What is Fluvial Geomorphology (FGM)?
Fluvial geomorphology is the study of the interactions between the physical shapes of rivers, their water and sediment transport processes, and the landforms they create.
It studies the ways that rivers move and change over time, focusing especially on how the flow of water interacts with the movement of sediment – dirt, sand, gravel, boulders – and debris, such as downed trees and branches. It also considers how the movement of water, sediment and debris interacts with the fixed, immobile features of the landscape, from bedrock canyons to human-built infrastructure like dams, bridges, and reinforced stream banks.
The starting points for understanding how rivers move and interact with their landscapes are:
- Rivers include sediment and debris as well as water; and as they flow, they apply force on, and release material to, the landscapes around them.
- As the water in a river travels, its pushes on the rocks, sands and silts in its bed and bank. Often it dislodges some of these sediments, and carries them into the channel and downstream. When the water is fast and voluminous, a river can erode and carry a lot of sediment, and bigger pieces.
- When a river slows or becomes shallow, sediments settle out.
The higher the stream power the larger the material size that a stream is able to move. Stream power is determined by the amount of water flowing through a stream (discharge) and the velocity at which that water is flowing. Generally, steep channels contain powerful streams that erode large materials. Low-gradient channels have low-powered streams that deposit fine materials.