Wash load refers to the fine sediment particles, such as silt and clay, that are transported in suspension by a river and do not come into frequent contact with the riverbed. Wash load is significant in fluvial geomorphology for understanding sediment transport dynamics, riverine sediment budgets, and the formation of floodplains and deltas.
Source Leopold, L. B., Wolman, M. G., & Miller, J. P. (1964). “Fluvial Processes in Geomorphology.” Dover Publications.