Debris flows: behaviour and hazard assessment

Debris flows are water‐laden masses of soil and fragmented rock that rush down mountainsides, funnel into stream channels, entrain objects in their paths, and form lobate deposits when they spill onto valley floors. Because they have volumetric sediment concentrations that exceed 40 percent, maximum speeds that surpass 10 m/s, and sizes that can range up to ～10⁹ m³, debris flows can denude slopes, bury floodplains, and devastate people and property. Computational models can accurately represent the physics of debris‐flow initiation, motion and deposition by simulating evolution of flow mass and momentum while accounting for interactions of debris’ solid and fluid constituents. The use of physically based models for hazard forecasting can be limited by imprecise knowledge of initial and boundary conditions and material properties, however. Therefore, empirical methods continue to play an important role in debris‐flow hazard assessment.     

Integrating uncertainty: Canyon Creek hyperconcentrated flows of November 1989 and 1990

Canyon Creek drains a 79 km² watershed in northwestern Washington State. Extensive logging occurred from the mid-1960s to 1980s, which resulted in numerous slope instabilities and a several order of magnitude increase in sediment supply to the creek. On November 9, 1989, a hyperconcentrated flow with a peak discharge of 450 m³/s destroyed one house on the fan. A forensic investigation of the event suggests that a temporary landslide dam may have formed at two coalescing earthflows about 4 km above the fan apex. The 1989 hyperconcentrated flow caused significant aggradation on the fan. One year later to the day, a significant flood occurred, which ran over the aggraded fan surface from the 1989 event. This latter event destroyed four more homes mostly through bank erosion and rendered a section of county road impassable. FLDWAV, a flood routing model capable of simulating unsteady flow conditions, was used to model landslide dam breaches for a number of different dam heights at the earthflows. Modeling results were then combined with historic air photograph interpretation, dendrochronology, and eyewitness accounts to construct a frequency–magnitude relationship for hyperconcentrated flows at Canyon Creek. FLDWAV results were combined with a hyperconcentrated flow runout model (FLO-2D) on the fan to estimate maximum flow depth and flow velocity for the design event, a 500-year return period with a predicted peak discharge of 710 m³/s. A large range of mitigation measures were reviewed, but it was concluded that buy-outs would be the most effective risk reduction measure. Property acquisition commenced in 2004.     

Debris flows caused by failure of fill slopes: early detection,warning, and loss prevention

This paper describes early detection, warning, and loss prevention for debris flows originating as failures of fill slopes. Worldwide, fill slopes constructed on steep terrain for roads, hillside residential developments, timber harvest landings, etc., are an increasing source of debris-flow hazards. Some fill failures that generate debris flows are the final stage of incremental failures that provide warning signs of instability in the months or years before the debris flow. Mapping and analysis of minor features, such as cracks and small scarps, on paved or unpaved surfaces of fills can identify incipient and impending fill failures that are major debris-flow hazards. Potential debris-flow paths can be mapped and risk assessments conducted. Loss prevention or reduction can be achieved by (1) prioritized maintenance, (2) prioritized repair, (3) monitoring, (4) warnings for emergency officials and the public, and (5) risk avoidance or reduction in land-use planning, zoning, cooperation between jurisdictions, and project development.     

James M. Harrison Award

The James M. Harrison Award for Outstanding Achievement was established by the IUGS Executive Committee in 2004 to honor individuals who served the Union in an extraordinary fashion for a long period of time, and who have no recognized posi- tion as an officer of the Union. The award is named for the late James M. Harrison, an internationally known and respected Cana- dian geologist （Geological Survey of Canada） who was one of the founding fathers of the lUGS and its first President （1961-1964）.     

James M. Harrison Awards

The James M. Harrison Award for Outstanding Achievement was established by the IUGS Executive Committee in 2004 to honor individuals who have served the Union in an extraordinary fashion for a long period of time, and who have no recognized position as an officer of the Union. The award is named for the late James M. Harrison, an internationally known and universally respected Canadian geologist (Geological Survey of Canada) who was one of the founding fathers of the IUGS and its first President (1961-1964).     

Debris flows in the Lushan earthquake area: formation characteristics,rainfall conditions,and evolutionary tendency

Debris flows often occur in the mountainous watersheds of earthquake-affected areas, and in the Lushan earthquake area of southwestern China, they have become a significant hazard. In this study, the influencing factors and spatial distribution of debris flows were analyzed through a review of their occurrence history. Debris flows are mainly distributed in the northwestern part of the study area, which hosts the greatest density of active faults. The debris flows are generally formed by the ‘progressive bulking’ effect in channels, and deep incision, lateral erosion, and blockage breaking are common processes that amplify the magnitude of such debris flows. Rainfall thresholds for different types of debris flow were proposed to explain the spatial differences between debris-flow regions, and the temporal variations of those thresholds highlighted how the rainfall conditions required for the occurrence of debris flows have changed. Natural vegetation recovery, reduction in the availability of solid material, and artificial debris-flow control projects play important roles in raising the threshold of the rainfall conditions required for triggering debris flows.

     

Debris flows of 28 June 2014 near the Arshan village (Siberia,Republic of Buryatia,Russia)

On 28 June 2014, high intensity rainfall resulted in seven simultaneous debris flows going down the slopes of the Tunka Ridge in the vicinity of Arshan village, which is a balneological and alpine resort (51° 54′ 31″ N, 102° 25′ 44″ E). The debris flows caused one life loss and several injuries, 112 buildings were damaged, and 15 were completely destroyed. The total volume of the transported deposits amounted to 3?×?10⁶ m³. Debris flows’ formation began with the failure of weak sediments in the hanging cirques. Similar phenomena had not been recorded in the study area for over 40 years. The article presents a complete picture of the event and analysis of geological, geomorphological, and meteorological conditions for debris flows formation, for which extreme local rainfall was the major cause.     

Debris flows and their toll on human life: a global analysis of debris-flow fatalities from 1950 to 2011

Debris flows cause significant damage and fatalities throughout the world. This study addresses the overall impacts of debris flows on a global scale from 1950 to 2011. Two hundred and thirteen events with 77,779 fatalities have been recorded from academic publications, newspapers, and personal correspondence. Spatial, temporal, and physical characteristics have been documented and evaluated. In addition, multiple socioeconomic indicators have been reviewed and statistically analyzed to evaluate whether vulnerable populations are disproportionately affected by debris flows. This research provides evidence that higher levels of fatalities tend to occur in developing countries, characterized by significant poverty, more corrupt governments, and weaker healthcare systems. The median number of fatalities per recorded deadly debris flow in developing countries is 23, while in advanced countries, this value is only 6 fatalities per flow. The analysis also indicates that the most common trigger for fatal events is extreme precipitation, particularly in the form of large seasonal storms such as cyclones and monsoon storms. Rainfall caused or triggered 143 of the 213 fatal debris flows within the database. However, it is the more uncommon and catastrophic triggers, such as earthquakes and landslide dam bursts, that tend to create debris flows with the highest number of fatalities. These events have a median fatality count >500, while rainfall-induced debris flows have a median fatality rate of only 9 per event.     

新型屋脊式拦砂坝拦挡输移性能试验研究

随着人们对泥石流拦砂坝的研究与应用,拦挡结构从竖向拦挡逐渐向水平筛分发展。为了对泥石流进行有效筛分和减小泥石流冲击力,提出新型屋脊式拦砂坝,并通过试验研究其对泥石流的拦挡筛分效果。本文通过试验,模拟不同泥石流来量、坝体格栅间距和坝体长度情况下,新型结构对泥石流的拦挡筛分效果（速度变化率、储流比、浆砂分离率）。试验结果表明:增加拦砂坝长度和减小格栅间距都会提高泥石流流速变化率;随着泥石流来量和坝体格栅间距增大,储流比反而减小,储流比最高能达到87.13%;新型结构对泥石流的拦粗排细效果较好,浆砂分离率随格栅间距增加呈现出先升高后降低的趋势,最高可达82.45%;通过二次式拟合得到格栅间距为d85时浆砂分离率最高,推荐将d85作为格栅间距。     

The Grand Canyon of the Colorado

The Grand Canyon is not only one of the greatest erosional features on Earth, it also reveals one of the finest stratigraphic records anywhere.     

Debris flows in the Swiss National Park: the influence of different flow models and varying DEM grid size on modeling results

In the Swiss National Park, debris flows are a frequent phenomenon and have repeatedly affected highways and hiking structures. In this study, we first investigated the main characteristics and dimensions of current debris flows by field work and empirical parameterization schemes. Additionally, we evaluated a topography-based flow-trajectory geographic information system model (MSF) and a flow-routing model (FLO-2D) in terms of debris flow-affected areas. Three generically different digital elevation models (DEM) with grid spacing of 25, 4, and 1 m were used in conjunction with the flow models. The evaluation of the DEM grid spacing shows that for both flow models the 25-m DEM can give an approximate estimation of the potential hazard zone. Four- and one-meter DEMs mostly confine the simulated debris flow to existing channels and are in accordance with observations of recent debris-flow events. The study shows that DEM quality and grid resolution are crucial for the resulting delineation of potentially affected areas and thus for hazard assessment and mapping.     

Debris flows triggered from non-stationary glacier lake outbursts: the case of the Teztor Lake complex (Northern Tian Shan,Kyrgyzstan)

One of the most far-reaching glacier-related hazards in the Tian Shan Mountains of Kyrgyzstan is glacial lake outburst floods (GLOFs) and related debris flows. An improved understanding of the formation and evolution of glacial lakes and debris flow susceptibility is therefore essential to assess and mitigate potential hazards and risks. Non-stationary glacier lakes may fill periodically and quickly; the potential for them to outburst increases as water volume may change dramatically over very short periods of time. After the outburst or drainage of a lake, the entire process may start again, and thus these non-stationary lakes are of particular importance in the region. In this work, the Teztor lake complex, located in Northern Kyrgyzstan, was selected for the analysis of outburst mechanisms of non-stationary glacial lakes, their formation, as well as the triggering of flows and development of debris flows and floods downstream of the lakes. The different Teztor lakes are filled with water periodically, and according to field observations, they tend to outburst every 9–10 years on average. The most important event in the area dates back to 1953, and another important event occurred on July 31, 2012. Other smaller outbursts have been recorded as well. Our study shows that the recent GLOF in 2012 was caused by a combination of intense precipitation during the days preceding the event and a rapid rise in air temperatures. Analyses of features in the entrainment and depositional zones point to a total debris flow volume of about 200,000 m³, with discharge ranging from 145 to 340 m³ s^?1 and flow velocities between 5 and 7 m s^?1. Results of this study are key for a better design of sound river corridor planning and for the assessment and mitigation of potential GLOF hazards and risks in the region.     

Chemical Classification of Space Debris

Space debris, here referring to all non-operating orbital objects, has steadily increased in number so that it has become a potential barrier to the exploration of space. The ever-increasing number of space debris pieces in space has created an increasingly threatening hazard to all on-the-orbit spacecraft, and all future space exploration activities have to be designed and operated with respect to the increasing threat posed by space debris. Generally, space debris is classified as large, medium and small debris pieces based on their sizes. The large debris piece is easily catalogued, but medium to small debris pieces are very difficult to track and also quite different in damage mechanisms from the large ones. In this paper, a scheme of chemical classification of space debris is developed. In our scheme, the first-order classification is employed to divide space debris into two groups: natural     

南水北调西线工程泥石流灾害及危险区划

南水北调西线工程是拟议中的国家重大建设工程,通过"五坝七洞一渠"共计260km的引水线路,引长江上游雅砻江和大渡河水入黄河。泥石流在工程区多有分布,现已查明,工程区共有不同危险度等级的泥石流沟103条。泥石流危险区划结果表明,研究区内没有泥石流极高危险区;泥石流高度危险区总面积为73km2,主要集中分布在杜柯河流域,达曲和泥曲流域有零星分布;泥石流中度危险区总面积114·75km2,各流域均有分布,其中杜柯河和达曲流域分布较多;泥石流低度危险区是分布最广的区域,总面积156·75km2,各流域均有分布,以杜柯河流域分布略多。研究表明,用单沟泥石流危险度值作为综合指标,以具有不同泥石流危险度等级的泥石流沟流域面积作为权重的加权平均方法,采用网格作为泥石流危险区划的基本单元,能够直接而真实地获得泥石流危险区划的成果。用本文提出的方法进行地质灾害的危险区划,无疑比用间接方法和替代指标得出的危险区划结果具有更高的可靠性。     

Empirical Relationships for Debris Flows

The assessment of the debris flow hazard potential has to rely on semi-quantitative methods. Due to the complexity of the debris-flow process, numerical simulation models of debris flows are still limited with regard to practical applications. Thus, an overview is given of empirical relationships that can be used to estimate the most important parameters of debris-flow behavior. In a possible procedure, an assessment of a maximum debris-flow volume may be followed by estimates of the peak discharge, the mean flow velocity, the total travel distance, and the runout distance on the fan. The applicability of several empirical equations is compared with available field and laboratory data, and scaling considerations are used to discuss the variability of the parameters over a large range of values. Some recommendations are made with regard to the application of the presented relationships by practicing engineers, apart from advocating field reconnaissance and searching for historic events wherever possible.     

Redetermination of lead isotopic composition in Canyon Diablo troilite

Redetermination of the lead isotopic composition in Canyon Diablo troilite shows that the original analysis was overcorrected for analytical fractionation. The new analysis indicates that the lead in nodule CDN-1 is a mixture of primordial lead plus a small amount of common lead.     

中建海底峡谷地貌及沉积特征的分段性

中建海底峡谷具有分段性,但分段的关键地貌特征、各段沉积充填及其控制因素缺乏精细描述和系统论证.综合利用高分辨率二维和三维地震资料,结合水深地貌数据,对中建海底峡谷地貌及沉积特征进行了详细分析,总结了其南北段沉积过程的主控因素.中建海底峡谷呈NW向顺直展布于广乐隆起与西沙隆起之间,以华光礁附近的地貌高点为拐点被分为南北两...     

Two-dimensional Dynamics Simulation of Two-phase Debris Flow

To investigate the movement mechanism of debris flow, a two‐dimensional, two‐phase, depth‐integrated model is introduced. The model uses Mohr‐Coulomb plasticity for the solid rheology, and the fluid stress is modeled as a Newtonian fluid. The interaction between solid and liquid phases, which plays a major role in debris flow movement, is assumed to consist of drag and buoyancy forces. The applicability of drag force formulas is discussed. Considering the complex interaction between debris flow and the bed surface, a combined friction boundary condition is imposed on the bottom, and this is also discussed. To solve the complex model equations, a numerical method with second‐order accuracy based on the finite volume method is proposed. Several numerical experiments are performed to verify the feasibilities of model and numerical schemes. Numerical results demonstrate that different solid volume fractions substantially affect debris flow movement.