Field Investigation of the Influence of Bed Texture on Aeolian Saltation

风对沉积物的搬运是从土壤侵蚀和污染物搬运到沙尘暴和荒漠化等各种环境问题的一个关键组成部分。这项研究将评估一个新的假设有关的基本机制的过程中，风吹泥沙运输。大多数比尘埃大的风吹颗粒都是在一个被称为跳跃的过程中移动的--一系列沿着地面沿着的过程。长期以来，跃移的理论模型一直基于一个基本假设，即风速的增加会导致粒子反弹得更高更远，从而导致传输速率的增加。然而，基于这一假设的运输模型已被证明无法始终如一地产生准确的预测。初步研究表明，跃移的基本概念可能是错误的-颗粒不会随着风速的增加而反弹得更高更远，相反，反弹的大小似乎受到床沉积物惯性的限制。在强风作用下，跃移颗粒增加的动能被转移到河床沉积物上，导致更多的颗粒被喷射到跃移中，从而增加了输送速率。本研究将测试这一假设，并量化的影响床粒度的尺寸跳跃啤酒花。将进行一项实地试验，利用沉积物收集器测量在河床以上不同高度和不同水平距离移动的沉积物的比例。这些捕集器将安装在人工河床的下风处，人工河床由经过筛选的粒度范围很窄的沉积物组成。人们预计，从大颗粒床反弹的颗粒将比从更细的材料床反弹的颗粒跳得更高更远，并且跳的尺寸将在很大程度上与风速无关。数值模拟将被用来重建所需的跳跃跳跃的分布，以产生运输的测量变化，并量化如何跳尺寸变化的床粒度的函数。这些研究结果将被用来构建一个新的理论模型的跃移过程中，将直接纳入本study. This研究中记录的床粒度的影响，严格审查风吹泥沙输运目前的科学观点的一个基本组成部分。这可能会改变对这一过程如何运作的普遍看法，其结果可能适用于其他环境中的沉积物迁移。有许多环境危害与风吹颗粒物，和跃移的增强了解将有助于理解和有效管理这些问题。虽然尘埃悬浮在空中，并不直接通过跳跃来输送，但人们普遍认为，跳跃颗粒的影响是造成尘埃脱落和喷出的原因。因此，对跃移的更好理解将有助于改进从表土、营养物质和有毒金属到经常附着在细颗粒上的化学污染物和微生物等物质排放的建模。从经济的角度来看，国家研究理事会最近发表了一份与风吹沉积物有关的场外成本估计，仅在美国西部，每年就超过10亿美元。更好地了解所涉及的过程将有助于缓解这些问题，减少其经济影响。这项研究还将为参与该项目的几名研究生提供教育机会和研究经验，并有助于促进新成立的地貌过程实验室的发展，这是一项旨在应用地貌知识解决环境问题的多所大学倡议。

The transport of sediment by wind is a key component of environmental problems ranging from soil erosion and contaminant transport, to dust storms and desertification. This research will evaluate a new hypothesis regarding the basic mechanics of the process of wind-blown sediment transport. Most wind-blown particles larger than dust are moved in a process known as saltation - a series of hops or bounces along the ground. Theoretical models of saltation have long been based on the fundamental assumption that increasing wind speeds cause particles to bounce higher and farther, resulting in the well-documented increase in the rate of transport. However, transport models based on this assumption have proven unable to consistently produce accurate predictions. Preliminary research has indicated that the underlying conceptualization of saltation may be in error - particles do not bounce higher and farther with increasing wind speed, rather, the size of the bounce appears to be limited by the inertia of the bed sediments. The increased kinetic energy of saltating particles under stronger winds is transferred to the bed sediments, causing ejection of additional grains into saltation and thereby increasing the rate of transport. This study will test this hypothesis, and quantify the influence of bed grain-size on the dimensions of saltation hops. A field experiment will be conducted in which sediment traps will be employed to measure the proportions of sediment moving at various elevations above the bed and various horizontal distances. These traps will be installed downwind of artificial beds composed of sediments that have been sieved into narrow grain-size ranges. It is expected that grains bouncing off beds of large particles will hop higher and farther than those bouncing off beds of finer material, and that hop dimensions will be largely independent of wind speed. Numerical modeling will be used to reconstruct the distribution of saltation hops needed to generate the measured variations in transport, and to quantify how hop dimensions change as a function of the bed grain-size. These findings will be used to construct a new theoretical model of the saltation process that will directly incorporate the influence of bed grain-sizes as documented in this study.This research critically examines a fundamental component of the current scientific view of wind-blown sediment transport. It is likely to alter the prevailing view of how the process works, and the results will potentially be applicable to sediment transport in other environments. There are many environmental hazards associated with wind-blown particulates, and enhanced understanding of saltation will contribute to understanding and effective management of these problems. Although dusts 'float' in suspension and are not directly transported by saltation, it is generally accepted that the impacts of saltating grains are responsible for dislodging and ejecting fines. Hence, improved understanding of saltation will contribute to improvement in modeling emissions of substances ranging from topsoil, nutrients and toxic metals to the chemical contaminants and microorganisms that often attach to fine particles. From an economic standpoint, the National Research Council recently published an estimate of off-site costs associated with wind-blown sediment, which in the western U.S. alone exceed $1 billion per year. Improved understanding of the processes involved will aid in mitigating these problems and reducing their economic impact. This research will also provide educational opportunities and research experience for several graduate students who will participate in the project, and help to foster the development of the newly formed Geomorphic Process Laboratory, a multi-university initiative aimed at applying geomorphic knowledge to solve environmental problems.