The Green River canyons of the eastern Uinta Mountains have experienced a 5- year period of high debris flow activity. Catchment factors were studied in watersheds and on debris fans with recent debris flows, leading to the development of a conceptual framework of the hillslope and debris flow processes that deliver sediment to the Green River. Two recent fan deposits were monitored to determine the magnitude and processes of reworking that occur during mainstem floods of varying magnitude. The dominant debris flow initiation mechanism, termed the firehose effect, occurs when overland flow generated on bedrock slopes cascades down steep cliffs and saturates and impacts colluvium stored in bedrock hollows, causing failure. The dry climate and high strength of bedrock cause hillslopes to be weathering-limited, prohibiting the formation of extensive regolith and vegetative cover. This reduces the degree vegetation regulates geomorphic processes and causes wildfire to have little influence on debris flow initiation. The dry climate and strong rocks also lead to high runoff ratios and steep escarpments that result in debris flow initiation via the firehose effect. This initiation process also dominates in Grand Canyon, where geologic and topographic characteristics are similar, but differs from locations in the Rocky Mountains where fire has a strong influence on debris flow processes. Monitoring of two recently aggraded debris fans shows that mainstem floods with magnitudes as low as 75% of the pre-dam 2-year flood cause significant erosion of fan deposits, whereas floods with magnitudes less than 40% of the pre-dam 2-year flood do little reworking. Armoring of the debris fan surface limited the degree ofreworking done by successive floods. Eroded material was deposited directly downstream of the fan, not at the expansion gravel bar. This depositional location represents a change in the organization of the fan-eddy complex, potentially altering the location of recirculating eddies and associated backwater habitats. These results indicate that the firehose effect may be the dominant initiation processes in the steep canyons of the Colorado Plateau and that dam releases that significantly rework fan deposits are within the operational range of large dams in the Colorado River system.

The stratigraphic record of lahars in the Whangaehu River reveals that in the past 180,000 years this route has been one of the main conduits for lahars from Mount Ruapehu, the highest active andesitic stratovolcano in the Central North Island of New Zealand. Both debris flows and hyperconcentrated flows have engulfed surfaces up to 160 km distance from the Volcano. Eight episodes of laharic activity are recognized by the distinctive lithology and similar age of their deposits. The newly defined upper Pleistocene Whangaehu Formation provides evidence for the earliest lahar event in the Valley, c. 180,000- 140,000 years ago. There is only meagre evidence for laharic activity following this event until the Ohakean and Holocene, although two new informally named deposits - the Mangatipona pumice sand (c. 37,000 years B.P.) and Apitian lahars (c. 32,000-25,500 years B.P) - are recognized, of minor extent. The formerly defined late Quaternary Te Heuheu (c. 25,500- 14,700 years B.P.), Tangatu (c. 14,700-5,370 years B.P.), Manutahi (c. 5 ,370-3,4600 years B.P.), Mangaio (c. 4,600 years B.P.) and Onetapu (< c. 1,850 years B.P.) Formations are here described and interpreted. Triggering mechanisms for lahar deposits are distinguished based on lithological criteria. (a) Bouldery deposits in the Whangaehu Formation are interpreted to have been emplaced by a single highly competent debris flow triggered by a southerly-directed flank collapse at Mount Ruapehu. This debris flow was competent enough to transport boulders up to 2 m in diameter over 140 km from the Volcano. Bouldery deposits are also recognized in the Onetapu Formation, but are restricted to higher gradient surfaces on the Mount Ruapehu ring plain. The Onetapu Formation deposits are interpreted to have been emplaced by lahars resulting from catastrophic drainage of Crater Lake, which occupies the active crater on Mount Ruapehu. (b) Pebbly and sandy deposits are interpreted to have been emplaced by low competence debris flows and hyperconcentrated flows. These lahar deposits are recognized in all formations described. The lithology in these deposits is commonly pumice and they are interpreted to have been triggered by eruptions and/or high rainfall events at the Volcano. Formations, and individual members within Formations, were dated by radiocarbon dating of organic material found below, within or above lahar deposits, or by coverbed stratigraphy. Both rhyolitic and andesitic tephras provided recognizable time planes in the late Quaternary coverbeds overlying lahar deposits. In this study quantitative analysis of quartz abundance, which is shown to vary between loesses and palaeosols, is used as an indirect means of establishing a surrogate for past climate changes which have been correlated to the deep sea oxygen isotope curve. A minimum age for the newly defined Whangaehu Formation is established by this method. The accumulation rate for lahars in the Whangaehu River has accelerated from 1 km3 every c. 23,000 years in the past c. 160,000 years to 1 km3 in 589 years in the past c. 2,000 years. This acceleration probably results from the increased frequency of lahars in the River following the development of Crater Lake c. 2,000 years B.P. According to this pattern an estimated 0.17 km3 volume of lahars could be anticipated over the next 100 years. If the 2,000 year accumulation rate were to be met over the next 100 years there would be 170 lahars of l0[superscript]6 m3 in this time interval , or 17 lahars of 10[superscript]7 m3 (or 1.7 lahars of 10[superscript]8 m3). The largest reported volume for an historic lahar is 10[superscript]6 m3 and these have occurred on average once every 30 years. The accumulation rate for historic lahars is 0.0054 km3 in 100 years. Therefore, although the accumulation rate appears to have slowed down, further large lahars with magnitudes 10 or 100 times greater than those witnessed could be expected.

In the past few decades, wildfires have increased in size and severity in the Southwest and across the western US. These recent trends in fire behavior are a drastic change in arid, ponderosa pine and mixed conifer forests of the Southwest compared with tree-ring records of fire history for the past ~ 400 years. This study presents a late Holocene record (~ 3,000 years) of fire history and related changes in fire regimes with climate variability over annual to multi-decadal time scales. Tree-ring and alluvial-sediment sampling sites were paired in four small, tributary basins located in the western San Juan Mountains of Colorado. In our study sites, tree-ring records show that fire return intervals were longer and fire behavior was more severe on the north-facing slopes with relatively dense mixed conifer stands. Increased fire barriers and steep topography decreased the fire frequency and extent relative to gentle terrain elsewhere in the range and leading to a lack of synchrony among fire years in different parts of the study area. The alluvial-sediment record showed four peaks in high-severity fire activity over the past 3,000 years ranging between 200 - 400 years in length. The timing of peaks coincided with decadal-length drought episodes and were often preceded by multiple decades of above average winter precipitation. The sampling of alluvial-sediment and tree-ring data allowed for site-level comparisons between recent alluvial deposits and specific fire years interpreted from the tree-ring records. We found good correspondence between the type of fire-related sediment deposit (i.e. geomorphic response) in the alluvial record and the extent of mixed and high-severity fire estimated from the tree-ring record, and the correspondence was well-supported by the debris flow probability model results. The two paleofire data tend to represent particular components of the historical fire regime, with alluvial-sediments biased towards infrequent, high-severity events during recent millennia, and the tree-ring record biased toward lower severity fires during recent centuries. The combined analyses of different paleofire proxy types in the same study sites, therefore, can enhance and expand our understanding of fire and climate history beyond what is possible with either proxy alone.

In a series of three studies, we assess modern debris-flow hazards in Arizona from extreme precipitation events and following wildfires. In the first study, we use a combination of surficial geologic mapping, ¹⁰Be exposure age dating and modeling to assess prehistoric to modern debris-flow deposits on two alluvial fans in order to place debris-flow hazards in the context of both the modern environment and the last major period of climate change. Late Pleistocene to early Holocene debris flows were larger and likely initiated by larger landslides or other mass movement failures, unlike recent debris flows that typically initiate from shallow (~1 m) failures and scour channels, thus limiting total volumes. In the second study we assess the predictive strengths of existing post wildfire debris-flow probability and volume models for use in Arizona's varied physiographic regions, and define a new rainfall threshold valid for Arizona. We show that all of the models have adequate predictive strength throughout most of the state, and that the debris-flow volume model over-predicts in all of our study areas. Our analysis shows that the choice of a model for a hazard assessment depends strongly on location. The objectively defined rainfall intensity-duration thresholds of I₁₀ and I₁₅ (52 and 42 mm h⁻¹, respectively) have the strongest predictive strengths, although all five of the threshold models performed well. In the third study, we explore various basin physiographic and soil burn severity factors to identify patterns and criteria that can be used to discriminate between potential non-debris-flow (nD) and debris-flow (D) producing basins. Findings from this study show that a metric of percent basins area with high soil burn severity on slopes ≥30 degrees provides a stronger discrimination between nD and D basins than do basin metrics, such as mean basin gradient or relief. Mean basin elevation was also found to discriminate nD from D basins and is likely a proxy for forest type and density, which relates to soil thickness, root density and the magnitude of post-disturbance erosion. Finally, we found that post-fire channel heads formed at essentially the same slope range (~30-40 degrees) as saturation-induced hill slope failures.

The stratigraphic record of lahars in the Whangaehu River reveals that in the past 180,000 years this route has been one of the main conduits for lahars from Mount Ruapehu, the highest active andesitic stratovolcano in the Central North Island of New Zealand. Both debris flows and hyperconcentrated flows have engulfed surfaces up to 160 km distance from the Volcano. Eight episodes of laharic activity are recognized by the distinctive lithology and similar age of their deposits. The newly defined upper Pleistocene Whangaehu Formation provides evidence for the earliest lahar event in the Valley, c. 180,000- 140,000 years ago. There is only meagre evidence for laharic activity following this event until the Ohakean and Holocene, although two new informally named deposits - the Mangatipona pumice sand (c. 37,000 years B.P.) and Apitian lahars (c. 32,000-25,500 years B.P) - are recognized, of minor extent. The formerly defined late Quaternary Te Heuheu (c. 25,500- 14,700 years B.P.), Tangatu (c. 14,700-5,370 years B.P.), Manutahi (c. 5 ,370-3,4600 years B.P.), Mangaio (c. 4,600 years B.P.) and Onetapu (< c. 1,850 years B.P.) Formations are here described and interpreted. Triggering mechanisms for lahar deposits are distinguished based on lithological criteria. (a) Bouldery deposits in the Whangaehu Formation are interpreted to have been emplaced by a single highly competent debris flow triggered by a southerly-directed flank collapse at Mount Ruapehu. This debris flow was competent enough to transport boulders up to 2 m in diameter over 140 km from the Volcano. Bouldery deposits are also recognized in the Onetapu Formation, but are restricted to higher gradient surfaces on the Mount Ruapehu ring plain. The Onetapu Formation deposits are interpreted to have been emplaced by lahars resulting from catastrophic drainage of Crater Lake, which occupies the active crater on Mount Ruapehu. (b) Pebbly and sandy deposits are interpreted to have been emplaced by low competence debris flows and hyperconcentrated flows. These lahar deposits are recognized in all formations described. The lithology in these deposits is commonly pumice and they are interpreted to have been triggered by eruptions and/or high rainfall events at the Volcano. Formations, and individual members within Formations, were dated by radiocarbon dating of organic material found below, within or above lahar deposits, or by coverbed stratigraphy. Both rhyolitic and andesitic tephras provided recognizable time planes in the late Quaternary coverbeds overlying lahar deposits. In this study quantitative analysis of quartz abundance, which is shown to vary between loesses and palaeosols, is used as an indirect means of establishing a surrogate for past climate changes which have been correlated to the deep sea oxygen isotope curve. A minimum age for the newly defined Whangaehu Formation is established by this method. The accumulation rate for lahars in the Whangaehu River has accelerated from 1 km3 every c. 23,000 years in the past c. 160,000 years to 1 km3 in 589 years in the past c. 2,000 years. This acceleration probably results from the increased frequency of lahars in the River following the development of Crater Lake c. 2,000 years B.P. According to this pattern an estimated 0.17 km3 volume of lahars could be anticipated over the next 100 years. If the 2,000 year accumulation rate were to be met over the next 100 years there would be 170 lahars of l0[superscript]6 m3 in this time interval , or 17 lahars of 10[superscript]7 m3 (or 1.7 lahars of 10[superscript]8 m3). The largest reported volume for an historic lahar is 10[superscript]6 m3 and these have occurred on average once every 30 years. The accumulation rate for historic lahars is 0.0054 km3 in 100 years. Therefore, although the accumulation rate appears to have slowed down, further large lahars with magnitudes 10 or 100 times greater than those witnessed could be expected.

The stratigraphic record of lahars in the Whangaehu River reveals that in the past 180,000 years this route has been one of the main conduits for lahars from Mount Ruapehu, the highest active andesitic stratovolcano in the Central North Island of New Zealand. Both debris flows and hyperconcentrated flows have engulfed surfaces up to 160 km distance from the Volcano. Eight episodes of laharic activity are recognized by the distinctive lithology and similar age of their deposits. The newly defined upper Pleistocene Whangaehu Formation provides evidence for the earliest lahar event in the Valley, c. 180,000- 140,000 years ago. There is only meagre evidence for laharic activity following this event until the Ohakean and Holocene, although two new informally named deposits - the Mangatipona pumice sand (c. 37,000 years B.P.) and Apitian lahars (c. 32,000-25,500 years B.P) - are recognized, of minor extent. The formerly defined late Quaternary Te Heuheu (c. 25,500- 14,700 years B.P.), Tangatu (c. 14,700-5,370 years B.P.), Manutahi (c. 5 ,370-3,4600 years B.P.), Mangaio (c. 4,600 years B.P.) and Onetapu (< c. 1,850 years B.P.) Formations are here described and interpreted. Triggering mechanisms for lahar deposits are distinguished based on lithological criteria. (a) Bouldery deposits in the Whangaehu Formation are interpreted to have been emplaced by a single highly competent debris flow triggered by a southerly-directed flank collapse at Mount Ruapehu. This debris flow was competent enough to transport boulders up to 2 m in diameter over 140 km from the Volcano. Bouldery deposits are also recognized in the Onetapu Formation, but are restricted to higher gradient surfaces on the Mount Ruapehu ring plain. The Onetapu Formation deposits are interpreted to have been emplaced by lahars resulting from catastrophic drainage of Crater Lake, which occupies the active crater on Mount Ruapehu. (b) Pebbly and sandy deposits are interpreted to have been emplaced by low competence debris flows and hyperconcentrated flows. These lahar deposits are recognized in all formations described. The lithology in these deposits is commonly pumice and they are interpreted to have been triggered by eruptions and/or high rainfall events at the Volcano. Formations, and individual members within Formations, were dated by radiocarbon dating of organic material found below, within or above lahar deposits, or by coverbed stratigraphy. Both rhyolitic and andesitic tephras provided recognizable time planes in the late Quaternary coverbeds overlying lahar deposits. In this study quantitative analysis of quartz abundance, which is shown to vary between loesses and palaeosols, is used as an indirect means of establishing a surrogate for past climate changes which have been correlated to the deep sea oxygen isotope curve. A minimum age for the newly defined Whangaehu Formation is established by this method. The accumulation rate for lahars in the Whangaehu River has accelerated from 1 km3 every c. 23,000 years in the past c. 160,000 years to 1 km3 in 589 years in the past c. 2,000 years. This acceleration probably results from the increased frequency of lahars in the River following the development of Crater Lake c. 2,000 years B.P. According to this pattern an estimated 0.17 km3 volume of lahars could be anticipated over the next 100 years. If the 2,000 year accumulation rate were to be met over the next 100 years there would be 170 lahars of l0[superscript]6 m3 in this time interval , or 17 lahars of 10[superscript]7 m3 (or 1.7 lahars of 10[superscript]8 m3). The largest reported volume for an historic lahar is 10[superscript]6 m3 and these have occurred on average once every 30 years. The accumulation rate for historic lahars is 0.0054 km3 in 100 years. Therefore, although the accumulation rate appears to have slowed down, further large lahars with magnitudes 10 or 100 times greater than those witnessed could be expected.

Corrida de detritos é um tipo de movimento que se caracteriza por uma massa fluída bastante densa, constituída por lama, água, rochas e outros detritos, capaz de atingir elevadas velocidades e possuir elevado potencial de destruição. Essas características colocam esse tipo de movimento entre os mais catastróficos desastres naturais, com grande potencial de destruição, principalmente quando ocorre em áreas urbanizadas, onde os prejuízos e perdas podem ser enormes. Como apoio para definição de medidas de prevenção ou mitigação desses desastres, as ferramentas computacionais para modelagem desses movimentos têm se mostrado de grande utilidade, sendo que para isso atualmente existem diferentes abordagens. Nesse sentido, o atual trabalho se baseia na aplicação do software RAMMS em um estudo de caso a fim de verificar a aplicabilidade dessa ferramenta no estudo de casos típicos de corridas de massa em condições brasileiras. Este software, desenvolvido pelo órgão suíço WSL, se baseia no modelo de atrito de Voellmy-Salm, que divide a resistência ao cisalhamento em duas parcelas: atrito seco e atrito turbulento, sendo que para cada uma destas parcelas existe um coeficiente característico, sendo, respectivamente, μ e ξ. Neste trabalho é feita a análise de movimentos de massa que ocorreram no Rio de Janeiro no ano de 1996, nos canais dos rios Quitite e Papagaio, em que foi mobilizado cerca de 130.000m³ de material por cerca 1,5 km. Neste trabalho é feita uma retroanálise desses movimentos através do software RAMMS, de modo a se obter a calibração dos parâmetros de atrito do modelo Voellmy-Salm. Para isso foram realizadas diversas simulações dos movimentos de massa, fazendo-se a comparação dos resultados com os dados dos movimentos reais. As análises realizadas possibilitaram a calibração dos parâmetros de atrito do modelo Voellmy-Salm de modo a reproduzir de maneira satisfatória os movimentos ocorridos. Para o coeficiente de atrito seco (μ), os valores obtidos ficaram entre 0,075 para o material mais fino e 0,25 para o material mais grosseiro. Para o coeficiente de atrito turbulento (ξ) o valor obtido também foi variável de acordo com o trecho, entre 150 e 400 m/s², aproximadamente. Também foi observado que ambos os parâmetros apresentam variação ao longo do trecho da corrida. Esses valores podem vir a servir de base para estudos de novos movimentos em condições similares, através do software RAMMS, auxiliando assim em programas para prevenção ou mitigação das consequências relacionadas às corridas de detritos. / Debris flows is a mass movement characterized as a dense fluid, consisting of mud, water, rocks and other debris, which is able to reach high speeds and to have a high destructive potential. These characteristics classify this type of mass movement among the most catastrophic natural disasters, with great potential for destruction especially when it occurs in urban areas, where losses can be enormous. Computational tools to model these movements have proved to be very useful as support for studies of preventive or mitigation measures for such disasters and there are a number of different approaches currently. The current work is based on the application of RAMMS software in a case study to verify the applicability of this tool on the study of cases under Brazilian conditions. The software was developed by the Swiss agency WSL and is based on the Voellmy-Salm friction model, which divides the shear resistance into two portions: dry friction and turbulent friction, and for each of these portions assumes a characteristic coefficient, μ and ξ, respectively. In this work the analysis of the debris flows that occurred in the Quitite and Papagaio streams, Rio de Janeiro, 1996, which mobilized about 130.000m³ of material for about 1.5 km. Back analysis of these movements were performed using the software RAMMS to obtain calibration parameters for the friction model of Voellmy-Salm. For this purpose, several simulations of mass movements were performed allowing the comparison of the results with data from real movements. These analyzes had allowed the parameters calibration of the Voellmy-Salm friction model which reproduced satisfactorily the movements. For the coefficient of dry friction (μ), the values obtained were between 0.075, for fine material, and 0.25, for coarse material. For the turbulent friction coefficient (ξ) the values were also variable between 150 and 400 m/s, approximately, according to the geometric segment studied. It was also observed that both parameters changed along the stretch. These values may be used as a base for studies of new movements in similar conditions using RAMMS software and can help in prevention or mitigation of debris flows.

Made available in DSpace on 2014-06-11T19:32:20Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-11-10Bitstream added on 2014-06-13T18:43:37Z : No. of bitstreams: 1 lopes_ess_dr_rcla.pdf: 8893056 bytes, checksum: d240d8729b6b1662f31ac0ef417e5386 (MD5) / Um modelo dinamico com caracteristicas friccionais, que utiliza como parametros basicos o angulo de atrito interno do material ( int Ó ) e basal ( bed Ó ) com a superficie onde ocorre o movimento, foi calibrado e aplicado com objetivo de simular as mesmas condicoes em que ocorreram corridas de massa nos anos de 1985, 1994 e 1999, em tres bacias da Serra do Mar, na regiao de Cubatao (SP-Brasil), na escala 1:10.000. Um modelo estatico de estabilidade por talude infinito, definido atraves do indice de estabilidade (SI), foi aplicado para subsidiar o estudo de areas com potencial aos processos de escorregamentos translacionais rasos, que podem evoluir para corridas de massa. Um inventario de cicatrizes tambem foi elaborado a partir da interpretacao de produtos de sensoriamento remoto, utilizado para validar o modelo estatico, assim como para definir pilhas de materiais deflagradas no modelo dinamico. Os resultados com o modelo estatico mostraram-se mais adequados quando se utilizaram as unidades litologicas para variacao dos parametros geotecnicos. Mais de 85% das cicatrizes ficaram dentro dos limites inferior de estabilidade e superior de instabilidade. As simulacoes com o modelo dinamico permitiram criar diferentes cenarios, com caracteristicas como trajetoria e alcance do material mobilizado, semelhantes aos eventos ocorridos no passado. Para tal modelo, diferentes configuracoes de pilhas de materiais e variacoes do angulo de atrito basal, em funcao do mapa de materiais, permitiram simulacoes mais realistas. / A dynamic model with frictional characteristics that uses as basic parameters internal friction angle of the material ( int Ó ) and bed friction angle ( bed Ó ) with the surface where movement occurs was calibrated and applied to simulate the same conditions under which debris flows occurred in the years 1985, 1994 and 1999, in three watersheds of the Serra do Mar, in the region of Cubatao (Sao Paulo, Brasil), on a scale of 1:10.000. A static model of infinite slope stability, defined using the stability index (SI), was applied to inform the study of areas that have potential for processes of shallow translational landsliding that could evolve into debris flows. Landslide inventory data was also elaborated based on the interpretation of remote sensing products, used to validate the static model as well as to define deflagrated pile material in the dynamic model. The results with the static model proved to be more satisfactory when the lithological boundaries were used for variation of the geotechnical parameters. More than 85% of the scarps were within the lower threshold stability and upper threshold instability. The simulations with the dynamic model allowed the creation of different scenarios with characteristics, such as trajectory and range of the mobilized material, similar to the events that occurred in the past. For this model, different configurations of pile material and variations in the bed friction angle, as a function of the materials map, made it possible to carry out more realistic simulations.

Corrida de detritos é um tipo de movimento que se caracteriza por uma massa fluída bastante densa, constituída por lama, água, rochas e outros detritos, capaz de atingir elevadas velocidades e possuir elevado potencial de destruição. Essas características colocam esse tipo de movimento entre os mais catastróficos desastres naturais, com grande potencial de destruição, principalmente quando ocorre em áreas urbanizadas, onde os prejuízos e perdas podem ser enormes. Como apoio para definição de medidas de prevenção ou mitigação desses desastres, as ferramentas computacionais para modelagem desses movimentos têm se mostrado de grande utilidade, sendo que para isso atualmente existem diferentes abordagens. Nesse sentido, o atual trabalho se baseia na aplicação do software RAMMS em um estudo de caso a fim de verificar a aplicabilidade dessa ferramenta no estudo de casos típicos de corridas de massa em condições brasileiras. Este software, desenvolvido pelo órgão suíço WSL, se baseia no modelo de atrito de Voellmy-Salm, que divide a resistência ao cisalhamento em duas parcelas: atrito seco e atrito turbulento, sendo que para cada uma destas parcelas existe um coeficiente característico, sendo, respectivamente, μ e ξ. Neste trabalho é feita a análise de movimentos de massa que ocorreram no Rio de Janeiro no ano de 1996, nos canais dos rios Quitite e Papagaio, em que foi mobilizado cerca de 130.000m³ de material por cerca 1,5 km. Neste trabalho é feita uma retroanálise desses movimentos através do software RAMMS, de modo a se obter a calibração dos parâmetros de atrito do modelo Voellmy-Salm. Para isso foram realizadas diversas simulações dos movimentos de massa, fazendo-se a comparação dos resultados com os dados dos movimentos reais. As análises realizadas possibilitaram a calibração dos parâmetros de atrito do modelo Voellmy-Salm de modo a reproduzir de maneira satisfatória os movimentos ocorridos. Para o coeficiente de atrito seco (μ), os valores obtidos ficaram entre 0,075 para o material mais fino e 0,25 para o material mais grosseiro. Para o coeficiente de atrito turbulento (ξ) o valor obtido também foi variável de acordo com o trecho, entre 150 e 400 m/s², aproximadamente. Também foi observado que ambos os parâmetros apresentam variação ao longo do trecho da corrida. Esses valores podem vir a servir de base para estudos de novos movimentos em condições similares, através do software RAMMS, auxiliando assim em programas para prevenção ou mitigação das consequências relacionadas às corridas de detritos. / Debris flows is a mass movement characterized as a dense fluid, consisting of mud, water, rocks and other debris, which is able to reach high speeds and to have a high destructive potential. These characteristics classify this type of mass movement among the most catastrophic natural disasters, with great potential for destruction especially when it occurs in urban areas, where losses can be enormous. Computational tools to model these movements have proved to be very useful as support for studies of preventive or mitigation measures for such disasters and there are a number of different approaches currently. The current work is based on the application of RAMMS software in a case study to verify the applicability of this tool on the study of cases under Brazilian conditions. The software was developed by the Swiss agency WSL and is based on the Voellmy-Salm friction model, which divides the shear resistance into two portions: dry friction and turbulent friction, and for each of these portions assumes a characteristic coefficient, μ and ξ, respectively. In this work the analysis of the debris flows that occurred in the Quitite and Papagaio streams, Rio de Janeiro, 1996, which mobilized about 130.000m³ of material for about 1.5 km. Back analysis of these movements were performed using the software RAMMS to obtain calibration parameters for the friction model of Voellmy-Salm. For this purpose, several simulations of mass movements were performed allowing the comparison of the results with data from real movements. These analyzes had allowed the parameters calibration of the Voellmy-Salm friction model which reproduced satisfactorily the movements. For the coefficient of dry friction (μ), the values obtained were between 0.075, for fine material, and 0.25, for coarse material. For the turbulent friction coefficient (ξ) the values were also variable between 150 and 400 m/s, approximately, according to the geometric segment studied. It was also observed that both parameters changed along the stretch. These values may be used as a base for studies of new movements in similar conditions using RAMMS software and can help in prevention or mitigation of debris flows.

Corrida de detritos é um tipo de movimento que se caracteriza por uma massa fluída bastante densa, constituída por lama, água, rochas e outros detritos, capaz de atingir elevadas velocidades e possuir elevado potencial de destruição. Essas características colocam esse tipo de movimento entre os mais catastróficos desastres naturais, com grande potencial de destruição, principalmente quando ocorre em áreas urbanizadas, onde os prejuízos e perdas podem ser enormes. Como apoio para definição de medidas de prevenção ou mitigação desses desastres, as ferramentas computacionais para modelagem desses movimentos têm se mostrado de grande utilidade, sendo que para isso atualmente existem diferentes abordagens. Nesse sentido, o atual trabalho se baseia na aplicação do software RAMMS em um estudo de caso a fim de verificar a aplicabilidade dessa ferramenta no estudo de casos típicos de corridas de massa em condições brasileiras. Este software, desenvolvido pelo órgão suíço WSL, se baseia no modelo de atrito de Voellmy-Salm, que divide a resistência ao cisalhamento em duas parcelas: atrito seco e atrito turbulento, sendo que para cada uma destas parcelas existe um coeficiente característico, sendo, respectivamente, μ e ξ. Neste trabalho é feita a análise de movimentos de massa que ocorreram no Rio de Janeiro no ano de 1996, nos canais dos rios Quitite e Papagaio, em que foi mobilizado cerca de 130.000m³ de material por cerca 1,5 km. Neste trabalho é feita uma retroanálise desses movimentos através do software RAMMS, de modo a se obter a calibração dos parâmetros de atrito do modelo Voellmy-Salm. Para isso foram realizadas diversas simulações dos movimentos de massa, fazendo-se a comparação dos resultados com os dados dos movimentos reais. As análises realizadas possibilitaram a calibração dos parâmetros de atrito do modelo Voellmy-Salm de modo a reproduzir de maneira satisfatória os movimentos ocorridos. Para o coeficiente de atrito seco (μ), os valores obtidos ficaram entre 0,075 para o material mais fino e 0,25 para o material mais grosseiro. Para o coeficiente de atrito turbulento (ξ) o valor obtido também foi variável de acordo com o trecho, entre 150 e 400 m/s², aproximadamente. Também foi observado que ambos os parâmetros apresentam variação ao longo do trecho da corrida. Esses valores podem vir a servir de base para estudos de novos movimentos em condições similares, através do software RAMMS, auxiliando assim em programas para prevenção ou mitigação das consequências relacionadas às corridas de detritos. / Debris flows is a mass movement characterized as a dense fluid, consisting of mud, water, rocks and other debris, which is able to reach high speeds and to have a high destructive potential. These characteristics classify this type of mass movement among the most catastrophic natural disasters, with great potential for destruction especially when it occurs in urban areas, where losses can be enormous. Computational tools to model these movements have proved to be very useful as support for studies of preventive or mitigation measures for such disasters and there are a number of different approaches currently. The current work is based on the application of RAMMS software in a case study to verify the applicability of this tool on the study of cases under Brazilian conditions. The software was developed by the Swiss agency WSL and is based on the Voellmy-Salm friction model, which divides the shear resistance into two portions: dry friction and turbulent friction, and for each of these portions assumes a characteristic coefficient, μ and ξ, respectively. In this work the analysis of the debris flows that occurred in the Quitite and Papagaio streams, Rio de Janeiro, 1996, which mobilized about 130.000m³ of material for about 1.5 km. Back analysis of these movements were performed using the software RAMMS to obtain calibration parameters for the friction model of Voellmy-Salm. For this purpose, several simulations of mass movements were performed allowing the comparison of the results with data from real movements. These analyzes had allowed the parameters calibration of the Voellmy-Salm friction model which reproduced satisfactorily the movements. For the coefficient of dry friction (μ), the values obtained were between 0.075, for fine material, and 0.25, for coarse material. For the turbulent friction coefficient (ξ) the values were also variable between 150 and 400 m/s, approximately, according to the geometric segment studied. It was also observed that both parameters changed along the stretch. These values may be used as a base for studies of new movements in similar conditions using RAMMS software and can help in prevention or mitigation of debris flows.