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的大部分陆地表面，可能完全覆盖着风化层，或由裸露的基岩表面组成，或涉及这些条件的混合物。 由于山坡行为在景观动力学中的核心作用，以及土壤和土壤迁移在维持地球上大部分生命的关键区过程中的重要性，山坡上的沉积物迁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，这一主题是在地貌研究的重点是运输的描述，可用于模型的山坡和景观演变的中心。 该项目旨在澄清有助于“局部”迁移的因素，其中下坡沉积物运动涉及受当地土壤和地表条件控制的小颗粒运动，而“非局部”迁移与土壤滑动，生物干扰（例如，树木抛掷）、着火后的颗粒散开等，这可能涉及相对快速的长距离沉积物运动。 这项研究将结合联合收割机的理论，实验和实地工作在俄勒冈州海岸山脉和内华达州山脉的山脉，以澄清泥沙运输率和运输的影响不断变化的陡坡地形。 这项工作是一项合作研究和教育工作，涉及学生和教师从范德比尔特大学和俄勒冈州大学。 它将提供教学工具，从可视化的实验和数值模拟，它将提供数据集的科学界最近的工作对山坡泥沙输运表明，需要澄清的成分和影响的“非本地”与“本地”的运输过程和相关配方的泥沙通量，预期在这两种条件下的山坡行为是完全不同的。 然而，支持理论已经超过了为这一理论提供信息所需的实验和实地观察。 该项目旨在缩小这一差距，因为了解山坡演变的影响是深远的。 该项目将：（1）将联合收割机试验与尺度分析相结合，阐明了稀薄颗粒在下坡运动过程中与地表相互作用的成分，因为这些成分影响着泥沙的退卷过程：（2）探索了平面形状为收敛-发散的二维地形的非局部输运理论公式;（3）将联合收割机野外观测与模拟工作结合起来，模拟工作以俄勒冈州海岸山脉的山坡和内华达州山脉的冰碛为中心，选择这些山坡和冰碛来揭示非局部输送行为的成分;（4）用适当的时空平均法来描述非局部输运，以考虑到陡坡上泥沙运动的不连续性（斑片状、间歇性），这是将泥沙通量作为时间可微量处理所必需的。

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.