International Journal of Sediment Research最新文献

A depth-averaged linearized meander evolution model was used to numerically evaluate the spatiotemporal evolution of the meandering channel centerline in the plane at various mean annual flows and width–depth ratios for capturing the overall average trend of the meandering channel planform. This analysis was done to better understand the consistent responses of the river morphology to possible future tectonic and climatic changes. The computational cases included an idealized sine-generated meandering channel with a moderate maximum deflection angle and a typical natural meander for the Jiyun River in China. The study results showed phased development and response characteristics of the meandering channel centerline (to the mean annual flow), along with increases in the specified mean annual width (B)–depth (H) ratio (represented by B/H). First, the spatial meander straightening trend over time weakened during Phase 1 (B/H ≤ 16.5) and gradually changed to a meander developing trend during Phase 2 (16.5 < B/H ≤ 27) with an overall insensitivity to the flow magnitude. Second, starting from the downstream tail during Phase 3 (27 < B/H ≤ 28.9), the symmetric development form along the transverse direction (perpendicular to the mean flow direction) was disrupted, while flow effects were highlighted when the mean annual B/H exceeded 28. Finally, an obvious onset and jump process of the channel sensitivity in response to flow occurred during Phase 4 (28.9 < B/H ≤ 29.5). These event characteristics are very similar to the transition from laminar to turbulent flow in fluid mechanics. This study provides insights for more in-depth exploration of meandering mechanisms and technical support for effective river management.

Dredged sediment is complex material composed of mineral phases, organics phases, and liquid phases. For the characterization of sediment in the laboratory, the material should be dried before applying some tests, such as the determination of organic matter content, X-ray diffraction (XRD) analysis, X-ray fluorescence (XRF) analysis, specific surface area, specific gravity, and many other tests. To do such tests, in test standards, no specific drying method is recommended. This paper evaluates the effects of drying methods on the measured characteristics of dredged sediment. The drying methods investigated in the current study are oven-drying, freeze-drying, and air drying. From the results obtained, it seems that the drying method affects the results of the test done on the sediment. Among the drying methods, freeze-drying has less effect on sediment properties when the results are compared to a few properties measured on undried material. However, from the point of view of materials classification in road construction, no effects of drying methods are recorded.

The B1 dam of Córrego do Feijão Mine, owned by Vale, S.A. mining company and located on the Ferro-Carvão stream, collapsed and injected 2.8 Mm³ of clayey, silty, and sandy iron- and manganese-rich tailings into the Paraopeba River (Minas Gerais state, Brazil). The accident occurred on 25 January 2019 and the tailings have been co-transported with coarser natural sediment since then, being partly trapped in the Igarapé Weir reservoir located on the Paraopeba River nearly 45 km downstream the injection point. The general purpose of the current study was to model suspended sediment transport in the vicinity of the Igarapé Weir aiming to assess the concomitant barrier effect imposed by this structure. Specifically, the spatial distributions of suspended clay, silt, and very fine-grained sand fractions (CSS) of sediment were mapped around the Igarapé Weir under low-flow (16 m³/s) and high-flow (5 to 10,000 years return period stream discharge; 699–2,699 m³/s) regimes, using RiverFlow2D as the modelling tool. The concentrations of the various grain materials in the upstream and downstream sectors were quantified linking the barrier effect to concentration reductions in the direction of stream flow. It was also a study goal to calculate differences of iron and manganese concentrations in the sediment + tailings mixtures along the Paraopeba River. The study results showed reductions in the CSS between 6.6% and 18%, from upstream to downstream of the Igarapé Weir, related with backwater effects, free and submerged hydraulic jumps, bank sedimentation in periods of high flow, and streambed sedimentation controlled by channel sinuosity and tailings density. These reductions were accompanied by drops in the concentrations of iron and manganese present in the clay and silt fractions, which varied between 6% and 42% under low flows and between 16% and 44% under high flows. Bank sedimentation was viewed as a potential threat to the riparian vegetation in the long-term. Dredging is the potentially most effective mitigation measure to help lead the Paraopeba River to a pre-rupture condition. The retention of sediment + tailings transported in suspension is less effective than the trapping of bedload sediment + tailings behind the Igarapé weir. The efficacy of sediment trapping is expected to be larger for natural sediment because it is much coarser than the tailings. In that context, the simulations revealed for the low-flow period that 33.6% of the sediment deposition comprised suspended transport of natural sediment (thus, was comprised 66.4% of bedload transport), this proportion rose to 86.9% for mixtures of natural sediment + tailings, a result that did not differ much for the high-flow periods.

Freshwater reservoirs are essential owing because of their ecological, economic, and social importance. They are particularly vulnerable to contamination, as of metal and metalloids, derived from anthropogenic activities like mining. The temporal variations in trace element concentrations (arsenic (As), mercury (Hg), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn)), enrichment, fluxes, and possible sources were evaluated by studying two sediment cores from the La Angostura (ANG) Reservoir (northwest Mexico), using ²¹⁰Pb geochronology. The enrichment factors showed from null to minor enrichment for most elements, but moderate to severe enrichment of mercury (Hg). Most trace element concentrations had a detrital origin, and notable Hg concentration increases since the past decade were associated with severe drought periods, likely resulting from wildfires. The observed sediment concentrations of As and Hg can cause adverse effects on biota in the ecosystem since they are above the probable effect level (PEL). Development of strategies for metal attenuation in this reservoir is recommended and metals should be controlled until specific ecotoxicological studies are performed.

The evaluation of the trend of flood stage changes in alluvial rivers downstream of dams is important for flood management. However, the flood stage associated with a given discharge generally is nonstationary in river reaches with multiple tributaries. This is not only because of the dam-induced shifting in the cross-sectional area and/or channel roughness but also because of the backwater induced by high flows from the tributaries. To determine the total trend of the flood stage and quantify the separate contributions of hydrological and geomorphic effects, the current study proposed a framework approach consisting of hydrological analysis and multiscenario numerical modeling. By this means, the trend in the flood stage could be distinguished from the stage oscillation driven by varying factors, including extreme hydrologic events. The effects of chronic changes, including channel incision and flow resistance increase, also were quantitatively separated. This framework was applied to the Chenglingji–Datong (CD) reach downstream of the Three Gorges Dam (TGD) in the Yangtze River, China. The results indicated that the effect of the roughness increase counterbalanced the effect of channel incision when the flow discharge was beyond the bankfull level. The backwater effect induced by tributary inflow was the major cause of the flood stage rise in recent years. The method presented in the current study provides a useful tool for managers and engineers to obtain better insight into the driving mechanisms of flood stage changes in river reaches that are downstream of dams. These findings indicate that the flood stage may not decline or may even occasionally increase, although the cross-sectional area was enlarged by channel incision. Special attention should be given to the flood risk situation in the study reach after the TGD began operation.