Bedforms

Bedforms are morphologic features that develop on sediment beds as a result of fluid flow, typically by water or wind. They arise when the shear stress exerted by the flow entrains grains, and subsequent transport and deposition create organized patterns. Bedforms occur in subaqueous and aeolian environments, including rivers, oceans, lakes, beaches, deserts, and can be preserved in the geological record for interpreting past flow conditions.

The most common bedforms are ripples and dunes. Ripples are smaller, with wavelengths ranging from centimeters to decimeters, and have crests oriented roughly perpendicular to the flow; they migrate downstream at limited speeds. Dunes are larger features with asymmetrical profiles and slip faces, migrating more slowly but over greater distances. In rivers, dunes can reach meters to tens of meters in height and influence channel morphology. In deserts, dunes can be tens to hundreds of meters tall and form diverse forms such as crescentic (barchan), linear, or star dunes.

Subaqueous bedforms form under traction-dominated transport and may transition to antidunes at high flow velocities and shallow depths, where bedforms can migrate rapidly and, in some cases, upstream. Aeolian bedforms are shaped by wind-driven saltation and include a variety of dune types, with morphology controlled by wind regime and sediment supply.

The presence and arrangement of bedforms reflect flow strength, grain size, sediment supply, and water depth, providing insights into transport conditions and helping to interpret past environmental settings. Field measurements, laboratory flume studies, and remote sensing are used to analyze bedform characteristics and dynamics.