Transport Sediment Research Articles

Aeolian process-induced hyper-concentrated flow in a desert watershed

Ephemeral desert channels are characterized by very high rates of sediment transport during infrequent flood events. Here we show that aeolian process-induced hyper-concentrated (AHC) flows occur in the Sudalaer desert watershed in the Ordos Plateau of China, which primarily transport 0.08–0.25 mm non-cohesive aeolian sand and have a peak suspended sediment concentration of 1.1–1.4 × 106 mg l−3. Aeolian sand supply and storage in the channel play a crucial role in causing hyper-concentrated flow. Our results indicate that non-cohesive aeolian sand can be entrained from the bed and suspended in the turbulent flow when the channel bed slope exceeds a critical threshold (0.0003). We also show that if the frequency ratio of wind-blown sandstorms to rainstorms Tw/Tp exceeds β(γ − γ0)/α (P/V3) (A/L) (where α is the wind-blown sand transport coefficient, β is the runoff coefficient, γ − γ0 is the increase in suspension concentration caused by addition of aeolian sands, P is the density of rainstorms, V is the wind speed of sandstorms, A is the runoff-generating area, L is the aeolian sand-filled channel length), an AHC flow occurs during the passage of a flood in a desert channel. Since high-frequency aeolian processes provide an adequate quantity of transportable sediment and promote AHC flow, most of the infrequent rainfall-induced floods occurring in arid zones can develop as AHC flows.

Controls on the distribution of channel reach morphology in selectively glaciated catchments

To assess the controls on the distribution of channel reach morphology in a selectively glaciated landscape, we used field mapping and a geographical information system (GIS) in the River Dee catchment, northeast Scotland. Controls on channel morphology were investigated using (1) continuous longitudinal assessment of channel morphology distribution in relation to geology, glacial history, topography, and total stream power (Ω) in two subcatchments, and (2) slope (S), Ω, and a slope–drainage area (S–A) framework to understand the occurrence of 173 widely distributed bedrock, mixed bedrock–alluvial, and alluvial (three different types) reaches. The S–A framework used indicators of transport capacity (Qc) and sediment supply (Qs) to differentiate channel types. The study highlights the disjointed nature of channel reach distribution at the river scale that reflects variable lithology and glacial modification. Because of the subdued topography in contrast to other regions, colluvial forcing of channel morphology in the headwaters was lacking. However, in common with other glaciated landscapes, repeated sequences of channel reach type progression determined by valley steps were evident. The S–A analysis successfully discriminated 87.2% of alluvial and 91.4% of bedrock reaches despite the variable land use and glacial modification. Discrimination of the full range of channel types using S, Ω, or the S–A framework was poor however. Notably, a third of the transport alluvial reaches were located in the bedrock S–A domain, and the majority of mixed reaches were widely distributed mostly within the bedrock domain and not close to the critical slope (Sc). In comparison to other regions, the Sc above which Qc>Qs and bedrock reaches dominate, was notably higher. We hypothesise that a drier climate and the higher entrainment threshold of coarse, granite-dominated bed materials create a higher Sc.

Research of Sediment Transport Test Based Suction Jet Technology

Suction jet scheme has brought forward sediment suspension transport work parameter in the scheme of water and sediment transporting and sediment adding in discharge water before the flood season of Xiaolangdi Reservoir. Suction jet system starts suspended sediments as per 1 natural bottom slope of Xiaolangdi Reservoir while jet pump eject muddy water, which forms into density current and transport forward, and makes longitudinal deposition in the process of sediment transport. Transport distance shall be 1,264~1,903m while 50% longitudinal attenuation of sediments as effective transport distance. Bottom slope of sediment deposition is reduced to 6.7 with obscure longitudinal attenuation of sediments and can transport to longer distance.

Spatial Effects of a Washout on Sandy Beach Macrofauna Zonation and Abundance

ABSTRACT Gandara-Martins, A.L.; Borzone, C.A.; Guilherme, P.D.B., and Vieira, J.V., 2015. Spatial effects of a washout on sandy beach macrofauna zonation and abundance. Washouts have an important function in backshore zone drainage and remobilization of sediments for littoral transport. It is known that they can change beach morphology along its course, but their effects on the macrofauna community still represent a gap in knowledge of sandy beach ecology. Based on previous studies developed in larger systems, such as channels and estuaries, we aimed to assess how the macrofauna community responds to the presence of a permanent sandy beach washout. The study was carried out at an exposed sandy beach in southern Brazil, where six cross-cut transects 0, 3, 9, 27, 81, and 243 m in distance from the washout were defined. Biological and environmental samples were taken at nine levels along each transect. As expected, beach morphology and water table salinity were affected by the washout, resulting in changes i...

Relations between bed recharge and magnitude of mountain streams erosions

Because flood risks in mountain streams depend not only on flow intensity, but also on the volume of transported sediments, this paper presents the results of a long flume experiment aiming to investigate the relations between bed recharge and magnitude of erosion events. This 46-h experiment conducted with a natural bimodal mixture produced quasi-periodical fluctuations of transport rates and slope, despite constant feeding conditions (for water and sediments). These fluctuations were associated with successive bed armouring and erosion as well as bedload sheet production and migration.Short and long erosion events were recorded, covering a wide range of transport rates and sediment volumes. No correlation was observed between transport rates and transported volumes. Analysis showed that transported volumes were related to the degree of bed recharge only. Superposed periods were measured in the time evolution of the slope signal. A Fourier transform analysis showed that these periods reflect the influence of the different parts of the flume, which do not erode and aggrade at the same rate. All this complex behaviour was observed despite constant feeding rates and was strongly controlled by grain sorting. By extrapolating the mechanisms observed locally to the entire flume length, it was possible to propose a simple conceptual model linking bed deposition and magnitude of erosion events.Although this flume experiment still needs to be reproduced to account for all variability affecting natural flows, these results could have strong implications in risk mitigation strategies where not only exceptional flow events should be considered because (1) the volume of transported sediments depends essentially on the bed recharge and (2) the frequency of moderate flows able to transport sediments can play an important role over the long term by limiting in-channel accumulations between two major floods. Recommendations are made for risk mitigation strategies.

The Use of Stream Power as an Indicator of Channel Sensitivity to Erosion and Deposition Processes

Stream power is a measure of the main driving forces acting in a channel and determines a river's capacity to transport sediment and perform geomorphic work. Recent digital elevation models allow the calculation of channel gradient and consequently stream power at unprecedented spatial resolution, opening promising and novel opportunities to investigate river geomorphic processes and forms. The present paper investigates the suitability of map-derived information on total and specific stream power (SSP) to identify dominant processes within the channel (i.e. erosion, transport or deposition). SSP has been already used to identify a threshold for channel stability. This paper tests this knowledge and investigates whether or not attributes of stream power profiles are statistically correlated with distinctive field morphological forms. Two gravel bed single-thread English rivers are used as case studies, the Lune and the Wye. Available deposition and erosion features surveyed in the field from 124 different locations are used to classify channel reaches as erosion, transport or deposition dominated. Meaningful patterns emerge between the stream power attributes and the field-based channel classification. An SSP threshold, which erosion is triggered, compares favourably with the ones in the literature. Information about upstream stream power profiles helps to determine the dominant processes. The joint configuration of local and upstream stream power information uniquely classifies reaches into four classes of different sensitivity to erosion and deposition. Copyright © 2013 John Wiley & Sons, Ltd.

Downstream geomorphic variation and local bedrock influence of a steep transitional river: Blue Ridge to Piedmont, South Carolina

Spatial patterns in geomorphic variations are examined in a river transition from the Southern Blue Ridge to the Piedmont physiographic regions. Downstream hydraulic geometry (DHG), fining of bed material, and changes in reach-scale channel-bed morphology (bedforms) were sampled and analyzed. DHG power functions were well developed (r2 > 0.75 for channel area, width, and depth). Bed material showed a general downstream exponential decrease in caliber (from 940 mm to sand). However, variations within the general downstream trends reflect local variations and a rapid transition in hydraulic variables and bedforms at a key zone with substantial tributary inputs, decreases in slope, and a punctuated longitudinal profile. Structurally controlled bedrock knickpoints are associated with anomalous spatial patterns of bedforms and can be distinguished through relationships between dimensionless sediment transport capacity and sediment supply using a sediment regime diagram that is independent of drainage area. Plots of relative grain submergence (R/D84), relative form submergence (R/H), Darcy–Weisbach friction factor (f), and slope vs. area also reveal trends that suggest local factors that are missed by downstream hydraulic progressions. The findings of this study corroborate the utility of scale-independent methods, especially in mountain or transitional environments where fluvial controls may be longitudinally sporadic.

Residual Sediment Fluxes in Weakly-to-Periodically Stratified Estuaries and Tidal Inlets

Abstract In this idealized numerical modeling study, the composition of residual sediment fluxes in energetic (e.g., weakly or periodically stratified) tidal estuaries is investigated by means of one-dimensional water column models, with some focus on the sediment availability. Scaling of the underlying dynamic equations shows dependence of the results on the Simpson number (relative strength of horizontal density gradient) and the Rouse number (relative settling velocity) as well as impacts of the Unsteadiness number (relative tidal frequency). Here, the parameter space given by the Simpson and Rouse numbers is mainly investigated. A simple analytical model based on the assumption of stationarity shows that for small Simpson and Rouse numbers sediment flux is down estuary and vice versa for large Simpson and Rouse numbers. A fully dynamic water column model coupled to a second-moment turbulence closure model allows to decompose the sediment flux profiles into contributions from the transport flux (product of subtidal velocity and sediment concentration profiles) and the fluctuation flux profiles (tidal covariance between current velocity and sediment concentration). Three different types of bottom sediment pools are distinguished to vary the sediment availability, by defining a time scale for complete sediment erosion. For short erosion times scales, the transport sediment flux may dominate, but for larger erosion time scales the fluctuation sediment flux largely dominates the tidal sediment flux. When quarter-diurnal components are added to the tidal forcing, up-estuary sediment fluxes are strongly increased for stronger and shorter flood tides and vice versa. The theoretical results are compared to field observations in a tidally energetic inlet.

Water cycle evolution in the Haihe River Basin in the past 10000 years

The water shortage problem in the Haihe River Basin is the most severe in China, and has restricted its economic development. Over-extraction of groundwater has been very severe in the past 30 years. To solve this problem, scientific decisions should be made from a historical perspective. It is important to describe water cycle evolution in the Haihe River basin over the past 10000 years. Datasets of paleoclimate, paleogeography, palynoflora, historical record, isotopic abundance ratio and content were collected for research on different time scales. Some interesting conclusions were drawn by a comprehensive analysis method. First, radiation was the intrinsic force driving the evolution of water cycle. Generally, precipitation increased with temperature. Second, precipitation was high during 8 ka-5 ka B.P., the so-called Yangshao warm period of the Middle Holocene, which recharged the major part of the Quaternary groundwater. Third, heavy floods during this period transported sediment to the seaside, forming the Coastal Plain where cities such as Tianjin, Huanghua, Cangzhou are now located. In the last 3000 years, intermittent moderate floods did not have enough energy to transport sediment to the sea. Rivers usually overflowed in the piedmont region of the Taihang Mountains, and sediment deposited there formed the Piedmont Plain, where locate Shijiazhuang, Xingtai, Handan, Baoding and other cities. Precipitation had a high correlation with temperature in Haihe River Basin in the past 10000 years: the high temperature usually coupled with high precipitation. Today precipitation in the Haihe River Basin is relatively low, owing to low temperature. This study reveals the relationship between temperature, precipitation and river networks in the past 10000 years in Haihe River Basin, which has great scientific and practical importance in understanding the current water circulation and water shortage.

A simplified approach to address turbulence modulation in turbidity currents as a response to slope breaks and loss of lateral confinement

Turbidity currents traversing canyon-fan systems flow over bed slopes that decrease in the downstream direction. This slope decrease eventually causes turbidity currents to decelerate and enter a net-depositional mode. When the slope decrease is relatively rapid in the downstream direction, the turbidity current undergoes a concomitantly rapid and substantial transition. Similar conditions are found when turbidity currents debouch to fan systems with loss of lateral confinement. In this work a simplified approach to perform direct numerical simulation of continuous turbidity currents undergoing slope breaks and loss of lateral confinement is presented and applied to study turbulence modulation in the flow. The presence of settling sediment particles breaks the top–bottom symmetry of the flow, with a tendency to self-stratify. This self-stratification damps turbulence, particularly near the bottom wall, affecting substantially the flow’s ability to transport sediment in suspension. This work reports results on two different situations: turbidity currents driven by fine and coarser sediment flowing through a decreasing slope. In the case of fine sediment, after the reduction in the slope of the channel, the flow remains turbulent with only a modest influence on turbulence statistics. In the case of coarse sediments, after the change in slope, turbulence is totally suppressed.

Influence of bed patchiness, slope, grain hiding, and form drag on gravel mobilization in very steep streams

AbstractSteep streams are a major portion of channel networks and provide a link to transport sediment from hillslopes to lower gradient rivers. Despite their importance, key unknowns remain, perhaps foremost of which is evaluating in steep streams empirical laws for fluvial sediment transport developed for low‐gradient rivers. To address this knowledge gap, we painted sediment in situ over 3 years to monitor incipient sediment motion and sediment‐patch development in five small (drainage areas of 0.04–2 km2) and steep (slopes of 5–37%) tributaries of Elder Creek, California, United States. We found that channel beds organized into size‐sorted sediment patches which displayed active fluvial transport of gravel annually, consistent year‐to‐year patch median grain sizes, partial transport of bed material, and significantly higher values of critical Shields stress for incipient sediment motion compared to that observed for lower gradient rivers. The high critical Shields stresses (up to ≈0.5 for the median grain size) agree within a factor of ~3 to theoretical predictions which account for slope‐dependent hydraulics, grain hiding, and sediment patches. For grains of approximately the same size as the roughness length scale, slope‐dependent hydraulics and bed patchiness are the dominant controls on critical Shields stress values, while grain hiding is important for grains larger or smaller than the roughness length scale. Form drag exists in our monitored tributaries but has a smaller influence than the above effects. Our field observations show fluvial processes contribute to sediment mobilization in steep channels which are often considered to be dominated by debris flows.

Analysis of Plio-Quaternary deep marine systems and their evolution in a compressional tectonic regime, Eastern Black Sea Basin

Facies architecture of submarine fans and channel–levee complexes in the Eastern Black Sea Basin and their evolution from the Late Miocene until the present day are studied using a three-dimensional seismic data set covering an area of approximately 1161 km2. The interpretation of the observations reveals the outcome of the changing interplay between rate of sedimentation and compressional tectonism in the area through time.The Upper Tertiary sedimentary succession in the Eastern Black Sea Basin is characterized by various depositional elements of northeasterly sourced turbidite systems that were deposited in a progressively deforming basin at settings ranging from lower to upper slope. Depositional elements interpreted from seismic character and geometry include canyons, canyon-confined channels, levees, mass transport complexes, sediment waves, sheets and hemipelagic drapes.Two anticlines formed in a compressional tectonic regime subdividing the study area into three mini-basins acted as sediment barriers and controlled the geometry of the basin, and thus, the accommodation space, throughout the Plio-Quaternary period. Sheets that were deposited due to abrupt reduction in structural slope gradients and knickpoints that mark the boundary between site of incision and site of deposition within canyons both have displayed southwestward migration through time, which clearly reflects the basinward advance of compressional deformation in the Eastern Black Sea Basin.

Influence of basin connectivity on sediment source, transport, and storage within the Mkabela Basin, South Africa

Abstract. The management of sediment and other non-point source (NPS) pollution has proven difficult, and requires a sound understanding of particle movement through the drainage system. The primary objective of this investigation was to obtain an understanding of NPS sediment source(s), transport, and storage within the Mkabela Basin, a representative agricultural catchment within the KwaZulu–Natal Midlands of eastern South Africa, by combining geomorphic, hydrologic and geochemical fingerprinting analyses. The Mkabela Basin can be subdivided into three distinct subcatchments that differ in their ability to transport and store sediment along the axial valley. Headwater (upper catchment) areas are characterized by extensive wetlands that act as significant sediment sinks. Mid-catchment areas, characterized by higher relief and valley gradients, exhibit few wetlands, but rather are dominated by a combination of alluvial and bedrock channels that are conducive to sediment transport. The lower catchment exhibits a low-gradient alluvial channel that is boarded by extensive riparian wetlands that accumulate large quantities of sediment (and NPS pollutants). Fingerprinting studies suggest that silt- and clay-rich layers found within wetland and reservoir deposits of the upper and upper-mid subcatchments are derived from the erosion of fine-grained, valley bottom soils frequently utilized as vegetable fields. Coarser-grained deposits within these wetlands and reservoirs result from the erosion of sandier hillslope soils extensively utilized for sugar cane, during relatively high magnitude runoff events that are capable of transporting sand-sized sediment off the slopes. Thus, the source of sediment to the axial valley varies as a function of sediment size and runoff magnitude. Sediment export from upper to lower catchment areas was limited until the early 1990s, in part because the upper catchment wetlands were hydrologically disconnected from lower parts of the watershed during low to moderate flood events. The construction of a drainage ditch through a previously unchanneled wetland altered the hydrologic connectivity of the catchment, allowing sediment to be transported from the headwaters to the lower basin where much of it was deposited within riparian wetlands. The axial drainage system is now geomorphically and hydrologically connected during events capable of overflowing dams located throughout the study basin. The study indicates that increased valley connectivity partly negated the positive benefits of controlling sediment/nutrient exports from the catchment by means of upland based, best management practices.

Non-hydrostatic modeling of cohesive sediment transport associated with a subglacial buoyant jet in glacial fjords: A process-oriented approach

Fine sediment transport produced by a subglacial freshwater discharge is simulated with a 2D non-hydrostatic model. The circulation pattern revealed a buoyant jet issuing from the aperture representing the subglacial tunnel, a vertically buoyant plume and a surface gravity current forming part of an estuarine circulation. Momentum-dominated experiments are more sensitive to the presence of suspended sediment in the discharge. At low concentrations, the sediment stays in the vertical plume and surface gravity current, and its concentration is progressively decreased by mixing but no settling is observed through the water column. At high concentrations, the sediment settles in the far field and is transported back to the near field by the landward estuarine current. Sediment settled from the surface layer through convective sedimentation, a process that was more effective than flocculation to transport sediment vertically, and showed vertical velocities faster than 1.0×10-2ms−1. Implications of these results are discussed.

Modeling of Erosion at Göksu Coasts

Numanoğlu Genç, A., İnan, A., Yılmaz, N. and Balas, L., 2013. Modeling of Erosion at Göksu Coasts.Göksu coastal area, located in the south of Silifke County of Mersin on the coastal plain formed by Göksu River, is one of the Specially Protected Areas with an area of almost 15000 hectares and at an altitude of 0–5 m. The Eastern and Western parts of the Göksu river mouth along the Mediterranean coast and the coast of Paradeniz Lagoon are suffering significantly from erosion. As a result of the coastal erosion and the consequent coastal recession problem along the coasts of Göksu, agricultural fields located near the coast are being lost, and especially the narrow barrier beach which separates Paradeniz Lagoon from the sea is getting narrower, creating a risk of uniting with the sea, thus disappearing of the Lagoon. In order to propose solutions for the problem, and to protect the coastal zone and the habitats of Göksu against coastal erosion, coastal dynamic processes and sediment transport characteristics of the region causing the erosion should be investigated and identified. Therefore, longshore sediment transport and suspended sediment transport in Göksu coastal area are examined. First of all, the wind and wave climate of the study area are determined. Then, current pattern, wave propagation, and longshore sediment movements are modeled numerically utilizing three dimensional hydrodynamic transport model HYDROTAM-3D. HYDROTAM-3D is a three (3) dimensional numerical Hydrodynamic and Transportation Model which simulates current patterns due to wind and wave actions, pollutant transport, wave propagation over mild slopes, and longshore sediment transport rates. Model includes hydrodynamics, transport, turbulence, wind and wave climate and wave propagation sub models. HYDROTAM 3D, is developed using “cloud computing” architecture and tightly integrated with Geographic Information System. The study outputs will be used for the determination of the coastal erosion.

The reverse sediment transport trend between abandoned Huanghe River (Yellow River) Delta and radial sand ridges along Jiangsu coastline of China—an evidence from grain size analysis

To reveal the sediment transporting mechanism between the abandoned Huanghe River (Yellow River) Delta and radial sand ridges, "End Member" Model and grain size trend analysis have been employed to separate the "dynamic populations" in the surficial sediment particle spectra and to determine the possible sediment transporting pathway. The results reveal four "dynamic subpopulations" (EM1 to EM4) and two reverse sediment transporting directions: a northward transport tend from the radial sand ridges to mud patch, and a southward transport trend in deep water area outside the mud patch. Combined with the published hydrodynamic information, the transporting mechanism of dynamic populations has been discussed, and the main conclusion is that the transporting of finer subpopulations EM1 and EM2 is controlled by the "anticlockwise residual current circulation" forming during tidal cycle, which favor a northward transporting trend and the forming of mud patch on the north of radial sand ridges, while the transporting of coarser EM3 is mainly controlled by wind driven drift in winter, which favors a southward transporting direction.

Transport‐limitations on fluvial sediment supply to the sea

The ability to understand and predict the flux and fate of sediment delivered to the sea by rivers remains an outstanding scientific challenge. Approaches to this challenge are necessarily synthetic, spanning wide ranges in spatial and temporal scales. Here a conventional sediment transport theory used by engineers and sedimentologists at reach and channel scales is applied at the basin scale. Specifically, a straightforward expression proposed by Bagnold and modified accordingly predicts the observed importance of combined wetness and steepness of a source basin as a control of sediment supply to the sea. The reasonable, key assumption underlying the application of sediment transport theory in this context is that the river‐mouth sites for which suspended‐sediment loads are reported are alluviated, and thus characterized by transport‐limited flux of sediment. This analysis also indicates the potential significance of additional, as yet poorly documented factors constraining sediment supply to the sea. These factors, some of which appear to covary systematically with climate, include river‐profile concavity, river‐mouth channel width and friction, and the characteristic size of sediment in transport.

Study on Critical Conditions of Scour-and-Siltation in Flood Seasons of Ningmeng Reach in the Upper Yellow River

Based on the actual measurement datum in flood seasons in the Ningmeng Reach of the Upper Yellow River Reach, Authors search the law of erosion and deposition and sediment transport characteristics with built the quantitative correlation of erosion and deposition efficiency and water and sediment combination (sediment coming coefficient, sediment concentration/discharge)of the flood season. When the sediment coming coefficients of flood season is0.0038kg.s/m6 the Ningmeng reach in relative equilibrium state. The Ningmeng reach has the characteristic of “the more sediment coming, the more depositing, the more sediment transporting”, the sediment discharge increases with sediment concentration of coming flow increasing. The result of these research can be used in the Yellow River management and alluvial channel regulation.

The influence of landscape configuration upon patterns of sediment storage in a highly connected river system

Orthoimages are used to analyze the influence of valley width, channel slope, and the area of landslides that deliver sediment to valley floors upon the downstream pattern of sediment storage in the Liwu basin, eastern Taiwan. Confined valley settings dominate this steep, deeply dissected, uplifting mountainous basin. Although they occupy 82% of the whole channel network, sediment storage is limited in these reaches. Partly confined valley settings are restricted to relatively short reaches of two tributary systems. Over 95% of sediment storage in the Liwu River is found within the short alluvial section of laterally unconfined valley close to the river mouth. Lateral bars are the primary features associated with sediment storage in confined reaches (54% in total volume), while floodplains dominate the partly confined and laterally unconfined reaches (95% in total volume). Downstream patterns of sediment storage are controlled primarily by valley confinement (i.e., valley width) and landscape configuration. Channel slope and locations of contemporary landslides are not key determinants of sediment storage patterns. Sediment accumulation at confluence zones is not determined by the catchment area of tributaries or by landslide area; rather, it is determined by valley confinement of the trunk stream at the confluence and the associated downstream sequence of river types. Sediment conveyance is very effective within this highly connected river system.

Relationships between block quarrying, bed shear stress, and stream power: A physical model of block quarrying of a jointed bedrock channel

We examine interactions among substrate characteristics, hydraulic forces, and erosive processes acting on a jointed, resistant substrate in a flume experiencing supercritical flow. We conducted six experimental runs with no sediment in transport, constant slope, varying discharge, varying channel width, and varying geometry of concrete blocks forming the channel bed. The initial downstream boundary was a vertical knickpoint lip perpendicular to flow. Observed changes in bed morphology occurred primarily by episodic horizontal knickpoint retreat. The knickpoint lip can develop a curve that reflects interlocking of the irregular boundaries between otherwise physically disjointed blocks during rotation of the blocks. Sometimes a block acts like a keystone in an arch and mobilization of the key block facilitates mobilization of the linked blocks on either side, resulting in a large magnitude event. In contrast to previous studies where blocks were vertically plucked, blocks were removed by sliding from the knickpoint. Building on previous work, we develop a theoretical force threshold for sliding block mobilization, which suggests that increased block side length parallel to flow increases block stability, whereas increased side length perpendicular to flow decreases block stability. Stream power was also linked to observed erosion rates as a function of block length, consistent with the idea that block loosening rates play a key role in controlling average erosion rates. Inferred amplification of bed shear stress and pressure at the knickpoint lip, stream power, and joint spacing correlate with the rate of block erosion. The results, although limited in scope and scale, suggest a linear relationship between bed shear stress and stream power with the rate of block erosion. Block sliding, especially at near-vertical knickpoints, can play a key or even dominant role in the morphologic dynamics of the river channel.