The removal and transport of soil, rock, and sediment by water, wind, ice, or gravity. Water erosion is the dominant process shaping river valleys and is a major concern for water quality and land degradation.
Erosion is the geomorphic process by which Earth materials are detached, entrained, and transported from their original location by natural agents including flowing water, wind, ice, and gravity. In the context of water resources, fluvial erosion by rivers and streams is the primary mechanism carving valleys, shaping channels, and delivering sediment to downstream depositional environments. Sheet erosion occurs as thin, uniform layers of soil are removed by overland flow; rill erosion concentrates flow into small channels; and gully erosion creates deep incisions that are difficult to remediate. Bank erosion along river channels contributes sediment and can threaten infrastructure, while bed erosion (incision) deepens channels and can undermine structures. The Universal Soil Loss Equation (USLE) and its revised version (RUSLE) are widely used empirical models for predicting sheet and rill erosion based on rainfall erosivity, soil erodibility, slope, crop management, and conservation practices. Erosion is a major source of non-point-source water pollution, as eroded sediment carries adsorbed nutrients (phosphorus), pesticides, and pathogens into waterways. Climate change is expected to alter erosion patterns through changes in rainfall intensity, vegetation cover, wildfire frequency, and permafrost thaw.