Debris Flows at the River Mletis Khevi (Greater Caucasus Mountains, Georgia) and its Assessment Methods

The erosional debris flow processes on the right side of the riverbed of Mletis-Khevi, a tributary of the Tetri Aragvi, are assessed on the basis of field and laboratory studies. The values of the mountain slope erosion in the Mletis-Khevi catchment area have been determined on the basis of field studies, taking into account the time factor and the extent of slope damage. Dependences are derived by means of the maximum discharge of debris flow of various intensities. Furthermore the volume of transported debris flow mass is calculated. A physical-mechanical and chemical analysis of the debris flow mass has been carried out in the laboratory. The results can be used at a subsequent stage for predicting the various basic characteristics of debris flows. --debris flow,discharge,erosion coefficient,catchment area

Direct Detection of Dark Matter Debris Flows

Tidal stripping of dark matter from subhalos falling into the Milky Way produces narrow, cold tidal streams as well as more spatially extended "debris flows" in the form of shells, sheets, and plumes. Here we focus on the debris flow in the Via Lactea II simulation, and show that this incompletely phase-mixed material exhibits distinctive high velocity behavior. Unlike tidal streams, which may not necessarily intersect the Earth's location, debris flow is spatially uniform at 8 kpc and thus guaranteed to be present in the dark matter flux incident on direct detection experiments. At Earth-frame speeds greater than 450 km/s, debris flow comprises more than half of the dark matter at the Sun's location, and up to 80% at even higher speeds. Therefore, debris flow is most important for experiments that are particularly sensitive to the high speed tail of the dark matter distribution, such as searches for light or inelastic dark matter or experiments with directional sensitivity. We show that debris flow yields a distinctive recoil energy spectrum and a broadening of the distribution of incidence direction.Comment: 22 pages, 7 figures; accepted for publication in PR

Estimation of magnitudes of debris flows in selected torrential watersheds in Slovenia

In this paper the application of different methods for estimation of magnitudes of rainfall-induced debris flows in 18 torrents in the Upper Sava River valley, NW Slovenia, and in 2 torrents in Pohorje, N Slovenia is described. Additional verification of the methods was performed in the torrential watersheds with active debris flows in the recent past (Predelica and Brusnik in the Soca River basin, W Slovenia). For some of the methods, the knowledge of morphometric characteristics of a torrential watershed, torrential channel and torrential fan is enough. For other methods, a mathematical tool (HEC-HMS) had to be applied in order to develop a hydrologic run-off model of precipitation that can trigger debris flows. Computed debris-flow magnitudes were of the order between 6,500 m(3) and 340,000 m(3). Their values are a function of torrential watershed parameters, such as: watershed area, Melton number, fan gradient, and torrential channel gradient. The investigated fans were classified into 3 groups with regard to the debris-flow hazard: debris-flow fans (hazard exists), torrential fans (no hazard), and transitional fans (debris flows are possible, but with low possibility). A limit between debris-flow fans and torrential fans is proposed: Melton number 0.3 and torrential fan gradient 4 degrees, that is, 7%. Out of 24 investigated torrential fans, 13 fans were classified into the group of debris-flow fans, 5 fans were classified into the group of torrential fans, and the rest 6 fans were classified into the group of transitional fans

Comparison of measurement methods of the front velocity of small-scale debris flows

Debris flow is a gravity-driven process, which is characterized by a travelling dense surge including large boulders, and it is followed by a more fluid tail. These characteristics make difficult the measurement of the mean flow velocity by means of common hydraulic techniques. Different methods can be used at real scale and small-scale to measure the front velocity but a dedicate comparison between available methods is still lacking. This research aims to compare the front velocity measurements in the transport zone of a miniature debris flow using three devices: i) a common digital video camera (29 frames per second); ii) a high speed thermo camera (60 fps); and iii) a laser photoelectric sensors system. The statistical analysis of data has highlighted no significant differences exist between front velocities obtained by means of the video camera and the thermo camera, whereas photocells data statistically differ from those achieved via the other systems. Some lack of data recorded by photocell was documented, while the thermo camera technique did not show significant loss of information being also helpful to detect the kinematic behaviour of single particles. Finally, the tests confirmed the influence of the solid volumetric concentration in the debris-flow mechanics, which promotes, ceteris paribus, the debris-flow slowing down

Atmospheric circulation patterns, cloud-to-ground lightning, and locally intense convective rainfall associated with debris flow initiation in the Dolomite Alps of northeastern Italy

The Dolomite Alps of northeastern Italy experience debris flows with great frequency during the summer months. An ample supply of unconsolidated material on steep slopes and a summer season climate regime characterized by recurrent thunderstorms combine to produce an abundance of these destructive hydro-geologic events. In the past, debris flow events have been studied primarily in the context of their geologic and geomorphic characteristics. The atmospheric contribution to these mass-wasting events has been limited to recording rainfall and developing intensity thresholds for debris mobilization. This study aims to expand the examination of atmospheric processes that preceded both locally intense convective rainfall (LICR) and debris flows in the Dolomite region. 500 hPa pressure level plots of geopotential heights were constructed for a period of 3 days prior to debris flow events to gain insight into the synoptic-scale processes which provide an environment conducive to LICR in the Dolomites. Cloud-to-ground (CG) lightning flash data recorded at the meso-scale were incorporated to assess the convective environment proximal to debris flow source regions. Twelve events were analyzed and from this analysis three common synoptic-scale circulation patterns were identified. Evaluation of CG flashes at smaller spatial and temporal scales illustrated that convective processes vary in their production of CF flashes (total number) and the spatial distribution of flashes can also be quite different between events over longer periods. During the 60 min interval immediately preceding debris flow a majority of cases exhibited spatial and temporal colocation of LICR and CG flashes. Also a number of CG flash parameters were found to be significantly correlated to rainfall intensity prior to debris flow initiation

Numerical Simulation of Non-Homogeneous Viscous Debris-Flows Based on the Smoothed Particle Hydrodynamics (SPH) Method

Non-homogeneous viscous debris flows are characterized by high density, impact force and destructiveness, and the complexity of the materials they are made of. This has always made these flows challenging to simulate numerically, and to reproduce experimentally debris flow processes. In this study, the formation-movement process of non-homogeneous debris flow under three different soil configurations was simulated numerically by modifying the formulation of collision, friction, and yield stresses for the existing Smoothed Particle Hydrodynamics (SPH) method. The results obtained by applying this modification to the SPH model clearly demonstrated that the configuration where fine and coarse particles are fully mixed, with no specific layering, produces more fluctuations and instability of the debris flow. The kinetic and potential energies of the fluctuating particles calculated for each scenario have been shown to be affected by the water content by focusing on small local areas. Therefore, this study provides a better understanding and new insights regarding intermittent debris flows, and explains the impact of the water content on their formation and movement processes

RRS Charles Darwin Cruise 126, 11 Mar-20 Mar 2001. Piston coring of debris flows and turbidites west and south of the Canary Islands

The major cruise objective was to obtain sediment cores at various locations to the west and southwest of the Canary Islands with the aims of :· Sampling debris flow sediments in the Canary and Saharan debris flows· Obtaining dateable sediments immediately above and below the debris flow sediments· Sampling turbidite sediments associated with the debris flows· Sampling sediments on either flank of a sediment wave west of La PalmaIn addition, it was planned to:· obtain seabed video footage, using the SHRIMP towed camera station, at several localities where downslope sediment transport was believed to be active at the present day, and undertake some test deployments of the SOC Scatterometer syste

Delineation of risk area in Log pod Mangartom due to debris flows from the Stoze landslide

The paper shows in detail the case of delineation of risk area in the village of Log pod Mangartom in the Koritnica River valley due to possible debris flows that might in future be triggered on the Stoze slope above the Mangart Mountain pasture. On the basis of field and laboratory investigations of the debris flow of November 17, 2000, that devastated the Koritnica River valley, the possible scenarios of triggering new debris flows on the Stoze slope were investigated. For the determination of debris flow hazard area in the Koritnica River valley, the results of one- and two-dimensional modelling of selected debris flows of known magnitudes and different viscosities were applied. For the determination of risk area, the existing and the possible new infrastructures were taken into account, and the risk area was divided into 3 zones. The paper presents the expert bases summarised by the legislator in the relevant decree issued by the Government of the Republic of Slovenia on the conditions and limitations governing the construction in the debris-flow risk area of Log pod Mangartom. This regulation is the first of its kind in Slovenia