A bedform is a depositional feature on the bed

Stream bed

A stream bed is the channel bottom of a stream, river or creek; the physical confine of the normal water flow. The lateral confines or channel margins, during all but flood stage, are known as the stream banks or river banks. In fact, a flood occurs when a stream overflows its banks and flows onto...

 of a river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 (fluvial

Fluvial

Fluvial is used in geography and Earth science to refer to the processes associated with rivers and streams and the deposits and landforms created by them...

 processes) or other body of flowing water that is formed by the movement of the bed material due to the flow. Bedforms are characteristic to the flow parameters, and are particularly to flow depth and velocity, and therefore the Froude number

Froude number

The Froude number is a dimensionless number defined as the ratio of a characteristic velocity to a gravitational wave velocity. It may equivalently be defined as the ratio of a body's inertia to gravitational forces. In fluid mechanics, the Froude number is used to determine the resistance of an...

.

Bedforms vs. flow

Typical unidirectional bedforms represent a specific flow velocity, assuming typical sediments (sands and silts) and water depths, and a chart such as below can be used for interpreting depositional environments, with increasing water velocity going down the chart.

Flow Regime	Bedform	Preservation Potential	Identification Tips
Lower
	Lower plane bed Lower plane bed In geology, lower plane bed refers to the configuration of the bed of a river that is flat and characterized by low rates of sediment transport....	High	Flat laminae, almost lack of current
	Ripple marks Ripple marks In geology, ripple marks are sedimentary structures and indicate agitation by water or wind.- Defining ripple cross-laminae and asymmetric ripples :...	High	Small, cm-scale undulations
	Sand waves	Medium to low	Rare, longer wavelength than ripples
	Dunes/Megaripples	High	Large, meter-scale ripples
Upper
	Upper plane bed Upper plane bed In geology, upper plane bed refers to the configuration of the bed of a river that is flat and characterized by a unidirectional flow high with rates of sediment transport as both bed load and suspended load. Upper plane bed conditions can produce current lineations In geology, upper plane bed...	High	Flat laminae, +/- aligned grains (parting lineations)
	Antidunes	Low	Water in phase with bedform, low angle, subtle laminae
	Pool and chute	Very low	Mostly erosional features

This chart is for general use, because changes in grain size and flow depth can change the bedform present and skip bedforms in certain scenarios. Bidirectional environments (e.g. tidal flats) produce similar bedforms, but the reworking the sediments and opposite directions of flow complicates the structures.

See also

• Sedimentation
  Sedimentation
  Sedimentation is the tendency for particles in suspension to settle out of the fluid in which they are entrained, and come to rest against a barrier. This is due to their motion through the fluid in response to the forces acting on them: these forces can be due to gravity, centrifugal acceleration...
  
  
• Sedimentary structures
  Sedimentary structures
  Sedimentary structures are those structures formed during sediment deposition.Sedimentary structures such as cross bedding, graded bedding and ripple marks are utilized in stratigraphic studies to indicate original position of strata in geologically complex terrains and understand the depositional...