Bedform segregation and locking increase storage of natural and synthetic particles in rivers

Abstract

While the ecological significance of hyporheic exchange and fine particle transport in rivers is well established, these processes are generally considered irrelevant to riverbed morphodynamics. We show that coupling between hyporheic exchange, suspended sediment deposition, and sand bedform motion strongly modulates morphodynamics and sorts bed sediments. Hyporheic exchange focuses fine-particle deposition within and below mobile bedforms, which suppresses bed mobility. However, deposited fines are also remobilized by bedform motion, providing a mechanism for segregating coarse and fine particles in the bed. Surprisingly, two distinct end states emerge from the competing interplay of bed stabilization and remobilization: a locked state in which fine particle deposition completely stabilizes the bed, and a dynamic equilibrium in which frequent remobilization sorts the bed and restores mobility. These findings demonstrate the significance of hyporheic exchange to riverbed morphodynamics and clarify how dynamic interactions between coarse and fine particles produce sedimentary patterns commonly found in rivers.

Kaolinite Deposition Dynamics and Streambed Clogging During Bedform Migration Under Losing and Gaining Flow Conditions

“…Bedform celerity also declined significantly with the accumulation of kaolinite (Figure 5). In addition, bedform movement completely stopped, reaching a locked state (sensu Dallmann et al, 2021) under losing flow conditions, and under a gaining flux of 20 cm/day. This result can be seen in the number of bedform celerity measurements that reach zero toward the end of experiments (Figure 5).…”

“…For studies on bed mobility, the focus is often on the physical structure of the channel or on the morphology at the interface between the water and the sediments (Ashley, 1990; Leopold, 1994). However, streambed mobilization and re‐deposition can either increase (Cui et al., 2021; Mathers et al., 2021; Wu et al., 2015) or decrease (Dallmann et al., 2021; Teitelbaum et al., 2021) the hydraulic conductivity of the bed, depending on the specific conditions at the sites. Streambeds containing coarse bed material episodically move only during infrequent events.…”

“…Wharton et al. (2017) refer to colmation as a “pernicious problem” because it can: (a) impede surface‐groundwater fluxes (Nowinski et al., 2011; Partington et al., 2017); (b) affect streambed stability (Dallmann et al., 2021); (c) affect biogeochemical processes (Mathers et al., 2021), and (d) influence various ecological processes (Brunke & Gonser, 1997; Harvey & Gooseff, 2015; Nogaro et al., 2010). Indeed, many cases of sandy streambed clogging have been reported recently (Datry et al., 2015; Korus et al., 2020; Shrivastava et al., 2020).…”

Discontinuity in Equilibrium Wave‐Current Ripple Size and Shape and Deep Cleaning Associated With Cohesive Sand‐Clay Beds

“…It is likely that the stronger cohesion within the bed at C 0 = 12.3% prevented these ripples from evolving into the two-dimensional ripples with discontinuous crest lines of C 0 = 11.6% or even the straight-crested and continuous ripple trains of C 0 ≤ 10.6%. The fact that T b changes sign in the C 0 = 12.3% case in Figure 6c suggests that the ripples would be unlikely to evolve further, even if the experiment had been run for a longer duration (Dallmann et al, 2021).…”

Streambed migration frequency drives ecology and biogeochemistry across spatial scales

“…Thus, resource transfer to hyporheic communities below the migrating layer is reduced (Elliott & Brooks, 1997; Wolke et al, 2020; Zheng et al, 2019). At the same time, suspended particulate matter is trapped by migrating sediments and accumulates in the zone below the migrating layer (Dallmann et al, 2020; Dallmann et al, 2021; Harvey et al, 2012; Teitelbaum et al, 2022). This accumulation can lead to clogging of the streambed by clay particles (Teitelbaum et al, 2021) but also to increased biogeochemical activity utilizing organic matter (Phillips et al, 2019).…”