Re: How are whirlpools formed in the river ? Are they in Seas and Oceans also ?

Shashi,

Whirlpools result from the turbulent flow of water.  In rivers, we often 
think of water as flowing smoothly, except when it comes to some object 
blocking its path.  The water flows around the object (a submerged rock, a 
bridge pylon, etc.) and this may cause the water to lose its smooth- 
flowing properties.  As the water flows in around the object, 
a 'whirlpool' may be created.  Another method that creates turbulence is 
to increase the flow of water through the riverbed.  The faster the flow, 
the more likely turbulent flow will develop and the more energetic the 
turbulence. 

In the oceans the process is only a little different.  We don't usually 
think of ocean water as flowing, but it does.  There are huge ocean rivers 
that flow all around the Earth.  Uneven heating of the ocean waters by the 
Sun, forces caused by the Earth's rotation (coriolis force), and uneven 
salt content of the various ocean waters, all contribute to the driving 
forces that keep these waters flowing.  Sometimes, these currents run past 
each other or actually collide.  Conflicting tidal flows can also 
interact.  When this happens, turbulence similar to that described for a 
river can result.  According to the 'Book of Popular Science', the best 
known tidal-generated whirpool in the world occurs in the Maelstrom, a 
strait about three miles wide in Norway's Lofoten Islands, between 
Moskenesoy and Mosken Islet.  One famous and fanciful, description of this 
whirlpool is in a story by Edger Alan Poe, called 'Descent Into the 
Maelstrom".  You may find it interesting if not very factual.

The whirlpool of Garofalo, in the Strait of Messina, between the island of 
Sicily and Italy, is produced by winds that flow against the direction 
tidal currents.  

The destructive effects of such whirlpools have been rather exaggerated; 
small boats may be entrapped and wrecked in them, but not larger craft.  
However, even a large boat may find steering almost impossible until the 
whirlpool subsides. 

If you are interested in a book that looks at this process from the 
viewpoint of the Chaos Theory, read 'Turbulent Mirror" by John Briggs and 
F. David Peat, Harper & Row, 1990.

More recently, Paul Harvey (a U.S. radio commontator) told of a lake, I 
believe in Wisconsin, USA, that developed a huge whirlpool and acutally 
sucked several boats down.  It was later determined that an underground 
cavern developed an opening into the bottom of the lake and drained the 
water.  Inflowing water from rivers refilled the lake.

The various kinds of turbulent flow can be a very interesting study.
I hope this helps.