sandbar

A sandbar is a long, narrow ridge of sand formed by the action of waves, currents, and sediment transport in coastal, estuarine, and riverine settings. Sandbars occur offshore near beaches, across bays or lagoons, or may connect to the mainland to form spits. They can also appear as banks within river channels, and may be exposed at low tide or submerged at high tide.

Formation typically occurs through longshore drift, where waves strike the shore at an angle and drive a current parallel to the coast, transporting sand grains along the beach. When the energy of the moving water decreases, sediment is deposited to build up ridges just offshore or across a bay. In rivers, sandbars or mid-channel bars form where flow velocity drops, creating localized sediment accumulations.

Sandbars are dynamic and migratory features. They can shift position with seasonal wave climates, tides, and storms, or disappear and reappear over time. Some become vegetated and more stable, while others remain mobile or are washed away during extreme events. They may be connected to the shore as spits or stand independently as bars or barrier segments.

Ecologically, sandbars provide habitat for birds, serve as nurseries for some fish, and help dissipate wave energy to protect shores and nearby habitats. Humans interact with sandbars through coastal development, navigation channel management, and beach nourishment projects, which aim to maintain or modify sediment supply and shoreline configuration.