As we know, the work carried out by a river is related to the energy available to it. Each river has a certain quantity of potential energy determined by the height of its source region and the volume of water entering the river system.
This energy is converted to kinetic energy as it moves through the system. The products both of fluvial erosion and weathering constitute the load of the river which are carried downstream along with the flow of running water. That is to say that river transports its load due to the kinetic energy associated with its flow.
The percentage of contribution to the total load made by the aforesaid classes vary widely with the nature of the river, the climate, the lithology of the river-bed etc. A river carries the greatest amount of materials during floods and spates.
1. Chemical-Transportation
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A considerable amount of mineral matter is tranported in a dissolved state i.e. in solution. The load in solution actually becomes a part of the liquid in the stream.
Limestone, dolomite and salts are very much soluble and some compounds of iron, manganese, phosphorous etc. are transported in the form of collidal solution.
2. Mechanical Transportation
This is influenced by three main factors as follows:
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(a) Velocity of the river-current;
(b) Nature of the river-current; and
(c) Density of rock materials to be transported.