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GEOG 322 > Lec 11: Soil water & groundwater 1 > Flashcards

Lec 11: Soil water & groundwater 1 Flashcards

1
Q

Name the 8 components of hydrological cycle diagrams

A
  • precipitation
  • evaporation
  • storage
  • runoff
  • river discharge
  • interception
  • transpiration
  • evapotranspiration
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2
Q

Define precipitation

A

water condensed in clouds – which is too heavy to remain suspended in the air – that falls on land as rain, sleet, hail or snow

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2
Q

Define evaporation

A

Evaporation: liquid water in lakes, oceans, rivers and soils heated by the sun
that is converted to a gas (i.e., water vapor) and returned to the atmosphere

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3
Q

Define storage

A
  • Storage: water held in contained areas (e.g., in soil as soil moisture, in snow and
    ice caps, in depressions as depression storage) for a given amount of time
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4
Q

Define runoff

A

Runoff: water that moves away from a terrestrial location, via surface and/or
subsurface flow processes

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5
Q

Define river discharge

A

River discharge: flow of water within a river channel

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6
Q

Define interception

A

Interception: water that is prevented from reaching the ground by plant leaves
and branches
* Transpiration: liquid water from plant leaves and stems that is converted to
water vapor and returned to the atmosphere
* Evapotranspiration: combination of evaporation and transpiration

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7
Q

Define transpiration

A
  • Transpiration: liquid water from plant leaves and stems that is converted to
    water vapor and returned to the atmosphere
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7
Q

Define evapotranspiration

A

Evapotranspiration: combination of evaporation and transpiration

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7
Q

Define water table

A

Water table = subsurface boundary below which the ground is completely
saturated with water

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7
Q

Define percolation

A

water that moves vertically through the soil toward the water
table

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7
Q

Define capillary fringe

A

Capillary fringe: saturated zone above the water table, in which groundwater
seeps upward due to capillary forces

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7
Q

Define groundwater flow

A

Groundwater flow: water that is flowing below the water table

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7
Q

What happens after infiltration?

A

Water is stored in shallow soil layers as soil moisture

Water is redistributed vertically and laterally after infiltration
* Vertically: water percolates downward until the saturated zone (groundwater recharge)
* Laterally: governed by principles of unsaturated flow (or soil water flow) or
groundwater flow

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7
Q

What are horizons?

What are the 3 major horizons of most soils?

A

Distinct layers of a soil profile

differentiated by:
- color
- texture
- organic matter
- the degree of deposition (illuviation) or removal (eluviation) of material by physical and chemical processes

Surface horizon, subsoil, and substratum

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7
Q

What are the hydrologic horizons in the shallow subsurface?

A

root zone
intermediate zone
tension-saturated zone (capillary fringe)
ground water
impermeable layer

7
Q

Why is soil referred to as porous?

A

because it is permeated by an interconnected network of
pores (i.e., voids) filled with fluids (either
liquid or gas).

8
Q

what does soil texture describe?

A

Soil texture is a term used to describe the
grain size distribution (by weight) for particles
of less than 2 mm (upper boundary for sand)

9
Q

What determines the size of soil pores?

A

grain size

soil is a mixture of grain sizes

10
Q

rank the soil particle types (silt, sand, and clay) from smallest to largest particle size

A

clay (<0.002 mm)
silt (0.002-0.5 mm)
sand (0.05-2 mm)

11
Q

Porosity is a function of…

Total porosity (n) is a function of…

A

soil texture

the volume of the voids and the total volume of soil

n = v(voids)/v(total)

v(voids) = v(water) + v(gas)
v(total) = v(voids) + v(solids)

12
Q

What are the formulas for:

  • soil porosity
  • void ratio
  • soil moisture content by volume and by mass
  • degree of saturation
A

soil porosity (n) = v(voids)/v(total)

void ratio (e) = v(voids)/v(solids)

volumetric soil moisture (teta) = v(water)/v(total)

gravimetric soil moisture (G) = ((mass wet soil - mass dry soil)/mass dry soil)

degree of saturation (s) = v(water)/((vwater)+(vgas))

13
Q

What determines
the maximum amount
of space available in
the soil for water to be
retained/stored?

A

porosity

14
Q

What is soil profile according to hydrologists?

A

from highest to lowest

*vadose zone (unsaturated zone)
*capillary fringe
zone just above water table where water is drawn up by capillary action
*water table
upper limit of saturated zone
*phreatic zone (saturated zone)

15
Q

Define capillary action

Which two forces make capillary action possible?

When does capillary action occur?

A

Capillary action is the process of a liquid
moving in a narrow space, without the
assistance of (and sometimes even
against) gravity

cohesion (water molecules like to stay close together) and adhesion (water molecules are attracted to and stick to different materials)

occurs when the
adhesion forces of water to a solid
material are greater than the cohesive
forces between the liquid water
molecules

16
Q

What are the scientific terms for:
excess water
water held in pores
thin films of water

When do each of these occur?

A

excess water = gravitational water (occurs at saturation

water held in pores = capillary water (occurs in intermediate to wet conditions)

thin films of water = hygroscopic water (occurs in dry conditions)

17
Q

Define field capacity

A

The field capacity (FC) of a soil: maximum amount of water that a soil can hold after
gravitational drainage losses

18
Q

in relation to field capacity, when does subsurface flow occur?

A

Subsurface flow rarely occurs unless soil moisture content exceeds field capacity

19
Q

Define the permanent wilting point (WPW) of a soil

A

soil moisture content produced
after gravitational drainage + plant evapotranspiration losses

‒ Always lower than field capacity
‒ Corresponds to water content at which plants can no longer extract water from
the soil

20
Q

Define plant available water

A

the difference between field capacity and the permanent
wilting point

21
Q

For which grain size is plant available water highest?

A

Highest plant available
water occurs in intermediate grain sizes.

22
Q

Define soil water pressure and tension

A

*Water pressure is a force per unit area
applied by water in all directions
‒ It is conventionally measured relative to
atmospheric pressure

  • Soil water tension is a measure of how
    tightly water is held to soil particles
    ‒ It is expressed as a negative pressure

 Soil water tension is the minimum
pressure that must be exerted to extract
water from soil

23
Q

Define soil water pressure at different hydrological horizons

A

vadose zone: soil water pressure < atmospheric pressure

water table: soil water pressure = atmospheric pressure

saturated zone: soil water pressure > atmospheric pressure

24
Q

What is the relationship between soil water pressure and tension?

Describe soil water pressure in unsaturated vs saturated soils

A

Tension is negative pressure

unsaturated: P<1
water table: P = 0
saturated P>1

25
Q

What does a tensiometer measure?

How does it work?

A

for measuring soil suction in moist settings

Tube is partly filled
with water, low-permeability porous cup at bottom allows pressure
equilibration with soil, pressure gauge measures suction (i.e., pore pressure
relative to atmosphere)

26
Q

How does water move in the subsurface?

A

A water pressure gradient promotes the migration of water:
‒ from higher pressure (e.g., where water is less tightly bound to the soil grains, so
low tension)
‒ to lower pressure (e.g., where water is held more tightly, so high tension)

27
Q

Define hydraulic conductivity

Rank silt, sand, clay, and gravel from highest to lowest K

A

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

gravel, sand, silt, clay

GEOG 322 (20 decks)

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