Review of a Semi-Empirical Modelling Approach for Cohesive Sediment Transport in River Systems

In this paper, a review of a semi-empirical modelling approach for cohesive sediment transport in river systems is presented. The mathematical modelling of cohesive sediment transport is a challenge because of the number of governing parameters controlling the various transport processes involved in cohesive sediment, and hence a semi-empirical approach is a viable option. A semi-empirical model of cohesive sediment called the RIVFLOC model developed by Krishnappan is reviewed and the model parameters that need to be determined using a rotating circular flume are highlighted. The parameters that were determined using a rotating circular flume during the application of the RIVFLOC model to different river systems include the critical shear stress for erosion of the cohesive sediment, critical shear stress for deposition according to the definition of Partheniades, critical shear stress for deposition according to the definition of Krone, the cohesion parameter governing the flocculation of cohesive sediment and a set of empirical parameters that define the density of the floc in terms of the size of the flocs. An examination of the variability of these parameters shows the need for testing site-specific sediments using a rotating circular flume to achieve a reliable prediction of the RIVFLOC model. Application of the model to various river systems has highlighted the need for including the entrapment process in a cohesive sediment transport model.

Study on Parameters of Two Widely Used Cohesive Soils Erosion Models

The erosion rate of cohesive soils was typically modeled with the excess shear stress model and the Wilson model. Several kinds of research have been conducted to determine the erodibility parameters of the two models, but few attempts have been made hitherto to investigate the general trends and range of the erodibility parameter values obtained by the commonly used Erosion Function apparatus. This paper collected a database of 177 erosion function apparatus tests to indicate the variability of all erodibility parameters; the range of erodibility parameters is determined by data statistics and parameter theoretical value derivation. The critical shear stress (τc) and erodibility coefficient (Z0) in the over-shear stress model have a positive proportional relationship when the data samples are sufficient. However, there is no such relationship between the erodibility coefficient (b0) and erodibility coefficient (b1) in the Wilson model. It is necessary to express the soil erosion resistance by considering all erosion parameters in the erosion model. Equations relating erodibility parameters to water content, plasticity index, and median particle size were developed by regression analysis.

Laboratory measurements of the erodibility of gravelly soils

The critical shear stress and erodibility of soil are fundamental parameters for modeling embankment breaching. Unfortunately, very few studies have examined the erosion characteristics of soils consisting predominantly of particles larger than sand. This report presents results of an experimental study in which the erosion characteristics of gravelly soils were measured. A flume apparatus was developed in which 0.45-m-square samples were extruded into confined flow. A mechanical laser system allowed the measurement of scour in real time, resulting in a continuous and automated erosion test. The critical shear stress of a uniform gravel was found to match the expected values based on the Shields diagram, while tests that were composed largely of gravel but contained other soils, such as sand, silt, and clay, varied significantly with the critical shear stress and erodibility, depending highly on the characteristics of the finer soils.

Critical Shear Stress for Erosion of Sand-Mud Mixtures and Pure Mud

The erosion threshold of sand-mud mixtures is investigated by analyzing the momentum balance of a sand particle or a mud parcel in the mixture bed surface, and a formula for the critical shear stress of sand-mud mixtures is developed, which also applies for pure sand and mud. The developed formula suggests that the variation of the critical shear stress of sand-mud mixtures over mud content is mainly caused by the varying dry bulk density of the mud component in the mixture. The developed formula reproduces well the variation of the critical shear stress of sand-mud mixtures over mud content and can predict the critical shear stress of both sand-mud mixtures and pure mud in the process of consolidation. The developed formula promises to be convenient for application by relating the critical shear stress to mud content and the dry bulk density of sediment.

Adapting the WEPP hillslope model to predict unpaved road soil erosion in southern China

Process-based erosion models are efficient tools that can be used to predict where and when erosion occurs. On unpaved roads that have been recognized as important sediment sources, soil loss along road segments should be precisely predicted. This study was performed using the hillslope version of the Water Erosion Prediction Project (WEPP) to estimate soil loss from 20 typical road segments in the red soil region of South China. Terrestrial laser scanning (TLS)-measured soil losses were used to validate the model simulations. The results showed that the WEPP model could reasonably predict the total soil loss in relatively short (less than 100 m) and gentle (slope gradient lower than 10%) road segments. In contrast, the WEPP-simulated soil loss was underestimated for long or steep road segments. Detailed outputs along roads revealed that most of the peak soil loss rates could not be adequately calculated. The linear critical shear stress and the sediment equilibrium theory in the WEPP model for soil detachment simulation might be responsible for the underestimation. Additionally, the lack of upslope flow and the curved road tortuosity were found to be connected to the relatively low efficiency of the model outputs. Nevertheless, the WEPP simulation could accurately fit the trend of soil loss variation along road segments despite underestimation. Furthermore, the simulated results could provide a reliable prediction of the maximum soil loss positions. Therefore, the WEPP model could be adopted to evaluate the erosion risk of unpaved roads in the red soil region of South China.

Experimental Analysis of Incipient Motion for Uniform and Graded Sediments

So far, few studies have focused on the concept of critical flow velocity rather than bed shear stress for incipient sediment motion. Moreover, few studies have focused on sediment mixtures (graded sediment) and shape rather than uniform sediment for incipient motion condition. Different experiments were conducted at a hydraulic laboratory at the University of Guilan in 2015 to determine hydraulic parameters on the incipient motion condition. The aim of this study is to conduct a comparison between uniform and graded sediments, and a comparison between round and angular sediments. Experiments included rounded uniform bed sediments of 5.17, 10.35, 14 and 20.7 mm, angular uniform sediment of 10.35 mm, and graded sediment. Results demonstrated that angular sediment has a higher critical shear velocity than rounded sediment for incipient motion. Results also showed that for a given bed sediment, although critical shield stress and relative roughness increased with the bed slope, the particle Froude number (based on critical velocity) decreased. In terms of the sediment mixture, the critical shear stress (Vc*) was higher for the graded sediment than for the three finer uniform sediment sizes. The finer fractions of the mixture have a higher particle Froude number than their corresponding uniform sediment value, while the coarser fractions of the mixture showed a lower stability than their corresponding uniform sediment value. Results demonstrated that the reduction in the particle Froude number was more evident in lower relative roughness conditions. The current study provides a clearer insight into the interaction between initial sediment transport and flow characteristic, especially particle Froude number for incipient motion in natural rivers where stream beds have different gravel size distribution.

MODIFICATION PROPERTIES OF CONFECTIONARY FLOUR PRODUCTS WITH SYNBIOTIC

One of the main directions in the confectionery industry is creating new functional-purpose products. Besides meeting the dietary demand, they are supposed to be wholesome and health-giving. That is why so topical a task is enriching the composition of confections with synbiotics. They will have a positive effect on the manufacturing technology and impart physiological properties to final products.The paper studies how the synbiotic complex consisting of a synbiotic (microencapsulated bifidobacteria in a pectin matrix) supplemented with a prebiotic (inulin) determines changes in the structural and mechanical properties of flour confections, in particular, of fatty fillings for wafer biscuits. The mass fraction of inulin has been established after introducing 10, 20, and 30% of it into the filling to replace the equivalent amounts of fat. The quantity of bifidobacteria included in the recipe was determined considering the fact that in functional-purpose products, the physiologically active level of microorganisms should amount to 106–107 CFU/g of the intestinal contents.It has been studied how the synbiotic effects on the structural and mechanical properties of the fatty filling: its effective viscosity, adhesive strength, critical shear stress, and density. It has been found that introducing the synbiotic into the fatty filling and increasing the proportion of inulin adds to the effective viscosity in the test samples of the filling. Besides, the synbiotic makes the samples of filling stronger, which reduces the maturation time of wafer blocks. Thus, in the control sample, the blocks rest for 14 min, but in the test samples containing 10, 20, and 30% of inulin, this time is reduced to 12, 8, and 6 min respectively. With an increase in the mass fraction of inulin, the specific pull-off force has been established to decrease, as compared with the control sample.Experimentally, it has been revealed that there is dependence between the wafer filling density and the air phase characteristics (the size and number of air bubbles in the filling). It has been determined that the higher the density of the filling, the fewer air bubbles there are in the samples. The experimental findings prove that using the synbiotic in the wafer technology is practical.

Evaluation of erosion characteristics of soils using the pinhole test

This paper investigates the erosion characteristics of soils using the pinhole test. The tests were conducted with two undisturbed clay samples and five disturbed sandy soil samples. Based on the pinhole test results, a process to analyze the critical shear stress and erosion rate was proposed. The result indicates that the particle size distribution and coefficient of uniformity of soils are significant factors that affect the erosion characteristics of the soil. Samples with a grain size ranging from 0.2 to 0.6 mm is most susceptible to soil erosion. The erosion coefficients can be used to distinguish between the low erodible soils (ND3 and ND4) and high erodible ones (D1 and D2). Furthermore, it is interesting to note that the critical shear stress might be used as an identification parameter for erosion characteristics of the soil: τc > 3.5 Pa (ND3), 3.0 Pa < τc < 3.5 Pa (D2), and τc < 3.0 Pa (D1).