Total Suspended Sediment Flux Research Articles

Recent intensified erosion and massive sediment deposition in Tibetan Plateau rivers

Recent climate change has caused an increase in warming-driven erosion and sediment transport processes on the Tibetan Plateau (TP). Yet a lack of measurements hinders our understanding of basin-scale sediment dynamics and associated spatiotemporal changes. Here, using satellite-based estimates of suspended sediment, we reconstruct the quantitative history and patterns of erosion and sediment transport in major headwater basins from 1986 to 2021. Out of 13 warming-affected headwater regions, 63% of the rivers have experienced significant increases in sediment flux. Despite such intensified erosion, we find that 30% of the total suspended sediment flux has been temporarily deposited within rivers. Our findings reveal a pronounced spatiotemporal heterogeneity within and across basins. The recurrent fluctuations in erosion-deposition patterns within river channels not only result in the underestimation of erosion magnitude but also drive continuous transformations in valley morphology, thereby endangering local ecosystems, landscape stability, and infrastructure project safety.

Suspended sediment budget and intra-event sediment dynamics of a small glaciated mountainous catchment in the Northern Caucasus

The sediment dynamics of (peri-)glacial catchments can be highly variable and complex. Understanding these dynamics and their underlying causes is not only of interest from a scientific perspective but also required to address the practical problems with which they are often associated. In order to better understand the sediment dynamics of glaciated mountainous catchments, suspended sediment fluxes in the 9.1 km2 Djankuat catchment (North Caucasus, Russia) were monitored intensively during the 2017 ablation season. The intra-event suspended sediment dynamics were studied using a newly proposed simple hysteresis index (SHI), quantifying to what extent evolutions in sediment concentration are characterized by a clockwise or anticlockwise hysteresis loop. The resulting catchment suspended sediment yield was 1033 t km−2 year−1, with the glacier itself contributing 72% of the suspended sediment load. However, during rainfall events, also hillslope erosion in the proglacial area became a very significant sediment source. Clockwise hysteresis loops occurred in 61.8% of the events, while anticlockwise in 11.8%. On the other hand, only 47.8% of the total suspended sediment flux was transported during clockwise events. Our observations clearly indicate that events showing a stronger clockwise pattern (i.e., a higher SHI) are associated with a larger sediment input from the proglacial area. Overall, our results provide data and insights on sediment dynamics in an understudied environment. They illustrate that the type and characteristics of sediment concentration hysteresis loops are to some extent linked to the dominant sediment sources during the event. As such, the proposed methodology and SHI may also help with a better understanding of sediment dynamics in other environments.

Baroclinic Residual Circulation and Mass Transport Due to Internal Tides

AbstractBaroclinic (BC) tidal residual circulation due to internal tides is investigated around islands over a shallow ridge using a numerical ocean model. Internal tides enhance vertical mixing over shallow slopes, leading to horizontal density gradients that drive BC residual circulation along the main thermocline. For a strongly stratified summer case, the vertical diffusivity estimated by the Mellor and Yamada turbulence closure model exceeds 1 × 10−2 m2 s−1, and the velocity of BC residual circulations reaches 0.2 m s−1. The magnitude of BC residual circulation is larger than that of barotropic residual tidal circulation, implying that BC residual circulation due to internal tides plays an important role in coastal ocean circulation. Furthermore, BC residual flow accounts for an equal percentage (5%) of the total tidal kinetic energy as the barotropic residual flow under summer stratification conditions. Results from a coupled sediment resuspension and transport model show the growth of intermediate nepheloid layers formed by strong bottom shear stress and BC residual flow. The residual component contributes largely (23% of the total in summer) to the total suspended sediment flux. Seasonal variability is explored, with weaker winter stratification leading to reduced mixing, and thus weaker BC residual circulation and sediment flux. The magnitude of the BC residual circulation is also shown to be proportional to the square of the tidal amplitude.

Downstream erosion and deposition dynamics of fine suspended sediments due to dam flushing

Fine sediment dynamics downstream dams is a key issue when dealing with environmental impact of hydraulic flushing. This paper presents an analysis of six field campaigns carried out during dam flushing events (in June 2006, 2007, 2009, 2010, 2011, and 2012) in the Arc- Isère river system in the Northern French Alps. Suspended sediment concentrations (SSC) and discharges were evaluated using direct measurements or/and 1D hydraulic modelling at up to 14 locations along the 120 kilometres-long river channel. The total suspended sediment flux (SSF) is analysed along the Arc and Isère rivers for each Arc dam flushing event. Uncertainties were quantified based on a propagation method of both measurement and modelling errors. The resulting confidence interval provides elements of discussion on the significance of the sediment mass balance between two consecutive measurement sites. Whereas the discharge time-series of each flushing event is roughly the same, the quantity of fine sediments removed from the reservoirs varied from 10,000 tons in 2007 to 40,000 tons in 2006. Also, a significant erosion is observed in the river system for some events (20,000 tons in 2007) while the SSF barely varied for other events (in 2009 and 2011). This detailed data set allows to identify specific locations in the river network where deposition or erosion occurred. This dynamics is closely related to both the hydrology in the upper Isère River and the morphology of the Arc and Isère rivers, which have been affected by the 2008 and 2010 floods.

Catchment-scale weathering fluxes in the Southern Alps, New Zealand

The dissolved and suspended sediment flux in a small headwater in the Southern Alps, New Zealand over a 16-month period showed that mass transferred as dissolved load (91 t km−2 a−1) is a significant flux relative to the suspended sediment flux (210 t km−2 a−1). Export of dissolved load occurs mostly under baseflow, with 268 t being transported over 10 discrete events, relative to a total load of 1171 t over the experimental observation period; which is equivalent to 23% of the ionic flux occurring during event flow. Storm events contribute 2420 t of suspended sediment, accounting for 90% of the total suspended sediment flux. The chemical weathering flux was 43% of the physical weathering flux, and much higher than previous estimates of 1–9% for the Southern Alps. Such a high relative rate of chemical weathering is unlikely to be indicative of the full Southern Alps extent, but suggests that in some regions of the eastern Southern Alps mass loss via chemical weathering may be a significant portion of overall flux. During storm events, temporal exhaustion of sediment occurred and inferred limited sediment source production, rather than limited connectivity with the hillslope environment. Similar supply-limitation is expressed in the ionic flux, where rainfall events do not usually express hysteretic behaviour, and event flow is dominated by a simple dilution recession.

Estimating Surface/Subsurface Sediment Mixing in Karst Settings Using 7Be Isotopes

AbstractThis study shows that the cosmogenic radionuclide beryllium‐7 can be used to track sediment movement through caves. The activities of beryllium‐7 and cesium‐137 were measured in two different karst settings at both surface and subsurface sites before and after storm runoff events. At one site, 7Be‐enriched sediment was detected up to 1.5 km along a stream conduit after a moderate storm event; however, the activity of 137Cs was too variable to show a meaningful pattern. The percentages of surface sediment that was found ranged from 0 to 52% along the entire 3 km cave stream and from 33 to 52% along the upper 1.5 km. At the other site, as much as 96% of the sediment initially discharged at the spring during a storm event was fresh surface material that had traveled into and through the cave stream. Moreover, during the 4 day runoff event, approximately 23% of the total suspended sediment flux was estimated to originate from surface erosion with 78% being reworked sediment from within the cave. The data in this study show that cosmogenic radionuclides with multiyear half‐lives are too long‐lived to track sediment origins in the caves; whereas, 7Be with a 53.2 day half‐life, can be used to track movement of sediment along cave streams.

THE MAIN REGULARITIES OF THE RATIO BETWEEN RIVERBED AND BASIN COMPONENTS OF EROSION AND SUSPENDED SEDIMENT FLUX IN THE NORTHERN EURASIA’S RIVER BASINS

Suspended sediment flux is one of the objective and sufficiently accurate measures of the erosion activity in basins. Using the database for mean monthly values of water and suspended sediments runoff created for 460 rivers of the territory of the former USSR, the ratio of channel and basin components of erosion was analyzed. For this purpose the author proposed the special hydrological method (published early). For all analyzed river basins the share of riverbed erosion (δr) calculated by suspended sediment fluxes doesn’t exceed 15%. It amounts to 10.4±1.5% for the plain (lowland) rivers, to 4.9±0.9% for the low-altitude mountain rivers, and to 4.0±0.8% for the middle-altitude mountain rivers. The average δr for the whole Northern Eurasia is 7.2±0.8%. The ratio of channel and basin (δb) components depends distinctly on the landscape-climatic conditions, especially on latitudinal zoning. Thus, within the plains of Northern Eurasia the biggest δr occurs in the zones of tundra, taiga and mixed forests – more than 15–16% (15.0±9.6% in the tundra zone, 16.6±3.1% in the zone of taiga and mixed forests). In arid zones this value on the average does not exceed 5% (4.5±1.3 % in the steppes, 0.8% in the semi-deserts). Intermediate areas have a share of channel products of 5 to 10% (8.9±2.0% in the zone of broad-leaf forests, 5.2±1.6% in the forest-steppe zone). The same trend is observed in the low mountains but less distinctly than in the plains. There is a hyperbolic relationship between a total suspended sediment flux and its riverbed component. This dependence is clearly pronounced in the plains of the Northern Eurasia, but diminishes with increasing elevation of river basins. It’s shown also that the lithological factor (surface rocks’ composition) doesn’t play a significant role in the spatial variability of the δb/δr ratio.

Analysis of the Characteristics of Discharged Sediment in Yangtze River Estuary

The global estuarial studies have focused on water and sediment flux into the sea and the effect of human activities on the evolution of estuarial water and sediment. In the present study, we elaborated the impact of human activities on the water-sediment relation based on the water and sediment features at Datong Station (1951-2008). The results showed that the annual runoff of several years was slightly increased in 1990s in Yangtze River (Yangtze) River estuary. The changes were not obvious in these years. The suspended sediment flux (SSF) showed a phased downward trend, which was associated with water storage of the Three Gorges reservoir, the middle-and down-stream river-lake relationship, artificial sand excavation and water drinking and regulation. The ratio average of suspended sediment less than 0.01mm and 0.05mm was increased from 1987 to 2002 than the value before 1986. The value reached the maximal in 2003, and afterwards the sediment flux ratio of these two particle sizes was decreased. After 1986, the total SSF was reduced. The SSF less than 0.01mm showed a wavy decline along with the increase of suspended sediment ratio, while the SSF less than 0.05mm was decreased along with the reduction of the total suspended sediment flux. Meanwhile, the average of median suspended sediment particle size was 0.027mm before 1986 and was 0.0094mm from 1987 to 2008. The inflexion point appearing in 1986 was consistent with the inflexion point of SSF reduction. It was directly related to water storage of the Gezhouba Dam. The median particle diameter of riverbed sand had an increase of 0.01mm/10a in average after 1977. The maximal particle diameter of riverbed sand had changed little. Both suspended sediment and bed sand became fine along the estuary and slightly became coarse in the mouth, indicating that it was functioned as the estuarial filter. The above observations would provide valuable insights for science and objective evaluation of the effect of human activities on an estuary.

A comparison of the suspended and dissolved matter dynamics of two large inter‐tropical rivers draining into the Atlantic Ocean: the Congo and the Orinoco

AbstractThis study compares the total suspended sediment (TSS), total dissolved solids (TDS), and dissolved organic carbon (DOC) dynamics of two major inter‐tropical rivers, the Congo in Central Africa and the Orinoco in South America, focusing on sampling undertaken during the period 2006–2010. Both rivers are characterized by similar mean annual discharges into the Atlantic Ocean, on its eastern and western margins, respectively. For both rivers, the results presented are placed in the context of the available longer‐term hydrological time series (Congo: 1903–2010; Orinoco: 1926–2010). The key features of the recent records of material flux for both rivers were established and compared with other published data from the 20th century. The available discharge time series show that the rivers are characterized by similar maximum monthly discharges (Congo: 75 500 m3 s‐1; Orinoco: 85 500 m3 s‐1) and similar inter‐annual variability (Congo: 1.69; Orinoco: 1.66). However, contrasts in low‐flow regime (minimum low flows: Congo: 23 000 m3 s‐1; Orinoco: 2300 m3 s‐1) and seasonal variability (Congo: 3.3; Orinoco: 37.2), as well as in material fluxes were identified. Specific suspended sediment yields for the Orinoco (89 t km‐2 yr‐1) were very significantly higher than those for the Congo (9.4 t km‐2 yr‐1). These differences are mainly explained by contrasts in the physiographic characteristics of the two river basins, such as their contrasting relief. The differences between the TSS fluxes calculated for the Orinoco in this study and those indicated by published data from the second half of the 20th century can be explained by the impact of the hydroelectric dams built in the foothills of the Andean Cordillera. Changes in the TSS fluxes of the Congo are mainly explained by the impact of climatic change on total runoff. Copyright © 2013 John Wiley & Sons, Ltd.

Muted responses of streamflow and suspended sediment flux in a wildfire-affected watershed

In August 2003 a severe wildfire burnt 62% of Fishtrap Creek, a 158km2 watershed in central British Columbia, Canada. Streamflows were obtained for the period 1980–2010 and suspended sediment fluxes were determined for the period 2004–2010 for Fishtrap Creek and these were compared to data for nearby Jamieson Creek, which was not affected by the wildfire. Peak streamflows in Fishtrap Creek after the wildfire were not significantly higher than before the wildfire, although total annual runoff had increased. Perhaps the most important change in streamflows following the wildfire was that peak flows associated with the annual freshet occurred earlier in the year (by ca. 2weeks). Following the wildfire, monthly total suspended sediment fluxes peaked in April in Fishtrap Creek and May in Jamieson Creek, which reflects the change in timing of peak streamflows in Fishtrap. Specific suspended sediment yields were low in the first year following the wildfire (2004), and peak values for the 2004–2010 monitoring period occurred in 2006. Average specific suspended sediment yields over the monitoring period were similar for both watersheds at 2.8 and 2.9tkm−2year−1 for Fishtrap and Jamieson watersheds, respectively. The muted responses of streamflows and suspended sediment fluxes following this severe wildfire are due to the lack of winter precipitation and the low intensities of summer rainfall events in the first year following the wildfire. Greater winter precipitation and associated snowmelt in subsequent years coincided with vegetation recovery. The major changes in the wildfire-affected watershed were increased bank erosion and channel migration due to a loss of root strength and cohesion, which occurred 3–5years after the fire. This work demonstrates that the hydrological and geomorphological responses of watersheds to wildfires are a function of the severity of the wildfire and the timing and nature of driving forces (i.e. rainfall intensity, winter precipitation and snowmelt) during the progression of vegetation recovery.

Suspended Sediment Transport in Rip Currents on a Macrotidal Beach

Thorpe, A., Miles, J., Masselink, G., Russell, P., Scott, T., Austin, M., 2013. Sediment Transport In Rip Currents on a Macrotidal BeachRip currents are offshore-directed flows in the surf zone that may be responsible for significant offshore transport of sediment. In this study high frequency surface elevation and current velocity data were collected alongside suspended sediment concentrations in a rip channel on a high energy, macro-tidal beach. At low tide (water depth over the rip channel (h) = 0.9 m), when the rip current was active (maximum offshore directed flow = ~ 0.4 m/s), net suspended sediment transport was directed offshore, and 88% of the flux was due to the mean flow component. The rip current was found to pulse at very low frequencies (VLF) and this contributed significantly to offshore sediment transport, accounting for 48% of total oscillatory flux (not considering direction). Infra-gravity (IG) frequency oscillations had a marginal contribution to offshore sediment transport within the rip (10% of total oscillatory flux) and incident wave transport was onshore (42% of total oscillatory flux). The relative influence of the wave component increased as tidal elevations increased and the rip current became inactive. For comparison, at mid-tide (h = 3.5 m) the total suspended sediment flux was in the offshore direction and four times less than during low tide. The mean flux accounted for 34% of the total transport at mid-tide. At high tide (h = 6.1 m) the total sediment transport was in the onshore direction due to the incident waves, with a 0% contribution from the mean flux.

An improved method for evaluating the seasonal variability of total suspended sediment flux field in the Yellow and East China Seas

The suspended sediment flux field in the Yellow and East China Seas (YECS) displays its seasonal variability. A new method is introduced in this paper to obtain the flux field via retrieval of ocean color remote sensing data, statistical analysis of historical suspended sediment concentration data, and numerical simulation of three-dimensional (3D) flow velocity. The components of the sediment flux field include (i) surface suspended sediment concentration inverted from ocean color remote sensing data; (ii) vertical distribution of suspended sediment concentration obtained by statistical analysis of historical observation data; and (iii) 3D flow field modeled by a numerical simulation. With the improved method, the 3D suspended sediment flux field in the YECS has been illustrated. By comparison with the suspended sediment flux field solely based on the numerical simulation of a suspended sediment transport model, the suspended sediment flux field obtained by the improved method is found to be more reliable. The 3D suspended sediment flux field from ocean colour remote sensing and in situ observation are more closer to the reality. Furthermore, by quantitatively analyzing the newly obtained suspended sediment flux field, the quantity of sediment erosion and deposition within the different regions can be evaluated. The sediment exchange between the Yellow Sea and the East China Sea can be evident. The mechanism of suspended sediment transport in the YECS can be better understood. In particular, it is suggested that the long-term transport of suspended sediment is controlled mainly by the circulation pattern, especially the current in winter.

Modeling catchment controls on organic carbon fluxes in a meso-scale mountainous river (Luodingjiang), China

This study applied a partial least square regression (PLSR) technique to investigate the relationships between organic carbon fluxes and catchment environmental factors in the Luodingjiang, a meso-scale mountainous tributary of the Zhujiang (Pearl River), China. Catchment environmental characteristics were extracted from various ecological datasets, and river data were developed based on 13 sampling points during six sampling campaigns in 2005. Modeling results indicate that the lithology characterized by rock erodibility in the catchment is the most important control on riverine organic carbon fluxes (dissolved organic carbon (DOC) flux, and particularly particulate organic carbon (POC) flux) and total suspended sediment (TSS) flux in the Luodingjiang. Besides rock erodibility, more environmental variables are positively involved in the model of DOC flux, including precipitation, urban and agricultural area percentages, as well as basin area, while basin slope is negatively involved. Soil organic carbon (SOC) content does not exert a significant control on DOC flux in the study due to its unique spatial distribution with other environmental factors having reverse relationships with DOC flux, such as basin morphology and anthropogenic impacts. The dominant control of lithology on POC flux and TSS flux is considered as a result of the availability of highly erodible rocks in the region, such as coarse-grained granite and poor-cemented purple sandstone. The models developed in this study may be only applicable in the local catchments with similar environmental characteristics, such as hilly regions with weak underlying bedrock. The findings highlight the need for investigating the geographical variations when conducting studies about riverine organic carbon fluxes at the regional or global scale.

The nature and transport of the fine‐grained component of Swift Creek Landslide, Northwest Washington

AbstractExtreme sedimentation in Swift Creek, located in the Cascades foothills in NW Washington (48°55′N, 122°16′W), results from erosion of the oversteepened, unvegetated toe of a large (55 hectares) active landslide. Deposition of landslide‐derived sediment has necessitated costly mitigation projects in the channel including annual dredging and temporary sediment traps in an attempt to reduce the risk of flooding and damage to man‐made structures downstream. This study attempts to understand the process of sediment production along with the corresponding erosion rates of the sediment source to help with the development of mitigation plans and construction of optimal sediment reservoirs.The bedload and suspended sediment in the creek are a direct result of the weathering process of the serpentinitic bedrock underlying the landslide. The serpentinite does not weather to smectite clay, as previously thought. Instead, it weathers to asbestiform chrysotile with minor amounts of chlorite, illite and hydrotalcite, all of which occur in clay seeps on the unvegetated surface of the landslide. The chrysotile fibers average 2 µm in length and make up at least 50%, by volume, of the suspended load transported in Swift Creek. This study does not address the environmental or health implications of the asbestiform chrysotile transport or deposition.During the sampled time between February 2005 and February 2006, 127 discrete suspended sediment samples were collected and discharge was measured 66 times. The suspended sediment concentrations ranged from 0·02 g L−1 to 41·6 g L−1 and the discharge ranged from 0·0 m3 s−1 to 0·5 m3 s−1. A nonlinear functional model estimated the total suspended sediment flux from detailed precipitation records and discrete suspended sediment concentration and discharge measurements to be 910 t km−2 yr−1. When the suspended sediment flux is coupled with estimates of downstream deposition of coarse sediment, the estimated erosion rate for the entire Swift Creek landslide is 158 mm yr−1. The majority of the material entering Swift Creek is presumed to originate on the unvegetated toe of the landslide, for which the erosion rate is thus approximately 1 m yr−1. Copyright © 2010 John Wiley & Sons, Ltd.