Fluvial terrace

Fluvial terrace

Fluvial terrace is an abandoned floodplain with a long, narrow stairs that were formed when the river flowed at a higher level than at present. Fluvial terraces consist of two parts; a tread, which is the flat surface at the upper side of fluvial terrace, and a scarp, which is the steep slope connecting the tread to the downside.

Classification

Fluvial terraces are divided into Rock terraces or gravel terraces according to structure materials. They are classified as Tectonic terraces or Climate terraces depending on how they were formed.

Cross section of Fluvial terrace

Erosional terraces are terraces where the tread has been formed primarily by lateral erosion. During a low water level stage, fine sediment is deposited and coarse sediment is deposited at the end of a high water event. When the river reaches its highest level, it moves all the channel sediment and scours the underlying bedrock before coarse detritus is deposited again on the channel floor.

Depositional terraces are terraces where the tread represents the surface of a valley fill. Valley filling occurs when the amount of sediment produced in a basin is more than the river system can carry away. It is usually triggered by glacial outwash, climate change, or change in base level, slope, or load caused by rising water level. Depositional terraces are climatically controlled. Erosional terraces are tectonically controlled..