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| Titel |
Influence of initial heterogeneities and recharge limitations on the evolution of aperture distributions in carbonate aquifers |
| VerfasserIn |
B. Hubinger, S. Birk |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 15, no. 12 ; Nr. 15, no. 12 (2011-12-14), S.3715-3729 |
| Datensatznummer |
250013052
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| Publikation (Nr.) |
 copernicus.org/hess-15-3715-2011.pdf |
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| Zusammenfassung |
| Karst aquifers evolve where the dissolution of soluble rocks causes the
enlargement of discrete pathways along fractures or bedding planes, thus
creating highly conductive solution conduits. To identify general
interrelations between hydrogeological conditions and the properties of the
evolving conduit systems the aperture-size frequency distributions resulting
from generic models of conduit evolution are analysed. For this purpose, a
process-based numerical model coupling flow and rock dissolution is employed.
Initial protoconduits are represented by tubes with log-normally distributed
aperture sizes with a mean μ0 = 0.5 mm for the logarithm of
the diameters. Apertures are spatially
uncorrelated and widen up to the metre range due to dissolution by chemically
aggressive waters. Several examples of conduit development are examined
focussing on influences of the initial heterogeneity and the available amount
of recharge. If the available recharge is sufficiently high the evolving
conduits compete for flow and those with large apertures and high hydraulic
gradients attract more and more water. As a consequence, the positive
feedback between increasing flow and dissolution causes the breakthrough of a
conduit pathway connecting the recharge and discharge sides of the modelling
domain. Under these competitive flow conditions dynamically stable bimodal
aperture distributions are found to evolve, i.e. a certain percentage of
tubes continues to be enlarged while the remaining tubes stay small-sized.
The percentage of strongly widened tubes is found to be independent of the
breakthrough time and decreases with increasing heterogeneity of the initial
apertures and decreasing amount of available water. If the competition for
flow is suppressed because the availability of water is strongly limited
breakthrough of a conduit pathway is inhibited and the conduit pathways widen
very slowly. The resulting aperture distributions are found to be unimodal
covering some orders of magnitudes in size. Under these suppressed flow
conditions the entire range of apertures continues to be enlarged. Hence, the
number of tubes reaching aperture sizes in the order of centimetres or
decimetres continues to increase with time and in the long term may exceed
the number of large-sized tubes evolving under competitive flow conditions.
This suggests that conduit development under suppressed flow conditions may
significantly enhance the permeability of the formation, e.g. in deep-seated
carbonate settings. |
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