Water level in the ocean is not constant. It is defined by inflows and otliva which in certain cases can turn a current of the rivers back.
Why there are inflows and otliva?
Increase and reduction of water level in the sea happens two times a day. Within six hours, water gradually arrives to the coast, and then, within the next six hours recedes. Such movement of level of the ocean on the coast is caused by position of Earth concerning the Moon and the Sun. At gravitational impact of the Moon on Earth in the ocean the hump is formed tidal. This thickness of water moves to the coast, thereby increasing water level at it. Tidal the hump because of the centrifugal force of Earth is formed also on the opposite side from influence of the Moon.
What does the size of inflows and otliv depend on?
The size of inflows and otliv changes with frequency in one month. The maximum and minimum water levels arise during a new moon and a full moon. Such inflows are called syzygy. They happen as a result of finding of the Sun and the Moon on one straight line. Thereby gravitational forces of the Moon and the Sun are summarized. The weakest tidal currents occur when the Moon is disposed at right angle to the Sun and their attractions begin to interfere with each other.
Where do the biggest inflows happen?
Tide height depends on structure of a bottom and a relief of the coast. An important factor in tidal range are the directions of a current at the coast. At the coast of Ireland and England the inflows reach height of nine meters. At coast of Alaska the tidal water level can reach twelve meters. But the highest inflows happen in the Bay of Fundy at the Canadian coast. They reach 18 meters. During inflow the wave moves with a speed more than 14 km/h.