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| Titel |
Nonlinear effects of locally heterogeneous hydraulic conductivity fields on regional stream–aquifer exchanges |
| VerfasserIn |
J. Zhu, C. L. Winter, Z. Wang |
| 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 ; 19, no. 11 ; Nr. 19, no. 11 (2015-11-12), S.4531-4545 |
| Datensatznummer |
250120849
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| Publikation (Nr.) |
 copernicus.org/hess-19-4531-2015.pdf |
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| Zusammenfassung |
| Computational experiments are performed to evaluate the effects of locally
heterogeneous conductivity fields on regional exchanges of water between
stream and aquifer systems in the Middle Heihe River basin (MHRB) of
northwestern China. The effects are found to be nonlinear in the sense that
simulated discharges from aquifers to streams are systematically lower than
discharges produced by a base model parameterized with relatively coarse
effective conductivity. A similar, but weaker, effect is observed for stream
leakage. The study is organized around three hypotheses: (H1) small-scale
spatial variations of conductivity significantly affect regional exchanges of
water between streams and aquifers in river basins, (H2) aggregating
small-scale heterogeneities into regional effective parameters systematically
biases estimates of stream–aquifer exchanges, and (H3) the biases result
from slow paths in groundwater flow that emerge due to small-scale
heterogeneities. The hypotheses are evaluated by comparing stream–aquifer
fluxes produced by the base model to fluxes simulated using realizations of
the MHRB characterized by local (grid-scale) heterogeneity. Levels of local
heterogeneity are manipulated as control variables by adjusting coefficients
of variation. All models are implemented using the
MODFLOW (Modular Three-dimensional Finite-difference Groundwater Flow Model) simulation
environment, and the PEST (parameter estimation) tool is used to calibrate effective conductivities defined over
16 zones within the MHRB. The effective parameters are also used as expected
values to develop lognormally distributed conductivity (K) fields on local
grid scales. Stream–aquifer exchanges are simulated with K fields at both
scales and then compared. Results show that the effects of small-scale
heterogeneities significantly influence exchanges with simulations based on
local-scale heterogeneities always producing discharges that are less than
those produced by the base model. Although aquifer heterogeneities are
uncorrelated at local scales, they appear to induce coherent slow paths in
groundwater fluxes that in turn reduce aquifer–stream exchanges. Since
surface water–groundwater exchanges are critical hydrologic processes in
basin-scale water budgets, these results also have implications for water
resources management. |
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