An empirical investigation of gully widening rates in upland concentrated flows

Soil erosion, in its myriad forms, devastates arable land and infrastructure. As an integral landscape feature, gully erosion is a complex system as its evolution is controlled by upstream migration of a gully head (headcut face), incision of the gully bed (plunge pool) and gravitational mass-movement (widening) on gully channel sidewalls. Bed incision is often limited by the presence of a less erodible soil layer. When erosion reaches such a layer, the gully typically widens, creating a wide shallow cross section. Once a gully is initiated, transport and deposition of the eroded soil and widening of the channel further govern its evolution. Our knowledge of these processes within agricultural regions, however, is still quite limited with theory largely borrowed from river hydraulics. Experiments were conducted to examine gully expansion (widening) as a function of channel slope and overland flow discharge. Packed soil beds were subjected to simulated rainstorms followed by clear-water overland flow. As bed slope and discharge increased, channel widening increased. An empirical equation, based upon measured channel width from constant discharge experiments, was developed in terms of slope and discharge. By further quantifying key aspects of gully erosion processes, results from this experimental campaign will significantly improve soil erosion prediction technology for use in agricultural regions.