Welcome to BRE542! Vadose Zone Transport

1. Welcome to BRE542!Vadose ZoneTransport

2. 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

3. Logistical Issues • BRE 542, Vadose Zone Transport, Fall 2003 • Department of Bioengineering • John S. Selker • Telephone: 541-737-6304 email: selkerj@engr.orst.edu • Office hours: MWF 10am-11am, or by appointment • Lab help hours: Monday 4:00-4:45 • Websites: • Vadose kits: http://bre.orst.edu/faculty/selker/vadose_teaching.asp • Lectures: http://bre.orst.edu/vzp • How the BRE 542 will be run • •Three exciting lectures/wk • •Numerical simulation project (you don’t need to write code) • Homework largely from experiments • •Experimental and data-based homework.

4. 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.

5. 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.

6. 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 tension;Characteristic 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

7. 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-Permeability • • Funicular and residual saturation • • Special problems with continuum assumptions: non-spreading oil. • 6. Special Processes (2 lect.) • • Macropore Flow • • Fingered Flow • • Biological considerations

8. 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 • 4:00-4:45 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.

9. The Numerical Component of BRE542 • 1. Learning the interfaceA. 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.

10. ¡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%). • 7:00-9:30 evening donut and coffee evening sessions of 12 minute presentations. Must come to both sessions. • Phase 4. Final submission Dec 5. <10pgs + figures.

11. Drivers, start your engines!

12. Disciplinary Context • Related Texts • Definition/importance of Vadose Zone • Related areas of study

13. HISTORY OF INVESTIGATION • It’s 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

14. 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.

15. 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

16. First quantitative application to unsaturated flow • 1870’s Bousinesq extended Darcy’s 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

17. Rigorous foundation for Darcy’s 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.

18. Slichter – some of his figures

19. Extension of Darcy’s 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

20. Extension of Darcy’s 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.

21. Time passes...time passes We need a few tools!! • Early 1920’s, W. Gardner’s 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).

22. Moisture contents depends on history of wetting • Haines (1930) wetting proceeds as “jumps” • Still largely ignored, but essential to unsaturated flow processes.

23. 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 R’s 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

24. 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

25. Then things took off! • Lots of great stuff in the 50’s and early 60’s • 1956: Miller and Miller: relationship of grain size to fluid properties

26. More 50’s and 60’s • 1957: Philip start to deal with infiltration • 1962: Poulovassilis: independent domain model of hysteresis (finally Haines stuff can be included)

27. 1970’s: limitations of the assumptions • Biggar & Nielson (1970) • field scale heterogeneity • Hill & Parlange (1972) • fingered flow • Others: • macropores • Kung (1988): Funnel Flow

28. 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!

29. Differences

30. 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

31. 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?