Channel Processes

Question 1

Hydraulicking

Answer 1

Removal of sediments from alluvial channels by force of water alone

• Loose particles subject to drag and lift force by water
• Water accelerates over protruding grains
• As flow velocity increases, forces tending to move particles are exactly balanced by friction (critical erosion velocity) - then after that, increasing velocity causes movement of the particle.

Question 2

Attrition

Answer 2

Particle sizes are reduced as they strike one another such that they become easier to transport

Question 3

Abrasion

Answer 3

Coarse bedloads are dragged along the river bed (so, we can tell this is more prominent in the upland rivers).

It wears away the solid rock bed of the channel, having a grinding effect on beds and banks so it smooths out the river bed

Question 4

Potholing (subset of abrasion)

Answer 4

Pebbles are whirled around in turbulent flow to etch out cylindrical depressions - this process is responsible for much of the downcutting

Question 5

Infiltration excess flow

Answer 5

Occurs when rainfall intensity exceeds instantaneous infiltration capacity of the unsaturated soil
Happens in areas where the ground is highly impermeable (eg urbanised areas, crusty soils of arid regions)
Infiltration happens at the capacity rate, excess water accumulates at the ground surface

Question 6

Saturation overland flow

Answer 6

Occurs when infiltration capacity of the soil exceeds rainfall intensity
Infiltration is occurring at the capacity rate, such that water is unable to infiltrate anymore into the saturated soil
Seen both on the slope surface and at its base, when throughflow occurring below the surface is forced outwards due to the rise in the water table from prolonged precipitation or continued input from throughflows
As precipitation events drag on, more parts of the slope undergo SOF

Question 7

Concentrated overland flow

Answer 7

Occurs in rills and gullies, on steep unvegetated slopes

Stones and crusts concentrate flow into these linear depressions

Question 8

Infiltration

Answer 8

Process by which water is drawn into the upper surface layers of the soil by gravity and capillary action

Question 9

Percolation

Answer 9

Movement of water downward under the influence of gravity and usually continues downward to the groundwater zone
Controlled by rock permeability, as well as gravity and pressure differences - water percolates from where is high to where water table is low