Water Potential Diagrams for Systems at Equilibrium

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Water Potential Diagrams for Systems at
Equilibrium
System 1 A soil/water system is in equilibrium
with the water table (WT) at a depth of -700 mm
from the surface. If the gravitational reference
level (ZR) is set at the WT, construct the water
potential diagram for the overall system where H
z p h.
2
Zdepth
0
-200mm
-400mm
PE
-600mm
-800mm
-1000mm
- PE
3
Zdepth
0
H
-200mm
z
h
-400mm
-600mm
? WT -700mm ZR 0
-800mm
-1000mm
Equilibrium ?H 0 HWT z p h 0 H 0
throughout
p
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System 2 A soil/water system is in equilibrium
with the water table (WT) at a depth of -700 mm
from the surface. If the gravitational reference
level (ZR) is now set at the soil surface,
construct the water potential diagram for the
overall system where H z p h.
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Equilibrium ?H 0 HWT z p h - 700mm H
- 700 mm throughout
Zdepth
ZR
0
H
-200mm
-400mm
-600mm
h
? WT -700mm
-800mm
-1000mm
z
p
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Water Potential Diagrams for Systems at
Non-Equilibrium
System 3 A soil/water system has a water table
(WT) at a depth of - 400 mm from the surface.
Water is evaporating at the soil surface. If the
gravitational reference level (ZR) is set at the
soil surface, construct the water potential
diagram for the overall system where H z p
h.
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Equilibrium ?H ? 0 HWT z p h - 400mm H
- 400 mm below the WT only
Zdepth
?
ZR
0
h
-200mm
? WT - 400mm
?
Evp
-400mm
-600mm
-800mm
-1000mm
H
z
p
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System 4 The following figure shows two
piezometers (1 and 2) in a soil profile.
Piezometer 1 is installed to a depth of 1.2 m
and piezometer 2 to a depth of 0.7 m. Given the
reference point (z 0) at the soil surface,
construct the water potential diagram (H, z, p,
and h) for the complete system assuming the total
hydraulic potential (H) to be a linear function
of height. At what height is the water table? Is
there water flow, and if so in which direction?
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You must first consider the status of each
piezometer independently.
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? h
z
WT -.51
? H2
? H1
? p