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Topic 7 - Case Studies of Debris Flows

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Topic 7 - Case Studies of Debris Flows
This paper deals with the flow-like mass movements which occurred on 15-16 December 1999 in Cervinara (Southern Italy). During this event, a huge amount of water, debris and boulders was transported from the hillslopes towards the piedmont areas causing victims, damage to buildings as well as the flooding of a large part of the urban area of the municipality. In this paper, a study is carried out with reference to the modelling of the propagation stage of the occurred phenomena which has yet to be satisfact
Topic 7 - Case Studies of Debris Flows
The Quebrada del Toro is the valley of Río Toro, located southwest of Salta City, in northwestern Argentina. During the summer months, in the catchment of its tributaries, debris flows occur with relative frequency. Such processes of mass transport bring important volumes of materials inside of the main collector (Río Toro) and its alluvial plain, and they produce the narrowing, or sometimes the occlusion (landslide dam) of the main riverbed. These processes frequently occur, for example, in the Río Cand
Topic 7 - Case Studies of Debris Flows
As with other compound disasters caused by climate change, the occurrence probabilities of landslide dams and their secondary disasters have increased and became a serious issue after the 2009 Morakot typhoon in Taiwan. This paper describes the mechanism of the landslide dam formation. Different types of landslide dams are classified by their danger level. This study also describes the inducements behind earthquakelandslide- triggered and typhoon-triggered landslide dams and compared their differences. Fina
Topic 7 - Case Studies of Debris Flows
The purpose of this study, which is currently underway, is the analysis of debris flows from the lithology of the bedrocks (source rocks) that gives rise to the loose material, through the triggering process, to the routing and deposition phases. In particular three methods of analysis have been linked: a geological model, a triggering model that couples the results of a distributed kinematic hydrological model with a critical discharge relationship and a numerical model based on Cellular Automata for the s
Topic 7 - Case Studies of Debris Flows
The upper reaches of Changjiang River are the most serious regions of debris flow disasters. Nearly 50 counties and cities as well as hundreds of towns are under menaces of 6 800 gullies of debris flow. Every year debris flow claims deaths of tens to hundred and causes economic loss amounting to 120-180 million US dollars, which has lagged and limited the development in the areas. Debris flow gullies are widely distributed in the Upper Changjiang, which stretches eastwards across two geomorphologic transiti
Topic 7 - Case Studies of Debris Flows
Typhoon Morakot was “born” on August 4, 2009 at approximately 22.4° N and 133.8° E in the North Pacific Ocean, about 1,000 km far from northeastern Philippines, moving west at a speed of 10-30 km/hr towards Taiwan, landing on Hualien, eastern Taiwan on August 7, and then moving across over northwestern Taiwan on August 8 with a wind speed up to 40 m/s. Unexpectedly, Typhoon Morakot brought severe rainfalls and caused catastrophic disasters, such as a large number of debris flows, shallow landslides, d
Topic 7 - Case Studies of Debris Flows
Steep, recently burned watersheds can be vulnerable to debris flows. In southern California, USA, the combination of mountainous terrain, dense population, and high fire frequency put new areas at risk to debris flows each year. In an effort to improve predictions of the timing and magnitude of post-fire debris flows, the U.S. Geological Survey (USGS) established five debris-flow monitoring sites in different southern California watersheds burned in 2009. These sites recorded, for the first time, detailed m
Topic 7 - Case Studies of Debris Flows
Typhoon Morakot struck southern Taiwan on August, 8, 2009 with high rainfall intensity and accumulated rainfall as high as 2860 mm for 72 hours. Severe landslides and debris flow hazards were induced. The debris flow cases resulted in severe impacts to local communities were selected for case study, for which field investigation and analysis were conducted. Most severe landslide and debris flow cases originated from the rainfall center, which is Alishan mountain, and distributed with decreasing elevation. T
Topic 7 - Case Studies of Debris Flows
A torrential rainstorm on June 1, 2005 in Meigu county of Sichuan province, SW China, resulted in the generation of debris flows from two drainage basins. Map (1:50000 scale) of topography and depositing materials, coupled with the data from meteorological station and field investigation, are used to evaluate the geomorphology and hazard characteristics of debris flows. The return period of debris flows is 20 years and its magnitude is small-moderate scale. Rainstorm and hail with short duration and high in
Topic 7 - Case Studies of Debris Flows
Debris flows initiated by surface-water runoff during short duration, moderate- to high-intensity rainfall are common in steep, rocky, and sparsely vegetated terrain. Yet large uncertainties remain about the potential for a flow to grow through entrainment of loose debris, which make formulation of accurate mechanical models of debris-flow routing difficult. Using a combination of in situ measurements of debris-flow dynamics, video imagery, tracer rocks implanted with passive integrated transponders (PIT) a
Topic 7 - Case Studies of Debris Flows
In this paper, we examine the debris flows which occurred in the mountain rivers in Hofu City, Japan on July 21, 2009. We estimate velocity and discharge of the debris flows in the rivers at Manao and Ishihara districts from field survey and numerical simulation. The numerical simulation indicates that the peak discharge is 181 m3/s in the river at Manao district and 258 m3/s in the river at Ishihara district. It is found that sediment yield volume by riverside erosion is larger than landslide sediment volu
Topic 7 - Case Studies of Debris Flows
Debris flows often cause substantial losses to human life and the economy. The amount of damage can be effectively reduced using numerical simulation models, which can describe the debris-flow process and determine the possible effects of sabo dams or erosion and sediment control dams. Although various models have been developed, many existing debris-flow numerical simulations do not have efficient graphical user interfaces (GUIs). In addition, actual debris flows are composed of mixed grain-size sediment,
Topic 7 - Case Studies of Debris Flows
This is Part I of a two-part causation analysis of the January 10, 2005 La Conchita, California, USA landslide. This paper describes the geology and geomorphology of the event, which killed 10 persons and damaged or destroyed 36 residences. The landslide is located in a complex and active tectonic setting. It was triggered by two weeks of heavy rainfall, which initiated a failure in the backscarp of a large slump that had occurred ten years earlier. The 2005 landslide displaced older landslide deposits deri
Topic 7 - Case Studies of Debris Flows
This is Part II of a two-part causation analysis of the January 10, 2005 La Conchita landslide. This paper describes the development and application of a twodimensional finite difference model (FLO-2D) model to simulate the debris flow over a fixed substrate. The model domain consisted of 25,614 square grid cells, each measuring 1.52 m on a side, and was developed using digitized pre- and post-event topographic maps. An inflow hydrograph, representing the volume of displaced material, was specified as a lin
Topic 7 - Case Studies of Debris Flows
High resolution topographic data that quantify changes in channel form caused by sequential debris flows in natural channels are rare at the reach scale. Terrestrial laser scanning (TLS) techniques are utilized to capture morphological changes brought about by a high-frequency of debris-flow events at Chalk Cliffs, Colorado. The purpose of this paper is to compare and contrast the topographic response of a natural channel to the documented debris-flow events. TLS survey data allowed for the generation of hi
Topic 7 - Case Studies of Debris Flows
Numerous landslide that provided abundant material for the mobilization of debris flows were triggered in the Mozi gully on the right bank of Mingjiang River in response to the M8.0 Wenchuan earthquake of May 12, 2008. Following the earthquake, debris flows occurred during July through September of 2008 and again in September of 2009. Five of these events blocked the Mingjiang River. This paper estimates the volume of landslide material contributed to the valley by comparing remote sensing images before and
Topic 7 - Case Studies of Debris Flows
The Manival near Grenoble (French Prealps) is a very active debris-flow torrent equipped with a large sediment trap (25 000 m3) protecting an urbanized alluvial fan from debris-flows. We began monitoring the sediment budget of the catchment controlled by the trap in Spring 2009. Terrestrial laser scanner is used for monitoring topographic changes in a small gully, the main channel, and the sediment trap. In the main channel, 39 cross-sections are surveyed after every event. Three periods of intense geomorph
Topic 7 - Case Studies of Debris Flows
Better knowledge of the movement mode of fluidized landslide masses, which cause severe damage over wide areas, is very important for preventing sedimentrelated disasters. We analyzed a population of longtraveling landslides in Japan in terms of their travel coefficient and the conditions of the landslide mass, defining the ratio of travel distance (L2) to the original length of a landslide mass (L1) as the travel coefficient (Tr = L2/L1). After classifying long-traveling landslides by movement mode into fu
Topic 7 - Case Studies of Debris Flows
Clarifying geomorphic changes to landslide dams following overtopping is important for mitigation of future disasters. Past modelling experiments have not provided adequate information about geomorphic and grain size distribution changes at landslide dams. We used field survey data, aerial photographs, and LiDAR imagery to analyze the geomorphic changes of a landslide dam formed during the 2008 Iwate and Miyagi inland earthquake and the effect of subsequent overtopping erosion on the dam morphology and grai
Topic 7 - Case Studies of Debris Flows
The Weigou Gully, a branch of Pingtong River, is located in Guixi Township, Beichuan County. The area was seriously affected by the Wenchuan earthquake and its aftermath. Debris flows occurred on September 24, 2008, July 14, 2009, and September 10, 2009, threatening the safety of the inhabitants and their property. Debris flows in Weigou Gully were mainly supplied by landslides triggered by the earthquake. The debris flows had characteristics of high frequency, high bulk density and coarse particle size. Fo
Topic 7 - Case Studies of Debris Flows
The negative impact of debris flow processes on vital facilities is expected to increase as a result of the forecasted degradation of mountain glaciation, related to the changes in the climate. In the Caucasus region of Russia, where debris flows stand out for the frequency of occurrence in space, time and the power of their energetic manifestation and are mostly of glacial origin, that follows from the analysis of the developing situation, which relies on the knowledge of facts of the last 30 years (events
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