For an alluvial river the change in channel bankfull dimensions is a direct result of erosion and sedimentation caused by the nonequilibrium transport of sediment in the channel The discharge and the

of the channel.

Discharge refers to the volume of water flowing through the channel, which is influenced by factors such as precipitation, groundwater inputs, and upstream inflows. Higher discharge rates result in greater erosional forces, leading to wider and deeper channels.

Sediment load refers to the amount of sediment carried by the river. Sediment can be eroded from the riverbed, banks, or upstream sources, and is transported downstream by the flow of water. Sediment load can vary depending on factors such as the geology and vegetation of the river's catchment area, as well as human activities like agriculture or construction.

When the sediment load exceeds the transport capacity of the river, sediment is deposited along the channel. This deposition can cause the channel to become shallower and narrower, reducing its cross-sectional area. Conversely, when the sediment load is less than the transport capacity, erosion occurs, resulting in a wider and deeper channel.

The change in channel bankfull dimensions is therefore a response to the dynamic balance between erosion and sedimentation processes. Over time, the channel adjusts its dimensions to accommodate the sediment load and maintain equilibrium. However, due to natural and human-induced disturbances, such as floods or channel modifications, the sediment transport can become temporarily or permanently out of equilibrium, leading to changes in the channel's dimensions