Hysteretic sediment fluxes in rainfall‐driven soil erosion: Particle size effects

Abstract

A detailed laboratory study was conducted to examine the effects of particle size on hysteretic sediment transport under time‐varying rainfall. A rainfall pattern composed of seven sequential stepwise varying rainfall intensities (30, 37.5, 45, 60, 45, 37.5, and 30 mm h−1), each of 20 min duration, was applied to a 5 m × 2 m soil erosion flume. The soil in the flume was initially dried, ploughed to a depth of 20 cm and had a mechanically smoothed surface. Flow rates and sediment concentration data for seven particle size classes (<2, 2–20, 20–50, 50–100, 100–315, 315–1000, and >1000 µm) were measured in the flume effluent. Clockwise hysteresis loops in the sediment concentration versus discharge curves were measured for the total eroded soil and the finer particle sizes (<2, 2–20, and 20–50 µm). However, for particle sizes greater than 50 µm, hysteresis effects decreased and suspended concentrations tended to vary linearly with discharge. The Hairsine and Rose (HR) soil erosion model agreed well with the experimental data for the total eroded soil and for the finer particle size classes (up to 50 µm). For the larger particle size classes, the model provided reasonable qualitative agreement with the measurements although the fit was poor for the largest size class (>1000 µm). Overall, it is found that hysteresis varies amongst particle sizes and that the predictions of the HR model are consistent with hysteretic behavior of different sediment size classes.

The stochastic nature of the transport of coarse material in rain-impacted flows

“…The qualitative model developed by Kinnell (1994) is not designed to predict soil loss in experiments like those reported by Cheraghi et al (2016). However, it is clear the approach to the modelling erosion by rain-impacted flows using the classical mass conservation approach does not capture how particles are detached and transported in rain-impacted flow well.…”

“…Likewise, raindrop induced rolling is a pulsed transport system that operates randomly in time and space. Cheraghi et al (2016) applied the version of Hairsine and Rose model developed for unsteady conditions by Sander et al (1996) to an experiment using simulated rainfall over a 6 m flume containing a loamy agricultural soil and observed that the Hairsine and Rose model results agreed well with the total eroded soil and particles < 50 µm. However, the agreement declined for particles > 50 µm and was poor for particles > 1000 µm.…”

Applicability of the landscape evolution model in the absence of rills

“…These differences are likely due to the local scale fluid-particle and particle-particle interactions that are not accounted for in the model. One of these processes is the armoring effect (Polyakov and Nearing, 2003;Wang et al, 2014;Cheraghi et al, 2016;Lisle et al, 2017). Due to shorter erosion time scales, the fine sediment particles are rapidly removed while the larger particles are deposited on the surface or are not moved at all, resulting in a surface covered by pebbles (Figure 5).…”

Characterization of Multi‐Scale Fluvial Suspended Sediment Transport Dynamics Across the United States Using Turbidity and Dynamic Regression

“…Studies show that the bulk of sediment can be transported during individual floods (Aguilera & Melack, 2018; Duvert et al., 2010), at times upwards of 80% of SS in a year (Tena et al., 2011). Relationships between turbidity ( T n ), suspended sediment concentration (SSC) and discharge during extreme events can be characterized by highly variable hysteresis response patterns that are still not completely understood (Aguilera & Melack, 2018; Hamshaw et al., 2018) and are particularly prevalent for fine sediment (Cheraghi et al., 2016). Others have found seasonal variations in the SS‐ Q relationship (Duvert et al., 2010; Hirsch et al., 2010), as well as persistent SS behavior over sub‐annual to inter‐decadal time scales (Ahn & Steinschneider, 2019; Dethier et al., 2016; Gray et al., 2018; Yellen et al., 2014).…”