Transportation of sediment is an important and frequent phenomenon in rivers. Sediment is mobilized as bed-load with particles sliding, saltating, and rolling over the river bed, or as a suspended-load, where particles move with the turbulent water flow away from the bed.

Sediment Transport and Movable Bed s

http://www.catalytics.asia/wp-content/themes/catalytics/flood/Bates%20et%20al%202010%20new%20lisflood.pdf

A simple inertial formulation of the shallow water equations for efficient two-dimensional flood inundation modelling.

High resolution schemes for hyperbolic conservation laws

Thank you for downloading magnetic resonance imaging physical principles and sequence design. As you may know, people have look numerous times for their chosen books like this magnetic resonance imaging physical principles and sequence design, but end up in harmful downloads. Rather than enjoying a good book with a cup of coffee in the afternoon, instead they juggled with some malicious bugs inside their laptop.

Magnetic Resonance Imaging Physical Principles And Sequence Design

This paper reviews state-of-the-art empirical, hydrodynamic and simple conceptual models for determining flood inundation. It explores their advantages and limitations, highlights the most recent advances and discusses future directions. It addresses how uncertainty is analysed in this field with the various approaches and identifies opportunities for handling it better. The aim is to inform scientists new to the field, and help emergency response agencies, water resources managers, insurance companies and other decision makers keep up-to-date with the latest developments. Guidance is provided for selecting the most suitable method/model for solving practical flood related problems, taking into account the specific outputs required for the modelling purpose, the data available and computational demands. Multi-model, multi-discipline approaches are recommended in order to further advance this research field. This paper reviews state-of-the-art flood inundation models.It explores their advantages and limitations.It highlights the most recent advances and discusses future directions.It addresses how uncertainty is analysed and identifies opportunities for handling it better.

Flood inundation modelling

This paper describes benchmark testing of six two-dimensional (2D) hydraulic models (DIVAST, DIVASTTVD, TUFLOW, JFLOW, TRENT and LISFLOOD-FP) in terms of their ability to simulate surface flows in a densely urbanised area. The models are applied to a 1·0 km × 0·4 km urban catchment within the city of Glasgow, Scotland, UK, and are used to simulate a flood event that occurred at this site on 30 July 2002. An identical numerical grid describing the underlying topography is constructed for each model, using a combination of airborne laser altimetry (LiDAR) fused with digital map data, and used to run a benchmark simulation. Two numerical experiments were then conducted to test the response of each model to topographic error and uncertainty over friction parameterisation. While all the models tested produce plausible results, subtle differences between particular groups of codes give considerable insight into both the practice and science of urban hydraulic modelling. In particular, the results show that the terrain data available from modern LiDAR systems are sufficiently accurate and resolved for simulating urban flows, but such data need to be fused with digital map data of building topology and land use to gain maximum benefit from the information contained therein. When such terrain data are available, uncertainty in friction parameters becomes a more dominant factor than topographic error for typical problems. The simulations also show that flows in urban environments are characterised by numerous transitions to supercritical flow and numerical shocks. However, the effects of these are localised and they do not appear to affect overall wave propagation. In contrast, inertia terms are shown to be important in this particular case, but the specific characteristics of the test site may mean that this does not hold more generally.

/pdf/benchmarking-2d-hydraulic-models-for-urban-flooding-4epkxyg0fl.pdf

Benchmarking 2D hydraulic models for urban flooding

This paper presents one of the first dedicated studies on mobile bed hydraulics of dam-break flow and the induced sediment transport and morphological evolution. A theoretical model is built upon the conservative laws of shallow water hydrodynamics, and a high-resolution numerical solution of the hyperbolic system is achieved using the total-variation-diminishing version of the second-order weighted average flux method in conjunction with the HLLC approximate Riemann solver and SUPERBEE limiter. It is found that a heavily concentrated and eroding wavefront first develops and then depresses gradually as it propagates downstream. In the early stage of the dam-break, a hydraulic jump is formed around the dam site due to rapid bed erosion, which attenuates progressively as it propagates upstream and eventually disappears. While the backward wave appears to migrate at the same speed as over a fixed bed, the propagation of the forward wavefront shows a complex picture compared to its fixed-bed counterpart as a result of the domination of rapid bed erosion initially, the density difference between the wavefront and the downstream ambient water in the intermediate period, and the pattern of the deformed bed profile in the long term. It is also found that the free surface profiles and hydrographs are greatly modified by bed mobility, which has considerable implications for flood prediction. The computed wave structure in the intermediate period exhibits great resemblance to available experiments qualitatively, and yet the existence of a shear wave is found in lieu of a secondary rarefaction postulated in an existing analysis. Finally, the use of the complete, rather than simplified, conservation equations is shown to be essential for correct resolution of the wave and bed structures, which suggests that previous models need reformulating.

Computational Dam-Break Hydraulics over Erodible Sediment Bed

The turbulent structure of open-channel flow over a mobile gravel bed was investigated in an 8 m long, 0.3 m wide, and 0.3 m deep tilting flume. A flow visualization technique was used and complemented by measurements of flow velocity fluctuations near the bed. The experiments reveal that turbulent flow consists of a sequence of large-scale eddies with a vertical size close to the flow depth, an average length equal to four to five depths, and a width of about two depths. The downstream motion of these eddies causes quasiperiodic fluctuations of the local flow velocity components. The development of longitudinal troughs and ridges on the mobile bed and preferential transport of bed particles along troughs are related to the effect of the eddies. The experimental results indicate that the depth-scale eddies are an important turbulence mechanism contributing to sediment transport.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000WR900280

Macroturbulent structure of open-channel flow over gravel beds

An experimental study of the incipient motion of coarse uniform sediments was undertaken in an 8 m long by 0.3 m wide tilting flume. The concept of critical shear stress for the initial motion of streambeds has been linked to the probability of sediment entrainment through the intensity of sediment transport. The experiments have revealed that critical flow conditions for uniform sediment motion are dependent not only on the grain size but also on the ratio of flow depth to grain diameter. A revised Shields diagram relating critical stress, grain Reynolds number, and depth to grain size ratio has been derived. This has implications for the calculation of sediment transport rates, design of stable alluvial channels, and physical hydraulic modeling.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999WR900312

Flume study of the effect of relative depth on the incipient motion of coarse uniform sediments

The Shields diagram remains the most widely used criterion for incipient motion of sediment. However its implicit nature makes applications rather inconvenient. By deploying Guo’s logarithmic matching method twice, this technical note develops an explicit formulation of the Shields diagram, enabling the critical Shields parameter to be determined directly from fluid and sediment characteristics without resorting to any trial and error procedure or iteration. An extended application of the logarithmic matching method is demonstrated.

Gareth Pender

Papers

Benchmarking 2D hydraulic models for urban flooding

Computational Dam-Break Hydraulics over Erodible Sediment Bed

Macroturbulent structure of open-channel flow over gravel beds

Flume study of the effect of relative depth on the incipient motion of coarse uniform sediments

Explicit Formulation of the Shields Diagram for Incipient Motion of Sediment