The volume of the river is affected by numerous factors. These factors are the size of the drainage basin, vegetation cover, Climate and permeability of rock.
A large drainage basin would have a higher volume of water as it has a greater number of tributaries. Tributaries help to increase the volume of water in the river.
A drainage basin with vegetation cover would be able to intercept rain and allow it to infiltrate into the ground. Therefore, there would be less surface runoff. A drainage basin with little or no vegetation would not be able to intercept rain and little rain would be infiltrated into the ground. Hence, there would be more surface runoff. The surface runoff would flow directly into the river thus increasing its volume.
There are two climatic factors that can affect the volume of the river. They are the amount of precipitation and temperature. The higher the amount of precipitation, the higher is the volume of the river. In the dry seasons, some rivers may even dry up. When monsoon or cyclones rain strike, the river would be filled with water and its volume increase.
Temperature affect the volume of the river as on a hot day, the rate of evaporation would be higher and more water would be evaporated from the river. On the other hand, in spring when snow on the mountain melts and water flows into the river, the volume of the river may increase and even flood the surrounding area.
The permeability of the rock refers to the ability to allow water to flow through it. A permeable rock would allow water to flow through it. When water flow over an area of permeable rock, the water would flow into the ground and there would be less surface runoff. The river would thus have a lower volume. Examples of permeable rock are sandstone and limestone. Impermeable rocks would result in a large surface runoff. Example of an impermeable rock is granite.