1. Soil Physics 2010 Outline Announcements Aeration Permeability Relative permeability Air permeability

2. Soil Physics 2010 Review session Friday, 11:00 – 1:00 Homework 5 due now Exam II on Friday, April 2 Remember I’ll be gone most of next week Announcements

3. Soil Physics 2010 And now Delise, on the topic of Aeration

4. Soil Physics 2010 Aeration mechanisms Advection (also called convection, mass movement, mass flow) Diffusion We’ll look at advection today, and start diffusion on Friday.

5. Soil Physics 2010 Advection Darcy’s law is about advection (or mass flow): Mass moved (flux density) Proportionality coefficient Potential gradient

6. Soil Physics 2010 Now replace the water with molasses (keep the same soil, same potential gradient) Same flux? Same proportionality coefficient? Same potential gradient K s has 2 parts: Soil properties Fluid properties

7. Soil Physics 2010 Parts of Darcy’s K s Soil property: PermeabilitykL 2 Fluid property: FluidityfL -1 T -1 Fluidity is often given as  g/  :  fluid density ggravitational acceleration  fluid viscosity

8. Soil Physics 2010 What’s with the L 2 ? PermeabilitykL 2 The actual length L that is squared for a soil’s permeability is quite small. It is usually interpreted as the soil’s effective pore diameter.

9. Soil Physics 2010 Back to water, molasses, etc. Soil permeability fluidity The soil’s permeability does not depend on the fluid’s properties. So permeability can also describe the flow of air

10. Soil Physics 2010 Relative permeability k r Water permeability of saturated soil Air permeability of dry soil = krkr 0 1 SwSw 0 1 SaSa 1 0 Little pores Big pores

11. Soil Physics 2010 Relative permeability krkr 0 1 SwSw 0 1 SaSa 1 0 Petroleum engineers, and some geologists, use these “relperm” plots

12. air entry value Soil Physics 2010 Air permeability k a SwSw 0 1 kaka 0 1 SaSa 1 0 h 0 No air flow until soil has dried to the air entry value. This is like  r for hydraulic conductivity: K(  r ) = 0

13. Soil Physics 2010 Measuring air permeability