Agriculture Reference
In-Depth Information
Solution
We know
K
i
d
i
d
i
K
H
=
Putting the values,
K
H
=
(0.20
×
0.50)
+
(0.15
×
0.4)
+
(0.25
×
0.3)
1.2
= 0.235 m
3
m
2
/
/
h(Ans.)
Example 9.3
A field soil has four distinct soil layers within 1.4 m depth from the surface. The
depth and vertical hydraulic conductivity of the layers are 0.3, 0.4, 0.3, and 0.4 m;
and 1.0, 0.5, 0.7, and 0.6 m
3
/m
2
/d, respectively. A constant water supply of 0.88
m/d is provided at the soil surface. What will be the resultant hydraulic conductivity
of the soil column through the bottom of the soil layer? Comment on the pressure
distribution at the up and bottom of the second layer.
Solution
The soil layers are schematically depicted in figure below:
q = 0.88 m/d
1
0.3m
K
1
= 1.0 m
3
/m
2
/d
2
0.4 m
K
2
=0.5 m
3
/m
2
/d
3
0.3m
K
3
= 0.7 m
3
/m
2
/d
K
4
= 0.6 m
3
/m
2
/d
0.4m
4
The second layer has the lowest conductivity and it is less than the supply (0.88
m/d), and hence, the vertical water movement will be restricted by this layer. Thus,
the resultant hydraulic conductivity at the bottom of the layers will be 0.5 m
3
/m
2
/d.
At the top of the second layer (that is at the bottom of the first layer), the supply
or the conductivity is higher than the conductivity of the second layer, thus positive
pressure will exist. On the other hand, at the top of the third layer, the conductivity
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