geology Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...

, degradation refers to the lowering of a fluvial surface, such as a

stream bed A streambed or stream bed is the bottom of a stream or river and is confined within a Stream channel, channel or the Bank (geography), banks of the waterway. Usually, the bed does not contain terrestrial (land) vegetation and instead supports d ...

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river. Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high Discharge (hydrolog ...

, through erosional processes. Degradation is the opposite of aggradation. Degradation is characteristic of channel networks in which either bedrock erosion is taking place, or in systems that are

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

-starved and are therefore entraining more material than they are depositing. When a stream degrades, it leaves behind a

fluvial terrace Fluvial terraces are elongated Terrace (geology), terraces that flank the sides of floodplains and fluvial valleys all over the world. They consist of a relatively level strip of land, called a "tread", separated from either an adjacent floodplai ...

. This can be further classified as a strath terrace—a bedrock terrace that may have a thin mantle of

alluvium Alluvium (, ) is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluvium is also sometimes called alluvial deposit. Alluvium is ...

—if the river is incising through bedrock. These terraces may be dated with methods such as cosmogenic radionuclide dating, OSL dating, and paleomagnetic dating (using reversals in the Earth's magnetic field to constrain the timing of events) to find when a river was at a particular level and how quickly it is downcutting.

References

* * Geological processes Sedimentology Geomorphology Fluvial landforms Water streams {{geo-term-stub