coastlines

Coastlines are the dynamic interfaces between land and sea, where the terrestrial and marine realms meet. They are defined by landforms and processes that continually reshape the boundary, driven by waves, currents, tides, wind, and sediment supply. The position of a coastline can change with tides and storms and with longer-term sea-level rise and tectonics.

Coastal zones host a range of landforms, including beaches, cliffs, dunes, estuaries, deltas, spits, bays, and lagoons. Rocky shores, sandy shores, mangrove swamps, and coral reefs create varied habitats and influence how coastlines respond to wave action and erosion.

Key processes include erosion, which removes material; deposition, which adds material; longshore drift that redistributes sediment along the coast; and coastal accretion or retreat driven by storms and sea-level change.

Coastlines are mapped for navigation, hazard assessment, and planning. Because the shoreline changes with tides and weather, measurements rely on shorelines defined for a fixed tide level, alongside satellite imagery, aerial photography, and topographic and bathymetric data.

Humans settle and develop coastlines for ports, tourism, fisheries, and housing. Coastal hazards include erosion, flooding, storm surges, and tsunamis. Management combines hard engineering (walls, groynes) and soft approaches (beach nourishment, dune restoration) within integrated coastal zone management to reduce risk and conserve ecosystems.

Climate change threatens coastlines through sea-level rise, increasing storm intensity, and altered sediment supply, leading to faster erosion and habitat loss. Adaptation strategies aim to balance protection with ecological values and sustainable use of coastal resources.