TIDE & TIDAL STREAMS - VARIOUS IMPORTANT DEFINITIONS INCLUDING BORE, SPRING, NEAP TIDE ETC

TIDE & TIDAL STREAMS - VARIOUS IMPORTANT DEFINITIONS INCLUDING BORE, SPRING, NEAP TIDE ETC

TIDES are the periodic motion of the waters of the sea due to differences in the attractive
forces of the Moon and Sun, upon different parts of the rotating earth.
TIDAL CURRENTS are the periodic horizontal flow of water accompanying the rise and fall of
the tide.
Tide rises and falls. Tidal current floods and ebbs.
EBB CURRENT: -The horizontal movement of water away from shore following a high tide
or downstream.
FLOOD CURRENT: - The horizontal movement of water toward shore following low tide or
upstream.
RANGE OF TIDE: - The difference in height between consecutive high and low water.
SPRING TIDES: - Tides that occur at times of New and Full Moon (Sun and Moon are in
Conjunction and at Opposition with the earth).
NEAP TIDES: - Tides that occur at times of First and Last Quarters (Sun and Moon are in
Quadrature with the earth).
PERIGIAN TIDE: - Occurs when the moon is at the point in its orbit nearest the earth.The
lunar semidiurnal range is increased.
APOGEAN TIDE: - Occurs when the moon is at the point in its orbit farthest the earth.
The lunar semidiurnal range is decreased.
BORE TIDE: - The "bore" is a tidal phenomenon in which the leading edge of the incoming tide clashes with the flow of the outgoing tide to form a wave that travels up a river or narrow bay. The bore can only occur in long, narrow channels.
A tidal bore occurs along a coast where a river empties into an ocean or sea. A tidal bore is a strong tide that pushes up the river, against the current. A tidal bore is a true tidal wave.
A tidal bore is a surge. A surge is a sudden change in depth. When a channel suddenly gets
deeper, it experiences a positive surge. When a channel suddenly gets shallower, it experiences a negative surge. Tidal bores are positive surges.
Tidal window: - A tidal window is the time span in which the tidal elevation is high enough
for a vessel to pass.
MEAN HIGH WATER SPRINGS (MHWS): - Average level of high waters that occur at the times of spring tides.
MEAN HIGH WATER (MHW): - The average height of all high waters over a 19-year period.
MEAN HIGH WATER NEAPS (MHWN): - Average height of the high waters of the neap tides.

MEAN LOW WATER NEAPS (MLWN): - Average height of the low waters of the neap tides.
MEAN LOW WATER (MLW): - The average height of all low waters at a given place.

MEAN LOW WATER SPRINGS (MLWS): - Average level of low waters that occur at the
times of spring tides.