River processes: Basic Concepts

• Rivers are perhaps the most important denudation agent.
• They carve channels, form valleys,transport and deposit regolith  over great distances and other material to form other types of landforms.

Terms used in describing a river channel.

River channel. Image credit Usgs.gov

• A channel is an area that contains flowing water confined by banks.
• Channel width is the distance in meters across the surface of a river, it is the distance between the two banks i.e. the distance from bank to the other.
• Depth is the distance in meters of the level of water down to the river bed. This is the vertical distance from the surface to the bed.
• Gradient/Slope is the angle between the horizon and the river’s surface.
• Velocity is the speed at which the water flows through the channel. Speed is low at the sides near the banks and at the river bed due to friction and highest at the center.
• The source is where the river begins.
• The mouth is where a river empties/ends usually into a lake, sea or ocean.

Flow of water in streams

• Rivers always flow downstream because of the pull of gravity.
• A river’s erosion, transport and deposition depends on the flow of water in its channel.
• This flow is determined by several factors viz:
• The energy which is provided by gravity and is affected directly by they gradient of the river’s bed the steeper the slope the more energy a river has.
• Volume is the amount of water in a river’s channel. Volume increases during the wet seasons when most of the precipitation occurs or if a river’s course passes through a region experiencing wet climatic conditions
• Conversely a river’s volume falls during dry seasons such as winter and spring in Zimbabwe or if it passes through arid conditions/regions experiencing dry conditions.
• The nature of flow also affects and channel shape also affect a river’s energy.

To access more topics go to the Geography Notes page.