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Hyperconcentrated flow in nature and in practical application
Published in Zhaohui Wan, Zhaoyin Wang, Hyperconcentrated Flow, 2020
Density current occurs along a sloping ocean bottom provided liquid adjacent to the bottom contains suspended sediment that causes the average density of the mixture to be greater than the density of the surrounding clear water. Such flow is called turbidity current by geologists. Turbidity current may be initiated by a turbid river entering the sea, by wave action, or by earthquake-induced mud slump. Earthquake-induced mud slump may be of large-scale and develops into a huge turbidity current at extremely high concentrations. It is also a kind of hyperconcentrated flow.
Process-based approach on tidal inlet evolution – Part 1
Published in C. Marjolein Dohmen-Janssen, Suzanne J.M.H. Hulscher, River, Coastal and Estuarine Morphodynamics: RCEM 2007, 2019
D.M.P.K. Dissanayake, J.A. Roelvink
Patterns of parallel submarine gullies with regular transverse spacing have been found at continental margins for recent few decades. These gullies are thought to be formed by turbidity currents. Turbidity currents are density currents, which contains appreciable quantity of suspended sediment. The suspended sediment concentration increases by the entrainment of sediment into the flowing water, and decreases by the deposition of sediment onto the ocean floor. If the amount of suspended sediment carried by turbidity currents is continuously increased, the flow is persistently accelerated in the downslope direction, and travels an unexpectedly long distance. When the entrainment dominates the deposition, the ocean floor is subject to erosion, resulting in the formation of gullies. The formation of submarine canyons is initiated by gullies formed at the downstream end of continental shelves due to erosion induced by turbidity currents.
Geohazards
Published in White David, Cassidy Mark, Offshore Geotechnical Engineering, 2017
Slope failures initiate movement of material down-slope in the form of run-out, or mass gravity flows. Material involved in a slide originates as a solid material and gradually transforms towards a fluid state as it remoulds and softens during down-slope transport entraining additional water. Mass gravity flows following a submarine slope failure are generally described as debris flows and turbidity currents. The terminology of these phenomena is not standardised; Niedoroda et al. (2003) suggest the following distinctions. Debris flows are mass movements in which the source sediment travels downslope, coming to rest after the initially stored potential energy is dissipated by friction. During debris flows, the source sediment is remoulded and reconstituted, and the degree to which this occurs, including the amount of water entrained, determines the rheological and flow properties. The soil mass travels as a visco-plastic material with distinct stress–strain rate characteristics and flow is generally laminar. Turbidity currents are sediment rich heavy liquid flows that proceed from debris flows. Suspended sediment provides the density contrast with the ambient water in a turbulent current resulting in a gravitational energy that drives the flows. As turbidity currents travel downslope, they may pick up more sediment, becoming denser and accelerating, resulting in flow that is primarily turbulent. The density of a turbidity current is typically 2–4 per cent greater than the ambient water and speeds range from less than 1 m/s to more than 10 m/s.
Effect of an obstacle on the depositional behaviour of turbidity currents
Published in Journal of Hydraulic Research, 2019
Ahmadreza Farizan, Sina Yaghoubi, Bahar Firoozabadi, Hossein Afshin
Density currents are generated due to the density difference between two fluids. These currents are also called gravity currents because the gravitational force drives the flow. Many gravity currents are formed in nature. Sea-breeze fronts, thunderstorm outflows, snow avalanches, pyroclastic flows and turbidity currents are examples of natural gravity currents (Simpson, 1982). Furthermore, these currents may arise from various man-made disasters such as the propagation of oil impurities in deep waters and accidental emissions of hazardous substances at chemical plants (Ermanyuk & Gavrilov, 2005a). Turbidity currents are density flows in which the density difference is due to the suspended sediments. Particle concentrations are often low in turbidity currents so that the fluid turbulence (rather than the particle–particle interaction) holds the particles in suspension (Meiburg & Kneller, 2010; Middleton, 1993). These currents are much more complicated than other gravity currents because the particle concentration changes with time and position along the flow (Bonnecaze, Huppert, & Lister, 1993), and therefore affects the structure and dynamics of the current. Turbidity currents can travel along the bed at high velocities (De Cesare, Schleiss, & Hermann, 2001) and consequently they are responsible for damage to submarine cables and seafloor equipment, erosion of underwater canyons and formation of tsunamis (Meiburg & Kneller, 2010; Simpson, 1982). In addition, deposits of turbidity currents may be hydrocarbon-rich and thus they can form good hydrocarbon reservoirs over long times (Mulder & Alexander, 2001). Therefore, accurate prediction of changes in deposit thickness is highly important.
Sedimentology in metamorphic rocks, the Willyama Supergroup, Broken Hill, Australia
Published in Australian Journal of Earth Sciences, 2018
B. P. J. Stevens, G. M. Bradley
The classic turbidite model is now being modified and/or overturned by abundant new data from offshore petroleum exploration cores of submarine fan systems, and oceanographic measurement of deep-sea bottom currents (water depths 46–4200 m) (Shanmugam, 2000, 2002, 2003, 2012). In the classic turbidite paradigm, sequences typically exhibit graded bedding, load casts, flute and groove casts, and flame structures. It was thought that these sediments were carried into deep water by turbidity currents, where the ‘turbidites’ were less likely to be reworked by other currents, and such ‘turbidites’ are a well-documented component of deep-water submarine fans.
Image thresholding process for combining photometry with intrusive flow instruments
Published in Journal of Hydraulic Research, 2018
Richard I. Wilson, Heide Friedrich, Craig Stevens
Sediment-laden underflows are a dynamic fluid process, which occur in riverine, limnic, marine and atmospheric environments. Often referred to as turbidity currents, they are caused by the difference in density between an ambient fluid and an introduced fluid, laden with suspended sediment. This ultimately causes a propagating flow. In a marine setting, turbidity currents pose a significant risk to submarine cables where they are known to have caused breakage following earthquakes and flood events (Carter, Milliman, Talling, Gavey, & Wynn, 2012; Cattaneo et al., 2012; Heezen & Ewing, 1952; Hsu et al., 2008).