tidal currents & it's mechanisms

1. A PRESENTATION ON TIDAL CURRENT & IT’S
MECHANISM ON THE MOUTH OF THE ESTUARY
SUBMITTED TO :
MD. WAHIDUL ALAM
ASSISTANT PROFESSOR
INSTITUTE OF MARINE SCIENCES & FISHERIES
UNIVERSITY OF CHITTAGONG
SUBMITTED BY : GROUP C

2. ESTUARIES
An estuary is a narrow, semi-enclosed coastal body of water which
has a free connection with the open sea at least intermittently and
within which the salinity of the water is measurably different from
the salinity in the open ocean.
A classical definition of estuaries used by the United Nations
Educational, Scientific and Cultural Organization (UNESCO) and
reproduced in textbooks is-
An estuary is a semi-enclosed coastal body of water having free
connection to the open sea and within which sea water is
measurably diluted with fresh water deriving from land drainage .
(Cameron and Pritchard, 1963).

3. 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.
Causes of tides :
•Moon gravitational pulls
•Sun gravitational pulls
•Sun-Moon position relative to the
earth

4. TIDAL CURRENTS
The rise and fall of sea water may cause horizontal
movements of water which are known as tidal
currents. This tidal current is caused by the
gravitational attraction between the moon and sun.
Tidal currents have amuch lower velocity. They
never excced 0.8 m/s. They are largest during
spring tides & lowest during neap tides.

5. MECHANISM OF TIDAL CURRENT
The tidal current is strong at the mouth of the estuary
where the salinity is the same adjacent sea.
The tidal currents push the river water back up the
patterns of salt penetration depend on the volumes of
salt and fresh water involved. If the volume of salt
water is much greater than the volume of fresh water,
a typical wedge will occur, with fresh water firmly
darmed. ( fig-1 )
If the fresh water flow is greater than salt water flow,
the fresh water will flow over salt water.
( fig - 2 )

6. Wedge effect
Sea water
fresh
Limit mixing zone
surface
d
e
p
p
e
r
bottom 35%
Profile : Salinity Profile : Velocity
Fig : 1

7. Two layer flow
salt
fresh
surface
bottom 35%
Profile : Salinity Profile : Velocity
Fig : 2