Flow and sediment transport in a sharp river bend using a 3D-RANS model

Flow dynamics and sediment transport in a river bend have recently been studied using experimental and numerical investigations. A three-dimensional numerical modeling model named NaysCUBE was used in this study to describe the flow pattern and process of sediment transport in a sharp river bend as a complement to the prior work of the physical hydraulic model. The model uses the RANS equation to simulate flow where a fully complex 3D flow is governed. Despite the limitations of the RANS model, NaysCUBE well reproduces the flow pattern and turbulence phenomena in a movable bed channel with sharp curvature. Compared with data from a prior experiment, the morphological adjustment is simulated sufficiently. The three-dimensional flow structures are useful for determining the appropriate countermeasures for local scouring and riverbank protection.

Sediment transport modeling at Stono Inlet and adjacent beaches, South Carolina

This report documents a numerical modeling investigation for dredged material from nearshore borrow areas and placed on Folly Beach adjacent to Stono Inlet, South Carolina. Historical and newly collected wave and hydrodynamic data around the inlet were assembled and analyzed. The datasets were used to calibrate and validate a coastal wave, hydrodynamic and sediment transport model, the Coastal Modeling System. Sediment transport and morphology changes within and around the immediate vicinity of the Stono Inlet estuarine system, including sand borrow areas and nearshore Folly Beach area, were evaluated. Results of model simulations show that sand removal in the borrow areas increases material backfilling, which is more significant in the nearshore than the offshore borrow areas. In the nearshore Folly Beach area, the dominant flow and sediment transport directions are from the northeast to the southwest. Net sediment gain occurs in the central and southwest sections while net sediment loss occurs in the northeast section of Folly Island. A storm and a 1-year simulation developed for the study produce a similar pattern of morphology changes, and erosion and deposition around the borrow areas and the nearshore Folly Beach area.

Sediment Transport Dynamism in the Confluence Area of Two Rivers Transporting Mainly Suspended Sediment Based on Sentinel-2 Satellite Images

Downstream of the confluence of rivers, complex hydrological and morphological processes control the flow and sediment transport. This study aimed to analyze the spatio-temporal dynamics of suspended sediment in the confluence area of the Tisza and its main tributary Maros River using Sentinel-2 images and to reveal the correlation between the hydrological parameters and the mixing process through a relatively long period (2015–2021). The surficial suspended sediment dynamism was analyzed by applying K-means unsupervised classification algorithm on 143 images. The percentages of the Tisza (TW) and Maros (MW) waters and their mixture (MIX) were calculated and compared with the hydrological parameters in both rivers. The main results revealed that the areal, lateral, and longitudinal extensions of TW and MIX have a better correlation with the hydrological parameters than the MW. The Pearson correlation matrix revealed that the discharge ratio between the rivers controls the mixing process significantly. Altogether, 11 mixing patterns were identified in the confluence area throughout the studied period. The TW usually dominates the confluence in November and January, MW in June and July, and MIX in August and September. Predictive equations for the areal distribution of the three classes were derived to support future water sampling in the confluence area.

Mathematical modelling of flow and sediment transport – the Tisa dam case study

High flow velocities downstream of the Tisa Dam at Novi Bečej (Serbia), produced by the large difference between water levels in the upstream and downstream reaches, cause bank erosion by the right bank immediately downstream of the emergency spillway, threatening stability of the dam itself. Due to complex interaction between the parameters of flow and sediment transport at the given location, an approach involving a spatial (3D) mathematical model of flow and sediment transport, aimed at solving such complex processes, is investigated in this paper. An optimum solution meeting all requirements for the stability of structures in question has been reached by the model, through comparison of the results generated by the existing conditions with the result provided by the measures proposed to fix the problems.

Changes of Flow and Sediment Transport in the Lower Min River in Southeastern China under the Impacts of Climate Variability and Human Activities

The Min River is the largest river in Fujian Province in southeastern China. The construction of a series of dams along the upper reaches of the Min River, especially the Shuikou Dam, which started filling in 1993, modified the flow processes at the lower Min River, leading to the significant increase in low-flows and slightly decrease in flood-flows. At the same time, reservoirs have more effects on the sediment transport process than flow process by trapping most sediment in the reservoirs, and greatly reduced the amount of sediment transporting downstream. Increase in vegetation cover also contributes to the decrease in sediment yield. The reduction in sediment together with excessive sand mining in the lower Min River resulted in the severe downward erosion of the riverbed. Using a reformulated elasticity approach to quantifying climatic and anthropogenic contributions to sediment changes, the relative contribution of precipitation variability and human activities to sediment reduction in the lower Min River are quantified, which shows that the sediment reduction is fully caused by human activities (including land use/land cover changes and dam construction).