Flow resistance, sediment transport, and bedform development in a steep gravel-bedded river flume

Abstract

Highlights: Flow resistance increased with shallow flow, bedforms, and high sediment transport intensity  Downstream and upstream migrating alternate bars developed on bed slopes up to 20%  Transition to upper plane bed coincided with development of concentrated sheetflow Abstract: Quantifying flow resistance and sediment transport rates in steep streams is important for flood and debris flow prediction, habitat restoration, and predicting how mountainous landscapes evolve. However, most studies have focused on low gradient rivers and the application of this work is uncertain for steep mountain streams where surface flows are shallow and rough, subsurface flows are not negligible, and there is form-drag from bed-and channelforms that differs from those in low gradient rivers. To evaluate flow resistance relations and sediment transport rates for steep channel beds, experiments were conducted using a range of water discharges and sediment transport rates in a 12 m long recirculating flume with bed slopes of 10%, 20%, and 30%, and a bed of nearly uniform natural gravel. Flow resistance for planar beds and beds that developed bedforms match empirical models that account for bedloaddependent roughness. Some bedforms were atypical for natural rivers at these bed slopes, such as ACCEPTED MANUSCRIPTA C C E P T E D M A N U S C R I P T 2 stepped alternate bars and upstream migrating alternate bars. Total flow resistance increased with decreasing particle submergence and energetic sediment transport and drag on bedforms. Using linear stress partitioning to calculate bed stresses due to grain resistance alone, sediment flux relations developed for lower gradient rivers perform well overall, but they overestimate fluxes at 20% and 30% gradients. Based on previous theory, mass failure of the bed, which did not occur, was predicted for the highest Shields stresses investigated at 20% and 30% bed slopes; instead a concentrated layer, four to ten particle diameters deep, of highly concentrated granular sheetflow was observed.

The variability of antidune morphodynamics on steep slopes

“…The existence of bedload transport pulses has been related to bedform migration (Gomez et al, 1989), a relationship that has been investigated in gravel‐bed flumes through experimental investigations into alternate bars (e.g. Dhont & Ancey, 2018; Palucis et al, 2018). When alternate bars are associated with near‐critical flows, antidunes may develop locally and contribute to sediment transport (see Movie S3 in Dhont & Ancey, 2018).…”

Agitation and its control on excess pore water pressure and debris‐flow behaviour

“…Being somewhat different from that in the idling tests (Table 2), gear‐specific P fluctuates when the rotor operates at a certain gear in the tested mixture. This should be in relation to the fundamental granular nature of the slurries (debris flows) (Coussot & Ancey, 1999; Palucis et al, 2018). On the other hand, the standard deviation of 27 P time series for nine runs is on the order of only 0.99–9.77 W. It shows that P is essentially to remain roughly constant during the individual stages of each run, given the magnitudes of the mean values of the series of P ( P avg ), ranging from 236.61 to 337.45 W. Therefore, stepped vertical ascending pattern of the plots of P versus t is still significant.…”

Exploring the relationship between soil erosion and hydraulic parameters on slopes with clipped herbaceous vegetation through Bayesian network modeling

“…This higher flow velocity results in reduced runoff depth, lower pressure difference in the vortex area behind the vegetation, decreased potential energy, and critical initial runoff energy. As a consequence, the kinetic energy and power of the runoff are enhanced, leading to increased soil loss (Li et al, 2022; Palucis et al, 2018; Papanicolaou et al, 2018). Consistent with this study, Zhang et al (2018) demonstrated that the change in slope gradient directly affects slope runoff energy.…”