International Research Fellowship Program: Modeling the Morphodynamics of Bedrock Meandering

纳尔逊国际研究奖学金计划使美国科学家和工程师能够在国外进行9到24个月的研究。该计划的奖励为联合研究提供了机会，并利用独特或互补的设施、专业知识和国外的实验条件。该奖项将支持Peter A. Nelson博士与Giovanni Seminara博士在意大利热那亚大学开展为期18个月的研究。蜿蜒的基岩河流在视觉上是大自然的壮观例子？形成模式的能力。基岩弯曲的起源和行为已经争论了一个多世纪，但今天我们仍然无法回答关于它们的最基本的问题；例如，弯曲是如何在基岩中形成的，是什么决定了弯曲波长的选择？该项目的目的是建立一个基岩弯曲的理论形态动力学模型，作为能够回答这些问题的重要一步。主持人和PI正在利用文献中的现有研究和可用的地形数据集，对自然界的基岩曲流进行全面的描述，并建立在冲积曲流的现有理论和我们对基岩侵蚀机制的理解的最新进展的基础上，这些观察结果被用来发展基岩曲流形成的理论。理论发展包括以下内容：1)利用新方法估算由跃变床荷载和悬浮荷载磨损引起的局部垂直和横向侵蚀，以及由风化作用引起的基岩破坏；2)对基本状态进行线性稳定性分析，以确定横向侵蚀是否可能为弯曲生长提供机制；3)建立弯曲通道内流动的三维模型，其轴可以同时显示弯曲和扭转；4)建立通道中心线的三维平台演化方程，以说明预测的通道行为。该项目促进了地貌学家和理论形态动力学家之间的合作。由于对基岩河流的行为知之甚少，这个项目有可能极大地扩大我们对基岩系统的基本理解。我们提出的工作将结合冲积蜿蜒和基岩切割的最先进的理论形态动力学，我们开发的理论框架将是同类中第一个采用纯侵蚀机制的理论框架，包括沉积物供应的影响，并且本质上是三维的。这项工作的新方面，特别是泥沙供应限制效应的结合，应该适用于广泛的地貌问题，包括可能的人为或气候对河流行为的影响。我们希望这个项目将为现在和将来的理论家和地貌学家之间的持续国际合作提供机会。

0965064NelsonThe International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.This award will support an eighteen-month research fellowship by Dr. Peter A. Nelson to work with Dr. Giovanni Seminara at the University of Genoa in Italy.Meandering bedrock rivers are visually spectacular examples of nature?s ability to form patterns. The origin and behavior of bedrock meanders have been debated for over a century, yet today we are still unable to answer very basic questions about them; for instance, how do meanders form in bedrock, and what determines the selection of a meander wavelength? The aim of this project is to develop a theoretical morphodynamic model for bedrock meandering as an important step toward being able to answer these questions. The host and PI are using available studies in the literature and available topographic datasets to develop a comprehensive description of bedrock meanders in nature, and, building upon existing theory for alluvial meandering and recent advances in our understanding of the mechanics of bedrock erosion, these observations are used to develop a theory for bedrock meander formation. Theory development includes the following: 1) new approaches to estimate local vertical and lateral erosion due to abrasion from saltating bed load and suspended load, and bedrock breakdown due to weathering; 2) a linear stability analysis of a basic state to ascertain whether lateral erosion may provide a mechanism for bend growth; 3) the development of a 3D model for flow in a curved channel whose axis may display both bending and torsion; and 4) the development of a 3D planform evolution equation for the channel centerline to illustrate predicted channel behavior. This project promotes cooperation between geomorphologists and theoretical morphodynamicists. Since so little is known about the behavior of bedrock rivers, this project has the potential to dramatically broaden our basic understanding of bedrock systems. Our proposed work will combine the state-of-the-art in theoretical morphodynamics of alluvial meandering and bedrock incision, and the theoretical framework we develop will be the first of its kind to employ a purely erosive mechanism, to include the effects of sediment supply, and to be intrinsically 3D. The novel aspects of this work, particularly the incorporation of sediment supply-limited effects, should be applicable to a broad range of geomorphic problems, including possible anthropogenic or climatic effects on river behavior. We expect this project will provide opportunities for continual international collaboration between theoreticians and geomorphologists now and in the future.