Bed Material Load Research Articles

Multiple Linear Regression Model for Total Bed Material Load Prediction

A new total bed material load equation that is applicable for rivers in Malaysia was developed using multiple linear regression analyses. A total of 346 hydraulic and sediment data were collected from nine natural and channelized rivers having diverse catchment characteristics in Malaysia. The governing parameters were carefully selected based on literature survey and field experiments, examined and grouped into five categories namely mobility, transport, sediment, shape, and flow resistance parameters. The most influential parameters from each group were selected by using all possible regression model method. The suitable model selection criteria namely the R-square, adjusted R-square, mean square error, and Mallow's Cp statistics were employed. The accuracy of the derived model is determined using the discrepancy ratio, which is a ratio of the calculated values to the measured values. The best performing models that give the highest percentage of prediction from the validation data were chosen. In general, the newly derived model is best suited for rivers with uniform sediment size distribution with a d50 value within the range of 0.37-4.0 mm and performs better than the commonly used Graf, Yang, and Ackers-White total bed material load equations.

FLUVIAL GEOMORPHOLOGICAL METHODOLOGY FOR NATURAL STABLE CHANNEL DESIGN

: A fluvial geomorphological methodology for designing natural stable channels is being widely applied for river restoration. It is an analogue procedure, as the W/d ratio and sinuosity from a reference reach are scaled to determine the restoration design. The choice of reference reach is crucial and published criteria specify that it should be stable, correspond to the stream type at the restoration site, have the same valley type, and be from the same hydrophysiographic region. For stable, meandering gravel cobble bed rivers flowing through alluvial flood plains (C3 and C4 stream types), UK regime equations are used to evaluate the procedure. Successful design requires particular combinations of the ratios of bankfull discharge, bed material size and load, valley slope, and bank vegetation category between the reference and restoration sites. These critical ratios, which are confirmed by U.S. field data, provide guidelines for selecting a suitable reference reach for C3-C4 stream types. They also indicate that the reference reach can be in any valley type or hydrophysiographic region. The geomorphological procedure will apply to all stable stream types, provided the reference reach is correctly identified. Specific guidelines for each stream type await the development of additional regime equations.

The Holocene record of Loch Etive, western Scotland: Influence of catchment and relative sea level changes

Two sediment cores from inner Loch Etive, a deep fjord basin on the west coast of Scotland, reveal a continuous sediment sequence spanning the last 10,000 yr. Benthic foraminiferal assemblages indicate that marine conditions prevailed in Loch Etive throughout the Holocene. However, changes in sediment grain size composition and magnetic susceptibility suggest that the strength and frequency of deep water renewal events has varied through time. This exchange with coastal water is controlled mainly by relative sea level changes (influencing sill depth) and the influx of freshwater to the loch. The very early Holocene sediments are well-sorted coarse silt–fine sands, with a diverse assemblage of calcareous foraminifera indicating frequent renewal of bottom waters. During this period, immediately following the withdrawal of Younger Dryas glaciers, denudation rates were high in the catchment area. The period 9–7 ky BP, during which relative sea level rose in this part of W Scotland, is characterised by highly variable environments. The grain size data indicate an enhanced transport of sandy bed load material from the ‘Bonawe Sill’ region to the basin deep during the mid-Holocene relative sea level high (8–9 m higher than present). High relative sea levels at this time would explain the occurrence of frequent, vigorous deep water renewal events and an increased tidal current regime in the loch. The late Holocene record is characterised by an upward fining of sediment grain size, disappearance of calcareous benthic foraminifera and increasing organic content; suggesting a development towards a more restricted fjordic circulation in response to the progressive lowering of relative sea level. A sudden acceleration in this late Holocene trend took place during the last millennium, during which time human land use and deforestation have influenced the sediment and organic material flux to Loch Etive. It appears that average Holocene sediment accumulation rates in the ‘Bonawe Deep’ were about 0.01–0.03 g cm − 2 yr − 1 , which is far below modern estimates for the site. This can be explained by vigorous bottom current activity during much of the Holocene, leading to a low net depositional rate.

Room for rivers: An integrative search strategy for floodplain restoration

River restoration aims to re-establish the ecological integrity of a river ecosystem. However, restoration measures are nowadays mainly a reactive, site-by-site activity, driven by a single driver (e.g. fisheries, flood protection) rather than based on strategic planning. This study presents an integrated search strategy to identify stream systems where present environmental (e.g. natural flow, sufficient bed load material) and socio-economic (e.g. public attitude) template conditions favour the eco-morphological restoration of floodplains and their biocoenosis. This ‘pre-screening’ process reveals where the greatest benefits (judged according to ecological and socio-economic criteria) are to be expected and thus justify further specific and detailed investigations. It helps to set priorities and thus avoid inefficiency. The search strategy presented in this study is designed to perform a pre-screening process at national level. It is based particularly on spatially explicit information and is balanced between accuracy and costs. A hierarchical filter process combines the facilities of GIS with multiple criteria decision analysis (MCDA) to generate restoration suitability maps. The filter process is based on a list of criteria and indicators that capture the ecological key factors that drive floodplain restoration (hydrology, bed load, connectivity, biodiversity, water quality), as well as crucial socio-economic aspects (e.g. flood protection, public attitude) that need to be taken into account when planning for floodplain restoration. Inevitable limitations, arising from the transfer from theory into practice, are accepted, as the search strategy is dedicated to practical application. A modified Delphi process survey of nine river ecology experts was used to assess the appropriateness of each indicator and to estimate the single indicator suitability function. We used ModelBuilder 1.0a (an ArcView extension) to integrate different data layers into a single Ecological Restoration Suitability Index (ERSI) layer. The practical application of the integrative search strategy for floodplain restoration is illustrated through a case study from the Rhône-Thur Project in Switzerland.

Behavior of Meandering Overbank Channels with Graded Sand Beds

Measurements of velocity distributions, depth variation, and sediment transport have been made under bankfull and overbank flow conditions in meandering channels with a graded sand bed, using the large-scale U.K. Flood Channel Facility. The overbank conditions depend upon the relative strength of opposing secondary circulation cells generated by shear at the channel crossover and centrifugal forces around the meander bend. Generally the shear-generated secondary flow either reversed or weakened the centrifugal circulation around the next downstream bend. This led to considerable modification of the main channel bed morphology, which, in turn, altered flow distributions. Measurements of the lateral distribution of bed load were made using a 14-scale Helley–Smith sampler. This demonstrated that the bed load was generally concentrated within a limited width of the channel and tended to take the shortest route through the meanders. Comparisons of observed and calculated bed material load gives an indication of how secondary circulation around meanders, under both bankfull and overbank conditions, affects the predictive performance of formulas derived for predominantly one-dimensional flow.

Comparison of U–Th, paleomagnetism, and cosmogenic burial methods for dating caves: Implications for landscape evolution studies

Caves are useful in landscape evolution studies because they often mark the level of previous water tables and, when dated, yield incision rates. Dating caves is problematic, however, because their ages are only constrained by the oldest deposits contained within, which may be far younger than the cave itself. We dated cave deposits in the Sierra Nevada using U–Th dating of speleothems, paleomagnetic dating of fine sediment, and cosmogenic 26Al/ 10Be burial dating of coarse sediment. The sampled caves formed sequentially as the water table lowered, providing an important stratigraphic test for the dating methods. Large discrepancies between deposit ages from similar cave levels demonstrate that, even when accurately determined, deposit ages can seriously underestimate the timing of cave development. Drip-type speleothems are most prone to this minimum age bias because they can accumulate long after caves form, and because the U–Th method is limited to ∼400 ka. Paleomagnetic dating requires correlation with the global reversal chronology, and is hindered by a lack of continuous stratigraphy. The fine sediment analyzed for paleomagnetism is also highly susceptible to remobilization and deposition in cave passages well above base level. Cosmogenic 26Al/ 10Be dates bedload material deposited when caves were at or very near river level, and can date material as old as ∼5 Ma. In the Sierra Nevada, speleothem U–Th ages and sediment burial ages from the same cave levels differ by as much as an order of magnitude. These results suggest speleothem ages alone may significantly underestimate cave ages and thereby overestimate rates of landscape evolution. Cosmogenic burial dating of coarse clastic sediment appears to be the most reliable method for dating cave development in mountainous regions.

Wash Load and Bed-Material Load Transport in the Yellow River

It has been the conventional assumption that wash load is supply limited and is only indirectly related to the hydraulics of a river. Hydraulic engineers also assumed that bed-material load concentration is independent of wash load concentration. This paper provides a detailed analysis of the Yellow River sediment transport data to determine whether the above assumptions are true and whether wash load concentration can be computed from the original unit stream power formula and the modified unit stream power formula for sediment-laden flows. A systematic and thorough analysis of 1,160 sets of data collected from 9 gauging stations along the Middle and Lower Yellow River confirmed that the method suggested by the conjunctive use of the two formulas can be used to compute wash load, bed-material load, and total load in the Yellow River with accuracy.

A PREDICTION METHOD FOR WEARING OF THE CONCRETE FLUME IN THE FLOW WITH BED MATERIAL LOAD

In this paper, it is described a calculation method of wearing the concrete flume influenced by bed material load. It is proposed a physical model for the process of the concrete plate undermined by the particles. A collision period time between a grass bead panicle and the concrete plate in water was determined in the experiments used high speed CCD camera. The percentage of the particles with vector to bottom in the particles near the bottom was determined in the experiments. The calculated results by the prediction model shows a good agreement on the experimental results what the bottom of concrete flume was wearing by bed material load.

Prediction of total bed material discharge

A new and user-friendly formula for the computation of total bed material load in alluvial channels under equilibrium transport conditions has been developed based on the stream power concept and diffusion theory. The advantages of this formula include: high accuracy in prediction, the ease of computation and the wide range of application. The total sediment concentration is computed directly using the variables of flow depth, mean flow velocity, energy slope, median sediment size and sand density, and water temperature. The verification for the new equation uses over 3500 published total-load data from flume studies, and the over-all results show that 84% of the data are predicted within 0.5 and 2 times the measured values. This is an encouraging score considering the large database and the range of variables covered.

Prediction of Concerted Sediment Flushing

A proprietary one-dimensional numerical model was developed for predicting the amounts of sediment flushed and deposited in the reservoirs in series, the bed evolutions, and variations of the suspended solids concentrations along a river during the concerted sediment flushing events. The model consists of a flow movement module and sediment transport module in which the bed material load is taken as sediment mixture. The nonuniform property of the bed material load is modeled by the introduction of a mixing layer, transition layer, and deposition strata. The model was calibrated on the basis of the field data at Dashidaira and Unazuki reservoirs on the Kurobe River in Japan. The calculated results are in good agreement with the measurements. For the reservoirs out of Japan, the Ashida and Michiue bed load formula used in the model should be verified or replaced by other formulas.

Bed-Material Load Computations for Nonuniform Sediments

The nonuniformity of bed material affects the bed-material load calculations. A size gradation correction factor \IK\dd\I is developed to account for the lognormal distribution of bed material. The use of \IK\dd\N in conjunction with bed-material load equations originally developed for single particle sizes improves the accuracy of transport calculations for sediment mixtures. This method is applicable to laboratory flumes and natural rivers with median diameter \id\D50\N of bed material in the sand size ranges. The improvement on transport rate by \IK\dd\N factor is significant for data with standard deviation σ\i\dg of bed material greater than 2, while the correction is negligible for data with σ\i\dg less than 1.5. Sediment in transport also follows a lognormal distribution with a median diameter \id\D50\it\N generally finer than the corresponding \id\D50\N. As the size gradation increases, \id\D50\it\N becomes much finer than the corresponding value of \id\D50\N. The relationship between \id\D50\it\N and \id\D50\N is defined as a function of σ\i\dg and agrees well with field data. The previously recommended use of \id\D35\N as representative size of the bed material is found not to be generally applicable.

Sedimentology and morphodynamics of a barrier island shoreface related to engineering concerns, Outer Banks, NC, USA

Forty-nine vibracores were collected from a barrier island shoreface following 12.4 years of biweekly profile surveying. The sedimentologic architecture of the shoreface was linked to time-series elevation change and profile shape to determine relationships between morphodynamics, facies development, erosional processes, profile closeout, and cross-shore transport. The modern shoreface mass, which erosionally overlies a tidal inlet-associated complex, attains a maximum thickness of 3–4 m below the beach to middle profile before pinching out seaward between 9 and 12 m depth. Concave erosional surfaces overlain by cross-stratified fine to medium sand and gravel make up most of the lower half of the shoreface prism below the beach through middle profile reflecting longshore trough incision and subsequent current-dominated aggradation. At the landward margin, gravel-rich laminae record episodic seaward progradation of beach surfaces over coarse inner-trough settings. Seaward, a parallel-laminated fine-sand facies dominates the upper part of the prism recording intermittent shoal zone buildup, including trough filling, under high-velocity plane-bed conditions. Similarly, a bioturbated parallel-laminated, fine- to very fine-sand facies makes up the entire prism below the outermost lower ramp sector, again indicating buildup under high-velocity conditions. However, accretion of the lower ramp results from major storms that cause trough scour along landward locations and simultaneous displacement of fine sand onto the lower ramp. Conversely, lower ramp erosion typically occurs during less energetic conditions as sediment is slowly returned shoreward causing inner-shoreface buildup. Close spacing of major storms during some years led to net progradation of the shoreface. The upper and lower limits of surveyed elevation change (ULe and LLe) repeatedly develop similar limit-profile shapes over shoreface accretion–erosion cycles. The ULe reflects accretion maxima resulting from beach, bar, and lower ramp buildup. The LLe and lower sedimentologic limit (LLs) along the inner 250 to 300 m of the active shoreface are a product of storm-trough scour down to a maximum depth of ∼5.5 m. Below the lower ramp facies, the LLe and LLs are primarily products of less energetic wave erosion down to ∼5 m (shoreward) and 9 m (offshore) depths. The LLe closely matches the LLs documenting that >90% of the shoreface prism was reworked during the 12.4-year period whereas actual ages for erosional events indicate a potential of 2 to 4 years for complete reworking of the shoreface mass. Textural distribution indicates net long-term transport direction and loci of deposition for different sized material. The coarsest material is concentrated at landwardmost locations and well-sorted fine to very fine sand at seaward locations. Medium sand to gravel tends to remain within the trough zone, even during extreme storm events. The ULe and LLe also represent the upper and lower limits for profile closure events. A location of about 4.5 m depth at 300 to 350 m from shoreline marks the boundary between inner profile- and lower ramp-associated closure events, the boundary between trough-associated and lower ramp facies, and the lower ramp morphologic break, all of which correspond to the juncture between longshore-current- and shoaling wave-dominated zones. The lower-ramp zone of closure is a zone of seaward decreasing storm transport in which fine to very fine sand is the typical bedload material.

Environmental impacts of coordinated sediment flushing

The environmental impacts of sediment flushing are predicted by a one-dimensional model for prediction and evaluation of sediment flushing (PESF1D). The model computes one-dimensional unsteady flow and non-equilibrium transport of non-uniform sediment mixtures. In the sediment transport module, bed material load is taken as sediment mixtures for calculating the bed evolution and wash load concentration is computed in consideration of the mixing action between the fine sediments in the flowing water and bed porewater. The influences of tributaries on the concentrations are taken into account in diffusion equations of wash load and suspended load. The non-uniform property of the bed material load is modeled by introduction of a mixing layer, transition layer and deposition strata. PESF1D was calibrated on the basis of the observations during the concerted flushing at Dashidaira and Unazuki reservoirs in 2001. The suspended solid concentrations predicted for potential flushing in 2002 are in good agreement with the measurements during the concerted flushing in July 2002. The dissolved oxygen concentration of the lower Kurobe River would not have strong relationship to the suspended solid concentration. The sediment budget shows the riverbed has been eroded after completion of Unazuki dam in 2001.

INVESTIGATION OF TAN CHAU REACH IN LOWER MEKONG USING FIELD DATA AND NUMERICAL SIMULATION

This paper presents field data for channel change, bed material, water surface elevation and hydrograph in Tan Chau reach in Vietnam to understand mechanism of the river change. These show that bank shifting tends to occur toward anti-clock wise and sand bars migrate downstream, resulting in a much larger bar, which is influenced by co-presence of non-cohesive and cohesive sediment and by artificial protection works. In addition, bed material loads are originated by bank erosion. A 2-D numerical model is proposed to treat such river changes by introducing erosion rate formula for cohesive material and formula for estimating the thickness of sediment transport layer into a usual method. The new method is applied to the study reach which is 12km long and is supposed to be applicable for predicting channel change of natural river with fine sediment.

Experimental investigation of bed-load and suspended-load transport over weirs

An experimental investigation was undertaken to model the transport of bed-load and suspended-load sediment over steep slopes such as dikes and weirs. Six tests were performed using a vertical wall weir and a sloped (1 : 4) wall weir. Measurements were made of bed-load and suspended-load transport rates upstream and downstream of the test section. It was found that upstream of a vertical weir a strong down-flow vortex forms. This vortex creates a scour hole at the base of the weir and entrains sediment entering the region so that all of the sediment is transported in suspension over the weir. Downstream of the weir a strong reverse vortex traps a proportion of the material in suspension and creates a deposition zone. The sediment supply and flow rate control the temporal development of this deposit. For a sloped weir the down-flow vortex is eliminated at the upstream weir face. However the strong acceleration of the flow moving up the slope is sufficient to entrain all of the bed-load material so again, all sediment is transported over the weir in suspension. No sediment deposition was noted for the region upstream of the weir, although ripples were able to move partway up the slope before being completely entrained. Downstream, deposition in the deceleration zone occurred as expected. The results for both weir shapes differ from the expected sediment depositional patterns. In the field deposition has been noted on the upstream slope of dikes after flood events. Possible reasons for the difference between field and experimental observations are discussed.

Middle Danube tributaries: Constraints and opportunities in lowland river restoration.

Modifications to large active rivers to aid navigation, reduce flood risk, improve land drainage or generate hydroelectric power have adversely affected river habitats and the hydrological connectivity between the river and its floodplain. Consideration of natural river processes helps to identify sustainable rehabilitation options within constraints imposed by the need to maintain required river functions and any restrictions imposed by space limitations due to floodplain development. A brief review of rehabilitation opportunities for active lowland rivers constrained by river functions is presented. This approach is used to identify suitable rehabilitation measures for two lowland meandering Slovak rivers, the Morava and Hron, which have been significantly influenced by engineering works. Both rivers differ in hydrological, morphological and ecological characteristics. Previous rehabilitation efforts based on locally targeted ecological and landscape restoration measures have actually exacerbated ecological degradation due to their failure to consider the abiotic processes which control river morphology. For rehabilitating cut-off meanders, full meander integration is recommended as the best solution for lowland rivers, such as the Morava, which actively transport bed material load. On the Hron River, an alternative method for improving the water regime and ecological quality of cut-off meanders is required due to engineering constraints. The study demonstrates the need for an integrated interdisciplinary approach to river restoration.

Bed load transport in managed steep‐gradient headwater streams of southeastern Alaska

Bed load transport was investigated in four headwater streams in southeastern Alaska subjected to different management and disturbance regimes. Bed load yield was positively correlated to peak discharge during the fall 1999 monitoring period. Fine bed load materials (1–11 mm) that were supplied from hillslope sources were equally mobilized during most storm events. Medium‐sized bed materials (11–200 m) were only partially mobilized even during large storms, whereas large particles (>200 mm) were immobile and often formed interlocking channel structures. The transport distances of medium‐size materials depended on amount of channel obstructions (e.g., woody debris) and sediment supply conditions; both of these factors were influenced by the occurrence of mass movement, timber harvesting, and the related recovery processes. The highest total bed load yield was observed in a channel affected by a debris flow in 1993. Total sediment yields are similar among channels with old‐growth, clear cut (logged 4 years before monitoring), and young alder (affected by landslides and debris flows in 1961) riparian stands. By comparing the old‐growth and young alder channels, it appears that bed load yield recovers from debris flow disturbances in about 40 years; however, recovery of channel conditions (e.g., reach types and woody debris) may take much longer. Effects of timber harvesting on bed load transport are controlled by sediment linkages between hillslopes and channels related to the occurrence of mass movement.

Progradational sand-mud deltas in lakes and reservoirs. Part 1. Theory and numerical modeling

Deltas are cone-shaped deposits formed at the confluence of rivers with standing bodies of water. One of the most common stream morphologies associated with deltas is that of the sand-bed stream. Such streams usually carry significantly more mud as wash load than they do sand as bed material load. Deltas typically form so that the sand deposits fluvially in the river channel and avalanches into deeper water to create a prograding delta face. The remaining muddy river inflow often plunges over the steep delta face and continues flowing downslope as a bottom turbidity current. The mud carried into deep water by the underflow settles out on the bed of the lake or reservoir. A variety of numerical models dealing separately with either fluvial deposition or depositional turbidity currents have been proposed to date. The work reported here pertains to an integral, physically-based, moving boundary model of deltaic sedimentation in lakes and reservoirs that captures the co-evolution of the river-delta morphology and the associated deposits. The formulation unites fluvial and turbidity current morphodynamics in a single numerical model. The model is tested against the results of the two experiments described in a companion paper.

Can Dispersive Pressure Cause Inverse Grading in Grain Flows?: Discussion

The concept of dispersive pressure was originally proposed by Bagnold (1954), who showed experimentally that sheared granular material develops a dispersive pressure that is proportional to shear stress and particle concentration. Legros (2002) presented a theoretical analysis suggesting that dispersive pressure cannot account for inverse grading commonly observed in grain flows, modified grain flows or traction carpets, contrary to what has been accepted for decades by many sedimentologists. He pointed out that, if dispersive pressure in a sheared granular mass increases and exceeds applied normal stress or static pressure, net upward force acting upon bed causes it to expand, as has in fact been observed in experiments. Bed expansion immediately causes a decrease in particle concentration and consequently in dispersive pressure, until latter balances static pressure and expansion stops. If dispersive pressure becomes less than static pressure, net downward force acting upon granular bed causes compaction, thus increasing particle concentration and dispersive pressure. This is an important concept enhancing our understanding of an as yet poorly understood process. However, Legros (2002) went further to state that the dispersive pressure must always equal applied normal shear stress at every level (emphasis mine) through shearing granular bed. This implies that whole sheared bed is in constant equilibrium, which is probably not case. In this discussion a modified process is proposed that accounts for bipartite traction carpet structure proposed by Sohn (1997). Traction carpets are moving layers of highly concentrated bedload material developed beneath and driven by an overlying turbulent flow (Dzulynski and Sanders 1962). Sohn (1997), on basis of numerical analyses, computer simulations, field measurements, and experimental studies (Bagnold 1955, 1963; Hanes and Bowen 1985; Wan …

Evaluation of sediment transport in the lower part of the Fitzroy River, Queensland

Comprehensive sediment sampling carried out by the Queensland Department of Natural Resources and Mines (DNRM) at the Laurel Banks site located about 76 km upstream of the Fitzroy River mouth during four flood events in the period 1994 -1999 allowed the evaluation of 14 different sediment transport formulae. The bed material load was accurately predicted by the formula of Bagnold and by the formula of Pacheco-Ceballos. Finally the authors have developed a sediment transport formula best suited to the Fitzroy River conditions. By applying acceptable formulae to hydrograph data for 35 years it was confirmed that approximately 20 million tons of sediment might be eroded from the catchment during the most severe flood events. The mean annual total sediment discharge has been computed to be more than 5 million tons, and the mean bed material discharge sums up to about 260,000 tons.