 |
| Titel |
Measurements of the micro-scale water flow through snow using laser imaging techniques |
| VerfasserIn |
Benjamin Walter, Stefan Horender, Michael Lehning |
| Konferenz |
EGU General Assembly 2013
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250084758
|
|
|
|
|
|
| Zusammenfassung |
| Snow avalanches and flood events as a result of partially wet and melting snow cause
annually several accidents in the European Alps, demonstrating the need for a better
understanding of the formation of these events. Water flow in snow is typically a result
of snowmelt caused by strong solar irradiation or turbulent heat fluxes into the
snowpack, the latter often in combination with rain on snow. Previous studies mainly
quantified the total flow through snow for different snowpack layers neglecting
the micro-scale flow dynamics. A detailed description as a basis for quantitative
understanding, however, requires knowledge of the micro-scale water flow through
snow.
We present spatiotemporally highly resolved Fluorescent Particle Tracking Velocimetry
(FPTV) measurements of the water flow in the pore space of a wet snow sample. For these
first experiments, ice-cooled water seeded with fluorescent micron-sized tracer
particles of diameters of d = 20 – 50 μm was sprinkled on top of the snow sample
to produce saturated flow conditions. The snow sample was illuminated with a
green laser light sheet and the fluorescent light of the tracer particles was filmed
with a high-speed camera. The measurement window was 15 mm à 15 mm. After
processing the raw images, tracking algorithms were applied to obtain the particle
trajectories and velocities which are assumed to represent local water flow paths and flow
velocities.
Results for a gravity driven, downward flow, and for an upward flow driven by capillary
forces are presented. A flow loop found in a pore space in case of the gravity flow as well as
the high tortuosity of the trajectories show that the water flow in wet snow is highly
3-dimensional. The average vertical flow velocities in the pore spaces were -10.1 mm s-1 for
the downward gravity flow and +8.7 mm s-1 for the upward flow driven by capillary forces.
Velocity histograms show that the fraction of the total water flowing against the average flow
direction was about 3-5%, and that the horizontal velocities average to about zero for
both, the gravity and the capillary flow. The maximum flow acceleration for the
gravity flow was 2.1 m s-2 and stronger than the maximum deceleration whereas the
maximum deceleration for the capillary flow was -1.9 m s-2 and stronger than
the acceleration. Generally, FPTV measurements in snow open a wide range of
potential investigation to increase the fundamental knowledge on water flow through
snow, and may thus help to improve theories describing water flow rates in snow. |
|
|
|
|
|
|