river processes

Before looking at river landforms it is important to understand the more general role of rivers and to develop an awareness of the processes at work within rivers. It is through this knowledge that we will better undertand the processes at work in the geomorphology of the drainage basin. The role of rivers can be understood in very simple terms. The river's role is to balance its load and transport it to the ocean. But this this idea of rivers as merely transporting weathered material to the ocean is too simplistic. In reality the river changes in energy, discharge, velocity, channel charactersitics and load as it extends down its course. These changes show a recognisable pattern, that you may be familiar with from the Geography textbook. In reality however, there is a great deal more variation. The river is in constant interaction with its physical environment as well as climatic and human factors. This interaction leads to considerable variation in both the landforms and processes of rivers. These variations can be seen at both aspatial and temporal scale.

--------------------------------------------------------------------------------

Picture

It's well known that rivers increase in size as they transport water from their source in their headwaters to the mouth. The river channel becomes wider and deeper and as a result its cross-sectional area increases. We can also observe along the river's course an increase in both quantity of water and bedload. The nature of bedload also changes downstream. In the upper course of the river bedload is larger and more angular. As we track the river downstream bedload becomes much smaller and smoother. In the lower course bedload can only really be found in the form of fine sediments and muds, known as alluvium.

Some other changes in the river are measurable rather than observed. Two of these changes are an increase in discharge and and increase in velocity downstream. Remember that discharge is the quantity