River flows Flashcards
What 3 factors is river energy determined by?
- Mass of water
- Height of the river above sea level
- Gradient of the channel
What happens to a rivers energy when friction is present?
Friction with the bed and bank reduces energy.
What 3 factors is river velocity affected by?
- Channel slope
- The roughness of the channels bed (friction) - Manning’s N
- The cross section/channel shape (friction) - Hydraulic radius
What is river discharge?
The volume water flowing through a river channel, measured in cumecs.
How do you calculate river discharge?
D = Velocity x Mean width x Mean depth
What 3 things is river discharge dependent on?
- Precipitation
- Evapotranspiration
- Storage factors
What are the two main functions of a river?
- Transport water
- Transport sediment
What does the type of flow in a river depend on?
- Gradient
- Volume of water
- Channel shape
- Friction
What are the 3 flow types?
- Laminar
- Turbulent
- Helicoidal
What is laminar flow?
Where water flows smoothly in a straight channel
What is turbulent flow?
Occurs where the shape of the rivers channel is varied with pools, meanders, and rapids.
Why can a turbulent flow carry more sediment?
As it disturbs more sediment from the river banks and beds
What is helicoidal flow?
The cork-screw like flow of water in a meander.
What fluvial landforms does helicoidal flow contribute to the development of?
- Slip-off slopes
- River cliffs
- Riffles and pools
What is a thalweg?
(A line drawn to join the lowest points along the entire length of a stream bed, defining its deepest channel)
- This usually marks the line of fastest flow, as they are subject to the least friction.
