Sediment dynamics

This chapter provides descriptions of essential features of modelling of a broad range of problems involving many classes of sediment, flow, applications and research top¬ics. The experimental reproduction of hydraulic processes involving sediment dynam¬ics is focussed on the sediments and not the hydrodynamic processes, which are covered in other chapters. Since a great deal of experimental research on sediment dynamics remains to be done, laboratory experiments to elucidate process knowledge (research) as well as physical modelling of site-specific applications (consultancy) will be covered

A Lagrangian model for simulating the dispersal of sand-sized particles in coastal waters

A model, SandTrack, has been established to simulate movements of sand-sized particles in coastal waters within a Lagrangian framework. The model can be applied to assess the dispersal of contaminated particulate material, such as may be associated with industrial discharges, or the dispersal of dredged spoil. For such applications, the Lagrangian approach is essential, as the identity of the particles is important. Although Lagrangian models existed previously which could simulate fine sediment constantly in suspension, there are certain applications, such as dealing with the movement of bed particles, in which intermittent physical processes are critical. SandTrack has been tested against field observations from the coastal waters near Dounreay, United Kingdom. The tests strengthened confidence in the model predictions, and enabled appropriate values of some of the model's main physical parameters to be set. Some features of the particle distributions simulated by SandTrack are consistent with field observations, and are not achievable with simpler sediment transport models. The model's run times are sufficiently short for simulations of particle movement in moderately large coastal areas over several decades to be practical

Settling velocity and mass settling flux of flocculated estuarine sediments

New formulations are presented for the settling velocity and mass settling flux (the product of settling velocity and sediment concentration) of flocculated estuarine mud. Physics-based formulae for these are developed based on assumptions of a two-class floc population (microflocs and Macroflocs) in quasi-equilibrium with the flow. The settling velocities of microflocs and Macroflocs are related to floc size and density via the Kolmogorov microscale as a function of turbulent shear-stress and sediment concentration, including height-dependence and floc-density-dependence. Coefficients in the formulae are calibrated against an existing large data-set of in situ observations of floc size and settling velocity from Northern European estuaries. Various measures of performance show that the resulting formulae achieve an improved level of agreement with data compared with other published prediction methods. The new formulae, with the original calibration coefficients, perform well in tests against independent measurements made in two estuaries

SARS-CoV-2-specific nasal IgA wanes 9 months after hospitalisation with COVID-19 and is not induced by subsequent vaccination

BACKGROUND: Most studies of immunity to SARS-CoV-2 focus on circulating antibody, giving limited insights into mucosal defences that prevent viral replication and onward transmission. We studied nasal and plasma antibody responses one year after hospitalisation for COVID-19, including a period when SARS-CoV-2 vaccination was introduced. METHODS: In this follow up study, plasma and nasosorption samples were prospectively collected from 446 adults hospitalised for COVID-19 between February 2020 and March 2021 via the ISARIC4C and PHOSP-COVID consortia. IgA and IgG responses to NP and S of ancestral SARS-CoV-2, Delta and Omicron (BA.1) variants were measured by electrochemiluminescence and compared with plasma neutralisation data. FINDINGS: Strong and consistent nasal anti-NP and anti-S IgA responses were demonstrated, which remained elevated for nine months (p < 0.0001). Nasal and plasma anti-S IgG remained elevated for at least 12 months (p < 0.0001) with plasma neutralising titres that were raised against all variants compared to controls (p < 0.0001). Of 323 with complete data, 307 were vaccinated between 6 and 12 months; coinciding with rises in nasal and plasma IgA and IgG anti-S titres for all SARS-CoV-2 variants, although the change in nasal IgA was minimal (1.46-fold change after 10 months, p = 0.011) and the median remained below the positive threshold determined by pre-pandemic controls. Samples 12 months after admission showed no association between nasal IgA and plasma IgG anti-S responses (R = 0.05, p = 0.18), indicating that nasal IgA responses are distinct from those in plasma and minimally boosted by vaccination. INTERPRETATION: The decline in nasal IgA responses 9 months after infection and minimal impact of subsequent vaccination may explain the lack of long-lasting nasal defence against reinfection and the limited effects of vaccination on transmission. These findings highlight the need to develop vaccines that enhance nasal immunity. FUNDING: This study has been supported by ISARIC4C and PHOSP-COVID consortia. ISARIC4C is supported by grants from the National Institute for Health and Care Research and the Medical Research Council. Liverpool Experimental Cancer Medicine Centre provided infrastructure support for this research. The PHOSP-COVD study is jointly funded by UK Research and Innovation and National Institute of Health and Care Research. The funders were not involved in the study design, interpretation of data or the writing of this manuscript

Large-scale phenotyping of patients with long COVID post-hospitalization reveals mechanistic subtypes of disease

One in ten severe acute respiratory syndrome coronavirus 2 infections result in prolonged symptoms termed long coronavirus disease (COVID), yet disease phenotypes and mechanisms are poorly understood1. Here we profiled 368 plasma proteins in 657 participants ≥3 months following hospitalization. Of these, 426 had at least one long COVID symptom and 233 had fully recovered. Elevated markers of myeloid inflammation and complement activation were associated with long COVID. IL-1R2, MATN2 and COLEC12 were associated with cardiorespiratory symptoms, fatigue and anxiety/depression; MATN2, CSF3 and C1QA were elevated in gastrointestinal symptoms and C1QA was elevated in cognitive impairment. Additional markers of alterations in nerve tissue repair (SPON-1 and NFASC) were elevated in those with cognitive impairment and SCG3, suggestive of brain–gut axis disturbance, was elevated in gastrointestinal symptoms. Severe acute respiratory syndrome coronavirus 2-specific immunoglobulin G (IgG) was persistently elevated in some individuals with long COVID, but virus was not detected in sputum. Analysis of inflammatory markers in nasal fluids showed no association with symptoms. Our study aimed to understand inflammatory processes that underlie long COVID and was not designed for biomarker discovery. Our findings suggest that specific inflammatory pathways related to tissue damage are implicated in subtypes of long COVID, which might be targeted in future therapeutic trials

Threshold of motion of bimodal sand sizes in the SandTrack model - A new hiding/exposure function

The report describes the development of a new hiding/exposure function for determining the threshold of motion of ‘tagged’ grains in the SandTrack particle tracking model. It applies to a bimodal (or more strictly binary) grain-size distribution in which the tagged grains are a different size to the underlying (uniform) indigenous sand bed. The new function was presented in a paper by Soulsby et al. (2011, Eq 16), but the derivation was not given there due to length restrictions. The method is deliberately kept simple, and is expressed as a function purely of the ratio of the diameters of the tagged grain and the indigenous bed grains. Comparisons are presented of the new formula and previous methods, and the formula is found to agree well with more elaborate models in the range of diameters modelled by Soulsby et al. (2011), as well as with published data. For tagged grains smaller than the indigenous grains, the behaviour of this binary case is different to the more commonly considered case of a continuously-graded sediment. A step by step guide to application of the method in models is given in the Conclusions. This report was referenced by Soulsby et al. (2011) as HR Wallingford Report TR190 (Soulsby, 2010). Due to a change in the internal system, the correct citation is: Soulsby, R.L. (2012). Threshold of motion of bimodal sand sizes in the SandTrack model: a new hiding/exposure function (Report TR190). Report DEK2138-RT001-R01-00, HR Wallingford

Dynamics of marine sands

Dynamics of marine sands' specifically deals with coastal and offshore sea areas, as well as rivers and estuaries, for sand and gravel sediments. The book presents a convenient and useable introduction to sediment processes in a form that is accessible to a wide readership. Contents: Introduction, including sections on a general procedure and errors and sensitivities; Properties of water and sand; Currents; Waves; Combined waves and currents; Threshold of motion; Bed features; Suspended sediment; Bedload transport; Total load transport; Morphodynamics and scour; Handling the wave-current climate; Case studies

Bedform migration in sandy estuaries - summary report

Sandwaves occur extensively in tidal estuaries and coastal regions frequently in conjunction with suspended sand transport. The two processes interact mutually, and should be considered together in prediction of their effect on engineering applications such as approach channel dredging, offshore navigation, pipeline stability, harbour and marina siltation, and cooling water intakes

The relative contributions of waves and tidal currents to marine sediment transport

In many tidal sea areas the long-term mean sediment transport is the resultant of a wide range of different combinations of save and tidal current conditions occurring during the course of a year, from calm conditions during neap tides to extreme events of major storms coupled with Spring tides. It is shown, using wave and current data from the North Sea, that the most important contributions to the long-term transport are made by fairly large but not too infrequent waves, combined with tidal currents lying between the mean neap and spring maxima. Weak currents and low waves make small contributions because, although they occur very frequently, their potential for sediment transport is small. Equally the most extreme events do not make large contributions because, although they have a large potential for sediment transport, they occur too infrequently. As the wave climate becomes effectively weaker, due for example to increasing the water depth, the important events shift to smaller save-heights and larger currents

Simplified calculation of wave orbital velocities

Many coastal problems require the calculation of wave-generated oscillatory (orbital) velocities at the sea-bed for applications such as sediment mobility, transport and suspension, bed protection measures, and forces on structures. This is most commonly performed by using linear wave theory to transform the wave height and period to the orbital velocity in a given water depth as described by e.g. Sleath (1984). Only nonbreaking waves are considered in this report. The use of linear wave theory to obtain orbital velocities is justified by the experimental work of Kirkgöz (1986), who found that linear theory gave reasonable agreement with observed orbital velocities under wave crests over his entire range of parameter settings, even at the transformation point of plunging breakers where higher-order theories might be expected to give significantly better results. The velocity under wave troughs was significantly smaller than the predicted linear-theory value. Depending on the complexity of the problem, either a regular (monochromatic) wave or irregular (spectral) waves may be considered. However, the expression for the orbital velocity amplitude cannot be written explicitly in terms of depth, wave height and period, so indirect methods must be used. This report extends earlier work by Soulsby and Smallman (1986) and Soulsby (1987) to give calculation methods which are simple enough to be written in a single cell of a spreadsheet, for ease of use in practical applications using spreadsheet methods. It is less accurate than some methods, but is adequate to give at least a reasonable estimate for many desk-study applications. Despite enormous increases in computer speed and power since 1986, it is still often a limitation when using fine grids, long-term simulations, multiple sensitivity tests, or stochastic simulations in present day studies. Efficiency of repeated computations is thus still a desirable goal, especially when wave orbital velocities need to be calculated at every grid point and every time-step of a numerical model. The simple methods may therefore sometimes be preferred to more accurate methods even in numerical models