Field Investigation of the Influence of Bed Texture on Aeolian Saltation

床质对风蚀影响的现场调查

基本信息

  • 批准号:
    0317930
  • 负责人:
  • 金额:
    --
  • 依托单位:
  • 依托单位国家:
    美国
  • 项目类别:
    Continuing Grant
  • 财政年份:
    2003
  • 资助国家:
    美国
  • 起止时间:
    2003-08-15 至 2008-07-31
  • 项目状态:
    已结题

项目摘要

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.
风对泥沙的输送是从土壤侵蚀和污染物输送到沙尘暴和荒漠化等各种环境问题的关键组成部分。这项研究将评估一种关于风沙运动过程的基本力学的新假说。大多数比尘埃更大的被风吹来的颗粒都是在一种被称为跳跃的过程中运动的--一系列沿着地面的跳跃或反弹。长期以来,跳跃的理论模型一直基于这样一个基本假设,即风速增加会导致粒子反弹得更高、更远,从而导致运输率的增加,这是有据可查的。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,对跃迁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层沉积物惯性的限制。在强风作用下,悬浮颗粒增加的动能被转移到底泥中,导致更多的颗粒被抛出进入跃迁,从而增加了输送速度。这项研究将验证这一假设,并量化床面颗粒大小对跃迁跳跃尺寸的影响。将进行现场试验,其中将使用泥沙捕集器来测量泥沙在床面以上不同高度和不同水平距离处的运动比例。这些捕集器将安装在人工床的顺风方向,人工床由已被筛选成狭窄粒度范围的沉积物组成。预计从大颗粒床反弹的颗粒将比从更细物质床反弹的颗粒跳得更高、更远,而且颗粒的大小在很大程度上与风速无关。数值模拟将被用来重建产生测量的输运变化所需的跃变跳跃的分布,并量化跳跃尺寸如何作为河床颗粒大小的函数变化。这些发现将被用来构建一个新的跃迁过程理论模型,该模型将直接包括床面颗粒大小的影响,如本研究所述。本研究批判性地检验了当前风沙输运科学观点的一个基本组成部分。这可能会改变人们对这一过程如何工作的普遍看法,其结果可能也适用于其他环境中的泥沙输送。与风吹来的颗粒物有关的环境危害很多,加强对跃迁的了解将有助于理解和有效管理这些问题。虽然粉尘在悬浮物中“漂浮”,并不直接通过跳跃运输,但人们普遍认为,跳跃颗粒的影响导致了粉尘的移开和抛射。因此,更好地理解跃迁将有助于改进对物质排放的模拟,这些物质包括表土、营养物质和有毒金属,以及通常附着在细颗粒上的化学污染物和微生物。从经济角度来看,美国国家研究委员会(National Research Council)最近发布了一份与风沙相关的非现场成本估计,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并减少其经济影响。这项研究还将为将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大学倡议。

项目成果

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Steven Namikas其他文献

Steven Namikas的其他文献

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{{ truncateString('Steven Namikas', 18)}}的其他基金

Doctoral Dissertation Research: Investigation of Factors Controlling the Dynamics of Beach-Surface Moisture Content
博士论文研究:海滩表面水分含量动态控制因素的研究
  • 批准号:
    1102650
  • 财政年份:
    2011
  • 资助金额:
    --
  • 项目类别:
    Standard Grant
Doctoral Dissertation Research: Field Investigation of the Influence of Surface Moisture on the Initiation of Motion in Wind-Blown Sand Transport on Beaches
博士论文研究:表面湿度对海滩风沙输送运动启动影响的现场调查
  • 批准号:
    0928014
  • 财政年份:
    2009
  • 资助金额:
    --
  • 项目类别:
    Standard Grant

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