Magnitude Of Debris Flows Research Articles

A debris flow calendar derived from sediments of lake Lago di Braies (N. Italy)

In this study lake sediments were used for developing a high resolution calendar of past debris flow events. Debris flows frequently occur in the high-alpine catchment of the lake Lago di Braies (N. Italy). While the coarse grained material accumulates on the debris flow cones, the fine grained material is flushed into the lake. This material forms characteristic layers in the lake sediments, which are different from the typical annual lamination. By analysing thin sections of sediment, debris flow events of the last 2250 years were reconstructed with an annual resolution. Since debris flow frequency varies strongly, periods with high and low frequencies can be distinguished. However, neither a debris flow magnitude–frequency relationship nor a strong reaction of debris flow activity to past climate changes was identifiable in this study.

Stereophotogrammetry of archive data and topographic approaches to debris‐flow torrent measurements: calculation of channel‐sediment states and a partial sediment budget for Manival torrent (Isère, France)

AbstractThis paper focuses on a topographic methodology to characterize the amount of sediment stored in channels and the use of historical photographs for aerial survey by stereophotogrammetry, as part of wider research on debris‐flow magnitude prediction. The topographic methodology uses equidistant four‐point cross‐sections along the long profile of the channel. Each cross‐section is representative of a 50‐m reach of the channel. To calculate the volume of each reach, the difference is calculated between a reference level and the topographic surface. The reference level is the lowest level where the debris flow can erode, and in the current method this level is estimated from fixed points along the long profile of the channel. The accuracy of the method has been estimated by comparing results of a detailed topographic survey, with a standard deviation corresponding to about 6 per cent of the total calculated sediment volume.This topographic methodology has been used on aerial photographs by photogrammetry. This tool was applied to photographs taken on 12 past dates. The scales of the archive photographs used range from 1:3000 to 1:30 000, but results are consistent and permit us to calculate sediment states of the channel for different past dates with an uncertainty of about 6 per cent of the total volume. The application of the technique to the Manival debris‐flow torrent has permitted us to propose some partial sediment budgets and erosion‐rate estimates. Copyright © 2006 John Wiley & Sons, Ltd.

Kuskonook Creek, an example of a debris flow analysis

Two debris flows occurred on Kuskonook Creek in British Columbia, Canada, in August and September 2004. The initiation factors included a major forest fire in the catchment in 2003, in association with relatively small rainfall events and the accumulation of sediment in the creek channels since the last large debris flow event. Previous regional studies and morphometric comparisons with other similar catchments indicate that Kuskonook Creek has characteristics predisposed to debris flows, even without the affects of a forest fire. Based on the investigations and analyses, a magnitude/frequency relationship for future debris events on Kuskonook Creek was developed, and this information was used to carry out a partial risk assessment. It is suggested that for design purposes, a 1/50-year return period and the corresponding debris flow magnitude of 15,000 m3 would provide conservative protection to the users of the provincial highway at the mouth of the creek.

Debris flow erosion and deposition in Jiangjia Gully, Yunnan, China

The erosion and deposition of debris flows at Jiangjia Gully in Dongchuan section of Yunnan province, southwestern China, was surveyed at 12 cross sections from 1999 to 2003. Deposition occurred in most sections because of the low debris-flow magnitude. The result was an increase in their elevations except for two sections at D17 and D19, where the channel was diverted in September 1999. As the annual sediment discharge of debris flow increased, the deposited volume decreased in the upper channel and increased in the lower channel. In each debris flow event, the erosion or deposition at the upper and the lower channel were different, but the eroded/deposited volume and the trend of erosion or deposition were similar between the neighboring sections. The average elevation change of all cross sections between consecutive surveys can reasonably represent the debris flow influence on the channel. Its relationship with the total sediment discharge between two surveys follows a three-stage pattern: when debris flow magnitude is small, deposition in the channel increases with the magnitude. When the magnitude reaches a certain level, the deposition begins to decrease and eventually erosion takes place. In three typical cross sections which had similar channel width, the debris flow showed a clear trend that the deposited volume decreased, while the eroded volume increased as the discharge of debris flow sediments increased.

A size classification for debris flows

A 10-fold classification for debris flow size is proposed based on total volume, peak discharge and area inundated by debris. Size classes can be used for regional overview studies where detailed site investigations are either unnecessary, too costly or where the highest hazard and risk creeks need to be identified for further study. They are also useful to compare the regional impact between affected areas and the effects of rainstorms, and they allow lay-people to obtain an understanding of debris flow magnitude and consequences. Finally, different size classes allow the estimation of travel times to points of interest based on empirically derived equations. It is proposed that agencies concerned with debris flows should establish a documentation of debris flow size according to this classification, which serves as a data base for hazard and risk planning.

Estimation of debris‐flow magnitude in the Eastern Italian Alps

AbstractThe estimation of debris‐flow magnitude is an essential step in the assessment of debris‐flow hazard. Although different methods have been developed for the assessment of debris‐flow magnitude, this is still a difficult task because of the complexity of flow processes and the lack of data to test estimation procedures in many mountainous regions. Data on debris‐flow magnitude from 127 basins in the Eastern Italian Alps have been collected from scientific and technical journals, technical reports, historical documents gathered from local archives, and field surveys. These data were used to develop and test different predictive approaches, encompassing regression equations, geomorphological surveys and probabilistic analysis of time series. Regression techniques were used to correlate debris‐flow magnitude to morphometric parameters and geological characteristics of the basins. Values of the channel debris yield rate (contribution per unit length of channel), proposed in the literature, were compared with data from the study area for identifying reference values for channel stretches of different morphological characteristics. Although limited to the few basins in which sufficient data were available, the probabilistic analysis of time series of debris‐flow magnitude provides indications about the relations between magnitude and frequency of debris flows. Some observations about the capability and drawbacks of considered methods are presented and the combined use of different approaches for the estimation of debris‐flow magnitude is suggested. Copyright © 2004 John Wiley & Sons, Ltd.

Comparison of Two Empirical Models for Gully-Specific Debris Flow Hazard Assessment in Xiaojiang Valley of Southwestern China

Two sets of empirical models for debris flow hazard assessment on gully-specific scale are presented herein, which may be the first step toward developing a formalized procedure for debris flow hazard assessment. Emphasis is put on comparison of the two models between Multiple Factor Composite Assessment Model (MFCAM) and Multivariate Stepwise Regression Assessment Model (MSRAM). From the aspects of data acquisition and model construct, this paper shows the advantages and limitations of two models. From the assessment results, two models are still of uncertainty. Fundamental researches of debris flow hazard, especially the relationship between debris flow magnitude and its frequency of occurrence should be given a priority in future study.

Debris-fan reworking during low-magnitude floods in the Green River canyons of the eastern Uinta Mountains, Colorado and Utah

The magnitude and frequency of tributary debris flows and the historical range of main- stem river discharges are the main factors that create and modify rapids in the Colorado River system. Monitoring of two recently aggraded debris fans in the Green River canyons of the eastern Uinta Mountains shows that main-stem floods with magnitudes between 40% and 75% of the predam 2 yr flood cause significant reworking of fan deposits. Cutbanks formed at fan margins during both small and large flows, indicating that lateral bank erosion is an important reworking mechanism. Armoring of the debris-fan surface limited the degree of reworking by successive floods, even when subsequent flood magnitudes were similar to those that caused significant reworking. Peak discharges increased the width of the reworked zone, decreased fan constrictions, and lowered the water-surface elevation of the ponded backwater. Contrary to predam geomorphic evidence, monitoring indicated that eroded material from recently aggraded debris fans was deposited in bars adjacent to the downstream parts of both fans. This change in the organization of the fan-eddy complex has the potential to alter the location of recirculating eddies and associated areas of fine-grained sediment deposition and storage.

Self-organization criticality of debris flow rheology

Based on the viewpoint of stress and strain self-organization criticality of debris flow mass, this paper probes into inter-nonlinear action between different factors in the thixotropic liquefaction system of loose clastic soil on slope to make clastic soil in slope develop naturally towards critical stress status, and slope debris flow finally occurs under trigging by rainstorm. Also according to observation and analysis of self-organization criticality of sediment run-off system of viscous debris flow surges in ravines and power relation between magnitude and frequency of debris flows, this paper expounds similarity of the self-organized structure of debris flow mass. The self-organized critical system is a weak chaotic system. Debris flow occurrences can be predicted accordingly by means of observation at certain time scale and analysis of self-organization criticality of magnitude, frequency and time interval of debris flows.

Gully-specific debris flow hazard assessment in China

Techniques of gully-specific debris flow hazard assessment developed in four periods since the end of the 1980s have been discussed in the present paper. The improvement for the empirical assessment method is the sectionalized function transformation for the factor value, rather than the classified logical transformation. The theoretical equation of the gully-specific debris flow hazard is expressed as the definite integral of an exponential function and its numerical solution is expressed by the Poisson Limit Equation. Current methods for assessment of debris flow hazard in China are still valid and practical. The further work should be put on the study of the reliability (or uncertainty) of the techniques. For the future, we should give a high priority to the relationship between debris flow magnitude and its frequency of occurrence, make more developments of prediction model on debris flow magnitude, so as to finally reach the goal of assessing the hazard of debris flow by theoretical model, and realize both actuality assessment and prediction appraisal of debris flow.

Debris flows in Glacier National Park, Montana: geomorphology and hazards

Debris flows are one of the many active slope-forming processes within Glacier National Park, Montana. Most debris flow landforms exhibit classic morphology with a distinct failure scarp, incised channel, channel levees, and toe deposits that often develop a lobate form. The Precambrian metasediments that dominate Glacier National Park's geology weather into angular clasts that range in size from platy gravels to boulders. Classic debris flows occur in areas where the topographic expression provides a debris source from cliff faces and an accumulation of regolith, often in the form of talus slopes. Many of these debris flows have long runout zones and can travel many hundreds of meters. Often they cross hiking trails or roads, including the main east–west highway, Going-to-the-Sun Road. Debris flows impacting the road have resulted in several near fatalities, and hikers have been forced to cross active debris flows to reach safe ground. The magnitude of debris flows varies between high magnitude channel incising events and low magnitude channel filling and/or reworking events. The frequency of debris flow events is irregular and appears to be controlled by the hydrology of triggering storms and antecedent moisture conditions, not by the debris supply. As a result, debris flow magnitude is not a function of frequency, but is more closely related to the characteristics of antecedent conditions and individual storms.

Magnitude–frequency relationship for debris flows on the fan of the Chalance torrent, Valgaudemar (French Alps)

AbstractIn 1996 a large debris flow occurred on the fan of the Chalance torrent system, a tributary of the Séveraisse river, French Alps. To investigate the magnitude and frequency of such debris flows on this fan, fieldwork was carried out in the summer of 1998. Detailed investigation revealed that several debris flows have occurred in the past 200 years. Lichenometry was used as a dating technique to obtain the frequency of these debris‐flow events. Also the volume of these flows was estimated. With these data a magnitude–frequency relationship was constructed. This relationship shows a maximum magnitude of at least 50 × 103 m3. Based on data for the past c. 150 years, a debris flow of such a volume appears to have a recurrence interval of approximately 34 years. Copyright © 2002 John Wiley & Sons, Ltd.

Empirical assessment of debris flow risk on a regional scale in Yunnan province, southwestern China.

Adopting the definition suggested by the United Nations, a risk model for regional debris flow assessment is presented. Risk is defined as the product of hazard and vulnerability, both of which are necessary for evaluation. A Multiple-Factor Composite Assessment Model is developed for quantifying regional debris flow hazard by taking into account eight variables that contribute to debris flow magnitude and its frequency of occurrence. Vulnerability is a measure of the potential total losses. On a regional scale, it can be measured by the fixed asset, gross domestic product, land resources, population density, as well as the age, education, and wealth of the inhabitants. A nonlinear power-function assessment model that accounts for these indexes is developed. As a case study, the model is applied to compute the hazard, vulnerability and risk for each prefecture of the Yunnan province in southwestern China.

Debris flow magnitude in the Eastern Italian Alps: data collection and analysis

The estimation of debris flow magnitude is essential for the assessment of debris flow hazard. Historical data are an important basis for evaluating magnitude and frequency of debris flows in a given geographical region. Data on debris flow magnitude concerning 130 basins of the Eastern Italian Alps have been collected from scientific and technical journals, technical reports and historical documents gathered from local archives and through field surveys carried out in the last few years. The analysis of collected data includes various approaches. Regression techniques were used to correlate debris flow magnitude to morphometric parameters and to geological characteristics of the basins. A comparison of historical magnitudes with geomorphic field estimations carried out in recent years is presented and the relations between debris flow magnitude and frequency for a few selected cases are analysed. Some proposals about the possible combined use of considered techniques are then suggested.

The role of debris supply conditions in predicting debris flow activity

Debris flow frequency and magnitude were determined for 33 basins in southwest British Columbia. Basins were first classifiedaseitherweathering-limitedortransport-limitedusingadiscriminantfunctionbasedondebris-contributingarea, an area-weighted terrain stability number, and drainage density. Multiple regression was used to predict magnitude, peak discharge, frequency and activity (frequency times magnitude) within each group of basins. Model performance was improved by stratifying the total sample of debris flow basins into weathering-and transport-limited groups. Explained varianceincreasedbyanaverageof15percentinthetransport-limitedsample,indicatingthatsedimentsupplyconditionsin themoreactivebasinsarefundamentalinpredictingdebrisflowactivity.Anindependenttestoftheregressionmodelswith 11basinsyieldedgenerallygoodresultsfordebrisflowmagnitudeandpeakdischarge.Predictionofdebrisflowfrequency provedproblematicalinweathering-limitedbasins.Themethodsdevelopedhereprovideestimatesofdebrisflowattributes in basins for which few data on past events are available. Copyright # 1999 John Wiley & Sons, Ltd.

Debris-flow magnitude—frequency relationships for mountainous regions of Central and Northwest Europe

Debris-flow activity within a given area can be defined in terms of magnitude and frequency. When for such an area ranges of event magnitudes can be related to the corresponding frequencies, the regional characteristics of debris-flow activity will be obtained. From the viewpoint of hazard assessment this magnitude-frequency characteristic is an essential element of the debris-flow process. For larger areas, (supra)regional comparison may also be undertaken on this basis. However, the data available often specify magnitude insufficiently. For the present study, published data specifying both magnitude and frequency (a very limited amount) were used for the Alps, the Tatra Mountains, Scotland, Norway, and Swedish Lapland in addition to material for the French Alps from the author's research. Activity levels within Northwest European mountains were found to be lower than in the Alps or the Tatras. Possible explanations are discussed, in which precipitation patterns and debris availability play a prominent part. However, the general conclusions has to be that firm statements about the causes of observed differences in magnitude-frequency patterns cannot yet be given.

Data Analysis for Predicting the Magnitude of Debris Flow

Data Analysis for Predicting the Magnitude of Debris Flow

Boulder Streams, Debris Fans, and Pleistocene Climate Change in the Blue Ridge Mountains of Central Virginia

The west slope of the Blue Ridge mountains in central Virginia is a polygenetic landscape containing interglacial and periglacial features. This paper proposes a general model relating the distribution and origin of hillslope and toeslope Quaternary landforms to climatically influenced geomorphic processes. Two generations of interglacial debris fans in the study area differ in their degree of soil development and clast weathering. Boulder streams, which clog debris flow chutes for the upper debris fans, are interpreted as solifluction features formed during successive periglacial episodes. Growth of the boulder streams and associated talus slopes can influence the magnitude and frequency of debris flows and fan formation during interglacials.

Magnitude and frequency of debris flows : Johnson, P A; McCuen, R H; Hromadka, T V J HydrolV123, N1/2, Feb 1991, P69–82

Magnitude and frequency of debris flows : Johnson, P A; McCuen, R H; Hromadka, T V J HydrolV123, N1/2, Feb 1991, P69–82

Magnitude and frequency of debris flows

Debris flows periodically result in the loss of lives and property. Engineering structures designed to control debris flows are often inadequate because of lack of knowledge of the magnitude of debris events. The objective of this study was to develop a method that could be used to estimate the magnitude and frequency of debris flows. The data base for the study included 29 watersheds in the Los Angeles area, with drainage areas < 3 mile 2. Assuming a log-normal distribution, prediction equations for 2-, 5-, 10-, 25-, 50-, and 100-year return periods were developed as a function of relief ratio, hypsometric index, the interval between burns, and drainage area. Principal components and correlation analyses were used to select the predictor variables. Numerical optimization was used to calibrate the model. The prediction equations can be used to estimate the magnitude of debris flows for ungaged watersheds where estimates are required for debris basin and channel design, protection of culverts and roads, land use planning, and zoning and establishing insurance rates.