• Hydrogeomorphology and steep creek hazard mitigation lexicon: French, English and German

      Camiré, Félix; Piton, Guillaume; Schwindt, Sebastian (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Geoscientists, researchers and engineers study and work on similar projects all over the world. The exchange of information between colleagues of different countries who work on homologous projects or in similar fields requires a common technical vocabulary. Differences in the usage of technical terms and their varying definitions in different regions of the world may constrain the transfer of knowledge, for example in guidelines. Translations of technical papers and of presentations are particularly complicated and troublesome. Moreover, writers waste valuable time when they try to find proper technical terms in a different language. This is currently the case in the fields of fluvial geomorphology and steep creek hazard mitigation since several countries are active in these domains. Papers, guidelines, and policies are published in several languages, such as Japanese, Italian, French, German, English, Korean, Chinese and Spanish. International delegates are also submitting papers to journals, presenting and participating at conferences that are predominantly in English. Finally, working groups with multinational participants have been formed to advance research and transfer of knowledge in fluvial geomorphology and steep mountain creek hazard mitigation. Therefore, standardization and better definitions of technical terms are required. We propose in this paper a lexicon of French, English and German technical terms, and their definitions, related to the fields of fluvial geomorphology and steep mountain creek hazard mitigation. This paper focuses on the most important terms. In the future, other languages and supplemental terms could be added to this document with the help of other contributors.
    • Review of the mechanisms of debris-flow impact against barriers

      Poudyal, Sunil; Choi, Clarence E.; Song, Dongri; Zhou, Gordon G.D.; Yune, Chan-Young; Cui, Yifei; Leonardi, Alessandro; Busslinger, Matthias; Wendeler, Corinna; Piton, Guillaume; et al. (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Our limited understanding of the mechanisms pertaining to the force exerted by debris flows on barriers makes it difficult to ascertain whether a design is inadequate, adequate, or over-designed. The main scientific challenge is because flow-type landslides impacting a rigid barrier is rarely captured in the field, and no systematic, physical experimental data is available to reveal the impact mechanisms. An important consideration in flow-structure interaction is that the impact dynamics can differ radically depending on the composition of the flow. Currently, no framework exists that can characterize the impact behavior for a wide range of flow compositions. This review paper examines recent works on debris-flow structure interactions and the limitations of commonly used approaches to estimate the impact load for the design of barriers. Key challenges faced in this area and outlook for further research are discussed.
    • Debris-flow risk assessment and mitigation design for pipelines in British Columbia, Canada

      Gartner, Joseph E.; Jakob, Matthias (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Pipelines in mountainous terrain in British Columbia, Canada often cross debris-flow fans and channels along valley bottoms and can be susceptible to various geohazard impacts, including debris flows. The design of new pipeline infrastructure and maintenance of existing pipelines necessitates debris-flow risk assessments and appropriate mitigation design. A methodology is presented for assessing debris-flow risk along pipeline routes that consists of estimating the probability of a debris flow causing a pipeline loss of containment or disruption in service. The methodology consists of estimating debris-flow frequency, scour potential, and the vulnerability of the pipeline to break if impacted. Debris-flow frequency is estimated based on field observations of debris-flow deposits, degree of vegetative growth on debris-flow deposits, evidence of debris-flow impacts on trees near the pipeline crossing, documented debris-flow events, review of historical air photos and terrain mapping based on LiDAR-generated topography. Debris-flow scour potential is estimated based on channel morphology, presence of bedrock and grain size distribution of channel bed material. Vulnerability is estimated based on flow width and velocity and can be modified for different pipe diameters and wall thicknesses. Mitigation options for buried pipelines include those intended to decrease the likelihood of bed and bank scour (e.g. rip rap bed and bank protection), decrease the likelihood of the pipeline being exposed (increasing the burial depth of the pipeline) and to increase the resiliency of the pipeline to debris-flow impacts if exposed, (e.g. increasing pipeline wall thickness, adding concrete coating to the pipeline). The final option is to prevent debris flows from reaching the pipeline by designing and installing debris-flow deflection berms or sedimentation basins. The methodology presented is embedded in risk-informed thinking where pipeline owners and regulators can define probability thresholds to pipeline exposure or rupture and the pipeline designer needs to show that the proposed mitigation measures achieve these threshold criteria in ways that honor the ‘as low as reasonably practicable’ (ALARP) principle.
    • Evaluation of shallow landslide-triggering scenarios through a physically based approach: a case study from Bulathsinhala area, Sri Lanka

      Jayasekara, E. I.; Weerasekara, N. K.; Jayathissa, H. A. G.; Gunatilake, A. A. J. K. (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Transient Rainfall Infiltration and Grid-based Regional Slope-stability analysis (TRIGRS) is a regional, physically based stability model which could be applied to predict shallow landslides. It is important to evaluate the accuracy of TRIGRS for the prediction of landslide locations using actual events before use the TRIGRS model for further applications. This study presents the application of TRIGRS for Bulathsinhala area, Kaluthara in south western part of Sri Lanka where the number of shallow landslides occurred on 26th May 2017 and many of those events transitioned into damaging and killing debris flows. A back analysis of that landslide event was executed to authenticate the model by using different methods and techniques for the definition of the input parameters. Reliability of the model was evaluated through comparison with the 2017 landslide inventory in the particular area and it was revealed that most of the actual landslides were occurred in the predicted area (FS<1) of the model. In order to quantify the effectiveness of the model, an index was proposed in the study called LRclass (landslide ratio for each predicted FS class). The obtained values of the LRclass index realize the trustworthiness of the model which indicates the considerably higher value (60%) for the lowest stability class. With this particular manner, the output of the study could be used to implement more reliable land use management and development plans and resettlement procedures. Further the TRIGRS model is advantageous for susceptibility mapping and landslide flow path analysis, particularly when linked with various advanced applications using GIS spatial functions.
    • Weather-radar inferred intensity and duration of rainfall that triggered the January 9, 2018, Montecito, California, disaster

      Keaton, Jeffrey R. (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Slopes above Montecito burned by the Thomas Fire in December 2017 produced disastrous debris flows in response to a short period of intense precipitation on January 9, 2018, killing 23 people, injuring many others, destroying and damaging residential buildings, and community infrastructure. The intense precipitation was in a narrow cold frontal rainband which obviously exceeded the intensity and duration threshold for post-wildfire debris flows. Rain gauges with self-activating radio transmitters reported by County of Santa Barbara Department of Public Works documented the precipitation in the Montecito area as it occurred, which allowed short-duration intensities to be calculated. Data from the rain gauge on Montecito Creek was used in this paper and showed that the rainband that produced the precipitation that generated the debris flows passed over Montecito in about one-half hour. Two weather radar stations operated by the National Weather Service are located within about 100 km of Montecito. Both stations were operational and recorded radar reflectivity on a frequency of about five minutes during the entire storm; data from the KVTX station located east of Montecito was used for this paper. Montecito is located on a coastal plain south of the Santa Ynez Mountains, which shield the lower elevations in the Montecito area from direct view of the radar stations. Composite radar reflectivity represents the amount of water droplets in the atmosphere in line-of-sight above the ground. The weather radar shows patterns similar to the precipitation documented by the rain gauges. Radar reflectivity at the coordinates of the rain gauge on Montecito Creek and at the coordinates of a point in the Santa Ynez Mountains on the west side of the Santa Ynez Creek watershed was extracted and converted to an approximate rainfall depth using a general National Weather Service relationship. The results are used to demonstrate the value of weather radar reflectivity for visualization and for developing approximate rainfall intensity and duration estimates at positions of interest remote from rain gauges for comparison with post-wildfire debris-flow thresholds.. The analysis in this paper was developed as part of the Geotechnical Extreme Event Reconnaissance (GEER) Association response to the Montecito disaster.
    • 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.
    • Numerical simulation for evaluating the phase-shift of fine sediment in stony debris flows

      Uchida, Taro; Nishiguchi, Yuki; McArdell, Brian W.; Satofuka, Yoshifumi (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      To predict hazard-endangered areas and debris-flow velocity, a variety of physically-based numerical simulation models have been developed. In these models, the relatively large sediment particles such as boulders move as a laminar flow, but the interstitial fluid between sediments behaves like a turbulent flow. Moreover, several recent models assumed that fine sediments act as a fluid. This behavior of fine sediment is referred to as the “phase-shift” of fine sediment. However, because it is difficult to observe the phase-shift of fine sediment in the field, adequate data on the phase-shift of debris flow are still lacking. In the last two decades, intensive monitoring for debris flow has been conducted all over the world, and observations have dramatically increased. For example, in the Illgraben catchment, Switzerland, observations of bulk density, pore pressure, flow depth, front velocity, and temporal and spatial patterns of erosion due to debris flows are available. So, we used these data for model input conditions. We applied the numerical simulation model Kanako-LS to evaluate the phase-shift concept for describing a variety of debris flow properties and behaviors at the Illgraben, Switzerland. Here we successfully describe a variety of observed debris flow behaviors, such as erosion and deposition pattern and shape and velocity of debris-flow fronts. However, if we ignored effects of phase-shift, the deposition volume was overestimated and flow velocity was underestimated.
    • Effect of rheological properties on debris-flow intensity and deposition in large scale flume experiment

      Nguyen, Ba-Quang-Vinh; Lee, Ji-Sung; Kim, Yun-Tae; Lee, Seung-Rae; Kwon, Tae-Hyuk (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Debris flows are one of the most serious hazards in the mountainous areas. To assess and mitigate the debris-flow hazard, debris- flow intensities and deposition on fans must be estimated. Rheological properties including yield stress and viscosity are major parameters to describe and predict behaviors of debris flow. In the present study, the effect of rheological properties on debris-flow intensities and deposition on fans of natural clay was investigated using large scale flume experiments. The experimental device employed in the tests consists of a tilting flume with an inclination 17°, on which a steel tank with a removable gate was installed. A final horizontal plane works as the deposition area. Natural soil samples of different water contents were tested. Rheological properties of soil mixtures were obtained from vane-rheometer tests. Non-linear regression analysis was used to assess the effect of yield stress and viscosity on debris-flow velocity, runout distance, deposited area and deposited volume. We found that the relationship between surface velocity profile and horizontal distance was complicated and could be expressed by sixth order polynomial function. Mean velocity, runout distance, deposited area decreased following a power law with an increase in yield stress and viscosity. Empirical equations were proposed to estimate these properties. The results of laboratory tests compared reasonably well with the results from numerical analysis. The results indicated that yield stress and viscosity play a significant role in the behavior of debris flow.
    • Seamless numerical simulation of a hazard cascade in which a landslide triggers a dam-breach flood and consequent debris flow

      George, David L.; Iverson, Richard M.; Cannon, Charles M. (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Numerical simulations of hazard cascades downstream from moraine-dammed lakes commonly must specify linkages between models of discrete processes such as wave overtopping, dam breaching, erosion, and downstream floods or debris flows. Such linkages can be rather arbitrary and can detract from the ability to accurately conserve mass and momentum during complex sequences of events. Here we describe an alternative methodology in which we use high-resolution lidar topography and 2-D, two-phase conservation laws to seamlessly simulate all stages of a hazard-cascade that culminates in a debris flow. Our simulations employ our depth-integrated numerical model D- Claw to evaluate hazards from prospective breaching of a moraine dam that impounds Carver Lake on the eastern flank of South Sister volcano in central Oregon, USA. We simulate a “worst-case scenario” sequence of events that begins with a hypothetical 1.6 million m3 landslide that originates near the summit of South Sister and enters Carver Lake. Wave generation and displacement of lake water then leads to dam overtopping, breach erosion, and a downstream debris flow that funnels into Whychus Creek and eventually reaches the community of Sisters, Oregon, about 20 km away. Notably, our simulations predict that much of the debris is directed away from Sisters as a result of natural avulsion and flow diversion that occurs near the head of a low-gradient alluvial fan upstream from Sisters. Consequently, predicted hazards to downtown Sisters are less severe than those predicted by 1-D shallow-water simulations of a Carver Lake dam breach that were performed in the 1980s.
    • Flume experiments and numerical simulation focused on fine sediments in stony debris flow

      Hina, Junya; Uchida, Taro; Matsumoto, Naoki; Sakurai, Wataru; Nishiguchi, Yuki; Murakami, Masato (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      In stony debris flow, it has been considered that the gravels move like laminar flow, but the interstitial water behave as turbulent flow. Moreover, fine particles can behave with the interstitial water as fluid and many previous studies call this process of fine sediment as shifting solid phase to fluid phase, “phase-shift”. Phase-shifted sediment affect the fluidity of debris flow. Therefore, it is necessary to consider fine sediments behavior to describe run-out processes of debris flow. However, the hydraulic conditions that fine sediment can behave as a fluid are not well understood. Here, we analyzed this hydraulic condition through flume experiments and numerical simulations. We examined effects of grain size distribution on the equilibrium sediment concentration, which has been defined as the sediment concentration that in which there is neither erosion nor deposition on the experimental flume bed. We found that for the same hydraulic conditions the equilibrium sediment concentration differed due to variations in the grain size distribution. Based on these experimental results, we tested the following three models for describing the conditions that fine sediment can behave as a fluid. First, we fixed fine sediment concentration in interstitial fluid (Model 1), then, we fixed the maximum diameter of phase-shifted sediment (Dc) (Model 2). In Model 3, Dc is assumed to be variable according to the ratio of the friction velocity to the settling velocity of Dc. As the result, the experimental relationship between grain size distribution and longitudinal gradient of deposited sediment surface under steady-state condition can be described by using the Models 2 and 3, but Model 1 could not describe.
    • Deciphering debris-flow seismograms at Illgraben, Switzerland

      Wenner, Michaela; Walter, Fabian; McArdell, Brian; Farinotti, Daniel (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Mass wasting, such as rockfalls, landslides and debris flows in steep mountain terrain, has a high destructive potential, and plays a key role in both erosion and landscape evolution. As an alternative to many conventional approaches, seismology allows monitoring of such mass movements at safe distances, provides estimates of event location and timing, and can give insights into dynamics and rheology granular flows. Here, we analyze seismic data recorded during the 2017 and 2018 debris-flow seasons at Illgraben, a steep canyon located in Switzerland. Yearly precipitation is controlled by summer rainstorms with high rainfall intensity during which mass wasting including rock-slope failure and debris flows occur regularly. The frequent debris-flow occurrence (on average three events per year) makes the Illgraben an ideal site for cross-validating a seismically-derived event catalog of mass movements with “ground-truth data”, such as digital terrain models, flow depths estimates and other in-torrent measurements. We present seismic frequency characteristics of the Illgraben debris-flow series and investigate how the seismic signature depends on actual debris-flow characteristics, such as grain sizes, and on propagation effects of the generated seismic waves. Whereas these two effects are usually difficult to separate, the source component contains valuable information on the flow’s material composition. Stations that are close to the torrent, we find that dominant frequencies in the recorded signal reflect the distance to the dominant source. For one particular station, this is shown on recordings of several events, where a dominant frequency of about 5.5 Hz indicates the passing of the flow at a 48m check dam. Power spectral densities at that instance give an estimate of the particle content of the debris flow. We also find that a jump in dominant frequency does not necessarily reflect the location of the flow front. Seismic studies of debris-flow dynamics and material composition should therefore not be limited to entire debris-flow seismograms, but instead focus on individual time windows and consider different sensors separately. The presented analysis underlines the use of seismic data in torrent and landscape studies.
    • Numerical investigation of deposition mechanism of submarine debris flow

      Liu, Dingzhu; Cui, Yifei; Choi, Clarence E.; Bazai, Nazir Ahmed; Yu, Zhilin; Lei, Mingyu; Yin, Yanzhou (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Submarine debris flow can damage oil and gas transport pipelines with potentially adverse consequences to the environment and to the industrial activity itself. The deposition process of submarine debris flow, which is related to the flow viscosity, is complex due to the slurry diffusion process that happens during the interaction of water and slurry. In addition, a quantitative characterization of the characterize the flow mechanism as influenced by the material density during the deposition process remains a scientific challenge. To fundamentally understand the mechanisms of solid-fluid interactions in fast-flowing submarine debris flows, a series of three-dimensional (3D) numerical simulations using Computational Fluid Dynamics (CFD) were conducted. The Herschel- Bulkley (HB) model was used to define the submarine slurry’s rheological characterization as calibrate through simple rheological experiment. Results reveal that deposition is a mass diffusion process. Shear stress at the bottom and at the top of the slurry leads to velocity differences in the vertical direction which in turn generates a huge vortex, which contributed to a separation of slurry into two parts: the frontal head, and the tail. The velocity difference in vertical direction is helpful for hydroplaning. For higher slurry viscosity case, the flow profile is longer and thicker with a front head that has a lower averaged densities and sharper head angles. In addition, highly viscous slurries have lower average frontal velocities during the deposition process. The mixture density decreases in two stages: quick decreasing stage and stable decreasing stage. In the first stage, the slurry expands quicker than the second stage. Higher viscosities also lead to larger volume expansions which consequently leads to quicker density decrease.
    • Debris flows in the North Pacolet River valley, Polk County, North Carolina, USA: case studies and emergency response

      Bauer, Jennifer B.; Wooten, Richard M.; Cattanach, Bart L.; Fuemmeler, Stephen J. (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      The North Pacolet River valley is incised into the Blue Ridge Escarpment (BRE) near Tryon in southwestern North Carolina. The BRE is a mountain front that marks the change from the mountainous Blue Ridge physiographic province to the lower, rolling topography of the foothills zone of the Piedmont provinces. This escarpment is often comprised of steep slopes with exposed bedrock cliffs and shallow colluvial soils. The down slope sides of the escarpment have evidence of past slope movements in the form of large scale deposits, debris fans, talus slopes, and dormant debris slides. Debris flows have been documented along the BRE in multiple past storm events including those in 1916, 1940, 1996, and 2004. On May 18, 2018, debris flows again initiated near the top of the BRE slopes and travelled down to the North Pacolet River valley floor during heavy rains on soils with high antecedent moisture contents. At least 27 debris flows were initiated, travelling up to ~966 meters (~3,170 feet) down drainages below. At least 6 homes were damaged or destroyed and one fatality occurred due to these debris flows. Main highways, interstates, and multiple private roads were covered by the debris. Appalachian Landslide Consultants, PLLC (ALC) and the North Carolina Geological Survey (NCGS) responded to this emergency situation in order to provide Polk County Emergency Management information about the stability of the slopes before the arrival of Tropical Depression Alberto just 9 days after the May 18 rains. During this reconnaissance, ALC and the NCGS identified areas of potential instability in the coming rains. County Emergency Management used this information when deciding to issue a voluntary evacuation recommendation to the people of the North Pacolet River valley. This paper discusses the findings of the reconnaissance mapping, as well as a general overview of the integration of geological information into emergency response and preparation.
    • Hillslope evaluation in the vicinity of the Wolsong nuclear power plant after 12th September 2016 Gyeongju earthquake, South Korea

      Pradhan, Ananta Man Singh; Lee, Ji-Sung; Lee, Seung-Rae; Kwon, Tae-Hyuk; Kim, Yun-Tae (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Landslides result not only from the environmental background conditions of slopes but also from triggering factors, such as rainfall and earthquake. Severe landslides and debris flows are common natural disasters in South Korea since it is characterized by high rainfall and rugged topography. A secondary effect of an earthquake could be slope instability. A 5.8-magnitude (ML) earthquake, the most powerful seismic activity since the nation started measuring tremors, struck the historic city of Gyeongju, North Gyeongsan Province, at 20:32:54 KST. The Wolsong nuclear power plant is situated in the foothills of a mountainous area about 26 km SE of the earthquake epicenter. South Korea’s biggest historical earthquake raised the nuclear safety concerns. To assess regional landslide hazard under the conditions of heavy rainfall and after 5.8 ML Gyeongju earthquake, this study, a coupled hydrological model with infinite slope model was used to find the hillslope stability under the roles of rainfall and earthquake.
    • Estimation of temporal changes of debris flows and hydraulic model tests of channel works with multi-drop structures

      Watabe, Haruki; Ikeshima, Tsuyoshi; Nishi, Yotaro; Nagarekawa, Yohei; Matsuda, Satoru; Nakayama, Takashi; Itoh, Takahiro; Mizuyama, Takahisa (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      A debris-flow disaster took place in the Nashizawa creek in Kiso River catchment, Nagano Prefecture, Japan on 9th July 2014 due to intensive rainfall from the typhoon Neoguri. There were few data available for estimation of debris-flow discharge in the catchment. A CCTV camera and a high sensitivity seismometer were installed along Nashizawa creek prior to the debris flows. Surges of debris flows were recorded by CCTV camera, though the camera was eventually destroyed by those surges during debris flows. The shape of debris-flow surges was estimated using the discharge analysed by CCTV camera data and fitting curve of relations between debris-flow discharge and acceleration of vibration. Peak discharge was extrapolated from peak acceleration of the vibration, and was estimated about 756 m3/s. At the Nashizawa creek, channel works with multi-drop structures were planned for construction after the debris-flow disaster. Some research was conducted experimentally for planning and design of channel works such as multi-drop structures. This research pointed out several problems for multi-drop structures in supercritical flow such as scouring and flow depth increases due to shock waves. We investigated characteristics of shockwaves and countermeasures using multi-drop structures in a steep channel with supercritical flow experimentally to design the channel works. We found that stair-type dissipaters are effective for mitigating shockwaves from multi-drop structures.
    • Implementation of an integrated management strategy to deal with landslide triggered debris flows: the Valloire case study (Savoie, France)

      Laigle, Dominique; Jongmans, Denis; Liebault, Frédéric; Baillet, Laurent; Rey, Etienne; Fontaine, Firmin; Borgniet, Laurent; Bonnefoy-Demongeot, Mylène; Ousset, Frédéric (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      The Rieu Benoît is a debris-flow-prone catchment located in Valloire (Savoie, France). In 2011, a lateral landslide was detected about 600 m upstream of the fan apex where houses are present. This landslide has evolved slowly since 2011 but is likely, in case of rapid collapse, to provide up to 150,000 to 200,000 m3 of material to the channel and generate intense debris flows thus threatening human settlements on the fan and in the Valloire ski resort. This paper presents a contribution to the definition of a protection strategy based on the principle that a catastrophic evolution of the landslide can be detected sufficiently in advance to set up an effective alert procedure. Such early warning system can be designed provided (i) the landslide is instrumented to properly detect its evolution and characterize the volumes likely to mobilize into debris flows, this is carried out using photogrammetric, seismic, and electrical techniques; (ii) the interaction between the landslide and the channel is observed and sufficiently understood, this is carried out using a time-lapse camera taking a picture every two hours and at higher frequency once a flow is detected by a geophone; (iii) subsequent debris flows are observed and characterized in terms of flow thickness and velocity, this is carried out at a monitoring station located at the fan apex and equipped with a radar flow stage sensor and three geophones; (iv) consequences on urbanized areas are evaluated a priori on the basis of scenarios, this is carried out by simulating the spreading of debris flows for different volumes and material properties. The final step consists in building alert and evacuation procedures in collaboration with local authorities.
    • Discrete-element investigation of granular debris-flow runup against slit structures

      Du, Junhan; Zhou, Gordon G. D. (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Runup of granular debris flows against slit dams on slopes is a complex process that involves deceleration, deposition and discharge. It is imperative to understand the runup mechanism and to predict the maximum runup height for the engineering designs and hazards mitigation. However, the interaction between granular flows and slit dams, which affects the runup height significantly, is still not well understood. In this study, a numerical investigation of granular debris flow impacting slit dams by the discrete element method (DEM) was then conducted. The influence of the opening size of slit dams characterizing by the relative post spacing R=b/d (b: post spacing; d: particle diameter) on runup height was studied. Numerical study illustrates that there is a critical value of relative post spacing (RC): within the critical value, the maximum runup height is insensitive to the relative post spacing; once b/d exceeds the critical value, the maximum runup height decreases rapidly as the relative post spacing increases.
    • Monitoring of sediment runoff and observation basin for sediment movements focused on active sediment control in Jo-Gan-Ji River

      Nagayama, Takahiko; Furuya, Tomohiko; Matsuda, Satoru; Itoh, Takahiro; Fujita, Masaharu; Mizuyama, Takahisa (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Continuously measuring sediment runoff along multiple sections of the Jo-Gan-Ji River is necessary to understand both the propagation of sediment as well as the changing of grain sizes in order to appropriately evaluate sediment yielding from debris flows temporally and spatially. The present study proposes a combination of sediment monitoring tools and appropriate equipment to identify various sediment transport modes from wash load to bedload in mountainous torrents. As a result of monitoring runoff volume and grain sizes, sediment management can be achieved. In the Jo-Gan-Ji River basin in Japan, temporal and longitudinal sediment runoff has been measured continuously since the 1990's. Previous studies help determine the proper instrumentation suite for this type of sediment runoff monitoring. Bedload is measured with a Reid-type bedload slot sampler and by use of the hydrophone to survey acoustic waves. In addition, hydrophones and a velocity meter (vertically installed on a side wall) are used to quantify suspended loads. A turbidity meter is also used to measure wash load. Propagation of sediment particles can be observed during flooding in mountainous torrents. Specifically, bedload discharge rates of each particle are evaluated using of the hydrophone. Monitoring of the Jo-Gan-Ji river also identifies inactive bedload movements such as large boulders. Previous installations of this type monitoring equipment make it clear that the destructive nature of bedload collisions indicate a need for robust instruments. Alternate instrumentation methods, that are robust, are explored here. Moreover, in order to actively control sediment runoff in flooding, we developed a sabo dam with shutter and pilot operations that activate during flooding. Differences of those sediment transport characteristics with/without the shutter also shown through the sediment monitoring along the Jo-Gan-Ji River.
    • Steel stakes to capture debris-wood on an impermeable Sabo-type dam

      Harada, Norio; Satofuka, Yoshifumi (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      It is important to capture driftwood, namely, woody debris, in upstream areas to prevent debris flows from blocking downstream bridges. Specific details of the conditions of dams in Japan must be taken into consideration when investigating this issue. There have been recent proposals to use steel stakes as countermeasures to woody debris blockage at impermeable Sabo-type dams. To design such a countermeasure effectively, it is necessary to clarify the woody debris capture mechanisms implemented by the countermeasure. We proposed a structure composed of steel stakes for use at impermeable Sabo-type dams. This proposal is based on experiments that take into consideration the rotation of woody debris at Sabo dams and the mechanism by which woody debris is captured at the stakes.
    • Debris-flow hazard assessments: a practitioner's view

      Jakob, Matthias (Colorado School of Mines. Arthur Lakes LibraryAssociation of Environmental and Engineering Geologists, 2019)
      Substantial advances have been made in various aspects of debris-flow hazard and risk assessments over the past decade. These include sophisticated ways to date previous events, runout models including multi-phase flows and debris entrainment options, and applications of extreme value statistics to assemble frequency-magnitude analyses. Finally, quantitative risk management (QRM) has emerged as the most rational and defensible method to assess debris- flow risk and optimize mitigation efforts. Pertinent questions, of course, have remained the same: How often, how big, how fast, how deep, how intense, how far and how bad? Similarly, while major life loss attributable to debris flows can often, but not always, be avoided in developed nations, debris flows remain one of the principal geophysical killers in mountainous terrains. Substantial differences persist between nations in hazard or risk management. Some rely on a design magnitude associated with a specific return period, others use relationships between intensity and frequency, and some allow for, but do not mandate, in-depth quantitative risk assessments. The range in return periods considered in hazard and risk assessments varies over two orders of magnitude from 1:100 to 1:10,000. In many nations, access to funding and lack of at least regional prioritization provides the biggest obstacles to widespread safeguarding against debris flows. Two factors conspire to challenge future generations of debris flow researchers, practitioners and decision makers: Population growth and climate change. The former will invariably invite continued development in debris-flow prone areas, especially fans, floodplains and terraces subject to lahars or landslide/moraine dam/glacial outburst floods which, at times, assume debris-flow characteristics. As far as debris flows are concerned, climate change is manifesting itself increasingly by augmenting hydroclimatic extremes, especially a several-fold increase in the frequency of short-duration high-intensity rainfall that may soon exceed historical precedents. While researchers will undoubtedly finesse future remote sensing, dating and runout techniques and models and bring some of those to a degree of maturity, the practitioners will need to focus on translating those advances into practical cost- efficient tools and closely collaborate with clients to integrate those tools into meaningful long-term debris-flow risk management. Future debris flow disasters will not occur due to a lack of quantitative methods, but likely due to the lack of recognition, wilful ignorance of debris-flow hazards, lack of enforcement of risk management policies, or simply a lack of means to mitigate against known debris flow risks.