Gully erosion is an advanced and severe form of erosion in which concentrated surface runoff creates large, well-defined channels, called gullies, that are too deep and wide to be removed by normal grading or routine land management practices. These channels typically exceed several inches in depth and can grow to several feet deep and wide, significantly altering the landscape.
Gully erosion develops when smaller flow paths, such as those associated with rill erosion, continue to concentrate runoff over time. As flow depth, velocity, and shear stress increase, the erosive forces exceed the soil’s resistance, causing rapid downward cutting, known as incision, and lateral expansion through bank collapse and sloughing. This process creates a self-reinforcing system, where the gully captures and conveys more runoff, further accelerating erosion.
Gullies often form on disturbed or unprotected soils, including construction sites, agricultural lands, roadside embankments, and areas with poor drainage design. Factors such as steep slopes, highly erodible soils, lack of vegetation, and increased runoff from impervious surfaces can all contribute to their initiation and growth.
From a stormwater management perspective, gully erosion is particularly problematic because it generates large volumes of sediment, destabilizes land surfaces, damages infrastructure, and can significantly degrade downstream water quality and aquatic habitats. Gullies can also intercept and redirect natural drainage patterns, sometimes leading to increased flooding or unintended conveyance of stormwater.
Control and remediation of gully erosion are complex and often require engineered solutions. Preventative measures focus on controlling runoff before it concentrates, stabilizing soils with vegetation, and reducing slope length and gradient. Once a gully has formed, stabilization may involve reshaping the channel, installing grade control structures, armoring with stone or other materials, and implementing upstream stormwater controls to reduce flow energy and volume.