A PRESENTATION ON TIDAL CURRENT & IT’S MECHANISM ON

THE MOUTH OF THE ESTUARY

SUBMITTED TO : MD. WAHIDUL ALAMASSISTANT PROFESSOR

INSTITUTE OF MARINE SCIENCES & FISHERIES

UNIVERSITY OF CHITTAGONG

SUBMITTED BY : GROUP C

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).

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

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.

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 )

Wedge effect

Sea waterfresh

Limit mixing zone surface

depper

bottom 35%

Profile : Salinity Profile : Velocity

Fig : 1

Two layer flow

salt

fresh

surface

bottom 35%

Profile : Salinity Profile : Velocity

Fig : 2