Transmissivity (hydrogeology)

The transmissivity , sometimes as transmissibility referred, is a term used in hydrogeology . It is a measure of the ability of an aquifer to transport water and is closely related to the coefficient of permeability (the so-called -value). In contrast to this, it is a property of the entire aquifer and not just a material property of the subsoil. ${\displaystyle k_{f}}$

The concept of transmissivity was introduced in 1935 by Charles Vernon Theis under the name of the transmissibility coefficient and can be determined, for example, by means of pumping tests .

definition

For a horizontally lying aquifer made of an isotropic, porous medium with constant thickness , the transmissivity is defined as ${\displaystyle M}$ ${\displaystyle T}$

${\displaystyle T=k_{f}\cdot M}$

Here, denotes the permeability coefficient of the medium in meters per second. ${\displaystyle k_{f}}$

If the aquifer is built up in layers, the transmissivity of the entire aquifer results from the sum of the transmissivities of the individual layers. So if the conductor consists of layers, each with thicknesses and permeability coefficients , then is ${\displaystyle n}$ ${\displaystyle M^{(1)},M^{(2)},\dots ,M^{(n)}}$ ${\displaystyle k_{f}^{(1)},k_{f}^{(2)},\dots ,k_{f}^{(n)}}$

${\displaystyle T=\sum _{i=1}^{n}T^{(i)}=\sum _{i=1}^{n}k_{f}^{(i)}\cdot M^{(i)}}$

The unit of transmissivity is square meters per second. As an abbreviation there is also . ${\displaystyle T}$ ${\displaystyle T_{GW}}$

Determination of the transmissivity

In addition to the direct calculation of the transmissivity by determining the thickness of the aquifer and the value of the rock, the following options are available: ${\displaystyle k_{f}}$

• For strained aquifers using the well formula according to Dupuit-Thiem .
• For unconstrained aquifers, the Jacobian correction method based on this exists .
• About the settling process. The water level in the well is lowered using compressed air. After releasing the pressure, conclusions can be drawn about the transmissivity from the oscillating behavior of the water level.
• The Theis method and the straight line method by Cooper and Jacob exist for unsteady flow conditions .

Individual evidence

1. ^ ^{A b} Bernward Hölting, Wilhelm Georg Coldewey: Hydrogeology . Introduction to General and Applied Hydrogeology. 8th edition. Springer-Verlag, Berlin / Heidelberg 2013, ISBN 978-3-8274-2353-5 , pp. 33 , doi : 10.1007 / 978-3-8274-2354-2 .
2. ↑ ^{a b} Helmut Prinz, Roland Strauss: Engineering Geology . 5th, revised and expanded edition. Spektrum Akademischer Verlag, Heidelberg 2011, ISBN 978-3-8274-2472-3 , p. 90-91 .
3. ^ Horst-Robert Langguth, Rudolf Voigt: Hydrogeological methods . 2nd Edition. Springer-Verlag, Berlin / Heidelberg 2004, ISBN 3-540-21126-8 , pp. 206 .
4. ^ Gunnar Vorteilmann, Hans Moser: Elements of an analytical hydrology . Processes - interactions - models. Springer Spectrum, Wiesbaden 2016, ISBN 978-3-658-00310-4 , p. 91-92 , doi : 10.1007 / 978-3-658-00311-1 .
5. ^ ^{A b} Bernward Hölting, Wilhelm Georg Coldewey: Hydrogeology . Introduction to General and Applied Hydrogeology. 8th edition. Springer-Verlag, Berlin / Heidelberg 2013, ISBN 978-3-8274-2353-5 , pp. 290 , doi : 10.1007 / 978-3-8274-2354-2 .
6. ↑ Helmut Prinz, Roland Strauss: Engineering Geology . 5th, revised and expanded edition. Spektrum Akademischer Verlag, Heidelberg 2011, ISBN 978-3-8274-2472-3 , p. 96 .