Isolating roughness scales of gravel‐bed patches
Isolating roughness scales of gravel‐bed patches
复制标题
隔离砾石层斑块的粗糙度尺度
DOI：
10.1002/2016wr020205
复制
发表时间：
2017
影响因子：
5.4
通讯作者：
H. Friedrich
中科院分区：
文献类型：
--
作者：
S. Bertin;Jane Groom;H. Friedrich
越来越多的共识是，砾石床粗糙度应根据床面地形参数化，而不仅仅是沉积物大小。一个好处是可能识别各种空间尺度的表面粗糙度和评价其各自的贡献流阻（也推移质运输）。在以前的工作中，在不同的尺度粗糙度之间的关系是显而易见的，这目前限制了粗糙度参数化的地形和应用在流动建模。本研究探讨了在砾石层数字高程模型（DEM）上使用移动窗口去趋势来隔离粗糙度尺度及其各自的特征。分析使用了来自实验室和现场的35个水力碎石床补丁的大型数据集。测量的床地形分为两个不同的DEM：一个代表颗粒，其他代表小床形。对于所有DEM，确定了测量垂直粗糙度、叠瓦和空间相关性的床面高程参数。我们的研究结果表明，不同的地形之间的签名颗粒和底形DEM。我们表明，颗粒垂直粗糙度与床面材料尺寸之间存在强正线性关系。表层沉积物的排列也决定了底形的形状，粗糙的沉积物在表层形成隆起，而较细的沉积物则隐藏在凹陷中。斑块尺度垂直粗糙度不能简单地估计为颗粒和底形垂直粗糙度的总和。相反，我们的研究结果表明加权求和和普遍的加权系数的存在。讨论了使用DEM研究砾石床粗糙度和水流模拟的实际应用。
There is a growing consensus that gravel‐bed roughness should be parameterized based on bed‐surface topography, not only sediment size. One benefit is the possible identification of various spatial scales of surface roughness and evaluation of their respective contributions to flow resistance (and also to bedload transport). The absence of relationships between roughness at the different scales is apparent in previous work, which currently limits roughness parameterization from topography and application in flow modeling. This study examines the use of moving‐window detrending on gravel‐bed digital elevation models (DEMs) for isolating roughness scales and their respective signatures. A large data set of 35 water‐worked gravel‐bed patches from both the laboratory and the field was used for the analysis. The measured bed topography was separated into two distinct DEMs: one representing grains, the other representing small bedforms. For all DEMs, bed‐elevation parameters measuring vertical roughness, imbrication, and spatial correlations were determined. Our results show distinct topographic signatures between grain and bedform DEMs. We show strong positive linear relationships between grain vertical roughness and the size of the bed‐surface material. Surface sediment arrangement also determined bedform shape, with groupings of coarse sediment forming humps on the surface, and finer sediment sheltered in hollows. Patch‐scale vertical roughness could not be estimated simply as the sum of grain and bedform vertical roughness. Instead, our results suggest weighted summation and the existence of universal weighting coefficients. Practical applications for studies on gravel‐bed roughness and flow modeling using DEMs are discussed.