Representative Values of Hydraulic Properties
by Glenn M. Duffield, President, HydroSOLVE, Inc.
Aquifer tests (pumping tests, slug tests and constanthead tests) are performed to estimate the hydraulic properties of aquifers and aquitards including horizontal and vertical hydraulic conductivity, storativity, specific yield and porosity. The following sections present representative hydraulic property values reported in the literature.
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hydraulic conductivity 
transmissivity 
anisotropy
storativity  specific
yield  porosity
Hydraulic Conductivity (K)
Hydraulic conductivity is the rate of flow under a unit hydraulic gradient through a unit crosssectional area of aquifer (opening A). Transmissivity is the rate of flow under a unit hydraulic gradient through a unit width of aquifer of thickness m (opening B). Diagram from Ferris et al. (1962).
What is hydraulic conductivity? Hydraulic conductivity is a measure of a material's capacity to transmit water. It is defined as a constant of proportionality relating the specific discharge of a porous medium under a unit hydraulic gradient in Darcy's law:
ν = Ki
where ν is specific discharge [L/T], K is hydraulic conductivity [L/T] and i is hydraulic gradient [dimensionless]. Coefficient of permeability is another term for hydraulic conductivity.
Note that hydraulic conductivity, which is a function of water viscosity and density, is in a strict sense a function of water temperature; however, given the small range of temperature variation encountered in most groundwater systems, the temperature dependence of hydraulic conductivity is often neglected.
What is transmissivity? Transmissivity is the rate of flow under a unit hydraulic gradient through a unit width of aquifer of given saturated thickness. The transmissivity of an aquifer is related to its hydraulic conductivity as follows:
T = Kb
where T is transmissivity [L^{2}/T] and b is aquifer thickness [L].
The following tables show representative values of hydraulic conductivity for various unconsolidated sedimentary materials, sedimentary rocks and crystalline rocks (from Domenico and Schwartz 1990):
Unconsolidated Sedimentary Materials  
Material  Hydraulic Conductivity (m/sec) 
Gravel  3x10^{4} to 3x10^{2} 
Coarse sand  9x10^{7} to 6x10^{3} 
Medium sand  9x10^{7} to 5x10^{4} 
Fine sand  2x10^{7} to 2x10^{4} 
Silt, loess  1x10^{9} to 2x10^{5} 
Till  1x10^{12} to 2x10^{6} 
Clay  1x10^{11} to 4.7x10^{9} 
Unweathered marine clay  8x10^{13} to 2x10^{9} 
Sedimentary Rocks  
Rock Type  Hydraulic Conductivity (m/sec) 
Karst and reef limestone  1x10^{6} to 2x10^{2} 
Limestone, dolomite  1x10^{9} to 6x10^{6} 
Sandstone  3x10^{10} to 6x10^{6} 
Siltstone  1x10^{11} to 1.4x10^{8} 
Salt  1x10^{12} to 1x10^{10} 
Anhydrite  4x10^{13} to 2x10^{8} 
Shale  1x10^{13} to 2x10^{9} 
Crystalline Rocks  
Material  Hydraulic Conductivity (m/sec) 
Permeable basalt  4x10^{7} to 2x10^{2} 
Fractured igneous and metamorphic rock  8x10^{9} to 3x10^{4} 
Weathered granite  3.3x10^{6} to 5.2x10^{5} 
Weathered gabbro  5.5x10^{7} to 3.8x10^{6} 
Basalt  2x10^{11} to 4.2x10^{7} 
Unfractured igneous and metamorphic rock  3x10^{14} to 2x10^{10} 
To Convert  Multiply By  To Obtain 
m/sec  100  cm/sec 
m/sec  2.12x10^{6}  gal/day/ft^{2} 
m/sec  3.2808  ft/sec 
Hydraulic conductivity of selected consolidated and unconsolidated geologic materials (from Heath 1983).
Hydraulic Conductivity Anisotropy Ratio (Kz/Kr)
An anisotropy ratio relates hydraulic conductivities in different directions. For example, verticaltohorizontal hydraulic conductivity anisotropy ratio is given by K_{z}/K_{r} where K_{z} is vertical hydraulic conductivity and K_{r} is radial (horizontal) hydraulic conductivity. Anisotropy in a horizontal plane is given by K_{y}/K_{x} where K_{x} and K_{y} are horizontal hydraulic conductivities in the x and y directions, respectively.
Todd (1980) reports values of K_{z}/K_{r} ranging between 0.1 and 0.5 for alluvium and possibly as low as 0.01 when clay layers are present.
The following table shows representative values of horizontal and vertical hydraulic conductivities for selected rock types (from Domenico and Schwartz 1990):
Material  Horizontal Hydraulic Conductivity (m/sec) 
Vertical Hydraulic Conductivity (m/sec) 
Anhydrite  10^{14} to 10^{12}  10^{15} to 10^{13} 
Chalk  10^{10} to 10^{8}  5x10^{11} to 5x10^{9} 
Limestone, dolomite 
10^{9} to 10^{7}  5x10^{10} to 5x10^{8} 
Sandstone  5x10^{13} to 10^{10}  2.5x10^{13} to 5x10^{11} 
Shale  10^{14} to 10^{12}  10^{15} to 10^{13} 
Salt  10^{14}  10^{14} 
Storativity (S)
Storativity of a confined (artesian) aquifer (from Ferris et al. 1962).
What is storativity? The storativity of a confined aquifer (or aquitard) is defined as the volume of water released from storage per unit surface area of a confined aquifer (or aquitard) per unit decline in hydraulic head. Storativity is also known by the terms coefficient of storage and storage coefficient.
In a confined aquifer (or aquitard), storativity is defined as
S = S_{s}b
where S is storativity [dimensionless], S_{s} is specific storage [L^{1}] and b is aquifer (or aquitard) thickness [L]. Specific storage is the volume of water that a unit volume of aquifer (or aquitard) releases from storage under a unit decline in head by the expansion of water and compression of the soil or rock skeleton.
What is specific storage? Specific storage is related to the compressibilities of the aquifer (or aquitard) and water as follows:
S_{s} = ρg(α + n_{e}β)
where ρ is mass density of water [M/L^{3}], g is gravitational acceleration (= 9.8 m/sec^{2}) [L/T^{2}], α is aquifer (or aquitard) compressibility [T^{2}L/M], n_{e} is effective porosity [dimensionless], and β is compressibility of water (= 4.4x10^{10} m sec^{2}/kg or Pa^{1}) [T^{2}L/M].
Storativity of an unconfined (watertable) aquifer (from Ferris et al. 1962).
In an unconfined aquifer (or aquitard), storativity is given by
S = S_{y} + S_{s}b
where S_{y} is specific yield. Because S_{s}b is typically small in comparison to S_{y}, storativity in an unconfined aquifer is often simply equated with specific yield.
The storativity of a confined aquifer, which varies with specific storage and aquifer thickness, typically ranges from 5x10^{5} to 5x10^{3} (Todd 1980); in unconfined aquifers, storativity ranges from 0.1 to 0.3 (Lohman 1972).
The following table provides representative values of specific storage for various geologic materials (Domenico and Mifflin [1965] as reported in Batu [1998]):
Material  Ss (ft^{1}) 
Plastic clay  7.8x10^{4} to 6.2x10^{3} 
Stiff clay  3.9x10^{4} to 7.8x10^{4} 
Medium hard clay  2.8x10^{4} to 3.9x10^{4} 
Loose sand  1.5x10^{4} to 3.1x10^{4} 
Dense sand  3.9x10^{5} to 6.2x10^{5} 
Dense sandy gravel  1.5x10^{5} to 3.1x10^{5} 
Rock, fissured  1x10^{6} to 2.1x10^{5} 
Rock, sound  < 1x10^{6} 
To Convert  Divide By  To Obtain 
ft^{1}  0.3048  m^{1} 
Freeze and Cherry (1979) provided the following compressibility values for various aquifer materials:
Material  Compressibility, α (m^{2}/N or Pa^{1}) 
Clay  10^{8} to 10^{6} 
Sand  10^{9} to 10^{7} 
Gravel  10^{10} to 10^{8} 
Jointed rock  10^{10} to 10^{8} 
Sound rock  10^{11} to 10^{9} 
Pa^{1} = m^{2}/N = m sec^{2}/kg

Use compressibility data to estimate the storativity of a 35ft
thick confined sand aquifer (assume ρ = 1000 kg/m^{3}
and n_{e} = 0.3).
S = S_{s}b = ρg(α + n_{e}β)b = (1000 kg/m^{3})(9.8 m/sec^{2}) [10^{8} m^{2}/N + (0.3) (4.4x10^{10} m^{2}/N)](35 ft)(0.3048 m/ft) = 1.1x10^{3}
How much does the expansion of water contribute to the total storativity in this example?
S_{w} = ρgn_{e}βb = (1000 kg/m^{3})(9.8 m/sec^{2})(0.3) (4.4x10^{10} m^{2}/N)(35 ft)(0.3048 m/ft) = 1.4x10^{}^{5}

Use specific storage data to estimate storativity for the same
aquifer given in the preceding example.
S = S_{s}b = (5x10^{5} ft^{1})(35 ft) = 1.8x10^{3}
Specific Yield (Sy)
Specific retention (S_{r}), specific yield (S_{y}) and total porosity (n) (from Heath 1983).
What is specific yield? Specific yield is defined as the volume of water released from storage by an unconfined aquifer per unit surface area of aquifer per unit decline of the water table.
Bear (1979) relates specific yield to total porosity as follows:
n = S_{y} + S_{r}
where n is total porosity [dimensionless], S_{y} is specific yield [dimensionless] and S_{r} is specific retention [dimensionless], the amount of water retained by capillary forces during gravity drainage of an unconfined aquifer. Thus, specific yield, which is sometimes called effective porosity, is less than the total porosity of an unconfined aquifer (Bear 1979).
Heath (1983) reports the following values (in percent by volume) for porosity, specific yield and specific retention:
Material  Porosity (%)  Specific Yield (%) 
Specific Retention (%) 
Soil  55  40  15 
Clay  50  2  48 
Sand  25  22  3 
Gravel  20  19  1 
Limestone  20  18  2 
Sandstone (unconsolidated)  11  6  5 
Granite  0.1  0.09  0.01 
Basalt (young)  11  8  3 
The following table shows representative values of specific yield for various geologic materials (from Morris and Johnson 1967):
Material  Specific Yield (%) 
Gravel, coarse  21 
Gravel, medium  24 
Gravel, fine  28 
Sand, coarse  30 
Sand, medium  32 
Sand, fine  33 
Silt  20 
Clay  6 
Sandstone, fine grained  21 
Sandstone, medium grained  27 
Limestone  14 
Dune sand  38 
Loess  18 
Peat  44 
Schist  26 
Siltstone  12 
Till, predominantly silt  6 
Till, predominantly sand  16 
Till, predominantly gravel  16 
Tuff  21 
Porosity (n)
Void volume, total volume and porosity (from Heath 1983).
What is porosity? Porosity is defined as the void space of a rock or unconsolidated material:
n = V_{v}/V_{T}
where n is porosity [dimensionless], V_{v} is void volume [L^{3}] and V_{T} is total volume [L^{3}].
The following tables show representative porosity values for various unconsolidated sedimentary materials, sedimentary rocks and crystalline rocks (from Morris and Johnson 1967):
Unconsolidated Sedimentary Materials  
Material  Porosity (%) 
Gravel, coarse  24  37 
Gravel, medium  24  44 
Gravel, fine  25  39 
Sand, coarse  31  46 
Sand, medium  29  49 
Sand, fine  26  53 
Silt  34  61 
Clay  34  57 
Sedimentary Rocks  
Rock Type  Porosity (%) 
Sandstone  14  49 
Siltstone  21  41 
Claystone  41  45 
Shale  1  10 
Limestone  7  56 
Dolomite  19  33 
Crystalline Rocks  
Rock Type  Porosity (%) 
Basalt  3  35 
Weathered granite  34  57 
Weathered gabbro  42  45 
See also: Argonne National Laboratory