Flume‐ and field‐based evaluation of a time‐integrated suspended sediment sampler for the analysis of sediment properties

Suspended sediment has been identified as a vector for nutrient and contaminant transport in the fluvial environment. A time‐integrated sampler (the Phillips sampler), which emerged over a decade ago as a cost‐effective tool for in situ suspended sediment collection, is increasingly being used to collect samples for the analysis of sediment properties such as particle size composition, and nutrient and contaminant concentrations. This study evaluates the sampler under both flume and field conditions for efficiency in the mass and grain size of the suspended sediment collected. The sampler was tested in a flume using both kaolinite and sediment samples (sieved to < 180 µm) collected from the Quesnel River, British Columbia, Canada. In the kaolinite trails, the sampler preferentially collected coarser grain sizes compared to the original sediment, probably due to finer sediment remaining in suspension and therefore passing through the sampler, and also possibly due to flocculation of the kaolinite upon introduction to the flume. Conversely, the sampler collected river sediment that was finer than the original sediment, probably due to some settling of coarser sediment observed at the bottom of the flume. Once allowance was made for these operational issues associated with the flume, maximum sediment mass efficiency for kaolinite and river sediment was 43% and 87%, respectively. Sediment collected by the time‐integrated sampler during field deployment and adjacent channel bed sediment were also compared. The sampler collected sediment with a representative grain size distribution. However, there were differences in the geochemical (arsenic and selenium) concentrations of channel bed sediment and sediment collected by the Phillips sampler which may be a function of differences in the behavior of geochemical elements associated with the two types of sediment. This work suggests that further research is needed to evaluate the role of the Phillips sampler in collecting sediment for contaminant and nutrient analysis. Copyright © 2014 John Wiley & Sons, Ltd.     

Flocculation: a key process in the sediment flux of a large,glacier‐fed lake

This study investigates the consequences of flocculation for sediment flux in glacier‐fed Lillooet Lake, British Columbia based on density, fractal dimension, in situ profiles of sediment concentration and size distribution, and settling velocity equations presented in the literature. Sediment flux attributed to macroflocs during the late spring and summer accounts for a significant portion of sediment flux in the lake, equivalent to at least one‐quarter of the average annual sediment flux. Fine sediment is reaching the lake floor faster in flocs than occurs if settling as individual grains. This flux varies both spatially and temporally over the observation period, suggesting a link between deposition via flocculation and the properties of bottom sediments. Macrofloc flux increased through June, reached a peak during July, and then declined into August. Macrofloc flux was greatest in the distal end of the first basin, approximately 10 km from the point of inflow. Relatively high excess densities (～0·1 g cm^–3 at 500 µm) for flocs in situ are consistent with a composition dominated by inorganic primary particles. Microlaminations within Lillooet Lake varves have been linked by earlier workers to discharge events, and the action of turbidity currents, emanating from the Lillooet River. While turbidity currents undoubtedly occur in Lillooet Lake, these results demonstrate flocculation as an adjunct process linking discharge, lake level, macrofloc flux, bulk density and microlaminations. In situ measurements of sediment settling velocity in glacier‐fed lakes are required to better constrain flux rates, and permit comparison between flocculation in lacustrine environments with existing studies of estuarine, marine and fluvial flocculation. Copyright © 2009 John Wiley & Sons, Ltd.     

Dynamics of suspended sediment delivery to the Eastern Mediterranean continental shelf

This study provides data on the fluvial sediment transport at the Eastern Mediterranean, an area in which the regional importance for comparative study has often been raised by investigators but the data are rather scarce. We analysed long‐ and short‐term hydrologic and sedimentological data from one of the largest coastal streams of Israel, Qishon River (1100 km²), and its estuarine environment. The results indicate that during 65 years (1944–2009), a total 140 floods have contributed to the sea an amount of approximately 2.58 × 10⁶ tons of sediment. During this period, (i) the number of floods with a return period of more than 10 years has almost doubled during the last 30 years, and (ii) the mean annual discharge during last 10 years increased by approximately 175%. The analysis of the short (2 years) hydrological and sediment data revealed that approximately 30% of the upstream channel loads do not reach the river mouth and are deposited along the channel bed, even during major flood events. This observation was attributed largely to the facts that the lower river bed is incised below sea level, to the very low slopes and to the correspondingly low stream power and transport capacity. The results of this study highlight the effect of interchannel dynamics as well as the constraints of interaction between fluvial system and estuarine processes on sediment transport. Copyright © 2012 John Wiley & Sons, Ltd.     

Dynamics of suspended sediment transport at field‐scale drain channels of irrigation‐dominated watersheds in the Sonoran Desert,southeastern California

Suspended sediment is a major source of pollution in irrigation‐dominated watersheds. However, little is known about the process and mechanisms of suspended sediment transport in drain channels directly connected to agricultural fields. This paper explains sediment dynamics using averaged 5 min flow discharge Q (m³ s^?1) and suspended sediment concentration C (mg l^?1) collected during one crop season in a small catchment containing a first‐order drain channel and its connected six agricultural fields within the Salton Sea watershed. The statistical properties and average trends of Q and C were investigated for both early (i.e. November) and late (i.e. January) stages of a crop season. Further in‐depth analysis on sediment dynamics was performed by selecting two typical single‐field irrigation events and two multiple‐field irrigation events. For each set of irrigation events, the process of suspended sediment transport was revealed by examining hydrograph and sediment graph responses. The mechanisms underlying suspended sediment transport were investigated by analysing the types of corresponding hysteresis loop. Finally, sediment rating curves for both hourly and daily data at early and late stages and for the entire crop season were established to seek possible sediment‐transport predictive model(s). The study suggests that the complicated processes of suspended sediment transport in irrigation‐dominated watersheds require stochastic rather than deterministic forecasting. Copyright © 2007 John Wiley & Sons, Ltd.     

Predictability of river flow and suspended sediment transport in the Mississippi River basin: a non‐linear deterministic approach

As the Mississippi River plays a major role in fulfilling various water demands in North America, accurate prediction of river flow and sediment transport in the basin is crucial for undertaking both short‐term emergency measures and long‐term management efforts. To this effect, the present study investigates the predictability of river flow and suspended sediment transport in the basin. As most of the existing approaches that link water discharge, suspended sediment concentration and suspended sediment load possess certain limitations (absence of consensus on linkages), this study employs an approach that presents predictions of a variable based on history of the variable alone. The approach, based on non‐linear determinism, involves: (1) reconstruction of single‐dimensional series in multi‐dimensional phase‐space for representing the underlying dynamics; and (2) use of the local approximation technique for prediction. For implementation, river flow and suspended sediment transport variables observed at the St. Louis (Missouri) station are studied. Specifically, daily water discharge, suspended sediment concentration and suspended sediment load data are analysed for their predictability and range, by making predictions from one day to ten days ahead. The results lead to the following conclusions: (1) extremely good one‐day ahead predictions are possible for all the series; (2) prediction accuracy decreases with increasing lead time for all the series, but the decrease is much more significant for suspended sediment concentration and suspended sediment load; and (3) the number of mechanisms dominantly governing the dynamics is three for each of the series. Copyright © 2005 John Wiley & Sons, Ltd.     

The influence of neap–spring tidal variation and wave energy on sediment flux in salt marsh tidal creeks

Sediment flux in marsh tidal creeks is commonly used to gauge sediment supply to marshes. We conducted a field investigation of temporal variability in sediment flux in tidal creeks in the accreting tidal marsh at China Camp State Park adjacent to northern San Francisco Bay. Suspended‐sediment concentration (SSC), velocity and depth were measured near the mouths of two tidal creeks during three 6‐ to 10‐week deployments: two in winter and one in summer. Currents, wave properties and SSC were measured in the adjacent shallows. All deployments spanned the largest spring tides of the season. Results show that tidally averaged suspended‐sediment flux (SSF) in the tidal creeks varied from slightly landward to strongly bayward with increasing tidal energy. SSF was negative (bayward) for tidal cycles with maximum water surface elevation above the marsh plain. Export during the largest spring tides dominated the cumulative SSF for each deployment. During ebb tides following the highest tides, velocities exceeded 1 m s^?1 in the narrow tidal creeks, resulting in negative tidally averaged water flux, and mobilizing sediment from the creek banks or bed. Storm surge also produced negative SSF. Tidally averaged SSF was positive in wavy conditions with moderate tides. Spring tide sediment export at the creek mouth was about twice that at a station 130 m further up the tidal creek. The negative tidally averaged water flux near the creek mouth during spring tides indicates that in the lower marsh some of the water flooding directly across the bay–marsh interface drains through the tidal creeks, and suggests that this interface may be a pathway for sediment supply to the lower marsh as well. Copyright © 2018 John Wiley & Sons, Ltd.     

A non‐equilibrium sediment transport model for rill erosion

Sediment transport in rill flows exhibits the characteristics of non‐equilibrium transport, and the sediment transport rate of rill flow gradually recovers along the flow direction by erosion. By employing the concept of partial equilibrium sediment transport from open channel hydraulics, a dynamic model of rill erosion on hillslopes was developed. In the model, a parameter, called the restoration coefficient of sediment transport capacity, was used to express the recovery process of sediment transport rate, which was analysed by dimensional analysis and determined from laboratory experimental data. The values of soil loss simulated by the model were in agreement with observed values. The model results showed that the length and gradient of the hillslope and rainfall intensity had different influences on rill erosion. Copyright © 2006 John Wiley & Sons, Ltd.     

Estimating suspended sediment concentrations in areas with limited hydrological data using a mixed‐effects model

Sediment rating curves are commonly used to estimate the suspended sediment load in rivers and streams under the assumption of a constant relation between discharge (Q) and suspended sediment concentrations (SSC) over time. However, temporal variation in the sediment supply of a watershed results in shifts in this relation by increasing variability and by introducing nonlinearities in the form of hysteresis or a path‐dependent relation. In this study, we used a mixed‐effects linear model to estimate an average SSC–Q relation for different periods of time within the hydrologic cycle while accounting for seasonality and hysteresis. We tested the performance of the mixed‐effects model against the standard rating curve, represented by a generalized least squares regression, by comparing observed and predicted sediment loads for a test case on the Chilliwack River, British Columbia, Canada. In our analyses, the mixed‐effects model reflected more accurate patterns of interpolated SSC from Q data than the rating curve, especially for the low‐flow summer months when the SSC–Q relation is less clear. Akaike information criterion scores were lower for the mixed‐effects model than for the standard model, and the mixed‐effects model explained nearly twice as much variance as the standard model (52% vs 27%). The improved performance was achieved by accounting for variability in the SSC–Q relation within each month and across years for the same month using fixed and random effects, respectively, a characteristic disregarded in the sediment rating curve. Copyright © 2012 John Wiley & Sons, Ltd.     

A new approach for linking event‐based upland sediment sources to downstream suspended sediment transport

In this study, we proposed a new approach for linking event sediment sources to downstream sediment transport in a watershed in central New York. This approach is based on a new concept of spatial scale, sub‐watershed area (SWA), defined as a sub‐watershed within which all eroded soils are transported out without deposition during a hydrological event. Using (rainfall) event data collected between July and November, 2007 from several SWAs of the studied watershed, we developed an empirical equation that has one independent variable, mean SWA slope. This equation was then used to determine event‐averaged unit soil erosion rate, Q_S/A, (in kg/km²/hr) for all SWAs in the studied watershed and calculate event‐averaged gross erosion E_ea (in kg/hr). The event gross erosion E_t (in kilograms) was subsequently computed as the product of E_ea and the mean event duration, T (in hours) determined using event hydrographs at the outlet of the studied watershed. Next, we developed two linear sediment rating curves (SRCs) for small and big events based on the event data obtained at the watershed outlet. These SRCs, together with T, allowed us to determine event sediment yield SY_e (in kilograms) for all events during the study period. By comparing E_t with SY_e, developing empirical equations (i) between E_t and SY_e and (ii) for event sediment delivery ratio, respectively, we revealed the event dynamic processes connecting sediment sources and downstream sediment transport. During small events, sediment transport in streams was at capacity and dominated by the deposition process, whereas during big events, it was below capacity and controlled by the erosion process. The key of applying this approach to other watersheds is establishing their empirical equations for Q_S/A and appropriately determining their numbers of SWAs. Copyright © 2011 John Wiley & Sons, Ltd.     

Hydro‐meteorological drivers and sources of suspended sediment flux in the pro‐glacial zone of the retreating Castle Creek Glacier,Cariboo Mountains,British Columbia,Canada

Glaciers are major agents of erosion that increase sediment load to the downstream fluvial system. The Castle Creek Glacier, British Columbia, Canada, has retreated ~1.0 km in the past 70 years. Suspended sediment concentration (SSC) and streamflow (Q) were monitored independently at five sites within its pro‐glacial zone over a 60 day period from July to September 2011, representing part of the ablation season. Meteorological data were collected from two automatic weather stations proximal to the glacier. The time‐series were divided into hydrologic days and the shape and magnitude of the SSC response to hydro‐meteorological conditions (‘cold and wet’, ‘hot and dry’, ‘warm and damp’, and ‘storm’) were categorized using principal component analysis (PCA) and cluster analysis (CA). Suspended sediment load (SSL) was computed and summarized for the categories. The distribution of monitoring sites and results of the multivariate statistical analyses describe the temporal and spatial variability of suspended sediment flux and the relative importance of glacial and para‐glacial sediment sources in the pro‐glacial zone. During the 2011 study period, ~ 60% of the total SSL was derived from the glacial stream and sediment deposits proximal to the terminus of the glacier; during ‘storm’ events, that contribution dropped to ~40% as the contribution from diffuse and point sources of sediment throughout the pro‐glacial zone and within the meltwater channels increased. While ‘storm’ events accounted for just 3% of the study period, SSL was ~600% higher than the average over the monitoring period, and ~20% of the total SSL was generated in that time. Determining how hydro‐meteorological conditions and sediment sources control sediment fluxes will assist attempts to predict how pro‐glacial zones respond to future climate changes. Copyright © 2015 John Wiley & Sons, Ltd.     

Short‐term spatial and temporal patterns of suspended sediment transfer in proglacial channels,small River Glacier,Canada

Alpine glacial basins are a significant source and storage area for sediment exposed by glacial retreat. Recent research has indicated that short‐term storage and release of sediment in proglacial channels may control the pattern of suspended sediment transfer from these basins. Custom‐built continuously recording turbidimeters installed on a network of nine gauging sites were used to characterize spatial and temporal variability in suspended sediment transfer patterns for the entire proglacial area at Small River Glacier, British Columbia, Canada. Discharge and suspended sediment concentration were measured at 5 min intervals over the ablation season of 2000. Differences in suspended sediment transfer patterns were then extracted using multivariate statistics (principal component and cluster analysis). Results showed that each gauging station was dominated c. 80% of days by diurnal sediment transfer patterns and ‘low’ suspended sediment concentrations. ‘Irregular’ transfer patterns were generally associated with ‘high’ sediment concentrations during snowmelt and rainfall events, resulting in the transfer of up to 70% of the total seasonal suspended sediment load at some gauging stations. Suspended sediment enrichment of up to 600% from channel storage release and extrachannel inputs occurred between the glacial front and distal proglacial boundary. However, these patterns differed significantly between gauging stations as determined by the location of the gauging station within the catchment and meteorological conditions. Overall, the proglacial area was the source for up to 80% of the total suspended sediment yield transferred from the Small River Glacier basin. These results confirmed that sediment stored and released in the proglacial area, in particular from proglacial channels, was controlling suspended sediment transfer patterns. To characterize this control accurately requires multiple gauging stations with high frequency monitoring of suspended sediment concentration. Accurate characterization of this proglacial control on suspended sediment transfer may therefore aid interpretation of suspended sediment yield patterns from glacierized basins. Copyright © 2004 John Wiley & Sons, Ltd.     

The distribution and residence time of suspended sediment stored within the channel margins of a gravel‐bed bedrock river

Previously undocumented deposits are described that store suspended sediment in gravel‐bedded rivers, termed ‘fine‐grained channel margin’ (FGCM) deposits. FGCM deposits consist of sand, silt, clay, and organic matter that accumulate behind large woody debris (LWD) along the margins of the wetted perimeter of the single‐thread, gravel‐bed South River in Virginia. These deposits store a total mass equivalent to 17% to 43% of the annual suspended sediment load. Radiocarbon, ²¹⁰Pb and ¹³⁷C dating indicate that sediment in FGCM deposits ranges in age from 1 to more than 60 years. Reservoir theory suggests an average turnover time of 1·75 years and an annual exchange with the water column of a mass of sediment equivalent to 10% to 25% of the annual sediment load. The distribution of ages in the deposits can be fitted by a power function, suggesting that sediment stored in the deposits has a wide variety of transit times. Most sediment in storage is reworked quickly, but a small portion may remain in place for many decades. The presence of FGCM deposits indicates that suspended sediment is not simply transported downstream in gravel‐bed rivers in agricultural watersheds: significant storage can occur over decadal timescales. South River has a history of mercury contamination and identifying sediment sources and sinks is critical for documenting the extent of contamination and for developing remediation plans. FGCM deposits should be considered in future sediment budget and sediment transport modeling studies of gravel‐bed rivers in agricultural watersheds. Copyright © 2010 John Wiley & Sons, Ltd.     

Time‐integrated sampling of fluvial suspended sediment: a simple methodology for small catchments

Fine‐grained (<62·5 µm) suspended sediment transport is a key component of the geochemical flux in most fluvial systems. The highly episodic nature of suspended sediment transport imposes a significant constraint on the design of sampling strategies aimed at characterizing the biogeochemical properties of such sediment. A simple sediment sampler, utilizing ambient flow to induce sedimentation by settling, is described. The sampler can be deployed unattended in small streams to collect time‐integrated suspended sediment samples. In laboratory tests involving chemically dispersed sediment, the sampler collected a maximum of 71% of the input sample mass. However, under natural conditions, the existence of composite particles or flocs can be expected to increase significantly the trapping efficiency. Field trials confirmed that the particle size composition and total carbon content of the sediment collected by the sampler were representative statistically of the ambient suspended sediment. Copyright © 2000 John Wiley & Sons, Ltd.     

Predicting suspended sediment concentrations in the Meuse river using a supply‐based rating curve

A rating curve provides a reasonable estimate of the suspended sediment concentration at a given discharge. However, analysis of a detailed 9‐year time‐series of suspended sediment concentration (SSC) and discharge Q of the Meuse River in The Netherlands indicates that SSC is (besides discharge) controlled by exhaustion and replenishment of different sediment sources. Clockwise hysteresis and other effects of sediment exhaustion can be observed during and after flood events, and the effects of stockpiling of sediment in the river bed during low‐discharge periods are obvious in the SSC of the next flood. In a single regression equation we have implemented a parameter that represents the presence or absence of stock for sediment uptake. In comparison with a rating curve of SSC and Q, adding this parameter is shown to be a more reliable and comprehensive method to predict SSCs at all discharge regimes with all preceding discharge conditions, for single‐peaked and multi‐peaked runoff events as well as for low flow conditions. The method is probably applicable to other small‐ to medium‐scaled river basins. Copyright © 2007 John Wiley & Sons, Ltd.     

Patterns of grain‐size dependent sediment transport in low‐ordered,ephemeral channels

Sediment data were analyzed to determine grain‐size dependant factors affecting sediment transport in a low‐ordered, ephemeral watershed. Sediment and flow samples were collected during 22 flow events at the outlet of a 4·53 ha sub‐watershed within the Walnut Gulch Experimental Watershed in south‐eastern Arizona. Measured concentrations ranged from 4191 to 115 045 mg l^?1 and included grain sizes up to 8·0 mm in diameter. Two grain‐size dependent transport patterns were observed, that of the finer grain‐size fraction (approximately < 0·25 mm) and that of a coarser grain‐size fraction (approximately ≥ 0·25 mm). The concentration of the fine fraction decreased with flow duration, peaking near the beginning of a flow event and declining thereafter. The concentration of the fine fraction showed slight trends with season and recovery period. The concentration of the coarse fraction displayed a slight negative trend with instantaneous discharge and was not correlated with event duration. These patterns typically produced a condition where the majority of the fine fraction of the sediment yield was evacuated out of the watershed before the hydrograph peak while the majority of the coarser sediment was evacuated during the falling limb of the hydrograph. Each grain‐size dependent transport pattern was likely influenced by the source of the associated sediment. At the flow event time scale, the fines were primarily wash load, supplied from the hillslopes and the coarser grains were entrained from the channel bed. Because transport patterns differ based on grain size, attempts to define the total sediment concentration and sediment yield by the behavior of a single grain‐size fraction may lead to erroneous results, especially when a large range of sediment grain sizes are present. Copyright © 2010 John Wiley & Sons, Ltd.     

Physics‐based numerical modelling of large braided rivers dominated by suspended sediment

Physics‐based models have been increasingly developed in recent years and applied to simulate the braiding process and evolution of channel units in braided rivers. However, limited attention is given to lowland braided rivers where the transport of suspended sediment plays a dominant role. In the present study, a numerical model based on the basic physics laws of hydrodynamics and sediment transport is used to simulate the evolution process of a braided river dominated by suspended load transport. The model employs a fractional method to simulate the transport of graded sediments and uses a multiple‐bed‐layer approach to represent the sediment sorting process. An idealized braided river has been produced, with the hydrodynamic, sediment transport and morphological processes being analysed. In particular, the formation process of local pool–bar units in the predicted river has been investigated. A sensitivity analysis has also been undertaken to investigate the effects of grid resolution and an upstream perturbation on the model prediction. A variety of methods are applied to analyse the geometrical and topographical properties of the modelled river. Self‐organizing characteristics related to river geometry and topography are analysed by state‐space plots, which indicate a close relationship with the periodical erosion and deposition cycles of braiding. Cross‐sectional topography and slope frequency display similar geometries to natural rivers. Scaling characteristics are found by correlation analysis of bar parameters. Copyright © 2014 John Wiley & Sons, Ltd.     

Suspended sediment transport regime in a debris‐flow gully on Vancouver Island,British Columbia

In debris‐flow‐prone channels, normal fluvial sediment transport occurs (nearly exclusively in suspended mode) between episodic debris‐flow events. Observations of suspended sediment transport through a winter season in a steepland gully in logged terrain revealed two event types. When flows exceeded a threshold of 270 l s⁻¹, events yielded significant quantities of sediment and suspended sediment concentration increased with flow. Smaller events were strongly ‘supply limited’; sediment concentration decreased as flow increased. Overall, there is no consistent correlation between runoff and sediment yield. Within the season, three subseasons were identified (demarcated by periods of freezing weather) within which a pattern of fine sediment replenishment and evacuation occurred. Finally, a signature of fine sediment mobilization and exhaustion was observed within individual events. Fine sediment transport occurred in discrete pulses within storm periods, most of the yield occurring within 5 to 15% of storm runoff duration, so that it is unlikely that scheduled sampling programs would identify significant transport. Significant events are, however, generally forecastable on the basis of regional heavy rainfall warnings, providing a basis for targeted observations. Radiative snowmelt events and rain‐on‐snow remain difficult to forecast, since the projection of temperatures from the nearest regular weather station yields variable results. Copyright © 2004 John Wiley & Sons, Ltd.     

Impact of dissipation and dispersion terms on simulations of open‐channel confluence flow using two‐dimensional depth‐averaged model

The flow patterns in confluence channel and the simulation of confluence flow are more complex than that in straight channel. Additional terms in the momentum equations, i.e. dissipation terms, denoting the impact of turbulence, and dispersion terms, denoting the vertical non‐uniformity of velocity, show great impacts on the accuracy of numerical simulations. The dissipation terms, i.e. the product of eddy viscosity coefficient and velocity gradient, are much larger than those of the flow in straight channel. In this study, the zero equation model and the depth‐averaged k‐ε model are used to analyse the impact of eddy viscosity. Meanwhile, the dispersion terms in the momentum equation, depending on the vertical non‐uniformity of velocity, are usually neglected in routine simulation. With the use of detailed experimental data for verification, this study presents the distribution of parameters of vertical non‐uniformity and the intimated connection between non‐uniformity parameters and accuracy of numerical simulations of confluence flow with depth‐averaged models. The results present that simulation accuracy of confluence flow is very sensitive to the turbulence modes, which cannot be handled by normal, simple turbulence model. On the contrary, the impact of dispersion terms is both flow‐condition‐dependent and place‐dependent, and such impact is negligible when secondary circulation is weak. The results indicate the key elements in modelling confluence flow and are helpful for selecting suitable numerical model and solving engineering problems encountered in confluence channel. Copyright © 2013 John Wiley & Sons, Ltd.     

Evaluating fine sediment mobilization and storage in a gravel‐bed river using controlled reservoir releases

Two controlled flow events were generated by releasing water from a reservoir into the Olewiger Bach, located near Trier, Germany. This controlled release of near bank‐full flows allowed an investigation of the fine sediment (<63 µm) mobilized from channel storage. Both a winter (November) and a summer (June) release event were generated, each having very different antecedent flow conditions. The characteristics of the release hydrographs and the associated sediment transport indicated a reverse hysteresis with more mass, but smaller grain sizes, moving on the falling limb. Fine sediment stored to a depth of 10 cm in the gravels decreased following the release events, indicating the dynamic nature and importance of channel‐stored sediments as source materials during high flow events. Sediment traps, filled with clean natural gravel, were buried in riffles before the release of the reservoir water and the total mass of fine sediment collected by the traps was measured following the events. Twice the mass of fine sediment was retained by the gravel traps compared with the natural gravels, which may be due to their altered porosity. Although the amount of fine sediment collected by the traps was not significantly related to measures of gravel structure, it was found to be significantly correlated to measures of local flow velocity and Froude number. A portion of the traps were fitted with lids to restrict surface exchange of water and sediment. These collected the highest amounts of event‐mobilized sediments, indicating that inter‐gravel lateral flows, not just surface infiltration of sediments, are important in replenishing and redistributing the channel‐stored fines. These findings regarding the magnitude and direction of fine sediment movement in gravel beds are significant in both a geomorphic and a biological context. Copyright © 2006 John Wiley & Sons, Ltd.     

三峡水库运用后荆江段非均匀悬沙恢复特性

三峡工程运用后,坝下游荆江段来沙量大幅度减小,处于严重的不平衡输沙状态,次饱和水流冲刷河床使悬沙量沿程恢复.基于实测水沙资料,分析了三峡工程运用后荆江段非均匀悬沙恢复特点.提出了恢复效率的概念用以表征悬移质沿程恢复的程度,并根据实测水沙资料计算了荆江段1994-2017年非均匀悬沙的恢复效率.结果表明：三峡工程运用前,荆江段各粒径组悬沙恢复效率绝对值均接近0,故该时期内各粒径组泥沙冲淤幅度不大;三峡工程运用后,各粒径组悬沙恢复效率绝对值均明显增大,且粗沙（d>0.125 mm）恢复效率绝对值远大于细沙（d<0.125 mm）,故粗沙恢复程度更高.这主要是由于荆江段床沙组成中粗沙部分含量大,而细沙含量小.最后建立了三峡水库蓄水后非均匀悬沙恢复效率与来水来沙条件（来沙系数）的关系,结果表明：各粒径组悬移质恢复效率均与来沙系数呈正相关关系,全沙、细沙和中沙的决定系数（R²）分别为0.89、0.67和0.69,相关性较高,故荆江段各粒径组悬移质泥沙恢复效率较大程度上受到来水来沙条件的影响.