International Journal of Sediment Research最新文献

A parameterized expression for sand wave morphology in rivers is established using a flow resistance law while accounting for sediment incipient velocity. A distinct relation is drawn between the proposed characteristic parameters and the sand wave morphology based on flume data. Support vector machines (SVMs) are then used to separate the boundaries of the sand wave morphology due to the high classification accuracy of SVMs. The boundary line data from each sand wave morphology is extracted and fitted to establish a discriminant standard, which is then successfully validated using experimental and quantifiable data. Also, based on the foregoing methodoly, it is further discovered that the short-term significant fluctuation of sand wave morphology is closely correlated with significant channel changes in rivers with a high width-depth ratio, using Yellow River Estuary as an example.

Aquatic ecosystems, especially freshwater ecosystems, are facing increasing anthropogenic disturbances, highlighting the urgency for accurate ecosystem assessment for informed decision-making and effective management. While ecosystem health and integrity assessments have been widely applied, they often focus on ecosystem elements, overlooking their interconnections and dynamic characteristics. Establishing an integrated ecosystem assessment framework is vital to apply a comprehensive perspective in evaluations. In the current paper, a systematic review of aquatic ecosystem assessment methods is done, encompassing health and integrity assessment, network analysis, and stability and regime shift assessment. These approaches consider not only the individual elements but also the complex interconnections and dynamic characteristics within the ecosystem, which have been rarely studied due to limitations in field data availability. A case study of Poyang Lake is further presented for practical demonstration on the specific operation of the combined assessments. The integration of aquatic ecosystem assessment with ecological modeling is strongly advocated because it not only helps overcome the limitations of field data for assessing historical or current conditions, but it also enables prediction of future developments.

The Shields diagram has been widely used in the description of the threshold condition for incipient sediment motion. Because the current definition of the Shields criterion is generally subjective, the relevant data are subject to high uncertainty. To date, several efforts have been made to define the threshold condition quantitatively, but they are all based on certain low bedload rates that were empirically chosen. The current study aims to provide a theoretical framework to quantify the Shields criterion based on the concept of the pickup probability of sediment particles. The results show that the Shields criterion can be reasonably described with a low pickup probability (p = 1%), which can be further converted to a low dimensionless bedload rate (i.e., $\varphi /{\theta }^{1.5}=0.13$, where $\varphi$ is the Einstein number and $\theta$ is the Shields number). The new approach is finally validated with experimental data of bedload rates published in the literature.

As reservoir sedimentation is rapidly progressing on a global scale, intensified and better adapted monitoring of sediment accumulation is needed to design optimal counter measures. In the current study, different methods on how to assess the siltation status of different reservoir types are represented by including the availability of previous data. Four different techniques are described by means of detailed case studies, including topographic differencing as the most widely used method. Examples of sub-bottom profiling, dynamic free-fall penetrometer measurements, and long sediment coring also are presented. The methods are explained through the application of each technique under varying conditions. The aim of the current study was to assess the advantages and disadvantages of each method and to discuss each methods applicability, depending on the reservoir type, sediment characteristics, and sediment thickness. Based on the case studies and literature an overview table of available techniques for sediment detection was created including a qualitative estimation of the strengths and weaknesses. Additionally, a decision path is presented to choose the most promising technique dependent on the individual situation of a reservoir. With this review, sediment-related decisions are supported for dam operators and authorities as well as dredging companies.

Estimating the cover and management factor (C-factor) for Universal Soil Loss Equation (USLE) that varies spatially and temporally within a watershed is time-consuming and resource-intensive. The Normalized Difference Vegetation Index (NDVI) approach can offer a potential alternative for this process. The current study examines nine NDVI models to compare and evaluate their performance in estimating the C-factor values for an agricultural watershed in southwestern Ontario, Canada. Satellite imagery from 2013 to 2020 was used to analyze the models’ similarities and differences on a detailed spatial and temporal scale. The results showed different C-factor values for each model, reflecting that they were developed for different geographical areas and purposes. While the Karaburun model differed from all other models on an annual basis, a detailed combined analysis of different spatial and temporal scales revealed that it was similar to other models. Seasonal analysis was found to be adequate for the current study, as it reduced the resources required and provided an overall view of the vegetation situation. However, a detailed monthly analysis may be necessary when investigating a specific season. The current analysis found that the summer months of June, July, and August have similar trends when comparing different models for different land uses and individual months, which aligns with the seasonal analysis. In conclusion, the current study highlights the importance of incorporating spatial and temporal scales in hydrological modeling and provides valuable insight into the applicability of different NDVI models for estimating the C-factor for southwestern Ontario watersheds. These findings can help inform future research and aid in developing accurate models for estimating soil erosion in this region. The results also emphasize that the NDVI approach has the potential for estimating the USLE C-factor and improving the estimation of soil erosion from agricultural watersheds by incorporating a variable C-factor over time and space. However, further research is needed to validate each model and determine which model best suits the study area.

In one of the world's worst mining disasters, after flowing 670 km down the Doce River, about 20 million m³ of tailings reached the coast of Brazil in November 2015. The occurrence of persistent northerly winds favored the detachment of the river plume from the coastline and its displacement southward. However, observations of the sediment plume along the coast during the year following the breach, using aerial photographs, indicated that the plume is more extensive and persistent in a northerly direction. Previous studies have shown that although the most persistent winds are from the northern sector (70%), there is a greater incidence of waves from the southern sector (62%), especially with greater heights and periods. In this research, the effect of gravity waves on the transport of sediments is investigated, and, therefore, tailings from the Doce River and deposited on the adjacent inner continental shelf, mixed with the fluvial mud deposit also are investigated. Two mechanisms were investigated: 1) the effect of waves on sediment resuspension and their combination with tidal and wind forcings, using a two-dimensions in the horizontal directions (2DH) numerical model within the DELFT3D software, and 2) the capture of the fluvial plume by littoral drift, calculated by means of analytical models using data from wave propagation modeling. Both mechanisms were studied for 2019, also considering two major meteorological events in the region. Both effects were relevant for the northward dispersion of fine sediment, highlighting the effect of waves on the potential for northward transport of tailings towards the Abrolhos Bank.

The current study focuses on the environmental radioactivity and multi-risk assessment of nearshore sediment as a source of marine pollution along the Bay of Bengal. The study examines the distribution of primordial radionuclide concentrations using a thallium-activated sodium iodide (NaI(Tl)) detector-based gamma-ray spectrometer and Potentially Toxic Elements (PTE) through atomic adsorption analysis. The data also were used to characterize ecological threats, radiological risks, and the geospatial distribution of toxic compounds in nearshore sediment as a proxy for marine pollution. The active concentration of primordial radionuclides such as uranium-238 (²³⁸U), thorium-232 (²³²Th), and potassium-40 (⁴⁰K) was found in the range from ≤ 3 to 68 (11.4), ≤ 9.5 to 142.7 (41.2), and 85.2 to 603.4 (362) Bq/kg, and the results show that the average radioactive concentration of the average radionuclides was less than suggested by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) ranges. Potentially toxic elements iron (Fe), chromium (Cr), nickel (Ni), lead (Pb), and zinc (Zn) were higher in deeper water depths. The current study reveals that mud distribution primarily controls such elements. A decreasing order has been seen as follows by the ecological risk index of individual elements: copper (Cu) > lead (Pb) > nickel (Ni) > chromium (Cr) > zinc (Zn). The significant Pb, Cu, and Zn concentrations indicated high pollution at most stations, possibly resulting from regional and terrestrial sources such as industrial activity, urban drainage, manufacturing, and farming. The migration of contaminated soil from the industrial and transportation sectors may be the source of the increased levels of hazardous elements and naturally occurring radionuclides in the sediment transported into the coastal ecosystems of Bay of Bengal.

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.