soil water ges175, science of soils. water movement - surface water moves due to gravitational force...
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SOIL WATERSOIL WATER
GES175, GES175, Science of SoilsScience of Soils
Water Movement- Surface water moves due to gravitational force
Does water always flow downward?
3.2
CapillarityCapillarity Water moves into capillary soil poresWater moves into capillary soil pores
- due to adhesive and cohesive forces- due to adhesive and cohesive forces
3.3
OH
H
OH
H
OH
H OH
H
OH
H
OH
H
OH
H
OH
H
K+
Cl-
OH
H
Osmotic Force
Water movement across semi-permeable membrane
3.4
Energy ConceptEnergy Concept
Water moves from Water moves from high to low free energyhigh to low free energy
wet soil wet soil dry soil dry soilHH22O movementO movement
HH22O freeO free H H22O freeO free energy isenergy is energy is energy is
higherhigher lower lower
- difference in free energy causes H- difference in free energy causes H22O to moveO to move
3.5
Large Pores Small Pores
Properties of WaterProperties of WaterHydrogen bondingHydrogen bonding
3.6
Capillary ForcesCapillary Forces
- smaller pores hold water with greater energy - smaller pores hold water with greater energy - nondirectional- nondirectional
h = 0.15/rh = 0.15/r
2T cos r d gh =
T = surface tension = wetting angler = radius of pored = density of waterg = gravity
3.7
Water Movement by Capillary Action3.8
3.9
UnitsUnits
cm Hcm H22OO barsbars kPakPa
300300 -0.3 -0.3 -30-30
1,0001,000 -1 -1 -100-100
10,00010,000 -10-10 -1000-1000
15,00015,000 -15-15 -1500-1500
see Table 5.1 in textsee Table 5.1 in text
3.10
1 atm = 760 mm Hg = 1020 cm H2O = 1 bar = 100 KPa
3.11
Sandy Soil
Clayey Soil
Water Content (%)
Suc
tion
(ba
rs)
0
-20
Water Retention Curves
Aggregated Soil
Water Content (%)
Suc
tion
(ba
rs)
0
-100
Compacted Soil
Water Retention Curves 3.12
Hysteresis
drying
wetting
Suction (bars)
2r
2R
drying
wetting
0 -100
0.5
3.13
Soil Water:Soil Water: Classification and AvailabilityClassification and Availability
physical biological0
-30
-15
-0.3
gravitational
capillary
vapor
values are only semiquantitativevalues are only semiquantitative
unavailable (drainage)
available
unavailable
(bars)
3.14
3.15
clayey
sandy
H2O
Concepts of Movement
sandy
clayey
H2O
clayey
sandy
H2O
3.16
Hpi
Hgi
Hinlet= Hpi + Hgi
Reference level
soil
Hpo
Hgo
Ho = Hpo + Hgo
H
H= Hinlet - Houtlet
= Hpi - Hpo
Saturated Flow- Horizontal Column
L
3.17
H1
L
inlet
Reference plainoutlet
Hi = H1 + L
Ho = 0 + 0
Saturated Flow- Vertical Column
H = H1 + L
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