaking. Currents can cause scouring, erosion, deposition, and impact marine structures. Littoral drift is the alongshore sediment movement in the

1. Natural Phenomenon
Presented by :
Parth Desani (116470306049)

2. Index
 Wind
 Wind Characteristics
 Wind Rose
 Forces due to Wind
 Tides
 Types of Tides
 Uses of Tides
 Mean Sea Level
(M.S.L.)
 Currents
 Causes of Currents
 Effects of Currents
 Littoral Drift

3. Wind
 Wind can be defined as air in motion. It is the
horizontal movement of air due to differences in air
pressure which are caused by differential heating
and cooling.

4. Wind Characteristics
 The important wind characteristics are :
 The direction of wind
 The frequency of wind
 The intensity of wind
 The direction of wind is usually specified by the compass.
 The frequency of wind is the percentage of time in a year
it will blow from a particular direction.
 The intensity gives the velocity of the wind. In maritime
works, speed of wind is expressed in KNOTS.
 1 knot = 1.85 km/hr

5. Wind Rose
 The three wind characteristics, namely direction,
duration and intensity can be graphically represented
by a diagram known as WIND ROSE.
 Generally, wind data for a period of at least 5 years
should be collected to obtain an average data with
sufficient accuracy.

6.  In this figure, the
radial lines indicates
the wind direction
and each circle
represents the
duration (frequency)
of the wind.
 The irregular lines
shows the intensity
(speed) of the wind.

7. Force Due To Wind
 The intensity of pressure due to the wind varies with the square of
the velocity.
p = CV²
Where, p = wind pressure intensity (kg/m²)
C = a constant = 0.00481
V = wind velocity (km/h)
 The total wind force is given by :
F = Ks∙p∙A
Where, F = total wind force (kg)
Ks = a shape factor of the structure
p = wind pressure (kg/m²)
A = area of the exposed surface (m²)
Type of structure Ks
Low flat surface of a ship or dock 1.3
Sides of buildings 1.5
Beams 1.5
Cylinders 0.5

8. Tides
 Due to gravitational forces of sun and moon there is
periodic rise and fall of ocean waters. This
phenomenon is known as tides.
 The rise in ocean water level is called high tide and
the fall in ocean water level is called low tide.
 Generally there are two high tides and two low tides
every lunar day.
 Two successive high tides or low tides is about 12
hours 25 min. Every day the tide comes 50 min. later
than the tide of previous day.

9. Types of Tides
 Spring tides : These are highest tides which occur
at intervals of half a lunar month. They occur when
generating forces of the moon and the sun are
additives.
 Neap tides : This is the lowest tide of the month. It
occurs when the lines connecting the earth with the
sun the moon from right angle.
 Semi-diurnal tide : these are the tides which occurs
twice each lunar day. Moon crosses the observer’s
meridian twice in 24 hours and hence, generates two
tides a day.

10.  Diurnal tide : These are the high tides which occur
only one time a day.
 Mixed tide : If one of the two daily high tides does
not reach the height of the previous tide, it is called a
mixed diurnal tide.
 Tidal bore : These are high crested waves caused
by the rush of flood tide up a river. They have a
regular occurrence at certain locations as in the bay
of Fundy.

11. Uses of Tides
 Tides can be used for harnessing the power. The
central water and power research station is studying
the possibilities of harnessing the tidal power at,
 Gulf of Kutch
 Gulf of Cambay
 Sundarbans
 Tides are used for the entry and exit of ships in the
harbours.
 Fisherman takes an advantages of tides.
 Due to tides the seashore and ports remains clean.
 High tide water can be used for harvesting salt.

12. Mean Sea Level (M.S.L.)
 It can be defined at the average sea level about
which the tides oscillate.
 M.S.L. is important in establishing a fundamental
bench mark for land surveys. It is not generally used
as a reference plane for marine structures.

14. Currents
 Currents are essentially a horizontal movement of
water.
 Primary Ocean Currents
 Turbidity Currents
 Tidal and wind drift currents
 Wind stress currents
 Littoral currents

15. Causes of Currents
 Tides
 Wind blowing over the ocean surface
 Differences in temperature and salinity of sea water
 Turbidity of water
 Wave breaking at an angle to the beach

16. Effects of Currents
 Scouring and erosion
 Deposition (silting)
 Increase in corrosion rate
 Modification of wave effects
 Impact of ice on marine structures
 Delay in construction operations
 Significant forces on marine structures
 Loads on moored vessels

17. 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 longshore
current transporting the sediment which is then
brought in to suspension by the breaking waves.