sandbank

A sandbank is a submerged or exposed accumulation of sand that forms in coastal and riverine environments. Sandbanks typically consist of fine to medium sand and can occur in estuaries, bays, and open seas, as well as within river channels. Depending on tides and water depth, a sandbank may be visible at low tide or lie entirely underwater.

Formation and dynamics: Sandbanks form where sediment carried by currents, waves, and tides is deposited faster than it is removed. Longshore drift can build offshore or alongshore bars; in rivers, braided channels create mid-channel sandbanks as flow splits and slows. Subaqueous sandbanks migrate shoreward or seaward with changes in sediment supply and hydrodynamics. They are often dynamic, changing shape and position over time, sometimes rapidly after floods or storms.

Ecology and navigation: Sandbanks provide habitats for shorebirds, crustaceans, and burrowing organisms when exposed; when submerged they influence water depth, currents, and sedimentation patterns, affecting habitats for fish and invertebrates. They can pose hazards to boating and navigation by altering channels or creating shallow areas; in coastal engineering, sandbank management may include dredging, beach nourishment, or the construction of groynes and offshore barriers to stabilize shorelines.

Terminology: The term "sandbank" is often used interchangeably with sandbar or shoal, though usage varies by region. A sandbar commonly refers to a bank connected to a coastline or island, while a shoal may denote any shallow area where water is shallow enough to affect navigation.