Suspended sediment monitoring in alluvial gullies: A laboratory and field evaluation of available measurement techniques

Gully erosion is a significant source of fine suspended sediment (<63 μm) and associated nutrient pollution to freshwater and marine waterways. Researchers, government agencies, and monitoring groups are currently using monitoring methods designed for streams and rivers (e.g., autosamplers, rising stage samplers, and turbidity loggers) to evaluate suspended sediment in gullies. This is potentially problematic because gullies have several hydrological features and monitoring operational challenges that differ to those of continually flowing streams and rivers (e.g., short and intense flows, high suspended sediment concentrations, and rapid scouring and aggradation). Here we present a laboratory and field-based assessment of the performance of common suspended sediment monitoring techniques applied to gullies. We also evaluate a recently-described method; the pumped active suspended sediment (PASS) sampler, which has been modified for monitoring suspended sediment in gully systems. Discrete autosampling provided data at high temporal resolution, however, it had poor collection efficiency (25 ± 10%) of coarser sediment particles (i.e., sand). Rising stage sampling, while robust and cost-effective, suffered from large amounts of condensation under field conditions (25–35% of sampler volume), due to harsh climatic conditions creating large diurnal temperature differences at the field site, thereby diluting sample concentrations and introducing additional measurement uncertainty. The turbidity logger exhibited a highly variable response when calibrated at each site with physically collected suspended sediment samples (R² = 0.17–0.83), highlighting that this approach should be used with caution. The modified PASS sampler proved to be a reliable and representative measurement method for gully sediment water quality, however, the time-integrated nature of the method limits its temporal resolution compared to the other monitoring methods. We recommend monitoring suspended sediment in alluvial gully systems using a combination of complementary techniques (e.g., PASS and RS samplers) to account for the limitations associated with individual methods.     

Evaluation of a simple,inexpensive, in situ sampler for measuring time‐weighted average concentrations of suspended sediment in rivers and streams

The accurate measurement of suspended sediment (<200 μm) in aquatic environments is essential to understand and effectively manage changes to sediment, nutrient, and contaminant concentrations on both temporal and spatial scales. Commonly used sampling techniques for suspended sediment either lack the ability to accurately measure sediment concentration (e.g., passive sediment samplers) or are too expensive to deploy in sufficient number to provide landscape‐scale information (e.g., automated discrete samplers). Here, we evaluate a time‐integrated suspended sediment sampling technique, the pumped active suspended sediment (PASS) sampler, which collects a sample that can be used for the accurate measurement of time‐weighted average (TWA) suspended sediment concentration and sediment particle size distribution. The sampler was evaluated against an established passive time‐integrated suspended sediment sampling technique (i.e., Phillips sampler) and the standard discrete sampling method (i.e., manual discrete sampling). The PASS sampler collected a sample representative of TWA suspended sediment concentration and particle size distribution of a control sediment under laboratory conditions. Field application of the PASS sampler showed that it collected a representative TWA suspended sediment concentration and particle size distribution during high flow events in an urban stream. The particle size distribution of sediment collected by the PASS and Phillips samplers were comparable and the TWA suspended sediment concentration of the samples collected using the PASS and discrete sampling techniques agreed well, differing by only 4% and 6% for two different high flow events. We should note that the current configuration of the PASS sampler does not provide a flow‐weighted measurement and, therefore, is not suitable for the determination of sediment loads. The PASS sampler is a simple, inexpensive, and robust in situ sampling technique for the accurate measurement of TWA suspended sediment concentration and particle size distribution.     

Determination of the particle load based on detailed suspended sediment measurements at a hydropower plant

Suspended sediment particles contained in inflows of water systems of hydropower plants (HPPs) cause hydro-abrasive erosion of the hydraulic turbines and structures leading to significant maintenance costs, efficiency reductions, and downtime. Relevant parameters such as suspended sediment concentration (SSC), particle size distribution (PSD), shape, and mineralogical composition were measured with an online multi-frequency acoustic instrument and based on manually taken samples from the end of the sand trap of the Toss HPP in the Himalayan region, India. In the laboratory, the samples were analyzed using the gravimetric method, laser diffraction, turbidity, dynamic digital image processing, scanning electron microscope, petrography analysis, energy-dispersive X-ray spectroscopy, and X-ray diffraction. The online instrument and the samples provided measurement results at a single point. To investigate vertical gradients in concentration and particle sizes, additional samples were collected 9 times at 7 relative water depths. The SSC, most particle sizes, and particle shape were found to be evenly distributed over depth except d90, i.e. the diameter which is not exceeded by 90% of the particle mass. d90 measured at 76% of the water depth was in the range of fine sand and was multiplied by 1.05 to obtain an average value representative for the entire depth. Improved methodologies to quantify both particle shape and size in an analytical model for hydro-abrasive erosion are proposed. Also, the PSD measuring performance of laser diffraction and dynamic imaging was studied and similar values of the median particle sizes were obtained from both instruments. Further, multi-frequency acoustic, turbidity and laser diffraction techniques were found suitable for SSC measurement at the test case HPP.     

The particle size characteristics of fine‐grained channel deposits in the River Exe Basin,Devon, UK

Deposition and storage of fine‐grained (<62·5 μm) sediment in the hyporheic zone of gravel bed rivers frequently represents an important cause of aquatic habitat degradation. The particle size characteristics of such fine‐grained bed sediment (FGBS) exert an important control on its hydrodynamic properties and environmental impact. Traditionally, particle size analysis of FGBS in gravel bed rivers has focused on the absolute size distribution of the chemically dispersed mineral fraction. However, recent work has indicated that in common with fluvial suspended sediment, significant differences may exist between the absolute and the in situ, or effective, particle size composition of FGBS, as a result of the existence of aggregates, or composite particles. In the investigation reported in this paper, sealable bed traps that could be remotely opened to sample sediment deposited during specific storm runoff events and a laser back‐scatter probe were used to quantify the temporal and spatial variability of both the absolute and effective particle size composition of FGBS, and the associated suspended sediment from four gravel bed rivers in the Exe Basin, Devon, UK. The absolute particle size distributions of both the FGBS and suspended sediment evidenced c. >95%<62·5 μm sized primary particles and displayed a seasonal winter–summer fining, while the opposite trend was displayed by the effective particle size distribution of the FGBS and suspended sediment. The effective particle size distributions of both were typically highly aggregated, comprising up to 68%>62·5 μm sized particles. Spatial variation in the effective particle size and aggregation parameters was of secondary importance relative to temporal variation. The effective particle size distribution of the FGBS was consistently coarser and more aggregated than the associated suspended sediment and there was evidence of aggregate break‐up in samples of resuspended bed sediment. The implications of these findings for sediment transport modelling are considered. Copyright © 1999 John Wiley & Sons, Ltd.     

SEDIMENT LOAD AND ITS INFLUENCE ON CHANNEL PROCESSES OF SOME LARGE RIVERS IN RUSSIA AND CHINA~1

I INTRODUCTIONThe volume and regime of sediment load are the most important factors, which are responsible for theformation, direction and deformation rate of the river channels. Despite the long history of study anddevelopment of sediment load calculation methodology, there are still numerous problems that remain tobe solved such as river pattern and sediment movement and so on (Wang et al, 1997).In this respect, the comparative analysis of sediment load and river channel processes of la…     

The transformation of the runoff of the suspended load in Kamchatkan rivers due to volcanism

This paper considers the influence of volcanic eruptions on the variation in the characteristics of the runoff of the suspended river load (suspended sediment concentration, discharge, rate of runoff, and grain-size distribution) on a variety of space–time scales (daily, seasonal, and long-term). The main factors that affect the yield of suspended load in rivers that flow in volcanic areas include the water runoff, drainage area, and the abundance of unconsolidated volcanic deposits. The areas of recent volcanism in Kamchatka are characterized by the maximum values of potential scour of particles, the mean long-term suspended sediment concentration, and specific suspended sediment yield. The largest increment in the transport of suspended river load in areas of volcanic activity is observed after major eruptions. The daily variations in the transport of suspended load are controlled by the water regime of rivers on the slopes of active volcanoes, namely, periodic cessations of surface runoff because of filtering into volcanic deposits.     

Prediction of depth‐integrated fluxes of suspended sediment in the Amazon River: particle aggregation as a complicating factor

Large rivers have been previously shown to be vertically heterogeneous in terms of suspended particulate matter (SPM) concentration, as a result of sorting of suspended solids. Therefore, the spatial distribution of suspended sediments within the river section has to be known to assess the riverine sedimentary flux. Numerous studies have focused on the vertical distribution of SPM in a river channel from a theoretical or experimental perspective, but only a few were conducted so far on very large rivers. Moreover, a technique for the prediction of depth‐integrated suspended sediment fluxes in very large rivers based on sediment transport dynamics has not yet been proposed. We sampled river water along depth following several vertical profiles, at four locations on the Amazon River and its main tributaries and at two distinct water stages. Depending on the vertical profile, a one‐ to fivefold increase in SPM concentration is observed from river channel surface to bottom, which has a significant impact on the ‘depth‐averaged’ SPM concentration. For each cross section, a so‐called Rouse profile quantitatively accounts for the trend of SPM concentration increase with depth, and a representative Rouse number can be measured for each cross section. However, the prediction of this Rouse number would require the knowledge of the settling velocity of particles, which is dependent on the state of aggregation affecting particles within the river. We demonstrate that in the Amazon River, particle aggregation significantly influences the Rouse number and renders its determination impossible from grain‐size distribution data obtained in the lab. However, in each cross section, the Rouse profile obtained from the fit of the data can serve as a basis to model, at first order, the SPM concentration at any position in the river cross section. This approach, combined with acoustic Doppler current profiler (ADCP) water velocity transects, allows us to accurately estimate the depth‐integrated instantaneous sediment flux. Copyright © 2010 John Wiley & Sons, Ltd.     

Particle size characteristics of suspended sediment in Southern Ontario rivers tributary to the great lakes

In spite of the important relationship between sediment particle size and the transport/deposition of adsorbed pollutants in fluvial systems, little information regarding the size characteristics of suspended sediment transported by southern Ontario Great Lakes tributaries is currently available. This paper examines long-term sediment and hydrometric data collected by the Water Resources Branch of Environment Canada in order to provide information on (1) typical particle size distributions of suspended sediment, (2) relationships between source material and particle size characteristics of suspended sediment, and (3) temporal variation in the particle size characteristics of suspended sediment from six southern Ontario rivers. Results illustrate the complex behaviour and variability of sediment particle size transport in these rivers and demonstrate the need for a better understanding of seasonal effects on sediment availability and conveyance processes in fluvial systems.     

Evaluation of the method of collecting suspended sediment from large rivers by discharge-weighted pumping and separation by continuous-flow centrifugation

A method for collecting suspended sediment samples has been developed that pumps a discharge-weighted volume of water from fixed depths at four to 40 locations across a river and separates the suspended sediment in the sample using a continuous-flow centrifuge. The efficacy of the method is evaluated by comparing the particle size distributions of sediment collected by the discharge-weighted pumping method with the particle size distributions of sediment collected by depth integration and separated by gravitational settling. The pumping method was found to undersample the suspended sand sized particles (> 63 μm) but to collect a representative sample of the suspended silt and clay sized particles (< 63 μm). The centrifuge separated the silt and clay sized particles (< 63 μm) into three fractions. Based on the average results of processing 17 samples from the Mississippi River and several of its large tributaries in 1990, about 10% of the silt and clay sized material was trapped in a centrifuge bowl-bottom sealing unit containing the nozzle and consisted of mostly medium and coarse silt from 16 to 63 μm. About 74% was retained on a Teflon liner in the centrifuge bowl and consisted of sizes from 0–1 to 63 μm. About 9% was discharged from the centrifuge in the effluent and was finer than 0–1 μm. About 7% was lost during the processes of removing the wet sediment fractions from the centrifuge, drying and weighing. The success of the discharge-weighted pumping method depends on how homogeneously the silt and clay sized particles (< 63 μm) are distributed in the vertical direction in the river. The degree of homogeneity depends on the composition and degree of aggregation of the suspended sediment particles.     

Fine-sediment mineralogy of source rocks and suspended sediment,rother catchment,West Sussex

The clay and silt mineralogy of the Cretaceous bedrocks of the Rother drainage basin is restricted to seven minerals. The mineralogy of soils and alluvium is similar to the bedrock upon which they are developed although minor variations can be found. The mineralogy of bedrock, soils and alluvium is reflected to some extent in the suspended sediment of rivers draining over them, and three different mineral assemblage zones are identified. Subtle controls of mineralogical variation in suspended sediment may include the ratio of groundwater/surface runoff contribution to river flow, rate of reaction of soil and bedrock to precipitation, preferential settling of non-platy grains in quieter stretches of water, and the precipitation of material from solution as waters equilibriate with the atmosphere.     

TEMPORAL AND SPATIAL DYNAMICS OF DIFFERENT PARTICLE SIZE OF SUSPENDED SEDIMENT IN THE LIU RIVER CATCHMENTS,CHINA

1 INTRODUCTION The particle size of sediment eroded from basins can provide basic information about erosion processes (Meyer et al., 1980), which can be divided into sheet wash sediment processes on hill slopes and fluvial sediment processes in rivers. In…     

Tide‐modulated hyperpycnal flows off the Huanghe (Yellow River) mouth,China

Few hyperpycnal flows have ever been observed in marine environments although they are believed to play a critical role in sediment dispersal within estuarine and deltaic depositional systems. The paper describes hyperpycnal flows observed in situ off the Huanghe (Yellow River) mouth, their relationship to tidal cycles, and the mechanisms that drive them. Simultaneous observations at six mooring stations during a cruise off the Huanghe mouth in the flood season of 1995 suggest that hyperpycnal flows observed at the river mouth are initiated by high concentrations of sediment input from river and modulated by tides. Hyperpycnal flows started near the end of ebb tides, when near‐bottom suspended sediment concentration (SSC) increased rapidly and salinity decreased drastically (an inverse salt wedge). The median grain size of suspended particles within the hyperpycnal layer increased, causing strong stratification of the suspended sediments in the water column. Towards the end of flood tides, the hyperpycnal flow attenuated due to frictions at the upper and lower boundaries of the flow and tidal mixing, which collapsed the stratification of the water column. Both sediment concentration and median grain size of suspended particles within the bottom layer significantly decreased. The coarser sediment particles were deposited and the hyperpycnal flows stopped. The intra‐tidal behaviors of hyperpycnal flows are closely associated with the variations of SSC, salinity, and stratification of the water column. As nearly 90% of riverine sediment is delivered to the sea during the flood seasons when hyperpycnal flows are active, hyperpycnal flows at the Huanghe mouth and the river's high sediment loads have caused rapid accretion of the Huanghe delta. Copyright © 2010 John Wiley & Sons, Ltd.     

Deposition and fate of reactive Fe,Mn, P,and C in suspended particulate matter in the Bay of Biscay

Hydrographic structure of the water column, dissolved nutrient concentrations and the distribution of suspended particulate matter were recorded from CDT measurements and Niskin bottles sampling on the continental slope of the Bay of Biscay and on the axis of Capbreton canyon. Ascorbate extraction was applied here for the first time on marine suspended particles to determine the content of reactive Fe- and Mn-oxides, and P associated with Fe-oxides. Hydrographic structure of the south-eastern part of the Bay of Biscay did not change during the last three decades. Particulate organic carbon (POC) contents dropped strongly with depth, showing that organic matter mineralization was efficient in the water column. Organic matter mineralized in the water column had a Redfield N:P ratio. POC percent of particles collected at depth were higher during a bloom period, suggesting that some new organic matter reached the bottom. Contents of Fe and Mn extracted with the ascorbate leaching solution showed that suspended particles originated from the Gironde estuary, one of the major sources of particles in the Bay of Biscay. Intermediate and deeper nepheloid layers occurred in the Capbreton canyon. Particles of nepheloid layers were enriched in Mn- and Fe-oxides because they originated from resuspension of surface sediment.     

Composite suspended sediment particles and flocculation in glacial meltwaters: preliminary evidence from Alpine and Himalayan basins

Research over the last decade has shown that the suspended sediment loads of many rivers are dominated by composite particles. These particles are also known as aggregates or flocs, and are commonly made up of constituent mineral particles, which evidence a wide range of grain sizes, and organic matter. The resulting in situ or effective particle size characteristics of fluvial suspended sediment exert a major control on all processes of entrainment, transport and deposition. The significance of composite suspended sediment particles in glacial meltwater streams has, however, not been established. Existing data on the particle size characteristics of suspended sediment in glacial meltwaters relate to the dispersed mineral fraction (absolute particle size), which, for certain size fractions, may bear little relationship to the effective or in situ distribution. Existing understanding of composite particle formation within freshwater environments would suggest that in‐stream flocculation processes do not take place in glacial meltwater systems because of the absence of organic binding agents. However, we report preliminary scanning electron microscopy data for one Alpine and two Himalayan glaciers that show composite particles are present in the suspended sediment load of the meltwater system. The genesis and structure of these composite particles and their constituent grain size characteristics are discussed. We present evidence for the existence of both aggregates, or composite particles whose features are largely inherited from source materials, and flocs, which represent composite particles produced by in‐stream flocculation processes. In the absence of organic materials, the latter may result solely from electrochemical flocculation in the meltwater sediment system. This type of floc formation has not been reported previously in the freshwater fluvial environment. Further work is needed to test the wider significance of these data and to investigate the effective particle size characteristics of suspended sediment associated with high concentration outburst events. Such events make a major contribution to suspended sediment fluxes in meltwater streams and may provide conditions that are conducive to composite particle formation by flocculation. Copyright © 2002 John Wiley & Sons, Ltd.     

Measuring and modeling vertical gradients in suspended sediments in the Solimões/Amazon River

Accurately measuring sediment flux in large rivers remains a challenge due to the spatial and temporal cross‐sectional variability of suspended sediment concentrations in conjunction with sampling procedures that fail to accurately quantify these differences. This study presents a field campaign methodology that can be used to improve the measurement of suspended sediment concentrations in the Amazon River or similarly large rivers. The turbidity signal and Rouse model are together used in this study to define the spatial distribution of suspended sediment concentrations in a river cross‐section, taking into account the different size fractions of the sediment. With this methodology, suspended sediment fluxes corresponding to each sediment class are defined with less uncertainty than with manual samples. This paper presents an application of this methodology during a field campaign at different gauging stations along a 3,000‐km stretch of the Solimões/Amazon River during low water and flood periods. Vertical concentration profiles and Rouse model applications for distinctive sediment sizes are explored to determine concentration gradients throughout a cross‐section of the river. The results show that coupling both turbidity technology and the Rouse model may improve our understanding of the spatial distribution of different sediments fractions sizes in the Solimões/Amazon River. These data are very useful in defining a pertinent monitoring strategy for suspended sediment concentrations in the challenging context of large rivers.     

Mineral composition and particle size distribution of river sediment and loess in the middle and lower Yellow River

Hyperconcentrated flows often occur in the middle and lower Yellow River(MLYR)and its tributaries,within which the main sediment source originates from the Loess Plateau of China due to serious water erosion.Little is known about the properties of river sediment that is transported by hyperconcentrated flows,particularly with respect to the mineral composition and size distribution.Samples of sediment and loess were collected in the northern,middle,and southern Loess Plateau and the mainstream and tributaries of the MLYR.A total of 18 loess samples and 24 river sediment samples were analyzed to determine their sediment size distribution and mineral composition.The bottom loess samples reflected the original sedimentary features of the Loess Plateau,and the median particle size reduced,and the clay content increased from the north to the south of the study region.The surface loess has been weathered under the action of wind and rainfall,and the clay particle content in the surface loess samples was higher than that in the undisturbed bottom loess.Erosion of the surface soil due to rainfall and surface runoff means that fine particles(mostly clay)have been washed away.The median diameter of surface loess particles was a little larger than that of the bottom loess particles where water erosion dominates.The particle size became coarser with increasing distance from the estuary in the MLYR,which reflects depositional sorting in the river channel.Significant logarithmic relations were found between the median diameter of the sediment particles and the i)non-clay mineral content and ii)clay mineral content.Thus,clay and non-clay mineral compositions can be conveniently estimated from the particle size distribution.     

An investigation of the spatial variability of the grain size composition of floodplain sediments

River floodplains have been widely recognized as important sinks for storing suspended sediment and associated contaminants transported by river systems. The grain size composition of floodplain deposits exerts an important influence on contaminant concentrations, and commonly exhibits significant spatial variability in response to the dynamic nature of overbank flow and sediment transport. Information on the spatial variability of the grain size composition of overbank deposits is therefore essential for developing an improved understanding of the processes controlling sediment transport on floodplains, and for investigating the fate of sediment-associated contaminants. Such information is also important for validating existing floodplain sedimentation models. This paper reports the results of a study aimed at investigating the spatial variability of the grain size composition of floodplain sediments at different spatial scales, through analysis of surface sediment samples representative of contemporary floodplain deposits collected from frequently inundated floodplain sites on five British lowland rivers. Significant lateral and downstream variations in the grain size composition of the sediment deposits have been identified in the study reaches. An attempt has been made to relate the observed spatial distribution of the grain size composition of the overbank deposits to the local floodplain geometry and topography. The importance of the particle size characteristics of the suspended sediment transported by the rivers in influencing the spatial variability of the grain size composition of the overbank sediments deposited on these floodplains is also considered. © 1998 John Wiley & Sons, Ltd.     

PREDICTION OF THE GRAIN SIZE OF SUSPENDED SEDIMENT： IMPLICATIONS FOR CALCULATING SUSPENDED SEDIMENT CONCENTRATIONS USING SINGLE FREQUENCY ACOUSTIC BACKSCATTER

Collection of samples of suspended sediment transported by streams and rivers is difficult and expensive. Emerging technologies, such as acoustic backscatter, have promise to decrease costs and allow more thorough sampling of transported sediment in streams and rivers. Acoustic backscatter information may be used to calculate the concentration of suspended sand-sized sediment given the vertical distribution of sediment size. Therefore, procedures to accurately compute suspended sediment size distributions from easily obtained river data are badly needed. In this study, techniques to predict the size of suspended sand are examined and their application to measuring concentrations using acoustic backscatter data are explored. Three methods to predict the size of sediment in suspension using bed sediment, flow criteria, and a modified form of the Rouse equation yielded mean suspended sediment sizes that differed from means of measured data by 7 to 50 percent. When one sample near the bed was used as a reference, mean error was reduced to about 5 percent. These errors in size determination translate into errors of 7 to 156 percent in the prediction of sediment concentration using backscatter data from 1 MHz single frequency acoustics.     

Estimating sand concentrations using ADCP-based acoustic inversion in a large fluvial system characterized by bi-modal suspended-sediment distributions

Quantifying sediment flux within rivers is a challenge for many disciplines due, mainly, to difficulties inherent to traditional sediment sampling methods. These methods are operationally complex, high cost, and high risk. Additionally, the resulting data provide a low spatial and temporal resolution estimate of the total sediment flux, which has impeded advances in the understanding of the hydro-geomorphic characteristics of rivers. Acoustic technologies have been recognized as a leading tool for increasing the resolution of sediment data by relating their echo intensity level measurements to suspended sediment. Further effort is required to robustly test and develop these techniques across a wide range of conditions found in natural river systems. This article aims to evaluate the application of acoustic inversion techniques using commercially available, down-looking acoustic Doppler current profilers (ADCPs) in quantifying suspended sediment in a large sand bed river with varying bi-modal particle size distributions, wash load and suspended-sand ratios, and water stages. To achieve this objective, suspended sediment was physically sampled along the Paraná River, Argentina, under various hydro-sedimentological regimes. Two ADCPs emitting different sound frequencies were used to simultaneously profile echo intensity level within the water column. Using the sonar equation, calibrations were determined between suspended-sand concentrations and acoustic backscatter to solve the inverse problem. The study also analyzed the roles played by each term of the sonar equation, such as ADCP frequency, power supply, instrument constants, and particle size distributions typically found in sand bed rivers, on sediment attenuation and backscatter. Calibrations were successfully developed between corrected backscatter and suspended-sand concentrations for all sites and ADCP frequencies, resulting in mean suspended-sand concentration estimates within about 40% of the mean sampled concentrations. Noise values, calculated using the sonar equation and sediment sample characteristics, were fairly constant across evaluations, suggesting that they could be applied to other sand bed rivers. © 2018 John Wiley & Sons, Ltd.     

Particle size analysis of the sediment suspended in a proglacial stream: Glacier De tsidjiore Nouve,Switzerland

Hourly, at-a-point samples of suspended sediment taken from the outflow stream of Glacier de Tsidjiore Nouve, Switzerland, over a 60 day sampling period (n = 1440) are shown to be dominantly composed of silt-sized particles. Particle size, SEM, and XRD analyses indicate a subglacial provenance for the suspended sediment. Temporal variations in particle size and sorting correspond poorly to fluctuations in water discharge, being dominated by erratic hour-to-hour fluctuations and clockwise hysteresis over diurnal flow events. Examination of grain size and sorting dynamics over snowmelt- and icemelt-related ablation events, during precipitation events, and during glacier drainage events enables some inferences to be drawn regarding sediment source areas and supply regimes. We conclude that although the bulk of the suspended sediment in the proglacial stream of Glacier de Tsidjiore Nouve is derived directly from subglacial sources (with occasional contributions from the valley train during rapid snowmelt and heavy rainfall periods), a portion of the suspended load undergoes intermittent ‘flush-fall’ transfer through the proglacial zone, which acts as a sediment source during rising flows and as a sink during periods of waning flow.