Effects of Sand Addition and Bed Flushing on Gravel Bed Surface Microtopography and Roughness

Bertin, Stéphane; Friedrich, Heide

doi:10.1029/2018wr024615

Cited by 6 publications

(8 citation statements)

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“…Increased channel energy conditions likely occurred due to pulse‐derived increases in local channel slope, bed fining from sediment pulse fines draped over coarser bed sediment, and/or pool and bed topography filling. Previous studies have also demonstrated that fine sediment draped over, or infiltrating into, a coarser bed can result in a smoother bed with lower bed roughness (Bertin & Friedrich, 2019), increase near‐bed velocities, and even enhance bed mobilization in some contexts (Venditti et al, 2010). Sediment pulses from other dam removals have also been associated with channel fining, including higher‐gradient removals such as those on the Elwha River (East et al, 2018) and in lower‐gradient channels (Harrison et al, 2018).…”

Section: Discussionmentioning

confidence: 99%

Channel response to a dam‐removal sediment pulse captured at high‐temporal resolution using routine gage data

Cashman

Gellis

Boyd

et al. 2021

Earth Surf Processes Landf

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In this study, we captured how a river channel responds to a sediment pulse originating from a dam removal using multiple lines of evidence derived from streamflow gages along the Patapsco River, Maryland, USA. Gages captured characteristics of the sediment pulse, including travel times of its leading edge ($7.8 km yr −1 ) and peak ($2.6 km yr −1 ) and suggest both translation and increasing dispersion. The pulse also changed local hydraulics and energy conditions, increasing flow velocities and Froude number, due to bed fining, homogenization and/or slope adjustment. Immediately downstream of the dam, recovery to pre-pulse conditions occurred within the year, but farther downstream recovery was slower, with the tail of the sediment pulse working through the lower river by the end of the study 7 years later.The patterns and timing of channel change associated with the sediment pulse were not driven by large flow or suspended sediment-transporting events, with change mostly occurring during lower flows. This suggests pulse mobility was controlled by process-factors largely independent of high flow.In contrast, persistent changes occurred to out-of-channel flooding dynamics. Stage associated with flooding increased during the arrival of the sediment pulse, 1 to 2 years after dam removal, suggesting persistent sediment deposition at the channel margins and nearby floodplain. This resulted in National Weather Serviceindicated flood stages being attained by 3-43% smaller discharges compared to earlier in the study period.This study captured a two-signal response from the sediment pulse: (1) short-to medium-term (weeks to months) translation and dispersion within the channel, resulting in aggradation and recovery of bed elevations and changing local hydraulics; and (2) dispersion and persistent longer-term (years) effects of sediment deposition on overbank surfaces. This study further demonstrated the utility of US Geological Survey gage data to quantify geomorphic change, increase temporal resolution, and provide insights into trajectories of change over varying spatial and temporal scales.

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Section: Discussionmentioning

confidence: 99%

Channel response to a dam‐removal sediment pulse captured at high‐temporal resolution using routine gage data

Cashman

Gellis

Boyd

et al. 2021

Earth Surf Processes Landf

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“…Six sand transport rates were obtained for each flow discharge tested, the results were then interpolated to determine the relationship between sand transport and water discharge. This approach of sand addition differs from previous studies (e.g., Bertin & Friedrich, 2019;Perret et al, 2018), where the sand was fed at a constant rate, irrespective of the flow discharge. A total of ∼145 and ∼281 kg of sand was added during each 1/1 and 1/3, 3/1 experimental run, respectively.…”

Section: Experimental Facilitiesmentioning

confidence: 87%

“…Mobile sediment was placed in the test section (Figure 1). To keep the mobile sediment horizontally aligned with the height of the artificial bed upstream and downstream of the test section, the vertically adjustable table underneath the test section was manually leveled upwards with screw jacks, a design that has been successfully used in previous gravel‐bed studies (Bertin & Friedrich, 2019; Heays et al., 2014).…”

Section: Experimental Design and Methodsmentioning

confidence: 99%

Hydrograph Shape Impact on Sand Infiltration and Sediment Transport Dynamics in Gravel‐Bed Rivers

Ravazzolo

Mao

Friedrich

2022

Water Resources Research

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A wide range of sediment grain sizes (from fine sand to pebbles) can be found in gravel-bed rivers. In fully alluvial systems, most of the size fractions (often differentiated into fine and coarse grains) can be actively transported during flood events. Sediment can be transported as bedload, suspended load, or can migrate inside the bed layer. For coarse grain sizes, the predominant transport process is bedload, whereas the influence of suspended load is negligible. In addition to bedload, fine grains can also be transported within the water column, by being kept in suspension by turbulence generated near the channel bed. The resultant turbulent flow must be equal or exceed the particle fall velocity to sustain suspended sediment load. Mobility and composition of the bed (e.g., grain size distribution, porosity) can change drastically during a flood event. In this gravel-bed study, we consider sand being transported as bedload only. Coarse grains can create interstitial spaces (pore space), that finer grains can occupy. The porosity of a channel bed will thus depend on the size and the heterogeneity of a sediment mixture (Standish & Borger, 1979). Two different processes govern the infiltration of sand for a gravel matrix, namely static sorting and kinetic sieving. Static sorting of sand into an immobile gravel framework Abstract Sand (i.e., < 2 mm) infiltration into a gravel bed is recognized to affect sediment dynamics of coarser fractions (i.e., entrainment and transport rate), near-bed velocities, bed morphology, and to pose significant engineering and ecological issues. Local hydraulics, sediment dynamics, and sand infiltration into the gravel matrix are related and mutually affect each other in gravel-bed rivers. However, relatively little research has been done to explore sediment dynamics and sand infiltration in a mobile gravel-bed under unsteady flow conditions. In the present study, we experimentally simulated three hydrographs of different durations of rising and falling limbs, and monitored sand infiltration over beds with a coarse and a fine grain size distribution. Results confirmed that the addition of sand enhances sediment dynamics. Moreover, the shape of the rising limb of the hydrograph was responsible for altering identified sand infiltration processes and bedload rate. Short time-to-peak floods (i.e., short time from the start to the peak of the hydrograph) experienced higher sediment transport rates during the falling limb than the rising limb of the hydrograph, favoring sand infiltration. In contrast, long time-to-peak floods (i.e., long time from the start to the peak of the hydrograph) experienced higher sediment transport rates during the rising limb than the falling limb of the hydrograph, resulting in reduced sand infiltration.Plain Language Summary Understanding how sediment is transported during floods is important, as their movement affects channel morphology and river ecology. Fine sediment can infiltrate gravel bed-rivers, a process that depends on the local hydraulics, the size...

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“…Sediment reworking on the beach and nearshore due to waves and currents traduces by the formation of topographic complexity (herewith generally called roughness), such as sedimentary bedforms. These topo-morphological features are the imprint of the processes that shaped them, and, as such, measuring bedforms can provide meaningful information on hydrodynamic forces [6][7][8][9][10]. Besides, bedforms are roughness elements that modify the flow and dissipate energy [11,12].…”

Section: Introductionmentioning

confidence: 99%

Assessment of RTK Quadcopter and Structure-from-Motion Photogrammetry for Fine-Scale Monitoring of Coastal Topographic Complexity

2022

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Advances in image-based remote sensing using unmanned aerial vehicles (UAV) and structure-from-motion (SfM) photogrammetry continue to improve our ability to monitor complex landforms over representative spatial and temporal scales. As with other water-worked environments, coastal sediments respond to shaping processes through the formation of multi-scale topographic roughness. Although this topographic complexity can be an important marker of hydrodynamic forces and sediment transport, it is seldom characterized in typical beach surveys due to environmental and technical constraints. In this study, we explore the feasibility of using SfM photogrammetry augmented with an RTK quadcopter for monitoring the coastal topographic complexity at the beach-scale in a macrotidal environment. The method had to respond to resolution and time constraints for a realistic representation of the topo-morphological features from submeter dimensions and survey completion in two hours around low tide to fully cover the intertidal zone. Different tests were performed at two coastal field sites with varied dimensions and morphologies to assess the photogrammetric performance and eventual means for optimization. Our results show that, with precise image positioning, the addition of a single ground control point (GCP) enabled a global precision (RMSE) equivalent to that of traditional GCP-based photogrammetry using numerous and well-distributed GCPs. The optimal model quality that minimized vertical bias and random errors was achieved from 5 GCPs, with a two-fold reduction in RMSE. The image resolution for tie point detection was found to be an important control on the measurement quality, with the best results obtained using images at their original scale. Using these findings enabled designing an efficient and effective workflow for monitoring coastal topographic complexity at a large scale.

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Effects of Sand Addition and Bed Flushing on Gravel Bed Surface Microtopography and Roughness

Cited by 6 publications

References 83 publications

Channel response to a dam‐removal sediment pulse captured at high‐temporal resolution using routine gage data

Channel response to a dam‐removal sediment pulse captured at high‐temporal resolution using routine gage data

Hydrograph Shape Impact on Sand Infiltration and Sediment Transport Dynamics in Gravel‐Bed Rivers

Assessment of RTK Quadcopter and Structure-from-Motion Photogrammetry for Fine-Scale Monitoring of Coastal Topographic Complexity

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