Erosion is the process by which soil, rock, or other surface materials are detached, entrained, and transported from their original location by natural forces such as flowing water, rainfall, wind, or ice. In stormwater management and hydrology, erosion most commonly refers to the removal and movement of soil particles due to the action of rainfall impact and surface runoff.
Erosion occurs when the forces exerted by water, particularly shear stress and flow velocity, exceed the resisting forces that hold soil particles in place, including cohesion, vegetation cover, and surface roughness. It typically begins with the detachment of particles by raindrop impact or flowing water, followed by their transport downslope or through a drainage system.
Several forms of erosion are recognized in stormwater contexts. Sheet erosion involves the uniform removal of a thin layer of soil across a broad area. Rill erosion occurs when runoff concentrates into small, shallow channels. Gully erosion is a more advanced stage, where larger channels form and can significantly alter the landscape. Channel erosion refers to the scouring and enlargement of streambeds and banks due to increased flow velocities and volumes, often associated with changes in watershed hydrology.
Erosion is a critical concern in stormwater management because it is the primary source of sediment in runoff. This sediment can be transported downstream and deposited through sedimentation, leading to reduced water quality, impaired aquatic habitats, and decreased capacity in conveyance systems such as culverts and ditches. Excessive erosion can also undermine infrastructure, destabilize slopes, and contribute to flooding.
Effective erosion control strategies focus on reducing the energy of flowing water, stabilizing soil surfaces, and maintaining or establishing vegetation. Practices such as slope stabilization, erosion control blankets, check dams, and proper stormwater conveyance design are commonly used to minimize erosion and its associated impacts within a watershed.