A.1.2: River discharge

Question 1

Soil porosity

Answer 1

The amount of pores between soil particles

Some soils are more porous, e.g. sand infiltrate quicker than clay soils

Question 2

Saturated soil prevents infiltration because…

Answer 2

it is at maximum infiltration capacity therefore increases surface run off

Question 3

Arid and dry soils reduce infiltration because…

Answer 3

the baked soil cant hold much moisture and so reaches infiltration capacity quickly before turning into surface run off

Question 4

Antecedent moisture soil

Answer 4

pre existing levels of soil moisture

Question 5

Overland Flow

Answer 5

• If infiltration capacity is greater than the rainfall intensity then the stores will fill before overland flow can happen
• Related to vegetation slowing down the infiltration and therefore overland flow is less likely

Rock type – permeable = greater overland flow

Question 6

Climates

Answer 6

• In arid regions, such as the Sahel (thesub-Saharan region in Africa), the climate has a wet and dry season.
• During the dry season, surface storage dries up.
• During the wet season, there can be localised flooding.

Question 7

Hortonian flow diagram

Answer 7

The soil is not saturated, but the water can infiltrate (either because it is impermeable or the rainfall is too intense). It therefore flows over the surface as overland flow

Question 8

Saturated overland flow diagram

Answer 8

The soil is full up of water (saturated) so can not take any more so water flows over the surface as overland flow

Question 9

Hortonian Flow

Answer 9

• Flow of subsurface water
• Rainfall is TOO intense to precipitation exceeds the infiltration capacity of the soil
• Different to precipitation intensity and duration saturate the soil and brings the water table to the surface.- this is saturation overland flow.
• In semi-arid/arid enviornments

Question 10

Bradshaw model of variations

Answer 10

• Shows the expected river characteristics, upstream and downstream.
• Does not account for human interference and other factors that may interfere it.

Question 11

Discharge formula

Answer 11

Cross sectional area * Mean velocity

Question 12

Hydraulic radius

Answer 12

• The efficiency of a river channel = a measure of the ability of a river channel to move water and sediment.
  • It depends on the friction the water comes up against which is shown by thehydraulic radius of the river
  • This is the proportion of water in a channel that is in contact with the beds and banks

Question 13

Hydraulic radius formula

Answer 13

Hydraulic radius = Cross sectional area ÷ Wetted perimeter

Question 14

Manning’s formula

Answer 14

• Velocity = Hydraulic radius * Gradient ÷ roughness (n)
• The higher the value of n, the rougher the bed.

Question 15

Laminar Flow

Answer 15

• Water flows in sheets (laminae) parallel to the channel bed
• It requires a smooth, straight river channel with a low velocity.
• Rarely occurs

Question 16

Turbulent Flow

Answer 16

• Water flows in irregular patterns
• This occurs when a river has a complex channel morphology and a high velocity
• Bed roughness also creates turbulence

Question 17

Helicoidal Flow

Answer 17

• Water flows in a corkscrew motion (not down the centre)
• This is due to alternating pools (deeper parts) and riffles (shallow parts
• This flow forms meanders

Question 18

River discharge

Answer 18

The rate of the volume of water passing a point per unit of time