The impact of hydrograph variability and frequency on sediment transport dynamics in a gravel‐bed flume

Abstract

A laboratory study was undertaken to investigate how changes in flow regime and hydrograph shape (number of cycled hydrographs and duration of each hydrograph) together impact bedload transport and resulting bed morphology. Three hydrologic conditions (experiments) representing different levels of urbanization, or analogously different flow regimes, were derived from measured hydrometric field data. Each experiment consisted of a series of hydrographs with equal peak discharge and varying frequency, duration and flashiness. Bedload transport was measured throughout each hydrograph and measurements of bed topography and surface texture were recorded after each hydrograph. The results revealed hysteresis loops in both the total and fractional transport, with more pronounced loops for longer duration hydrographs, corresponding to lower rate of unsteadiness until reaching the peak discharge (pre‐urbanization conditions). Shorter duration hydrographs (urban conditions) displayed more time above critical shear stress thresholds leading to higher bedload transport rates and ultimately to more variable hysteresis patterns. Surface textures from photographic methods revealed surface armoring in all experiments, with larger armor ratios for longer duration hydrographs, speculated to be due to vertical sorting and more time for bed rearrangements to occur. The direction of bed surface adjustment was linked to bedload hysteresis, more precisely with clockwise hysteresis (longer hydrographs) typically resulting in bed coarsening. More frequent and shorter duration hydrographs result in greater relative channel adjustments in slope, topographic variability and surface texture. © 2019 John Wiley & Sons, Ltd.

How Large Immobile Sediments in Gravel Bed Rivers Impact Sediment Transport and Bed Morphology

“…STR is a measure of the level of sediment storage within the flume, indicating erosive or depositional trends. Bedload hysteresis was calculated by evaluating the hysteresis ratio, which is defined as the ratio of total bedload transport on the rising limb to the total bedload transport on the falling limb (Juez et al 2018, Plumb et al 2019. The hysteresis ratio was then plotted against the large particle spacing ( / ) to determine any trends amongst the test cases.…”

The Role of Bedload Transport in the Development of a Proglacial River Alluvial Fan (Case Study: Scott River, Southwest Svalbard)

“…The results of many field and laboratory studies highlight how changes in the flow regime and hydrograph shape describe bedload transport and the resulting bed morphology [12][13][14][15]. Hassan and Church [15] highlighted that the hysteresis loops were more pronounced for hydrograms of longer durations, which corresponded to less instability until the peak discharge was reached.…”

“…The relation between flow activities and bedload transport rates has been highlighted by Arnborg et al [12] and Williams [13]. Both field and laboratory experiments indicated that discharge and bedload transport relationships can be analyzed on the basis of hysteresis loops [14]. They found that for long-existing and continuous sediment concentrations associated with a long flood, the relationship between bedload transport and discharge in the relationship diagram is represented by a figure eight with a clockwise loop for high flows and a counterclockwise loop for low flows.…”

The Connection between a Suspended Sediments and Reservoir Siltation: Empirical Analysis in the Maziarnia Reservoir, Poland

“…It has been shown that the frequency of rainfall and their intensity significantly affect the load and size of soil particles implemented into rivers [52,53].…”