Sediment Transport Capability Research Articles

Future Sediment Transport Ability and its Consequences in the Urbanized River Basin

The urbanization process of the Kathmandu Valley has a significant impact on LULC change, river runoff, and sediment transport capability. The historical sediment flow pattern indicates that the sediment transport capacity of the basin has increased even when precipitation and river discharge decreased. So, the sediment regression model is developed in this study in relation to discharge, precipitation, and built-up area change. Model parameters are calibrated and validated through the measured sediment discharge of the basin and the performance of the model is evaluated through NSE, PBIAS, and R2. In the future, the sediment transport capacity of the channel is projected for average monthly, maximum, and minimum flow conditions by +4.33%, +6%, and -2.66% respectively per decade due to the rise in the urban area (+6% per decade). Increasing the rigid ground surface through urbanization reduces the sediment generation through the watershed and balances the sediment transport capability, excess erosion is produced in the river channel causing a change in the river morphology. The findings of this study will be useful for planning and management of the river basin and the river structures.

Empirical roughness coefficients for moderate floods in an open conduit cave: Fullers stream canyon, Culverson Creek Cave System, West Virginia

Open conduit modeling of cave stream floods can yield useful information about water velocities and shear stresses, which can in turn be used to estimate sediment transport capabilities. All such calculations require roughness coefficients for estimating energy losses and a priori knowledge of either discharge or flow depths to set model boundary conditions. However, the difficulties associated with observing in-cave floods generally preclude measuring discharge; roughness coefficients must be assumed based on channel properties. To overcome these challenges, we monitored stream flow depths in Fullers Cave, Greenbrier County, West Virginia using pressure transducers, and simultaneously measured stage and discharge in a karst window immediately upstream of the cave. Five pressure transducers were deployed opportunistically along a 93-meter-long reach in a 10+ meter high canyon averaging 1.5 to 3 meters wide. Stage-discharge relationships were determined for the karst window using an electromagnetic flow meter for floods with peak discharges of 1.66 m3 s-1 or less. The collected data was used to obtain the empirical Manning’s n roughness values, head losses, and energy gradients. Calculated floodwater velocities are comparable to values obtained from scallops on passage walls. Major energy losses were observed where breakdown partially occludes the passage. At peak flow, Manning n values average 0.053 for reaches typified as cobble-floored canyons, but n was 0.069 in the breakdown reach. Roughness values declined exponentially with increasing discharge, but friction slopes calculated using head losses show more complex relationships with discharge. Notably, n values back calculated using bed gradients differ from those calculated using measured head losses by as little as 12%, so the use of bed gradients in roughness estimations will generally yield reasonable approximations of flow conditions. Fullers Cave experiences significantly larger open conduit floods than we observed, so additional work is needed to estimate roughness coefficients for higher discharges. Our empirical roughness coefficients can be applied to similar cave passages in other caves and contexts, including modeling slot canyon-like channels, and our methods demonstrate a technique for measuring hard to obtain data. The addition of data for open conduit conduits significantly expands the range of environments that can be modeled using empirical data beyond pipe-full caves. Applications include studying flooding, sediment transport, and bedrock erosion process. All of these topics will be addressed in Fullers in the future.

Spatial variation of flow characteristics in a subarctic meandering river in ice‐covered and open‐channel conditions: A 2D hydrodynamic modelling approach

AbstractTo be able to understand year‐round river channel evolution both at present and in the future, the spatial variation of the flow characteristics and their sediment transport capabilities under ice cover need to be detected. As the measurements done through cross‐sectional drill holes cover only a small portion of the river channel area, the numerical simulations give insight into the wider spatial horizontal variation of the flow characteristics. Therefore, we simulate the ice‐covered flow with a hydrodynamic two‐dimensional (2D) model in a meandering subarctic river (Pulmanki River, Finland) in mid‐winter conditions and compare them to the pre‐winter open‐channel low flow situation. Based on the simulations, which are calibrated with reference measurements, we aim to detect (1) how ice‐covered mid‐winter flow characteristics vary spatially and (2) the erosion and sedimentation potential of the ice‐covered flow compared to open‐channel conditions.The 2D hydrodynamic model replicated the observed flow characteristics in both open‐channel and ice‐covered conditions. During both seasons, the greatest erosional forces locate in the shallow sections. The narrow, freely flowing channel area found in mid‐winter cause the main differences in the spatial flow variation between seasons. Despite the causes of the horizontal recirculating flow structures being similar in both seasons, the structures formed in different locations depended on whether the river was open or ice covered. The critical thresholds for particle entrainment are exceeded more often in open‐channel conditions than during ice‐covered flow. The results indicate spatially extensive sediment transport in open‐channel conditions, but that the spatial variability and differences in depositional and erosional locations increase in ice‐covered conditions. Asymmetrical bends and straight reaches erode throughout the year, whereas symmetrical, smaller bends mainly erode in open‐channel conditions and are prone to deposition in winter. The long ice‐covered season can greatly affect the annual morphology of the submerged channel. © 2019 John Wiley & Sons, Ltd.

Effects of thawed depth on the sediment transport capacity by melt water on partially thawed black soil slope

AbstractThis study proposed an apparatus for measuring the sediment transport capacity, which is an important parameter for rill erosion prediction and modeling. Laboratory experiments were conducted to measure the sediment transport capacity of partially thawed black soil slope under different hydraulic conditions and thawed depths (five slope gradients of 5°, 10°, 15°, 20°, and 25°; three flow discharges of 1, 2, and 4 dm3 min−1; and four thawed depths of 1, 2, 5, and 10 cm). The effect of thawed depth on sediment transport capacity was quantified with experimental data under different slope gradients and flow discharges. A quadratic model was used to relate sediment transport capacity to thawed depth, slope gradient, and flow discharge, and its key factors that influenced sediment transport capacity were determined by using stepwise regression. Results showed that sediment transport capacity decreased with the increase of thawed depth from 1 to 5 cm, but it tended to be steady when the thawed depth was greater than 5 cm. Model‐fitting results showed that sediment transport capacity was positively correlated with slope gradient and flow discharge but negatively correlated with thawed depth. The proposed method and experimental device solved the difficulties of insufficient sediment supply on the measurement of sediment transport capability, and it can be used to measure the sediment transport capacity of concentrated water flow under different conditions of slope gradient, thawed depth, and flow discharge. The method is helpful to the research of erosion process of partially thawed soil under concentrated water.

Effect of rainfall moving direction on surface flow and soil erosion processes on slopes with sealing

Although rainfall characteristics play important roles in runoff generation and soil erosion, our understanding about how rainfall moving direction impacts surface flow and soil erosion on slopes considering spatial process of soil surface sealing is still poor. In this study, a series of laboratory experiments was conducted using a soil flume and a movable rainfall simulator to investigate this impact. Two rainfall moving directions (i.e. upslope-moving and downslope-moving) and two soil surface moisture conditions (i.e. dry runs with no antecedent rainfall and wet runs with antecedent rainfall) were considered in the experiments with different slope gradients and rainfall intensities. The results showed that the upslope-moving rainfalls generated more surface flow from 25% to 700% and less soil erosion than the downslope-moving rainfalls in the dry runs due to the different spatial developing processes of soil surface sealing. The difference between the runoff coefficients of the two moving direction rainfalls decreased remarkably (more than 50%) with slope gradient increasing from 15° to 25°. In the wet runs, surface flow was similar for the upslope-moving and downslope-moving rainfalls, as all of the soil surface had been sealed before the experiments. Soil erosion in the downslope-moving rainfalls was larger than that in the upslope-moving rainfalls due to higher sediment transport capability of the surface flow. For both rainfall moving directions with same rainfall conditions, the total soil erosion in a dry run was mostly larger than that in a wet run because of less erodible soil particles on the sealed slope in the wet run. The result of this study implied that different rainfall moving directions can lead to distinct spatial processes of soil surface sealing and caused large differences in surface flow and soil erosion processes on slopes.

RANS-based simulation of wave-induced sheet-flow transport of graded sediments

A one-dimensional vertical (1DV) turbulence-closure flow model, coupled with sediment transport capabilities, is extended to incorporate graded sediment mixtures. The hydrodynamic model solves the horizontal component of the incompressible Reynolds-averaged Navier–Stokes (RANS) equations coupled with k–ω turbulence closure. The sediment transport description includes both bed and suspended load descriptions. So-called high-concentration effects (turbulence damping and hindered settling velocities) are likewise included. The sediment transport model treats the bed and suspended load individually for each grain fraction, including effects associated with increased exposure of larger particles within a mixture. The suspended sediment transport model also makes use of modified reference concentration approach, wherein reference concentrations computed individually for each fraction are translated to a common level, conveniently enabling use of a single computational grid for the simulation of suspended sediments. Parametric study shows that these two effects combine to help alleviate an otherwise systematic tendency towards over- (under-) predicted transport rates for fine (coarse) sand fractions. The sediment transport model is validated against sheet-flow experimental oscillatory tunnel measurements beneath velocity-skewed wave signals, and demonstrates similar accuracy (transport rates generally within a factor of two) for both graded and uniform sands. The model is likewise validated against an extensive data set involving sheet-flow transport beneath acceleration-skewed wave signals (limited to uniform sands). It is then utilized to study potential effects of gradation on the net transport beneath such flows. The simulations suggest that gradation effects can both increase, as well as decrease, the total transport rate, depending largely on the behavior of the fine sand fraction. The model is implemented within the Matlab environment, and is freely available upon request to the corresponding author.

Sediment Transport Capacity Carries Many Meanings

The current definitions of sediment transport capability don't match up with observations of actual geomorphic systems.

Testing the Effects of Detachment Limits and Transport Capacity Formulation on Sediment Runoff Predictions Using the U.S. Army Corps of Engineers GSSHA Model

The physics-based Gridded Surface Subsurface Hydrologic Analysis (GSSHA) model was developed by the U.S. Army Corps of Engineers for hydrologic, sediment transport, and water quality analyses. GSSHA simulates erosion and transport of sediments on the overland flow plain based on rainfall intensity and overland flow depth and velocity. The original sediment transport capabilities in GSSHA were taken from the GSSHA predecessor, CASC2D-SED. Independent testing of the sediment transport methods in CASC2D-SED by researchers identified several deficiencies in the formulation that caused significant overestimation of sediment yield during hydrologic events that were much larger than a calibration event. Sediment detachment limits and a variety of overland sediment transport equations were incorporated into the GSSHA model to address these deficiencies. This paper presents an evaluation of these modifications in terms of GSSHA sediment yield predictions of both single-event and summer growing season sediment yields. Simulation results are compared with research-quality sediment discharge data set from the USDA Goodwin Creek Experimental Watershed (GCEW). Results show that the reformulated GSSHA sediment transport model predicts event-total sediment discharge volume within (±) 50% over hydrologic events that vary by three orders of magnitude. The transport capacity method selected for use in the simulation had a large effect on the model results.

Advantages of beachrock slabs for interpreting high-energy wave transport: Evidence from Ludao Island in south-eastern Taiwan

Powerful typhoons frequently affect eastern Taiwan. On Dabaisha beach on the SW coast of Ludao Island, a small volcanic island lying SE off mainland Taiwan, the presence of numerous beachrock slabs provides evidence of the sediment transport capabilities of high-energy waves generated by these storms. With a well-defined beachrock source from which the slabs were derived, it is easy to differentiate clasts transported in run-up or backwash flow based on their current position relative to the outcrop. In order to estimate the wave-generated flow velocities from the measured beachrock slabs, the hydrodynamic equations for boulder transport by Nandasena et al. (2011) have been rearranged so that they are appropriate for this particular geomorphic setting, where exposed in situ beachrock outcrops liberate clasts which may then be transported either by run-up onto the beach or backwash flow onto adjacent reef platforms. Such settings are common on tropical coastlines with fringing coral reefs and beaches comprising mostly biogenic sediments. In the Dabaisha beach case, the lowest flow velocities required to transport all measured beachrock slabs from their source outcrop to current positions are 2.18–3.16m/s for run-up and 1.76–3.24m/s for backwash. With a discussion of advantages and limitations on the use of beachrock clasts for interpreting wave behaviour, this paper presents another proxy for studying high-energy wave events that is highly suitable for certain carbonate-rich coastlines.

Discussion on the Mechanism of the Differences of Sediment Transport Capability of the Different Alluvial Reaches in the Yellow River

Abstract According to the principles of hydraulics,fluvial processes study and river sediment dynamics, the authors discuss the mechanism of different capabilities of sediment transport of different alluvial reaches in the Yellow River. The results are: the main reason of low sediment transport capability in Ningmeng Reach is weak hydrodynamic power, the narrow and deep cross-section profile determines the high sediment tranport capability and the frequent hyper- concentrated floods during which the sediment settling velocity reduced by the increasing of hydro-viscosity and density resulting from high sediment concrentration also improve the capabiliity of sediment transort in the Lower Weihe, in the Lower Yellow River the strong hydrodynamic power is the most important factor conducing the high sediment transport capability, for the Xiaobeiganliu reach though the hydro-dynamic power is strong the big particle size of suspended sediments reduces the sediment transport capability.

Sediment-transport modeling on Southern Californian shelves: A ROMS case study

Suspended sediment-transport processes in Santa Monica and San Pedro Bay are analyzed using the sediment-transport capabilities of the Regional Oceanic Modeling System ( roms). A one-month simulation for December 2001 has been carried out with a set of nested domains. The model inputs include tides, winds, surface waves, and idealized initial sediment conditions for sand and non-cohesive silt. Apart from the control run, the sensitivity of the results to surface waves, ripple roughness and bed armoring has been analyzed. From the control experiment, the horizontal transport of sand turns out to be limited to within a few km of the nearshore erosion zones. During high wave events, silt is transported over further distances and also partly offshelf in distinct plumes. The effectiveness of horizontal silt transport depends strongly on vertical mixing due to both surface wind stress and wave-enhanced bottom stress. High wave events coincident with strong winds (hence strong vertical mixing) are the most optimal conditions for sediment-transport. Excluding wave effects in the simulation shows that surface waves are the dominant factor in resuspending bed material on the Southern Californian shelves. The sensitivity experiments also show that the direct influence of additional ripple roughness on erosion and deposition is relatively weak. Switching off bed armoring locally results in increases of near-bottom concentrations by a factor of 20 for silt and a factor of 5 for sand as well as stronger spatial gradients in grain size.

A model study of tidally induced suspended sediment transport in the Iberian shelf edge region

Across shelf suspended sediment transport due to tides is investigated using a three-dimensional baroclinic hydrodynamic model, including a sediment transport capability, and parameterizing sub-grid scale diffusion using a turbulence energy model. The model in cross shelf form, with topography characteristic of the shelf edge off the west coast of Spain, is used to examine sediment movement due to both barotropic and baroclinic tides and an along-shelf flow. Calculations showed that the bed stress due to the barotropic tide and an along-shelf flow exceeded the critical bed stress for part of the tidal cycle, leading to sediment suspension. The across shelf residual flow (due to tidal rectification and the bottom Ekman transport associated with the along-shelf flow) was on shelf in the surface layer and off shelf near the bed and produced a net off shelf sediment transport in the bottom boundary layer. When a fixed stratification representing the thermocline was imposed, this inhibited the upward diffusion of sediment, thereby increasing its concentration in the bottom boundary layer. Comparison with and without stratification allowed its influence upon sediment concentration to be quantified. Calculations in which the stratification evolved with the flow field produced internal tides with an associated increase in current amplitude at a number of locations, leading to greater spatial variability in the tidal residual, and an additional residual due to the across shelf tidally induced thermal front. Increased diffusion and vertical velocity associated with the internal tide produced a thickening of the sediment bottom boundary layer. A detailed examination of terms in the sediment transport equation enabled the importance of each in different regions to be quantified. It showed that in the near bed layer, the main balance was between vertical diffusion and settling. However, sediment concentration in the upper part of the water column was increased by the presence of the internal tide due to enhanced vertical advection and diffusion into the region. Changes in vertical stratification, were found to influence both the horizontal and vertical distributions of sediment, due to its influence upon the internal tide.

Sediment Deposition within Fry Emergence Traps: A Confounding Factor in Estimating Survival to Emergence

We provide evidence that the effects of sediment infiltration and deposition within fry emergence traps can lead to a potential negative bias when estimating survival to emergence (STE) of salmonid fry. Fry emergence traps were placed over 12 redds of brown trout Salmo trutta located in sections of three streams in the upper Clark Fork River system in Montana. The redds were capped in March 1989 and monitored through June 1989. During this period, sediment deposition became noticeable inside 8 of the 12 traps. During the final removal of the traps, substrate core samples were collected from a location inside and outside of each emergence trap. Substrate size gradation analysis indicated that concentrations of fine sediments (≤0.84 mm in diameter) were significantly higher in samples collected inside the traps than outside. These results suggested that the local sediment transport capacity was reduced within the emergence traps, resulting in increased deposition of fines. An understanding of the hydrology, ambient sediment concentrations, and sediment transport capabilities of river systems is important when considering the use of fry emergence traps. Without consideration for this potential confounding factor, STE estimates that involve the use of fry emergence traps may underestimate actual STE values.

FACTORS CONTROLLING CHANGES TO AN OPEN COAST BEACH

A study of historical information and field measurements in Sargent Beach, Texas, reveal that the shoreline is retreating with historic rates increasing from -10 feet per year in the late 1800's to -31 feet per year (-9.8 m/year) in the early 1970's. The cause of this erosion is the lack of an adequate sand supply to the beach zone. This sand deficiency is due to: a) reduced updrift sand input to the coast by the Brazos River beginning in 1945 and caused by decreased sediment transport capability of the river, b) increased sand storage in the Brazos Delta encouraged by jetties and vegetation, and c) possible offshore losses of sand due to hurricane wave energy focusing on the Brazos Delta in conjunction with river jetting during peak river flows.

Discussion of “Sediment Transport Capability in Erodible Channels”

Discussion of “Sediment Transport Capability in Erodible Channels”

Influence of turbidity currents upon basin waters : Emery, K. O., J. Hulsemann and K. S. Rodolfo 1962 Limnol. & oceanogr. 7(4): 439–446

Powerful typhoons frequently affect eastern Taiwan. On Dabaisha beach on the SW coast of Ludao Island, a small volcanic island lying SE off mainland Taiwan, the presence of numerous beachrock slabs provides evidence of the sediment transport capabilities of high-energy waves generated by these storms. With a well-defined beachrock source from which the slabs were derived, it is easy to differentiate clasts transported in run-up or backwash flow based on their current position relative to the outcrop. In order to estimate the wave-generated flow velocities from the measured beachrock slabs, the hydrodynamic equations for boulder transport by Nandasena et al. (2011) have been rearranged so that they are appropriate for this particular geomorphic setting, where exposed in situ beachrock outcrops liberate clasts which may then be transported either by run-up onto the beach or backwash flow onto adjacent reef platforms. Such settings are common on tropical coastlines with fringing coral reefs and beaches comprising mostly biogenic sediments. In the Dabaisha beach case, the lowest flow velocities required to transport all measured beachrock slabs from their source outcrop to current positions are 2.18–3.16 m/s for run-up and 1.76–3.24 m/s for backwash. With a discussion of advantages and limitations on the use of beachrock clasts for interpreting wave behaviour, this paper presents another proxy for studying high-energy wave events that is highly suitable for certain carbonate-rich coastlines.