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GEOG 322 > 5. Soil water & groundwater > Flashcards

5. Soil water & groundwater Flashcards

1
Q

Soil horizon

A

Layer typically parallel to the soil surface with physical characteristics that are different from those of the layers above and below

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2
Q

What is the soil profile made up of?

A

Sequences of soil horizons

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3
Q

What are soil horizons delimited by? (5)

A
  • color
  • texture
  • organic matter
  • degree deposition (illuviation)
  • removal (eluviation) of material by physical and chemical processes
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4
Q

What is the development of soil profiles dependent on? (5)

A
  • climate
  • topography
  • disturbances (erosion, deposition)
  • parent material
  • time elapsed since weathering
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5
Q

Five hydrologic soil horizons in the shallow subsurface

A
  1. Root zone
  2. Intermediate zone
  3. Capillary fringe (tension-saturated zone)
  4. Ground water
  5. Impermeable layer
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6
Q

Which zones are unsaturated?

A

The intermediate zone, and the capillary fringe

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7
Q

Which zones are saturated?

A

Ground water

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8
Q

What is the capillary layer?

A
  • a sub zone
  • just above the water table
  • it is a belt of variable thickness
  • water is drawn by capillary action
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9
Q

What happens after infiltration? (2)

A
  1. Water is stored in shallow soil layers
  2. Water is redistributed:
    → vertically: after infiltration, water percolates downward until the saturated zone
    → laterally: governed by principles of unsaturated flow or groundwater flow
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10
Q

Infiltration

A

movement of water from the soil surface downward

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11
Q

Percolation

A

downward movement of water in the unsaturated zone

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12
Q

Recharge

A

addition of water to the saturated zone (groundwater recharge)

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13
Q

Capillary rise

A

movement of water from the saturate zone upwards into the unsaturated zone

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14
Q

Interflow or subsurface flow

A

flow occurring in the unsaturated zone in the lateral direction

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15
Q

Groundwater flow

A

flow occurring in the saturated zone

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16
Q

soil def

A
  • a mixture of mineral grains, air, water, and organic matter
  • it is porous
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17
Q

Size classification of sand clay and silt (smallest to largest)

A

clay < silt < sand

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18
Q

Total porosity (n)

A

n = V voids / V total
where
- V voids = V water + V gas
- V total = V voids + V solid

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19
Q

Void ratio (e)

A

e = V voids / V solids
where
- V voids = V water + V gas

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20
Q

Volumetric soil moisture content (θ)

A

θ = V water / V total

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21
Q

Gravimetric soil moisture (G)

A

G = ( M wet soil - M dry soil ) / M dry soil

22
Q

Volumetric soil moisture content (θ)

A

θ = V water / V total
or
G = ρb / ρw * G
where ρ is bulk density of soil and water density

23
Q

Degree of saturation (S)

A

S = V water / ( V water + V gas )

24
Q

What does soil porosity (n) determine?

A

Soil porosity determines how much is available in the soil for water to be retained/stored

25
Q

3 different types of soil water

A
  • gravitational water
  • capillary water
  • hygroscopic water
26
Q

Gravitational water

A

Excess water that drains under the influence of gravity at saturation

27
Q

Capillary water

A

Water that is held in soil pores in intermediate to wet conditions

28
Q

Hygroscopic water

A

Thin films of water that hold onto soil grains in dry conditions

29
Q

Field capacity (FC)

A

Maximum amount of water that a soil can hold after gravitational drainage

30
Q

When does subsurface flow occur?

A

Usually when soil moisture content (θ) exceeds field capacity (FC)

31
Q

Permanent wilting point (WPW)

A

Minimum soil moisture content produced after gravity drainage and plant evapotranspiration

32
Q

Characteristics of permanent wilting point (WPW)

A
  • always lower than FC
  • corresponds to water content at which plants can no longer extract water from the soil
33
Q

Plant available water (PAW)

A

The difference between field capacity (FC) and the permanent wilting point (WPW)
→ PAW = FC - WPW

34
Q

Soil moisture (θ) in the root zone (as compared to θ PWP, θ FC and n)

A

θ PWP < θ < n

35
Q

Soil moisture (θ) in the intermediate zone (as compared to θ PWP, θ FC and n)

A

θ FC < θ < n

36
Q

Soil moisture (θ) in the capillary fringe (as compared to θ PWP, θ FC and n)

A

θ = n

37
Q

Soil moisture (θ) in ground water (as compared to θ PWP, θ FC and n)

A

θ = n

38
Q

How does water move in soils?

A

From higher pressure to lower pressure

39
Q

What is the soil water pressure (P) at the water table?

A

P=0

40
Q

Is the soil water pressure (P) positive or negative in saturated soils? (below the water table)

A

Soil water pressure is positive

41
Q

Is the soil water pressure (P) positive or negative in unsaturated soils? (above the water table)

A

Soil water pressure is negative

42
Q

What are other terms to call negative water pressure? (2)

A

Tension or suction

43
Q

What is hydraulic conductivity?

A

Hydraulic conductivity (K) describes the ease with which water can move through pore spaces or fractures in soil

44
Q

What has larger hydraulic conductivity K values? Sand or clay?

A

Sand has larger hydraulic conductivity values

45
Q

What is infiltration?

A

Infiltration is the flow of water into the ground through the earth surface

46
Q

What are the two ways in which we can “see” infiltration?

A

As a rate or a total. So in mm/hr or mm for example

47
Q

What is the rainfall rate i ?

A

It is the rainfall intensity measured in units of length over time (e.g. mm/hr)

48
Q

What is infiltration capacity fc?

A

It is the maximum rate at which soil can absorb water through its surface

49
Q

What is infiltration rate f(t) ?

A

It is the time-variable rate of water entering the soil through the surface (measured in length over time)

50
Q

What is cumulative infiltration F(t) ?

A
  • The depth of infiltration from the beginning of rainfall to any time t.
  • It is also the area below the infiltration rate curve
51
Q

What is a wetting front?

A

A wetting front is present when the change of soil moisture content with depth is so great that there is a sharp discontinuity in the soil profile, between the wet soil above and the dry soil below

52
Q

What is time of ponding H(t) ?

A

Time at which the surface soil layer becomes saturated after the rainfall rate exceeds the hydraulic conductivity

GEOG 322 (10 decks)

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