Recent increase of river–floodplain suspended sediment exchange in a reach of the lower Amazon River

We analyzed variation of channel–floodplain suspended sediment exchange along a 140 km reach of the lower Amazon River for two decades (1995–2014). Daily sediment fluxes were determined by combining measured and estimated surface sediment concentrations with river–floodplain water exchanges computed with a two‐dimensional hydraulic model. The average annual inflow to the floodplain was 4088 ± 2017 Gg yr^?1 and the outflow was 2251 ± 471 Gg yr^?1, respectively. Prediction of average sediment accretion rate was twice the estimate from a previous study of this same reach and more than an order of magnitude lower than an estimate from an earlier regional scale study. The amount of water routed through the floodplain, which is sensitive to levee topography and increases exponentially with river discharge, was the main factor controlling the variation in total annual sediment inflow. Besides floodplain routing, the total annual sediment export depended on the increase in sediment concentration in lakes during floodplain drainage. The recent increasing amplitude of the Amazon River annual flood over two decades has caused a substantial shift in water and sediment river–floodplain exchanges. In the second decade (2005–2014), as the frequency of extreme floods increased, annual sediment inflow increased by 81% and net storage increased by 317% in relation to the previous decade (1995–2004). Copyright © 2017 John Wiley & Sons, Ltd.     

The effect of El Niño Southern Oscillation cycles on the decadal scale suspended sediment behavior of a coastal dry‐summer subtropical catchment

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 (Q_mean) 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 × Q_mean), and moderate (~10 × Q_mean) 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.     

Determining suspended sediment loads from turbidity records / La détermination des charges en suspension des rapports sur la turbidité

Abstract

The Pennsylvania Department of Transportation and the US Geological Survey are cooperating in several field studies to evaluate sediment control measures used during highway construction. Among the parameters being monitored are suspended sediment concentration and turbidity. Sediment loads are calculated from suspended sediment and water discharge data, but some sediment loads must be determined indirectly because it is virtually impossible to obtain sufficient suspended sediment samples to define all runoff conditions adequately. Sediment discharge-water discharge correlation curves have proved unreliable for streams affected by highway construction, so an alternative method using the turbidity record was developed during these studies.

The field data reveal a good correlation between daily mean discharge-weighted turbidity and daily mean discharge-weighted suspended sediment concentration. Turbidity is monitored and recorded continuously, and the daily mean discharge-weighted turbidity is calculated from the turbidity and water discharge data. During periods when there are insufficient suspended sediment data, the daily mean discharge-weighted suspended sediment concentration is determined from the turbidity-sediment correlation and used with the daily mean water discharge to calculate a daily sediment load.

This method of determining sediment loads from the turbidity record suggests a possiblity for computation of sediment loads by computer. Instrumentation now in use for recording water quality parameters on digital punch tape could be used to record the output from a turbidimeter. Then, for streams having a good correlation between suspended sediment concentration and turbidity, simultaneous water discharge and turbidity data could be used to determine sediment loads by computer.     

Temporal changes in suspended sediment transport in a gullied loess basin: the lower Chabagou Creek on the Loess Plateau in China

Suspended sediment dynamics are still imperfectly understood, especially in the loess hilly region on the Loess Plateau, with strong temporal variability, where few studies heretofore have been conducted. Using a dataset up to eight years long in the Lower Chabagou Creek, the variability in suspended sediment load at different temporal scales (within‐flood variability, monthly–seasonal and annual) is analyzed in this paper. The results show that, on the within‐flood scale, most of the sediment peaks lag behind peak discharges, implying that slope zones are the main sediment source area; independent of the occurring sequences of the peaks of sediment and discharge, all the events could present an anti‐clockwise hysteresis loop resulting from the abundant material and the influence of hyperconcentrated flows on suspended sediment concentration. At monthly and seasonal scales, there is a ‘store–release’ process, i.e. sediment is prepared in winter, spring and late autumn, and exported in summer and early autumn. At the annual scale, the high variability in concentration and sediment yield are highly correlated with water yield, resulting from the number and magnitude of floods recorded yearly, and almost all the suspended load is transported during these events. Copyright © 2008 John Wiley & Sons, Ltd.     

Variation in suspended sediment concentration during storm discharges in three small streams in upper osun basin,Central Western Nigeria

The suspended sediment concentration response of three small streams draining quartzites and quartz-schists in southwestern Nigeria to storms of varying magnitude are presented. A total of 1468 water samples from 62 storm responses with peak stream discharge values ranging from 80 to 120 l s^?2 were analysed and storm and suspended sediment concentration hydrographs and hysteresis loops were used to depict the response patterns. The six different types of responses identified include the single and multiple discharge peak rises with sediment lead and lag and also the mixed response patterns. Both valley slope and channel erosion constituted important sources of suspended sediment. However, sediment availability, exhaustion, and flushing effects determined the variation in the different response types.     

RETENTION OF WATER AND SEDIMENT BY GRASS STRIPS

This paper discusses aspects of grass vegetation in relation to soil erosion control. By means of a literature research, four options for using grass vegetation were recognized, each having its own requirements concerning maintenance, vegetation characteristics and field layout. The main filter mechanisms, application in the field and effects on runoff and soil loss are discussed. Field experiments on filter strips were carried out to determine whether literature data for water and sediment retention by vegetation can be applied to sloping loess soils in South Limburg (The Netherlands). The field experiments simulated a situation in which surface runoff carrying loess sediment from an upslope field enters a grass strip. The retention of water and sediment by grass strips was determined by measuring runoff discharge and the sediment concentration at the inflow and outflow points from bordered plots. Two locations with different grass age and agricultural management were studied. Results show that grass strips are effective in filtering sediment from surface runoff as long as concentrated flow is absent. Outflow sediment concentrations could be described as a function of inflow concentrations and strip width. Reductions of sediment discharge varied between 50–60, 60–90 and 90–99% for strips of 1, 4–5 and 10 m width, respectively. Old grass, extensively used as pasture, is more effective in reducing erosion than the younger grass which was often accessed by tractors for mowing. Differences in water retention between both grass locations appear to be caused mainly by differences in grass density.     

Modelling reservoir sedimentation and estimating historical deposition rates using a data-based mechanistic (DBM) approach

Abstract

The data-based mechanistic (DBM) modelling methodology is applied to the study of reservoir sedimentation. A lumped-parameter, discrete-time model has been developed which directly relates rainfall to suspended sediment load (SSL) at the reservoir outflow from the two years of measured data at Wyresdale Park Reservoir (Lancashire, UK). This nonlinear DBM model comprises two components: a rainfall to SSL model and a second model, relating the SSL at the reservoir inflow to the SSL at the reservoir spillway. Using a daily measured rainfall series as the input, this model is used to reconstruct daily deposition rates between 1911 and 1996. This synthetic sediment accretion sequence is compared with the variations in sand content within sediment cores collected from the reservoir floor. These profiles show good general agreement, reflecting the importance of low reoccurrence, high magnitude events. This preliminary study highlights the potential of this DBM approach, which could be readily applied to other sites.     

Small river basin and estuarine sediment fluxes: The magnitude necessary for coastal dispersion and siltation effects on a coral reef

Increasing continental suspended sediment influx to coral reefs is an example of land-sea coupling that requires the identification of sources, magnitude of transport, and controlling processes. In Brazil, a small coastal basin (Macaé River) was identified as a source of suspended sediment to a coral reef on the coast of Cape Armação dos Búzios. Biannual suspended sediment loads were measured at the basin as were fluxes within the estuary and towards the coast during eight tidal cycles. Particle load and yield from this basin were typical of small coastal basins, showing high to moderate slopes and transitional land management. However, the magnitude of the river loads was lower than the sediment transport within the estuary, indicating that the estuary amplifies river fluxes and sustains the transference of suspended sediment alongshore to the coral reef. Nonetheless, the estuary displays both suspended particle retention and export capacity and, therefore, fluxes to the coast and the coral reef occur as episodic events.     

Reconstructing the early 19th‐century Waal River by means of a 2D physics‐based numerical model

Suspended‐sediment concentration data are a missing link in reconstructions of the River Waal in the early 1800s. These reconstructions serve as a basis for assessing the long‐term effects of major interventions carried out between 1850 AD and the early 20th century. We used a 2D physics‐based morphodynamic model accounting for the influence of floodplain vegetation to fill in this gap. Historical discharge hydrographs were derived from a correlation between flow discharge records at Cologne and water level measurements of the Rhine branches in the Netherlands, taking into account the discharge distribution between the branches. Historical floodplain sedimentation rates were estimated using old cartographic information and recent geomorphologic field work. The computed historical sedimentation rates are found to be within the range of measured data, which suggests that fine suspended sediment concentrations in the early 1800s were comparable to contemporary ones. The computations show also how vegetation enhances the formation of natural levees close to the main channel and at the same time decreases the sedimentation rates in farther areas of the floodplain. A sensitivity analysis shows suspended sediment composition to have a strong influence on the resulting quantities and patterns of floodplain deposition. The reconstruction has also provided validation of the modelling tools to reproduce the effects of vegetation on sediment dynamics, enabling their implementation to study other cases. Copyright © 2010 John Wiley & Sons, Ltd.     

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…     

Suspended sediment dynamics associated with snowmelt runoff in a small mountain stream of Lake Tahoe (Nevada)

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.     

Hydrological and thermal regimes in a supra-glacial lake: Imja,Khumbu, Nepal Himalaya

Abstract

Supraglacial Imja Lake (lake level, 5010 m a.m.s.l.), Khumbu, Nepal Himalaya, has increased its size on the tongue of Imja Glacier since the 1950s. In order to clarify the mechanism of the lake expansion, the physical conditions, water budget and heat budget of the lake were examined by measuring water temperature, water turbidity, lake level, meteorology and water discharge. These measurements were carried out in the monsoon season of July 1997, when the glacier melt occurred in the ablation area with air temperature of more than 0°C. Density stratification in the lake is built up by an effect of water pressure on lake water, but, neglecting the effect, lake water density is defined by suspended sediment concentration rather than temperature. Glacier-melt water from the subaqueous part of the glacier terminus mixed with lake surface water of 4–8°C, and diffused the water of about 3°C into the deeper zone of the lake. This advective, thermal diffusion occurs by sediment-laden underflow and relatively clear density interflow. The sediment-laden underflow is induced by intermittent glacier-melt sediment discharge at the terminus, while the density interflow is probably produced by continuous glacier-melt water discharge. Calculation of water budget of the lake indicates that meltwater inflow at the glacier terminus and surface water outflow at the outlet determine the hydrological conditions of the lake. The net heat transfer by melting of the terminal ice and dead ice, connected to the lake expansion, was evaluated by calculating the heat budget of the lake.     

Dynamics and behaviour of suspended sediment in macrotidal estuaries along the south coast of the English Channel

A review is given of suspended sediment dynamics in macrotidal regimes using examples of estuaries situated along the French coast of the English Channel. Characteristic features of estuarine turbidity maxima are described over a range of time-scales, which includes semidiurnal and neap-spring tidal cycles, and seasonal fluctuations of river discharge. The present behaviour of the fluvial sediment influx within these systems is described, taking into account the geological history of estuarine infilling.     

Oscillatory bedload transport: Data review and simple formulation

This review displays over 700 rates of sediment transport by oscillatory flow from 20 sources. Sediments include fine sands to pebbles, both of quartz and of lightweight materials, and the transport rates in water range over seven orders of magnitude. Most data are average gross (to and fro) bedload rates collinear with laboratory flow over a horizontal sediment bed, although other situations with net transport, suspended load, or oblique field waves are considered.As peak flow velocity nears twice the threshold velocity for sediment motion, bedload appears to be fully developed and the transport rate is near that given by a simple formula including flow frequency and peak velocity, and sediment size and density. At lesser peak velocities, bedload rates are markedly smaller and distinctly different regimes of sediment mobilization and transport may be identified.     

Relative velocities of discharge and sediment waves for the River Severn,UK

Abstract

It is generally accepted that the celerity of a discharge wave exceeds that of a floodwave. The discharge wave is the initial wavefront (shown by an increase in stage at a particular site), whereas the floodwave refers to the body of water moving downstream. Yet, few studies have investigated the varying relationship between discharge and suspended sediment concentration as floods propagate downstream. This paper examines the relative velocities of the discharge and sediment waves for natural flood events on the River Severn, UK. Four monitoring stations were established within the upper 35 km reach of the River Severn (drainage basin area 380 km2). Discharge was monitored using fixed structures, and suspended sediment concentrations were monitored at similar locations using Partech IR40C turbidity meters. Results showed discharge wave celerity increased with flood magnitude, but relationships were more complex for sediment wave celerity. Sediment wave celerity was greater than discharge wave celerity, and is attributed to the dominant source of sediment, which is most probably bank erosion.     

Dynamics of suspended sediment transport and yield in a large agricultural catchment,southwest France

The dynamics of suspended sediment transport were monitored continuously in a large agricultural catchment in southwest France from January 2007 to March 2009. The objective of this paper is to analyse the temporal variability in suspended sediment transport and yield in that catchment. Analyses were also undertaken to assess the relationships between precipitation, discharge and suspended sediment transport, and to interpret sediment delivery processes using suspended sediment‐discharge hysteresis patterns. During the study period, we analysed 17 flood events, with high resolution suspended sediment data derived from continuous turbidity and automatic sampling. The results revealed strong seasonal, annual and inter‐annual variability in suspended sediment transport. Sediment was strongly transported during spring, when frequent flood events of high magnitude and intensity occurred. Annual sediment transport in 2007 yielded 16 614 tonnes, representing 15 t km^?2 (85% of annual load transport during floods for 16% of annual duration), while the 2008 sediment yield was 77 960 tonnes, representing 70 t km^?2 (95% of annual load transport during floods for 20% of annual duration). Analysis of the relationships between precipitation, discharge and suspended sediment transport showed that there were significant correlations between total precipitation, peak discharge, total water yield, flood intensity and sediment variables during the flood events, but no relationship with antecedent conditions. Flood events were classified in relation to suspended sediment concentration (SSC)–discharge hysteretic loops, complemented with temporal dynamics of SSC–discharge ranges during rising and falling flow. The hysteretic shapes obtained for all flood events reflected the distribution of probable sediment sources throughout the catchment. Regarding the sediment transport during all flood events, clockwise hysteretic loops represented 68% from river deposited sediments and nearby source areas, anticlockwise 29% from distant source areas, and simultaneity of SSC and discharge 3%. Copyright © 2010 John Wiley & Sons, Ltd.     

Spatio‐temporal sedimentation patterns in beaver ponds along the Chevral river,Ardennes, Belgium

With the recovery of the European beaver (Castor fiber) and their capacity to engineer fluvial landscapes, questions arise as to how they influence sediment transport, including the spatio‐temporal trends and patterns of sedimentation in beaver ponds. The Chevral river (Ardennes, Belgium) contains two beaver dam sequences, which appeared in 2004. Volumes of sediment deposited behind the dams were measured, and grain‐size distribution patterns were determined. Flow discharges and sediment fluxes were measured at the inflow and outflow of each dam sequence. Between 2004 and 2011, 1710.1 m³ of sediment was deposited behind the beaver dams, with an average sediment thickness of 25.1 cm. The thickness of the sediment layer was significantly (p < 0.001) related to the area of the beaver ponds. Along the stream, beaver pond sediment thickness displayed a sinusoidal deposition pattern, in which ponds with thick sediment layers were preceded by a series of ponds with thinner sediment layers. A downstream textural coarsening in the dam sequences was also observed, probably because of dam failures subsequent to surges. Differences in sediment flux between the inflow and outflow at the beaver pond sequence were related to the river hydrograph, with deposition taking place during the rising limbs and slight erosion during the falling limbs. The 7‐year‐old sequences have filtered 190.19 ton of sediment out of the Chevral river, which is of the same order of magnitude as the 374.4 ton measured in pond deposits, with the difference between the values corresponding to beaver excavations (60.24 ton), inflow from small tributaries, and runoff from the valley flanks. Hydrogeomorphic effects of C. fiber and Castor canadensis activity are similar in magnitude. The detailed analysis of sedimentation in beaver pond sequences confirms the potential of beavers to contribute to river and wetland restoration, and catchment management. Copyright © 2013 John Wiley & Sons, Ltd.     

Hyperconcentrated flows as influenced by coupled wind-water processes

Hyperconcentrated flow is a natural phenomenon, which is widely observed on the Loess Plateau of China[1,2]. So far, much research has been done with hyperconcentrated flows in China[1―7], although hy-perconcentrated flows are also observed in many riv-ers in other countries[8―10]. In the monograph edited by Chien[11], hyperconcnetrated flows were studied in depth, involving the physical properties, resistance, sediment-carry behavior and channel-forming pro- cesses. Wang and Chien el al.[…     

Quantifying sediment storage on the floodplains outside levees along the lower Yellow River during the years 1580–1849

The lower Yellow River channel was maintained by artificial levees between 1580 and 1849. During this period, 280 levee breaches occurred. To estimate sediment storage on the floodplains outside the levees, a regression model with a decadal time step was developed to calculate the outflow ratio for the years when levee breaching occurred. Uncertainty analysis was used to identify the likely outflow ratio. Key variables of the model include annual water discharge, a proxy for levee conditions, and potential bankfull discharge of the channel before flood season. Uncertainty analysis reveals an outflow ratio of 0.35–0.56. We estimate that during this period, 18.8–30.1% of the total ~312 Gt of sediment load was deposited on the floodplains outside the levees. Human-accelerated erosion in the Loess Plateau caused a 4-fold increase in sediment delivery to the lower Yellow River, which could not be accommodated by channel morphodynamic changes. As a result, 21.2–27.5% of the total sediment load was deposited within the levees, creating a super-elevated channel bed that facilitated an uncommonly high breach outflow ratio. Hence, the factor of a large super-elevation relative to the mean main channel depth should be considered when designing diversions to restore floodplains. © 2018 John Wiley & Sons, Ltd.