Runout Distances Of Debris Flows Research Articles

Prediction of the run-out distance of the debris flow based on the velocity attenuation coefficient

Our aim is to determine the run-out distance of the debris flow that is crucial in the assessment, prevention and control of the debris flow hazard. Based on the variation characteristic of debris flow velocity in the alluvial fan, this paper proposes the calculation method of the velocity attenuation coefficient of the debris flow. By defining the velocity attenuation coefficient and deducing its calculating formula, this paper puts forward a new method to determine the run-out distance of the debris flow based on the velocity attenuation coefficient, and Gangou debris flow in Luding County, Sichuan Province is selected as a case for calculation and verification. Having 10 m as its measuring spacing, this paper measured 19 sections at the alluvial fan of the Gangou debris flow (among them, 11 sets of data are valid). And based on the measurement, this paper analyzes the characteristic of the velocity attenuation and calculates its velocity attenuation coefficient after the 2005 debris flow. The study indicates that when the velocity of Gangou debris flow at the alluvial fan is greater than 12 % of the initial velocity (at the mouth of gully), the attenuation is quite remarkable. But when the velocity at the alluvial fan is less than 12 % of the initial velocity, the attenuation is quite slow. Besides, when Gangou debris flow rushes out of the gully mouth (the initial velocity is 10 m/s) and when it attenuates to the 32 time, its velocity is less than 0.1 m/s, the debris flow is considered to stop flowing, and the run-out distance of Gangou debris flow is calculated to be 320 m. But the present alluvial fan of Gangou debris flow is measured to be 285 m in length, and the calculated run-out distance is 320 m, which is 35 m longer than its present length. This means when the debris flow runs out in 2005, it blocked up the main river (Dadu River) in some extent. And this finding is generally in accordance with that from the field survey. The findings can be of theoretical and practical significance in the debris flow hazard assessment, as well as its prevention and mitigation.

Characteristics of Runout Distance of Debris Flows in Korea

Characteristics of Runout Distance of Debris Flows in Korea

Field and laboratory investigations of runout distances of debris flows in the Dolomites (Eastern Italian Alps)

The estimation of runout distances on fans has a major role in assessing debris-flow hazards. Different methods have been devised for this purpose: volume balance, limiting topographic methods, empirical equations, and physical approaches. Data collected from field observations are the basis for developing, testing, and improving predictive methods, while laboratory tests on small-scale models are another suitable approach for studying debris-flow runout under controlled conditions and for developing predictive equations. This paper analyses the problem of assessing runout distance, focusing on six debris flows that were triggered on July 5th, 2006 by intense rainfall near Cortina d'Ampezzo (Dolomites, north-eastern Italy). Detailed field surveys were carried out immediately after the event in the triggering zone, along the channels, and in the deposition areas. A fine-scale digital terrain model of the study area was established by aerial LiDAR measurements. Total travel and runout distances on fans measured in the field were compared with the results of formulae from the literature (empirical/statistical and physically oriented), and samples of sediment collected from deposition lobes were used for laboratory tests. The experimental device employed in the tests consists of a tilting flume with an inclination from 0° to 38°, on which a steel tank with a removable gate was installed at variable distances from the outlet. A final horizontal plane works as the deposition area. Samples of different volumes and variable sediment concentrations were tested. Multiple regression analysis was used to assess the length of the deposits as a function of both the potential energy of the mass and the sediment concentration of the flow. Our comparison of the results of laboratory tests with field data suggests that an energy-based runout formula might predict the runout distances of debris flows in the Dolomites.

Calibration of numerical models for small debris flows in Yosemite Valley, California, USA

Abstract. This study compares documented debris flow runout distances with numerical simulations in the Yosemite Valley of California, USA, where about 15% of historical events of slope instability can be classified as debris flows and debris slides (Wieczorek and Snyder, 2004). To model debris flows in the Yosemite Valley, we selected six streams with evidence of historical debris flows; three of the debris flow deposits have single channels, and the other three split their pattern in the fan area into two or more channels. From field observations all of the debris flows involved coarse material, with only very small clay content. We applied the one dimensional DAN (Dynamic ANalysis) model (Hungr, 1995) and the two-dimensional FLO-2D model (O'Brien et al., 1993) to predict and compare the runout distance and the velocity of the debris flows observed in the study area. As a first step, we calibrated the parameters for the two softwares through the back analysis of three debris- flows channels using a trial-and-error procedure starting with values suggested in the literature. In the second step we applied the selected values to the other channels, in order to evaluate their predictive capabilities. After parameter calibration using three debris flows we obtained results similar to field observations We also obtained a good agreement between the two models for velocities. Both models are strongly influenced by topography: we used the 30 m cell size DTM available for the study area, that is probably not accurate enough for a highly detailed analysis, but it can be sufficient for a first screening.

Hazard assessment of debris flows for Leung King Estateof Hong Kong by incorporating GIS with numericalsimulations

Abstract. As over seventy percent of the land of Hong Kong is mountainous, rainfall-induced debris flows are not uncommon in Hong Kong. The objective of this study is to incorporate numerical simulations of debris flows with GIS to identify potential debris flow hazard areas. To illustrate this approach, the proposed methodology is applied to Leung King Estate in Tuen Mun. A Digital Elevation Model (DEM) of the terrain and the potential debris-flow sources were generated by using GIS to provide the required terrain and flow source data for the numerical simulations. A theoretical model by Takahashi et al. (1992) improved by incorporating a new erosion initiation criterion was used for simulating the runout distances of debris flows. The well-documented 1990 Tsing Shan debris flow, which occurred not too far from Leung King Estate, was used to calibrate most of the flow parameters needed for computer simulations. Based on the simulation results, a potential hazard zone was identified and presented by using GIS. Our proposed hazard map was thus determined by flow dynamics and a deposition mechanism through computer simulations without using any so- called expert opinions, which are bounded to be subjective and biased.

Regional-scale GIS-models for assessment of hazards from glacier lake outbursts: evaluation and application in the Swiss Alps

Abstract. Debris flows triggered by glacier lake outbursts have repeatedly caused disasters in various high-mountain regions of the world. Accelerated change of glacial and periglacial environments due to atmospheric warming and increased anthropogenic development in most of these areas raise the need for an adequate hazard assessment and corresponding modelling. The purpose of this paper is to pro-vide a modelling approach which takes into account the current evolution of the glacial environment and satisfies a robust first-order assessment of hazards from glacier-lake outbursts. Two topography-based GIS-models simulating debris flows related to outbursts from glacier lakes are presented and applied for two lake outburst events in the southern Swiss Alps. The models are based on information about glacier lakes derived from remote sensing data, and on digital elevation models (DEM). Hydrological flow routing is used to simulate the debris flow resulting from the lake outburst. Thereby, a multiple- and a single-flow-direction approach are applied. Debris-flow propagation is given in probability-related values indicating the hazard potential of a certain location. The debris flow runout distance is calculated on the basis of empirical data on average slope trajectory. The results show that the multiple-flow-direction approach generally yields a more detailed propagation. The single-flow-direction approach, however, is more robust against DEM artifacts and, hence, more suited for process automation. The model is tested with three differently generated DEMs (including aero-photogrammetry- and satellite image-derived). Potential application of the respective DEMs is discussed with a special focus on satellite-derived DEMs for use in remote high-mountain areas.

Debris flow characteristics and relationships in the Central Spanish Pyrenees

Abstract. Unconfined debris flows (i.e. not in incised channels) are one of the most active geomorphic processes in mountainous areas. Since they can threaten settlements and infrastructure, statistical and physically based procedures have been developed to assess the potential for landslide erosion. In this study, information on debris flow characteristics was obtained in the field to define the debris flow runout distance and to establish relationships between debris flow parameters. Such relationships are needed for building models which allow us to improve the spatial prediction of debris flow hazards. In general, unconfined debris flows triggered in the Flysch Sector of the Central Spanish Pyrenees are of the same order of magnitude as others reported in the literature. The deposition of sediment started at 17.8°, and the runout distance represented 60% of the difference in height between the head of the landslide and the point at which deposition started. The runout distance was relatively well correlated with the volume of sediment.

Remote sensing based assessment of hazards from glacier lake outbursts: a case study in the Swiss Alps

Glacier lakes are a common phenomenon in high mountain areas. Outbursts from glacier lakes have repeatedly caused the loss of human lives as well as severe damage to local infrastructure. In several high mountain ranges around the world, a grave uncertainty about the hazard potential of glacier lakes still exists, especially with respect to the effects of accelerating rates of glacier retreat as a consequence of atmospheric warming. Area-wide detection and modeling of glacier lake hazard potentials is, therefore, a major challenge. In this study, an approach integrating three scale levels allows for the progressive focus on critical glacier lakes. Remote sensing methods for application in glacier lake hazard assessment are presented, and include channel indexing, data fusion, and change detection. Each method matches the requirements of a certain scale level. For estimating potential disaster amplitudes, assessments must be made of maximum discharge and runout distance of outbursts floods and debris flows. Existing empirical relations are evaluated and complementary ones as derived from available data are proposed. Tests with observations from a recent outburst event from a moraine-dammed lake in the Swiss Alps show the basic applicability of the proposed techniques and the usefulness of empirical relations for first hazard assessments. In particular, the observed runout distance of the debris flow resulting from the outburst does not exceed the empirically estimated maximum runout distance. A list of decision criteria and related remote sensing techniques are discussed in conclusion. Such a list is an essential tool for evaluating the hazard potential of a lake. A systematic application of remote sensing based methods for glacier lake hazard assessment is recommended.Key words: glacier lake outburst, hazard potential, remote sensing, empirical parameters.

Debris Flow Run-Out and Landslide Sediment Delivery Model Tests

Five models are investigated for determining the percentage delivery of sediment to streams for shallow landslides that evolve into debris flows. Models I–III are based on debris flow run-out distance, Model IV on snow avalanche run-out distance. For these it is assumed that percentage delivery is 100% for slopes above 10° and zero for slopes below 4°. For intermediate slopes, delivery is based on the run-out distance estimate. Model V, derived from field data, estimates percentage delivery directly without the need for slope conditions. The model performances are investigated using 100 hypothetical hillslopes and a limited database on landslide sediment delivery in Idaho. Model IV performs best but Model I is a close second and its design (run-out distance varying with elevation drop) may be preferable for modeling purposes. Model II (run-out distance varying with debris flow slope and volume) provides a conservative upper limit on percentage delivery. Parallel use of models to provide bounds on the perc...

A Mass-Change Model for the Estimation of Debris-Flow Runout

We analyzed the runout potential of debris flows using a simple mathematical model based on the principle of conservation of momentum. This model is unique in that it evaluates the effect of a change in mass of a debris flow over the distance the flow travels. The model is used to examine the influence of viscous resistance alone, the paired influence of a change in mass of the flow with travel and viscous resistance, and finally, the combined effects of mass change, viscosity, friction, and slope angle on the longitudinal velocity distributions and runout distances of debris flows. Evaluations of the model with the combined influences of each of the variables indicate that a gain in mass by the flow with travel will result in longer total runout distances, and that the flow will maintain lower velocities over the distance traveled. A loss of mass with travel will result in shorter total runout distances, and the flow will maintain higher velocities over the distance traveled. Increasing slope angles allo...