1. SOIL WATER GES175, Science of Soils

2. Water Movement - Surface water moves due to gravitational force Does water always flow downward? 3.2

3. Capillarity Water moves into capillary soil pores Water moves into capillary soil pores - due to adhesive and cohesive forces 3.3

4. O H H O H H O H H O H H O H H O H H O H H O H H K+K+ Cl - O H H Osmotic Force Water movement across semi-permeable membrane 3.4

5. Energy Concept Water moves from high to low free energy wet soil dry soil wet soil dry soil H 2 O movement H 2 O free H 2 O free H 2 O free H 2 O free energy is energy is energy is energy is higher lower higher lower - difference in free energy causes H 2 O to move 3.5 Large PoresSmall Pores

6. Properties of Water Hydrogen bonding 3.6

7. Capillary Forces - smaller pores hold water with greater energy - nondirectional h = 0.15/r 2T cos r d g h = T = surface tension = wetting angle r = radius of pore d = density of water g = gravity 3.7

8. Water Movement by Capillary Action 3.8

9. 3.9

10. Units cm H 2 ObarskPa 300 -0.3-30 300 -0.3-30 1,000 -1-100 1,000 -1-100 10,000-10-1000 10,000-10-1000 15,000-15-1500 15,000-15-1500 see Table 5.1 in text 3.10 1 atm = 760 mm Hg = 1020 cm H 2 O = 1 bar = 100 KPa

11. 3.11 Sandy Soil Clayey Soil Water Content (%) Suction (bars) 0 -20 Water Retention Curves

12. Aggregated Soil Water Content (%) Suction (bars) 0 -100 Compacted Soil Water Retention Curves 3.12

13. Hysteresis drying wetting Suction (bars) 2r 2R drying wetting 0-100 0.5 3.13

14. Soil Water: Classification and Availability physicalbiological 0 -30 -15 -0.3 gravitational capillary vapor 3values are only semiquantitative unavailable (drainage) available unavailable (bars) 3.14

15. 3.15 clayey sandy H2OH2O Concepts of Movement sandy clayey H2OH2O sandy H2OH2O

16. 3.16 H pi H gi H inlet = H pi + H gi Reference level soil H po H go H o = H po + H go H H= H inlet - H outlet = H pi - H po Saturated Flow - Horizontal Column L

17. 3.17 H1H1 L inlet Reference plain outlet H i = H 1 + L H o = 0 + 0 Saturated Flow - Vertical Column H = H 1 + L