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| Titel |
Shallow rainwater lenses in deltaic areas with saline seepage |
| VerfasserIn |
P. G. B. Louw, S. Eeman, B. Siemon, B. R. Voortman, J. Gunnink, E. S. Baaren, G. H. P. Oude Essink |
| 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 (2011-12-07), S.3659-3678 |
| Datensatznummer |
250013048
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| Publikation (Nr.) |
 copernicus.org/hess-15-3659-2011.pdf |
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| Zusammenfassung |
| In deltaic areas with saline seepage, freshwater availability is often
limited to shallow rainwater lenses lying on top of saline groundwater. Here
we describe the characteristics and spatial variability of such lenses in
areas with saline seepage and the mechanisms that control their occurrence
and size. Our findings are based on different types of field measurements
and detailed numerical groundwater models applied in the south-western delta
of the Netherlands. By combining the applied techniques we could extrapolate
measurements at point scale (groundwater sampling, temperature and
electrical soil conductivity (TEC)-probe measurements, electrical cone
penetration tests (ECPT)) to field scale (continuous vertical electrical
soundings (CVES), electromagnetic survey with EM31), and even to regional
scale using helicopter-borne electromagnetic measurements (HEM). The
measurements show a gradual mixing zone between infiltrating fresh rainwater
and upward flowing saline groundwater. The mixing zone is best characterized
by the depth of the centre of the mixing zone Dmix, where the salinity
is half that of seepage water, and the bottom of the mixing zone Bmix,
with a salinity equal to that of the seepage water (Cl-conc. 10 to 16 g l−1).
Dmix is found at very shallow depth in the confining top layer, on
average at 1.7 m below ground level (b.g.l.), while Bmix lies about 2.5 m b.g.l.
The model results show that the constantly alternating upward and
downward flow at low velocities in the confining layer is the main mechanism
of mixing between rainwater and saline seepage and determines the position
and extent of the mixing zone (Dmix and Bmix). Recharge, seepage
flux, and drainage depth are the controlling factors. |
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