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| Titel |
Joint inversion of hydrogeophysical data for porous media characterization. A real case |
| VerfasserIn |
Michele De Biase, Francesco Chidichimo, Enzo Rizzo, Salvatore Masi, Salvatore Straface |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093175
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| Publikation (Nr.) |
 EGU/EGU2014-7669.pdf |
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| Zusammenfassung |
| We present a multi-physical approach developed for the hydrodynamic characterization of
real porous media using hydrogeophysical information. Several pumping tests have been
performed in the Hydrogeosite, a controlled site designed and constructed at the
CNR-IMAA laboratory, in Marsico Nuovo (Basilicata Region, Southern Italy). The facility
consists of a pool (10x7x3 m3) completely covered with a steel shed, used to study
water infiltration processes, to simulate the space and time dynamics of subsurface
contamination phenomena, to improve and to find new relationship between geophysical and
hydrogeological parameters, to test and to calibrate new geophysical techniques and
instruments. The pool, because of its dimensions, is made by reinforced concrete,
representing an intermediate stage between laboratory experiments and field survey.
Therefore, the Hydrogeosite has the advantage to carry out controlled experiments,
like in a flow-cell or sand-box, but at field comparable scale. The data collected
during the experiments have been used to validate the following joint inversion
model.
Water flow in a variably saturated porous medium can be represented by the modified
Richards equation (Richards, 1931; Panday et al., 1993):
- -
[K (θ)-h ] = (S S + C (θ)) -h
w s -t
(1)
where K is the hydraulic conductivity, h is the hydraulic head [m], θ is the water
content[-
], Sw is the reduced water content [-
], Ss is the specific storage coefficient
[m-1], and C(θ) is a function called “specific moisture capacity” [m-1], defined as
C(θ) = -θ--Ï, and could be determined for different soil types using curve
fitting and laboratory experiments measuring the rate of infiltration of water into soil
column.
The Poisson equation provides a relationship between the self potential φ [V], which
naturally occurs among points of the soil surface owing to the presence of an electric field
produced by the motion of underground electrolytic fluids through porous systems, and the
charge density Je [Am-2]:
- -
[Ïă(Sw )- φ - Je] = 0
(2)
where Ïă is the electrical conductivity.
Combining the equations (1) and (2), we obtain the Richards – Poisson model:
(
|{ - -
[K (θ)-h ] = (SwSs + C (θ)) -h
- -
[Ïă(S )-φ + C-′Ïăsat-u] = 0-t
|( w K(θ)Sw
(3)
Once the spatial distributions of the hydraulic head (h) and the self potential signal (φ),
monitored during a pumping test, are known; once the electrical conductivity field of the
medium (Ïă) has been reconstructed through ERT tests, and once the infiltration parameters of
the soil have been measured, it’s possible to estimate the hydraulic conductivity and the
storage coefficient distributions by means of joint inversion of these data into the Richards -
Poisson model.
Hydraulic conductivity obtained by means of this joint inverse model was able to
reconstruct the drawdown measured in the boreholes, and this is a validation of the inversion
strategy.
References
Panday, S., Huyakorn, P., Therrien, R., Nichols, R., 1993. Improved three-dimensional
finite-element techniques for field simulation of variably saturated flow and transport. J.
Contam. Hydrol. 12, 3-33.
Richards, L. A., 1931. Capillary conduction of liquids through porous media. Physics 1,
318-333. |
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