Analysis and Study of Flow Patterns and Sediment Deposition in the Forebay of a Forward Intake Pumping Station

In Northwest China, the sediment concentration of the Yellow River is high. A project to investigate the operation of a pumping station shows that the flow patterns in the forebay and inlet tank are disordered, and there is sediment deposition that endangers the normal operation and safety of the pumping station. To solve this problem, the three-dimensional two-phase water-sediment flow in the forebay of the pumping station is modeled by using fluid simulation software, and diagrams of the sediment volume fraction content and vector distribution in the flow layers of different sections are obtained. Combined with the multiphase flow theory of mixtures and the realizable turbulent kinetic energy equation, the location and formation mechanism of each vortex, as well as the area and degree of sediment deposition in the forebay, are analyzed. The actual engineering and numerical simulation results are compared to verify the accuracy of the simulation. The results show that the main reason for sediment deposition is the high sediment concentration of the Yellow River, but the flow pattern disorder is affected by a specific design defect of the forebay, which makes the sediment deposition worse. The results of this study provide specific guidance and methods for the construction and transformation of the forebay of the pump station in the future; construction to weaken the return area to a certain extent can reduce the degree of sedimentation.

Escherichia coli concentration, multiscale monitoring over the decade 2011–2021 in the Mekong basin, Lao PDR

Bacterial pathogens in surface waters may threaten human health, especially in developing countries, where untreated surface water is often used for domestic needs. The objective of the long-term multiscale monitoring of Escherichia coli concentration in stream water, and that of associated variables (temperature, electrical conductance, dissolved oxygen concentration and saturation, pH, oxidation-reduction potential, turbidity, and total suspended sediment concentration), was to identify the drivers of bacterial dissemination across tropical catchments. This data description paper presents three datasets (see section Data availability) collected at 31 sampling stations located within the Mekong river and its tributaries in Lao PDR (0.6–25,946 km2) from 2011 to 2021. The 1,602 records have been used to describe the hydrological processes driving in-stream Escherichia coli concentration during flood events, to understand land-use impact on bacterial dissemination on small and large catchment scales, to relate stream water quality and diarrhea outbreaks, and to build numerical models. The database may be further used e.g. to interpret new variables measured in the monitored catchments, or to map the health risk posed by fecal pathogens.

Effect of precipitation and sediment concentration on the loss of nitrogen and phosphorus in the Pasikhan River

Natural and anthropogenic factors influence the entry of pollutants into surface waters and their accumulation in aquatic ecosystems. This study aimed to investigate precipitation and sediment concentration on the outflow of different forms of phosphorus (P) and nitrogen (N) in three primary land-use types along the Pasikhan River, the biggest river entering the Anzali Wetland in the Southern Caspian sea. Water sampling was performed on a monthly basis during the time bracket of 2017–2018. Different forms of P including total, soluble, particulate, total reactive, and dissolved reactive, and total Kjeldahl N, soluble N, particulate N, and were determined in the water samples. Total phosphorus and total Kjeldahl nitrogen contents lay within the range of 2.2–4.7 and from 0.14 to 0.33 mg l−1, respectively, downstream of the river. The highest monthly outflow of P from the watershed at the Agriculture station was recorded in October. Substantial conformity was found between the monthly trends of and and the trend of precipitation. The results indicated that sediment load intensified after an increase in the rainfall rate, leading to elevated N and P concentrations in the river water, mainly as particulate phosphorus and soluble nitrogen. It can also be inferred from the result that the concentration of N and P is directly related to the sediment concentration increase due to the rainfall. Increasing levels of nutrients such as N and P in the Pasikhan River can cause eutrophication in the Anzali Wetland, which needs conservative measures for reducing these elements' dynamic in the watershed.

Review of Suspended Sediment Transport Mathematical Modelling Studies

This paper reviews existing studies relating to the assessment of sediment concentration profiles within various flow conditions due to their importance in representing pollutant propagation. The effects of sediment particle size, flow depth, and velocity were considered, as well as the eddy viscosity and Rouse number influence on the drag of the particle. It is also widely considered that there is a minimum threshold velocity required to increase sediment concentration within a flow above the washload. The bursting effect has also been investigated within this review, in which it presents the mechanism for sediment to be entrained within the flow at low average velocities. A review of the existing state-of-the-art literature has shown there are many variables to consider, i.e., particle density, flow velocity, and turbulence, when assessing the suspended sediment characteristics within flow; this outcome further evidences the complexity of suspended sediment transport modelling.

Assessment of Erosion Characteristics in Purple and Yellow Soils Using Simulated Rainfall Experiments

Soil erosion of sloped lands is one of the important sources of substantive sediments in watersheds. In order to investigate erosion characteristics of sloped lands during rainfall events in the Three Gorges Reservoir Area, erosion processes of purple and yellow soils under different slope gradients and rainfall intensities were studied by using a rainfall simulator. The results showed that the sediment concentration in runoff was closely correlated with rainfall intensity. The sediment concentration in runoff gradually rose to a peak with time, and then gradually declined and approach a steady rate during simulation rainfall events. The particle size distribution of surface soils before the rainfall was different from that after the rainfall. Soil erosion mainly resulted in the loss of fine particles of surface soil through runoff, and the fine particles of soil were enriched in sediments. Soil erosion rates were gradually increased with the slope gradient when the slope gradient was less than 10°, and significantly increased when the slope gradient was more than 10°. The slope factor of yellow soil could be fitted well to that calculated by the formula of Universal Soil Loss Equation (USLE). The trend of the slope factor of purple soil was similar to that of the slope factor that was derived from USLE. Therefore, the effect of slope gradients on soil erosion need to be further researched when USLE was applied to predict erosion in purple soil area.

Estimation of Suspended Sediment Concentration in Downstream of the Ba River Basin using Remote Sensing Images

Assessing the tendency of suspended sediment concentration (SSC) in the river watershedsenables a better understanding of the hydromorphological properties of its basins and the associatedprocesses. In addition, analyzing this trend is essential to address several important issues such as erosion,water pollution, human health risks, etc. Therefore, it is critical to determine a proper method to quantifyspatio-temporal variability in SSC. In recent years, remote sensing and GIS technologies are being widelyapplied to support scientists, researchers, and environmental resource investigators to quickly andsynchronously capture information on a large scale. The combination of remote sensing and GIS data willbecome the reliable and timely updated data source for the managers, researchers on many fields. Thereare several tools, software, algorithms being used in extracting information from satellites and support forthe analysis, image interpretation, data collection. The information from satellite images related to waterresources includes vegetational cover, flooding events on a large scale, rain forecast, populationdistribution, forest fire, landslide movements, sedimentation, etc., and especially information on waterquality, sediment concentration. This paper presents the initial result from LANDSAT satellite imageinterpretation to investigate the amount of sediment carried downstream of the Ba river basin.

Sediment Load Concentration and Resultant Channel Planform in the Lower Gandak Plain

Erosion, transportation and deposition by running water are closely related and these works are performed in association and not in isolation. One cannot be performed without others. These works are determined on other factors like topography, geology, structure and composition of rocks, slope, amount of water availability and its characteristics, climate etc. Huge catchment area of the Gandak River is lying in the Himalayan mountainous region. This region is receiving good amount of rainfall concentrated in four months of monsoonal period June to September (JJAS). This period has also high temperatures leading to large amount of glacial ice melt. Hence, enormous water is drained off the mountain steep slope. The Himalaya is very young and has fragile rocks and ecosystem. Anthropogenic activities in those areas are primary cause, apart from natural weathering, for generation of more and more shattered materials which are brought by running water downstream much easily. Therefore, highly sediment concentrated water brings large quantity of loads. It is deposited in suitable conditions along its paths in the plain and with flood water. It results the formation of flood plain. According to the erosion and deposition, different types of major and minor features are formed. In other words, water and sediment determine the layout of the plain appearance. In this background, it is attempted to (i) study sediment concentration in discharged water and (ii) illustrate the channel planform of the Gandak River in the plain. To achieve these aims, secondary data has been collected and analyzed. It is expected that this study will help in executing an integrated development plan for the flood affected area of Lower Gandak River Plain. Keywords: sediment load, channel bars, channel planform, meandering, braiding, slope/gradient and channel cutoff.

Suspended sediment in lowland rivers – towards identifying the ratios of mineral and organic components and their variation during the year

Concentrations of suspended sediment transported by rivers are influenced by interactions between multiple drivers that act on a range of spatial and temporal scales. Such levels vary over the year, as well as across multi-year periods. Most conventional approaches to determining suspended load are based upon analyses of total suspended sediment concentration (SSC), i.e., the sum of mineral and organic matter. This approach makes it difficult, if not impossible, to determine the impact of multiple environmental factors on changes in suspension concentration precisely. The present paper focuses on the mineral and organic components of suspended sediment with the aim of determining how our knowledge of the share of each individual component can improve interpretations of SSC fluctuations during a hydro-logical year. The analysis conducted (personal and other researchers’ results) has shown that mineral and organic suspensions demonstrate mutually incompatible opposite trends under influence of environmental factors. This analysis of organic components identifies clear seasonal trends, which indicates that organic suspensions of autogenous origin have a strong influence on the dynamics of changes in suspension concentration; such analyses are rarely included in assessments of SSC dynamics.