ebb

Ebb refers to the period during which the water level falls as the tide moves away from the shore. In coastal regions, tides are caused by the gravitational forces of the Moon and Sun and modulated by Earth's rotation. After high tide, the water retreats toward the sea; this phase is called the ebb tide. The opposite phase, when water rises toward the shore, is the flood tide.

An individual tidal cycle includes both phases and typically repeats about every 12 hours 25 minutes in areas with semidiurnal tides, though the exact timing and amplitude depend on local bathymetry, coastline geometry, wind, and atmospheric pressure. Some locations experience diurnal tides with one high and one low per day, while others have mixed tides with varying heights.

In estuaries and coastal inlets, the ebb current can be strong, creating swift outward flows that may affect navigation, erosion, and sediment transport. The ebb also exposes intertidal zones, influencing biology and nutrient cycling.

Beyond physical meaning, ebb is used metaphorically to describe any receding or diminishing quantity, value, or influence, as in the ebb of fortunes.