• 4000-year history of debris flows in north-central Washington State, USA: preliminary results from trenching and surficial geologic mapping at the Pope Creek fan

      Coe, Jeffrey A.; Bessette-Kirton, Erin K.; Slaughter, Stephen L.; Rengers, Francis K.; Contreras, Trevor A.; Mickelson, Katherine A.; Taylor, Emily M.; Kean, Jason W.; Jacobacci, Kara E.; Hanson, Molly A. (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Long-term records of the magnitude and frequency of debris flows on fans are rare, but such records provide critical information needed for debris-flow hazard and risk assessments. This study explores the history of debris flows on a fan with seasonally inhabited cabins at Pope Creek along the Entiat River about 48 km upstream from the town of Entiat, Washington. Motivation for this study was provided by the Duncan Fire, a wildfire which burned the Pope Creek basin in 2014 and resulted in debris flows and water-dominated floods on the fan between August 2014 and October 2016. We excavated and mapped seven 6-m long (2.4- m deep) trenches, mapped deposits on the surface of the fan, and constrained the ages of deposits using radiocarbon dating and the computer program OxCal. Preliminary results indicate that there have been at least 10 debris-flow events (DFEs) since 4000 cal yr BP. The mean recurrence interval between events was 433 +/-44 years, but intervals range from 724 to 20 years. The four most recent events have the shortest recurrence intervals. The largest event had an estimated sediment volume of 97,000 m3 and occurred at about 285 cal yr BP (1665 AD) during the Little Ice Age. The most recent debris-flow event that was triggered by rainstorms following the Duncan Fire was about 8x smaller than the largest event. These results may indicate that the largest DFE was triggered by an exceptional meteorological event that occurred during a cool, wet time, and that smaller DFEs were triggered by less exceptional meteorological events that occurred following wildfires.
    • Analysis of rainfall and runoff for debris flows at the Illgraben catchment, Switzerland

      Hirschberg, Jacob; McArdell, Brian W.; Badoux, Alexandre; Molnar, Peter (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      For hazard analysis, scenario design and mitigation there is a need to accurately and objectively predict the volume of debris flows. One approach is to base the calculation on rainfall properties. Herein we present an analysis of rainfall and debris-flow volume using data from the Illgraben catchment in Switzerland. The Illgraben debris-flow observation station, operated starting in the year 2000, has successfully recorded 75 debris flows and debris floods, with volume and bulk density estimates available for most of these events since 2000 and 2004, respectively. Here we describe results for 52 debris flows with sufficient data. Runoff coefficients determine the proportion of precipitation discharged from a catchment and support estimates on flow magnitudes. For each debris flow, runoff coefficients were determined by considering the event rainfall and the water contained in the debris flow. The events can further be characterized by the 14-day antecedent wetness. Runoff coefficients comprise a wide range from near 0 to close to 1. Clear trends are apparent, such as larger runoff coefficients during the snowmelt season. Furthermore, the debris-flow volumes are more sensitive to the antecedent rainfall than to the rainfall amount that triggered the event, likely because a wet channel bed enhances entraining. This study gives insights on which climate variables control the debris-flow volume. This will be further investigated and incorporated into the SedCas (Sediment Cascade) model (Bennett et al., 2014) to improve prediction of debris-flow activity.
    • Application of an innovative, low-maintenance weir to protect against debris flows and floods in Ottone, Italy

      Morstabilini, Chiara; Boschini, Ilaria; Zambrini Federica; Menduni Giovanni; Deana, Marco Luigi; Zorzi, Nadia (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      The need of a low-maintenance and easy-applicable apparatus against debris flow led Maccaferri Innovation Center and the Politecnico of Milan to a new hydraulic-based approach that was focused on the application of a special weir called Mini Skirt Check Dam (MSCD). After a three-years research on applicable equations, a construction site in Ottone (Italy) was identified to have been affected by destructive debris flow in the past years. The site is characterized by the presence of an underground pipe that collects the stream flow rate flowing under the village square. The purpose of this work is to design a MSCD, able to prevent a pressure driven flow in the underground pipe and to avoid the related risk for the inhabitant of the village. MSCD is a special weir, which consists in large wings to slow the flow and a ring net to block boulders and logs, as to become a sifting filter of the debris. As to design the best performing apparatus, materials and type of anchoring are crucial; for this reason, an analysis of the impact pressure was performed. The case study has considered several different aspects: hydrology, size of the material and its characteristics and previous events to have a complete analysis of what could happen in the next events. The result of this collaboration is the complete design of a MSCD, ready to be installed.
    • Application of an MPS-based model to the process of debris-flow deposition on alluvial fans

      Suzuki, Takuro; Hotta, Norifumi; Tsunetaka, Haruka; Sakai, Yuichi (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      A modified moving particles simulation model (MPS-DF) to simulate inundation and sediment deposition of debris flows is presented. This model is based on the moving particles semi-implicit (MPS) method, which was originally used for incompressible viscous fluid flows with free surfaces. In the MPS-DF model, the constitutive equations of Egashira is introduced to the MPS method. In Egashira’s theory, debris flows are treated as a continuum and sand grains are expressed using sediment concentration. Thus, each particle has a variable sediment concentration value. In this study, we tested the applicability of the MPS-DF model for the formation process of alluvial fans. For this purpose, flume experiment was conducted. The experimental flume consisted of a straight channel 6.0m long and 0.1m wide, with an inclination of 15°, connected to an outflow plain. The inclination of the outflow plain decreased gradually from 12° to 3°. At the straight channel, 5.0m long erodible bed with a thickness of 0.2m was present. Water was supplied from upper end for 60 s. at the rate of 3,000 cm3/s and debris flow was generated by entraining the erodible bed. Debris flow inundated and deposited sediment at the outflow plain and an alluvial fan was formed. Numerical simulations were also performed with the MPS-DF as well as a depth-integrated method based on the shallow water equations (2D simulation). 2D Simulation results of alluvial fan shape and flooding area were laterally spread and significantly different from those of experiment. The results of the MPS-DF were more similar to experimental results. Natural channels and lateral levees were formed as well as experiment. However, the alluvial fan shape of MPS-DF was slightly wider than that created during the experiment. This is thought to be due to the behavior of pore water of deposied layer, such as the seepage of water out of the deposited layer once the deposition process has been completed.
    • Application of knowledge-driven method for debris-slide susceptibility mapping in regional scale

      Das, Raja; Nandi, Arpita (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Debris-slides are a frequent hazard in fragile decomposed metasedimentary rocks in the Anakeesta rock formation in Great Smoky Mountain National Park. The spatial distribution of an existing debris-slide area could be used to prepare susceptibility map for future debris-slide initiation zones. This work aims to create a debris-slide susceptibility map by using a knowledge-driven method in a GIS platform in Anakeesta formation of Great Smoky Mountain National Park. Six geofactors, namely, elevation, annual rainfall, slope curvature, landcover, soil texture and various slope failure modes were used to create the susceptibility map. Debris- slide locations were mapped from the satellite imagery, previous studies, and field visits. A Weighted Overlay Analysis was performed in order to generate the final susceptibility map, where individual classes of geofactors were ranked and were assigned weights based on their influence on debris-slide. The final susceptibility map was classified into five categories: very low, low, moderate, high and very high susceptible zones. Validation of the result shows very high category predicted ~10%, high and moderate categories predicted 75.5% and ~14.5% of the existing debris-slide pixels respectively. This study successfully depicts the advantage and usefulness of the knowledge-driven method, which can save considerable amount of time and reduce complicated data analysis unlike statistical or physical based methods. However, the accuracy of the model highly depends on the researcher’s experience of the area and selection of respective geofactors.
    • Characteristics of debris flows just downstream the initiation area on Punta Nera cliffs, Venetian Dolomites

      Bernard, Martino; Berti, Matteo; Crucil, Giacomo; Simoni, Alessandro; Gregoretti, Carlo (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      The Piees de ra Mognes fan at the base of the Punta Nera cliffs, in the Venetian Dolomites (Italy), has been subject to debris flow activity for decades. Until recently, these debris flows never reached the National Road 51 on the valley bottom. Debris flows usually initiated at the base of an incised rocky channel in the Punta Nera cliffs where runoff is delivered to loose scree deposits of the fan. The main debris flow channel is strongly incised at the apex of the fan and splits into several minor channels at lower elevations. During the autumn 2014 and May 2016, two cliff collapses produced large debris deposits. Since then, the frequency of debris flows increased considerably because of the availability of debris deposits at very steep slope that lowered the runoff discharge needed for the debris flow initiation. In a few cases, debris flows that initiated in the rocky channel reached and interrupted the National Road 51, about 2 km downstream the well-known touristic village of Cortina d’Ampezzo. On July 2016, a monitoring station was placed at the beginning of the debris flow channel just downstream the base of the rocky channel. In the period between July and -September, the monitoring station recorded six debris flow events. Analysis of these data is used to describe the characteristics of debris flow initial routing. Moreover, we use video image analysis to investigate the velocity and depth of the surge from the 5 August 2016 event.
    • Characterizing debris transfer patterns in the White Canyon, British Columbia with terrestrial laser scanning

      Bonneau, David A.; Hutchinson, D. Jean; McDougall, Scott (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      In the Thompson-Fraser Rail Corridor in Interior British Columbia, the Canadian National (CN) rail line traverses several alluvial fans, which are subject to occasional debris flows. Debris flows pose a significant geohazard due to the combination of high flow velocities, large impact forces, long runout distances and poor temporal predictability. When a debris flow occurs, the cost of repairs, maintenance, and construction along these single-track railway lines is compounded by the fact that these activities also impede the flow of rail traffic, which has financial repercussions for the operators. As a result, it is vital to be able to identify and prioritize the slopes that pose the greatest hazard to the rail lines. A thorough understanding of the geohazards present on site is an essential component of risk assessment. The Canadian Railway Ground Hazard Research Program (RGHRP) was established in 2003 with the aim of better understanding the natural hazards impacting railway operations across Canada. The present study is part of this initiative and focuses on an active site called the White Canyon, which is located 275 kilometers northeast of Vancouver, BC. In this study, we use terrestrial laser scanning (TLS) and panoramic imagery datasets to analyze the debris recharge patterns that develop between debris flows in a select channel in the White Canyon. TLS scans taken before and after the events provide insight into the volumes of material mobilized and how we can leverage this series of TLS data to give insight into the amount of debris accumulating in the channels prior to failure. The temporal data acquisition rate was found to have a significant influence on the amount of movement that can be interpreted from the TLS change detection analysis and panoramic images. Therefore, the temporal data acquisition rate is key consideration when using TLS to support the determination of accurate return periods on debris flows.
    • Commonalities between debris flows and flow failures

      Moss, Robb Eric S. (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Debris flow and flow failure are terms used to describe large displacement slope failures. The initiation or triggering often differs due to the nature and state of the material, but once triggered these two failure mechanisms both tend to behave like a Bingham plastic exhibiting a yield strength and a strain-rate dependent strength. In this paper the rheology of these failures is examined and compared to field data and lab data to find commonalities. A future goal is to move towards a common definition of the physics and a joint empirical database for improved statistics and predictive models. The authors own field investigations in Chile and lab investigations using shake table experiments will be reviewed along with studies by other researchers.
    • Comparison of an empirical and a process-based model for simulating debris-flow inundation following the 2010 Schultz Fire in Coconino County, Arizona, USA

      Youberg, Ann M.; McGuire, Luke A. (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      The importance of understanding the extent of areas threatened by post-wildfire debris flows cannot be overstated, as illustrated by the post-Thomas Fire flows through Montecito, California, in January 2018. Methods and models developed by the U.S. Geological Survey to identify burned basins at risk of producing post-wildfire debris flows are well established, effective and commonly used. In contrast, there is no similarly established methodology for delineating debris-flow hazard zones downstream of basins prone to producing post-fire debris flows. Understanding potential inundation zones is critical for protecting human life, property and infrastructure. Recently, some communities and local government agencies have begun assessing potential risks from post-wildfire hazards before an area burns (pre-fire hazard assessments). These assessments utilize modeled burn severity maps and existing methodologies to identify basins likely to generate post-fire debris flows should the basins burn. In most studies, however, there have been no attempts to delineate hazard zones downstream of the basins that could produce post-fire debris flows. This information is critical for identifying mitigation opportunities and for establishing emergency evacuation routes and procedures. Here, we report on work using a newly developed process-based model and an empirical model, Laharz using two different sets of mobility coefficients, to assess debris-flow runout from a recently burned basin. The actual extent of debris-flow runout is known, which allows us to compare model performance. Laharz is efficient for assessing large areas but requires the user to select the location of deposition a priori, and mobility coefficients for post-fire debris flows have not yet been developed. Laharz did not adequately predict the downstream extent of deposition using either set of mobility coefficients. The process-based model using two sets of parameters, friction angle, φ, and ratio of pore fluid pressure to total basal normal stress, λ, provided a range of results. The simulation using parameters = 0.8 and φ = 0.35 provided the best match between mapped and modeled deposits and provided a better estimate of inundation relative to Laharz. This two-model approach is helpful for assessing the shortcomings and benefits of each model, and for identifying the next steps needed for developing a method to identify post-fire debris-flow hazard zones before a fire begins.
    • Complexity of a debris-flow system at Forest Falls, California

      Cato, Kerry; Goforth, Brett (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Historical patterns of debris flows have been reconstructed at the town of Forest Falls in the San Bernardino Mountains using a variety of field methods (mapping flow events after occurrence, dendrochronology evidence, soil chrono sequences). Large flow events occur when summer thunderstorms produce brief high-intensity rainfall to mobilize debris, however the geomorphic system exhibits properties of non-linear response rather than being a single-event precipitation-driven process. Previous studies contrasted the relative water content of flows generated by varying intensity summer thunderstorms to model factors controlling their velocity and pathway of deposition. We hypothesize that variation in sediment discharge also results from complexity in this geomorphic system, and this paper presents ongoing empirical field studies focused on sources of complexity in three formative components of recently monitored debris-flows at Snow Creek Canyon: 1) thresholds of sediment delivery from sources at the higher reaches of bedrock canyons; 2) storage effects in sediment transport down the bedrock canyons; and 3) feedbacks in deposition and transport of sediment as flows from the bedrock canyon collect into a single active channel on a fan landform downslope. An example of the first component occurred in March 2017, when snow melt generated a rapid translational landslide/debris slide of about 80,000 m3; this sediment was deposited in the bedrock canyon, but moved no further down-gradient. A second component has been observed when accumulation of meta-stable sediments in the active channel remain in place until fluvial erosion or subsequent debris flow created dynamic instability to mobilize the mass downslope. The third component occurred in the active channel where low-water content debris flows deposited sediments that filled the channel, raising the channel grade level to levy elevation, allowing for subsequent spread of non-channelized flows onto the fan and new scouring channel pathways down fan. Assessment of spatial and temporal complexities in a debris-flow system can improve risk prediction.
    • Compressibility of solid phase of debris flow and erosion rate

      Miyamoto, Kuniaki; Itoh, Takahiro; Kisa, Hiroshi (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      The change in sediment concentration of debris flow causes erosion and sedimentation of the solid phase of debris flows. Moreover, the changing affects the mobility of the flow. Therefore, knowledge of the mechanism of the changing is important to understand the mechanism of debris flow. The changing can be considered as compressibility of the flow of the solid phase. We developed a constitutive equation set of debris flow by concerning energy dissipation. A part of the energy dissipation is due to inelastic collision of particles. This process must be compressible. Therefore, we reinvestigate the process of the inelastic collisions and the effect to the compressibility. As the result, we lead internal energy to control the compressibility and so-called erosion rate equation. According to the erosion rate equation, it depends on bed gradient and energy loss gradient. A flume test is conducted to evaluate the erosion rate equation. by using a prismatic steep slope channel, which inclination is set at 12 degrees. By comparison of experimental result with the erosion rate equation, it is found that the difference between energy gradient and bed gradient to control the erosion/deposition is not so large. It means that the erosion/deposition might be very much sensitive against the unbalance of the energy gradient and bed gradient.
    • Concentration distribution in debris flow consisting of particles with two different sizes

      Kisa, Hiroshi; Miyoshi, Iwao (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Debris flows contain solid particles of various sizes. The gaps between large particles contain fine-grained sediment, and this is known to maintain high pore pressures. Inverse grading in which large particles become increasingly concentrated towards the surface of the flow is also known to occur. Therefore, to determine the flow behavior, it is important to clarify the grain-size distribution for not only large particles, but also fine sediment in the depth direction of the flow. In the present study, we generated a debris flow by eroding riverbed material consisting of large particles and fine-grained sediment in an experimental flume, and measured the concentration of different sized particles in layers at three different depths. The test results showed that the highest concentration of large particles was in the middle layer. The highest concentration of fine-grained sediment was in the bottom layer, and this concentration decreased towards the surface of the flow. Inverse grading was observed from the bottom layer to the middle layer; however, no noticeable inverse grading occurred from the middle layer to the upper layer. The reason for this kind of concentration distribution is considered to be that there was insufficient turbulence in the gaps between large particles in the bottom layer, and so fine-grained sediment settled, while in the upper layer, interstitial turbulent stress developed and fine-grained sediment was dispersed. We calculated the concentration distribution of fine-grained sediment from the middle to the upper layer on this basis, and the results were in general agreement with the measured distribution in the dispersion region.
    • Conceptual framework for assessing disturbance impacts on debris-flow initiation thresholds across hydroclimatic settings

      Mirus, Benjamin B.; Staley, Dennis M.; Kean, Jason W.; Smith, Joel B.; Wooten, Rick; McGuire, Luke A.; Ebel, Brian A. (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      The destructive and deadly nature of debris flows has motivated research into empirical rainfall thresholds to provide situational awareness, inform early warning systems, and reduce loss of life and property. Disturbances such as wildfire and land-cover change can influence the hydrological processes of infiltration and runoff generation; in steep terrain this typically lowers empirical thresholds for debris-flow initiation. However, disturbance impacts, and the post-disturbance recovery may differ, depending on the severity, nature, extent, and duration of the disturbance, as well as on the prevailing hydroclimatic conditions. Thus, it can be difficult to predict impacts on debris-flows hazards in regions where historically such disturbances have been less frequent or severe. Given the increasing magnitude and incidence of wildfires, among other disturbances, we seek to develop a conceptual framework for assessing their impacts on debris-flow hazards across geographic regions. We characterize the severity of disturbances in terms of changes from undisturbed hydrologic functioning, including hillslope drainage and available unsaturated storage capacity, which can have contrasting influences on debris-flow initiation mechanisms in different hydroclimatic settings. We compare the timescale of disturbance-recovery cycles relative to the return period of threshold exceeding storms to describe vulnerability to post-disturbance debris flows. Similarly, we quantify resilience by comparing the timescales of disturbance-recovery cycles with those of disturbance-recurrence intervals. We illustrate the utility of these concepts using information from U.S. Geological Survey landslide monitoring sites in burned and unburned areas across the United States. Increasing severity of disturbance may influence both recovery timescales and lower the return period for debris-flow inducing storms, thus increasing the vulnerability to disturbance-related hazards while also decreasing system resilience. The proposed conceptual framework can inform future data acquisition and model development to improve debris-flow initiation thresholds in areas experiencing increasingly frequent, severe, and even overlapping landscape disturbances.
    • Constraining parameter uncertainty in modeling debris-flow initiation during the September 2013 Colorado Front Range storm

      Baum, Rex L.; Scheevel, Caroline R.; Jones, Eric S. (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      The occurrence of debris flows during the September 2013 northern Colorado floods took the emergency management community by surprise. The September 2013 debris flows in the Colorado Front Range initiated from shallow landslides in colluvium. Most occurred on south- and east-facing slopes on the walls of steep canyons in crystalline rocks and on sedimentary hogbacks. Previous studies showed that most debris flows occurred in areas of high storm-total rainfall and that strength added by tree roots accounts for the low number of landslides in densely forested areas. Given the lack of rainfall thresholds for debris flow occurrence in northern Colorado, we want to parameterize a numerical model to assess potential for debris flows in advance of heavy rainfall. Natural Resources Conservation Service (NRCS) soil mapping of the area, supplemented by laboratory testing and field measurements, indicates that soil textures and hydraulic properties of landslide source materials vary considerably over the study area. As a step toward modeling storm response, available soil and geologic mapping have been interpreted to define zones of relatively homogeneous properties. A new, simplified modeling approach for evaluating model input parameters in the context of slope and depth of observed debris flow source areas and recorded debris-flow inducing rainfall helps narrow the range of possible parameters to those most likely to produce model results consistent with observed debris flow initiation. Initial results have narrowed the strength parameters to about one third of possible combinations of cohesion and internal friction angle and narrowed hydraulic conductivity to a range spanning slightly more than one order of magnitude.
    • Correlation between the slump parameters and rheological parameters of debris-flow

      Jan, Chyan-Deng; Yang, Chih-Yuan; Hsu, Ciao-Kai; Dey, Litan (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Rheological characteristics are important information for understanding or simulating debris-flow movement. Debris-flow movements involves complex and heterogeneous material with grain size distributions ranging from silt to large rocks. Conventional rheometers are usually limited to measure the rheological parameters of debris-flow of fine particles. Slump-tests has been used to evaluate the flow behaviour of fresh concretes which allow the tested concrete slurries to have larger particles. In this study, the relationship between the parameters obtained from rheometer measurements and slump tests for debris-flow slurries with/without big particles were investigated. At the initial stage, we used fine-sediment slurries to conduct rheological experiments to find the relationship between the parameters obtained from the rheometer measurements and slump tests. The rheological parameters of slurries were measured using the ‘Brookfield DV-III rheometer’. The rheological behavior of the slurry samples used in this study follow the Bingham fluid model. Rheological parameters (i.e., yield stress and viscosity) are affected by the concentration of slurry, indicating that the higher the concentration, the greater the value of the rheological parameters. Slump test was then conducted using the same material samples prepared for rheometer test and the slumped height and spreading diameter of the tested sample were measured. The result shows that the slump height ratio and spreading ratio of the tested slurry decrease with the increase of slurry sediment concentration. Experimental sediment slurry samples were prepared by mixing coarse sands of about 1 mm in diameter. Our results show that the parameters obtained by rheometer measurements are closely related with those by slump tests for the slurries used in this study, indicating that there is a high potential to evaluate rheological parameters of debris-flow using a slump test as an alternative method.
    • Debris flow assessment from rainfall infiltration induced landslide

      Hsu, Yu-Charn; Liu, Ko-Fei; Shu, Hung-Ming (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      In the study, debris flows induced by landslides are studied through physical models. TRIGRS and DEBRIS-2D models are integrated for simulation of rainfall infiltration induced shallow landslide and the subsequent debris flows. TRIGRS is used to estimate unstable mass on the hillslope and provide the initial volume for debris flow simulation, and DEBRIS-2D is applied to simulate mass motion and assess the hazard zone mapping. The method is applied to Daniao tribe’s sediment disaster during Typhoon Morakot in Taiwan. The simulated final deposition zone and the disaster area in the real event are almost identical. All the geophysical parameters are obtained through official values and rheological parameters are obtained by in situ measurements.
    • Debris flow behavior in super- and subcritical conditions

      Scheidl, Christian; McArdell, Brian; Nagl, Georg; Rickenmann, Dieter (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Observations of debris-flow events all over the world cover a wide range of phenomenologically similar processes, consisting of different concentrations of water, fine and coarse sediment, and frequently wooden debris. For this reasons, empirically derived coefficients to be used in prediction models to estimate debris-flow dynamics often show a wide degree of scatter. Two of such empirically derived concepts, originally developed for pure water flows, are presented in this study, showing similar deviations from hydrostatic stress assumption in subcritical flow conditions. The first concept is used to estimate debris-flow velocities, based on superelevation data. Based on our experimental results as well as observations from real debris-flow events at the field monitoring station at Illgraben (canton Valais, Switzerland) we show that the empirical coefficient used in the superelevation equation to account for non-Newtonian flow effects correlates with the Froude number – the dimensionless ratio between gravitational and inertia forces in the flow. Interestingly, a similar relationship – the second concept presented – has been found in recent studies to estimate the maximum impact pressure of a debris-flow event. Our results suggest that for debris flows and decreasing Froude numbers inertia forces become more important and the hydrostatic pressure distribution may be an unrealistic assumption for empirically based prediction models in subcritical conditions.
    • Debris flow building damage level and vulnerability curve: a case study of a 2015 typhoon event in northern Taiwan

      Tsao, Ting-Chi; Hsu, Chih-Hao; Yin, Hsiao-Yuan; Cheng, Keng-Ping (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Physical vulnerability of the building is the key element for debris-flow hazard Quantitative Risk Analysis (QRA). Most vulnerability curves were related to the deposition height (Fuchs et al., 2007; Lo et al., 2012), or the combination of deposition height, velocity, and impact force (Quan Luna et al., 2011; Jakob et al., 2012; Kang and Kim, 2016). This study uses datasets obtained from a debris-flow hazard caught on video in northern Taiwan during a 2015 Typhoon event and compare with the existing building damage classes and vulnerability curves. The deposition heights, ranging from 0.1 to 5-m, and damage levels of the 15 houses were carefully documented. Of these 15 reinforced-concrete, reinforced-brick, and brick houses, 7 were considered as totally destroyed judging by their actual damage level, others sustained various damages. The debris-flow velocity and impact force were simulated with RAMMS
    • Debris flow mitigation – research and practice in Hong Kong

      Ho, Ken K. S.; Koo, Raymond C. H.; Kwan, Julian S. H. (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Dense urban development on a hilly terrain, coupled with intense seasonal rainfall and heterogeneous weathered profiles, gives rise to acute debris flow problems in Hong Kong. The Geotechnical Engineering Office (GEO) of the Hong Kong SAR Government has launched a holistic R&D programme and collaborated with various tertiary institutes and professional bodies to support the development of a comprehensive technical framework for managing landslide risk and designing debris flow mitigation measures. The scope of the technical development work includes compilation of landslide inventories, field studies of debris flows, development and calibration of tools for landslide runout modelling, back analysis of notable debris flows, physical and numerical modelling of the interaction of debris flow and mitigation measures, formulation of a technical framework for evaluating debris flow hazards, and development of pragmatic mitigation strategies and design methodologies for debris flow countermeasures. The work has advanced the technical understanding of debris flow hazards and transformed the natural terrain landslide risk management practice in Hong Kong. New analytical tools and improved design methodologies are being applied in routine geotechnical engineering practice.
    • Debris flow monitoring using load cells and pressure sensors on Sakura-jima Island

      Itoh, Takahiro; Fujimura, Naoki; Katou, Hitoshi; Tagata, Satoshi; Mizuyama, Takahisa (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Numerous debris flows have recently taken place frequently in Sakura-jima Island located at southwest in Japan due to rainfall events after ash deposition due to volcanic activities since 2010. Debris-flow measurement system with loadcell and pressure sensor (DFLP) had been applied for debris-flow monitoring (Osaka et al., 2014). In present study, a modified monitoring DELP system using load cells and a stainless-steel plate is employed. Mass density and sediment concentration are calculated using data obtained by the DFLP system and data measured by ultrasonic level meter and surface velocity by of image analyses of CCTV camera. (Results) Temporal changes of specific weight, sediment concentration and sediment volume of debris-flow in Nojiri and Arimura Rivers in 2014 were well measured using DFLP system. Sediment concentration and specific weight were calculated in both rivers, and there are at least 10 data in Arimura River and 8 data in Nojiri River for calculations of temporal changes of mass density and sediment concentration since 2012 and 2014, respectively. Averaged sediment concentration near peak discharge are calculated as 0.441 in Arimura River and 0.279 in Nojiri River, respectively. However, values of calculated concentration do not always take correlation with rainfall depth before debris-flow occurrences. Data analyses continuously need by more data collections of debris- flow events.