Turbidity Currents (White Paper)

Turbidity currents are density currents that are generated due to the density difference of suspended sediments and water in a mixture.

In turbidity currents, suspended sediment makes the density of the mixture greater than the density of the ambient water and provides the driving force; the sediment-laden flow must generate enough turbulence to hold the sediment in suspension. They can be observed in the flows entering large bodies of water containing a high concentration of suspended sediments. These are sediment-laden gravity currents that exchange sediment with the bed by erosion or deposition as the flow travels over the downslope. Turbidity currents derive this driving force from the sediment in suspension. They experience a resisting shear force on the bed and entrain water from above. Two types of turbidity currents can be distinguished: Low velocity, low density and high velocity, high density. High velocity, high-density turbidity currents often carry suspended materials introduced near the shore to the deep sea.

Turbidity currents can be originated by various processes. Discharges of large amounts of sediments, e.g., mine tailings, underwater landslides caused by earthquakes, and re-suspension of suspended materials by waves during storms are three possibilities. Turbidity currents can be eroding or depositing, accelerating or
decelerating, depending on the combination of initial conditions, bed slope, and size of sediment particles. A turbidity current with deposition and erosion is a flow in three components: clear ambient water, turbid water and sediment (bed material). The turbidity current entrains clear water into the flow and simultaneously either deposit suspended sediment on the channel bed, or entrains bed material into the flow. Actually turbidity current entrains and deposits at the same time, but there is a net flux either to the bed (depositing current) or from the bed (entraining current). Turbidity currents are self-generated currents. The flow will vanish when all suspended materials are deposited on the bottom, and grow when sediments are entrained from the bed.

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Taxonomy

• Water
• Treatment
• Technology
• Turbine