Abstract
Remote sensing of gravel-bed patches and resulting high-resolution digital elevation models (DEMs) allow for the identification of various spatial scales of surface roughness. Thus far, dimensions relating to grain and bedform roughness scales have been determined using semivariograms or equivalent structure/autocorrelation functions. However, it is difficult to clearly differentiate roughness scales and separate analysis of roughness properties is not possible. This study examines the use of moving-window detrending on gravel-patch DEMs for isolating grain and bedform roughness and their respective topographic signatures. An extensive dataset of water-worked gravel surfaces collected in both laboratory and field environments is used. The measured bed topography is separated into two distinct DEMs: one representing grains, the other representing bedforms, and roughness properties are determined separately for grain and bedform DEMs. The results show that both roughness scales are controlled by the size of the coarse sediment forming the bed surface, with positive linear relationships connecting bed composition and vertical roughness. Coarse sediment is controlling bedform development by forming humps on the surface, in the lee of which finer sediment is sheltered. We present synthesis relationships connecting vertical roughness of gravel patches to the vertical roughness of grains and bedforms.
Highlights
High-resolution digital elevation models (DEMs) of water-worked gravel beds show the superposition of reliefs due to the arrangement of sediment grains onto low-amplitude bedforms [1, 2]. far, spatial scales of gravel-bed roughness have been examined using semivariograms or equivalent structure/autocorrelation functions [e.g., 3, 4], from which dimensions relating to grain and bedform roughness scales have been determined
Spatial scales of gravel-bed roughness have been examined using semivariograms or equivalent structure/autocorrelation functions [e.g., 3, 4], from which dimensions relating to grain and bedform roughness scales have been determined
Bed undulations appear to be dependent on the arrangement of coarse sediment, with humps in the surface generally associated with groupings of coarse particles into smallscale structures such as clusters, lines, and stone cells, whereas smaller particles are confined in shelters formed by hollows
Summary
High-resolution digital elevation models (DEMs) of water-worked gravel beds show the superposition of reliefs due to the arrangement of sediment grains onto low-amplitude bedforms [1, 2]. far, spatial scales of gravel-bed roughness have been examined using semivariograms or equivalent structure/autocorrelation functions [e.g., 3, 4], from which dimensions relating to grain and bedform roughness scales have been determined. High-resolution digital elevation models (DEMs) of water-worked gravel beds show the superposition of reliefs due to the arrangement of sediment grains onto low-amplitude bedforms [1, 2]. Despite recent progress in remote sensing, measuring gravel-bed microtopography in a range of practical situations remains challenging. This is because of challenging measurement environments and the need to resolve individual grain arrangement requiring high-resolution and accurate data. Other studies calculated σZ from the bed topography without prior detrending of bedform roughness [7] This makes comparing bed roughness between studies difficult, as the quantities measured and subsequently compared do not necessarily encompass the same scales of surface roughness
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