Chapter - 3. Natural Phenomena

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    Dock, Harbour & AirportEngineering

    Chap – 3 “NATURALPHEN!ENA"

    PREPARED BY :-

    KARTIK ZALAAssi. Prof.,

    Civil Engg. Departent,!ICT.

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    CNTENT# "in#

    "aves

     Ti#es

    C$rrents

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    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 !nots" and wind stren#th is measured

    in !mph. 

    (1 knot = 1.8! km"hr#

    "I%D:-

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    Waves are periodic undulations of the sea surface. Water

    waves are #enerated by transfer of energy from air movin# overthe water.

    Causes of Sea Waves:-Wind$

    %evolution of the earth$

    &ravitational force of the moon and sun$'arthuake$

    )and slide and seashore$

    "A!E&:-

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    $ypes of Sea Waves:-

    *eep sea waves

    +hallow sea waves

    ,scillatory waves %un&ro!en waves' travellin# in deep water(

    -ranslatory waves

    apillary waves

    +urfs %low hei#ht and lon# waves produced &y wind(

    +urges %produced &y cyclone(-sunami %produced &y eruption of volcano or earthqua!e(

    "A!E& '(onti)*:-

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    "A!E& '(onti)*:-

    D))* S)+ W+,) SCI+$/0 W+,)S

    C+*I+/0 W+,)S

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    Wave ,elocity:-

    Where$ ) = )ength

      - = Wave /eriod

    Fetch:-

    +traight line stretch of open water available for wave growth

    without the interruption of land is called fetch. 

    Where$ 0 = Wave 0eight (m#

      = etch (km#

    "A!E& '(onti)*:-

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    Wave en#th:-

    Where$ ) = )ength of wave (m# =

    - = Wave /eriod (sec#

    "A!E& '(onti)*:-

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    Wave 1rea!in#:-

    Waves break when the forward velocity of the crest particlesexceeds the velocity of the wave propagation itself in deep water.

    cean waves on &rea!in# a#ainst marine structure #ive rise to2.

    ompression due to direct hori2ontal force$

    +hearing action at the pro3ection on the face of the wall$

    +uction effect due to return water$

    +ea bed 4 oundation disturbance due to downward force.

    "A!E& '(onti)*:-

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    +&ove effects results in2..

    Inertia orce

    5ibration

    Internal /ressure

    'xpansion and contraction of cavities of the structure.

    "A!E& '(onti)*:-

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    Wave /eflection:-

     6on breaking waves are acting on a vertical wall %&rea!

    water(' do not loose their energy by the impact but are

    reflected.

    *ue to continuous interaction of the incidents and reflected

    waves$ a wave of higher height %3 to 4 times( is formed which

    is called Standin# Waves %Clapotis(. 

    "A!E& '(onti)*:-

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    5ethods $o 5inimize Wave /eflection Inside $he

    6ar&our:-

    7reak water must in such a way that the reflected waves are not

    diverted towards piers or any other structure.

    -he interior slopes of breakwater can be designed for the wave

    to break$ which spend the wave energy.

    +pecial spending beaches can be planned at points of maximum

    waves take place.

     

    "A!E& '(onti)*:-

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    *ue to gravitational force of sun and moon there is rise and

    fall in ocean waters called $ID)S. -he rise in water level iscalled hi#h tide and fall in water level is called low tides.

    In 5editerranean sea$ height is . to 1. m.

    In the 7ulf of fundy$ height is 1 to !m.

     TIDE&:-

    Connecte$ to At%antic cean,Cop%ete%' enc%o(e$ b' %an$)

    *t i( on the At%antic Coa(t)

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    $ypes of $ides:-

    Sprin# $ide:- -hese are highest tides which occur when sun$

    moon and earth fall in line.

     TIDE& '(onti).*:-

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    $ypes of $ides:-

    8eap $ide:- -hese are lowest tides which occur when the lines

    connecting the earth with the sun and the moon form right angle.

     TIDE& '(onti).*:-

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    $ypes of $ides:-

    Semi-diurnal $ide:- -hese are the tides which occurs twice

    each lunar day.

    unar Day means time ta!en &y moon to ma!e a complete

    revolution around the earth.

    Diurnal $ide:- -hese are high tides occur only one time a day.'.g. at lorida.

     

     TIDE& '(onti).*:-

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    $ypes of $ides:-

    5i9ed $ide:- If one of the two daily high tides does not reach

    the height of the previous tide$ it is called a mixed tide. '.g. 9. +.

    :$ alifornia.

    $idal 1ore:- -hese are high crested waves caused by the rush of

    flood tide up a river. %egular occurrence in bay of fundy.

     

     TIDE& '(onti).*:-

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    ses of $ides:-

    -ides can be used for harnessing the power.

    -ides are used for entry and exit of ships in the harbour.

    isherman takes an advantage of tides./orts remain clean due to tides.

    0igh tide water can be used for harvesting salt.

     TIDE& '(onti).*:-

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    0ori2ontal movement of water is called current.

    Causes of Currents:-

    -ides$

    Wind blowing over ocean$

    *ifference in temperature$

    -urbidity of water$Wave breaking at an angle of a beach.

    C+RRE%T&:-

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    )ffects of Currents:-

    +couring and erosion$

    *eposition(silting#$

    Increase in corrosion rate$

    *elay in construction operations$

    +ignificant forces on marine structure$

    )oads on moored vessels.

     It is desira&le that to a lar#e e9tent 6ar&ours are free from

    erosion and siltin#.

    C+RRE%T& '(onti).*:-

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    $ypes of Currents:-

    /rimary urrent

    -urbidity urrent

    -idal and Wind drift urrent

    Wind stress urrent

    )ittoral urrent

    C+RRE%T& '(onti).*:-

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