 |
| Titel |
Onset of perched water in a gradually layered soil: a laboratory experiment |
| VerfasserIn |
S. Barontini, G. Belluardo, B. Bacchi, R. Ranzi |
| Konferenz |
EGU General Assembly 2009
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250028360
|
|
|
|
|
|
| Zusammenfassung |
| The genetic layering of the soil hydrological properties can significanly affect a number of
processes as the onset of soil–slips, the runoff production and those related to the interaction
between soil, water, plants and atmosphere. Therefore, with the aim of better understanding
some aspects of these processes, we focused on the effect, during an imbibition process, of
the decrease of the soil hydraulic conductivity at saturation Ks. A laboratory experiment was
setup in order to observe the conditions and dynamics of the onset of a perched water in a
gradually layered soil. A prismatic column was realised and filled with 9 different soil strata,
each 0.1 m deep, whose grain–size distribution curve and porosity were such as to
reproduce an exponential decay of Ks, on the basis of the application of a modified
Kozeny–Carman relatioship. The so–rebuilt soil was artificially wetted by means of a rainfall
simulator at a rate previously determined in order to maintain a constant water
content on the surface for 9 hours. Istantaneous volumetric water content profiles
were measured along the soil profile by means of 9 TDR probes and a multiplexer
device.
As a result of the experiment we observed and documented the formation of a water
content peak at about 0.15 m depth, about 1.5 h after the beginning of the imbibition process.
Then the peak emphasised and moved downward and a perched water formed at an
intermediate height in the column, about 6 h after the beginning of the experiment.
By this experiment we could then verify the formation of a water content peak,
as predicted by a previously developed theoretical model and by a finite volume
numerical simulation. The peak is then enveloped reaching the saturation as the wetting
front moves downward. The perched water depth then rapidly increased upward
while the wetting front slowly travelled downward. Before the transition toward
saturation, the experiment supported the phoenomenological aspects enlightened by
the analytical solution, although the adopted Gardner’s constitutive laws tend to
overestimate the unsaturated conductivity for most of the soils. A quantitative good
agreement was observed between the experimental data and the numerical simulations. |
|
|
|
|
|
|