Morphodynamics of Actively Migrating Headcuts in Rills and Gullies

Soil erosion remains the principal cause of soil degradation within the U.S. and worldwide, soil loss continues to be a critical concern for the sustainable management of agricultural resources, and off-site sedimentation from upland sources severely affects water quality, ecology, and ecological habitat. Areas of intense, localized erosion, such as rills and gullies, often are the primary cause of soil loss and the dominant source of sediment yield from such landscapes, and these geomorphic features are in close association with actively migrating headcuts?step-changes in bed surface elevation where this localized erosion and headward advance takes place. The primary goal of this research program is to understand the morphodynamics of actively migrating headcuts within experimental systems and to develop physically-based analytic expressions for this discrete erosion process. Using specially-built flumes equipped with rainfall simulators and prepared soil beds, we shall define experimentally the characteristics of developing and actively migrating headcuts in upland concentrated flows unconstrained by channel width and in response to an upstream sediment supply. We shall use this information to develop predictive equations for soil loss in concentrated flows based on modified jet impingement theory. The intellectual merit of the proposed work seeks to address the fundamental mechanics of soil erosion and land degradation by headcut growth and migration in upland concentrated flows typical of rills, crop furrows, and gullies. The broader impacts of the proposed work seeks to provide the critical addition to soil erosion prediction technology necessary to improve watershed management tools and reduce the further degradation of our Nation's soil resources, whose estimated annual costs in the U.S. are as much as $40 billion.