Short communication: Multiscalar roughness length decomposition in fluvial systems using a transform-roughness correlation (TRC) approach

Abstract

Abstract. In natural open-channel flows over complex surfaces, a wide range of superimposed roughness elements may contribute to flow resistance. Gravel-bed rivers present a particularly interesting example of this kind of multiscalar flow resistance problem, as both individual grains and bedforms may contribute to the roughness length. In this paper, we propose a novel method of estimating the relative contribution of different physical scales of in-channel topography to the total roughness length, using a transform-roughness correlation (TRC) approach. The technique, which uses a longitudinal profile, consists of (1) a wavelet transform which decomposes the surface into roughness elements occurring at different wavelengths and (2) a “roughness correlation” that estimates the roughness length (ks) associated with each wavelength based on its geometry alone. When applied to original and published laboratory experiments with a range of channel morphologies, the roughness correlation estimates the total ks to approximately a factor of 2 of measured values but may perform poorly in very steep channels with low relative submergence. The TRC approach provides novel and detailed information regarding the interaction between surface topography and fluid dynamics that may contribute to advances in hydraulics, bedload transport, and channel morphodynamics.

A comparison of 1D and 2D bedload transport functions under high excess shear stress conditions in laterally constrained gravel-bed rivers: a laboratory study

“…Experiments were performed in the Adjustable-Boundary Experimental System (A-BES) at the University of British Columbia (Fig. 1), some of which have been reported by Adams and Zampiron (2020). The A-BES comprises a 1.5 m wide by 12.2 m long tilting stream table; the experiments were run as generic Froude-scaled models based on 2003 field measurements from Fishtrap Creek in British Columbia, Canada.…”

Morphodynamics of an erodible channel under varying discharge

“…Adjustable‐boundary experimental system (A‐BES) at the University of British Columbia, showing the 30 cm channel configuration (Adams & Zampiron, 2020, CC BY 4.0) [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…The analysis is of an experiment reported by Adams and Zampiron (2020, Exp1c), which models the adjustment of a steep mountain channel to successive increases in discharge under pseudo‐recirculating conditions (i.e., material was recirculated at the same rate it was output, with a brief time lag). The experiment was conducted on a generic Froude‐scaled stream table (12.2 × 1.5 m) that is based on field measurements from Fishtrap Creek in British Columbia, Canada.…”

Morphodynamic styles: characterising the behaviour of gravel-bed rivers using a novel, quantitative index

“…The first dataset was used to develop the methodology for this throughput ratio, and comes from experiments with a fixed width and unerodible banks, henceforth known as the fixed bank experiment. These experiments have been published elsewhere testing a multi-scalar roughness decomposition (Adams and Zampiron, 2020). The dataset used to test the applicability of the concept with differing boundary conditions came from experiments using deformable banks (MacKenzie, 2019), henceforth known as the mobile bank experiment.…”

“…The mobile bank experiment collected elevation data with a laser scanner to produce 2 mm x 2 mm resolution DEMs of the bed surface (MacKenzie, 2019). In contrast, the fixed bank experiment used structure from motion photogrammetry to produce 1 mm x 1 mm resolution DEMs (Adams and Zampiron, 2020). In both, flow was ceased and water drained from A-BES prior to scanning the exposed bed surface.…”