Bedform
A bedform is a depositional feature on the bed of a river (fluvial 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,[1] and are particularly to flow depth and velocity, and therefore the Froude number.
Contents |
[edit] 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,[2] with increasing water velocity going down the chart.
| Flow Regime | Bedform | Preservation Potential | Identification Tips |
| Lower | |||
| Lower plane bed | High | Flat laminae, almost lack of current | |
| Ripple marks | 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 | 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.
[edit] Types of Bedforms
[edit] Lower Plane Bed
"Lower plane bed" refers to the flat configuration the bed of a river that is produced in via low rates of sediment transport.[3]
[edit] Upper Plane Bed
"Upper plane bed" features are 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 (a.k.a. parting laminations), or streaks on the surface due to the rapid motion of grains in the strong current.[3]
[edit] See also
[edit] References
- ^ Southard, J B (1991). "Experimental Determination of Bed-Form Stability". Annual Review of Earth and Planetary Sciences 19: 423. Bibcode 1991AREPS..19..423S. doi:10.1146/annurev.ea.19.050191.002231.
- ^ Prothero, D. R. and Schwab, F., 1996, Sedimentary Geology, pg. 45-49, ISBN 0-7167-2726-9
- ^ a b editors, Klaus K.E. Neuendorf, James P. Mehl, Jr., Julia A. Jackson. (2005). Glossary of geology. Alexandria: American Geological Institute. p. 382. ISBN 0-922152-76-4.
|
|||||||||||||||||||||||
 |
This geology article is a stub. You can help Wikipedia by expanding it. |
