Helicoidal flow is the cork-screw-like flow of water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 in a meander

Meander

A meander in general is a bend in a sinuous watercourse. A meander is formed when the moving water in a stream erodes the outer banks and widens its valley. A stream of any volume may assume a meandering course, alternately eroding sediments from the outside of a bend and depositing them on the...

. It is one example of a secondary flow

Secondary flow

In fluid dynamics, a secondary flow is a relatively minor flow superimposed on the primary flow, where the primary flow usually matches very closely the flow pattern predicted using simple analytical techniques and assuming the fluid is inviscid...

.

Helicoidal flow is a contributing factor to the formation of slip-off slopes and river cliffs in a meandering section of the river. The helicoidal motion of the flow aids the processes of hydraulic action

Hydraulic action

Hydraulic action is strong enough to loosen sediment along the river bed and banks this will take rocks from the side of the banks and add it to the rivers loads. The water compresses the air in the crack, pushing it right to the back. As the wave retreats, the highly pressurized air is suddenly...

 and corrasion

Corrasion

Corrasion is a geographical term for the process of mechanical erosion of a rock surface caused when materials are transported across it by running water, glaciers, wind, waves or gravitational movement downslope, for example, the wearing away of fine particles of rock on a river or seabed by a...

 on the outside of the meander, and sweeps sediment across the floor of the meander towards the inside of the meander.

See also

• Laminar flow
  Laminar flow
  Laminar flow, sometimes known as streamline flow, occurs when a fluid flows in parallel layers, with no disruption between the layers. At low velocities the fluid tends to flow without lateral mixing, and adjacent layers slide past one another like playing cards. There are no cross currents...
  
  
• Turbulent flow
• Baer's law
  Baer's law
  In geology, Baer's law, named after Karl Ernst von Baer, says that, because of the rotation of the earth, in the Northern Hemisphere, erosion occurs mostly on the right banks of rivers and in the Southern Hemisphere on the left banks...
  
  
• Secondary flow in river bends