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As wastewater is commonly disposed of in the form of sediment-laden jet from a submarine outfall, the sediment movement when the jet evolves in the ambient water and its final deposition are of great importance to marine engineers. This study aims to investigate the settling mechanism of the sediment from an inclined discharge nozzle and quantify the deposition profile for various jet conditions in the hydrostatic environment through physical experiments and dimensional analysis. In the experimental tests, separate flow visualizations for the fluid and sediment phases are achieved to enable the simultaneous observation of sediment particles and jet fluid movement, through which the analysis of the relationship between the fluid and the sediment movement is carried out. The results show that at locations close to the nozzle (s / D = 5), sediment mean velocity has an inverse relationship with the turbulence intensity while positively correlated with the initial jet momentum. The discharge angle is found to have dominant effect on alternating the sediment velocity profile from symmetrical to asymmetrical. With the newly defined momentum settling length scale l mi , the non-dimensional formulations for deposition rate and accumulated deposition profile involving the nozzle inclination have been validated by the experimental data and are potential to be applied to the prediction of depositional rate and final deposition distribution near the outfall for the full-scale wastewater discharge events. • Fluid and sediment phases are simultaneously observed for the sediment-laden jet. • Increase of inclined discharge angle enhances the asymmetry of sediment velocity profile. • A new momentum settling length scales l mi is introduced. • Uniform equation is achieved to describe the 1D deposition profile at the bottom. [ABSTRACT FROM AUTHOR]

The new toolbox ScourApp is presented and applied for analysis of the complex interactions between local scour and sediment deposition at bridges during floods and to determine the relative importance of the controlling parameters on scour depth. ScourApp represents the time-dependent sediment transport processes through modern empirical formulations to compute the evolution of scour depth at a bridge pier. Results show that the mathematical model reproduces observed scour depths with high accuracy and confirm that ScourApp is a suitable tool for scour analysis. The model parameters controlling the time dependent scour depth were the equilibrium scour depth, and two constants representing the effects of pier geometry, flow and sediment. Sensitivity analysis showed that all three scour model parameters exhibited a nearly linear relation with the final scour depth. Moreover, results considering sediment deposition obtained for the Rapel Bridge showed that scour depths are highly sensitive to the sediment supply rate. ScourApp is recommended in scour assessment for bridge planning, design, management, and forensic analysis, as well as for engineering education. • The open-source toolbox ScourApp for scour analysis is developed. • Complex interactions of time-dependent scour and scour hole refilling are analysed for several laboratory and real-life cases. • The relative importance of controlling parameters on scour is analysed. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) are globally ubiquitous in sediments and surface waters. Interactions between biota and MPs are complex and influence their fate and effects in the environment. Once MPs enter aquatic systems, they are colonized by biofilms that may form from the excretion of extracellular polymeric substances (EPS) from microalgae. Biofilm accumulation may change the density of the MPs, contributing to their transport to the sediments. Furthermore, benthic plantivores may consume biofilm laden MPs allowing them to enter the food web. Thus, it is crucial to understand the role algae plays in the vertical transport of MPs in the aquatic environment. In this study, Chlamydomonas was cultured with MPs at different concentrations (0–0.4 mg/mL), and temperatures ranging from 2.5 to 32.5 °C to understand the deposition dynamics and impacts of MPs on EPS production and algal density. Temperatures ranging up to 25 °C increased algal density and MPs deposition. However, at 32.5 °C, algal density and MPs deposition declined. The quantity of MPs also affected algal cell density and EPS production. MPs concentration from 0 to 0.4 mg/mL increased EPS production at all temperatures. Similarly, an increase in algal cell density and MPs deposition occurred when MPs concentration was raised to 0.3 mg/mL. Algal cultures exposed to 0.3–0.4 mg/mL of MPs had a decrease in algal cell density, with no corresponding decline in EPS production. At certain conditions, MPs can facilitate biofilm formation by stimulating EPS production, which can increase cell density thereby expediting MPs transport to the sediment. • Microplastics (HDPE) stimulated extracellular polymeric substances production. • Microplastics (HDPE) exposure up to 0.3 mg/mL increased the growth of Chlamydomonas. • Microplastics (HDPE) exposure over 0.3 mg/mL decreased the growth of Chlamydomonas. • Temperatures up to 25 °C increased algal density and microplastics deposition. • Microplastics exposure over 0.3 mg/mL increased extracellular polymeric substances. [ABSTRACT FROM AUTHOR]

• An efficient 2D shallow water hydro-sediment-morphodynamic model is presented. • Morphodynamic processes under the impact of cascade movable weirs are studied. • Disparate morphological changes may result under different operation schemes. • An alternating operation scheme is proposed to constrain morphological changes. Cascade movable weirs have been increasingly widely used for river landscaping, water storage and ecological wellbeing. The weirs disturb the prior equilibrium in line with fluvial hydrology, sediment transport and geomorphology, and may lead to profound changes in the river, of which, however, the understanding has so far remained poor. Here, the first of its kind, a computational modelling study is presented on the morphodynamic processes under the impact of cascade hydraulic lifting dams, a type of movable weirs, as to the middle Fen River, China. A two-dimensional shallow water hydro-sediment-morphodynamic model is applied to resolve the fluvial processes, which is physically coupled and computationally efficient based on Finite Volume Method, unstructured mesh, local time stepping and parallel computing. Computational results show that the cascade dams alter the flow and sediment transport locally and on the reach scale in a distinct manner under different operation schemes, which in turn incur disparate morphological changes. Collapse of all the dams all year round would lead to net degradation in the study reach, with the floodplains aggrading and the main channel degrading. Operation of all the dams all year round may induce an overall aggradation both on the floodplains and in the main channel. If all the dams collapse in flood seasons and operate in dry seasons (CF), degradation occurs in the main channel whereas the floodplains experience aggradation, with a net degradation. When only the dams in the main channel operate all year round (OM), the floodplains degrade while the main channel aggrades, resulting in a net aggradation in the study reach. Either aggradation or degradation may prevail locally on floodplains, in main channel and individual subreaches. The present findings lead us to propose a complex operation scheme of annually alternating CF and OM to constrain significant morphological changes. [ABSTRACT FROM AUTHOR]