WATER IN SOILS

1. WATER INSOILS

2. “water is a polar substance” - • Water – A unique substance A. Nonpolar vs. Polar Molecules Strong Surface Tension Strong Capillary Action + “Electrical charge of molecule is uniform in all directions” “Electrical charge of molecule is not uniform in all directions”

3. Water – A unique substance High Surface Tension High Heat of Vaporization High Boiling Point Strong Capillary Action Expansion During Freezing High Freezing Point

4. II. Soil Porosity

5. II. Soil Porosity A. Varies with Texture 1. Approximately 50% for Undisturbed Soils

7. III. Nature of Soil Water A. Water Table 1. Zone of Aeration 2. Zone of Saturation

9. Nuclear Gage Resistance Block Potentiometer

10. A thought experiment……

11. A thought experiment……

12. B. How Water is Held in Soils 1. Cohesion a. Forces Bonding Water to Itself 2. Adhesion a. Bonds Water to Soil Grains (Positive end of the water molecule bonds with the negatively charged clay particle (hydrogen bonding) b. Measured in Bars 1 Bar = 1 Atmosphere ~15 psi

13. Hygroscopic Water-- --water that is tightly bound to the soil particle and requires large expenditure of energy to remove it.

14. C. Water Available to Plants 1. Wilting Point: -15 Bars to 2. Field Capacity: -1/3 Bar D. Hygroscopic Water 1. Held by Adhesion a. Greater than -31 Bars saturation 0 bar

16. E. Water Availability vs.Texture 1. Greatest in Loamy Soils 2. Least in Sandy and Clayey Soils

18. F. Soil Drainage 1. Color a. Oxidation State of Iron Fe 2+ <> Fe 3+ + e- b. Organic Matter Wet Soil Preserves Organics c. Gleying d. Mottling

19. Well drained soil, Ferric iron

20. High organic matter

21. Gleyed soil

22. Mottled soil

24. G. Soil Drainage 1. Color a. Oxidation State of Iron Fe 2+ <> Fe 3+ + e- b. Organic Matter Wet Soil Preserves Organics c. Gleying d. Mottling 2. Fragipan Soils a. Can Cause Wetness

26. H. Vegetation 1. Hydrophilic Plants a. Cyprus b. Cattails c. Willows d. Reeds 2. Plants Requiring Good Drainage a. Oak-Hickory Biome b. Pines c. Most Grasses

27. Part II

28. Water Movement in Soil and Rocks

29. Two Principles to Remember: Water Movement in Soil and Rocks

30. Two Principles to Remember: Water Movement in Soil and Rocks 1. Darcy’s Law

31. Two Principles to Remember: Water Movement in Soil and Rocks 1. Darcy’s Law • Continuity Equation: mass in = mass out + change in storage “my name’s Bubba!”

32. Water Movement in Soil and Rocks I. Critical in Engineering and Environmental Geology A. Dams, Reservoirs, Levees, etc. “ Pore Pressure”

33. Water Movement in Soil and Rocks I. Critical in Engineering and Environmental Geology A. Dams, Reservoirs, Levees, etc. B. Groundwater Contamination Leaking Underground Storage Tanks Landfills Surface Spills

34. Water Movement in Soil and Rocks I. Critical in Engineering and Environmental Geology A. Dams, Reservoirs, Levees, etc. B. Groundwater Contamination C. Foundations - Strength and Stability

35. I. Critical in Engineering and Environmental Geology A. Dams, Reservoirs, Levees, etc. B. Groundwater Contamination C. Foundations - Strength and Stability

36. II. Water Flow in a Porous Medium A. Goal: Determine the permeability of the engineering material

37. II. Water Flow in a Porous Medium A. Goal: Determine the permeability of the engineering material Porosity Permeability

38. II. Water Flow in a Porous Medium A. Goal: Determine the permeability of the engineering material Porosity Permeability Porosity (def) % of total rock that is occupied by voids. Permeability (def) the ease at which water can move through rock or soil

39. II. Water Flow in a Porous Medium B. Darcy‘s Law Henri Darcy (1856) Developed an empirical relationship of the discharge of water through porous mediums.

40. II. Water Flow in a Porous Medium B. Darcy‘s Law 1. The experiment K

41. II. Water Flow in a Porous Medium B. Darcy‘s Law 2. The results • unit discharge α permeability • unit discharge α head loss • unit discharge α 1 / hydraulic gradient

42. Also…..

43. II. Water Flow in a Porous Medium B. Darcy‘s Law 2. The equation v = Ki

44. II. Water Flow in a Porous Medium B. Darcy‘s Law 2. The equation v = Ki where v = specific discharge (discharge per cross sectional area) (L/T) * also called the Darcy Velocity * function of the porous medium and fluid

45. Darcy’s Law: v = Ki where v = specific discharge (discharge per unit area) (L/T) K = hydraulic conductivity (L/T); also referred to as coefficient of permeability i = hydraulic gradient, where i = dh/dl (unitless variable)

46. Darcy’s Law: v = Ki where v = specific discharge (discharge per unit area) (L/T) K = hydraulic conductivity (L/T); also referred to as coefficient of permeability i = hydraulic gradient, where i = dh/dl (unitless variable)

47. Darcy’s Law: v = Ki where v = specific discharge (discharge per unit area) (L/T) K = hydraulic conductivity (L/T); also referred to as coefficient of permeability i = hydraulic gradient, where i = dh/dl (unitless variable) v = K dh dl

48. Darcy’s Law: v = Ki where v = specific discharge (discharge per unit area) (L/T) K = hydraulic conductivity (L/T); also referred to as coefficient of permeability i = hydraulic gradient, where i = dh/dl (unitless variable) v = K dh dl If Q = VA, then Q = A K dh dl

49. B. Darcy‘s Law 4. Some Representative Values for Hydraulic Conductivity

50. Darcy’s Law: The exposed truth: these are only APPARENT velocities and discharges Q = A K dh dl v = K dh dl Q = VA Vs.