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

Lec 11: Soil water & groundwater 1 Flashcards by jasmine boucley

Name the 8 components of hydrological cycle diagrams

precipitation
evaporation
storage
runoff
river discharge
interception
transpiration
evapotranspiration

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Define precipitation

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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Define evaporation

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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Define storage

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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Define runoff

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

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Define river discharge

River discharge: flow of water within a river channel

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Define interception

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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Define transpiration

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

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Define evapotranspiration

Evapotranspiration: combination of evaporation and transpiration

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Define water table

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

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Define percolation

water that moves vertically through the soil toward the water
table

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Define capillary fringe

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

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Define groundwater flow

Groundwater flow: water that is flowing below the water table

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What happens after infiltration?

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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What are horizons?

What are the 3 major horizons of most soils?

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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What are the hydrologic horizons in the shallow subsurface?

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

Why is soil referred to as porous?

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

what does soil texture describe?

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)

What determines the size of soil pores?

grain size

soil is a mixture of grain sizes

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

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

Porosity is a function of…

Total porosity (n) is a function of…

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)

What are the formulas for:

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

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))

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

porosity

What is soil profile according to hydrologists?

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)

Define capillary action Which two forces make capillary action possible? When does capillary action occur?

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

What are the scientific terms for: excess water water held in pores thin films of water When do each of these occur?

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)

Define field capacity

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

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

Subsurface flow rarely occurs unless soil moisture content exceeds field capacity

Define the permanent wilting point (WPW) of a soil

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

Define plant available water

the difference between field capacity and the permanent wilting point

For which grain size is plant available water highest?

Highest plant available water occurs in intermediate grain sizes.

Define soil water pressure and tension

*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

Define soil water pressure at different hydrological horizons

vadose zone: soil water pressure < atmospheric pressure water table: soil water pressure = atmospheric pressure saturated zone: soil water pressure > atmospheric pressure

What is the relationship between soil water pressure and tension? Describe soil water pressure in unsaturated vs saturated soils

Tension is negative pressure unsaturated: P<1 water table: P = 0 saturated P>1

What does a tensiometer measure? How does it work?

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)

How does water move in the subsurface?

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)

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

Hydraulic conductivity K describes the ease with which water can move through pore spaces or fractures in soils gravel, sand, silt, clay