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1.
The 9.5 km2 Illgraben catchment, located in the Rhône valley in the Central Alps of Switzerland, is one of the most active debris flow torrents in the Alps. In this paper we present sediment yield data collected in 2006 for segments where hillslopes and channels form a fully connected network and contrast these with sediment yields measured for disconnected hillslopes. The data reveal that sediment yields are 1–2 orders of magnitude larger in segments where hillslopes are connected with the channel network than on disconnected hillslopes. Support for this conclusion is provided by observations made on 1959, 1999 and 2004 aerial photographs that the vegetation cover in the disconnected segments is still intact, whereas denudation rates of several centimeters per year in the connected segments have inhibited the establishment of a stable vegetation cover. Furthermore, sediment supplied from hillslopes during the past 40 years has temporarily accumulated along the Illgraben channel, indicating that the channel aggraded over this period and has not yet recovered. An implication of this observation is that initiation of debris flows in the Illgraben catchment is limited more by the availability of intense rainfall than sediment. In contrast, on disconnected hillslopes, sediment flux does not appear to be driven by precipitation.The petrographic composition of the Illgraben fan deposits indicates two distinct sediment sources, one related to rockfall and the other to landslides and debris flows. The presence of clasts from both sources implies multiple processes of erosion, deposition, mixing and re-entrainment in the catchment before the material is exported to the Illgraben fan and to the Rhône River. In addition, delivery of large amounts of coarse-grained sediment to the Rhône causes a modification of the flow pattern from meandering or anastomosing upstream to braided downstream. Hence, the direct connectivity between hillslope and channelized processes in the Illgraben catchment causes not only rapid topographic modifications in the catchment, but also morphologic adjustment in the Rhône valley downstream.  相似文献   

2.
We describe the development, implementation, and first analyses of the performance of a debris-flow warning system for the Illgraben catchment and debris fan area. The Illgraben catchment (9.5 km2), located in the Canton of Valais, Switzerland, in the Rhone River valley, is characterized by frequent and voluminous sediment transport and debris-flow activity, and is one of the most active debris-flow catchments in the Alps. It is the site of an instrumented debris-flow observation station in operation since the year 2000. The residents in Susten (municipality Leuk), tourists, and other land users, are exposed to a significant hazard. The warning system consists of four modules: community organizational planning (hazard awareness and preparedness), event detection and alerting, geomorphic catchment observation, and applied research to facilitate the development of an early warning system based on weather forecasting. The system presently provides automated alert signals near the active channel prior to (5–15 min) the arrival of a debris flow or flash flood at the uppermost frequently used channel crossing. It is intended to provide data to support decision-making for warning and evacuation, especially when unusually large debris flows are expected to leave the channel near populated areas. First-year results of the detection and alert module in comparison with the data from the independent debris-flow observation station are generally favorable. Twenty automated alerts (alarms) were issued, which triggered flashing lights and sirens at all major footpaths crossing the channel bed, for three debris flows and 16 flood flows. Only one false alarm was issued. The major difficulty we encountered is related to the variability and complexity of the events (e.g., events consisting of multiple surges) and can be largely solved by increasing the duration of the alarm. All of the alarms for hazardous events were produced by storms with a rainfall duration and intensity larger than the threshold for debris-flow activity that was defined in an earlier study, supporting our intention to investigate the use of rainfall forecasts to increase the time available for warning and implementation of active countermeasures.  相似文献   

3.
Status and Trends in Research on Deep-Water Gravity Flow Deposits   总被引：3，自引：0，他引：3  
Deep-water gravity flows are one of the most important sediment transport mechanisms on Earth. After 60 years of study,significant achievements have been made in terms of classification schemes,genetic mechanisms,and depositional models of deep-water gravity flows. The research history of deep-water gravity flows can be divided into five stages: incipience of turbidity current theory; formation of turbidity current theory; development of deep-water gravity flow theory; improvement and perfection of deep-water gravity flow theory; and comprehensive development of deep-water gravity flow theory. Currently,three primary classification schemes based on the sediment support mechanism,the rheology and transportation process,and the integration of sediment support mechanisms,rheology,sedimentary characteristics,and flow state are commonly used.Different types of deep-water gravity flow events form different types of gravity flow deposits. Sediment slump retransportation mainly forms muddy debris flows,sandy debris flows,and surge-like turbidity currents. Resuspension of deposits by storms leads to quasi-steady hyperpycnal turbidity currents(hyperpycnal flows). Sustainable sediment supplies mainly generate muddy debris flows,sandy debris flows,and hyperpycnal flows. Deep-water fans,which are commonly controlled by debris flows and hyperpycnal flows,are triggered by sustainable sediment supply; in contrast,deep-water slope sedimentary deposits consist mainly of debris flows that are triggered by the retransportation of sediment slumps and deep-water fine-grained sedimentary deposits are derived primarily from finegrained hyperpycnal flows that are triggered by the resuspension of storm deposits. Harmonization of classification schemes,transformation between different types of gravity flow deposit,and monitoring and reproduction of the sedimentary processes of deep-water gravity flows as well as a source-to-sink approach to document the evolution and deposition of deep-water gravity flows are the most important research aspects for future studies of deep-water gravity flows study in the future.  相似文献   

4.
Arattano  M. 《Natural Hazards》1999,20(2-3):197-213
Debris flows constitute a major threat forseveral urban settlements located on the fans ofmountain catchments and for other infrastructures thatinteract with these fans, particularly highways andmotorways. Often structural measures such as theconstruction and maintenance of deposition basins,check dams, channel linings are both too expensive andnot capable of completely guaranteeing the safety forinhabitants of villages and users of infrastructuresaffected by debris flows. Therefore the search offunctional, reliable and possibly not expensivewarning systems should be pursued to increase theavailable tools to face this often devastating kind ofphenomenon. In this paper the use of seismic detectorsfor the determination of a debris flow occurrence ina torrent before its arrival on the fan will bediscussed, together with their potential use asmonitoring and warning systems. In 1995 a set of fourseismic detectors was placed at a distance of aboutone hundred meters from each other along a straightchannel reach of a debris flow prone torrent locatedon the Eastern Italian Alps. The purpose, in a firstphase of the research, was mainly to verify whichinformation could be obtained through this type ofdevice on the occasion of a debris flow occurrence. On5 July 1995, 22 June and 8 July 1996 three debrisflows were recorded by this seismic network: the datathat have been collected will be presented andconveniently processed for their interpretation. Theresults that have been obtained show that the passageof a debris flow in a torrent can be clearlyidentified using seismic devices placed at a safedistance from the channel bed and that in some casesa velocity estimation of the flowing mass is alsopossible through the processing of the seismic data.  相似文献   

5.
Experimental study on cascading landslide dam failures by upstream flows   总被引：1，自引：1，他引：0  
Landslide dams in mountainous areas are quite common. Typically, intense rainfalls can induce upstream flows along the sloping channel, which greatly affects the stability and failure modes of landslide dams. If a series of landslide dams are sequentially collapsed by an incoming mountain torrent (induced by intense rainfall), large debris flows can be formed in a short period of time. This also amplifies the magnitude of the debris flows along the flow direction. The catastrophic debris flows, which occurred in Zhouqu, China on August 8, 2010, were indeed caused by intense rainfall and the upstream cascading failure of landslide dams along the gullies. Experimental tests were conducted in a sloping channel to understand the dynamic process of cascading landslide dam failures and their effect on flow scale amplification. Similar to the Zhouqu conditions, the modeled landslide dams were distributed along a sloping channel and breached by different upstream flows. For each experiment, the front flows were sampled, the entrained grain sizes were analyzed, and the front discharge along the channel was measured. The results of these experiments show that landslide dams occurring along the channel can be destroyed by both high and low discharge flows, although the mechanisms are quite different for the two flow types. Regardless of flow type, the magnitude of the flows significantly increases after a cascading failure of landslide dams, resulting in an increase in both the diameter and the entrained coarse particles percentage.  相似文献   

6.
旦波北沟为雅砻江中游右岸河段的一级支流,历史上曾发生多次泥石流.在查明泥石流形成条件的基础上,分析了旦波北沟泥石流的运动特征,包括泥石流的流速、流量、冲击力.这一结论为评价该泥石流对水电站的建设和安全运行的影响具有现实意义.建议左岸前期施工场地和左岸上游备料场沿江设置挡墙,且场地要注意少占行洪断面,防止泥石流沉积淤塞河...  相似文献   

7.
李尧  崔一飞  李振洪  傅旭东 《地球科学》2022,47(6):1969-1984
川藏交通廊道沿线山高谷深,地层岩性多变,新构造运动活跃,气候恶劣复杂,导致滑坡、崩塌、泥石流、冰湖溃决洪水等灾害极其发育,对铁路施工及运营带来严重影响.林芝-波密段就是典型地质灾害高发区域,常年受到冰川泥石流的影响,是川藏交通廊道重大灾害防治的难点区段.虽然目前在单沟尺度上对冰川泥石流的形成条件、影响因素、物源性质取得了一定的认识,但对于川藏交通廊道沿线不同类型的冰川泥石流诱发因素、区域发展演化规律及灾变指标的研究还较为初步,尚未构建完善的监测预警体系.借助多源长时序遥感影像、气象监测数据,结合野外实地验证和历史数据分析发现:川藏交通廊道周边区域冰川泥石流沟谷共99条,主要分布于恰青冰川-易贡乡、加拉贝垒-南迦巴瓦峰和古乡沟-嘎隆寺冰川一带;过去40年冰川经历了复杂的流动速度变化,表现为较小高海拔悬冰川活动性增强,大型沟谷冰川活动性减弱;自1973年以来,研究区冰川泥石流呈现频率增高、规模增大的特征.此外,从冰川泥石流发育沟道比降来看,发生高陡地形的滑坡、冰-岩崩诱发的泥石流频率增加.未来,冰川持续退缩,促使冰川源区冰瀑消失,发育更大规模的悬冰川,会增加这类冰川泥石流的风险;冰川泥石流形成及演化过程具有明显的灾变指标,如悬冰川裂隙密度增加、冰川速度增强、冰湖面积快速增加等.因此,基于以上认识,建议针对不同类型的冰川泥石流地建立完善的监测预警指标,并提出了融合卫星、航空遥感平台,气象、水文地面监测平台,地震动监测平台的冰川泥石流“空-天-地”立体监测框架,针对不同类型冰川泥石流进行灾变信息监测与预警判识,为川藏交通廊道安全施工运营提供技术参考.   相似文献   

8.
Simulation of interactions among multiple debris flows   总被引：3，自引：2，他引：1  
Adjacent debris flows may interact in many ways: two or more concurrent debris flows may merge; one debris flow can run out over an existing debris flow fan. Such interactions may cause debris flow properties to change in the mixing process as well as more severe adverse effects than those caused by a single debris flow. This paper aims to investigate the interactions among channelized debris flows originated from adjacent catchments. Both concurrent and successive debris flows are considered. If several debris flows originate from different locations concurrently and merge, the volumetric sediment concentration (i.e., the ratio of the volume of solid material to the total volume of debris flow), C v, is a good index to capture the mixing process of these debris flows. The change in C v reflects where mixing occurs and the mixing degree. The debris flow properties (e.g., yield stress and dynamic viscosity) evolve in the mixing process and can be captured by the change in C v. The debris flow with a larger volume dominates the mixing process, and the properties of the mixed debris flow are more similar to those of the larger debris flow. The inundated areas and runout distances of successive debris flows are smaller than those of concurrent debris flows of the same total volume due to the smaller scales of the individual events and blockage by the earlier debris flows. However, the deposit depth in the interacting part of the debris flow fans of successive debris flows can be much larger than that of concurrent debris flows, leading to more destructive cascading hazards (e.g., the formation of debris barrier lakes). The sequence of successive debris flows not only significantly influences the runout characteristics of the debris flows but also substantially affects the cascading hazards.  相似文献   

9.
Debris flow hazard posts a big threat to the main downstream of Jinsha River where a number of huge power stations are under construction. The characteristics of spatial distribution of debris flows and the effect of their sediment yield on the reservoir areas have been studied. An automatic recognition module was developed to extract the geometry of debris flow channels from remote sensing data. Spatial distribution pattern of debris flows is obtained through combining the inventory database and multi-source remote sensing investigation. The distribution of debris flows has high dependency on the various factors including geology, geomorphology, climate, hydrology and human economic activities. The debris flows distributed in the study area are characterized by group and pair distribution, uncompleted deposition fans, highly controlled by faults and tectonic activities, spatial variation between left bank and right bank, and different subdivisions. The sediment yield caused by debris flow activates is evaluated using multi-year observation data from numerous observation stations. Quantitative studies have been performed on the relationship between the sediment yield and the debris flow area. A relatively fix ratio of 2.6 (×104 t/km2) has been found in different subdivisions of main downstream area which shows that the source of sediment discharged into Jinsha River primarily come from debris flow activities. Another ratio is evaluated to represent the transforming possibility of debris flow materials to bed-sediment load and suspended-sediment load in the river. Based on these findings, the potential effect of sediment yield caused by debris flows on reservoir areas is discussed. The zonation map shows the different effect of debris flow sediment on different dam site area which shows a good agreement with variation of debris flow spatial distribution.  相似文献   

10.
朱星  许强  汤明高  付小敏  周建斌 《岩土力学》2013,34(5):1306-1312
在刚性材料试验压力机上对花岗岩、灰岩、红砂岩、砂岩、千枚岩及泥岩6种典型的岩石试样进行了单轴全过程加载试验,通过自主研制的数字化次声波探测系统对加载过程中的岩石破裂发射出的次声波信号进行了实时探测。为了研究岩石微破裂过程是否存在发射低频次声波现象及其频率分布等特性,通过小波阈值去噪、短时傅立叶变换（STFT）时-频分析和时域累计振铃计数的方法对数字次声波信号进行了处理与分析。研究结果表明：①岩石在破坏前加载过程中存在明显的发射次声波现象;②岩石破裂产生突出次声信号的频率主要分布在2.0～6.0 Hz之间;③在结构较完整的情况下,硬岩（如花岗岩、灰岩）在变形破裂过程中产生的次声信号数量要比软岩（如泥岩）多。与一般声波相比,因次声波具有不容易衰减,不易被水和空气吸收,波长很长可绕开大型障碍物等独特性质,结合其他方法对岩石破裂产生次声波现象的进一步研究可为岩石（体）稳定性监测提供重要的研究方法和技术手段。  相似文献   

11.
Every year, and in many countries worldwide, wildfires cause significant damage and economic losses due to both the direct effects of the fires and the subsequent accelerated runoff, erosion, and debris flow. Wildfires can have profound effects on the hydrologic response of watersheds by changing the infiltration characteristics and erodibility of the soil, which leads to decreased rainfall infiltration, significantly increased overland flow and runoff in channels, and movement of soil. Debris-flow activity is among the most destructive consequences of these changes, often causing extensive damage to human infrastructure. Data from the Mediterranean area and Western United States of America help identify the primary processes that result in debris flows in recently burned areas. Two primary processes for the initiation of fire-related debris flows have been so far identified: (1) runoff-dominated erosion by surface overland flow; and (2) infiltration-triggered failure and mobilization of a discrete landslide mass. The first process is frequently documented immediately post-fire and leads to the generation of debris flows through progressive bulking of storm runoff with sediment eroded from the hillslopes and channels. As sediment is incorporated into water, runoff can convert to debris flow. The conversion to debris flow may be observed at a position within a drainage network that appears to be controlled by threshold values of upslope contributing area and its gradient. At these locations, sufficient eroded material has been incorporated, relative to the volume of contributing surface runoff, to generate debris flows. Debris flows have also been generated from burned basins in response to increased runoff by water cascading over a steep, bedrock cliff, and incorporating material from readily erodible colluvium or channel bed. Post-fire debris flows have also been generated by infiltration-triggered landslide failures which then mobilize into debris flows. However, only 12% of documented cases exhibited this process. When they do occur, the landslide failures range in thickness from a few tens of centimeters to more than 6 m, and generally involve the soil and colluvium-mantled hillslopes. Surficial landslide failures in burned areas most frequently occur in response to prolonged periods of storm rainfall, or prolonged rainfall in combination with rapid snowmelt or rain-on-snow events.  相似文献   

12.
The Wenchuan earthquake of May 12, 2008 produced large amounts of loose material (landslide debris) that are still present on the steep slopes and in the gullies. This loose material creates an important hazard as strong rainfall can cause the development of devastating debris flows that will endanger the resettled population and destroy the result of reconstruction efforts. On 14 August 2010, a total of 21 debris flows were triggered by heavy rainfall around the town of Yingxue, located near the epicenter of the Wenchuan earthquake. One of these debris flows produced a debris dam, which then changed the course of the river and resulted in the flooding of the newly reconstructed Yinxue town. Prior to this catastrophic event, debris flow hazard had been recognized in the region, but its potential for such widespread and devastating impacts was not fully appreciated. Our primary objective for this study was to analyze the characteristics of the triggering rainfall and the sediment supply conditions leading to this event. Our field observations show that even small debris flow catchment areas have caused widespread sediment deposition on the existing fans. It is concluded that the whole of the area shaken by the Wenchuan earthquake is more susceptible to debris flows, initiated by localized heavy rainfall, than had been assumed earlier. The results of this study contribute to a better understanding of the conditions leading to catastrophic debris flow events in the earthquake-hit area. This is essential for the implementation of proper early warning, prevention, and mitigation measures as well as a better land use planning in this area.  相似文献   

13.
Bin Yu 《Natural Hazards》2011,58(1):391-406
The accurate prediction of debris flows occurrence that will allow the reduction or prevention of economic losses and human casualties is presently the most difficult aspect of debris flows studies but also the aspect that receives most attention. Most prediction methods are based on rainfall as the basic parameter, with the moment of occurrence as only result, and without a prediction of debris flow travel time and size. This paper takes Jiangjia Gully in Dongchuan of Yunnan Province as an example, and considers, on the basis of the fulfillment of the essential condition: the abundant availability of loose materials, the conditions for the formation of debris flows. Based on the mechanism of the initiation of debris flows in channels and the volume of rainfall in the basin, this paper also gives a systematic analysis on the travel time and size of the debris flow and suggests that the hydrological condition for forming debris flow is the unit discharge of the flood ≥0.35 m3/s.m. It uses the 10-min rainfall intensity to calculate both the run-off of the rainfall and the unit discharge caused by the run-off, thus predicting the occurrence of debris flows. The velocity and the travel time of a debris flow can also be determined using the unit discharge of the run-off. The total volume of debris flows can be calculated using the 10-min intensity of rainfall and the total volume of the run-off, together with the volume concentration of the sediment in a debris flow.  相似文献   

14.
寺儿沟流域位于甘肃省兰州市西固区,历史上曾发生过大规模泥石流,造成重大人员伤亡和财产损失。文章基于野外调查和遥感解译,结合已有文献成果和室内测试,研究寺儿沟泥石流物源特征及影响因素,采用FLO-2D软件模拟分析泥石流的危险性。研究结果表明：寺儿沟以黏性泥石流为主,表现为低频活动,目前处于衰退期;寺儿沟流域内物源丰富,可分为坡面型物源、崩滑型物源、沟道型物源和人为型物源共4种,其中崩滑型、沟道型物源控制了泥石流的暴发规模;而一次性冲出量的大小主要取决于泥石流起动时崩滑体的发育程度,崩滑体越发育,一次性冲出量越大,泥石流规模越大;在临界降雨条件下,寺儿沟将会暴发泥石流,中—高危险区集中于流通区,严重威胁冲沟内构筑物如兰西高铁、环城高速等安全运营。当遭遇极端强降雨时,寺儿沟将暴发更大规模泥石流。因此,有必要进一步研究极端天气条件下泥石流的危险性,为区内泥石流的防灾减灾提供地质依据。  相似文献   

15.
Subaquatic glacigenic debris flows of Late Wisconsinan age occur as lobes within an ice-marginal glaciomarine lithofacies at Victoria, British Columbia. Flow was initiated by release of supraglacial debris during an interval of glacial ablation prior to advance and deposition of lodgement till. Many of the lobes developed a common morphology during deposition, consisting of an outer layer surrounding an inner core of rafted material. In the largest lobe reworking of the sediment during flow produced improved sorting, a coarsening of mean grain size, and a shift in skewness toward the negative. This occurred simultaneously within the core and outer layer as a result of different transformations in mechanisms of flow and support. Normal grading, produced in the outer layer, was conveyed around the nose and buried in an inverse position along the base of the flow. These data enable us to present a model that may be applicable to similar flows elsewhere. The flow studied demonstrates that transformations between flow types and sediment support mechanisms can occur simultaneously and serially in subaquatic debris flows.  相似文献   

16.
Debris flows are often triggered by Hortonian overland flow during high-intensity rainstorms. Data derived from debris flow trigger zones in the southern French Alps were fed into a physical model of debris flow triggering based on Takahashi. Using a Monte Carlo approach with 1000 runs, the results show a wide distribution of safety factor values, indicating that physical modelling based on actual field measurements may not always be practical.As all safety factor values obtained are well below 1 even though debris flows only occur during very high-intensity rainstorms, the model used must be inappropriate. Apparently, the composition of the overland flow plays an important role: during high-intensity rainstorms it usually has a very high sediment content and contains stones. This prevents it from flowing through the pores of coarse debris accumulations in the central gully of a trigger zone; it will rather run over the debris. This situation is more stable than with the fluid flowing through the pores. The behaviour switch of the fluid above a certain sediment and stone content thus drastically changes the triggering conditions for debris flows and it is concluded that debris flow triggering in the area requires the occurrence of both overland flow and landsliding.  相似文献   

17.
火后泥石流是一种裹挟大量松散物质的特殊性洪流,与林火密切相关,其成灾特征与常规泥石流差异显著,因此常规泥石流的防治经验对其不完全适用。西昌“3·30”火灾后,火烧迹地火后泥石流频发,严重威胁当地人民生命财产安全。研究火后泥石流的成灾特征,并针对性提出综合防治措施是必要且迫切的。文中以四川省凉山州西昌市新村电池厂沟为研究对象,分析了火烧迹地及流域特征,研究了火后泥石流成灾特征并提出相应的防治措施。结果表明,电池厂沟过火面积占总面积的83.37%,严重火烧区占33.47%,地表灰烬层广泛堆积于坡面,松散物源中坡面物源占69.83%。火后泥石流表现出频发性:首次暴发于火后一个月左右,首个雨季累计暴发5次;且泥石流起动降雨阈值低,易发性激增。据此,对该沟提出相应的防治措施:短期应急（坡面枯木清理、植被恢复、简易谷坊坝）;中期治理（沟内拦砂坝辅以坝后沉沙池）;长期预防（森林防火、植被保护、预警避险）。短期、中期方案已在电池厂沟实施,工程竣工后至今,综合治理效果得到了初步检验,可为今后火后泥石流防治提供参考。  相似文献   

18.
以吉林省江源县石人镇泥石流观测资料为背景,对该区泥石流形成及活动条件进行了较为全面的分析研究。提取出11项影响泥石流危险性的评价因子,利用灰色关联方法计算出评价因子间的关联度,并运用模糊数学综合评判法对石人镇13条泥石流沟进行了危险性评价,评价结果较为可信,对监测和整治泥石流具有较高的参考价值。  相似文献   

19.
低频泥石流特征及其预测初步探讨   总被引：4，自引：0，他引：4  
同高频泥石流相比,低频泥石流更具有潜在危害性。近年来,低频泥石流的暴发给我国山区人们的生命财产安全、经济发展和社会进步以及山区生态环境带来了极大的影响。本文通过对低频泥石流沟实地考察以及对近年来我国暴发的约30例典型低频泥石流资料进行搜集整理,从其隐蔽性、活动性、规模和破坏性以及灾情等方面探讨了低频泥石流的特征;以茶园沟为例,采用灰色灾变预测方法,建立灰色灾变预测模型对其进行预测,经检验预测结果与实际发生年份一致,并且预测出2042年或2043年前后以及2095年或2096年前后茶园沟发生大规模泥石流的可能性较大;最后,针对低频泥石流的特征,提出了相应的防治建议。  相似文献   

20.
通过对特大型泥石流灾害发生的思考,详细分析了蒋家沟1995—1997年43场泥石流暴发的不同权重的前期和始发日降雨量与泥石流产沙规模的关系。分析结果表明：泥石流的产沙规模与不同权重降雨的入渗范围、深度的土体极限应力状态（C、Ф、P,）有关。根据不同权重的前期和始发日降雨量与泥石流产沙规模的关系,可以将泥石流分为：土力型（A）和迳流型（B）两大类型。土力型（A）泥石流有24场占总样本的55．81％,而其产沙量却占样本总产沙量的85％。迳流型（B）泥石流有19场占总样本的44．19％,但该类泥石流的产沙量只占样本总产沙量的15％。  相似文献   

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