These are kind of rivers that are lowland in which the bed and banks are made up of mobile sediment and/or soil. These rivers are self-formed, meaning that their channels are shaped by the magnitude and frequency of the floods that they experience, and the ability of these floods to erode, deposit, and transport sediment.

As such, alluvial rivers can assume a number of forms based on the properties of their banks; the flows they experience; the local riparian ecology, and the amount, size, and type of sediment that they carry. These forms can be meandering, braiding, wandering and (occasionally) straight.