How a river transport

The materials which the river transports or carries along with it are collectively called its load. This load is made up of materials eroded by the river itself from its channel and weathered rock debris and vegetable matter brought down from the hillsides to the river channel by mass movement or surface rainwash.

Load is either transported by suspension, solution, traction & saltation. For sediment to move resisting forces have to be overcome, competent velocity has to be achieved, and critical tractive force must be achieved.

Since this load is of various sizes and chemical compositions, the river carries it along in various ways as it finds convenient, in the way indicated below.

Source

• The river drags or rolls heavier materials like coarse sand, gravel, boulders and logs along its bed as traction or bed load in a process called traction. The load moves intermittently and at a speed less than that of the river itself.'

• Finer particles, about 2mm in diameter bounce up and down as they move along with the river in a hop-step-and-jump manner called saltation. This load is therefore called saltation load.

• In a flowing river, fine particles, like silt and clay, are carried in suspension as suspension load, particularly when the river is in flood. Most tropical rivers carry a lot of deeply weathered materials in suspension and that is why they look murky during flood. The greater the turbulence and velocity of the river, the larger the quantity and size of particles which can be picked up.

• Finally, the chemically eroded materials are carried by the river in solution as dissolved load. Except in karst regions, the material in solution forms only a relatively small proportion of total load.

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