Understanding the impacts of hydrograph transience on sediment transport

2020 ◽  
Author(s):  
Colin Phillips ◽  
Eric Lajeunesse ◽  
Kimberly Hill ◽  
Chris Paola
Keyword(s):  
Sediment Transport ◽  
Laboratory Experiments ◽  
Scale Up ◽  
Sediment Flux ◽  
Bed Load ◽  
Length Scale ◽  
Transport Capacity ◽  
Natural Systems ◽  
Intermittency Factor

<p>Sediment transport is an inherently challenging process to predict due to a variety of granular and hydrodynamic phenomena. These challenges are only enhanced in natural systems where the forcing of the hydrograph and the availability of sediment is decidedly unsteady. Here we show through several field and laboratory experiments comprised of sediment flux and tracer displacement under unsteady hydrographs that their dynamics can be understood through the application of an integrated forcing metric (impulse), where the impulse represents the integrated excess transport capacity of a flood or a sequence of floods. When viewed through this framework we show that the cumulative bed load flux and tracer displacement from the particle flight length scale up to multi annual timescales are linearly related with the impulse parameter despite highly unsteady forcing. By considering the integrated forcing and sediment flux the transience of the hydrograph can be recast into a simple linear relation with parallels to long term landscape evolution models, where the details of the hydrograph are approximated as a characteristic flood stress times an intermittency factor. Through the use of an impulse metric we gain new insights that are obscured when only considering the instantaneous fluxes.</p>

scholarly journals CALCULATION OF THE RATE OF NET ON-OFFSHORE SEDIMENT TRANSPORT ON THE BASIS OF FLUX CONCEPT

1984 ◽  
Vol 1 (19) ◽  
pp. 91 ◽  
Author(s):  
Ichiro Deguchi ◽  
Toru Sawaragi
Keyword(s):  
Sediment Transport ◽  
Water Depth ◽  
Sediment Concentration ◽  
Suspended Load ◽  
Spatial Variations ◽  
Sediment Flux ◽  
Bed Load ◽  
Two Dimensional ◽  
Dimensional Model ◽  
Two Dimensional Model

Time and spatial variations of sediment concentration of both bed load and suspended load in the process of two-dimensional beach deformation were investigated experimentally. At the same time, the relation between the velocities of water-particle and sediment migration was analyzed theoretically. By using those results,a net rate of on-offshore sediment_ transport in the process of two-dimensional model beach deformation qf was calculated on the basis of sediment flux. It is found that Qf coincides fairly well with .the net rate of on-offshore sediment transport calculated from the change of water depth.

Testing seismic noise caused by highly concentrated sediment flows in laboratory experiments

2020 ◽  
Author(s):  
Marco Piantini ◽  
Florent Gimbert ◽  
Alain Recking ◽  
Hervé Bellot
Keyword(s):  
Sediment Transport ◽  
Seismic Noise ◽  
Laboratory Experiments ◽  
River Flow ◽  
Mechanistic Model ◽  
Transport Processes ◽  
Sediment Flux ◽  
Extreme Floods ◽  
Starting Point ◽  
Grain Sorting

<p>Sediment transport processes and fluxes play a key role in fluvial geomorphology and hazard triggering. In particular, extreme floods characterized by highly concentrated flows set the pace of mountain landscape evolution, where the linkage between streams and sediment sources leads to strong solid inputs characterized by significant grain sorting processes. The main observation that river processes generate ground vibrations has led to the application of seismic methods for monitoring purposes, which provides an innovative system that overcomes traditional monitoring difficulties especially during floods. Mechanistic models have been proposed in the attempt to invert river flow properties such as sediment fluxes from seismic measurements. Although those models have recently been validated in the laboratory and in the field for low transport rates, it remains unknown whether they are applicable to extreme floods.</p><p>Here we carry a set of laboratory experiments in a steep (18% slope) channel in order to investigate the link between seismic noise and sediment transport under extreme flow conditions with highly concentrated sediment flows. The originality of this set-up is that instead of feeding the flume section directly as usually done, we feed with liquid and solid discharge a low slope storage zone connected to the upstream part of the steep channel. This allows us to produce sediment pulses of varying magnitude (up to the transport capacity) and granulometric composition, traveling downstream as a result of alternate phases of deposition and erosion occurring in the storage area. We measure flow stage, seismic noise, sediment flux and grain size distribution. We find that the previously proposed relationships between seismic power, sediment flux and grain diameter often do not hold in such sediment transport situations. We support that this is due to granular interactions occurring between grains of different sizes within the sediment mixture and leading to complex grain sorting processes. In particular, we observe that bigger grains do not directly impact the bed but rather roll over fines or smaller grains, such that observed seismic power is much lower than expected. These results constitute a starting point for the development of a new mechanistic model for seismic power generated by highly concentrated bedload sediment flows.</p>

Particle velocity and sediment transport at the limit of deposition in sewers

2013 ◽  
Vol 67 (5) ◽  
pp. 959-967 ◽  
Author(s):  
J. J. Ota ◽  
G. S. Perrusquía
Keyword(s):  
Shear Stress ◽  
Sediment Transport ◽  
Particle Velocity ◽  
Water Velocity ◽  
Angle Of Repose ◽  
Bed Load ◽  
Bed Shear Stress ◽  
Transport Capacity ◽  
Sediment Particle ◽  
Velocity Measurements

This paper focuses on the sediment particle while it is transported at the limit of deposition in storm sewers, i.e. as bed load at the limit of concentration that leads to sediment deposition. Although many empirical sediment transport equations are known in the literature, there is only limited knowledge concerning particle velocity. Sediment particle and sphere velocity measurements were carried out in two pipe channels and these results led to the development of a semi-theoretical equation for sediment transport at the limit of deposition in sewers. Even in the transport process without deposition, sediment movement is slower than water velocity and depends on the angle of repose of sediment with a diameter d on the roughness k of the pipe channel. Instead of classical dimensionless bed shear stress ψ, a modified dimensionless bed shear stress ψ (d/k)2/3 was suggested, based on the angle of repose and this parameter was proved to be significant for quantifying the transport capacity. The main purpose of this article is to emphasize the importance of careful observation of experiments. Not only number of tests, but physical understanding are essential for better empirical equations.

Unsteady flow sediment transport in a sewer model

1999 ◽  
Vol 39 (9) ◽  
pp. 121-128 ◽  
Author(s):  
R. De Sutter ◽  
M. Huygens ◽  
R. Verhoeven
Keyword(s):  
Sediment Transport ◽  
Laboratory Experiments ◽  
Friction Velocity ◽  
Time Lag ◽  
Circular Cross Section ◽  
Complex Nature ◽  
Bed Load ◽  
Fundamental Understanding ◽  
State Formula ◽  
Cohesive Material

To initiate a fundamental understanding of the complex nature of unsteady sediment transport phenomena, laboratory experiments for two types of non-cohesive material are presented. These experiments were performed in a test flume with semi-circular cross-section. Friction velocity for the transient regime is obtained using the equations of de Saint-Venant, which are rearranged using the kinematic flow principle. Inertia of bed load material and material in suspension causes a time and forme discrepancy between the unsteady friction velocity and transport. Hence the friction velocity obtained with a steady state formula is chosen as basic parameter to setup an instantaneous relationship with transport. A correction for the time lag is clearly a function of the unsteady character of the flow.

scholarly journals Effects of Wave Orbital Velocity Parameterization on Nearshore Sediment Transport and Decadal Morphodynamics

2019 ◽  
Vol 7 (6) ◽  
pp. 188 ◽  
Author(s):  
Boechat Albernaz ◽  
Ruessink ◽  
Jagers ◽  
Kleinhans
Keyword(s):  
Sediment Transport ◽  
Measured Data ◽  
Orbital Velocity ◽  
Long Term Effects ◽  
Natural Systems ◽  
Coastal Systems ◽  
Nearshore Sediment Transport ◽  
Wave Orbital Velocity ◽  
Morphological Modelling

Nearshore morphological modelling is challenging due to complex feedback betweenhydrodynamics, sediment transport and morphology bridging scales from seconds to years.Such modelling is, however, needed to assess long-term effects of changing climates on coastalenvironments, for example. Due to computational efficiency, the sediment transport driven bycurrents and waves often requires a parameterization of wave orbital velocities. A frequently usedparameterization of skewness-only was found to overfeed the coast unrealistically on a timescale ofyears—decades. To improve this, we implemented a recently developed parameterization accountingfor skewness and asymmetry in a morphodynamic model (Delft3D). The objective was to compare theeffects of parameterizations on long-term coastal morphodynamics. We performed simulations withdefault and calibrated sediment transport settings, for idealized coastlines, and compared the resultswith measured data from analogue natural systems. The skewness-asymmetry parameterization wasfound to predict overall stable coastlines within the measured envelope with wave-related calibrationfactors within a factor of 2. In contrast, the original parameterization required stronger calibration,which further affected the alongshore transport rates, and yet predicted erosion in deeper areas andunrealistic accretion near the shoreline. The skewness-asymmetry parameterization opens up thepossibility of more realistic long-term morphological modelling of complex coastal systems.

scholarly journals Grain shape effects in bed load sediment transport

2021 ◽  
Author(s):  
Eric Deal ◽  
Jeremy Venditti ◽  
Santiago Benavides ◽  
Ryan Bradley ◽  
Qiong Zhang ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Grain Shape ◽  
Sediment Flux ◽  
Bed Load ◽  
Flume Experiments ◽  
Natural Sediment ◽  
Shape Effects ◽  
Load Transport ◽  
Bed Load Transport ◽  
Load Sediment

Bed load sediment transport, in which wind or water flowing over a bed of sediment causes grains to roll or hop along the bed, is a critically important mechanism in contexts ranging from river restoration to planetary exploration. Despite its widespread occurrence, predictions of bed load sediment flux are notoriously imprecise. Many studies have focused on grain size variability as a source of uncertainty, but few have investigated the role of grain shape, even though shape has long been suspected to influence transport rates. Here we show that grain shape can modify bed load transport rates by an amount comparable to the scatter in many sediment transport data sets. We develop a theory that accounts for grain shape effects on fluid drag and granular friction and predicts that the onset and efficiency of bed load transport depend on the mean drag coefficient and bulk friction coefficient of the transported grains. Laboratory flume experiments using a variety of grain shapes confirm these predictions. We propose a shape-independent sediment transport law that collapses our experimental measurements onto a single trend, allowing for more accurate predictions of sediment transport and helping reconcile theory developed for spherical particle transport with the behavior of natural sediment grains.

From Start-Up to Scale-Up

2018 ◽  
Author(s):  
Gilles Duruflé ◽  
Thomas Hellmann ◽  
Karen Wilson
Keyword(s):  
United States ◽  
Conceptual Framework ◽  
Public Policies ◽  
Scale Up ◽  
The United States ◽  
Smart Money ◽  
Start Up ◽  
The Us ◽  
The Creation

This chapter examines the challenge for entrepreneurial companies of going beyond the start-up phase and growing into large successful companies. We examine the long-term financing of these so-called scale-up companies, focusing on the United States, Europe, and Canada. The chapter first provides a conceptual framework for understanding the challenges of financing scale-ups. It emphasizes the need for investors with deep pockets, for smart money, for investor networks, and for patient money. It then shows some data about the various aspects of financing scale-ups in the United States, Europe, and Canada, showing how Europe and Canada are lagging behind the US relatively more at the scale-up than the start-up stage. Finally, the chapter raises the question of long-term public policies for supporting the creation of a better scale-up environment.

scholarly journals Adopt, adapt, or abandon technology-supported person-centred care initiatives: healthcare providers’ beliefs matter

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Kari Dyb ◽  
Gro Rosvold Berntsen ◽  
Lisbeth Kvam
Keyword(s):  
Information Technologies ◽  
Scale Up ◽  
Healthcare Providers ◽  
Healthcare Services ◽  
Analytical Framework ◽  
Development Project ◽  
Technology Support ◽  
Care Needs ◽  
Term Care

Abstract Background Technology support and person-centred care are the new mantra for healthcare programmes in Western societies. While few argue with the overarching philosophy of person-centred care or the potential of information technologies, there is less agreement on how to make them a reality in everyday clinical practice. In this paper, we investigate how individual healthcare providers at four innovation arenas in Scandinavia experienced the implementation of technology-supported person-centred care for people with long-term care needs by using the new analytical framework nonadoption, abandonment, and challenges to the scale-up, spread, and sustainability (NASSS) of health and care technologies. We also discuss the usability and sensitivity of the NASSS framework for those seeking to plan, implement, and evaluate technology-supported healthcare programmes. This study is part of an interdisciplinary research and development project called Patients and Professionals in Partnership (2016–2020). It originates at one of ten work packages in this project. Method The main data consist of ethnographic field observations at the four innovation arenas and 29 interviews with involved healthcare providers. To ensure continuous updates and status on work in the four innovation arenas, we have also participated in a total of six annual network meetings arranged by the project. Results While the NASSS framework is very useful for identifying and communicating challenges with the adoption and spread of technology-supported person-centred care initiatives, we found it less sensitive towards capturing the dedication, enthusiasm, and passion for care transformation that we found among the healthcare providers in our study. When it comes to technology-supported person-centred care, the point of no return has passed for the involved healthcare providers. To them, it is already a definite part of the future of healthcare services. How to overcome barriers and obstacles is pragmatically approached. Conclusion Increased knowledge about healthcare providers and their visions as potential assets for care transformation might be critical for those seeking to plan, implement, and evaluate technology-supported healthcare programmes.

scholarly journals Relative Transportability for Non-uniform Bed Load Sediment Transport

2018 ◽  
Vol 153 ◽  
pp. 042006
Author(s):  
Li Zhijing ◽  
Li Dazhi ◽  
Liu Xiaobin ◽  
Jin Zhongwu ◽  
Chen Dasong
Keyword(s):  
Sediment Transport ◽  
Bed Load ◽  
Load Sediment
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