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1.
Aggregation processes of fine sediments have rarely been integrated in numerical simulations of cohesive sediment transport in riverine systems. These processes, however, can significantly alter the hydrodynamic characteristics of suspended particulate matter (SPM), modifying the particle settling velocity, which is one of the most important parameters in modelling suspended sediment dynamics. The present paper presents data from field measurements and an approach to integrate particle aggregation in a hydrodynamic sediment transport model. The aggregation term used represents the interaction of multiple sediment classes (fractions) with corresponding multiple deposition behaviour. The k–ε–turbulence model was used to calculate the coefficient of vertical turbulent mixing needed for the two‐dimensional vertical‐plane simulations. The model has been applied to transport and deposition of tracer particles and natural SPM in a lake‐outlet lowland river (Spree River, Germany). The results of simulations were evaluated by comparison with field data obtained for two levels of river discharge. Experimental data for both discharge levels showed that under the prevailing uniform hydraulic conditions along the river reach, the settling velocity distribution did not change significantly downstream, whereas the amount of SPM declined. It was also shown that higher flow velocities (higher fluid shear) resulted in higher proportions of fast settling SPM fractions. We conclude that in accordance with the respective prevailing turbulence structures, typical aggregation mechanisms occur that continuously generate similar distribution patterns, including particles that settle toward the river bed and thus mainly contribute to the observed decline in the total SPM concentration. In order to determine time‐scales of aggregation and related mass fluxes between the settling velocity fractions, results of model simulations were fitted to experimental data for total SPM concentration and of settling velocity frequency distributions. The comparison with simulations for the case of non‐interacting fractions clearly demonstrated the practical significance of particle interaction for a more realistic modelling of cohesive sediment and contaminant transport. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

2.
Observations of suspended sediment concentration and discharge at two sites on the proglacial river network draining from a predominantly cold-based, High-Arctic glacier (Austre Brøggerbreen) are described. Analysis of these observations illustrates: (i) the relatively low suspended sediment yield from this basin in comparison with many other glacier basins reported in the open literature; (ii) sustained and possibly increasing availability of suspended sediment to the fluvial system as the ablation season progresses; and (iii) the role of the proglacial sandur as both a sediment source and sink. Field observations coupled with the results of the data analysis are used to make inferences concerning the changing nature and relative importance of sediment sources within the basin. © 1998 John Wiley & Sons, Ltd.  相似文献   

3.
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.  相似文献   

4.
Simulation approaches employed in suspended sediment processes are important in the areas of water resources and environmental engineering. In the current study, neuro‐fuzzy (NF), a combination of wavelet transform and neuro‐fuzzy (WNF), multi linear regression (MLR), and the conventional sediment rating curve (SRC) models were considered for suspended sediment load (S) modeling in a gauging station in the USA. In the proposed WNF model, the discrete wavelet analysis was linked to a NF approach. To achieve this aim, the observed time series of river flow discharge (Q) and S were decomposed to sub time series at different scales by discrete wavelet transform. Afterwards, the effective sub time series were added together to obtain a useful Q and S time series for prediction. Eventually, the obtained total time series were imposed as inputs to the NF method for daily S prediction. The results illustrated that the predicted values by the proposed WNF model were in good agreement with the observed S values and gave better results than other models. Furthermore, the WNF model satisfactorily estimated the cumulative suspended sediment load and produced relatively reasonable predictions for extreme values of S, while NF, MLR, and SRC models provided unacceptable predictions.  相似文献   

5.
Rivers display temporal dependence in suspended sediment–water discharge relationships. Although most work has focused on multi‐decadal trends, river sediment behavior often displays sub‐decadal scale fluctuations that have received little attention. The objectives of this study were to identify inter‐annual to decadal scale fluctuations in the suspended sediment–discharge relationship of a dry‐summer subtropical river, infer the mechanisms behind these fluctuations, and examine the role of El Niño Southern Oscillation climate cycles. The Salinas River (California) is a moderate sized (11 000 km2), coastal dry‐summer subtropical catchment with a mean discharge (Qmean) of 11.6 m3 s?1. This watershed is located at the northern most extent of the Pacific coastal North America region that experiences increased storm frequency during El Niño years. Event to inter‐annual scale suspended sediment behavior in this system was known to be influenced by antecedent hydrologic conditions, whereby previous hydrologic activity regulates the suspended sediment concentration–water discharge relationship. Fine and sand suspended sediment in the lower Salinas River exhibited persistent, decadal scale periods of positive and negative discharge corrected concentrations. The decadal scale variability in suspended sediment behavior was influenced by inter‐annual to decadal scale fluctuations in hydrologic characteristics, including: elapsed time since small (~0.1 × Qmean), and moderate (~10 × Qmean) threshold discharge values, the number of preceding days that low/no flow occurred, and annual water yield. El Niño climatic activity was found to have little effect on decadal‐scale fluctuations in the fine suspended sediment–discharge relationship due to low or no effect on the frequency of moderate to low discharge magnitudes, annual precipitation, and water yield. However, sand concentrations generally increased in El Niño years due to the increased frequency of moderate to high magnitude discharge events, which generally increase sand supply. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

6.
The HIRHAM regional climate model suggests an increase in temperature in Denmark of about 3 °C and an increase in mean annual precipitation of 6–7%, with a larger increase during winter and a decrease during summer between a control period 1961–1990 and scenario period 2071–2100. This change of climate will affect the suspended sediment transport in rivers, directly through erosion processes and increased river discharges and indirectly through changes in land use and land cover. Climate‐change‐induced changes in suspended sediment transport are modelled for five scenarios on the basis of modelled changes in land use/land cover for two Danish river catchments: the alluvial River Ansager and the non‐alluvial River Odense. Mean annual suspended sediment transport is modelled to increase by 17% in the alluvial river and by 27% in the non‐alluvial for steady‐state scenarios. Increases by about 9% in the alluvial river and 24% in the non‐alluvial river were determined for scenarios incorporating a prolonged growing season for catchment vegetation. Shortening of the growing season is found to have little influence on mean annual sediment transport. Mean monthly changes in suspended sediment transport between ? 26% and + 68% are found for comparable suspended sediment transport scenarios between the control and the scenario periods. The suspended sediment transport increases during winter months as a result of the increase in river discharge caused by the increase in precipitation, and decreases during summer and early autumn months. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

7.
Before 1900, the Missouri–Mississippi River system transported an estimated 400 million metric tons per year of sediment from the interior of the United States to coastal Louisiana. During the last two decades (1987–2006), this transport has averaged 145 million metric tons per year. The cause for this substantial decrease in sediment has been attributed to the trapping characteristics of dams constructed on the muddy part of the Missouri River during the 1950s. However, reexamination of more than 60 years of water‐ and sediment‐discharge data indicates that the dams alone are not the sole cause. These dams trap about 100–150 million metric tons per year, which represent about half the decrease in sediment discharge near the mouth of the Mississippi. Changes in relations between water discharge and suspended‐sediment concentration suggest that the Missouri–Mississippi has been transformed from a transport‐limited to a supply‐limited system. Thus, other engineering activities such as meander cutoffs, river‐training structures, and bank revetments as well as soil erosion controls have trapped sediment, eliminated sediment sources, or protected sediment that was once available for transport episodically throughout the year. Removing major engineering structures such as dams probably would not restore sediment discharges to pre‐1900 state, mainly because of the numerous smaller engineering structures and other soil‐retention works throughout the Missouri–Mississippi system. Published in 2009 by John Wiley & Sons, Ltd.  相似文献   

8.
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.  相似文献   

9.
This study investigates the dynamic behavior of suspended sediment load transport at different temporal scales in the Mississippi River basin. Data corresponding to five successively doubled temporal scales (i.e. daily, two‐day, four‐day, eight‐day and 16‐day) from the St. Louis gaging station in Missouri are analyzed. The investigation is focused on identifying possible low‐dimensional deterministic behavior in the suspended sediment load transport dynamics, with an aim towards reduction in model complexity. The correlation dimension method is used to identify low‐dimensional determinism. The suspended sediment load dynamics are represented through phase‐space reconstruction, and the variability is estimated using the (proximity of) reconstructed vectors in the phase space. The results indicate the presence of low‐dimensional determinism in the suspended sediment load series at each of the five temporal scales, with the variables dominantly governing the dynamics in the order of three or four. These results not only suggest the appropriateness of relatively simpler models but also hint at possible scale invariance in the suspended sediment load transport dynamics. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

10.
This study analyses archival discharge and sediment concentration data (1965–1988), monitored by Water Survey of Canada, to examine suspended sediment transport rates and their relationship to effective discharge (Qeff) based on daily discharge duration curves. Effective discharge was determined as the mid‐point of the discharge class transporting the greatest portion of the suspended sediment load (hence class‐based Qeff). Results showed that the concept of effective discharge was applicable to the Fraser River basin where the average class‐based Qeff occurred during 8·4% of the study period with individual values ranging from 0·03% to 16·1%. The durations of effective discharge classes ranged from 0·02% to 19·6% while the transport of 50% of total sediment loads ranged from 3% to 22% with an average of 14% of the time. Equations for predicting the class‐based Qeff in the Fraser River basin from bankfull discharge and drainage area are presented. The observed variations among stations in sediment‐discharge regimes based on subjectively selected 20 discharge classes, seem to reflect the influence of sediment controlling factors such as geology, physiography, catchment size and land use practice in the basin. Future directions of research on applications of the effective discharge concept are explored. As a solution to the problem of lack of an objective method for determining the effective discharge, the effective discharge should be determined from event based assessments of sediment transport (event‐based Qeff), avoiding any subjectivity in the selection of number of discharge classes used for its determination. In conclusion, it is proposed that continued use of the conventional method of determining Qeff should cease. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

11.
High‐frequency water discharge and suspended sediment concentration (SSC) databases were collected for 3 years on four contrasted watersheds: the Asse and the Bléone (two Mediterranean rainfall regime watersheds) and the Romanche and the Ferrand (two rainfall–snowmelt regime watersheds). SSCs were calculated from turbidity recordings (1‐h time step), converted into SSC values. The rating curve was calculated by means of simultaneous SSC measurement taken by water sampling and turbidity recording. Violent storms during springtime and autumn were responsible for suspended sediment transport on the Asse and the Bléone rivers. On the Ferrand and the Romanche, a large share of suspended sediment transport was also caused by local storms, but 30% of annual fluxes results from snowmelt or icemelt which occurred from April to October. On each watershed, SSC up to 50 g l?1 were observed. Annual specific fluxes ranged from 450 to 800 t km?2 year?1 and 40–80% of annual suspended sediment fluxes occurred within 2% of the time. These general indicators clearly demonstrate the intensity of suspended sediment transport on these types of watersheds. Suspended sediment fluxes proved to be highly variable at the annual scale (inter‐annual variability of specific fluxes) as well as at the event scale (through a hysteresis loop in the SSC/Q relationship) on these watersheds. In both cases, water discharge and precipitations were the main processes involved in suspended sediment production and transport. The temporal and spatial variability of hydro‐meteorological processes on the watershed provides a better understanding of suspended sediment dynamics. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

12.
The internal riverine processes acting upon phosphorus and dissolved silicon were investigated along a 55 km stretch of the River Swale during four monitoring campaigns. Samples of river water were taken at 3 h intervals at sites on the main river and the three major tributaries. Samples were analysed for soluble reactive phosphorus, total dissolved phosphorus, total phosphorus, dissolved silicon and suspended solid concentration. Mass‐balances for each determinand were calculated by comparing the total load entering the river with the total load measured at the downstream site. The difference, i.e. the residual load, showed that there was a large retention of phosphorus and silicon within the system during the March 1998 flood event, but the other three campaigns produced net‐exports. Cumulative residual loads were calculated for each determinand at 6 h intervals throughout each campaign. This incremental approach showed that the mass‐balance residuals followed relatively consistent patterns under various river discharges. During stable low‐flow, there was a retention of particulate phosphorus within the system and also a retention of total dissolved phosphorus and soluble reactive phosphorus, most likely caused by the sorption of soluble phosphorus by bed‐sediments. In times of high river‐discharge, there was a mobilization and export of stored bed‐sediment phosphorus. During overbank flooding, there was a large retention (58% of total input) of particulate phosphorus within the system, due to the mass deposition of phosphorus‐rich sediment onto the floodplain. Soluble phosphorus was also retained within the system by sequestration from the water column by the high concentration of suspended solids. The dissolved silicon mass‐balance residuals had a less consistent pattern in relation to river discharge. There was a large retention of dissolved silicon during overbank flooding, possibly due to sorption onto floodplain soil, and net‐exports during periods of both stable low‐flow and rising limbs of hydrographs, due to release of dissolved silicon from pore‐waters. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

13.
Alluvial gullies are often formed in dispersible sodic soils along steep banks of incised river channels. Field data collected by Shellberg et al. (Earth Surface Processes and Landforms 38: 1765–1778, 2013) from a gully outlet in northern Australia showed little hysteresis between water discharge and fine (<63 µm) and coarse (>63 µm) suspended sediment, indicating transport‐limited rather than source‐limited conditions. The major source of the fine (silt/clay) component was the sodic soils of upstream gully scarps, and the coarser (sand) component was sourced locally from channel bed material. In this companion paper at the same study site, a new method was developed for combining the settling velocity characteristics of these two sediment source components to estimate the average settling velocity of the total suspended sediment. This was compared to the analysis of limited sediment samples collected during flood conditions. These settling velocity data were used in the steady‐state transport limit theory of Hairsine and Rose (Water Resources Research 28: 237–243, 245–250, 1992) that successfully predicted field data of concentrations and loads at a cross‐section, regardless of the complexity of transport‐limited upstream sources (sheet erosion, scalds, rills, gullies, mass failure, bank and bed erosion, other disturbed areas). The analysis required calibration of a key model parameter, the fraction of total stream power (F ≈ 0.025) that is effective in re‐entraining sediment. Practical recommendations are provided for the prediction of sediment loads from other alluvial gullies in the region with similar hydrogeomorphic conditions, using average stream power efficiency factors for suspended silt/clay (Fw ≈ 0.016) and sand (Fs ≈ 0.038) respectively, but with no requirement for field data on sediment concentrations. Only basic field data on settling velocity characteristics from soil samples, channel geometry measurements, estimates of water velocity and discharge, and associated error margins are needed for transport limit theory predictions of concentration and load. This theory is simpler than that required in source‐limited situations. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

14.
《水文科学杂志》2013,58(6):899-915
Abstract

The results are described of 16 years operation of a measuring station for the automatic recording of water discharge, bed load and suspended sediment transport in the Rio Cordon catchment, a small alpine basin (5 km2) located in northeastern Italy. Hillslope erosion processes were investigated by surveying individual sediment sources repeatedly. Annual and seasonal variations of suspended sediment load during the period 1986–2001 are analysed along with their contribution to the total sediment yield. The results show that suspended load accounted for 76% of total load and that most of the suspended sediment transport occurred during two flood events: an extreme summer flash flood in September 1994 (27% of the 16-years total suspended load) and a snowmelt-induced event in May 2001 accompanied by a mud flow which fed the stream with sediments. The role of active sediment source areas is discussed in relation to the changes in flood peak—suspended load trends which became apparent after both the 1994 and the 2001 events.  相似文献   

15.
Proglacial suspended sediment transport was monitored at Haut Glacier d'Arolla, Switzerland, during the 1998 melt season to investigate the mechanisms of basal sediment evacuation by subglacial meltwater. Sub‐seasonal changes in relationships between suspended sediment transport and discharge demonstrate that the structure and hydraulics of the subglacial drainage system critically influenced how basal sediment was accessed and entrained. Under hydraulically inefficient subglacial drainage at the start of the melt season, sediment availability was generally high but sediment transport increased relatively slowly with discharge. Later in the melt season, sediment transport increased more rapidly with discharge as subglacial meltwater became confined to a spatially limited network of channels following removal of the seasonal snowpack from the ablation area. Flow capacity is inferred to have increased more rapidly with discharge within subglacial channels because rapid changes in discharge during highly peaked diurnal runoff cycles are likely to have been accommodated largely by changes in flow velocity. Basal sediment availability declined during channelization but increased throughout the remainder of the monitored period, resulting in very efficient basal sediment evacuation over the peak of the melt season. Increased basal sediment availability during the summer appears to have been linked to high diurnal water pressure variation within subglacial channels inferred from the strong increase in flow velocity with discharge. Basal sediment availability therefore appears likely to have been increased by (1) enhanced local ice‐bed separation leading to extra‐channel flow excursions and[sol ]or (2) the deformation of basal sediment towards low‐pressure channels due to a strong diurnally reversing hydraulic gradient between channels and areas of hydraulically less‐efficient drainage. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

16.
The Lake Tahoe basin is experiencing an environmental decline that is partly due to sediment intakes from its tributaries. Many studies have estimated suspended sediment loads in these streams with a discrete sampling programme by collecting water samples and using a rating technique. However, the relationship between stream discharge and suspended sediment concentration (SSC) in these tributaries is known to differ during the rising and falling limbs of the snowmelt‐dominated hydrograph. Because of this hysteresis effect, sediment rating curves are poor predictors of suspended sediment dynamics in the stream. In this study, suspended sediment transport was investigated using a turbidity meter to provide a continuous record of sediment concentration during the snowmelt period. Hysteresis in suspended sediment transport was also investigated and is quantified with an H index, which is the ratio of the areas under the curve at different stages of the hydrograph. The temporal lag between the peak of SSC and the peak of stream discharge was quantified using cross‐correlation analysis. For almost all events, SSCs were higher during the rising limb of the hydrograph for a given discharge, with SSC peaks occurring before discharge peaks, resulting in clockwise hysteresis (H > 1). The H indices increased (looser hysteresis loop) as the availability of sediments increased and as the lag between peaks in SSC and discharge was larger. A restriction of the proposed H index was that it could only be computed when stream discharge increased by more than 30% during a melt event. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

17.
River discharges vary strongly through time and space, and quantifying this variability is fundamental to understanding and modelling river processes. The river basin is increasingly being used as the unit for natural resource planning and management; to facilitate this, basin‐scale models of material supply and transport are being developed. For many basin‐scale planning activities, detailed rainfall‐runoff modelling is neither necessary nor tractable, and models that capture spatial patterns of material supply and transport averaged over decades are sufficient. Nevertheless, the data to describe the spatial variability of river discharge across large basins for use in such models are often limited, and hence models to predict river discharge at the basin scale are required. We describe models for predicting mean annual flow and a non‐dimensional measure of daily flow variability for every river reach within a drainage network. The models use sparse river gauging data, modelled grid surfaces of mean annual rainfall and mean annual potential evapotranspiration, and a network accumulation algorithm. We demonstrate the parameterization and application of the models using data for the Murrumbidgee basin, in southeast Australia, and describe the use of these predictions in modelling sediment transport through the river network. The regionalizations described contain less uncertainty, and are more sensitive to observed spatial variations in runoff, than regionalizations based on catchment area and rainfall alone. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

18.
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19.
A hydrology–sediment modelling framework based on the model Topkapi-ETH combined with basin geomorphic mapping is used to investigate the role of localized sediment sources in a mountain river basin (Kleine Emme, Switzerland). The periodic sediment mobilization from incised areas and landslides by hillslope runoff and river discharge is simulated in addition to overland flow erosion to quantify their contributions to suspended sediment fluxes. The framework simulates the suspended sediment load provenance at the outlet and its temporal dynamics, by routing fine sediment along topographically driven pathways from the distinct sediment sources to the outlet. We show that accounting for localized sediment sources substantially improves the modelling of observed sediment concentrations and loads at the outlet compared to overland flow erosion alone. We demonstrate that the modelled river basin can shift between channel-process and hillslope-process dominant behaviour depending on the model parameter describing gully competence on landslide surfaces. The simulations in which channel processes dominate were found to be more consistent with observations, and with two independent validations in the Kleine Emme, by topographic analysis of surface roughness and by sediment tracing with 10 Be concentrations. This research shows that spatially explicit modelling can be used to infer the dominant sediment production process in a river basin, to inform and optimize sediment sampling strategies for denudation rate estimates, and in general to support sediment provenance studies. © 2020 John Wiley & Sons, Ltd.  相似文献   

20.
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.  相似文献   

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