117,362 research outputs found
Numerical simulation of real debris-flows events
Full text linkA one-dimensional model is presented to
predict debris-flow runouts. The model is based on shallow
water type assumptions. The fluid is assumed to be
homogeneous and the original bed of the flow domain to be
unerodible. The fluid is characterized by a rheology of
Bingham type.
A numerical tool able to cope with the nature of debris
flows has been worked out. It represents an extension of a
second order accurate and conservative method of
Godunov type. Special care has been devoted to the
influence of the source terms and of the geometrical
representation of the natural cross sections, which play a
fundamental role.
The application concerns a monitored event in the
Dolomites in Italy, where field analyses allowed a
characterization of the behavior of solid-liquid mixture as a
yield stress material. The comparison between numerical
simulations and field observations highlights the
impossibility of representing all phases of the flow with
constant values of the rheological parameters. Nevertheless
the results show that it is possible to separately represent
the phase of the flow in the upstream reach and the phase of
the deposition in the alluvial fan, with a good agreement
with field observations
Controls Over Particle Motion and Resting Times of Coarse Bed Load Transport in a Glacier-Fed Mountain Stream
Full text linkCoarse bed load transport is a crucial process in river morphodynamics but is difficult to monitor in mountain streams. Here we present a new sediment transport data set obtained from 2 years of field-based monitoring (2014–2015) at the Estero Morales, a high-gradient stream in the central Chilean Andes. This stream features step-pool bed geometry and a glacier-fed hydrologic regime characterized by abrupt daily fluctuations in discharge. Bed load was monitored directly using Bunte samplers and by surveying the mobility of passive integrated transponder (PIT) tags. We used the competence method to quantify the effective slope, which is the fraction of the topographical slope responsible for bed load transport. This accounts for only 10% of the topographical slope, confirming that most of the energy is dissipated on macroroughness elements. We used the displacement lengths of PIT tags to analyze displacement lengths and virtual velocity of a wide range of tracer sizes (38–415 mm). Bed load transport in the Estero Morales shown to be size-selective, and the distance between steps influences the displacement lengths of PIT tags. Displacement lengths were also used to derive the statistics of flight distances and resting times. Our results show that the average length of flight scales inversely to grain size. This contradicts Einstein's conjecture about the linear relationship between grain size and intervals between resting periods in a steep step-pool stream in ordinary flood conditions
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