Environmental Engineering Reference
In-Depth Information
3.5.3 Hydraulic Conductivity
Hydraulic conductivity (K) is a parameter used to measure the relative ease water flows
through an aquifer or other geologic formations such as a confining unit.
Hydraulic
conductivity
(K) is defined as the ability of saturated geologic media to conduct water
under an induced hydraulic or pressure gradient (Payne et al. 2008). Geologic formations
composed of sands and gravels typically have a high hydraulic conductivity or K value
(e.g., 10
−2
-10
+1
cm/s). Geologic formations composed of clay that might be considered a
confining unit frequently have very low hydraulic conductivities (e.g., 10
−6
-10
−8
cm/s).
Figure 3.18 shows the average range of hydraulic conductivities for different geologic
materials.
In 1856, a researcher from France named Henry Darcy conducted an experiment to eval-
uate the flow of water through sand beds. His experiments resulted in the development
of Darcy's law.
Darcy's law
predicts the flow of water (Q [cm
3
is through a sand bed is
proportional
to its hydraulic conductivity (K), area (A [cm
2
]) and the water level difference
between each end of the sand bed (dH [cm]), and
inversely proportional
to the thickness (L)
of the sand bed.
Equation 3.1 presents Darcy's law.
dH
dL
Q K A
=
×
×
(3.1)
where
K is the hydraulic conductivity (cm/s)
A is the area (cm
2
)
dH is the change in height of the bed of sand
dL is the length of the bed of sand
Sandstone
Consolidated
Shale
Unfractured
Fractured
Carbonate rocks
Fractured
Cavernous
Glacial till
Unconsolidated
Clay
Silt
Silty sand
Sand
Fine
Coarse
Gravel
10
-10
10
-9
10
-8
10
-7
10
-6
10
-5
10
-4
10
-3
10
-2
10
-1
10
1
10
2
1
K = centimeters per second (cm/s)
FIGURE 3.18
Range of hydraulic conductivities for different geologic materials. (Modified from Heath, R.C.,
Basic Ground-
Water Hydrology
, United States Geological Survey, Water Supply Paper 2220, United States Government Printing
Office, Alexandria, VA, 1983.)
Search WWH ::
Custom Search