Sandbänke

Sandbänke are shallow, elongated banks of sand that form in rivers, estuaries and coastal seas where sediment is deposited by flowing water and waves. They are typically composed mainly of sand, and their shapes range from linear ridges to crescent-shaped shoals that can move with changing currents.

Formation and dynamics

Sandbänke develop when the transport capacity of water decreases, causing suspended and bed sediments to settle out. In rivers, braided channels and anisotropic flow can create shifting sandbars. In coastal and estuarine areas, longshore drift, tides and wave action continually rework sediment, causing banks to grow, migrate or disappear over time. Their depth usually remains shallow, but can vary with seasons and storms, leading to rapid changes in local navigation conditions.

Distribution and characteristics

Sandbänke occur worldwide in continental shelves, river mouths and tidal basins. They are often partly exposed at low water and submerged at high water, which makes their exact position and size highly dynamic. Their orientation generally reflects prevailing current directions.

Ecology and use

These features provide habitat for benthic communities and can serve as feeding or roosting sites for birds. They may act as nurseries for some fish species. For humans, sandbänke influence ship routes by creating shallow areas and are sometimes exploited as sources of sand for construction or beach nourishment. Coastal and river management often requires regular hydrographic surveys to monitor their changes.