Morphodynamics of headcut development and soil erosion in upland concentrated flows.

In agricultural regions, gully erosion is now recognized as a dominant source of soil loss, and the development and upstream migration of headcuts is critical to the initiation, incision, and dissection of these upland areas. This study examined the effect of soil texture on headcut development and migration using four common soils from the southeastern United States, tested on bed surface slopes ranging from 1 to 5% and overland flow rates ranging from 45 to 71 L min -1 . In response to this flow, actively migrating headcuts developed with migration rates ranging from 0.00001 to 0.0025 m s -1 , maximum scour depths ranging from 0.042 to 0.148 m, and sediment discharge rates ranging from 0.00017 to 0.0356 kg s -1 depending on the soil and boundary conditions imposed. Nearly all experimental runs resulted in steady-state soil erosion, wherein the headcut developed attained a constant rate of migration, shape, and sediment discharge as a function of time. These experimental observations were successfully compared with predictive equations for mass conservation, jet entry angle, maximum scour depth, and migration rate developed for actively migrating headcuts in upland concentrated flows. These results further demonstrate that systematic headcut development can occur in a range of soils, slopes, and flow rates, and that modified jet impingement theory can be used to predict the erosional characteristics of these headcuts, thus providing the necessary analytical framework for improving soil erosion prediction technology.