Abstract
Evaporation from desert sand dunes is studied practically using
laboratory columns and mathematically using both analytical and
numerical modeling. On outcropping cliffs of the dunes of Buwshar
(Oman), microstratification, with layers' thickness of 1-2 mm, was
observed. Loose sand and consolidated core samples were collected for
laboratory experiments. Imbibition into initially dry sand columns and
ensuing steady state evaporation from a capillary fringe above a
horizontal water table were studied. The evaporating, negative-pressure
topsoil of the columns was slanted mimicking the cliffs' tilt. In the
columns plugged by a thin composite "cap" made by tooling the dune
stratified clod, evaporation was impeded and reduced as compared with a
homogeneous column. The same outlet evaporating boundaries were
considered in HYDRUS-2D simulations, which showed that 2-D evaporation
from a homogenous column was significantly higher than that from the
column with a stratified "plug" at the top. Analytical solution for a
2-D tension-saturated homogeneous trapezium was obtained by conformal
mappings of pentagon in the physical plane onto a rectangle in the
Zhukovsky plain, via a reference plane. This solution combines the
versatility of the Toth model, where topology of flow is controlled by
an isobaric boundary of a flow tube, and of the Vedernikov model, which
assumes a constant hydraulic conductivity in the negative pressure zone
of a capillary fringe. Analytical formulae also manifest a decrease of
the flow rate with the increase of the angle of tilt of an evaporating
isobar.
Original language | English |
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Pages (from-to) | 2504-2520 |
Journal | Water Resources Research |
Volume | 55 |
Issue number | 3 |
DOIs | |
Publication status | Published - Mar 1 2019 |
Keywords
- capillary barrier
- dune hydrology
- evaporation
- HYDRUS modeling
- soil column experiment
- Vedernikov-Toth's model