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| Titel |
On the validity of modeling concepts for the simulation of groundwater flow in lowland peat areas – case study at the Zegveld experimental field |
| VerfasserIn |
P. Trambauer, J. Nonner, J. Heijkers, S. Uhlenbrook |
| 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. 9 ; Nr. 15, no. 9 (2011-09-28), S.3017-3031 |
| Datensatznummer |
250012968
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| Publikation (Nr.) |
 copernicus.org/hess-15-3017-2011.pdf |
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| Zusammenfassung |
The groundwater flow models currently used in the western part of The
Netherlands and in other similar peaty areas are thought to be a too
simplified representation of the hydrological reality. One of the reasons is
that, due to the schematization of the subsoil, its heterogeneity cannot be
represented adequately. Moreover, the applicability of Darcy's law in these
types of soils has been questioned, but this law forms the basis of most
groundwater flow models.
With the purpose of assessing the typical heterogeneity of the subsoil and
to verify the applicability of Darcy's law, geo-hydrological fieldwork was
completed at an experimental field within a research area in the western
part of The Netherlands. The assessments were carried out for the so-called
Complex Confining Layer (CCL), which is the Holocene peaty to clayey layer
overlying Pleistocene sandy deposits. Borehole drilling through the CCL with
a hand auger was completed and revealed the typical heterogeneous character
of this layer, showing a dominance of muddy, humified peat which is
alternated with fresher peat and clay.
Slug tests were carried out to study the applicability of Darcy's law, given
that previous studies suggested its non-validity for humified peat soils
due to a variable horizontal hydraulic conductivity Kh with head
differences. For higher humification degrees, the experiments indeed
suggested a variable Kh, but this appeared to be the result of the
inappropriate use of steady-state formulae for transient experiments in
peaty environments. The muddy peat sampled has a rather plastic nature, and
the high compressibility of this material leads to transient behavior.
However, using transient formulae, the slug tests conducted for different
initial groundwater heads showed that there was hardly any evidence of a
variation of the hydraulic conductivity with the applied head differences.
Therefore, Darcy's law can be used for typical peat soils present in The
Netherlands.
The heterogeneity of the subsoil and the apparent applicability of Darcy's
law were taken into account for the detailed heterogeneous model that was
prepared for the research area. A MODFLOW model consisting of 13 layers in
which 4 layers represent the heterogeneous CCL was set up for an average
year, assuming steady-state conditions; and for the winter of 2009 to 2010,
adopting transient conditions. The transient model was extended to simulate
for longer periods with the objective of visualizing the flow paths through
the CCL. The results from these models were compared with a 10 layer model,
whereby the CCL is represented by a single layer assuming homogeneity. From
the comparison of the two model types, the conclusion could be drawn that a
single layer schematization of the CCL produces flowpath patterns which are
not the same but still quite similar to a 4 layer representation of the CCL.
However, the single layer schematization results in a considerable
underestimation of the flow velocity, and subsequently a longer travel time,
through the CCL. Therefore, a single layer model of the CCL seems quite
appropriate to represent the general flow behavior of the shallow
groundwater system, but would be inappropriate for transport modeling
through the CCL. |
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