Bed Material Load Research Articles

A novel mixing mechanism in sinuous seafloor channels: Implications for submarine channel evolution

Previous experimental studies of density currents in sinuous seafloor channels have almost exclusively studied hydrodynamics either by considering time independent, instantaneous, flow measurements or by compiling time-averaged flow measurements. Here we present a novel study of the time dependent dynamics of a density driven flow in a sinuous channel fed by a source of constant discharge. The experiments show that whilst source conditions may be temporally steady, flow conditions are temporally unsteady with timescales of flow variation driven by flow interaction with channel topography. Temporal variations reveal that both downstream and cross-stream flows vary significantly from time average observations and predictions, across scales larger than those predicted for turbulence in equivalent straight channels. Large-scale variations are shown to increase the average production of turbulence across the height of the flow, providing a new mechanism for enhanced mixing of sediment within gravity currents. Further such large-scale variations in flow conditions are recorded in the change in orientation of near-bed secondary flow, providing a plausible mechanism to reduce the cross-stream transport of bedload material and explain the ultimate stabilisation of sinuous seafloor channel systems.

Reaction and relaxation in a coarse-grained fluvial system following catchment-wide disturbance

The Waiapu River catchment (drainage area of 1734-km2) is one of the most prolific conveyors of sediment in the world, annually delivering roughly 35Mt of fine material to the ocean from eroding gullies, hillslopes, and reworked sediment on valley floors. Tectonic and geologic influences, in combination with a dynamic climate influenced by tropical cyclones and clearance of vegetation from steep hillslopes, predisposes this region to high rates of erosion. The bedload sediment regime of the river is strongly influenced by several exceptionally large gullies and gully complexes that produce a coarse-grained, poorly sorted sediment mixture. Rapid abrasion and breakdown leads to high rates of suspended sediment yield. A wave of bedload material, manifesting as elevated bed levels and significant widening of active alluvial fills, has been triggered by large inputs of hillslope material from a few key tributary catchments following Cyclone Bola in 1988. We review the evidence for the relaxation process of the sedimentary system in the subsequent 29 years, appraising some of the legacy effects that may endure, as associated with reworking of the considerable alluvial stores within the Waiapu system. We use Structure-from-Motion (SfM) techniques and archival aerial photos to quantify changes in sediment storage at the base of two major gully systems in recent decades. A record of over 850 cross section surveys at 62 sites on 10 rivers throughout the catchment (1958–2017) indicates recent transition from a trend of continuous accumulation to downcutting and remobilisation of valley-bottom deposits. The channel cross sections provide a minimum estimate of sediment flux from source areas to the lower reaches of the river, giving a rudimentary but spatially extensive picture of the wave of material cascading through the drainage network. The largest impacts occur in the upper steepland rivers, closest to the landslide-derived sediment supply. Transport rates here, as inferred from cross section change, are at a maximum during an aggradational phase following Cyclone Bola then taper off, despite the large sediment accumulations remaining in the system. As of 2017, the river is in the process of incising the upper extents of this deposit on a trajectory of recovery toward pre-Bola conditions. The compilation of cross section data provides us with new insights into the sensitivity of particular sites in the landscape, as well as the changing relationship between reach sediment storage and transport rates during the response and relaxation phase of a major disturbance in a large catchment.

Geomorphic signature of a dammed Sandy River: The lower Trinity River downstream of Livingston Dam in Texas, USA

Reservoirs behind dams act as deposition sites for much of the sediment being transported by rivers. As a result, the downstream river flow can be well below the transport capacity for bed-material. This promotes bed erosion and other geomorphic changes over some length of river located immediately downstream from a dam. These adjustments have been characterized for the Trinity River, TX, downstream of Livingston Dam. Field measurements and results from a 1D numerical model define a 50–60 river kilometer segment of river undergoing bed erosion as the transport capacity for bed material is reestablished. Consequences of this erosion include lowering of the channel bed, reduction in the sediment volume of channel bars, coarsening of sediment on bar tops, steepening of channel banks, and reduction in lateral migration rates of river bends. Repeat surveys of the river long profile reveals that 40yr of dam closure has produced up to seven meters of channel-bottom incision downstream of the dam, transforming an initially linear profile into a convex-up long profile. The model output matches this observed change, providing confidence that calculated estimates for spatial and temporal changes in bed-material sediment flux can be used to explore the long-term signature of dam influence on the geomorphology of a sand-bed channel. Measurements of channel geometry, profile, lateral migration, and grain size of the lower Trinity River with distance downstream define both the trend and expected variability about the trend associated with the disruption to the bed-material load.

Bed material load estimation in channels using machine learning and meta-heuristic methods

AbstractThis study is trying to develop an alternative approach to the issues of sediment transport simulation. A machine learning method, named least square support vector regression (LSSVR) and a meta-heuristic approach, called particle swarm optimization (PSO) algorithm are used to estimate bed material load transport rate. PSO algorithm is utilized to calibrate the parameters involved in the model to facilitate a desirable simulation by LSSVR. Implementing on a set of laboratory and field data, the model is capable of performing more satisfactorily in comparison to candidate traditional methods. Similarly, the proposed method has a better performance than a specific version of decision tree method. To enhance the model, the variables are scaled in logarithmic form, leading to an improvement in the results. Thus, the proposed model can be an efficient alternative to conventional approaches for the simulation of bed material load transport rates providing comparable accuracy.

Estuaries Hidrofisis Characteristic

Estuaries hidrofisis characteristic can be based on the moon changes phases as the earth's major satellite, distribution of physical variable position, flow rate, bed material transport, and weather condition in Indonesia (dry and wet season). Physical characteristic of flow rate and the change of bed material transport sliding as bed load along the estuaries is spatially functioned by an expert to study water flow characteristic. Analysis of velocity pattern as well as the moon phases and seasons becomes the determiner of spreading pattern of bed load that is important to perform later. Analysis of flow rate variable and bed load is especially based on the phases of the moon and seasons. Their change along the river estuary can show the characteristic of erosion change and sediment deposition in the estuary. Measurement in the rainy season was done during full moon and first quarter moon, as well as in the dry season of full moon when sea level rises and downs. Identification of estuaries flow shows six measurement segments and seventeen measurement positions which becomes the basic analysis of hidrofisis variable change along the estuaries. The measured variable during high tide includes water flow around the riverbed surface, bed load concentration, material diameter of riverbed, water flow of river bed surface during high tide, and bed load concentration. Analysis of hidrofisis characteristic of estuaries will refer to two things, firstly, profile of water flow parameter and load change of basic material. Secondly, modeling and data interpolation stated in absolute mean deviation and bias in data of modeling result as well as interpolation towards data of measurement result. Water flow characteristic during low tide in rainy season of full moon shows higher price compared to the first quarter of rainy season. It becomes different in the rainy season of full moon and is much lower with the decrease of gradient, that happens during high tide. While estuary hidrofisis characteristic, bed material transport of dry season during high tide of full moon is larger than rainy season during high tide of full moon and first quarter moon. Water discharge improvement is always accompanied by flow rate increase (in the rainy season). During wet season, change of bed material transport is much more than dry season. Bed material transport curves sand in the Ranoyapo estuary is slightly small to be transported by flow velocity. It causes considerable high conveyance of bed material transport, even bed material load is not settled on river estuary but continued by stream into beach. Dry season of full moon with lower flow velocity compared to the rainy season of full moon and first quarter phase is evidently enough to settle bed material transport along the river estuary. Key Words: Bed Material Transport, Estuaries ups and downs, Moon Phases, Stream

Discussion on “Representative sediment sizes in predicting the bed-material load for nonuniform sediments” by Wan Hanna Melini Wan Mohtar, Junaidi, Suraya Sharil, Muhammad Mukhlisin [Int. J. Sed. Res. 31 (2016) 79–86

In this discussion, we want to highlight the important findings of the last two decades by Hunziker and Jäggi (2002) and Wong and Parker (2006), among others, who reanalyzed and revised the original data forming the basis of the MPM sediment transport equation. Furthermore, by using an actual adaptation of the original MPM formula, the prediction of the sediment transport rate for the data given in the paper under discussion seems to be acceptable.

Three-Dimensional Simulation of Local Scour around a Weir-Type Structure: Hybrid Euler-Lagrange Model for Bed-Material Load

AbstractThis paper presents a hybrid Euler-Lagrange model for bed-material load considering transition between the bed load and suspended load. The hydrodynamic model and suspended sediment transpo...

Bed material transport estimate in large gravel‐bed rivers using the virtual velocity approach

AbstractThis paper reports on a first attempt of using the virtual velocity approach to assess sediment mobility and transport in two wide and complex gravel‐bed rivers of northern Italy. Displacement length and virtual velocity of spray‐painted tracers were measured in the field. Also, the thickness of the sediment active layer during floods was measured using scour chains and post‐flood morphological changes as documented by repeated survey of channel cross‐sections. The effects of eight and seven floods were studied on the Tagliamento and Brenta Rivers, where 259 and 277 spray‐painted areas were surveyed, respectively. In the Tagliamento River 36% of the spray‐painted areas experienced partial transport, whereas in the Brenta River this accounted for 20%. Whereas, full removal/gravel deposition was observed on 37% and 26% of these areas on the Tagliamento and Brenta Rivers, respectively. The mean displacement length of particles, the thickness of the active layer and the extent of partial transport are well correlated with the dimensionless shear stress. The virtual velocity approach allowed calculation of bed material transport over a wide range of flood magnitudes. Annual coarse sediment transport was calculated up to 150 for the Tagliamento, and 30 × 103 m3 yr−1 for the Brenta. The outcomes of this work highlight the relevance of partial transport condition, as it could represent more than 70% of the total bed material transported during low‐magnitude floods, and up to 40% for near‐bankfull events. Results confirm that bed material load tends to be overestimated by traditional formulas. Copyright © 2016 John Wiley & Sons, Ltd.

Listen to the sound of moving sediment in a small gravel-bed river

In order to assess the dynamics of rivers, a reliable characterization of bedload transport particularly during unsteady flow regimes is required. In contrast to highly energetic cases in hillslope areas, we aim to answer the question whether the usage of acoustic measurements can improve the characterization of bedload in small rivers draining low land mountains with comparatively low water discharge and bedload. In addition to the investigation of natural flood events, controlled floods were generated by releasing water from a reservoir into a small gravel-bed stream. The controlled releases allow for an evaluation of bedload solely from channel storage or bank erosion. For acoustical in-situ characterization of bedload transport, hydrophones were mounted onto the bottom side of steel plates, thus recording the impacts of sediments via the acoustic vibrations on the surface of the plates while at the same time minimizing the disturbing noise resulting from water turbulence. Corresponding bedload traps are removable boxes with open lids fixed in the riverbed so that bedload material registered by the hydrophone is trapped. The acoustic signals correlate well with the quantity of the transported material. During summer flood events the highest transport rates occur at the beginning of the rising limb featuring clockwise hysteresis. This is due to the rising transport energy of the flow and the presence of loose, unconsolidated material. During typical winter flood events bedload shows anticlockwise loops. The intensification of bedload conveyance after the runoff peak can be explained by a decreasing stability of the bed material from the beginning to the end of a transport event. Anticlockwise behavior also results from a combination of bedload exhaustion in the vicinity of the monitoring station with a delayed arrival of new material from distal sources later in the hydrograph.

Bedload Model for Nonuniform Sediment

AbstractIn this study, a bedload model for nonuniform sediment is developed considering the density function of sediment entrainment with no active layer. The model is formulated based on physical considerations, dimensional reasoning, regression analysis, and laboratory data. Four parameters are incorporated in the model formulation, namely the Shields stress τ*g′, the critical Shields stress τ*cg, the Kramer coefficient of uniformity cu, and the relative grain size (size of the jth grain fraction to the geometric mean size, dj/dg). The model collectively accounts for the hiding effects and the variation of the transported bedload material fractions from the surface and subsurface material. The findings of the study show that at low values of τ*g′/τ*cg fractions within the range of 0.3<dj/dg<3.0 are present with larger amounts in the transported bedload material than in the substrate, whereas fractions finer or coarser than that range are present with larger amounts in the surface layer than in the subst...

Power increase of Lavey (Switzerland), hydroelectric power scheme, Lavey+ project

Lavey Hydroelectric Scheme is located in the French-speaking part of Switzerland. It was commissioned in 1950. Since then, and under an operating lease of 80 years, it produces about 400 GWh per year, covering 32% of the electricity needs of the City of Lausanne. At the start of the last decade, further to the political commitments (Energy 2050), Switzerland turned mainly to renewable energies. The City of Lausanne and its Public Utility, which produces and distributes electricity to more than 230'000 homes, have developed a project, called Lavey+, to increase the power and energy generation at Lavey power plant. Within the framework of the Lavey+ project, it was decided in 2008 to improve the present situation and to study the realization of a new water intake, a second headrace tunnel parallel to the existing one, to expand the present underground cavern, to put a fourth Kaplan turbine generator and to modernize the plant. To ensure a better operational flexibility, it is planned to connect the new gallery also to the third turbine, which is already in operation. Additional studies were also performed to improve the area of the reservoir in order to improve the conditions of bed load material transit. After more than 60 years of interruption, it was decided also to restore the passage of the fish fauna in the upstream and downstream migrations. Finally, a proposal to reassess the ecological flow, which would be annually modulated downstream from the dam, was made.

Review of Hans Albert Einstein: His Life as a Pioneering Engineer by Robert Ettema and Cornelia F. MutelASCE Press, Reston, VA 20191; 2014; ISBN 9780784413302; 330 pp.; $65.00

Review of <i>Hans Albert Einstein: His Life as a Pioneering Engineer</i> by Robert Ettema and Cornelia F. MutelASCE Press, Reston, VA 20191; 2014; ISBN 9780784413302; 330 pp.; $65.00

Partitioning and analyzing temporal variability of wash and bed material loads in a forest watershed in Iran

The amount of transported material from a hillslope or channel, mirrors the watershed health, which needs to be quantified. However, the contribution of different sediment sources to sediment load has not been adequately studied. In this study, 24 samples of suspended load, bed load and channel material were taken bi-weekly for a period of one year from the Kojour River of the Educational and Research Forest Watershed of Tarbiat Modares University in Iran. The suspended sediment concentration and particle-size distribution were determined. The total sediment load was then partitioned into bed load, wash load and suspended bed material load based on three criteria: (i) the upper limit of 63 micron, (ii) the Einstein method, and (iii) the lower limit of sediment particles in the channel material. The results suggested a significant contribution of wash load compared to suspended bed material and bed loads ratio of 96.8, 2.65 and 0.55%, respectively. The ratio of suspended bed material load to wash load varied from 13.12% (the maximum) in winter to 11.02, 2.70 and 0.91% in autumn, spring and summer, respectively. The results also showed the effects of flow discharge on different components of sediment loads. While, the flow discharge significantly affected bed load and wash load with respective correlation coefficients (r) of 0.520 and 0.464 < r < 0.535 for three methods with significant level (p) between 0.007 and 0.022. It had little influence on suspended bed material load (–0.243 < r < 0.277 with 0.190 < p < 0.253).

Paleodischarge of the Mojave River, southwestern United States, investigated with single-pebble measurements of10Be

The paleohydrology of ephemeral stream systems is an important constraint on paleoclimatic conditions in arid environments, but remains difficult to measure quantitatively. For example, sedimentary records of the size and extent of pluvial lakes in the Mojave Desert (southwestern USA) have been used as a proxy for Quaternary climate variability. Although the delivery mechanisms of this additional water are still being debated, it is generally agreed that the discharge of the Mojave River, which supplied water for several Pleistocene pluvial lakes along its course, must have been significantly greater during lake highstands. We used the 10 Be concentrations of 10 individual quartzite pebbles sourced from the San Bernardino Mountains and collected from a ca. 25 ka strath terrace of the Mojave River near Barstow, California, to test whether pebble ages record the timing of large paleodischarge of the Mojave River. Our exposure ages indicate that periods of discharge large enough to transport pebble-sized sediment occurred at least 4 times over the past ∼240 k.y.; individual pebble ages cluster into 4 groups with exposure ages of 24.82 ± 4.36 ka (n = 3), 55.79 ± 3.67 ka (n = 2), 99.14 ± 12.07 ka (n = 4) and 239.9 ± 52.16 ka (n = 1). These inferred large discharge events occurred during both glacial and interglacial conditions. We demonstrate that bedload materials provide information about the frequency and duration of transport events in river systems. This approach could be further improved with additional measurements of one or more cosmogenic nuclides coupled with models of river discharge and pebble transport.

Representative sediment sizes in predicting the bed-material load for nonuniform sediments

This paper evaluates the applicability of representative sediment size in terms of median grain size and the effective sediment sizes for the transport of non-uniform natural sediment mixtures. Natural sediment from the Krasak River, Yogjakarta was used. Bed samples were collected from three different river sections, i.e. upstream (U), midstream (M) and downstream (D). The median diameters, d50 and sediment geometric standard deviation, σg for sections U,M and D were 1.63mm, 0.91mm and 0.69mm, and 4.8, 2.3 and 1.5 respectively. Particular attention was paid to the effect of varying representative sediment sizes on the threshold sediment motion, where four threshold equations were employed. The threshold value varies when σg=4.8 and has little variation for sediment mixtures with σg<2.4. Analysis is extended to prediction of bedload transport using eight selected formulae which account for both with and without the threshold criteria of sediment motion. To account for the non-uniformity of the bed materials, a comparison between the calculated bedload discharge using d50 was made with the bedload prediction when a representative sediment diameters were used. Analysis shows that an improvement of the statistical analysis was only observed for predictions calculated using Brownlie (1981) and Camenen and Larson (2005) expressions when effective sediment sizes were employed for non-uniform sediment mixtures. Employing the effective sediment sizes de or dem to calculate the bedload discharge does not necessarily improve the bedload prediction and the use of d50 is seen as sufficient.

Experimental study on the bank erosion and interaction with near-bank bed evolution due to fluvial hydraulic force

Bank erosion is a typical process of lateral channel migration, which is accompanied by vertical bed evolution. As a main sediment source, the failed bank soil may directly cause the increase of sediment concentration and considerable channel evolution in a short time. The paper presents an experimental study on non-cohesive and cohesive homogenous bank failure processes, influence of the failed bank soil on bank re-collapse, as well as the interaction between bank failure and near-bank bed evolution due to fluvial hydraulic force. A series of experiments were carried out in a 180° bend rectangular flume. The results reveal the iteration cycle between bank erosion and bed deformation: undercutting of the riverbank, slip failure of the submerged zone of the bank, as well as cantilever failure of the overhang, failed bank soil staying at bank toe temporarily or hydraulic transportation, exchange between the failed bank soil and bed material, bed material load being re-transported either as bed load or as suspended load, and bed deformation. Same as bank failure, the mixing of failed bank soil and bed material is more severe near the curved flow apex. Moreover, non-cohesive bank failure tends to occur near the water surface while cohesive bank failure near the bank toe. For non-cohesive dense (sandy) soil, the bank erosion amount and residual amount of failed bank soil on the bed increase with the near-bank velocity or bed erodibility. But for cohesive soil, only bank erosion amount follows the above rule. The results are expected to provide theoretical basis for river management and flood prevention.

Determination of recovery factor for simulation of non-equilibrium sedimentation in reservoir

It is generally acceptable to assume that bed material load is equal to sediment transport capacity, if the exchange between bed and flow occurs instantaneously. However, for non-equilibrium sediment transport process, there are spatial and temporal delay effects. This is especially true for reservoir sedimentation processes. Recovery factor is a coefficient for non-equilibrium sediment transport. The determination of recovery factor can be obtained either experimentally or numerically. There is no consensus on the value of recovery factor in previous literatures. Numerical simulations with a semi-two dimensional sediment transport model, GSTARS4, were conducted in this study using various methods for the determination of recovery factor proposed by previous researches. Simulated results of a reservoir geometric change were sensitive to the selection of recovery factors. It was found that the recovery factor as a function of sediment size provided the most reasonable result. A functional relationship between recovery factor and sediment size was determined by comparing simulated and measured reservoir geometric change. Coarse sediment has small value of recovery factor.

Sediment sources, spatiotemporal variability and rates of fluvial bedload transport in glacier-connected steep mountain valleys in western Norway (Erdalen and Bødalen drainage basins)

Contemporary fluvial bedload transport rates are still very difficult to measure and, as a result of this, in many sites only quantitative data on suspended and solute transport are included in sediment budget studies carried out for defined drainage basin systems. The presented analysis of fluvial bedload dynamics in different defined subsystems of the glacier-connected Erdalen (79.5km2) and Bødalen (60.1km2) drainage basins in the steep fjord landscape of western Norway provides insights into (i) detectable relevant sediment sources, (ii) instream channel storage of bedload material, (iii) spatiotemporal variability and controls of bedload transport rates and bedload yields, and (iv) the absolute and relative importance of fluvial bedload transport within the sedimentary budgets of these steep cold climate mountain valleys. Rockfalls, snow avalanches, stream channel bank erosion, and fluvial transfers through small tributaries draining slope systems are relevant sediment sources for fluvial bedload transport in the main stream channels, whereas the main outlet glaciers in both drainage basins are not of importance as all bedload material delivered directly from these outlet glaciers is trapped within proglacial lakes. Narrow valleys within both drainage basin systems are characterized by a higher intensity of slope-channel coupling and display higher rates of sediment supply from slopes into the main stream channels than wider valleys. Snow avalanches are the most important sediment source in Erdalen, whereas fluvial transfers through small tributaries followed by snow avalanches are most important in Bødalen. Longer term, instream channel storage is not of great importance in the steep Bødalen drainage basin but currently plays an important role within the Erdalen drainage basin, which is characterized by a stepped longitudinal main valley bottom profile favoring deposition of bedload material within less steep main channel reaches. The mean annual bedload yields (2010–2013) are 2.4tkm−2y−1 for the entire Erdalen and 13.3tkm−2y−1 for the entire Bødalen drainage basin, which are comparably low values for steep and partly glacierized drainage basin systems. Because of supply-limited conditions, the intensity of fluvial bedload transport is generally much more related to the availability of sediments than to channel discharge. Fluvial bedload transport accounts for about one-third of the total fluvial transport and accordingly plays an important role within the sedimentary budgets of both drainage basin systems.

Paleoslope Reconstruction In Sandy Suspended-Load-Dominant Rivers

Constraining the depositional gradient of ancient alluvial river systems can aid in reconstructing landscapes and estimating paleodischarge by establishing boundaries on the climatic and tectonic history of continental sequences. We present three methods for estimating ancient depositional gradients based on the interpreted mode of sediment transport for the range of particle sizes found on the beds of modern rivers or preserved in channel fills. For sandy rivers with suspension as the dominant mode of sediment transport, these methods take advantage of observations that can be directly obtained from preserved strata, including measurements of paleo flow depth and grain size. The first method relates river slope to Shields number at bankfull flow. The second method is similar to the first but allows for variation in Shields number at bankfull flow with grain diameter. The final method relies on criteria required for both suspended- and bed-material load sediment transport in the same system and is the most comprehensive and physically justified method. We present each method and test them with modern river datasets to verify accuracy and help constrain uncertainty—the first step to adapting them to ancient systems. Results indicate that all methods estimate slope within a factor of two. These methods are potentially very powerful for interpreting sandy fluvial deposits because they can provide reasonably accurate quantitative estimates of paleoslope, an elusive yet important environmental variable.

Diversion of Mississippi River Water Downstream of New Orleans, Louisiana, USA to Maximize Sediment Capture and Ameliorate Coastal Land Loss

Boat-based field data and monitoring station data from the tidal reach of the Mississippi River are utilized to examine the sediment capture of large (>1,400 cms) proposed water and sediment diversions from the channel to build and sustain wetlands in the Mississippi delta. The purpose herein is to suggest the importance of siting the diversion relative to river morphology and operating it to optimize sediment capture. At the site of a proposed diversion near Myrtle Grove, LA, water and sediment data suggest that the washload (fine) fraction is strongly weighted toward the rising limb of individual freshets (e.g., flows >16,990 cms, 1 to 5 events/y over the last 49 y) based on daily turbidity records. Significant variability in suspended fines exists between freshets depending on whether they are the first peak of the water year, and on their tributary source. Much of the sand fraction in suspended load, since it is derived from the underlying bed (e.g., bed material load), is strongly tied to water discharge in this reach, and can be accurately predicted by ratings curve. An analytical model is presented that is utilized to test efficiency of sand capture in a diversion based on ADCP backscatter data calibrated by isokinetic water samplers. Using observations from the diversion site, the model predicts a 30 % more efficient sand capture for a 1,416 cms diversion (0–10 m withdrawal depth) at a discharge of 27,250 cms (March 2011) on the proposed lateral bar diversion site, relative to a thalweg site on the opposite bank. This suggests that the proximity of large dunes, and the turbulence induced by them, is a primary control on sand resuspension in the water capture zone, which in turn plays a strong role in efficiency of diversion sand capture.