INTEGRATED ASSESSMENT AND ANALYSIS OF PHYSICAL LANDSCAPE PROCESSES THAT IMPACT THE QUALITY AND MANAGEMENT OF AGRICULTURAL WATERSHEDS
Location: Watershed Physical Processes Research Unit
Title: An empirical investigation of gully widening rates in upland concentrated flows
Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 3, 2012
Publication Date: January 1, 2013
Citation: Wells, R.R., Momm, H.G., Rigby Jr, J.R., Bennett, S.J., Bingner, R.L., Dabney, S.M. 2013. An empirical investigation of gully widening rates in upland concentrated flows. Catena. 101(2013):114-121.
Interpretive Summary: Soil erosion is a destructive function of nature. Currently, our understanding of the mechanisms that drive channel bank expansion is limited. This study reports on experiments conducted in a laboratory flume to examine channel widening under controlled flow rates and bed slopes. Past research has examined freely adjustable boundaries (channel bed and banks are free to move); however, experimental data under fixed boundary conditions is limited. In most agricultural settings, a more resistant layer exists below the surface. This layer is often called a plow pan since its existence is dependent upon plow depth. Relations have been developed for freely adjustable boundaries but few studies were conducted to understand the mechanisms when a less erodible layer is present. Our study examined the channel expansion due to channel slope and overland flow discharge. A dynamic empirical relation was developed based upon constant discharge and slope that fits the measured dataset very well.
Soil erosion, in its myriad forms, devastates arable land and infrastructure. As an integral landscape erosion feature, gully erosion is a complicated system as its evolution is controlled by upward 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 non-erodible or impervious 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 gully channel, further govern its evolution. Our knowledge of these processes in shallow concentrated flows within agricultural soils, however, is still quite limited and largely scaled down from river hydraulics. Experiments were conducted to examine channel expansion due to channel slope and overland flow discharge. Packed soil beds were subjected to simulated rainstorms, followed by clear-water overland flow. As slope and discharge increase, channel widening processes accelerate. An empirical equation is developed based upon the measured channel width time series from constant discharge experiments and successfully applied to variable discharge experiments.