Morphodynamics of Actively Migrating Headcuts in Rills and Gullies

在美国和世界范围内，土壤侵蚀仍然是土壤退化的主要原因，土壤流失仍然是农业资源可持续管理的一个关键问题，高地来源的场外沉积严重影响水质、生态和生态栖息地。强烈的局部侵蚀区域，如小沟和沟壑，往往是土壤流失的主要原因，也是这种景观产生泥沙的主要来源，这些地貌特征与积极迁移的断头密切相关。这种局部侵蚀和向前推进发生在床面高程的阶跃变化。本研究项目的主要目标是了解实验系统中主动迁移侵蚀的形态动力学，并为这种离散侵蚀过程开发基于物理的解析表达式。利用配备有降雨模拟器和准备好的土床的特制水槽，我们将从实验上确定在不受河道宽度限制的高地集中水流中形成和主动迁移头切的特征，并对上游泥沙供应作出反应。我们将利用这些信息建立基于修正射流冲击理论的集中流土壤流失预测方程。所提议的工作的智力价值在于解决土壤侵蚀和土地退化的基本机制，这些机制是由山沟、作物沟和沟壑等典型的高地集中流的头部生长和迁移引起的。拟议工作的更广泛影响是为改善流域管理工具和减少我国土壤资源进一步退化提供必要的土壤侵蚀预测技术的关键补充，美国土壤资源的年成本估计高达400亿美元。

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.