Tidvattens

Tidvattens refers to the tidal waters and the periodic rise and fall of coastal sea level caused by the gravitational forces of the Moon and the Sun acting on the Earth's oceans. The primary expression of tidvattens is tides, which create high tides and low tides that shift along coastlines daily. The magnitude of tidvattens depends on coastline shape, bathymetry (depth and bottom topography), and ocean floor friction, leading to regional variations in tidal range from microtidal (less than 2 meters) to macrotidal (over 4 meters).

Two main tidal patterns occur: semidiurnal tides with roughly two high tides and two low tides per lunar day, and diurnal tides with one high and one low tide per day; some regions exhibit mixed tides. Spring tides occur when the Sun and Moon align, producing higher high tides and lower low tides; neap tides occur when they are at right angles, reducing tidal range.

Tidvattens phenomena include tidal currents, tidal bores in rivers, and estuarine mixing; these influence sediment transport, nutrient exchange, and coastal ecosystems, including habitats for birds and fish. From a human perspective, tidvattens affect navigation, harbor operations, and coastal flood risk; tidal ranges drive coastal erosion and sedimentation patterns. Tidal energy technologies aim to harness the kinetic energy of tidal streams and barrages, though environmental impacts must be assessed.

Measurement and prediction rely on tide gauges and harmonic analysis of tidal constituents (such as M2, S2) to generate tide tables used by shipping and coastal planning. Regions like the North Sea experience large tides, whereas the Baltic Sea experiences relatively small tidvattens. Historically, tides have influenced seafaring, harbor development, and coastal engineering; scientific understanding of tidvattens was advanced by observers and mathematicians through the 18th and 19th centuries.