Bed load is the portion of a sediment load that is transported along the bottom of a channel, stream, or conveyance system by rolling, sliding, or short, intermittent hopping movements known as saltation. In stormwater management and fluvial systems, bed load typically consists of coarser particles such as sand, gravel, and small stones that are too heavy to remain suspended in the water column under normal flow conditions.
The movement of bed load occurs when the shear stress exerted by flowing water on the channel bed exceeds the resisting forces holding the particles in place, including gravity and friction. As flow velocity and depth increase, the ability of the water to mobilize larger and heavier particles also increases. Unlike suspended load, which is carried within the water column, bed load remains in near-continuous contact with the channel surface and moves more slowly and intermittently.
Bed load transport plays a significant role in shaping channel morphology and influencing sediment deposition patterns. It contributes to processes such as channel erosion, aggradation, and the formation of features like bars and riffles. In engineered stormwater systems, excessive bed load can lead to sediment accumulation in pipes, culverts, and basins, reducing conveyance capacity and requiring maintenance.
From a management perspective, controlling bed load involves reducing upstream erosion, stabilizing channels and disturbed areas, and designing systems that can either convey or capture coarse sediment without clogging or damage. Practices such as check dams, sediment traps, and stabilized channels are commonly used to manage bed load transport and minimize its impacts on infrastructure and receiving waters.