Rivers, Floods and Management: Changing Channel Characteristics

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A Levels Geography (Physical Geography-AS) Mind Map on Rivers, Floods and Management: Changing Channel Characteristics, created by Andrew_Ellinas on 05/01/2014.
Andrew_Ellinas
Mind Map by Andrew_Ellinas, updated more than 1 year ago
Andrew_Ellinas
Created by Andrew_Ellinas almost 11 years ago
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Resource summary

Rivers, Floods and Management: Changing Channel Characteristics
  1. Downstream Changes to Velocity and Discharge
    1. Measurements suggest that both the velocity and discharge actually increase with the distance downstream.
      1. Because the river's gradient decreases with the distance downstream, the velocity might be expected to decrease too. However, the reduction in gradient is more than offset by an increase in the mass of water, as smaller tributaries join the main river.
        1. The 'roughness' of a river also decreases downstream. In a river's upper course, big boulders create a 'rough' channel. Further downstream, finer deposited sediments form smoother, less 'rough' lining to the riverbed and banks.
          1. Roughness creates turbulence and so slows down the flow of water.
            1. The channel further downstream also adopts more of a semi-circular shape, compared with the wide, shallow shape upstream.
              1. The semi-circular shape is much more efficient for transferring water because less energy is lost overcoming friction with the riverbed and banks.
                1. Hydraulic radius measures the efficiency of the channel. Hydraulic radius is calculated as the cross-sectional area divided by the wetted perimeter.
                  1. The higher the hydraulic radius, the more efficient the channel is in carrying water.
                  2. Downstream Changes to the River Channel
                    1. The volume of water carried by a river affects the size of its channel.
                      1. As more and more tributaries join the main channel, it has to carve an even larger channel itself to cope with the increasing volume.
                        1. While discharge is the primary factor affecting the size of a river channel, other actors can also affect it's shape or profile. For example:
                          1. A river might adopt a narrow, deep channel as it cuts through a resistant band of rock, or flows along a line of weakness - such as a fault or joint.
                            1. Human engineering can alter the shape of a channel - perhaps where it's lined with concrete, or has been dredged to deepen it.
                              1. Farm animals, like cattle, can trample riverbanks and alter the channel profile.
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