COLLABORATIVE RESEARCH: Clarifying the ingredients and significance of nonlocal versus local sediment transport on steepland hillslopes

不同陡度的山坡覆盖了地球表面的大部分，可能完全被风化覆盖，或者由裸露的基岩表面组成，或者涉及这些条件的混合。由于坡地行为在景观动态中的核心作用，以及土壤和土壤运移在维持地球上大部分生命的关键地带过程中的重要性，坡面泥沙运移的主题具有特别丰富的遗产。从人类的时间尺度来看，这一主题是农业和环境科学中侵蚀和侵蚀控制研究的核心。此外，这一主题是地貌学研究的中心，重点是描述可用于山坡和景观演变模型的运输。该项目旨在澄清促成“局部”迁移的因素，在这种情况下，向下的泥沙运动涉及受当地土壤和地表条件控制的微小颗粒运动，而“非本地”迁移则与土壤滑移、生物干扰(例如，树木抛掷)、火灾后颗粒崩塌等有关，后者可能涉及相对快速、远距离的泥沙运动。这项研究将结合俄勒冈海岸山脉和内华达山脉的理论、实验和实地工作，以阐明沉积物的运移速率和运移对变化的高原地形的影响。这项工作是一项合作研究和教育努力，涉及范德比尔特大学和俄勒冈大学的学生和教职员工。它将提供实验和数值模拟可视化的教学工具，并将向科学界提供数据集。最近关于山坡泥沙运移的工作表明，有必要澄清“非本地”与“本地”泥沙运移过程的成分和含义以及与泥沙通量相关的公式，因为预期这两种条件下的山坡行为截然不同。然而，支持这一理论的速度已经超过了为这一理论提供依据所需的实验和现场观测。该项目旨在缩小这一差距，因为对理解山坡演变的影响是深远的。该项目将：(1)将实验与尺度分析相结合，以阐明在其下坡运动中稀薄颗粒-表面相互作用的成分，因为这些作用影响泥沙剥离的关键过程；(2)探索平面上收敛-发散的二维地形的非局部输运的理论公式；(3)将现场观测与以俄勒冈海岸山脉的山坡和内华达山脉的冰雹为中心的模拟工作相结合，以揭示非局部输运行为的成分；以及(4)用适当的时空平均来描述非局部输运，以考虑陡坡上泥沙运动的不连续性(片状、间歇性)，这是将泥沙通量视为时间可微量所必需的。

Hillslopes of varying steepness cover much of Earth's terrestrial surface, and may be entirely mantled with regolith or consist of bare bedrock surfaces, or involve mixtures of these conditions. Because of the central role of hillslope behavior in landscape dynamics, and because of the importance of soils and soil transport in critical zone processes that sustain much of life on Earth, the topic of sediment transport on hillslopes has a particularly rich legacy. Viewed at a human timescale, this topic is central to studies of erosion and erosion control in the agricultural and environmental sciences. Further, this topic is central in geomorphic studies focused on descriptions of transport that can be used in models of hillslope and landscape evolution. This project is aimed at clarifying the factors that contribute to "local" transport, where downslope sediment movement involves small particle motions controlled by local soil and land-surface conditions, versus "nonlocal" transport associated with soil slips, biotic disturbances (e.g., tree-throw), particle ravel following fire, etc., which can involve relatively rapid, long-distance sediment motions. The research will combine theoretical, experimental, and field-based work in the Oregon Coast Range and the Sierra Nevada Mountains to clarify rates of sediment transport and the effects of transport on changing steepland topography. The work is a collaborative research and education effort involving students and faculty from Vanderbilt University and the University of Oregon. It will provide teaching tools deriving from visualizations of experiments and numerical simulations, and it will provide data sets to the science community.Recent work on hillslope sediment transport suggests the need to clarify the ingredients and implications of "nonlocal" versus "local" transport processes and associated formulations of the sediment flux, as expected hillslope behavior under these two conditions is quite different. However, the supporting theory has outpaced experimental and field-based observations needed to inform this theory. This project is aimed at closing that gap, as implications for understanding hillslope evolution are far-reaching. The project will: (1) combine experiments with scaling analyses to clarify ingredients of rarefied particle-surface interactions during their downslope motions, as these influence key processes of sediment disentrainment; (2) explore theoretical formulations of nonlocal transport for two-dimensional topography that is convergent-divergent in planform; (3) combine field observations with modeling work centered on hillslopes in the Oregon Coast Range and moraines in the Sierra Nevada Mountains that were selected to reveal ingredients of nonlocal transport behavior; and (4) formulate descriptions of nonlocal transport with appropriate space-time averaging to take into account the discontinuous (patchy, intermittent) nature of sediment motions on steepland hillslopes, as is necessary for treating the sediment flux as a time differentiable quantity.