FALL twice a day.Tides:The regular rise and fall of seawater brought up by the gravitational FORCE of the moon and sun refers to tides.These are the long-period waves, which occur twice a day.When the crest of a WAVE touches the coastline it is called HIGH tide and when trough does that LOW tide occurs.There are two types of tides:Spring Tides: These occur on new or full moon days. When the Moon, the Earth and the Sun align in a straight line, the increased gravitational pull gives rise to higher tides as compared. These are called spring tides.Neap Tides: These occur when the sun and the moon are at the right angle and earth at the vertex. During neap tides, the high tides are lower than general and low tides are higher than that.