Transcript WATER ENERGETICS - Stanford University

GES175, Science of Soils
SOIL WATER
Water Movement
- Surface water moves due to gravitational force
Does water always flow downward?
3.2
Capillarity
3.3
Water moves into capillary soil pores
- due to adhesive and cohesive forces
3.4
Osmotic Force
Water movement across semi-permeable membrane
H
H
O
O
H
H
K+
H
H
O
O
H
H
H
H
O
H
O
Cl-
H
O
H
H
H
O
H
H
O
H
3.5
Energy Concept
Water moves from high to low free energy
wet soil  dry soil
Large Pores
H2O free
energy is
higher
H2O movement
Small Pores
H2O free
energy is
lower
- difference in free energy causes H2O to move
Properties of Water
Hydrogen bonding
3.6
3.7
Capillary Forces
h = 0.15/r
2T cos a
h= rdg
T = surface tension
a = wetting angle
r = radius of pore
d = density of water
g = gravity
- smaller pores hold water with greater energy
- nondirectional
3.8
Water Movement by Capillary Action
3.9
3.10
Units
1 atm = 760 mm Hg = 1020 cm H2O = 1 bar = 100 KPa
cm H2O
300
1,000
10,000
15,000
bars
-0.3
-1
-10
-15
see Table 5.1 in text
kPa
-30
-100
-1000
-1500
Water Retention Curves
Suction (bars)
-20
Clayey Soil
Sandy Soil
0
Water Content (%)
3.11
Water Retention Curves
Suction (bars)
-100
Compacted Soil
Aggregated Soil
0
Water Content (%)
3.12
3.13
Hysteresis
2r
0.5
2R
wetting
drying
drying
q
wetting
0
Suction (bars)
-100
Soil Water: Classification and Availability
physical
biological
0
gravitational
unavailable
(drainage)
-0.3
available
Y (bars)
-15
capillary
unavailable
-30
vapor
values are only semiquantitative
3.14
3.15
Concepts of Movement
H2O
H2O
sandy
clayey
sandy
clayey
sandy
clayey
H2O
3.16
Saturated Flow
- Horizontal Column
DH= Hinlet - Houtlet
= Hpi - Hpo
Hinlet= Hpi +
Hgi
DH
Ho = Hpo +
Hgo
Hpi
L
Hpo
soil
Hgo
Hgi
Reference level
3.17
Saturated Flow
- Vertical Column
DH = H1 + L
H1
Hi = H1 + L
inlet
L
Ho = 0 +
0
outlet
Reference plain