WATER ON THE LAND

Process of Transportation

Process of Transportation

Process of transportation

Rivers carry material downhill in a number of separate ways, depending on the size of the material and force of the water:

* Traction: the force of the water rolls rocks and pebbles along the surface of the riverbed.

* Saltation: rocks and pebbles are lifted up and ‘bounce’ along the riverbed.

* Suspension: small visible particles of clay, silt and sand are carried downstream without touching the riverbed. Their presence can be seen by the naked eye.

* Solution: tiny dissolved particles (calcium, sodium), too small to be visible to the naked eye, are carried along.

The river deposits material according to the material’s volume and the force of the water. This process is the opposite of erosion and is called ‘deposition‘. Generally speaking heavier material is deposited higher upriver and lighter material deposited lower down.

When we talk about the shape of a river we refer to its ‘long profile‘ and its ‘changing cross profile‘. If you imagine a three-dimensional model of a river, if we slice it in half from its source to the sea or lake, this would be a long profile; if we take a slice from one side to the other, this is a changing cross profile.

The amount of water in a river fluctuates due to natural and man-made factors, such as dams.

The rate at which rivers flow varies due to a number of factors, including the amount and type of rainfall, the type of rock across which water flows, and human activity such as irrigation.

When there is heavy rainfall over a short period, the volume of the river will usually increase. However, prolonged rainfall can also affect the size of the river. If the ground beside the river becomes saturated the river cannot sink into it and floods can occur.

Some types of rock are more porous than others. Some rocks like granite are impermeable – water cannot soak into the rock and flows across it. Limestone on the other hand is permeable – as the river passes over it some is absorbed into the rock, slowing down the flow of the river.

Ever since human beings began farming, we have found ways to control the flow and direction of rivers. We do this to water our crops, to provide water for our livestock, and to try to prevent damage from floods. We also use water as a source of power, for instance by building dams, which have a huge impact on the flow of a river.