Sandtransport

Sandtransport refers to the movement of sand-sized particles caused by fluid flow. It occurs in rivers, oceans, and in air (aeolian processes) and is a key component of sediment dynamics and coastal morphodynamics. Transport mode and rate depend on grain size, flow or wind velocity, turbulence, and bed conditions.

In water, sand can move as bedload—rolling, sliding and saltating along the bed—and, under stronger turbulence or finer conditions, as suspended load. The initiation of motion is governed by bed shear stress and the Shields parameter. Bedload dominates at moderate flows and coarser sands, while suspension carries grains farther downstream or offshore and shapes turbidity. Bedforms such as ripples and dunes form as sand is deposited and eroded.

In air, aeolian sand transport is dominated by saltation, in which grains are lifted by the wind and impact the surface, ejecting other grains. A small fraction moves by surface creep. Threshold wind speeds depend on grain size, surface moisture, and roughness. Wind-driven sand movement shapes dunes and reshapes beaches and deserts; transport rates increase with wind speed and with grain-size-dependent saltation efficiency.

Coastal environments combine longshore transport (littoral drift) with cross-shore processes. Waves striking the shore at oblique angles generate currents that move sand along the coastline, while onshore-offshore flows redistribute sand to dunes and beaches. Understanding sandtransport informs coastal defense, beach nourishment, river engineering, and habitat management, and is affected by human interventions such as damming, dredging, and harbor construction.