riverbeds

Riverbeds are the bottoms of river channels, composed of exposed bedrock or accumulated sediments ranging from coarse gravel to fine silt. The bed defines the lower boundary of the channel and influences flow depth, velocity, and sediment transport. In bedrock rivers the channel cuts into solid rock; in alluvial rivers the bed is made of loose sediment that can be rearranged by flow.

Sediment transport: The river bed experiences shear stress from flowing water that dislodges and moves particles. Heavier particles move as bed load by rolling, sliding, or hopping (saltation), while finer materials are carried in suspension. As flow strength varies, the bed can develop surface forms such as ripples, dunes, and plane beds that reflect energy and sediment size.

Channel types: Rivers can have bedrock channels, or alluvial channels with gravel, sand, and silt; they may be straight, meandering, or braided depending on sediment supply and flow regime. Incised channels occur when base level drops, cutting into the bed.

Ecology and hydrology: The riverbed provides habitat for invertebrates and fish, with gravels important for spawning in some species. The interaction between bed and banks shapes floodplain connectivity and groundwater recharge.

Human impacts: Dams, reservoir sediment trapping, mining, or hydrological alterations change sediment delivery and flow, leading to bed erosion or aggradation, altered habitats, and increased flood risk. Management may involve sediment budgeting, bed stabilization, or restoration projects.