Welcome to BRE542! Vadose Zone Transport

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Welcome to BRE542!Vadose Zone Transport
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Today

• Introduction to Course
• Related Texts
• Definition/importance of Vadose Zone
• Related areas of study
• History of Investigation of Vadose Processes
• Relationship to Saturated Media

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Logistical Issues

• BRE 542, Vadose Zone Transport, Fall 2003
• Department of Bioengineering
• John S. Selker
• Telephone [phone] email
  selkerj_at_engr.orst.edu
• Office hours MWF 10am-11am, or by appointment
• Lab help hours Monday 400-445
• Websites
• Vadose kits http//bre.orst.edu/faculty/selker/v
  adose_teaching.asp
• Lectures http//bre.orst.edu/vzp
• How the BRE 542 will be run
• Three exciting lectures/wk
• Numerical simulation project (you dont need to
  write code)
• Homework largely from experiments
• Experimental and data-based homework.

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More Logistics ... Grading

• One homework per week given on Monday, due the
  following Monday by 5 PM. (1/2 grade).
• One numerical modeling project (presentation
  plus 7 page paper 1/6 of grade). Papers are due
  Dec 5. See special handout on this component.
• 10 min quizzes will be carried out after each
  of the 4 chapters, announced 1 week in advance
  (1/6 of grade).
• Final exam (1/6th of grade). A closed book
  exam which covers the most significant concepts
  presented in the course.

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Idiosyncrasies in the professor (the fine print)

• Interpretation 25 of the score of each problem
  is given for interpretation of the result
  (qualitative)
• Calculations Even if you have the right number
  written down for the answer, you are only 75 of
  the way done unless you have thought about what
  the results mean.
• Late homework is not accepted unless prior
  arrangements have been made, as homework is often
  handed back on the next class meeting.
• The Rules
• Group work Wonderful, but must list the group
  of helpers, and may not simply copy the work of
  others.
• Writing must be your own work, unless properly
  cited. If in doubt, ask me. Plagiarism of
  written work will result in failing the course.

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Course Outline

• 1. An Introduction to the Vadose Zone (4 lect.)
• History of investigation
• Modern concerns
• Relationship to saturated media
• Primer on soils
• 2. Physical Hydraulic Properties Unsaturated
  Media (8 lect)
• Basic definitions
• Hydrostatics (Surface tensionCharacteristic
  curves Hysteresis)
• Hydrodynamics in porous media (Darcy's law
  Richards equation)
• 3. Flow of Water in the Vadose Zone (10 lect.)
• The classic solutions (Green Ampt
  Evaporation from Water Table).
• Solution for capillary barriers
• Miller and Miller scaling
• Characterization of soil hydraulic properties

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Course Outline Continued

• 4. Solute Transport in the Vadose Zone (5 lect.)
• Processes - Advection, adsorption, diffusion,
  degradation.
• Advective Diffusive Equation (Linearity,
  superposition, solutions).
• 5. Three-phase flow (2 lect.)
• Surface tension, spreading pressure, layered
  menisci
• Constitutive relations Pressure-Saturation-Per
  meability
• Funicular and residual saturation
• Special problems with continuum assumptions
  non-spreading oil.
• 6. Special Processes (2 lect.)
• Macropore Flow
• Fingered Flow
• Biological considerations

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The Numerical Component of BRE542

• Software Description and Access
• The software is called HYDRUS-2D
• Developed by the staff of the US salinity lab in
  riverside CA.
• Windows based modules with excellent graphical
  interface.
• The users manual is very technical
• 400-445 PM help sessions Gilmore annex on
  Mondays.
• The computer in the upstairs of the annex is set
  up with new HP workstations they rip!
• You may use the computers on a first come first
  served basis at other unscheduled times.
• No machines should be left running over night in
  order to maintain access for other students.

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The Numerical Component of BRE542

• 1. Learning the interface A. Clicking through
  the menus and printing resultsB. Setting up a
  problem from scratch.
• 2. Running a simple problemDraining a profile
  from saturation to hydrostatic.
• 3. Project
• Rules for numerical homework
• Do all the key strokes for your problem with your
  own hands, but may talk to others and watch
  others do their problems as much as you like.
• Start a problem using the files indicated in the
  homework (either ones prepared by me, or new
  files).
• Only you can enter data in your problem. If you
  want help from a friend, they can show you by
  going through operations on their files.

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El Proyecto!

• Project is 1/6 of the grade for the course.
• Phase 1. Defining the problem.
• a. Due October 3 (15). 1 or 2 page statement
  of problem importance, boundary conditions, and
  expected outcome.
• b. Due October 13 (15). Layout of problem in
  HYDRUS-2D. Define in detail the full problem to
  be solved
• Phase 2. Initial simulation results Oct 31
  (20). Write up (1-3 pg text plus figures).
• Phase 3. Presentations. November 24 and 25 (25).
  
• 700-930 evening donut and coffee evening
  sessions of 12 minute presentations. Must come to
  both sessions.
• Phase 4. Final submission Dec 5. lt10pgs
  figures.

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Drivers, start your engines!
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Disciplinary Context

• Related Texts
• Definition/importance of Vadose Zone
• Related areas of study

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HISTORY OF INVESTIGATION

• Its worthwhile to understand the historical
  context of the study of unsaturated flow
• A young field with ongoing conceptual
  development
• Provides a preview of the topics covered in the
  course

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Evidence of ancient operational understanding of
hydrology

• Ancient qanats of Aden
• Marib dam in Yemen built in 500 b.c. and lasting
  to the beginning of alternate routes through the
  orient around 500 a.d. 600 meter face supporting
  agriculture for 100,000 people.
• 600 a.d. Sri Lanka builds a network of irrigation
  works that survive to this day.Yet I know of no
  evidence that the underlying quantitative
  relationships between soil type, pressure and
  flow were understood.

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Review First quantitative understanding of
saturated flow

• Darcy 1856 study of the aquifers under Dijon
  Introduced the concept of potential flow
• Water moves in direct proportion to
• the gradient of potential energy
• the permeability of the media

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First quantitative application to unsaturated flow

• 1870s Bousinesq extended Darcys law with two
  approximations (Dupiut-Forcheimer) to deal with
  drainage and filling of media.
• Free water surface problems.
• Useful solutions for dikes land drainage, etc.
  (all as a footnote in his book)
• Bousinesq equation is strongly nonlinear much
  tougher to solve!

Bousinesq
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Rigorous foundation for Darcys Law

• First encyclopedic source of practical solutions
  based on pore-scale analysis
• 1899 Slichter Theory of Flow Through Porous
  Media
• Exact solutions for multiple pumped wells
• Basis of aquifer testing.

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Slichter some of his figures
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Extension of Darcys Law to Unsaturated Conditions

• 1907 Buckingham (of Buckingham-pi fame) Darcy for
  steady flow with
• Conductivity a function of moisture content
• Potential includes capillary pressures

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Extension of Darcys Law (cont.)

• Rule Folks who write equations are remembered
  for eternity, while the poor work-a-days who
  solve them are quickly forgotten.
• Exception Green and Ampt, 1911. Key problem of
  infiltration.
• Modeled as a capillary tubes which filled in
  parallel, from dry to saturation.
• Still most widely used infiltration model.

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Time passes...time passes We need a few tools!!

• Early 1920s, W. Gardners lab develop the
  tensiometer direct measurement of the capillary
  pressure
• L.A. Richards extended idea to tension plate
  measure moisture content as a function of
  capillary pressure
• And then...
• 1931, Richards derived equation for unsaturated
  flow. (p.s. Richards just died in the last 5
  years).

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Moisture contents depends on history of wetting

• Haines (1930) wetting proceeds as jumps
• Still largely ignored, but essential to
  unsaturated flow processes.

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Time passes ... time passes

• Turns out that Richards equation is a bear to
  solve! Depends on three non-linear variables q,
  y, K
• First big break for Rs Eq.
• 1952, Klute rewrote Richards equation in terms of
  moisture content alone
• diffusion equation (AKA Fokker-Plank eq.)
• Klute gave solution to 1-D capillary infiltration

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Analytical vs. Numerical

• Since 1952, more analytical solutions have been
  presented, BUT non-linearity limited to special
  conditions.
• What is the use of Analytical results?
• They let you see the implications of the physical
  parameters
• computers allow solution of individual problems
  tough to generalize

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Then things took off!

• Lots of great stuff in the 50s and early 60s
• 1956 Miller and Miller relationship of grain
  size to fluid properties

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More 50s and 60s

• 1957 Philip start to deal with infiltration
• 1962 Poulovassilis independent domain model of
  hysteresis (finally Haines stuff can be included)

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1970s limitations of the assumptions

• Biggar Nielson (1970)
• field scale heterogeneity
• Hill Parlange (1972)
• fingered flow
• Others
• macropores
• Kung (1988) Funnel Flow

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Relationship to saturated media

• While the similarity has been very useful, it is
  a source of many errors
• Main distinctions in three areas.
• Capillarity (lateral, upward flow)
• Heterogeneity into the temporal domain
• Biochemical activity
• Diffusion is two orders of magnitude faster
• Ample oxygen
• Take-home message be very careful!

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Differences
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Contemporary Concerns with the Vadose Zone

• Water conservation (how to use minimum water to
  irrigate crops)
• Nutrient storage and transport
• Pesticide degradation and movement
• Salinity control
• Water budget for climatic modeling
• Bulk petroleum and organic contaminant transport
  (vapor and liquid) Industrial contamination

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Example

• Suppose that 2,000 liters of some nasty liquid
  spilled on a 10 m2 area above an aquifer that was
  at a depth of 10 m. How much makes it to the
  aquifer?