10/18/2013

Topic 5
Water in the Atmosphere,
Surface, and Subsurface
Distribution of Water
Properties of Water
Omit Humidity and
Atmospheric Moisture
The Hydrologic Cycle

The Water Balance
Concept
Groundwater
Characteristics
Groundwater Pollution
Water Use

Water on Earth
All water above, at, or below Earth's surface is result of out-gassing
A closed system; quantity is at equilibrium
BUT changes in sea level occur due to:
Eustasy - variations in distribution of water, primarily glacial ice vs. liquid water
Isostacy - subsidence or uplift of continental landmasses Distribution of Earth’s
Water Today

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10/18/2013

Distribution of Earth’s Water Today

Unique Properties of Water
Heat
Properties

Phase
Changes

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10/18/2013

A Hydrologic Cycle Model

Hydrologic Cycle
A system that describes the transfer of water between: Hydrosphere
Atmosphere
Lithosphere
Energy obtained from Sun and force of gravity
Includes all processes and mechanisms of transfer

Parts of the Hydrologic Cycle
Movement Toward or Away from Earth’s Surface
Precipitation
Evaporation/Transpiration
Condensation
Throughfall
Interception
Stemflow

Water at Earth’s Surface and Subsurface
Infiltration
Percolation
Sheetflow
Channelized Flow
Runoff
Saturated Overland Flow
Horton Overland Flow

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10/18/2013

A Hydrologic Cycle Model
Precipitation

Evaporation/
Transpiration

Condensation

Throughfall

Interception

Stemflow

Surface Water and Soil-Moisture Environment
Infiltration
Percolation
Runoff
Saturated Overland Flow
Horton Overland Flow
Sheetflow
Channelized Flow

Soil-Water Balance Concept
Accounting of water inputs and outputs
Developed by C. W. Thornthwaite to: describe allocation of water within hydrologic cycle describe surplus or deficit at a location over time determine timing and quantity of irrigation develop a climatic classification

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10/18/2013

The Soil-Water Balance Equation

Rain
Gauge

Precipitation
Input (P) in all forms (rain, snow, hail, sleet, fog, etc.)

Note: this is annual P.
How would P vary from month to month in Brandon?

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10/18/2013

Potential Evapotranspiration (PE)
Evaporative demand of atmosphere
Fcn. of temperature and relative humidity
Includes:
Evaporation from soil and other surfaces
Transpiration of water from vegetation

Measured:
Evaporimeter
weighing lysimeter

Thornthwaite estimated PE based on mean monthly temperature and daylength

Potential
Evapotranspiration
Note: this is annual PE..
How would PE vary from month to month in
Brandon?

Deficit (D)
PE is satisfied by either: precipitation (monthly) or soil moisture storage (monthly)

If PE is not met, a deficit (D) occurs
Example, in a given month:
P = 60 mm, but PE = 100 mm
Soil Moisture Storage = 20mm
Is there a deficit (D)?

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10/18/2013

Actual Evapotranspiration (AE)
Difference between PE and D is AE
Example, in a given month:
P = 60 mm, but PE = 100 mm
Soil Moisture Storage = 20mm
Deficit (D) = 20 mm
What is AE?
Would irrigation be required?

Surplus (S)
Occurs when:
P > PE AND soil moisture storage (ST) is at field capacity (amt. highly variable)
Surplus either: collects in ponds, puddles, etc. called detained water percolates through soil as gravitational water and recharges groundwater runs off as sheetflow or channelized flow
Problem: Thornthwaite model assumes that all excess precipitation goes into soil moisture