Bedload Discharge Research Articles

Characterization of bedload discharge in bores and very unsteady flows in an ephemeral channel

Bedload flux under steady flow conditions is calculated by a multitude of available methods and equations. Yet, very little is known about the effect of very unsteady flows, such as flash floods and specifically bores, on bedload flux. The unpredictable nature of the floods together with many logistic difficulties and safety issues in monitoring explain this gap in knowledge. Global climate change may increase flood event occurrence, making their understanding even more crucial. The methodology of our study is based on automatically monitoring bedload flux (Reid slot samplers). Automation allowed high frequency monitoring of hydraulic parameters and bedload flux. Added novelty includes pipe and plate microphones for capturing acoustic signals of bedload sediments and 3-D velocimetry for characterizing turbulence. Alerting sensors and cellular data transmission enabled onsite presence upon bore arrival. Calibration between the acoustic indirect sensors and the direct slot samplers allows determination of bedload flux at a frequency of 1 Hz. Analyses of flood events indicate an increase in turbulent kinetic energy, instantaneous vertical velocities, shear stress and bedload flux during the rising limb within the first two minutes after bore arrival. This has implications for the likely destabilization of the channel bed and for bedload transport after passage of the bore and during subsequent, less unsteady flows.

Insights into bedload transport processes of a large regulated gravel‐bed river

AbstractA comprehensive monitoring programme focusing on bedload transport behaviour was conducted at a large gravel‐bed river. Innovative monitoring strategies were developed during five years of preconstruction observations accompanying a restoration project. A bedload basket sampler was used to perform 55 cross‐sectional measurements, which cover the entire water discharge spectrum from a 200‐year flood event in 2013 to a rare low flow event. The monitoring activities provide essential knowledge regarding bedload transport processes in large rivers. We have identified the initiation of motion under low flow conditions and a decrease in the rate of bedload discharge with increasing water discharge around bankfull conditions. Bedload flux strongly increases again during high flood events when the entire inundation area is flooded. No bedload hysteresis was observed. The effective discharge for bedload transport was determined to be near mean flow conditions, which is therefore at a lower flow discharge than expected. A numerical sediment transport model was able to reproduce the measured sediment transport patterns. The unique dataset enables the characterisation of bedload transport patterns in a large and regulated gravel‐bed river, evaluation of modern river engineering measures on the Danube, and, as a pilot project has recently been under construction, is able to address ongoing river bed incision, unsatisfactory ecological conditions for the adjacent national park and insufficient water depths for inland navigation. Copyright © 2017 John Wiley & Sons, Ltd.

Estimation of bedload discharge in sewer pipes with different boundary conditions using an evolutionary algorithm

Sediment transport is a complex phenomenon due to the nonlinearity and uncertainties of the process. The present study applies Gene Expression Programming (GEP) to develop bedload transport models in sewer pipes. In this regard, two types of bedload were considered: loose bed (deposition state) and rigid bed (limit of deposition state). In order to develop the models, two scenarios with different input combinations were considered: Scenario 1 considers only hydraulic characteristics and Scenario 2 considers both hydraulic and sediment characteristics as inputs for modeling bedload discharge. The results proved the capability of GEP in prediction of sediment transport and it was found that for prediction of bedload transport in sewer pipes Scenario 2 performed more successfully than Scenario 1. According to the outcome of sensitivity analysis, Frm (Modified Froude number) and d50/y (relative particle size) for rigid boundary and Frm for loose boundary had key roles in the modeling. The outcome of the GEP models also was compared with existing empirical equations and it was found the GEP models yielded better results. It was also found that pipe diameter affected the transport capacity of the sewer pipe. Increasing pipe diameter caused an increase in model efficiency. A pipe with a diameter of 305mm yielded to the best results.

Passive acoustic monitoring of bed load discharge in a large gravel bed river

AbstractSurrogate technologies to monitor bed load discharge have been developed to supplement and ultimately take over traditional direct methods. Our research deals with passive acoustic monitoring of bed load flux using a hydrophone continuously deployed near a river bed. This passive acoustic technology senses any acoustic waves propagated in the river environment and particularly the sound due to interparticle collisions emitted during bed load movement. A data set has been acquired in the large Alpine gravel‐bedded Drau River. Analysis of the short‐term frequency response of acoustic signals allows us to determine the origin of recorded noises and to consider their frequency variations. Results are compared with ancillary field data of water depth and bed load transport inferred from the signals of a geophone array. Hydrophone and geophone signals are well correlated. Thanks to the large network of deployed geophones, analysis of the spatial resolution of hydrophone measurements shows that the sensor is sensitive to bed load motion not only locally but over distances of 5–10 m (10–20% of river width). Our results are promising in terms of the potential use of hydrophones for monitoring bed load transport in large gravel bed rivers: acoustic signals represent a large river bed area, rather than being local; hydrophones can be installed in large floods; they can be deployed at a low cost and provide continuous monitoring at high temporal resolution.

Towards the problem of the ratio between suspended and bed load discharges in a river flow

The review ofthe main methods for the estimation ofthe ratio between suspended and bed load discharges is presented. The estimates of discharge ratio are given for the Laba River. The contribution of bed load discharge to the total load discharge is computed for each phase of water regime. The obtained results of computations fully agree with the data of observations in the watercourse.

A particle counting system for calculation of bedload fluxes

Channel bed morphology depends on bedload fluxes which are difficult to determine even in controlled laboratory conditions. Particle counting can provide time resolved bedload fluxes. Determination of particle rates by means of digital image processing is computationally expensive and the requirement for optical access is not always met. Weighing methods are limited by short dynamic ranges. To overcome these difficulties this paper presents a prototype of a particle counter device that works by detecting impacts on a sensitive surface. The accuracy of the device is validated, by means of laboratory experiments, contrasting its results against those obtained by means of digital image analysis. This device proved to be capable of measuring bedload fluxes, determining long time series of bedload transport rates, in particles per unit time, with high accuracy and with a much lower computation cost relatively to digital image processing. The device is also able to gather meaningful data in real-time, like particle arrival time-series and real-time lateral bedload distribution. The parameters involved in the detection criterion must be previously set through a heuristic procedure. However, the method itself is direct—it requires no calibration between the acquired signal and bedload transport rates. Particle counts can be transformed in bedload discharges by a simple binning process or by taking finite differences of the cumulative mass function. First and second order moments of bedload discharge are in agreement with the values obtained by direct counting. The low requirement for data storage, allowing for very large data series, the real time analysis capabilities, the low cost of such system when compared with a digital image acquisition system constitute the main advantages of the device for the study of integral scales of bedload and bedload intermittency.

Integrated automatic and continuous bedload monitoring in gravel bed rivers

Bedload monitoring techniques have been developed and applied for many years in rivers ranging from steep mountain torrents to the large gravel-bed Danube River in Austria. Most monitoring stations use a combination of direct (mobile bag samplers, slot samplers) and indirect (geophones, hydrophones) measurement methods. Each individual technique is adequate, yet features particular boundary conditions and limitations related to hydraulic and sampling efficiency, functionality during floods, sampling duration or grain size. We show the capabilities and limitations of the different monitoring devices with respect to technical, operational and economic criteria, evaluating their suitability for determining bedload transport parameters. Bedload monitoring results of a measuring site at the Drau River in Carinthia/Austria are used to illustrate the specific range of the device application. We present an integrated automatic and continuous bedload monitoring system. It complements the specific limitations of single monitoring methods by additional measurement devices, enabling comprehensive monitoring of the bedload transport process. We then derive the Bedload Discharge Integrated Calculation Approach and the Bedload Rating Curve Approach and discuss their application for determining bedload discharge Qb and total bedload mass Vb. Whereas the integrated approach combines data from direct monitoring methods with indirect techniques, the rating curve approach uses only data from direct bedload monitoring devices. We demonstrate that applying an integrated automatic and continuous bedload monitoring system and combining the Bedload Discharge Integrated Calculation Approach and Bedload Rating Curve Approach yields accurate bedload discharge results.

Prediction of non-cohesive sediment transport in circular channels in deposition and limit of deposition states using SVM

Sedimentation in sewer pipes has a negative impact on the performance of sewerage systems. However, due to the complex nature of sedimentation, determining the governing equations is difficult and the results of the available classic models for computing bedload transport rate often differ from each other. This paper focuses on the capability of a support vector machine (SVM) as a meta-model approach for predicting bedload transport in pipes. The method was applied for the deposition and limit of deposition states of sediment transport. Two different scenarios were proposed: in Scenario 1, the input combinations were prepared using only hydraulic characteristics, on the other hand, Scenario 2 was built using both hydraulic and sediment characteristics as model inputs of bedload transport. A comparison between the SVM and the employed classic approaches in predicting sediment transport indicated the supreme performance of the SVM, in which more accurate results were obtained. Also it was found that for estimation of bedload transport in pipes, Scenario 2 led to a more valid outcome than Scenario 1. Based on the sensitivity analysis, parameters Frm and d50/y in the limit of deposition state and Frm in the deposition state had the more dominant role in prediction of bedload discharge in pipes than other parameters.

Discrete-Time Markov Chain Model for Transport of Mixed-Size Sediment Particles under Unsteady Flow Conditions

AbstractA nonhomogeneous discrete-time three-state Markov chain model is developed in this study to quantify the bedload and suspended load discharge under unsteady flow for mixed size sediment particles. When flow is subject to sudden changes, the particle holding time, defined as the amount of time for a sediment particle staying on the bed or in the moving state, needs to be carefully evaluated. The time step used in this study for single-step motion in the discrete-time Markov chain is represented by a characteristic timescale for particle motion. The transition probabilities are functions of flow conditions and particle properties. Specifically, the likelihood of particle movement between the bedload layer and the bed surface is evaluated by the entrainment probability. Exchange of sediment particles between the bedload layer and suspended load layer is quantified by the suspension probability. A nonhomogeneous Markov chain ensures the transition probabilities are time dependent as they are a functio...

An experimental analysis of bed load transport in gravel-bed braided rivers with high grain Reynolds numbers

Laboratory experiments were performed with nearly uniform fluvial gravel (D50=9mm, D10=5mm and D90=13mm) to analyse the relationship between stream power and bed load transport rate in gravel-bed braided rivers at high grain Reynolds numbers. The values of the unit-width dimensionless bed-load rate qb* and unit-width dimensionless stream power ω* were evaluated in equilibrium conditions based on ten different experimental runs. Then, they were plotted along with values obtained during particularly representative field studies documented in the literature, and a regression law was derived. For comparison, a regression analysis was performed using the data obtained from laboratory experiments characterized by smaller grain sizes and, therefore, referring to relatively low grain Reynolds numbers. A numerical integration of Exner's equation was performed to reconstruct the local and time-dependent functional dependence of qb* and ω*. The results led to the following conclusions: 1) At equilibrium, the reach-averaged bed load transport rate is related to the reach-averaged stream power by different regression laws at high and low grain Reynolds numbers. Additionally, the transition from bed to suspended load transport is accelerated by low Re*, with the corresponding bed load discharge increasing with stream power at a lower, linear rate. 2) When tested against the gravel laboratory measurements, the high Re* power law derived in the present study performs considerably better than do previous formulas. 3) The longitudinal variability of the section-averaged equilibrium stream power is much more pronounced than that characterizing the bed load rate, at least for high Re*. Thus, the stream power and its local-scale heterogeneity seem to be directly responsible for transverse sediment re-distribution and, ultimately, for the determination of the spatial and temporal scales that characterize the gravel bedforms. 4) Finally, the stochastic interpretation of the wetted bed elevation function mapped in a particularly representative sample run reveals that gravel-bed transport and braiding are associated with the persistence of multiple equilibrium energy states due to the presence of truly non-stationary, local-scale pseudo-periodicity.

Accommodation space in a high-wave-energy inner-shelf during the Holocene marine transgression: Correlation of onshore and offshore inner-shelf deposits (0–12 ka) in the Columbia River littoral cell system, Washington and Oregon, USA

The Columbia River Littoral Cell (CRLC), a high-wave-energy littoral system, extends 160km alongshore, generally north of the large Columbia River, and 10–15km in across-shelf distance from paleo-beach backshores to about 50m present water depths. Onshore drill holes (19 in number and 5–35m in subsurface depth) and offshore vibracores (33 in number and 1–5m in subsurface depth) constrain inner-shelf sand grain sizes (sample means 0.13–0.25mm) and heavy mineral source indicators (>90% Holocene Columbia River sand) of the inner-shelf facies (≥90% fine sand). Stratigraphic correlation of the transgressive ravinement surface in onshore drill holes and in offshore seismic reflection profiles provide age constraints (0–12ka) on post-ravinement inner-shelf deposits, using paleo-sea level curves and radiocarbon dates. Post-ravinement deposit thickness (1–50m) and long-term sedimentation rates (0.4–4.4mka−1) are positively correlated to the cross-shelf gradients (0.36–0.63%) of the transgressive ravinement surface. The total post-ravinement fill volume of fine littoral sand (2.48×1010m3) in the inner-shelf represents about 2.07×106m3year−1 fine sand accumulation rate during the last 12ka, or about one third of the estimated middle- to late-Holocene Columbia River bedload or sand discharge (5–6×106m3year−1) to the littoral zone. The fine sand accumulation in the inner-shelf represents post-ravinement accommodation space resulting from 1) geometry and depth of the transgressive ravinement surface, 2) post-ravinement sea-level rise, and 3) fine sand dispersal in the inner-shelf by combined high-wave-energy and geostrophic flow/down-welling drift currents during major winter storms.

Development and installation of bedload monitoring systems with submerged load cells

Bedload governs riverbed channel variations and morphology,it isnecessarytodeterminebedload discharge through an arbitrary cross sectionin a mountain river. A new system with submerged load cells has been developed to directly measure bedload discharge. The system consists of:(1) anironbox which is 1 m long, 0.5 m wide and 0.1 m in depth, (2) two submerged load cells 0.7 m apart, (3) a pressure sensor and,(4) an electromagnetic velocity meter. This system has been designed to exclude the effect of the hydraulic pressure of water on direct measurements ofbedload particle weight. Initialtestsin a laboratorywere conducted to examine the accuracy of measurements with the system underaerial conditions. The system has beeninstalled in the supercritical flume in Ashi-arai-dani River of the Hodaka Sedimentation Observatory of the Disaster Prevention Research Institute (DPRI) of Kyoto Universityto obtain bedload dischargeunder natural conditions. Flume tests were conductedin this channelby artificial supply of uniform sediment particles ofseveral grain sizes.The averagevelocity of the sediment particles near the bed wasestimated usingcross-correlation functions forweightwaves obtained bythe two load cells.Bedload dischargecalculations were based ontime integration oftheproduct of sediment velocity andsedimentweight obtained bythe twoload cells. Thisstudyclarifies thereasons whybedload measurements are difficult, and providessomesolutions using the monitoring systems with submerged load cells through the field measurements. Additionally, the applicabilityofbedload measurement with the submerged load cellsis explained based onexperimental artificial sediment supplydata.

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.

Assessment of bedload equations using data obtained with tracers in two coarse-bed mountain streams (Narcea River basin, NW Spain)

This paper evaluates the predictive power of nine bedload equations, comparing the results provided by the equations with the bedload rates obtained in a previous field-based tracer experiment accomplished in River Pigüeña and River Coto, two coarse bed streams from NW Spain. Rivers from NW Spain draining the northern watershed of the Cantabrian Mountain range flow into the Bay of Biscay in a short path (50–60km). In this region, they are developed forested catchments featured by fluvial networks with relatively steep slopes, single-thread sinuous channels, and where bed sediment is typically coarse (cobble and gravel).Tagged stones were used to trace bed sediment movement during flood events in River Pigüeña and River Coto, the two main tributaries of the Narcea River basin. With the tracer results, bedload transport rates between 0.2 and 4.0kg/s were estimated for six flood episodes.The tracer-based bedload discharges were compared with the bedload rates estimated with the bedload formulae (DuBoys–Straub, Schoklitsch, Meyer Peter–Müller, Bagbold, Einstein, Parker–Klingeman–McLean, Parker–Klingeman, Parker and Wilcock-Crowe). Our assessment shows that all of the bedload equations tend to overestimate when compared with the tracer-based results, with the Wilcock and Crowe (2003) equation the only exception in River Pigüeña.We linked these results to the particular geomorphology of coarse-bed rivers in humid and forested mountain environments. Within these rivers, armored textures and structural arrangements in the bed are ubiquitous; these features, together with a low sediment supply coming from upstream forested reaches, define a supply-limited condition for these channels limiting the potential use of bedload equations. The Wilcock and Crowe (2003) equation introduces complex corrections into the ‘hiding function’, and this could explain why it performs better.

Estimation of bedload transport in headwater streams using a numerical model (Moravskoslezké Beskydy Mts, Czech Republic)

The TOMSED numerical model, originally developed for Alpine torrents, was successfully applied on the May, 2010 flood event in headwater streams of the Czech part of the Western Flysch Carpathians. The Manning equation was used together with application of a reduced energy gradient and potential erosion limits. Contributions of form resistance and grain resistance to Manning’s roughness parameter were considered separately. The absence of bedload discharge measurement made it difficult to validate the model for local headwater channels, although channel reaches with recent erosional and depositional trends were recognized fairly well by the simulations. Bedload transport was calculated in the range from 480–1240 m3 for the richly-supplied headwater stream and 380–860 m3 for the stream with limited sediment-supply conditions. It turns out that the channel reaches with higher sediment supply have less developed bedforms (e.g. steps) and thus lower flow resistance resulting in a higher intensity of bedload transport.

Evaluation of bed load transport formulae in a large regulated gravel bed river: The lower Ebro (NE Iberian Peninsula)

This paper tests the predictive power of 10 bed load formulae against bed load rates obtained for a large regulated river (River Ebro) the armor layer of which is subject to repeated cycles of break-up and reestablishment. The theoretical principles of two of the 10 formulae explicitly include the effects of river bed armoring. The results obtained showed substantial differences in equation performance but no evident relationship between predictive power and theoretical approach (e.g., discharge, stream power and probability) was found. Overall, the predictive power of the tested formulae was relatively low. The average percentages of predicted bed load discharge that did not exceed factors of 2 (0.5 < r < 2) and 10 (0.1 < r < 10) in relation to the observed discharge were 19% and 57%, respectively (where r is the discrepancy ratio between the predicted and observed values). In particular, the formulae of Yang (1984) and Parker et al. (1982) presented the better levels of agreement with the observed bed load discharges. The bed load rating curve for the lower Ebro showed a similar degree of agreement to the best-performing formulae. However, its predictive power was limited because only flow discharge acts as an independent variable and river bed dynamics, such as armoring cycles, are not contemplated.

Relationship between bedload and suspended sediment in the sand-bed Exu River, in the semi-arid region of Brazil

Suspended sediment and bedload discharges in sand-bed rivers shape semi-arid landscapes and impact sediment delivery from these landscapes, but are still incompletely understood. Suspended sediment and bedload fluxes of the intermittent Exu River, Brazil, were sampled by direct measurements. The highest suspended sediment concentration observed was 4847.4 mg L-1 and this value was possibly associated with the entrainment of sediment that was deposited in the preceding year. The bedload flux was well related to the stream power and the river efficiently transported all available bedload with a mean rate of 0.0047 kg m-1 s-1, and the percentage of bedload to suspended sediment varied between 4 and 12.72. The bed sediment of Exu River was prone to entrainment and showed a proclivity for transport. Thus, sand-bed and gravel-bed rivers of arid environments seem to exhibit the same mobility in the absence of armour layer.Editor D. Koutsoyiannis; Associate editor B. TouaibiaCitation Cantalice, J.R.B., Cunha Filho, M., Stosic, B.D., Piscoya, V.C., Guerra, S.M.S., and Singh, V.P., 2013. Relationship between bedload and suspended sediment in the sand-bed Exu River, in the semi-arid region of Brazil. Hydrological Sciences Journal, 58 (8), 1789–1802.

Morphotextural characterization of dryland braided channels

Braided streams have been extensively studied in humid environments or in flumes that simulate them. Dryland rivers have bare catchments, rapid recession hydrographs, and unarmored beds, resulting in high bed-load discharges. Our objective was to characterize the morphotexture of the morphological elements—bar, anabranches, chutes, and confluences—in a dryland braided system. Morphological elements measured in Wadis Ze’elim, Rahaf, and Roded, located in southeast Israel, were scanned using terrestrial laser scanning, from which digital elevation models were generated. Roughness was evaluated from the standard deviation of detrended surfaces or from Wolman-sampled surface texture. Armoring of the bar and the adjacent anabranch was also evaluated. Scour chains were deployed in confluences to measure scour and fill during flow events. Dryland anabranches were finer grained and less armored than the adjacent bars. Bed load, deposited as midchannel bars or on top of existing bars and thus associated with the depositional braiding process, was enriched by the coarser fractions, while the remaining bed-load was deposited in the anabranches during the rapid flow recession. Chutes associated with erosional braiding processes were formed as topographic features with high local gradients, enabling winnowing of fines, deposited immediately downstream or transported further away. Scour chains inserted in the confluence zones demonstrated the formation and obliteration of a scour hole during a flow event. The terrestrial laser scanning–based digital elevation models and roughness analyses suggest that the hydrological regime of ephemeral channels with short-lived recessions is responsible for the morphotextural setting of braid systems in arid environments.

Continuous monitoring of bedload discharge in a small, steep sandy channel

This paper reports on bedload flux and texture monitored in a natural, steep, sandy ephemeral channel draining a small gullied sandy watershed, the Barranca de los Pinos (1.32 ha), Spain. Bedload flux was continuously monitored with two independent Reid-type slot samplers; bedload texture was determined from the sediment collected in the samplers. Channel morphology was surveyed with a high spatial resolution with a Terrestrial Laser Scanner. The monitored instantaneous bedload fluxes are among the highest measured in natural rivers, characterized by high temporal and spatial variability related to the presence of bedforms, shallow bars and sand sheets, and to the reworking of the dry bed between and at the end of individual flow events. The grain size distribution of the bedload indicates equal mobility; but bedload texture fluctuates, depicting the transport of coarser bar surfaces and of finer-grained anabranch surfaces as well as of the overall bed subsurface.

Continuous measurements of bedload transport rates in a small glacial river catchment in the summer season (Spitsbergen)

The study on bedload transport was conducted on the gravel-bed Scott River catchment with a glacial alimentation regime, located in the NW part of the Wedel Jarlsberg Land (Spitsbergen) with subpolar climatic conditions. In the melt season of 2010, bedload transport rate was continuously monitored at 24-hour intervals by means of four River Bedload Trap devices aligned across the width of the channel. The maximum bedload transport rate varied strongly at portions of the cross section from 16 to 152kgm−1d−1 in cross-profile I (c-p I) and 4 to 125kgm−1d−1 in cross-profile II (c-p II). The maximum channel-mean bedload transport rate (qa) amounted to 54kgm−1d−1 (c-p I) and 35kgm−1d−1 (c-p II). Mean daily bedload discharge (Qb) was estimated at a level of 97kgday−1 (c-p I) and 35kgm−1d−1 (c-p II), and the total bedload yield was determined at approx. 4345kg in the measurement period (2086kg — c-p I; 2203kg — c-p II from 13.07 to 10.08). The analysis of the relationship between channel-mean bedload transport rate and water velocity or shear stress revealed a significant value of the correlation coefficient (R2=0.6). Discharge and rate of bedload transport were dependent on the weather and number of days with flood discharge. Approx. 58% of the entire discharged bedload was transported during 3 violent ablation–precipitation floods. Bedload grain size distribution was right-skewed and showed moderate sorting.