suspendedload

Suspended load refers to the portion of sediment in a river or stream that is carried within the water column in suspension, kept aloft by turbulent eddies rather than rolling along the bed. It is typically dominated by fines such as silt and clay, though very fine sand can also be suspended during high flows. This contrasts with bed load, which moves near the bed by rolling or hopping, and with dissolved load, which consists of minerals dissolved in the water.

Entrainment of suspended sediment depends on flow conditions and particle properties. The critical shear stress required to lift particles decreases with smaller size and density; higher flow velocity and turbulence increase the capacity to suspend finer material. When transport capacity exceeds supply, concentration remains high; when flow slows, particles settle, increasing deposition and potentially forming bars or plugs.

Suspended sediment concentration (SSC) is commonly measured as mass per unit volume (for example mg/L) and is a key parameter in assessing water quality and sediment yield. SSC is often inferred from turbidity measurements using field or laboratory calibrations. Sediment discharge due to suspension is the product of SSC and water discharge.

Vertical distribution of suspended sediment is often described by concentration profiles that relate concentration with height above the bed to settling velocity, flow velocity, and turbulence intensity. The finer the particles and the higher the turbulence, the more uniform the vertical distribution tends to be.

Suspended load matters for river morphology, reservoir sedimentation, and nutrient and pollutant transport. Elevated suspended loads can reduce light penetration, affect aquatic life, and increase dredging needs. Understanding suspended load is central to sediment budgeting, flood management, and environmental planning.