Effect of stress history on sediment transport and channel adjustment in graded gravel-bed rivers

Abstract

Abstract. With the increasing attention on environmental flow management for the maintenance of habitat diversity and ecosystem health of mountain gravel-bed rivers, much interest has been paid to how inter-flood low flow can affect gravel-bed river morphodynamics during subsequent flood events. Previous research has found that antecedent conditioning flow can lead to an increase in critical shear stress and a reduction in sediment transport rate during a subsequent flood. However, how long this effect can last during the flood event has not been fully discussed. In this paper, a series of flume experiments with various durations of conditioning flow are presented to study this problem. Results show that channel morphology adjusts significantly within the first 15 min of the conditioning flow but becomes rather stable during the remainder of the conditioning flow. The implementation of conditioning flow can indeed lead to a reduction of sediment transport rate during the subsequent hydrograph, but such an effect is limited to within a relatively short time at the beginning of the hydrograph. This indicates that bed reorganization during the conditioning phase, which induces the stress history effect, is likely to be erased with increasing intensity of flow and sediment transport during the subsequent flood event.

Influence of Sediment Supply Timing on Bedload Transport and Bed Surface Texture During a Single Experimental Hydrograph in Gravel Bed Rivers

“…The light table underestimated D 10L by 20% on average and D 90L by 30% on average, with D 10L being the diameter such that 10% of the bedload sediment is finer. For further details on bedload transport measurements, we refer to Zimmermann et al (2008) and An et al (2021). Every 20 min, we calibrated the light table estimated mass and grain size against those measured in the bedload trap.…”

“…The light table can detect grains as small as 1 mm. An et al (2021) reported that the median bedload size (D 50L ) show that the light table overestimated D 50L by 3% on average (the subscript "L" denotes load). The light table underestimated D 10L by 20% on average and D 90L by 30% on average, with D 10L being the diameter such that 10% of the bedload sediment is finer.…”

“…In addition to the characteristics of an individual flood, flood history (defined as a sequence of floods of different magnitudes and duration) influences bedload transport capacity, sediment entrainment and transport, bed grain size distribution, bed surface armoring and surface structures (An et al., 2021; Curran et al., 2015; Frostick et al., 1984; Haynes & Pender, 2007; Mao, 2018; Piedra et al., 2012; I. Reid et al., 1985; Waters & Curran, 2015). Mao (2018) noticed that vertical sorting in flume experiment caused a 40% decrease in sediment transport rate when large flood follows an event of similar magnitude.…”

“…Digital elevation models (DEMs) of the bed were built from the laser scans. To determine the bed surface grain size distribution, we used cameras mounted on a motorized cart (An et al., 2021; Chartrand et al., 2018; Hassan, Saletti, Zhang, et al., 2020). Sediment grain sizes were detected from the photos with the GrainID image analyses software that was developed in our lab for the same material (Chen et al., 2022).…”

CNN for image-based sediment detection applied to a large terrestrial and airborne dataset

“…Bray, 1971), the Wolman method has been especially popular in the field due to the limited equipment required and its benefit of reducing sampling times whilst providing a relatively valid estimation of reach-scale grain-size distribution. Since then, various versions of the Wolman method were proposed with different approaches to collecting stones such as the random walk approach for particle collection (Leopold, 1970), superimposing gravel templates upon the sedimentological unit for reduced operator error (Bunte and Abt, 2001), and image-based Wolman method analysis (Hassan et al, 2020;An et al, 2021).…”