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| Titel |
Response to recharge variation of thin rainwater lenses and their mixing zone with underlying saline groundwater |
| VerfasserIn |
S. Eeman, S. E. A. T. M. Zee, A. Leijnse, P. G. B. Louw, C. Maas |
| 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 ; 16, no. 10 ; Nr. 16, no. 10 (2012-10-09), S.3535-3549 |
| Datensatznummer |
250013512
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| Publikation (Nr.) |
 copernicus.org/hess-16-3535-2012.pdf |
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| Zusammenfassung |
| In coastal zones with saline groundwater, fresh groundwater lenses may form
due to infiltration of rain water. The thickness of both the lens and the
mixing zone, determines fresh water availability for plant growth. Due to
recharge variation, the thickness of the lens and the mixing zone are not
constant, which may adversely affect agricultural and natural vegetation if
saline water reaches the root zone during the growing season. In this paper,
we study the response of thin lenses and their mixing zone to variation of
recharge. The recharge is varied using sinusoids with a range of amplitudes
and frequencies. We vary lens characteristics by varying the Rayleigh number
and Mass flux ratio of saline and fresh water, as these dominantly influence
the thickness of thin lenses and their mixing zone. Numerical results show a
linear relation between the normalised lens volume and the main lens and
recharge characteristics, enabling an empirical approximation of the
variation of lens thickness. Increase of the recharge amplitude causes
increase and the increase of recharge frequency causes a decrease in the
variation of lens thickness. The average lens thickness is not significantly
influenced by these variations in recharge, contrary to the mixing zone
thickness. The mixing zone thickness is compared to that of a Fickian mixing
regime. A simple relation between the travelled distance of the centre of
the mixing zone position due to variations in recharge and the mixing zone
thickness is shown to be valid for both a sinusoidal recharge variation and
actual records of daily recharge data. Starting from a step response
function, convolution can be used to determine the effect of variable
recharge in time. For a sinusoidal curve, we can determine delay of lens
movement compared to the recharge curve as well as the lens amplitude,
derived from the convolution integral. Together the proposed equations
provide us with a first order approximation of lens characteristics using
basic lens and recharge parameters without the use of numerical models. This
enables the assessment of the vulnerability of any thin fresh water lens on
saline, upward seeping groundwater to salinity stress in the root zone. |
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