River Long Profile & Cross Profiles
River characteristics
- All rivers have long and cross profiles
- Each river's long and cross profiles are unique but they do have common characteristics
- These profiles show changes in river characteristics from the source to the mouth
Long profile
- The long profile of a river shows the changes in the river gradient from the source to the mouth
- Most long profiles have a concave shape with similar characteristics:
- The source is usually in an upland area
- The upper course of the river includes areas which are steep with uneven surfaces where the river is eroding vertically
- In the middle course the gradient decreases and most of the erosion is lateral
- In the lower section the gradient decreases further until it becomes almost flat
Diagram of a typical long profile
Cross profiles
- The cross profiles of a river are cross-sections from one bank to another
- Cross profiles of the upper, middle and lower courses show the changes in the river channel
- Upper course characteristics include:
- Shallow
- Steep valley sides
- Narrow
- Low velocity
- Large bedload
- Rough channel bed
- High levels of friction
- Vertical erosion
- Middle course characteristics:
- Deeper than upper course channel
- Gentle valley sides
- Wider than upper course channel
- Greater velocity than upper course channel
- Material in river decreases in size
- Smoother channel bed
- Lower levels of friction than upper course channel
- Lateral erosion
- Lower course characteristics:
- Deeper than middle course channel
- Flat floodplains
- Wider than middle course channel
- Greater velocity than the middle course channel (apart from as the river enters the mouth)
- Material carried mainly sediment and alluvium
- Smooth channel bed
- Lowest friction
- Deposition is dominant
Worked example
Study Figure 1, a diagram showing the long and cross profiles of a typical river and its valley.
Describe how the cross profile changes downstream.
(2 marks)
- Answer can be two separate points or one developed idea
- No marks for changes in the river or channel
Answer:
- Valley slopes decrease in angle (1)
- The valley widens/broadens (1)
- Valley sides decrease in height (1)
- The valley floor becomes wider (1)
- The valley widens (1), a narrow floodplain develops (d) (1), eventually becoming a wide floodplain with levees/embankments (d) (1)
- Near the source the valley is steep-sided but by the middle stage the valley floor is wider (1) with gentler sides/bluffs (d)(1)
Exam Tip
Remember valley shape and river shape are not the same thing. If you are asked to describe valley shape you should focus on the gradient and shape of the land either side of the river channel.