describe a multi-stage gully development
process in the Appalachian Piedmont: (i) gullies initiate
along existing paths, tracks, ditches, or animal burrows, resulting in
concentrated runoff due to reduced infiltration; (ii) head scarp erosion
occurs from high energy, concentrated runoff in steeply sloped
land; (iii) gully deepening stabilizes when the saprolite layer and
the shallow groundwater zone are encountered; (iv) erosion continues
along the channel sidewalls and headwalls by slumping and
undercaving