Which of the following sets of three dimensional variables is typically used to analyze the initiation of motion of sediment transport?
Molecular diffusitivities (E, ah, v)…
Dispersion is…
There is always more bedload sediment transport than suspended sediment transport.
Diffusion- which of the following statement is/are true?
Molecular diffusivities (Em, ah, v) and turbulent diffusivities (Emt, hat, vt). What is correct?
The picture above shows a vertical slice of a stream in flow direction (V(u,0,0)) with an introduced substance completely mixes over the cross- sediment constant concentration over the flow depth as location x = Ly.
u(z) is the velocity profile and U the depth averaged velocity. At x = Ly + UDt..
Turbulent diffusion is…
Advection - Which of the following statements is/are true?
Turbulent diffusivities (Emt, hat, vt)…
The turbulence - resolved mathematical framework is well-posed, but the computational capacity is still insufficient to solve it for most practical applications. Indicate the engineering strategies to come to practical solutions.
Understanding of the systems behaviour is key, then computation can start. Strategies include:
physical scale models (model reproduction of prototype, relevant processes are mimicked)
reduced order equations (integration in time: turbulent fluctuations are modelled)
Which of the following processes are considered in the Streeter-Phelps model?
A depth-averaged 2-D model resolves transverse dispersion.
The initiation of motion of sediment transport (in a simplified system) depends on the following dominant variables.
The settling velocity of a certain density in water with a certain temperature can be estimated from the particles diameter.
What is the physical interpretation of the Shield number?
Which of the following is Fick’s law of diffusion?
What is the typical uncertainty/inaccuracy of sediment transport?
The transverse velocity distribution contributes more to mixing than the vertical one in shallow rivers.
Mixing and transport processes only occur in river flows.
The maximum concentration of oxygen that can be dissolved in the water…
Dispersion is a process that needs to be modelled in a Reynolds-averaged 3-D approach.
Briefly describe the difference in laminar and turbulent flow.
Laminar flow: Re<Re(cr) fluid travels smoothly or in regular paths
Turbulent: Re>Re(cr) flow undergoes irregular fluctuations and mixing
Describe briefly why the transport and mixing of sediment is imortant for the water quality.
Pollutants absorb on the sediments surface (small sediments have higher capacity to convey pollutants). Sediment transport processes shape the river corridor and landscape an thereby have an impact on the flood risk.
The picture below shows an oil spill. Name 4 relevant processes of the oil cloud regarding mixing and transport.
buoyancy
Mixing and transport of matter
Advection by currents
Reactions and transformations (long timescale)
The picture below shows the non-dimensional analytical solution for lateral spreading (y-direction) for infinite width B=12m (flow in x-direction). This is the solution for…
The picture below shows a forest fire. Name 4 processes of the smoke cloud regarding mixing and transport.
Mixing and transport of matter and temperature
Advection by buoyancy and wind
Turbulent diffusion
Reactions and transformations
For sediment transport, the following simplifications are used in the overwhelming majority of engineering applications.
A sufficiently high concentration of dissolved oxygen is a guarantee of good water quality.
Which of the following forces play a role in the suspense sediment transport?
We have considered the transport an mixing of physical quantities. Name at least three types of physical quantities that we have considered.
matter
Momentum
Heat (temperature)
The bedform’s of a river/flume depend on:
Passive and (re)active physical quantities - Which of the following statements is/are true?
Which of the following parameters are dominant in the theory of suspended sediment?
The longitudinal dispersion coefficient is at least one order of magnitude larger in cross-section-averaged 1-D models than in depth-averaged 2-D models.
The following equation shows the Reynold-averaged Navier-Stokes equation. In this form, is the equation exact or approximate?
If the bed shear stress is less than the critical bed shear stress, sediment begins to move. (There is bedload sediment)
You can use the same bedload transport rate formula for lowland rivers as for steep slope torrents.
Longitudinal dispersion is the combined effect of advection in flow direction and turbulent diffusion.
How do you evaluate whether a flow is laminar or turbulent?
Which of the following statements is/are true for determining the total sediment transport rate?
Reynolds-averaging …
Give three examples of processes that can be modelled as a first order reaction.
physical
Chemical
Biological
… processes remove or transform the substance at aerate proportional to the concentration e.g.: biochemical oxygen demand (BOD) in a sewage effluent or heat in cooling water discharged from a power plant,
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