River Characteristics (Cambridge International IGCSE Geography)

Specification checklist

This content page covers the following sections of the specification:

• 1.1.1- Characteristics of rivers: the long profile, width, depth, speed of flow/velocity, discharge, wetted perimeter and channel

• 1.1.2- The Bradshaw model.

• 1.1.5 - Processes which operate within a river:

  • erosion; hydraulic action, abrasion, attrition
  • solution, transportation; traction, suspension, saltation, solution
  • deposition.

Characteristics of river profiles

Spec point — Characteristics of rivers: the long profile, width, depth, speed of flow/velocity, discharge, wetted perimeter,

River characteristics

• All rivers have long and cross-profiles
• Each river's long and cross profiles are unique, but they do have some characteristics in common
• 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 steep areas with uneven surfaces
  • In the middle course, the gradient decreases
  • In the lower section, the gradient decreases further until it becomes almost flat

River 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 tend to include:

  • shallow
  • steep valley sides
  • narrow
  • low velocity
  • large bedload
  • rough channel bed
  • high levels of friction
  • vertical erosion

Cross-section of the upper river course

• Middle course characteristics tend to be

  • 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

Cross-section of the middle river course

• Lower course characteristics tend to be

  • 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

Cross-section of the lower river course

Exam Hint Remember, valley shape and river shape are not the same thing. If you are asked to describe a valley shape, you should focus on the gradient and shape of the land on either side of the river channel.

The Bradshaw Model

Spec point — The Bradshaw model

• As a result of erosion, transportation and deposition, the character of a river changes as it moves downstream as shown in the cross-profiles
• These changes are summarised in the Bradshaw model

The Bradshaw Model

• Bradshaw's model shows that the following characteristics increase with distance downstream (away from the source):

  • discharge
  • width
  • depth
  • velocity
  • load quantity

• Other characteristics decrease:

  • load size
  • bed roughness
  • gradient (slope angle)

Wetted perimeter and hydraulic radius

• The wetted perimeter is the length of the cross-sectional area where the water is in contact with the banks and bed

• The efficiency of the river is measured using hydraulic radius (cross-sectional area divided by wetted perimeter)

• The higher the ratio, the greater the efficiency and the less the friction

  • This increases the amount of erosion, which means the channel becomes wider and deeper

River processes

Spec point — "Processes which operate within a river: • erosion; hydraulic action, abrasion, attrition, solution • transportation; traction, suspension, saltation, solution • deposition"

River processes

Erosion

• Erosion is the wearing down of surfaces

• There are four erosion processes that change the shape of the river channel:

  • Hydraulic action

    • The force of the water, which removes material from the bed and banks of the river

  • Abrasion

    • When the materials carried by the river scrape away the banks and bed

  • Attrition

    • When the material being carried by the river hits each other, the pieces become rounder and smaller

  • Corrosion (solution)

    • When rocks are dissolved in slightly acidic water

Types of erosion

• Erosion can be mainly vertical or lateral:

  • Vertical erosion is dominant in the upper course of rivers. It increases the depth of the river and valley as the river erodes downwards
  • Lateral erosion is dominant in the middle and lower courses of rivers. It increases the width of the river and valley as it erodes sideways

Transportation

• There are four processes of transportation:

  • Traction

    • Occurs when larger rocks and materials are rolled along the riverbed

  • Saltation

    • Smaller material, which can be lifted by the water, bounces along the riverbed

  • Suspension

    • Lighter material carried within the river flow

  • Solution

    • When materials are dissolved in the river water

Types of transportation

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Exam Hint It can sometimes help to remember a word and the process it refers to if you know what it means.

Traction: the action of pulling something over a surface.

Saltation: leaping or jumping.

Deposition

• When a river does not have enough energy to carry materials, it drops them

  • This is deposition

• The causes of reduced energy include

  • Reduced discharge due to a lack of precipitation or abstraction upstream
  • Decreased gradient
  • Slower flow on the inside of a river bend or where the river is shallower
  • When the river enters a sea, ocean or lake

• The heaviest material is deposited first; this is known as the bedload

• The lighter materials, gravel, sand and silt, are known as alluvium and they are carried further downstream

• The dissolved materials are carried out to sea