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River Processes

River Processes. A short introduction. Transportation. Erosion Processes. Corrasion. Attrition . Corrosion. Hydraulic action. Activity: Show the four processes of erosion in the boxes. Try to use graphical representation as it will help you remember.

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River Processes

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  1. River Processes A short introduction

  2. Transportation

  3. Erosion Processes Corrasion Attrition Corrosion Hydraulic action

  4. Activity: Show the four processes of erosion in the boxes. • Try to use graphical representation as it will help you remember. • Brief descriptions are also required. Activity: Use P.282 to complete this – then in pairs explain the processes to each other

  5. Attrition • When Boulders and other material, which are being transported along the bed of the river, collide and break up into smaller pieces. • This is more likely to occur when rivers are still flowing in highland areas

  6. Hydraulic Action • When the sheer force of the river dislodges particles from the river’s banks and bed.

  7. Corrasion/ Abrasion • When smaller material, carried in suspension, rubs against the banks and bed of the river. • This process is more likely in lowland areas by which time the material will have been broken up small enough to be carried by suspension. • River banks are warn away by a sand papering action

  8. Corrosion • Acids in the river also dissolve rocks, such as limestone, which form the banks and bed. This can occur at any point in the rivers course

  9. Deposition • Deposition occurs when a river lacks enough energy to carry its load. Deposition, beginning with the heaviest material first, can occur following a dry spell when the discharge and velocity of the river drop. • It also occurs where the current slows down the inside of a meander bend or where the river enters the sea .

  10. Velocity Vs Sediment

  11. What is the Wetted Perimeter? The yellow line shows the wetted perimeter Wetted perimeter: the part of the bed and banks which is in contact with the water in the channel – how do you think hydrologists measure this?

  12. 5 meters This river has a higher wetted perimeter in comparison to its volume, which increases friction and reduces Velocity (upper course) Rocks and boulders This river has a smaller wetted perimeter in comparison with its volume, because it has smooth banks, friction is reduced and this allows velocity to increase (middle/lower course) 50 meters http://www.youtube.com/watch?v=mgBqfcMK4jI

  13. Hydraulic radius (Rh): the ratio between the area of the cross-section of a stream and the length of its wetted perimeter • The higher the hydraulic radius, the faster the river flow (Velocity) and the more efficient the river is, because there is less contact between the water in the channel and the bed and banks, so lower friction. (cross sectional)

  14. Measuring discharge in Cumecs (m³/s ) • In order to calculate the discharge of a river in cumecs (cubic meters per second), you need to calculate the cross sectional area (m) (width x depth) and times this by the velocity (speed in meters a second) Width = 10 meters Depth = 1.5 meters Speed of flow (velocity) = 10 meters a second Discharge in cumecs= 15 x 10 = 150 cumecs 10 x 1.5 = 15 (cross sectional area)

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